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  • Performance question: Inverting an array of pointers in-place vs array of values

    - by Anders
    The background for asking this question is that I am solving a linearized equation system (Ax=b), where A is a matrix (typically of dimension less than 100x100) and x and b are vectors. I am using a direct method, meaning that I first invert A, then find the solution by x=A^(-1)b. This step is repated in an iterative process until convergence. The way I'm doing it now, using a matrix library (MTL4): For every iteration I copy all coeffiecients of A (values) in to the matrix object, then invert. This the easiest and safest option. Using an array of pointers instead: For my particular case, the coefficients of A happen to be updated between each iteration. These coefficients are stored in different variables (some are arrays, some are not). Would there be a potential for performance gain if I set up A as an array containing pointers to these coefficient variables, then inverting A in-place? The nice thing about the last option is that once I have set up the pointers in A before the first iteration, I would not need to copy any values between successive iterations. The values which are pointed to in A would automatically be updated between iterations. So the performance question boils down to this, as I see it: - The matrix inversion process takes roughly the same amount of time, assuming de-referencing of pointers is non-expensive. - The array of pointers does not need the extra memory for matrix A containing values. - The array of pointers option does not have to copy all NxN values of A between each iteration. - The values that are pointed to the array of pointers option are generally NOT ordered in memory. Hopefully, all values lie relatively close in memory, but *A[0][1] is generally not next to *A[0][0] etc. Any comments to this? Will the last remark affect performance negatively, thus weighing up for the positive performance effects?

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  • Deploy custom web service to sharepoint server(2007/2010)?

    - by leif
    According to MSDN, for deploying custom web service, we need to create *wsdl.aspx and *disco.aspx files, and put them with .asmx together under _vti_bin folder (C:\Program Files\Common Files\Microsoft Shared\Web Server Extensions\14\isapi). And put the dll under bin folder of the root of sharepoint virtual directory. It works correctly for me. However, i also found that if i put .asmx file under the root virtual directory without creating those *wsdl.aspx and *disco.aspx files. It can work as well and much easier than the above way. So i'm wondering what's the potential issues in this way?

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  • Method Vs Property

    - by obsoleteattribute
    Hi, I'm a newbie to .NET. I have a class called Project, a project can have multiple forecasts.Now If I want to check if the projects has any forecasts or not should I use a readonly boolean property called HasForecast() or should I use a method named HasForecast() which basically returns a boolean value.From framework design guidelines I came to know that methods should be used when the operation is complex,since here I'm retrieving the value of forecasts from DB should I consider method, or since it is a logical data member should I use a property.If I use a property can I call a method in DBLayer from its getter.Please explain Regards, Ravi

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  • Minimum vs Minimal vertex covers

    - by panicked
    I am studying for an exam and one of the sample questions is as follows: Vertex cover: a vertex cover in a graph is a set of vertices such that each edge has at least one of its two end points in this set. Minimum vertex cover: a MINIMUM vertex cover in a graph is a vertex cover that has the smallest number of vertices among all possible vertex covers. Minimal vertex cover a MINIMAL vertex cover in a graph is a vertex cover that does not contain another vertex cover (deleting any vertex from the set would create a set of vertices that is not a vertex cover) Question: A minimal vertex cover isn't always a minimum vertex cover. Demonstrate this with a simple example. Can anyone get their head around this? I am failing to see the distinction between the two. More importantly, I'm having a hard time visualizing it. I seriously hope he's not gonna ask odd questions like this one on the exam!

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  • Anonymous union definition/declaration in a macro GNU vs VS2008

    - by Alan_m
    I am attempting to alter an IAR specific header file for a lpc2138 so it can compile with Visual Studio 2008 (to enable compatible unit testing). My problem involves converting register definitions to be hardware independent (not at a memory address) The "IAR-safe macro" is: #define __IO_REG32_BIT(NAME, ADDRESS, ATTRIBUTE, BIT_STRUCT) \ volatile __no_init ATTRIBUTE union \ { \ unsigned long NAME; \ BIT_STRUCT NAME ## _bit; \ } @ ADDRESS //declaration //(where __gpio0_bits is a structure that names //each of the 32 bits as P0_0, P0_1, etc) __IO_REG32_BIT(IO0PIN,0xE0028000,__READ_WRITE,__gpio0_bits); //usage IO0PIN = 0x0xAA55AA55; IO0PIN_bit.P0_5 = 0; This is my comparable "hardware independent" code: #define __IO_REG32_BIT(NAME, BIT_STRUCT)\ volatile union \ { \ unsigned long NAME; \ BIT_STRUCT NAME##_bit; \ } NAME; //declaration __IO_REG32_BIT(IO0PIN,__gpio0_bits); //usage IO0PIN.IO0PIN = 0xAA55AA55; IO0PIN.IO0PIN_bit.P0_5 = 1; This compiles and works but quite obviously my "hardware independent" usage does not match the "IAR-safe" usage. How do I alter my macro so I can use IO0PIN the same way I do in IAR? I feel this is a simple anonymous union matter but multiple attempts and variants have proven unsuccessful. Maybe the IAR GNU compiler supports anonymous unions and vs2008 does not. Thank you.

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  • ruby send vs __send__

    - by jaydel
    I understand the concept of some_instance.send but I'm trying to figure out why you can call this both ways? The Ruby Koans imply that there is some reason beyond providing lots of different ways to do the same thing and I'm wrestling with figuring this out. Here are the two examples of usage more concretely class Foo def bar? true end end foo = Foo.new foo.send(:bar?) foo.send(:bar?) Anyone have any idea about this? thanks in advance!

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  • Castle Windsor: Inject NameValueCollection vs. Dictionary

    - by Aren B
    I've already done many configs where dictionaries are passed into services in the <parameters> block. But what I find myself needing right now is to build a NameValueCollection (allowing multiple entries with the same key) or a Collection of KeyValuePair objects. The reason for this is im not using this dictionary to look up b when given a, im basically using it to pass in a Tuple (pair) of (a,b) to be used later in code. Im kind of new to castle windor and I was wondering how i would go about making a List of KeyValuePair's injected, or a NameValueCollection injected.

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  • Penalty of using QGraphicsObject vs QGraphicsItem?

    - by Dutch
    I currently have a hierarchy of items based off of QGraphicsItem. I want to move to QGraphicsObject instead so that I can put properties on my items. I will not be making use of signals/slots or any other features of QObject. I'm told that you shouldn't derive from QObject because it's "heavy" and "slow". To test the impact, I derive from QGraphicsObject, add a couple properties to my items, and look at the memory usage of the running app. I create 1000 items using both flavors and I don't notice anything more than 10k more memory usage. Since all I am adding on to my items are properties, is it safe to say that QObject only adds weight if you are using signals/slots?

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  • C# Threading vs single thread

    - by user177883
    Is it always guaranteed that a multi-threaded application would run faster than a single threaded application? I have two threads that populates data from a data source but different entities (eg: database, from two different tables), seems like single threaded version of the application is running faster than the version with two threads. Why would the reason be? when i look at the performance monitor, both cpu s are very spikey ? is this due to context switching? what are the best practices to jack the CPU and fully utilize it? I hope this is not ambiguous.

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  • static readonly field initializer vs static constructor initialization

    - by stackoverflowuser
    Below are 2 different ways to initialize static readonly fields. Is there a difference between the 2 approaches? If yes, when should one be preferred over the other? class A { private static readonly string connectionString = WebConfigurationManager.ConnectionStrings["SomeConnection"].ConnectionString; } class B { private static readonly string connectionString; static B() { connectionString = WebConfigurationManager.ConnectionStrings["SomeConnection"].ConnectionString; } } Thanks.

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  • ArrangeOverride Vs Storyboard Animation

    - by user275561
    Now I may not grasp the idea or this could be a mistake so feel free to correct me. I am doing a bubble breaker game in Silverlight. So when a bubble in a column gets bursted. I want to animate the above bubbles to simulate that they are being dropped. Each bubble knows its Row and column location and that gets updated in the View Model. Now my question is, Should I call invalidateArrange() on the Canvas from the ViewModel so it rearranges the bubbles or just have a storyboard animate the TranslateY. In my arrangeOverride Method I have something like this Rect childBounds = new Rect(CalculateLeft(dataContext.Column), CalculateTop(dataContext.Row), BubbleSize, BubbleSize); child.Arrange(childBounds); If there is a better way let me know. I am trying to learn the best practices.

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  • FreeLibrary vs implicit unloading DLL

    - by Adil
    I have implemented a DLL including DllMain() entry function:- BOOL APIENTRY DllMain( HMODULE hModule, DWORD ul_reason_for_call, LPVOID lpReserved ) { case DLL_PROCESS_ATTACH: ... case DLL_THREAD_ATTACH: ... case DLL_THREAD_DETACH: ... case DLL_PROCESS_DETACH: ... } Unfortunately i made a mistake in DLL_PROCESS_DETACH case and accessing illegal memorey (access violation). I made a sample program which loads the library using LoadLibrary() function, uses the library function and finally call FreeLibrary() and return. When i executed this program, i didnt get any error message. But if i remove FreeLibrary(), in that case the DLL_PROCESS_DETACH case is executed implicitly and this time it gives error dialog box mentioning that there is access violation. Why calling FreeLibrary() suppress this error? OR internally it handles this exception? What is suggested way.

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  • Core Data Inferred Migration – Automatic "lightweight" vs Manual

    - by ohhorob
    I've updated the model of an existing iPhone app in some simple ways (remove attribute, add attribute, remove index), and can use automatic lightweight migration to migrate the persistent store. Due to the typical size of the data set, the processing time is not insignificant, and warrants feedback for the user. NSMigrationManager provides a simple but useful migrationProgress value that sends KVO notifications as the migration is performed. That forms the basis of providing feedback, however attempting to use an inferred model ([NSMappingModel inferredMappingModelForSourceModel:destinationModel:error:]) results in drastically different timing for the exact same dataset. Profile results on and original iPhone (2G) Automatic inferred lightweight migration PROFILE: CacheManager -migrateStore PROFILE: 0.6130 (+0.6130) models loaded PROFILE: 1.1759 (+0.5629) delegate -CacheManagerWillMigrate: PROFILE: 1.2516 (+0.0757) persistent store coordinator loaded PROFILE: 5.1436 (+3.8920) automatic lightweight migration completed PROFILE: 5.5435 (+0.3999) delegate -CacheManagerDidFinishMigration:withError: Manual inferred migration PROFILE: CacheManager -migrateStore PROFILE: 0.6660 (+0.6660) models loaded PROFILE: 1.1471 (+0.4811) inferred mapping model generated PROFILE: 1.4046 (+0.2574) delegate -CacheManagerWillMigrate: PROFILE: 1.5058 (+0.1013) persistent store coordinator loaded PROFILE: 22.6952 (+21.1894) manual migration completed PROFILE: 23.1478 (+0.4525) delegate -CacheManagerDidFinishMigration:withError: So, with an inferred model, the manual migration takes over 5 times longer than automatic! It's a big inconsistency, and the lightweight option that NSPersistentStoreCoordinator -addPersistentStoreWithType:configuration:URL:options:error: provides absolutely no indication of progress while processing. Can anybody provide a supported way to get the migrationProgress values during automatic migration, OR a way to configure an inferred mapping model to be as fast during manual processing as automatic?

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  • Storing Templates and Object-Oriented vs Relational Databases

    - by syrion
    I'm designing some custom blog software, and have run into a conundrum regarding database design. The software requires that there be multiple content types, each of which will require different entry forms and presentation templates. My initial instinct is to create these content types as objects, then serialize them and store them in the database as JSON or YAML, with the entry forms and templates as simple strings attached to the "contentTypes" table. This seems cumbersome, however. Are there established best practices for dealing with this design? Is this a use case where I should consider an object database? If I should be using an object database, which should I consider? I am currently working in Python and would prefer a capable Python library, but can move to Java if need be.

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  • haml - if-else with different identations

    - by egarcia
    Hi everyone, I'm trying to render a calendar with rails and haml. The dates used come from a variable called @dates. It is a Date range that contains the first and last days to be presented on the calendar. The first day is always sunday and the last one is always monday. I'm planning to render a typical calendar, with one column per weekday (sunday is going to be the first day of the week) using an html table. So, I need to put a %tr followed by a %td on sundays, but the rest of the days I just need a %td. I'm having trouble modelling that on haml. This seems to require different levels of identation, and that's something it doesn't like. Here's my failed attempt: %table %tr %th= t('date.day_names')[0] # Sunday %th= t('date.day_names')[1] %th= t('date.day_names')[2] %th= t('date.day_names')[3] %th= t('date.day_names')[4] %th= t('date.day_names')[5] %th= t('date.day_names')[6] # Monday [email protected] do |date| - if(date.wday == 0) # if date is sunday %tr %td=date.to_s - else %td=date.to_s This doesn't work the way I want. The %tds for the non-sunday days appear outside of the %tr: <tr> <td>2010-04-24</td> </tr> <td>2010-04-25</td> <td>2010-04-26</td> <td>2010-04-27</td> <td>2010-04-28</td> <td>2010-04-29</td> <td>2010-04-30</td> I tried adding two more spaces to the else but then haml complained about improper identation. What's the best way to do this? Note: I'm not interested on rendering the calendar using unordered lists. Please don't suggest that.

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  • Confused about using SpringMVC Vs JEE project in Netbeans

    - by Sanju
    Hi all, I want to start a my first JEE project. I have read a lot that springMVC framework is a good choice (never used though) My earlier experience with java is not much. only some small app development using Netbeans. so I have some experience using Netbeans. but I see that I can start a JEE project in Netbeans. so what kind of framework netbeans is using underneath. PS: My understanding of framework (e.g. SpringMVC) is that you follow rule of framework to configure your app. and then framework take care or linking your View, controller and model. so if i am using netbeans, do i need to take care of linking of my MVC by myself?

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  • Linq2SQL vs NHibernate performance (have I gone mad?)

    - by HeavyWave
    I have written the following tests to compare performance of Linq2SQL and NHibernate and I find results to be somewhat strange. Mappings are straight forward and identical for both. Both are running against a live DB. Although I'm not deleting Campaigns in case of Linq, but that shouldn't affect performance by more than 10 ms. Linq: [Test] public void Test1000ReadsWritesToAgentStateLinqPrecompiled() { Stopwatch sw = new Stopwatch(); Stopwatch swIn = new Stopwatch(); sw.Start(); for (int i = 0; i < 1000; i++) { swIn.Reset(); swIn.Start(); ReadWriteAndDeleteAgentStateWithLinqPrecompiled(); swIn.Stop(); Console.WriteLine("Run ReadWriteAndDeleteAgentState: " + swIn.ElapsedMilliseconds + " ms"); } sw.Stop(); Console.WriteLine("Total Time: " + sw.ElapsedMilliseconds + " ms"); Console.WriteLine("Average time to execute queries: " + sw.ElapsedMilliseconds / 1000 + " ms"); } private static readonly Func<AgentDesktop3DataContext, int, EntityModel.CampaignDetail> GetCampaignById = CompiledQuery.Compile<AgentDesktop3DataContext, int, EntityModel.CampaignDetail>( (ctx, sessionId) => (from cd in ctx.CampaignDetails join a in ctx.AgentCampaigns on cd.CampaignDetailId equals a.CampaignDetailId where a.AgentStateId == sessionId select cd).FirstOrDefault()); private void ReadWriteAndDeleteAgentStateWithLinqPrecompiled() { int id = 0; using (var ctx = new AgentDesktop3DataContext()) { EntityModel.AgentState agentState = new EntityModel.AgentState(); var campaign = new EntityModel.CampaignDetail { CampaignName = "Test" }; var campaignDisposition = new EntityModel.CampaignDisposition { Code = "123" }; campaignDisposition.Description = "abc"; campaign.CampaignDispositions.Add(campaignDisposition); agentState.CallState = 3; campaign.AgentCampaigns.Add(new AgentCampaign { AgentState = agentState }); ctx.CampaignDetails.InsertOnSubmit(campaign); ctx.AgentStates.InsertOnSubmit(agentState); ctx.SubmitChanges(); id = agentState.AgentStateId; } using (var ctx = new AgentDesktop3DataContext()) { var dbAgentState = ctx.GetAgentStateById(id); Assert.IsNotNull(dbAgentState); Assert.AreEqual(dbAgentState.CallState, 3); var campaignDetails = GetCampaignById(ctx, id); Assert.AreEqual(campaignDetails.CampaignDispositions[0].Description, "abc"); } using (var ctx = new AgentDesktop3DataContext()) { ctx.DeleteSessionById(id); } } NHibernate (the loop is the same): private void ReadWriteAndDeleteAgentState() { var id = WriteAgentState().Id; StartNewTransaction(); var dbAgentState = agentStateRepository.Get(id); Assert.IsNotNull(dbAgentState); Assert.AreEqual(dbAgentState.CallState, 3); Assert.AreEqual(dbAgentState.Campaigns[0].Dispositions[0].Description, "abc"); var campaignId = dbAgentState.Campaigns[0].Id; agentStateRepository.Delete(dbAgentState); NHibernateSession.Current.Transaction.Commit(); Cleanup(campaignId); NHibernateSession.Current.BeginTransaction(); } Results: NHibernate: Total Time: 9469 ms Average time to execute 13 queries: 9 ms Linq: Total Time: 127200 ms Average time to execute 13 queries: 127 ms Linq lost by 13.5 times! Event with precompiled queries (both read queries are precompiled). This can't be right, although I expected NHibernate to be faster, this is just too big of a difference, considering mappings are identical and NHibernate actually executes more queries against the DB.

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  • Ambiguous Generic restriction T:class vs T:struct

    - by Maslow
    This code generates a compiler error that the member is already defined with the same parameter types. private T GetProperty<T>(Func<Settings, T> GetFunc) where T:class { try { return GetFunc(Properties.Settings.Default); } catch (Exception exception) { SettingReadException(this,exception); return null; } } private TNullable? GetProperty<TNullable>(Func<Settings, TNullable> GetFunc) where TNullable : struct { try { return GetFunc(Properties.Settings.Default); } catch (Exception ex) { SettingReadException(this, ex); return new Nullable<TNullable>(); } } Is there a clean work around?

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  • Rules Engine vs Expert System

    - by User1
    What is the difference between a rules engine and an expert system? Example1: Let's say that I have a program that determines the expiration date of a new driver's license. It takes inputs like visa expiration date, passport number, birthday, etc. It determines the expiration date of the driver's license from this input. It can even give an error if the input did not have enough valid identifications to allow a new driver's license. Example2: Let's say I am making an online version of the game Monopoly. I want the ability to change the rules of the game (say $400 for passing go or no one can buy properties until they land on the same property twice, etc). I have a module in the code to handle these rules. Are these both rules engines or are they expert systems? They both seem so similar. Is it just a synonym?

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  • AJAX vs ActiveX/Flash for browser-based game

    - by iconiK
    I have been following the usage of JavaScript for the past few years, and with the release of extremely fast scripting engines (V8, SquirrelFish Extrene, TraceMonkey, etc.) the possibilities of JavaScript have increased dramatically. However, the usage share of Internet Explorer coupled with it's total lack of support for recent standards makes me want to drop a bomb on Microsoft's HQ, as it creates a huge amount of problems for any website. The game will need to be pretty dynamic client-side, with animations and other eye-candy things, but not a full-blown game like those that run directly in the OS using DirectX or OpenGL. However, this might be a little stretch for JavaScript and will certainly feel extremely slow in Internet Explorer (given that the current IE engine can be hundreds of times slower than SFX; gotta see what IE9 will bring), would it be better to just do the whole thing in Flash? I know this means requiring the plug-in AND I have no experience whatsoever with Flash (other than browsing YouTube :P). It also means I can't just output directly from PHP, I would have to use XML or some other format to pass data to it (JSON is directly integrated in JS and PHP can deal with it easily). Another idea would be to provide an alternative interface just for IE, though I don't know how (ActiveX maybe? or with Flash, then why not just provide it to all browsers) or totally not supporting it and requiring the use of other browsers, although this is plain stupid from a business perspective. So here am I, wondering what approach to take and thus asking for your advice. How should I build the client-side? AJAX in all browsers, Flash in all browsers or a mix (AJAX for "modern" browsers and something else for the "grandpa": IE).

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  • plist vs static array

    - by morticae
    Generally, I use static arrays and dictionaries for containing lookup tables in my classes. However, with the number of classes creeping quickly into the hundreds, I'm hesitant to continue using this pattern. Even if these static collections are initialized lazily, I've essentially got a bounded memory leak going on as someone uses my app. Most of these are arrays of strings so I can convert strings into NSInteger constants that can be used with switch statements, etc. I could just recreate the array/dictionary on every call, but many of these functions are used heavily and/or in tight loops. So I'm trying to come up with a pattern that is both performant and not persistent. If I store the information in a plist, does the iphoneOS do anything intelligent about caching those when loaded? Do you have another method that might be related?

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