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• Scalable / Parallel Large Graph Analysis Library?

  - by Joel Hoff

  I am looking for good recommendations for scalable and/or parallel large graph analysis libraries in various languages. The problems I am working on involve significant computational analysis of graphs/networks with 1-100 million nodes and 10 million to 1+ billion edges. The largest SMP computer I am using has 256 GB memory, but I also have access to an HPC cluster with 1000 cores, 2 TB aggregate memory, and MPI for communication. I am primarily looking for scalable, high-performance graph libraries that could be used in either single or multi-threaded scenarios, but parallel analysis libraries based on MPI or a similar protocol for communication and/or distributed memory are also of interest for high-end problems. Target programming languages include C++, C, Java, and Python. My research to-date has come up with the following possible solutions for these languages: C++ -- The most viable solutions appear to be the Boost Graph Library and Parallel Boost Graph Library. I have looked briefly at MTGL, but it is currently slanted more toward massively multithreaded hardware architectures like the Cray XMT. C - igraph and SNAP (Small-world Network Analysis and Partitioning); latter uses OpenMP for parallelism on SMP systems. Java - I have found no parallel libraries here yet, but JGraphT and perhaps JUNG are leading contenders in the non-parallel space. Python - igraph and NetworkX look like the most solid options, though neither is parallel. There used to be Python bindings for BGL, but these are now unsupported; last release in 2005 looks stale now. Other topics here on SO that I've looked at have discussed graph libraries in C++, Java, Python, and other languages. However, none of these topics focused significantly on scalability. Does anyone have recommendations they can offer based on experience with any of the above or other library packages when applied to large graph analysis problems? Performance, scalability, and code stability/maturity are my primary concerns. Most of the specialized algorithms will be developed by my team with the exception of any graph-oriented parallel communication or distributed memory frameworks (where the graph state is distributed across a cluster).

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• Has anyone used Rational Team Concert (RTC)?

  - by FryGuy

  The company I work for is currently evaluating replacements for SourceSafe, and for various reasons, I think RTC will be chosen. I'm a little scared that we're going to end up with a solution that isn't the best for us in our situation. I've tried researching a little bit about what it is, but all I have been able to find are marketing things, but nothing about how it actually works (any of the paradigms it uses, etc). Our team is around 8 developers and 2 QA people on a single project (and 4-5 more people that would be using it for their independent project). It seems like RTC is targetted for larger teams, but our team is relatively small. Does anyone has experience using RTC in a smaller team? The project that would be using it is a .NET/WPF application, so we would be using primarily Visual Studio. Is the Visual Studio integration any good, or are we stuck having to have Eclipse open on top of Visual Studio? Personally, I have been using Bazaar as my personal source control (and checking out/into sourcesafe from a branch), as well as on personal projects. Does RTC incorporate features of "third generation" version control systems, such as first class branching/merging and changesets rather than file changes, and good visualization of where changes come from? Also, what are the general pros and cons for it?

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• TinyMCE + jQuery + custom plugin = tinymce is undefined?

  - by user368691

  The problem occurs when I try to create small plugin to allow me toggle on and off WYSIWYG on all textareas in the website. //$('form.default textarea').each(function(){ // console.log( $('<a href="#">Enable WYSIWYG editor</a>').insertAfter('form.default textarea').prev('textarea.wysiwyg').tinymce().hide() ); //}); The full (a bit simplified) code looks like this: $('textarea.wysiwyg').tinymce({ skin : 'cirkuit', theme : 'advanced', plugins : 'pagebreak,style,layer,advlink,inlinepopups,contextmenu,paste,directionality,noneditable,nonbreaking,xhtmlxtras,template', // Theme options theme_advanced_buttons1 : 'formatselect,fontsizeselect,forecolor,|,bold,italic,strikethrough,|,bullist,numlist,|,justifyleft,justifycenter,justifyright,|,link,unlink,|,image,|,code,paste,pastetext,pasteword,removeformat,|,backcolor,|,underline,justifyfull,sup,|,outdent,indent,|,hr,charmap,|,undo,redo', theme_advanced_buttons2 : '', theme_advanced_buttons3 : '', theme_advanced_toolbar_location : 'top', theme_advanced_toolbar_align : 'left', theme_advanced_statusbar_location: 'bottom', theme_advanced_resizing : true, theme_advanced_resize_horizontal : false, height : 500, theme_advanced_resizing_min_height : 500, document_base_url : 'http://static.<?=$settings['system_host']?>/' }); $('textarea.wysiwyg').each(function() { $(this).tinymce().hide(); }); What is the error? FireBug says that tinymce() in undefined; this message occurs in each() loop. Thus, tinymce() is actually initialized. I am really lost towards, what could be causing this.

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• Record/Playback with AudioQueue on iPhone

  - by Biranchi

  Hi, I am currently using Audio Queues on the iPhone to record and playback audio. What I would like to be able to do is to record some audio, allow the user to pause the record queue, and to seek back and forward through the audio to select a position from where they can start recording from again. I have got over the seeking issue by making the playback AudioQueueBuffer sizes small enough so that the play audio queue callback happens at a rate that allows the user to use a slider control to hear the audio as they adjust the slider back and forth. I think I can achieve the recording at a new position by setting the inStartingPacket parameter of the AudioFileWritePackets function that I call from the Audio Recording Queue callback. The trouble is this only inserts audio over the previously recorded audio. The file length obviously doesn't change so if the user were to go backwards and record less audio than before, the old audio still remains after the end of the newly recorded audio. Is there a way I can get the AudioFile to truncate at the point the user starts to insert the new audio, is there some other way I can remove the old audio starting at the insert position or is there a better way about going about this task? Thanks

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• Why isn’t my autoreleased object getting released?

  - by zoul

  Hello. I am debugging a weird memory management error and I can’t figure it out. I noticed that some of my objects are staying in memory longer than expected. I checked all my memory management and finally got to the very improbable conclusion that some of my autorelease operations don’t result in a release. Under what circumstances is that possible? I created a small testing Canary class that logs a message in dealloc and have the following testing code in place: NSLog(@"On the main thread: %i.", [NSThread isMainThread]); [[[Canary alloc] init] autorelease]; According to the code we’re really on the main thread, but the dealloc in Canary does not get called until much later. The delay is not deterministic and can easily take seconds or more. How is that possible? The application runs on a Mac, the garbage collection is turned off (Objective-C Garbage Collection is set to Unsupported on the target.) I am mostly used to iOS, is memory management on OS X different in some important way?

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• jQuery validator not working in unit testing

  - by Dbugger

  I have this small HTML file: <html> <head></head> <body> <form id='MyForm'> <input type='text' required /> <input type='submit' /> </form> <script src="/js/jquery-1.9.0.js"></script> <script src="/js/jquery.validate.js"></script> <script> var validator = $("#MyForm").validate(); alert(validator.form()); </script> </body> </html> This alerts me with "false", which is the expected behaviour. The problem comes when I go to unit testing, with js-test-driver: TestCase("MyTests", { setUp: function() { this.myform = "<form id='MyForm'><input type='text' required /><input type='submit' /></form>"; this.validator = $(this.myform).validate(); jstestdriver.console.log("Does the form validate? " + this.validator.form()); }, test_empty: function() { }, }); This code returns me the string Does the form validate? true This is a simplified version of my project of course, but the point is that I dont seem to be able to unit test the validation module im developing, since the jQuery validate plugin doesnt seem to work. What am I missing?

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• Problems with Merb on Snow Leopard

  - by hamhoagie

  I've recently started looking at Merb, for use with some small projects around the office. I'm trying to set up my first project following the docs, and am encountering an exception such as: foo:beta user$ merb Merb root at: /Users/user/code/merb/beta Loading init file from ./config/init.rb Loading ./config/environments/development.rb ~ Connecting to database... ~ Loaded slice 'MerbAuthSlicePassword' ... ~ Parent pid: 39794 ~ Compiling routes... ~ Activating slice 'MerbAuthSlicePassword' ... ~ ~ FATAL: Mongrel is not installed, but you are trying to use it. You need to either install mongrel or a different Ruby web server, like thin. I have installed Mongrel from gem as well as from MacPorts, and am confused by this exception. Significant stats: ruby 1.8.7 (2010-01-10 patchlevel 249) [i686-darwin10] From my installed gems: merb (1.1.0) merb-action-args (1.1.0) merb-assets (1.1.0) merb-auth (1.1.0) merb-auth-core (1.1.0) merb-auth-more (1.1.0) merb-auth-slice-password (1.1.0) merb-cache (1.1.0) merb-core (1.1.0) merb-exceptions (1.1.0) merb-gen (1.1.0) merb-haml (1.1.0) merb-helpers (1.1.0) merb-mailer (1.1.0) merb-param-protection (1.1.0) merb-slices (1.1.0) merb_datamapper (1.1.0) mongrel (1.1.5) Merb documentation is non-existent, so I find myself stuck. Thanks in advance.

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• Efficient Context-Free Grammar parser, preferably Python-friendly

  - by Max Shawabkeh

  I am in need of parsing a small subset of English for one of my project, described as a context-free grammar with (1-level) feature structures (example) and I need to do it efficiently . Right now I'm using NLTK's parser which produces the right output but is very slow. For my grammar of ~450 fairly ambiguous non-lexicon rules and half a million lexical entries, parsing simple sentences can take anywhere from 2 to 30 seconds, depending it seems on the number of resulting trees. Lexical entries have little to no effect on performance. Another problem is that loading the (25MB) grammar+lexicon at the beginning can take up to a minute. From what I can find in literature, the running time of the algorithm used to parse such a grammar (Earley or CKY) should be linear to the size of the grammar and cubic to the size of the input token list. My experience with NLTK indicates that ambiguity is what hurts the performance most, not the absolute size of the grammar. So now I'm looking for a CFG parser to replace NLTK. I've been considering PLY but I can't tell whether it supports feature structures in CFGs, which are required in my case, and the examples I've seen seem to be doing a lot of procedural parsing rather than just specifying a grammar. Can anybody show me an example of PLY both supporting feature structs and using a declarative grammar? I'm also fine with any other parser that can do what I need efficiently. A Python interface is preferable but not absolutely necessary.

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• Cannot delete an image file that is shown in a listview

  - by Enrico

  Hello all, In my listview I show thumbnails of small images in a certain folder. I setup the listview as follows: var imageList = new ImageList(); foreach (var fileInfo in dir.GetFiles()) { try { var image = Image.FromFile(fileInfo.FullName); imageList.Images.Add(image); } catch { Console.WriteLine("error"); } } listView.View = View.LargeIcon; imageList.ImageSize = new Size(64, 64); listView.LargeImageList = imageList; for (int j = 0; j < imageList.Images.Count; j++) { var item = new ListViewItem {ImageIndex = j, Text = "blabla"}; listView.Items.Add(item); } The user can rightclick on an image in the listview to remove it. I remove it from the listview and then I want to delete this image from the folder. Now I get the error that the file is in use. Of course this is logical since the imagelist is using the file. I tried to first remove the image from the imagelist, but I keep on having the file lock. Can somebody tell me what I am doing wrong? Thanks!

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• SQL Server 2005 database design - many-to-many relationships with hierarchy

  - by Remnant

  Note I have completely re-written my original post to better explain the issue I am trying to understand. I have tried to generalise the problem as much as possible. Also, my thanks to the original people who responded. Hopefully this post makes things a little clearer. Context In short, I am struggling to understand the best way to design a small scale database to handle (what I perceive to be) multiple many-to-many relationships. Imagine the following scenario for a company organisational structure: Textile Division Marketing Division | | ---------------------- ---------------------- | | | | HR Dept Finance Dept HR Dept Finance Dept | | | | ---------- ---------- ---------- --------- | | | | | | | | Payroll Hiring Audit Tax Payroll Hiring Audit Accounts | | | | | | | | Emps Emps Emps Emps Emps Emps Emps Emps NB: Emps denotes a list of employess that work in that area When I first started with this issue I made four separate tables: Divisions - Textile, Marketing (PK = DivisionID) Departments - HR, Finance (PK = DeptID) Functions - Payroll, Hiring, Audit, Tax, Accounts (PK = FunctionID) Employees - List of all Employees (PK = EmployeeID) The problem as I see it is that there are multiple many-to-many relationships i.e. many departments have many divisions and many functions have many departments. Question Giving the database structure above, suppose I wanted to do the following: Get all employees who work in the Payroll function of the Marketing Division To do this I need to be able to differentiate between the two Payroll departments but I am not sure how this can be done? I understand that I could build a 'Link / Junction' table between Departments and Functions so that I can retrieve which Functions are in which Departments. However, I would still need to differentiate the Division they belong to. Research Effort As you can see I am an abecedarian when it comes to database deisgn. I have spent the last two days resaerching this issue, traversing nested set models, adjacency models, reading that this issue is known not to be NP complete etc. I am sure there is a simple solution?

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• check RAM,page file, /PAE, /3GB, SQL server memory using powershell

  - by Manjot

  I am a powershell novice. After days of searching.... I have put together a small powershell script (as below) to check page file, /PAE switch, /3GB switch, SQL server max RAM, min RAM. I am running this on 1 server. If I want to run it on many servers (from a .txt) file, How can I change it ? How can I change it to search boot.ini file's contents for a given server? clear $strComputer="." $PageFile=Get-WmiObject Win32_PageFile -ComputerName $strComputer Write-Host "Page File Size in MB: " ($PageFile.Filesize/(1024*1024)) $colItems=Get-WmiObject Win32_PhysicalMemory -Namespace root\CIMv2 -ComputerName $strComputer $total=0 foreach ($objItem in $colItems) { $total=$total+ $objItem.Capacity } $isPAEEnabled =Get-WmiObject Win32_OperatingSystem -ComputerName $strComputer Write-Host "Is PAE Enabled: " $isPAEEnabled.PAEEnabled Write-Host "Is /3GB Enabled: " | Get-Content C:\boot.ini | Select-String "/3GB" -Quiet # how can I change to search boot.ini file's contents on $strComputer $smo = new-object('Microsoft.SqlServer.Management.Smo.Server') $strSQLServer $memSrv = $smo.information.physicalMemory $memMin = $smo.configuration.minServerMemory.runValue $memMax = $smo.configuration.maxServerMemory.runValue ## DBMS Write-Host "Server RAM available: " -noNewLine Write-Host "$memSrv MB" -fore "blue" Write-Host "SQL memory Min: " -noNewLine Write-Host "$memMin MB " Write-Host "SQL memory Max: " -noNewLine Write-Host "$memMax MB" Any comments how this can be improved? Thanks in advance

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• Recommended (remote) backup technique for SQL Compact?

  - by Cool Jon

  Hello. Is there a generally recommended approach to backing up an SQL CE/SQLite database over the Internet? The client source is .NET/Windows based, the backup destination runs Ubuntu. I am using a small SQL CE database and have been trying to figure out the most reasonable approach to doing this. The file size (in terms of transfer time/bandwidth) isn't a big deal. I had a look around, and so far the things I've given thought are: Online backup services (Dropbox, Mozy) Opening an FTP/SFTP connection Writing a custom protocol with public/private keys Unsure regarding #1 because I doubt they would like it if somebody transferred gigabytes of data using a POST; and they do not seem to offer native (or .NET) APIs. FTP/SFTP seems risky in terms of security and privileges (as the password/key would need to be stored on the client side). With the right user group/user privileges this may work. Custom protocol seems overkill, which is why I am hoping somebody has already defined a reasonable API for language/platform-independent backups over the Internet. Any hints S.O.?

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• How do you handle key down events on Android? I am having issues making it work.

  - by user279112

  For an Android program, I am having trouble handling key down and key up events, and the problem I am having with them can almost certainly be generalized to any sort of user input event. I am using Lunar Lander as one of my main learning devices as I make my first meaningful program, and I noticed that it was using onKeyDown as an overridden method to receive key down events, and it would call one of their more original methods doKeyDown. But when I tried to implement a very small version of my own onKeyDown overide and the actual handler that it calls, it didn't work. I would probably copy and paste my implementations of those two methods, but that doesn't seem to be the problem. You see, I ran the debugger and noticed that they were not getting called - at all. The same goes for my implementations of onKeyUp and the handler that it calls. Something is a little weird here, and when I tried to look at the Android documentation for it, that didn't help at all. I thought that if you had an overide for onKeyDown, then when a key was pressed during execution of the program, onKeyDown would be called as soon as reasonably possible. End of story. But apparently there's something more to it. Apparently you have to do something else somewhere - possibly in the XML when defining the layout or something - to make it work. But I do not know what, and I could not find what in their documentation. What's the secret to this? Thanks!

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• RelayCommand sender from ItemsControl item

  - by Padu Merloti

  I've been using MVVM's RelayCommand with success to bind actions to XAML, but I'm having a small problem with my ItemsControl. <ItemsControl ItemsSource="{Binding Devices}" > <ItemsControl.ItemTemplate> <DataTemplate> <Grid Width="100" Margin="4" > <Button Command="{Binding Path=SelectDeviceCommand}" > <Grid> <Image Source="img_small.png"></Image> <Image Source="{Binding Path=Logo}" /> </Grid> </Button> </Grid> </DataTemplate> </ItemsControl.ItemTemplate> </ItemsControl> In my view model: public RelayCommand SelectDeviceCommand { get; set; } private ObservableCollection<Device> Devices; Devices = CreateListOfDevices(); private void InitializeCommands() { SelectDeviceCommand = new RelayCommand((s) => MessageBox.Show(s.ToString())); } How do I define my SelectDeviceCommand in my view model in order to receive object that is bound to that item? My SelectDeviceCommand is not even being called... (but that I guess is because I need to make my Device a mini-viewmodel and implement the SelectDeviceCommand in it, is that correct?)

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• Intercepting method with Spring AOP using only annotations

  - by fish

  In my Spring context file I have something like this: <bean id="userCheck" class="a.b.c.UserExistsCheck"/> <aop:config> <aop:aspect ref="userCheck"> <aop:pointcut id="checkUser" expression="execution(* a.b.c.d.*.*(..)) &amp;&amp; args(a.b.c.d.RequestObject)"/> <aop:around pointcut-ref="checkUser" method="checkUser"/> </aop:aspect> </aop:config> a.b.c.UserExistsCheck looks like this: @Aspect public class UserExistsCheck { @Autowired private UserInformation userInformation; public Object checkUser(ProceedingJoinPoint pjp) throws Throwable { int userId = ... //get it from the RequestObject passed as a parameter if (userExists(userId)) { return pjp.proceed(); } else { return new ResponseObject("Invalid user); } } And the class that is being intercepted with this stuff looks like this: public class Klazz { public ResponseObject doSomething(RequestObject request) {...} } This works. UserExistCheck is executed as desired before the call is passed to Klazz. The problem is that this is the only way I got it working. To get this working by using annotations instead of the context file seems to be just too much for my small brain. So... how exactly should I annotate the methods in UserExistsCheck and Klazz? And do I still need something else too? Another class? Still something in the context file?

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• iPad: Displaying UIActionSheet with UIPickerView as subview

  - by E-Madd

  I'm in the process of migrating an iPhone app to a universal app. On one of my views, I present a UIActionSheet with a UIPickerView as a subview. On the iPhone this always worked just fine. Of course, on the iPad I had to change a little to present the ActionSheet in a popover control. Here's some psuedo-code to outline where I'm at... actionSheet = [[UIActionSheet alloc] initWithTitle:nil delegate:self cancelButtonTitle:nil destructiveButtonTitle:nil otherButtonTitles:nil]; pickerView = [[UIPickerView alloc] initWithFrame:CGRectMake(0,44,0,0)]; pickerView.delegate = self; pickerView.dataSource = self; pickerView.showsSelectionIndicator = YES; [actionSheet addSubview:pickerView]; if (UI_USER_INTERFACE_IDIOM() != UIUserInterfaceIdiomPad){ [actionSheet showInView:self.view]; [actionSheet setBounds:actRect]; }else{ [actionSheet showFromRect:buttonRect inView:[UIApplication sharedApplication].keyWindow animated:YES]; } The resulting popover on the iPad is very small and only the very top of the UIPickerView is visible. How can I set the size of the popover?

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• Will fixed-point arithmetic be worth my trouble?

  - by Thomas

  I'm working on a fluid dynamics Navier-Stokes solver that should run in real time. Hence, performance is important. Right now, I'm looking at a number of tight loops that each account for a significant fraction of the execution time: there is no single bottleneck. Most of these loops do some floating-point arithmetic, but there's a lot of branching in between. The floating-point operations are mostly limited to additions, subtractions, multiplications, divisions and comparisons. All this is done using 32-bit floats. My target platform is x86 with at least SSE1 instructions. (I've verified in the assembler output that the compiler indeed generates SSE instructions.) Most of the floating-point values that I'm working with have a reasonably small upper bound, and precision for near-zero values isn't very important. So the thought occurred to me: maybe switching to fixed-point arithmetic could speed things up? I know the only way to be really sure is to measure it, that might take days, so I'd like to know the odds of success beforehand. Fixed-point was all the rage back in the days of Doom, but I'm not sure where it stands anno 2010. Considering how much silicon is nowadays pumped into floating-point performance, is there a chance that fixed-point arithmetic will still give me a significant speed boost? Does anyone have any real-world experience that may apply to my situation?

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• Pattern for sharing data between views (MVP or MVVM)

  - by Dovix

  What is a good pattern for sharing data between related views?. I have an application where 1 form contains many small views, each views behaves independently from each other more or less (they communicate/interact via an event bus). Every so often I need to pass the same objects to the child views. Sometimes I need this same object to be passed to a child view and then the child passes it onto another child itself contains. What is a good approach to sharing this data between all the views contained within the parent form (view) ? I have looked into CAB and their approach and every "view" has a "root work item" this work item has dictionary that contains a shared "state" between the views that are contained. Is this the best approach? just a shared dictionary all the views under a root view can access? My current approach right now is to have a function on the view that allows one to set the object for that view. Something like view.SetCustomer(Customer c); then if the view contains a child view it knows to set it on the child view ala: this.childview1.SetCustomer(c); The application is written in C# 3.5, for winforms using MVP with structure map as a IoC/DI provider.

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• Efficiently Determine if EF 4 POCO Already in ObjectSet

  - by Eric J.

  I'm trying EF 4 with POCO's on a small project for the first time. In my Repository implementation, I want to provide a method AddOrUpdate that will add a passed-in POCO to the repository if it's new, else do nothing (as the updated POCO will be saved when SaveChanges is called). My first thought was to do this: public void AddOrUpdate(Poco p) { if (!Ctx.Pocos.Contains<Poco>(p)) { Ctx.Pocos.AddObject(p); } } However that results in a NotSupportedException as documented under Referencing Non-Scalar Variables Not Supported (bonus question: why would that not be supported?) Just removing the Contains part and always calling AddObject results in an InvalidStateException: An object with the same key already exists in the ObjectStateManager. The existing object is in the Unchanged state. An object can only be added to the ObjectStateManager again if it is in the added state. So clearly EF 4 knows somewhere that this is a duplicate based on the key. What's a clean, efficient way for the Repository to update Pocos for either a new or pre-existing object when AddOrUpdate is called so that the subsequent call to SaveChanges() will do the right thing? I did consider carrying an isNew flag on the object itself, but I'm trying to take persistence ignorance as far as practical.

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• .NET Working with Locking and Threads

  - by aherrick

  Work on this small test application to learn threading/locking. I have the following code, I would think that the line should only write to console once. However it doesn't seem to be working as expected. Any thoughts on why? What I'm trying to do is add this Lot object to a List, then if any other threads try and hit that list, it would block. Am i completely misusing lock here? class Program { static void Main(string[] args) { int threadCount = 10; //spin up x number of test threads Thread[] threads = new Thread[threadCount]; Work w = new Work(); for (int i = 0; i < threadCount; i++) { threads[i] = new Thread(new ThreadStart(w.DoWork)); } for (int i = 0; i < threadCount; i++) { threads[i].Start(); } // don't let the console close Console.ReadLine(); } } public class Work { List<Lot> lots = new List<Lot>(); private static readonly object thisLock = new object(); public void DoWork() { Lot lot = new Lot() { LotID = 1, LotNumber = "100" }; LockLot(lot); } private void LockLot(Lot lot) { // i would think that "Lot has been added" should only print once? lock (thisLock) { if(!lots.Contains(lot)) { lots.Add(lot); Console.WriteLine("Lot has been added"); } } } }

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• Soft Paint Bucket Fill: Colour Equality

  - by Bart van Heukelom

  I'm making a small app where children can fill preset illustrations with colours. I've succesfully implemented an MS-paint style paint bucket using the flood fill argorithm. However, near the edges of image elements pixels are left unfilled, because the lines are anti-aliased. This is because the current condition on whether to fill is colourAtCurrentPixel == colourToReplace (the colours are RGB uints) I'd like to add a smoothing/treshold option like in Photoshop and other sophisticated tools, but what's the algorithm to determine the equality/distance between two colours? if (match(pixel(x,y), colourToReplace) setpixel(x,y,colourToReplaceWith) How to fill in match()? Here's my current full code: var b:BitmapData = settings.background; b.lock(); var from:uint = b.getPixel(x,y); var q:Array = []; var xx:int; var yy:int; var w:int = b.width; var h:int = b.height; q.push(y*w + x); while (q.length != 0) { var xy:int = q.shift(); xx = xy % w; yy = (xy - xx) / w; if (b.getPixel(xx,yy) == from) { b.setPixel(xx,yy,to); if (xx != 0) q.push(xy-1); if (xx != w-1) q.push(xy+1); if (yy != 0) q.push(xy-w); if (yy != h-1) q.push(xy+w); } } b.unlock(null);

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• Regex: Use start of line/end of line signs (^ or $) in different context

  - by fgysin

  While doing some small regex task I came upon this problem. I have a string that is a list of tags that looks e.g like this: foo,bar,qux,garp,wobble,thud What I needed to do was to check if a certain tag, e.g. 'garp' was in this list. (What it finally matches is not really important, just if there is a match or not.) My first and a bit stupid try at this was to use the following regex: [^,]garp[,$] My idea was that before 'garp' there should either be the start of the line/string or a comma, after 'garp' there should be either a comma or the end of the line/string. Now, it is instantly obvious that this regex is wrong: Both ^ and $ change their behaviour in the context of the character class [ ]. What I finally came up with is the following: ^garp$|^garp,|,garp,|,garp$ This regex just handles the 4 cases one by one. (Tag at beginning of list, in the center, at the end, or as the only element of the list.) The last regex is somehow a bit ugly in my eyes and just for funs sake I'd like to make it a bit more elegant. Is there a way how the start of line/end of line characters (^ and $) can be used in the context of character classes?

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• Collision detection of huge number of circles

  - by Tomek Tarczynski

  What is the best way to check collision of huge number of circles? It's very easy to detect collision between two circles, but if we check every combination then it is O(n^2) which definitely not an optimal solution. We can assume that circle object has following properties: -Coordinates -Radius -Velocity -Direction Velocity is constant, but direction can change. I've come up with two solutions, but maybe there are some better solutions. Solution 1 Divide whole space into overlapping squares and check for collision only with circles that are in the same square. Squares needs to overlap so there won't be a problem when circle moves from one square to another. Solution 2 At the beginning distances between every pair of circles need to be calculated. If the distance is small then these pair is stored in some list, and we need to check for collision in every update. If the distance is big then we store after which update there can be a collision (it can be calculated because we know the distance and velocitites). It needs to be stored in some kind of priority queue. After previously calculated number of updates distance needs to be checked again and then we do the same procedure - put it on the list or again in the priority queue.

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• Reference for proper handling of PID file on Unix

  - by bignose

  Where can I find a well-respected reference that details the proper handling of PID files on Unix? On Unix operating systems, it is common practice to “lock” a program (often a daemon) by use of a special lock file: the PID file. This is a file in a predictable location, often ‘/var/run/foo.pid’. The program is supposed to check when it starts up whether the PID file exists and, if the file does exist, exit with an error. So it's a kind of advisory, collaborative locking mechanism. The file contains a single line of text, being the numeric process ID (hence the name “PID file”) of the process that currently holds the lock; this allows an easy way to automate sending a signal to the process that holds the lock. What I can't find is a good reference on expected or “best practice” behaviour for handling PID files. There are various nuances: how to actually lock the file (don't bother? use the kernel? what about platform incompatibilities?), handling stale locks (silently delete them? when to check?), when exactly to acquire and release the lock, and so forth. Where can I find a respected, most-authoritative reference (ideally on the level of W. Richard Stevens) for this small topic?

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• What is a good starter-project in Perl?

  - by Vivin Paliath

  A buddy of mine wants to learn Perl. He asked me how to go about it. I told him: To learn Perl, you must first write Perl code. This was seconded by another buddy of mine who writes a lot of good Perl code. It's very zen, but not helpful. The problem is that this is exactly how I learnt to write Perl. At my very first job I had to implement something in Perl and I pretty much just jumped into it and waded and stumbled around until I figured it out. I was thinking that the best way for him to learn Perl would be to do a small project in Perl. The problem is, I can't think of anything that would be a good starter-project in Perl. For just basic learning and understanding concepts, I have recommended going to PerlMonks, to read Learning Perl, and also to look at Perl Best Practices. Aside from this, I think a good starter-project would be useful for him to get a grasp of the language. Any suggestions?

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