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• Pseudorandom Number Generation with Specific Non-Uniform Distributions

  - by carnun

  Hello all, I'm writing a program that simulates various random walks (with differing distributions). At each timestep, I need randomly generated, two dimensional step distances and angles from the distribution of the random walk. I'm hoping someone can check my understanding of how to generate these random numbers. As I understand it I can use Inverse Transform Sampling as follows: If f(x) is the pdf of our random walk that has a non-uniform distribution, and y is a random number from a uniform distribution. Then if we let f(x) = y and solve to find x then we have a random number from the non-uniform distribution. Is this a feasible solution?

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• problems with Haskell's Number Types

  - by mindeavor.

  I have the following haskell code: fac n = product [1..n] taylor3s w0 f f' f'' t h = w1 : taylor3s w1 f f' f'' (t+h) h where hp i = h^i / fac i w1 = w0 + (hp 1) * f t w0 + (hp 2) * f' t w0 + (hp 3) * f'' t w0 taylor_results = take 4 $ taylor3s 1 f f' f'' 1 0.25 where f t x = t^4 - 4*x/t f' t x = 4*t^3 - 4*(f t x)/t + 4*x/t^2 f'' t x = 12*t^2 - 4*(f' t x)/t + 8*(f t x)/t^2 - 8*x/t^3 taylor_results is supposed to be a use case of taylor3s. However, there is something wrong with the number type inferencing. When I try to compile, this is the error I get: practice.hs:93:26: Ambiguous type variable `a' in the constraints: `Integral a' arising from a use of `taylor3s' at practice.hs:93:26-51 `Fractional a' arising from a use of `f' at practice.hs:93:37 Possible cause: the monomorphism restriction applied to the following: taylor_results :: [a] (bound at practice.hs:93:0) Probable fix: give these definition(s) an explicit type signature or use -XNoMonomorphismRestriction Can someone help me with understanding what the problem is?

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• How to start coding the "Dining Philosophers" simulation?

  - by GrizzlyGuru

  I'm not a beginner at C# but I really need to increase my understanding, so I've picked a classic deadlock problem to code to help teach myself some of the more advanced concepts of C#. The Dining Philosophers Problem seems like a good one, but I need a little help to get started. I know I need to approach the "diners" as objects, but to simulate the random delays between eating, should I look to threading with each diner in a separate thread? Do I need some kind of "master" to monitor all the actions? Any general design concept advice is welcome, but I'd like to do the grunt programming as an exercise. Thanks!

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• CruiseControl.NET merge nunit and nant output

  - by JK

  I've just started using ccnet so I'm having trouble understanding why the merging of nant and nunit outputs are not working. I've setup my ccnet.config with typical values as found on google: <merge> <files> <file>D:\ccnet\path1\nant-results.xml</file> <file>D:\ccnet\path2\TestResult.xml</file> </files> </merge> <xmllogger /> Nant and ccnet are half working: if I deliberately put in a code error, then ccnet will say build failed. The same happens if I deliberately put in a failing test, ccnet will say build failed. But the ViewBuildReport.aspx page does not show any of the output from nant or nunit. Obviously I must be missing something, but I don't know what, any ideas? Thanks, JK

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• Cocoa Interface Builder object initialization

  - by Stanley

  Base on the documentation and sample code that I have gone through, I got an impression that when a class defined in xcode is read into and configured in Interface Builder, an object based on the class is effectively created and stored in an xib or nib file. So the object is ready to be used when the corresponding application is launched. Alternatively, for classes that have not been handled by Interface Builder, code such as the "new" statements have to be written in xcode explicitly in order for the associated objects to be created and used. It will be very nice to have people who are more knowledgable than me to confirm or to correct my very naive understanding of Interface Builder ...

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• UITableViewController setting delegates and datasource

  - by the_great_monkey

  Hi iOS gurus, I'm a little bit confused about UITableViewController... As far as I concern they are typically the delegate and datasource of the UITableView (although it can be made such that they are different). However in some cases, like when embedding a UITableViewController in a UITabBarViewController in Interface Builder, we initiate our table view controller in IB. Therefore in my understanding, the default initialiser is being called. But in this case, I have this piece of code: @interface Settings : UITableViewController { } And in the IB I see that the delegate and datasource of the UITableView is hooked up to this class. My question is, why is it that we don't need to explicitly say that it is following: @interface Settings : UITableViewController <UITableViewDelegate, UITableViewDataSource> { } And in the .m file: - (void)viewDidLoad { [super viewDidLoad]; [tableView setDelegate:self]; [tableView setDataSource:self]; } I have indeed stumbled upon some cases where I have to explicitly code the above a few times to make something work. Although it is still a mystery for me as of why it is needed...

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• is putting N in front of strings in scripts considered a "best practice"?

  - by jcollum

  Let's say I have a table that has a varchar field. If I do an insert like this: INSERT MyTable SELECT N'the string goes here' Is there any fundamental difference between that and: INSERT MyTable SELECT 'the string goes here' My understanding was that you'd only have a problem if the string contained a Unicode character and the target column wasn't unicode. Other than that, SQL deals with it just fine and converts the string with the N'' into a varchar field (basically ignores the N). I was under the impression that N in front of strings was a good practice, but I'm unable to find any discussion of it that I'd consider definitive. Title may need improvement, feel free.

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• Can a real number "cover" all integers within its range?

  - by macias

  Is there a guarantee that a real number (float, double, etc) can "cover" all integers within its range? By cover I mean, that for every integer within its range there is such real number that this equality holds: real == int Or in another example, let's say I have the biggest real number which is smaller than given integer. When I add "epsilon" will I get this number equal to given integer or bigger than integer? (I know that among real numbers you should not write comparisons as == for equality, I am simply asking for better understanding subject, not for coding comparisons.)

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• C read part of file into cache

  - by Pete Jodo

  I have to do a program (for Linux) where there's an extremely large index file and I have to search and interpret the data from the file. Now the catch is, I'm only allowed to have x-bytes of the file cached at any time (determined by argument) so I have to remove certain data from the cache if it's not what I'm looking for. If my understanding is correct, fopen (r) doesn't put anything in the cache, only when I call getc or fread(specifying size) does it get cached. So my question is, lets say I use fread and read 100 bytes but after checking it, only 20 of the 100 bytes contains the data I need; how would I remove the useless 80 bytes from cache (or overwrite it) in order to read more from the file.

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• wcf net.tcp service fails to start when extra properties are set

  - by Pharabus

  i have a current project that runs fine with a self hosted net.tcp binding if I uses the following host.AddServiceEndpoint(typeof(IMonitorService), new NetTcpBinding() {PortSharingEnabled = false }, ""); host.AddServiceEndpoint(ServiceMetadataBehavior.MexContractName, MetadataExchangeBindings.CreateMexTcpBinding(), "mex"); however if I ammend to the below it fails to run with the message that there is already an endpoint on the port, can anyone explain why adding the extra properties causes it to fail? host.AddServiceEndpoint(typeof(IMonitorService), new NetTcpBinding() {PortSharingEnabled = false,ListenBacklog=1000,ReceiveTimeout=new TimeSpan(0,3,0) }, ""); host.AddServiceEndpoint(ServiceMetadataBehavior.MexContractName, MetadataExchangeBindings.CreateMexTcpBinding(), "mex"); Edit: testing confirms that the ReceiveTimeout property works Ok, as soon as I add the MaxConnections or ListenBacklog the service fails start Edit 2: this link seems to imply i ned portsharing is i want to modify these properies, not sure I am understanding it.

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• javasrcipt asyncronous function

  - by Ben

  Hi there, i have a problem understanding how this could/should be solved. I have two functions. In the first function ( I call it loadData() ) I'm doing an asyncronous request to the server to load some data. In the second function ( saveData() ) I'm also doing an asyn request to the server to write some data. In the callback of this request I'm callin loadData() to refresh the data. Now the problem: In the saveData() function I want to wait for loadData() to be finished bevore I show a dialog (like alert('Data saved')) I guess this is a common problem, but I couldn't find the solution for it (if there is one..) A solution would be to make the requests syncronous, but the framework I'm using doesn't offer that and I hope there's a better solution.. Thanks to all!

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• Multiple things at once (Threads?)

  - by Jonathan

  All, What is a really simple way of having a program do more than one thing at once, even if the computer does not necessarily have multiple 'cores'. Can I do this by creating more than one Thread? My goal is to be able to have two computers networked (through Sockets) to respond to each-other's requests, while my program will at the same time be able to be managing a UI. I want the server to potentially handle more than one client at the same time as well. My understanding is that the communication is done with BufferedReader.readLine() and PrintWriter.println(). My problem is that I want the server to be waiting on multiple readLine() requests, and also be doing other things. How do I handle this? Many thanks, Jonathan

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• How Matlab calculates the camera view angle?

  - by iman

  I am using matlab to visualise a scene. In order to zoom in the scene, I can do that by eather: - Fix the cameraposition and the cameratarget and change the cameraviewangle.or - Fix the cameratarget and the cameraview angle and moving the camera along the viewing line (defined by the cameraPosition and the cameraTarget). I know how to set the values of cameraposition CameraTarget and viewangle, but I do not how to define the optimal view angle. In auto mode of cameraviewangle, matlab calculate the smalest view angle that capture all the scene from the specefied camera position. I appreciate any help in understanding this. Iman

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• Is the offical Sun Java EE tutorial the best way to learn how to make Java web apps?

  - by Nick

  I've been a web developer for almost a decade. I've mostly used classic ASP/JavaScript and I'd like to move into Java based apps. I have a decent understanding of Java itself (enough to know how to lookup what I don't know) and I spent some time doing minor work on a JSF/Spring/Hibernate app, but from what a trusted coworker told me, this application is the example of what not to do. I want to learn the really hardcore stuff (EJBs, HA Clustering, etc), but I know I have to walk before I can run. Is the Sun Tutorial the best place to start? Or is there an definitive book (like K&R for C or Gang of Four for design patterns) that I should buy?

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• Replacing a C++ ActiveX component with a .NET implementation?

  - by Leon Breedt

  I have existing managed and unmanaged software using an ActiveX component supplied by a third party to perform some communications, but it is now required that this communication be routed through my application. Ideally I'd be able to install a .NET component which will expose exactly the same interface, and will be usable as a drop-in replacement. However, I am running into the limits of my understanding of COM, which admittedly is quite minimal. How best to ensure that my implementation of the interface is 100% binary compatible with the existing object? How do I ensure that applications use my implementation of the interface instead of the legacy implementation? Is it simply a matter of registering my implementation, and unregistering the legacy one? How do I ensure it's a "drop-in" replacement, and requires no changes to existing software? How do I ensure unmanaged code can use it without issue? Note: I am able to require that .NET 4.0 be used, if that will make things simpler.

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• Ideas for using R to create a T-shirt design (for useR 2010) ?

  - by Tal Galili

  There is now a competition for creating a T-shirt design for useR2010. Someone proposed the idea to use R for creating the T-shirt image. Which leads me to my questions: What type of images do you think might be fitting for this? How would you suggest to use R to create the images ? Would anyone here want to have a go at it? (p.s: I understand this is not a pure "programming" question. Yet it involves R programming, the understanding of R aesthetics, and some caring for the R community. I also understand I am at the risk of annoying people here with this question, so in case that happens - I deeply apologies! My only justification is that I am acting in good faith and in the purpose of having nice things for R users to enjoy, while learning something in the process) Related thread I once opened: http://stackoverflow.com/questions/2162131/how-can-i-learn-to-create-beautiful-infographics-with-connection-to-my-r-knowled

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• Encog 3.0 backpropagation

  - by Mohamed Shouman

  I have a question...I am using Encog framework to train a network using BP. I am training the network using images that has some object say a cat, telling the network which images are cats and which are not. Bellow are my Neural Network results actual=0.1545868370551181 ideal=0.0,actual=0.797896306829758 ideal=1.0,actual=0.1545868370551181 ideal=0.0,actual=0.797896306829758 ideal=1.0 It is my understanding that since different pictures are presented to network some look like cat for example then they should have higher percentage...but i keep getting same percentage for any pic that has a cat which is 0.79 and for other pics i get 0.15...how can i solve this issue!, what is the intuition behind whats going on! Many thanks

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• How to see contents of deployed datasource?

  - by callisto

  I've inherited a project (without a handy handover) that contains reports published to a Reporting Server (2005). MY SSRS knowledge is 4 years stale, so I need your help. I need to edit one of the published reports, is this possible? I also want to peek into the Data Source on the RS, coz that's probably where I can change stuff. I'll add more info as I get a better understanding of what exactly to ask. EDIT: I found a project for some of the reports, opened up in VS2005 BI. Still, how do see where the Data Source gets its data? It brins back 56 fields but I dont know which tables/stored procs/queries are used to get these.

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• Setting a form field's value during validation

  - by LaundroMat

  I read about this issue already, but I'm having trouble understanding why I can't change the value of a form's field during validation. I have a form where a user can enter a decimal value. This value has to be higher than the initial value of the item the user is changing. During clean(), the value that was entered is checked against the item's previous value. I would like to be able to re-set the form field's value to the item's initial value when a user enters a lower value. Is this possible from within the clean() method, or am I forced to do this in the view? Somehow, it doesn't feel right to do this in the view... (To make matters more complicated, the form's fields are built up dynamically, meaning I have to override the form's clean() method instead of using the clean_() method).

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• WPF: Creating instances of resources?

  - by oakskc

  I'm brand spanking new to WPF and am trying to play around with projects to better understand what I'm reading. My understanding of a resource is that it is the instance, you can't use it like a factory and create instances of it. For example, a XAML-defined rectangle. You can reference it, but you can't have numerous instances of it all over the surface. In WPF, what would be the way to do that? If I define a Rectangle as a resource with specific properties and wanted to have multiple instances of that within a dynamically-generated grid, how should I be going about it? Or is there a different way I should be trying to do this? Purely academic exercise with no real-world application.

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• How the websocket bi-directional concept work?

  - by GMsoF

  I think the main difference between websocket and http streaming (I am not refering to polling and long polling) is websocket allows bi-directional communication which is similar to usual raw socket programming. (above is my understanding, could be wrong, feel free to correct me.) My question is how the web client (browser) continue to send another request in the already-opened websocket? Usual http request will treat another request as new socket connection, but websocket does not, that is why I am confused, how it achieve that? It should be handled in Server side or Client (browser) side?

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• In Java how instance of and type cast(i.e (ClassName)) works on proxy object ?

  - by learner

  Java generates a proxy class for a given interface and provides the instance of the proxy class. But when we type cast the proxy object to our specific Object, how java handles this internally? Is this treated as special scenario? For example I have class 'OriginalClass' and it implements 'OriginalInterface', when I create proxy object by passing 'OriginalInterface' interface java created proxy class 'ProxyClass' using methods in the provided interface and provides object of this class(i.e ProxyClass). If my understanding is correct then can you please answer following queries 1) When I type cast object of ProxyClass to my class OriginalClass this works, but how java is allowing this? Same in case of instace of? 2) As my knowledge java creates a proxy class only with the methods, but what happen when I try to access attributes on this object? 3) Only interface methods are getting implemented in Proxy, but what happens when I try to access a method which not in interface and only mentioned in the class? Thanks, Student

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• Can't edit IORegistryEntry

  - by yangumi

  Hi, I am creating a software on Mac and I would like to change the value of an IORegistryEntry. I can view it on the IORegistryExplorer, but I can't edit it. So it's my understanding that I have to edit it via code. Here is my code: CFMutableDictionaryRef matchingDict = IOServiceNameMatching("AppleUSBMultitouchDriver"); io_service_t service = IOServiceGetMatchingService(kIOMasterPortDefault, matchingDict); if(service) { CFStringRef manufacturer = IORegistryEntryCreateCFProperty(service, CFSTR("Manufacturer"), kCFAllocatorDefault,0); NSLog(@"%@", (NSString*)manufacturer); kern_return_t err = IORegistryEntrySetCFProperty(service, CFSTR("Manufacturer"), CFSTR("test")); NSLog(@"error = %d", err); } This will output 2010-04-10 16:09:09.015 Test[41548:a0f] Apple Inc. 2010-04-10 16:09:09.015 Test[41548:a0f] error = 0 But after I check the value in the IORegistryExplorer, it still doesn't change. Does anybody have any suggestions? Thank you

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• Can I correctly debug assemblies loaded with the 'AssemblyResolve' event?

  - by Thiado de Arruda

  I'm experimenting with the AppDomain's 'AssemblyResolve' event by hidding the depedencies for an executable file in another folder. The assemblies seem to beloading and executing fine, however debugging seems to be crazy, sometimes it hits my break points, sometimes it doesnt , and sometimes it hits the same code twice(It seems absurd but I'm sure the code is executing only once). I don't understanding how debuggers works but I guess it has something to do with the PDB files. Anyone got an idea of what might be happening and how can I fix it? Edit: Let me add that I'm calling methods on the dynamically loaded assemblies using reflection, sometimes the method I'm stepping over throws an exception that only pops at a later time.

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• Implementing Clonable in Java

  - by Artium

  In which cases should I use this way: public A clone() throws CloneNotSupportedException { A clone = (A)super.clone(); clone.x= this.x; return clone; } And in which cases should I use that way: public ShiftedStack clone() throws CloneNotSupportedException { return new A(this.x); } What should I do if x is final and I want to use the first way? Regarding the first way, I understand it like this: we clone the super class and up-cast it, leading to some members uninitialized. After this initialize these members. Is my understanding correct? Thank you.

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