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  • GCD function in matlab

    - by SalemFayad
    hi, i am looking for a way to implement the "gcd" function used in matlab in another language but i really cant understand the way it functions. it says in http://www.mathworks.com/access/helpdesk/help/techdoc/ref/gcd.html that: "[G,C,D] = gcd(A,B) returns both the greatest common divisor array G, and the arrays C and D, which satisfy the equation: A(i).*C(i) + B(i).*D(i) = G(i)." but it says nothing about how it calculates C and D. i would be grateful if someone has a clearer idea about this subject! thanks:)

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  • GCD and AppleEvents / NSOperationQueue and AppleScript

    - by mahal tertin
    As i understood, the threads provided by GCD do have a runloop but no source/port. Now i use some of methods that call AppleScripts thru AppleEvents inside an NSOperationQueue. And sometimes my app crashes with following stacktrace. my questions: Usage of AppleScript inside a NSInvocationOperation or NSBlockOperation Usage of AppleEvents inside GCD-Threads do i have to add a source / port to a runloop of a gcd-thread before using AppleEvents? do i have to add a source / port to a runloop of a gcd-thread before using [CATransaction commit]? do i have to add a source / port to a runloop of a gcd-thread before using [NSObject performSelectorAfterDelay...] ? if yes, how? can i simply call CFRunLoopRunInMode(kCFRunLoopDefaultMode, 5.0, false); /// or 30 or the defined timeout of appleevent? .. Thread 9: Dispatch queue: com.apple.root.default-priority 0 libSystem.B.dylib 0x00007fff88276e82 semaphore_wait_signal_trap 10 1 libSystem.B.dylib 0x00007fff8827c3cd pthread_mutex_lock 469 2 com.apple.applescript 0x000000011d3d461f AppleScriptComponent 50 3 com.apple.applescript 0x000000011d3edbcc AGenericCall::Delegate(ComponentInstanceRecord*) 46 4 com.apple.applescript 0x000000011d3ed520 AGenericManager::HandleOSACall(ComponentParameters*) 54 5 com.apple.applescript 0x000000011d3ed4b0 GenericComponent 219 6 com.apple.openscripting 0x00007fff8381c6da OSAExecuteEvent 63 7 com.apple.Foundation 0x00007fff86f320d8 -[NSAppleScript(NSPrivate) _executeAppleEvent:withMode:error:] 161 8 xxx 0x0000000100048af0 -[TCallScript callScript:withArrayOfParameters:] 480 9 xxx 0x0000000100048ffd -[TCallScript callHandler:withParameters:] 477 10 xxx 0x0000000100036032 -[ZFOpenWindowController getSafariItemForCurrentTabForWindow:] 66 11 xxx 0x00000001000346af -[ZFOpenWindowController refreshWindowList:] 1679 12 xxx 0x000000010003541c -[ZFOpenWindowController bringZFToForegroundZoomOut:orJustLinkFrontMost:toItem:] 2988 13 xxx 0x0000000100053556 __-[ZFSelectionTool openWithPreferredApplication:]_block_invoke_516 54 14 com.apple.Foundation 0x00007fff86ed87d9 -[NSBlockOperation main] 140 15 com.apple.Foundation 0x00007fff86ec906d -[__NSOperationInternal start] 681 16 com.apple.Foundation 0x00007fff86ec8d23 ____startOperations_block_invoke_2 99 17 libSystem.B.dylib 0x00007fff882b2ce8 _dispatch_call_block_and_release 15 18 libSystem.B.dylib 0x00007fff88291279 _dispatch_worker_thread2 231 19 libSystem.B.dylib 0x00007fff88290bb8 _pthread_wqthread 353 20 libSystem.B.dylib 0x00007fff88290a55 start_wqthread 13 ... Thread 11 Crashed: Dispatch queue: com.apple.root.default-priority 0 com.apple.applescript 0x000000011d40f658 BCHandleError() 182 1 com.apple.applescript 0x000000011d4059ca UASExecute1() 2546 2 com.apple.applescript 0x000000011d3dd1d5 ASExecuteEvent(AEDesc const*, unsigned int, int, unsigned int*) 695 3 ...ple.CoreServices.CarbonCore 0x00007fff85388e04 CallComponentFunction 28 4 com.apple.applescript 0x000000011d3d4cad AppleScriptComponent 1728 5 com.apple.applescript 0x000000011d3edbcc AGenericCall::Delegate(ComponentInstanceRecord*) 46 6 com.apple.applescript 0x000000011d3ed520 AGenericManager::HandleOSACall(ComponentParameters*) 54 7 com.apple.applescript 0x000000011d3ed4b0 GenericComponent 219 8 com.apple.openscripting 0x00007fff8381c6da OSAExecuteEvent 63 9 com.apple.Foundation 0x00007fff86f320d8 -[NSAppleScript(NSPrivate) _executeAppleEvent:withMode:error:] 161 10 xxx 0x0000000100048af0 -[TCallScript callScript:withArrayOfParameters:] 480 11 xxx 0x0000000100048ffd -[TCallScript callHandler:withParameters:] 477 12 xxx 0x0000000100035c67 -[ZFOpenWindowController getItemForAXDocumentOfFrontMostWindow] 119 13 xxx 0x00000001000359f1 -[ZFOpenWindowController getItemForFrontMostWindow:] 721 14 xxx 0x00000001000348ac -[ZFOpenWindowController bringZFToForegroundZoomOut:orJustLinkFrontMost:toItem:] 60 15 xxx 0x0000000100053556 __-[ZFSelectionTool openWithPreferredApplication:]_block_invoke_516 54 16 com.apple.Foundation 0x00007fff86ed87d9 -[NSBlockOperation main] 140 17 com.apple.Foundation 0x00007fff86ec906d -[__NSOperationInternal start] 681 18 com.apple.Foundation 0x00007fff86ec8d23 ____startOperations_block_invoke_2 99 19 libSystem.B.dylib 0x00007fff882b2ce8 _dispatch_call_block_and_release 15 20 libSystem.B.dylib 0x00007fff88291279 _dispatch_worker_thread2 231 21 libSystem.B.dylib 0x00007fff88290bb8 _pthread_wqthread 353 22 libSystem.B.dylib 0x00007fff88290a55 start_wqthread 13

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  • What is the best way to attach extenstion methods to static classes rather than to instances of a cl

    - by John Gietzen
    If I have a method for calculating the greatest common divisor of two integers as: public static int GCD(int a, int b) { return b == 0 ? a : GCD(b, a % b); } What would be the best way to attach that to the System.Math class? Here are the three ways I have come up with: public static int GCD(this int a, int b) { return b == 0 ? a : b.GCD(a % b); } // Lame... var gcd = a.GCD(b); and: public static class RationalMath { public static int GCD(int a, int b) { return b == 0 ? a : GCD(b, a % b); } } // Lame... var gcd = RationalMath.GCD(a, b); and: public static int GCD(this Type math, int a, int b) { return b == 0 ? a : typeof(Math).GCD(b, a % b); } // Neat? var gcd = typeof(Math).GCD(a, b); The desired syntax is Math.GCD since that is the standard for all mathematical functions. Any suggestions? What should I do to get the desired syntax?

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  • What is the best way to attach static methods to classes rather than to instances of a class?

    - by John Gietzen
    If I have a method for calculating the greatest common divisor of two integers as: public static int GCD(int a, int b) { return b == 0 ? a : GCD(b, a % b); } What would be the best way to attach that to the System.Math class? Here are the three ways I have come up with: public static int GCD(this int a, int b) { return b == 0 ? a : b.GCD(a % b); } // Lame... var gcd = a.GCD(b); and: public static class RationalMath { public static int GCD(int a, int b) { return b == 0 ? a : GCD(b, a % b); } } // Lame... var gcd = RationalMath.GCD(a, b); and: public static int GCD(this Type math, int a, int b) { return b == 0 ? a : typeof(Math).GCD(b, a % b); } // Neat? var gcd = typeof(Math).GCD(a, b); The desired syntax is Math.GCD since that is the standard for all mathematical functions. Any suggestions? What should I do to get the desired syntax?

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  • Issue with GCD and too many threads

    - by dariaa
    I have an image loader class which provided with NSURL loads and image from the web and executes completion block. Code is actually quite simple - (void)downloadImageWithURL:(NSString *)URLString completion:(BELoadImageCompletionBlock)completion { dispatch_async(_queue, ^{ // dispatch_async(dispatch_get_global_queue(DISPATCH_QUEUE_PRIORITY_HIGH, 0), ^{ UIImage *image = nil; NSURL *URL = [NSURL URLWithString:URLString]; if (URL) { image = [UIImage imageWithData:[NSData dataWithContentsOfURL:URL]]; } dispatch_async(dispatch_get_main_queue(), ^{ completion(image, URLString); }); }); } When I replace dispatch_async(_queue, ^{ with commented out dispatch_async(dispatch_get_global_queue(DISPATCH_QUEUE_PRIORITY_HIGH, 0), ^{ Images are loading much faster, wich is quite logical (before that images would be loaded one at a time, now a bunch of them are loading simultaneously). My issue is that I have perhaps 50 images and I call downloadImageWithURL:completion: method for all of them and when I use global queue instead of _queue my app eventually crashes and I see there are 85+ threads. Can the problem be that my calling dispatch_get_global_queue(DISPATCH_QUEUE_PRIORITY_HIGH, 0) 50 times in a row makes GCD create too many threads? I thought that gcd handles all the treading and makes sure the number of threads is not huge, but if it's not the case is there any way I can influence number of threads?

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  • converting NSTimer running not on main runloop to GCD

    - by Justin Galzic
    I have a task that runs periodically and it was originally designed to run on a separate run loop than the main runloop using NSThread and NSTimer. What's the best way to adapt this to take advantage of GCD? Current code: -(void)initiateSomeTask { [NSThread detachNewThreadSelector:@selector(startTimerTask) toTarget:self withObject:nil]; } -(void)startTimerTask { // We won't get back the main runloop since we're on a new thread NSRunLoop *myRunLoop = [NSRunLoop currentRunLoop]; NSPort *myPort = [NSMachPort port]; [myRunLoop addPort:myPort forMode:NSDefaultRunLoopMode]; NSTimer *myTimer = [NSTimer timerWithTimeInterval:10 /* seconds */ target:self selector:@selector(doMyTaskMethod) userInfo:nil repeats:YES]; [myRunLoop addTimer:myTimer forMode:NSRunLoopCommonModes]; [myRunLoop run]; } Is there anything I can do besides replace detachNewThreadSelector with dispatch_async?

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  • Graceful termination of NSApplication with Core Data and Grand Central Dispatch (GCD)

    - by Vincent Mac
    I have an Cocoa Application (Mac OS X SDK 10.7) that is performing some processes via Grand Central Dispatch (GCD). These processes are manipulating some Core Data NSManagedObjects (non-document-based) in a manner that I believe is thread safe (creating a new managedObjectContext for use in this thread). The problem I have is when the user tries to quit the application while the dispatch queue is still running. The NSApplication delegate is being called before actually quitting. - (NSApplicationTerminateReply)applicationShouldTerminate:(NSApplication *)sender I get an error "Could not merge changes." Which is somewhat expected since there are still operations being performed through the different managedObjectContext. I am then presented with the NSAlert from the template that is generated with a core data application. In the Threading Programming Guide there is a section called "Be Aware of Thread Behaviors at Quit Time" which alludes to using replyToApplicationShouldTerminate: method. I'm having a little trouble implementing this. What I would like is for my application to complete processing the queued items and then terminate without presenting an error message to the user. It would also be helpful to update the view or use a sheet to let the user know that the app is performing some action and will terminate when the action is complete. Where and how would I implement this behavior?

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  • Updating UISearchDisplayController with Core Data results using GCD

    - by Brian Halpin
    I'm having trouble displaying the results from Core Data in my UISearchDisplayController when I implement GCD. Without it, it works, but obviously blocks the UI. In my SearchTableViewController I have the following two methods: - (BOOL)searchDisplayController:(UISearchDisplayController *)controller shouldReloadTableForSearchString:(NSString *)searchString { // Tell the table data source to reload when text changes [self filterContentForSearchText:searchString]; // Return YES to cause the search result table view to be reloaded. return YES; } // Update the filtered array based on the search text -(void)filterContentForSearchText:(NSString*)searchText { // Remove all objects from the filtered search array [self.filteredLocationsArray removeAllObjects]; NSPredicate *predicate = [CoreDataMaster predicateForLocationUsingSearchText:@"Limerick"]; CoreDataMaster *coreDataMaster = [[CoreDataMaster alloc] init]; // Filter the array using NSPredicate self.filteredLocationsArray = [NSMutableArray arrayWithArray: [coreDataMaster fetchResultsFromCoreDataEntity:@"City" UsingPredicate:predicate]]; } You can probably guess that my problem is with returning the array from [coreDataMaster fetchResultsFromCoreDataEntity]. Below is the method: - (NSArray *)fetchResultsFromCoreDataEntity:(NSString *)entity UsingPredicate:(NSPredicate *)predicate { NSMutableArray *fetchedResults = [[NSMutableArray alloc] init]; dispatch_queue_t coreDataQueue = dispatch_queue_create("com.coredata.queue", DISPATCH_QUEUE_SERIAL); dispatch_async(coreDataQueue, ^{ NSFetchRequest *fetchRequest = [[NSFetchRequest alloc] init]; NSEntityDescription *entityDescription = [NSEntityDescription entityForName:entity inManagedObjectContext:self.managedObjectContext]; NSSortDescriptor *nameSort = [[NSSortDescriptor alloc] initWithKey:@"name" ascending:YES]; NSArray *sortDescriptors = [NSArray arrayWithObjects:nameSort, nil]; [fetchRequest setEntity:entityDescription]; [fetchRequest setSortDescriptors:sortDescriptors]; // Check if predicate is set if (predicate) { [fetchRequest setPredicate:predicate]; } NSError *error = nil; NSArray *fetchedManagedObjects = [self.managedObjectContext executeFetchRequest:fetchRequest error:&error]; for (City *city in fetchedManagedObjects) { [fetchedResults addObject:city]; } NSDictionary *userInfo = [NSDictionary dictionaryWithObject:[NSArray arrayWithArray:fetchedResults] forKey:@"results"]; [[NSNotificationCenter defaultCenter] postNotificationName:@"fetchResultsComplete" object:nil userInfo:userInfo]; }); return [NSArray arrayWithArray:fetchedResults]; } So the thread hasn't finished executing by the time it returns the results to self.filteredLocationsArray. I've tried added a NSNotification which passes the NSDictionary to this method: - (void)updateSearchResults:(NSNotification *)notification { NSDictionary *userInfo = notification.userInfo; NSArray *array = [userInfo objectForKey:@"results"]; self.filteredLocationsArray = [NSMutableArray arrayWithArray:array]; [self.tableView reloadData]; } I've also tried refreshing the searchViewController like [self.searchDisplayController.searchResultsTableView reloadData]; but to no avail. I'd really appreciate it if someone could point me in the right direction and show me where I might be going wrong. Thanks

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  • Freezes (not crashes) with GCD, blocks and Core Data

    - by Lukasz
    I have recently rewritten my Core Data driven database controller to use Grand Central Dispatch to manage fetching and importing in the background. Controller can operate on 2 NSManagedContext's: NSManagedObjectContext *mainMoc instance variable for main thread. this contexts is used only by quick access for UI by main thread or by dipatch_get_main_queue() global queue. NSManagedObjectContext *bgMoc for background tasks (importing and fetching data for NSFetchedresultsController for tables). This background tasks are fired ONLY by user defined queue: dispatch_queue_t bgQueue (instance variable in database controller object). Fetching data for tables is done in background to not block user UI when bigger or more complicated predicates are performed. Example fetching code for NSFetchedResultsController in my table view controllers: -(void)fetchData{ dispatch_async([CDdb db].bgQueue, ^{ NSError *error = nil; [[self.fetchedResultsController fetchRequest] setPredicate:self.predicate]; if (self.fetchedResultsController && ![self.fetchedResultsController performFetch:&error]) { NSSLog(@"Unresolved error in fetchData %@", error); } if (!initial_fetch_attampted)initial_fetch_attampted = YES; fetching = NO; dispatch_async(dispatch_get_main_queue(), ^{ [self.table reloadData]; [self.table scrollRectToVisible:CGRectMake(0, 0, 100, 20) animated:YES]; }); }); } // end of fetchData function bgMoc merges with mainMoc on save using NSManagedObjectContextDidSaveNotification: - (void)bgMocDidSave:(NSNotification *)saveNotification { // CDdb - bgMoc didsave - merging changes with main mainMoc dispatch_async(dispatch_get_main_queue(), ^{ [self.mainMoc mergeChangesFromContextDidSaveNotification:saveNotification]; // Extra notification for some other, potentially interested clients [[NSNotificationCenter defaultCenter] postNotificationName:DATABASE_SAVED_WITH_CHANGES object:saveNotification]; }); } - (void)mainMocDidSave:(NSNotification *)saveNotification { // CDdb - main mainMoc didSave - merging changes with bgMoc dispatch_async(self.bgQueue, ^{ [self.bgMoc mergeChangesFromContextDidSaveNotification:saveNotification]; }); } NSfetchedResultsController delegate has only one method implemented (for simplicity): - (void)controllerDidChangeContent:(NSFetchedResultsController *)controller { dispatch_async(dispatch_get_main_queue(), ^{ [self fetchData]; }); } This way I am trying to follow Apple recommendation for Core Data: 1 NSManagedObjectContext per thread. I know this pattern is not completely clean for at last 2 reasons: bgQueue not necessarily fires the same thread after suspension but since it is serial, it should not matter much (there is never 2 threads trying access bgMoc NSManagedObjectContext dedicated to it). Sometimes table view data source methods will ask NSFetchedResultsController for info from bgMoc (since fetch is done on bgQueue) like sections count, fetched objects in section count, etc.... Event with this flaws this approach works pretty well of the 95% of application running time until ... AND HERE GOES MY QUESTION: Sometimes, very randomly application freezes but not crashes. It does not response on any touch and the only way to get it back to live is to restart it completely (switching back to and from background does not help). No exception is thrown and nothing is printed to the console (I have Breakpoints set for all exception in Xcode). I have tried to debug it using Instruments (time profiles especially) to see if there is something hard going on on main thread but nothing is showing up. I am aware that GCD and Core Data are the main suspects here, but I have no idea how to track / debug this. Let me point out, that this also happens when I dispatch all the tasks to the queues asynchronously only (using dispatch_async everywhere). This makes me think it is not just standard deadlock. Is there any possibility or hints of how could I get more info what is going on? Some extra debug flags, Instruments magical tricks or build setting etc... Any suggestions on what could be the cause are very much appreciated as well as (or) pointers to how to implement background fetching for NSFetchedResultsController and background importing in better way.

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  • Objective C ASIHTTPRequest nested GCD block in complete block

    - by T.Leavy
    I was wondering if this is the correct way to have nested blocks working on the same variable in Objective C without causing any memory problems or crashes with ARC. It starts with a ASIHttpRequest complete block. MyObject *object = [dataSet objectAtIndex:i]; ASIHTTPRequest *request = [[ASIHTTPRequest alloc]initWithURL:@"FOO"]; __block MyObject *mutableObject = object; [request setCompleteBlock:^{ mutableObject.data = request.responseData; __block MyObject *gcdMutableObject = mutableObject; dispatch_async(dispatch_get_global_queue(DISPATCH_QUEUE_PRIORITY_DEFAULT,0),^{ [gcdMutableObject doLongComputation]; dispatch_async(dispatch_get_main_queue(),^{ [self updateGUIWithObject:gcdMutableObject]; }); }); [request startAsynchronous]; My main concern is nesting the dispatch queues and using the __block version of the previous queue to access data. Is what I am doing safe?

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  • Creating futures using Apple's GCD

    - by jer
    I'm working on a library which implements the actor model on top of Grand Central Dispatch (specifically the C level API libdispatch). Basically a brief overview of my system is as such: Communication happens between actors using messages Multicast communication only (one actor to many actors) Senders and receivers are decoupled from one another using a blackboard where messages are pushed to. Messages are sent in the default queue asynchronously using dispatch_group_async() once a message gets pushed onto the blackboard. I'm trying to implement futures in the language right now, so I've created a new type which holds some information: A group of its own The value being 'returned' However, I have a problem since dispatch_block_t is of type void (^)(void) so it doesn't return anything. So my idea of in my future_new() function of setting up another group which can be used to execute a block returning a result, which I can store in my "value" member in my future_t structure, isn't going to work. The rest of the futures implementation is very clear, except it all depends on being able to get the value into the future back from the actor, acting on the message. When using the library, it would greatly reduce its usefulness if I had to ask users (and myself) to be aware when futures were going to be used by other parts of the system—It just isn't practical. I'm wondering if anyone can think of a way around this?

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  • NSThread vs. NSOperationQueue vs. ??? on the iPhone

    - by kubi
    Currently I'm using NSThread to cache images in another thread. [NSThread detachNewThreadSelector:@selector(cacheImage:) toTarget:self withObject:image]; Alternatively: [self performSelectorInBackground:@selector(cacheImage:) withObject:image]; Alternatively, I can use an NSOperationQueue NSInvocationOperation *invOperation = [[NSInvocationOperation alloc] initWithTarget:self selector:@selector(cacheImage:) object:image]; NSOperationQueue *opQueue = [[NSOperationQueue alloc] init]; [opQueue addOperation:invOperation]; Is there any reason to switch away from NSThread? GCD is a 4th option when it's released for the iPhone, but unless there's a significant performance gain, I'd rather stick with methods that work in most platforms.

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  • Could Grand Central Dispatch (`libdispatch`) ever be made available on Windows?

    - by elliottcable
    I’m looking into multithreading, and GCD seems like a much better option than manually writing a solution using pthread.h and pthreads-win32. However, although it looks like libdispatch is either working on, or soon going to be working on, most newer POSIX-compatible systems… I have to ask, what about Windows? What are the chances of libdispatch being ported to Windows? What are the barriers preventing that from happening? If it came down to it, what would I need to do to preform that portage? Edit: Some things I already know, to get the discussion started: We need a blocks-compatible compiler that will compile on Windows, no? Will PLBlocks handle that? Can we use the LLVM blocks runtime? Can’t we replace all the pthread.h dependencies in userspace libdispatch with APR calls, for portability? Or, alternatively, use pthreads-win32 I suppose…

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  • Could Grand Central Dispatch (`libdispatch`) ever be available on Windows?

    - by elliottcable
    I’m looking into multithreading, and GCD seems like a much better option than manually writing a solution using pthread.h and pthreads-win32. However, although it looks like libdispatch is either working on, or soon going to be working on, most newer POSIX-compatible systems… I have to ask, what about Windows? What are the chances of libdispatch being ported to Windows? What are the barriers preventing that from happening? If it came down to it, what would I need to do to preform that portage?

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  • Get aspect ratio of a monitor

    - by Alexander Stalt
    I want to get aspect ratio of a monitor as two digits : width and height. For example 4 and 3, 5 and 4, 16 and 9. I wrote some code for that task. Maybe it is any easier way to do that ? For example, some library function =\ /// <summary> /// Aspect ratio. /// </summary> public struct AspectRatio { int _height; /// <summary> /// Height. /// </summary> public int Height { get { return _height; } } int _width; /// <summary> /// Width. /// </summary> public int Width { get { return _width; } } /// <summary> /// Ctor. /// </summary> /// <param name="height">Height of aspect ratio.</param> /// <param name="width">Width of aspect ratio.</param> public AspectRatio(int height, int width) { _height = height; _width = width; } } public sealed class Aux { /// <summary> /// Get aspect ratio. /// </summary> /// <returns>Aspect ratio.</returns> public static AspectRatio GetAspectRatio() { int deskHeight = Screen.PrimaryScreen.Bounds.Height; int deskWidth = Screen.PrimaryScreen.Bounds.Width; int gcd = GCD(deskWidth, deskHeight); return new AspectRatio(deskHeight / gcd, deskWidth / gcd); } /// <summary> /// Greatest Common Denominator (GCD). Euclidean algorithm. /// </summary> /// <param name="a">Width.</param> /// <param name="b">Height.</param> /// <returns>GCD.</returns> static int GCD(int a, int b) { return b == 0 ? a : GCD(b, a % b); } }

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  • Compiler error: Variable or field declared void [closed]

    - by ?? ?
    i get some error when i try to run this, could someone please tell me the mistakes, thank you! [error: C:\Users\Ethan\Desktop\Untitled1.cpp In function `int main()': 25 C:\Users\Ethan\Desktop\Untitled1.cpp variable or field `findfactors' declared void 25 C:\Users\Ethan\Desktop\Untitled1.cpp initializer expression list treated as compound expression] #include<iostream> #include<cmath> using namespace std; void prompt(int&, int&, int&); int gcd(int , int , int );//3 input, 3 output void findfactors(int , int , int, int, int&, int&);//3 input, 2 output void display(int, int, int, int, int);//5 inputs int main() { int a, b, c; //The coefficients of the quadratic polynomial int ag, bg, cg;//value of a, b, c after factor out gcd int f1, f2; //The two factors of a*c which add to be b int g; //The gcd of a, b, c prompt(a, b, c);//Call the prompt function g=gcd(a, b, c);//Calculation of g void findfactors(a, b, c, f1, f2);//Call findFactors on factored polynomial display(g, f1, f2, a, c);//Call display function to display the factored polynomial system("PAUSE"); return 0; } void prompt(int& num1, int& num2, int& num3) //gets 3 ints from the user { cout << "This program factors polynomials of the form ax^2+bx+c."<<endl; while(num1==0) { cout << "Enter a value for a: "; cin >> num1; if(num1==0) { cout<< "a must be non-zero."<<endl; } } while(num2==0 && num3==0) { cout << "Enter a value for b: "; cin >> num2; cout << "Enter a value for c: "; cin >> num3; if(num2==0 && num3==0) { cout<< "b and c cannot both be 0."<<endl; } } } int gcd(int num1, int num2, int num3) { int k=2, gcd=1; while (k<=num1 && k<=num2 && k<=num3) { if (num1%k==0 && num2%k==0 && num3%k==0) gcd=k; k++; } return gcd; } void findFactors(int Ag, int Bg, int Cg,int& F1, int& F2) { int y=Ag*Cg; int z=sqrt(abs(y)); for(int i=-z; i<=z; i++) //from -sqrt(|y|) to sqrt(|y|) { if(i==0)i++; //skips 0 if(y%i==0) //if i is a factor of y { if(i+y/i==Bg) //if i and its partner add to be b F1=i, F2=y/i; else F1=0, F2=0; } } } void display(int G, int factor1, int factor2, int A, int C) { int k=2, gcd1=1; while (k<=A && k<=factor1) { if (A%k==0 && factor1%k==0) gcd1=k; k++; } int t=2, gcd2=1; while (t<=factor2 && t<=C) { if (C%t==0 && factor2%t==0) gcd2=t; t++; } cout<<showpos<<G<<"*("<<gcd1<<"x"<<gcd2<<")("<<A/gcd1<<"x"<<C/gcd2<<")"<<endl; }

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  • error in encryption program

    - by Raja
    #include<iostream> #include<math.h> #include<string> using namespace std; int gcd(int n,int m) { if(m<=n && n%m ==0) return m; if(n<m) return gcd(m,n); else return gcd(m,n%m); } int REncryptText(char m) { int p = 11, q = 3; int e = 3; int n = p * q; int phi = (p - 1) * (q - 1); int check1 = gcd(e, p - 1); int check2 = gcd(e, q - 1); int check3 = gcd(e, phi); // // Compute d such that ed = 1 (mod phi) //i.e. compute d = e-1 mod phi = 3-1 mod 20 //i.e. find a value for d such that phi divides (ed-1) //i.e. find d such that 20 divides 3d-1. //Simple testing (d = 1, 2, ...) gives d = 7 // double d = Math.Pow(e, -1) % phi; int d = 7; // public key = (n,e) // (33,3) //private key = (n,d) //(33 ,7) double g = pow(m,e); int ciphertext = g %n; // Now say we want to encrypt the message m = 7, c = me mod n = 73 mod 33 = 343 mod 33 = 13. Hence the ciphertext c = 13. //double decrypt = Math.Pow(ciphertext, d) % n; return ciphertext; } int main() { char plaintext[80],str[80]; cout<<" enter the text you want to encrpt"; cin.get(plaintext,79); int l =strlen(plaintext); for ( int i =0 ; i<l ; i++) { char s = plaintext[i]; str[i]=REncryptText(s); } for ( int i =0 ; i<l ; i++) { cout<<"the encryption of string"<<endl; cout<<str[i]; } return 0; }

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  • Solving the water jug problem

    - by Amit
    While reading through some lecture notes on preliminary number theory, I came across the solution to water jug problem (with two jugs) which is summed as thus: Using the property of the G.C.D of two numbers that GCD(a,b) is the smallest possible linear combination of a and b, and hence a certain quantity Q is only measurable by the 2 jugs, iff Q is a n*GCD(a,b), since Q=sA + tB, where: n = a positive integer A = capacity of jug A B= capacity of jug B And, then the method to the solution is discussed Another model of the solution is to model the various states as a state-space search problem as often resorted to in Artificial Intelligence. My question is: What other known methods exist which models the solution, and how? Google didn't throw up much.

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  • Project Euler 5: (Iron)Python

    - by Ben Griswold
    In my attempt to learn (Iron)Python out in the open, here’s my solution for Project Euler Problem 5.  As always, any feedback is welcome. # Euler 5 # http://projecteuler.net/index.php?section=problems&id=5 # 2520 is the smallest number that can be divided by each # of the numbers from 1 to 10 without any remainder. # What is the smallest positive number that is evenly # divisible by all of the numbers from 1 to 20? import time start = time.time() def gcd(a, b): while b: a, b = b, a % b return a def lcm(a, b): return a * b // gcd(a, b) print reduce(lcm, range(1, 20)) print "Elapsed Time:", (time.time() - start) * 1000, "millisecs" a=raw_input('Press return to continue')

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  • Least common multiple for 3 or more numbers

    - by paan
    How do you calculate the least common multiple of multiple numbers? So far I've only been able to calculate it between two numbers. But have no idea how to expand it to calculate 3 or more numbers. So far this is how I did it LCM = num1 * num2 / gcd ( num1 , num2 ) With gcd is the function to calculate the greatest common divisor for the numbers. Using euclidean algorithm But I can't figure out how to calculate it for 3 or more numbers.

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  • Optimizing list comprehension to find pairs of co-prime numbers

    - by user3685422
    Given A,B print the number of pairs (a,b) such that GCD(a,b)=1 and 1<=a<=A and 1<=b<=B. Here is my answer: return len([(x,y) for x in range(1,A+1) for y in range(1,B+1) if gcd(x,y) == 1]) My answer works fine for small ranges but takes enough time if the range is increased. such as 1 <= A <= 10^5 1 <= B <= 10^5 is there a better way to write this or can this be optimized?

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  • using lambda instead of let in scheme

    - by Radagaisus
    Hey, In SICP 1.2.1 there is a function that makes a rational number, as follow: (define (make-rat n d) (let ((g (gcd n d))) (cons (/ n g) (/ d g)))) I'm just curious how you can implement the same thing using lambda instead of let, without calling GCD twice. I couldn't figure it out myself.

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  • What are algorithmic paradigms?

    - by Vaibhav Agarwal
    We generally talk about paradigms of programming as functional, procedural, object oriented, imperative etc but what should I reply when I am asked the paradigms of algorithms? For example are Travelling Salesman Problem, Dijkstra Shortest Path Algorithm, Euclid GCD Algorithm, Binary search, Kruskal's Minimum Spanning Tree, Tower of Hanoi paradigms of algorithms? Should I answer the data structures I would use to design these algorithms?

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  • Nasty mono bug with F#

    - by Aurimas Anskaitis
    Hi, I have this monstrous f# 2.0 program My mono version is Mono JIT compiler version 2.9 (master/f593354 Sun Dec 26 03:15:55 EET 2010) Copyright (C) 2002-2010 Novell, Inc and Contributors. www.mono-project.com TLS: __thread SIGSEGV: altstack Notifications: epoll Architecture: x86 Disabled: none Misc: softdebug LLVM: supported, not enabled. GC: Included Boehm (with typed GC and Parallel Mark) //--------------------------------------------- module Main let rec gcd x y = if y = 0 then x else gcd y (x%y) let main = printfn "%i" (gcd 4 2) main //----------------------------------------------- And the problem is that output from running the program is as follows: Stacktrace: at (wrapper managed-to-native) System.Reflection.MonoMethodInfo.get_parameter_info (intptr,System.Reflection.MemberInfo) <0xffffffff at System.Reflection.MonoMethodInfo.GetParametersInfo (intptr,System.Reflection.MemberInfo) <0x00013 at System.Reflection.MonoCMethod.GetParameters () <0x00015 at System.Reflection.MonoCMethod.Invoke (object,System.Reflection.BindingFlags,System.Reflection.Binder,object[],System.Globalization.CultureInfo) <0x00035 at System.Reflection.MonoCMethod.Invoke (System.Reflection.BindingFlags,System.Reflection.Binder,object[],System.Globalization.CultureInfo) <0x00024 at System.Reflection.ConstructorInfo.Invoke (object[]) <0x0003f at System.Activator.CreateInstance (System.Type,bool) <0x0017c at System.Activator.CreateInstance (System.Type) <0x00012 at Microsoft.FSharp.Reflection.FSharpValue.MakeFunction (System.Type,Microsoft.FSharp.Core.FSharpFunc2<object, object>) <0x00145> at Microsoft.FSharp.Core.PrintfImpl.capture@529<b, c, d> (Microsoft.FSharp.Core.FSharpFunc2, Microsoft.FSharp.Core.FSharpFunc`2<char, Microsoft.FSharp.Core.Unit>, Microsoft.FSharp.Core.FSharpFunc`2,string,int,Microsoft.FSharp.Collections.FSharpList1<object>,System.Type,int) <0x00147> at Microsoft.FSharp.Core.PrintfImpl.gprintf<b, c, d, a> (Microsoft.FSharp.Core.FSharpFunc2, Microsoft.FSharp.Core.FSharpFunc`2<char, Microsoft.FSharp.Core.Unit>, Microsoft.FSharp.Core.FSharpFunc`2,Microsoft.FSharp.Core.PrintfFormat4<a, b, c, d>) <0x000dd> at Microsoft.FSharp.Core.PrintfModule.kprintf_imperative<a, b, c> (Microsoft.FSharp.Core.FSharpFunc2,b,Microsoft.FSharp.Core.FSharpFunc2<char, Microsoft.FSharp.Core.Unit>,Microsoft.FSharp.Core.PrintfFormat4) <0x00058 at Microsoft.FSharp.Core.PrintfModule.PrintFormatToTextWriterThen (Microsoft.FSharp.Core.FSharpFunc2<Microsoft.FSharp.Core.Unit, TResult>,System.IO.TextWriter,Microsoft.FSharp.Core.PrintfFormat4) <0x0004d at Microsoft.FSharp.Core.PrintfModule.PrintFormatLineToTextWriter (System.IO.TextWriter,Microsoft.FSharp.Core.PrintfFormat`4) <0x0004d at .$Main.main@ () <0x00042 Native stacktrace: mono() [0x80dc13b] mono() [0x811c65b] mono() [0x8059a11] [0x7af40c] mono() [0x8228214] mono() [0x8228214] mono() [0x8228214] mono() [0x8228214] mono() [0x8228214] mono() [0x8228214] mono() [0x8228214] mono() [0x8228214] mono() [0x8228282] mono() [0x822991e] mono() [0x822aa9d] mono(mono_array_new_specific+0xea) [0x813ba9a] mono() [0x81c63a1] mono() [0x8149ac8] [0xc04328] [0xc042e4] [0xc042be] [0xc0455e] [0xc0451d] [0xc044d8] [0xc0349d] [0xc0330b] [0xc02f9e] [0xbfe960] [0xbfe6c6] [0xbfe571] [0xbfe4de] [0xbfe44e] [0xbf9d2b] [0x9bf0724] [0x9bf0724] [0x9bf0724] [0x9bf0724] [0x9bf0724] [0x9bf0724] [0x9bf0724] [0x9bf0724] [0x9bf0724] [0x9bf0724] [0x9bf0724] [0x9bf0724] [0x9bf0724] [0x9bf0724] [0x9bf0724] [0x9bf0724] [0x9bf0724] [0x9bf0724] [0x9bf0724] [0x9bf0724] [0x9bf0724] [0x9bf0724] [0x9bf0724] [0x9bf0724] [0x9bf0724] [0x9bf0724] [0x9bf0724] [0x9bf0724] [0x9bf0724] [0x9bf0724] [0x9bf0724] [0x9bf0724] [0x9bf0724] [0x9bf0724] [0x9bf0724] [0x9bf0724] [0x9bf0724] [0x9bf0724] [0x9bf0724] [0x9bf0724] [0x9bf0724] [0x9bf0724] [0x9bf0724] [0x9bf0724] [0x9bf0724] [0x9bf0724] [0x9bf0724] [0x9bf0724] [0x9bf0724] [0x9bf0724] [0x9bf0724] [0x9bf0724] [0x9bf0724] [0x9bf0724] [0x9bf0724] [0x9bf0724] [0x9bf0724] [0x9bf0724] [0x9bf0724] [0x9bf0724] [0x9bf0724] [0x9bf0724] [0x9bf0724] [0x9bf0724] [0x9bf0724] [0x9bf0724] [0x9bf0724] [0x9bf0724] [0x9bf0724] [0x9bf0724] [0x9bf0724] [0x9bf0724] [0x9bf0724] [0x9bf0724] [0x9bf0724] [0x9bf0724] [0x9bf0724] [0x9bf0724] [0x9bf0724] [0x9bf0724] [0x9bf0724] [0x9bf0724] [0x9bf0724] [0x9bf0724] [0x9bf0724] [0x9bf0724] [0x9bf0724] [0x9bf0724] [0x9bf0724] [0x9bf0724] [0x9bf0724] [0x9bf0724] [0x9bf0724] [0x9bf0724] [0x9bf0724] [0x9bf0724] [0x9bf0724] [0x9bf0724] [0x9bf0724] [0x9bf0724] [0x9bf0724] [0x9bf0724] [0x9bf0724] [0x9bf0724] [0x9bf0724] [0x9bf0724] [0x9bf0724] [0x9bf0724] [0x9bf0724] [0x9bf0724] [0x9bf0724] [0x9bf0724] [0x9bf0724] [0x9bf0724] [0x9bf0724] [0x9bf0724] [0x9bf0724] [0x9bf0724] [0x9bf0724] [0x9bf0724] [0x9bf0724] [0x9bf0724] [0x9bf0724] [0x9bf0724] [0x9bf0724] [0x9bf0724] [0x9bf0724] [0x9bf0724] [0x9bf0724] [0x9bf0724] [0x9bf0724] [0x9bf0724] [0x9bf0724] [0x9bf0724] [0x9bf0724] [0x9bf0724] [0x9bf0724] [0x9bf0724] [0x9bf0724] [0x9bf0724] [0x9bf0724] [0x9bf0724] [0x9bf0724] [0x9bf0724] [0x9bf0724] [0x9bf0724] [0x9bf0724] [0x9bf0724] [0x9bf0724] [0x9bf0724] [0x9bf0724] [0x9bf0724] [0x9bf0724] [0x9bf0724] [0x9bf0724] [0x9bf0724] [0x9bf0724] [0x9bf0724] [0x9bf0724] [0x9bf0724] [0x9bf0724] [0x9bf0724] [0x9bf0724] [0x9bf0724] [0x9bf0724] [0x9bf0724] [0x9bf0724] [0x9bf0724] [0x9bf0724] [0x9bf0724] [0x9bf0724] [0x9bf0724] [0x9bf0724] [0x9bf0724] [0x9bf0724] [0x9bf0724] [0x9bf0724] [0x9bf0724] [0x9bf0724] [0x9bf0724] [0x9bf0724] [0x9bf0724] [0x9bf0724] [0x9bf0724] [0x9bf0724] [0x9bf0724] [0x9bf0724] [0x9bf0724] [0x9bf0724] [0x9bf0724] [0x9bf0724] [0x9bf0724] [0x9bf0724] [0x9bf0724] [0x9bf0724] [0x9bf0724] [0x9bf0724] [0x9bf0724] [0x9bf0724] [0x9bf0724] [0x9bf0724] [0x9bf0724] [0x9bf0724] [0x9bf0724] [0x9bf0724] [0x9bf0724] [0x9bf0724] [0x9bf0724] [0x9bf0724] [0x9bf0724] [0x9bf0724] [0x9bf0724] [0x9bf0724] [0x9bf0724] [0x9bf0724] [0x9bf0724] [0x9bf0724] [0x9bf0724] [0x9bf0724] [0x9bf0724] [0x9bf0724] [0x9bf0724] [0x9bf0724] Debug info from gdb: Could not attach to process. If your uid matches the uid of the target process, check the setting of /proc/sys/kernel/yama/ptrace_scope, or try again as the root user. For more details, see /etc/sysctl.d/10-ptrace.conf ptrace: Operation not permitted. ================================================================= Got a SIGSEGV while executing native code. This usually indicates a fatal error in the mono runtime or one of the native libraries used by your application. Aborted It is a huge problem with mono or f#? By the way, the same function works when using pattern matching instead of "if".

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