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• Pure Java open-source libraries for portfolio selection (= constrained, non-linear optimization)?

  - by __roland__

  Does anyone know or has experience with a pure Java library to select portfolios or do some similar kinds of quadratic programming with constraints? There seems to be a lot of tools, as already discussed elsewhere - but what I would like to use is a pure Java implementation. Since I want to call the library from within another open-source software with a BSD-ish license I would prefer LGPL over GPL. Any help is appreciated. If you don't know such libraries, which is the most simple algorithm you would suggest to implement? It has to cope with an inequality constraint (all x_i = 0) and an equality constraint (sum of all x_i = 1).

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• Mathematica Plot3D does not produce a plot when graphing a user-defined function?

  - by pythonscript

  I'm writing a simple Mathematica implementation of the black-scholes model and using Plot3D to plot the pricing surface. However, when I run this code, no plot is produced. My call and put functions to produce correct values when run separately, but no plot is produced. Code: Clear[d1, d2, call, put, stockPrice, strikePrice, riskFreeRate, timeToExp, volatility] d1[stockPrice_, strikePrice_, riskFreeRate_, timeToExp_, volatility_] := (Log[stockPrice / strikePrice] + (riskFreeRate + 0.5*volatility^2)*timeToExp) / (volatility * Sqrt[timeToExp]) d2[stockPrice_, strikePrice_, riskFreeRate_, timeToExp_, volatility_] := d1[stockPrice, strikePrice, riskFreeRate, timeToExp, volatility] - volatility*Sqrt[timeToExp] call[stockPrice_, strikePrice_, riskFreeRate_, timeToExp_, volatility_] := stockPrice * CDF[NormalDistribution[0, 1], d1[stockPrice, strikePrice, riskFreeRate, timeToExp, volatility]] - strikePrice * Exp[-riskFreeRate*timeToExp] *CDF[NormalDistribution[0, 1], d2[stockPrice, strikePrice, riskFreeRate, timeToExp, volatility]] Plot3D[call[stockPrice, 500, 0.0030, timeToExp, 0.39], {stockPrice, 10, 1000}, {timetoExp, 0.0833333, 5}] Other plots, like this sample from the reference, do work. Plot3D[{x^2 + y^2, -x^2 - y^2}, {x, -2, 2}, {y, -2, 2}, RegionFunction -> Function[{x, y, z}, x^2 + y^2 <= 4], BoxRatios -> Automatic]

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• Grails GORM on multiple Forms

  - by Fabien Barbier

  Usually I'm using One-to-many relationship by this way : class Subject { static hasMany = [ crfs : Crf ] String name ... } class Crf { String title String info ... } I can extend this relationship to others domains, Ex : static hasMany = [ crfs : Crf, crfb : CrfBlood ...] But in my case I have to link the Subject domain to 30 others domains, maybe more...(ex : CrfBlood, CrfMedical, crfFamily, etc...). What domain model implementation should I use in my case ? I would like to keep the dynamic finders usability in my project.

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• Implementing IComparer<T> For IComparer<DictionaryEntry>

  - by Phil Sandler

  I am using the ObservableSortedDictionary from Dr. WPF. The constructor looks like this: public ObservableSortedDictionary(IComparer<DictionaryEntry> comparer) I am really struggling to create an implementation that satisfies the constructor and works. My current code (that won't compile) is: public class TimeCreatedComparer<T> : IComparer<T> { public int Compare(T x, T y) { var myclass1 = (IMyClass)((DictionaryEntry)x).Value; var myclass2 = (IMyClass)((DictionaryEntry)y).Value; return myclass1.TimeCreated.CompareTo(myclass2.TimeCreated); } } It says I can't cast from T to DictionaryEntry. If I cast directly to IMyClass, it compiles, but I get a runtime error saying I can't cast from DictionaryEntry to IMyClass. At runtime, x and y are instances of DictionaryEntry, which each have the correct IMyClass as their Value.

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• Objective-C: Protocols

  - by Stu

  I'd like an instance variable object to adopt a protocol. @interface GameScene : Scene <AVAudioPlayerDelegate> { @private Layer *content <CocosNodeOpacity>; } For example I'd like my Layer object to adopt the <CocosNodeOpacity> so that I can get the methods -(GLubyte) opacity; //and -(void) setOpacity: (GLubyte) opacity; for free. The syntax shown above is invalid. Is it possible to achieve this without creating a new implementation file and creating a custom object? Thanks.

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• JavaFX Threading issue - GUI freezing while method call ran.

  - by David Meadows

  Hi everyone, I hoped someone might be able to help as I'm a little stumped. I have a javafx class which runs a user interface, which includes a button to read some text out loud. When you press it, it invokes a Java object which uses the FreeTTS java speech synth to read out loud a String, which all works fine. The problem is, when the speech is being read out, the program stops completely until its completed. I'm not an expert on threaded applications, but I understand that usually if I extend the Thread class, and provided my implementation of the speech synth code inside an overridden run method, when I call start on the class it "should" create a new Thread, and run this code there, allowing the main thread which has the JavaFX GUI on to continue as normal. Any idea why this isn't the case? Thanks a lot in advance!

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• How to avoid having very large objects with Domain Driven Design

  - by Pablojim

  We are following Domain Driven Design for the implementation of a large website. However by putting the behaviour on the domain objects we are ending up with some very large classes. For example on our WebsiteUser object, we have many many methods - e.g. dealing with passwords, order history, refunds, customer segmentation. All of these methods are directly related to the user. Many of these methods delegate internally to other child object but this still results in some very large classes. I'm keen to avoid exposing lots of child objects e.g. user.getOrderHistory().getLatestOrder(). What other strategies can be used to avoid this problems?

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• Examining mmaped addresses using GDB

  - by Mikeage

  I'm using the driver I posted at http://stackoverflow.com/questions/647783/direct-memory-access-in-linux/ to mmap some physical ram into a userspace address. However, I can't use GDB to look at any of the address; i.e., x 0x12345678 (where 0x12345678 is the return value of mmap) fails with an error "Cannot access memory at address 0x12345678". Is there any way to tell GDB that this memory can be viewed? Alternatively, is there something different I can do in the mmap (either the call or the implementation of foo_mmap there) that will allow it to access this memory? Note that I'm not asking about /dev/mem (as in the first snippet there) but amount a mmap to memory acquired via ioremap(), virt_to_phys() and remap_pfn_range()

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• posmax: like argmax but gives the position(s) of the element x for which f[x] is maximal

  - by dreeves

  Mathematica has a built-in function ArgMax for functions over infinite domains, based on the standard mathematical definition. The analog for finite domains is a handy utility function. Given a function and a list (call it the domain of the function), return the element(s) of the list that maximize the function. Here's an example of finite argmax in action: http://stackoverflow.com/questions/471029/canonicalize-nfl-team-names/472213#472213 And here's my implementation of it (along with argmin for good measure): (* argmax[f, domain] returns the element of domain for which f of that element is maximal -- breaks ties in favor of first occurrence. *) SetAttributes[{argmax, argmin}, HoldFirst]; argmax[f_, dom_List] := Fold[If[f[#1]>=f[#2], #1, #2]&, First[dom], Rest[dom]] argmin[f_, dom_List] := argmax[-f[#]&, dom] First, is that the most efficient way to implement argmax? What if you want the list of all maximal elements instead of just the first one? Second, how about the related function posmax that, instead of returning the maximal element(s), returns the position(s) of the maximal elements?

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• ICalendar parser in PHP that supports timezones

  - by Vincent Robert

  I am looking for a PHP class that can parse an ICalendar (ICS) file and correctly handle timezones. I already created an ICS parser myself but it can only handle timezones known to PHP (like 'Europe/Paris'). Unfortunately, ICS file generated by Evolution (default calendar software of Ubuntu) does not use default timezone IDs. It exports events with its a specific timezone ID exporting also the full definition of the timezone: daylight saving dates, recurrence rule and all the hard stuff to understand about timezones. This is too much for me. Since it was only a small utility for my girlfriend, I won't have time to investigate further the ICalendar specification and create a full blown ICalendar parser myself. So is there any known implementation in PHP of ICalendar file format that can parse timezones definitions?

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• how start implement MVVM pattern

  - by netmajor

  Hello, So i decide to to develop my asp.net site into Silverlight. I today start to search articles about MVVM pattern which i want use in my Silverlight app, and i am confused :/ It's hart to me understand how works this pattern. I am find 3 frameworks which supports MVVM pattern in Silverlight - Caliburn, MVVM Light Toolkit and GoodLight. Should i start from own implementation of pattern or use framework? Is this frameworks only a project solutions in which i can insert my code? Which framework is the best for novice and which for professional? I ask for this, cause i must start to rewrite my app from asp.net to Silverlight and i don't know that i can do it first and later (when i understand MVVM pattern and framework) implement this pattern in finished app ? Or from begining rewrite project to MVVM framework?

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• WCF Business logic handling

  - by Raj

  I have a WCF service that supports about 10 contracts, we have been supporting a client with all the business rules specific to this client now we have another client who will be using the exact same contracts (so we cannot change that) they will be calling the service exactly the same way the previous client called now the only way we can differentiate between the two clients is by one of the input parameters. Based on this input parameter we have to use a slightly different business logic – the logic for both the Client will be same 50% of the time the remainder will have different logic (across Business / DAL layers) . I don’t want to use if else statement in each of contract implementation to differentiate and reroute the logic also what if another client comes in. Is there a clean way of handling a situation like this. I am using framework 3.5. Like I said I cannot change any of the contracts (service / data contract ) or the current service calling infrastructure for the new client. Thanks

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• Programmatically allow write access for a Registry key

  - by Kerido

  Hi everybody, I need to programmatically modify the Access Descriptors on a known Registry key during product installation. The way I want it to work is: The installer is run in Administrative mode. A Registry key is created. A function (the one I need) queries the ACL from the key. If this function finds that the group 'Users' already has write access, nothing should be done. If not, it should add a new permission allowing write access to the 'Users' group. The permissions are saved for the Registry key. This question is similar to Setting Registry key write permissions using .NET, however, I need a C++/Win32 implementation. Thanks in advance

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• XSLT good choice for web framework?

  - by Xepoch

  I've always thought of XML (and SGML before that) data as the devil's format. I'm of the old database and flat files school. Nonetheless, we are developing a commercially-available web product who's framework is based off of translating/transforming XML data in chains. As we're interviewing for positions as well talking to potential customers, they love the concept of what it will do but are weary of supporting XSLT long-term. One person even called it the proverbial "dead." Dead like COBOL, Unix, and C or dead like Apple Business BASIC? Anyway, I'm curious if building a web framework on XSLT is really not cutting edge enough (oddly) for companies. Are there inherent XSLT implementation problems that make this venture something worth reconsidering?

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• viewDidLoad never called in Sub-classed UIViewController

  - by Steve

  I've run into some trouble with loading a sub-classed UIViewController from a nib. My viewDidLoad function is never called. The super-class has no nib, but the sub-classes each have their own. i.e. @interface SuperClass : UIViewController { } @end @interface SubClass : SuperClass{ } @end @implementation SubClass - (id)initWithNibName:(NSString *)nibNameOrNil bundle:(NSBundle *)nibBundleOrNil { self = [super initWithNibName:nibNameOrNil bundle:nibBundleOrNil]; if (self) { } return self; } - (void)viewDidLoad{ // Never called } The view is loaded from a nib as follows: SubClass *scvc = [[SubClass alloc] initWithNibName:@"SubClass" bundle:nil]; [self.navigationController pushViewController:scvc animated:YES]; [scvc release]; There is a nib file with this name and it has it's file owner's class set properly. viewDidLoad is not called in the child or super. Any ideas?

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• Refactor/rewrite code or continue?

  - by Dan

  I just completed a complex piece of code. It works to spec, it meets performance requirements etc etc but I feel a bit anxious about it and am considering rewriting and/or refactoring it. Should I do this (spending time that could otherwise be spent on features that users will actually notice)? The reasons I feel anxious about the code are: The class hierarchy is complex and not obvious Some classes don't have a well defined purpose (they do a number of unrelated things) Some classes use others internals (they're declared as friend classes) to bypass the layers of abstraction for performance, but I feel they break encapsulation by doing this Some classes leak implementation details (eg, I changed a map to a hash map earlier and found myself having to modify code in other source files to make the change work) My memory management/pooling system is kinda clunky and less-than transparent They look like excellent reasons to refactor and clean code, aiding future maintenance and extension, but could be quite time consuming. Also, I'll never be perfectly happy with any code I write anyway... So, what does stackoverflow think? Clean code or work on features?

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• NHibernate session management in ASP.NET MVC

  - by Kevin Pang

  I am currently playing around with the HybridSessionBuilder class found on Jeffrey Palermo's blog post: http://jeffreypalermo.com/blog/use-this-nhibernate-wrapper-to-keep-your-repository-classes-simple/ Using this class, my repository looks like this: public class UserRepository : IUserRepository { private readonly ISessionBuilder _sessionBuilder; public UserRepository(ISessionBuilder sessionBuilder) { _sessionBuilder = sessionBuilder; } public User GetByID(string userID) { using (ISession session = _sessionBuilder.GetSession()) { return session.Get<User>(userID); } } } Is this the best way to go about managing the NHibernate session / factory? I've heard things about Unit of Work and creating a session per web request and flushing it at the end. From what I can tell, my current implementation isn't doing any of this. It is basically relying on the Repository to grab the session from the session factory and use it to run the queries. Are there any pitfalls to doing database access this way?

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• How to best deal with photos passed to IFilter?

  - by sharptooth

  I'm implementing an IFilter for indexing image formats. One problem is photos - many users have tons of photos, photos are huge and loading and searching for text on them is time consuming. Yes, sometimes people use cameras instead of scanners for digitizing documents, but the potential problems IMO far outweight the possibility of encountering a document digitized with a photo camera. So my implementation will not extract text from photos at all. What should the IFilter do once it detects that a given file is a photo image - indicate an error or return empty text?

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• Objective-C categories: Can I add a property for a method not in my category?

  - by Squeegy

  I want to use a category to make a method on the original class available as a property as well. Class A: @interface ClassA - (NSString*)foo; @end Class A category @interface ClassA (Properties) - (void)someCategoryMethod; @property (nonatomic, readonly) NSString *foo; @end Now when I do this, it seems to work, but it gives me warnings because I am not synthesizing the property in my category implementation. How do I tell the compiler everything is actually just fine since the original class synthesizes the property for me?

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• Is it possible to create thread-safe collections without locks?

  - by Andrey

  This is pure just for interest question, any sort of questions are welcome. So is it possible to create thread-safe collections without any locks? By locks I mean any thread synchronization mechanisms, including Mutex, Semaphore, and even Interlocked, all of them. Is it possible at user level, without calling system functions? Ok, may be implementation is not effective, i am interested in theoretical possibility. If not what is the minimum means to do it? EDIT: Why immutable collections don't work. This of class Stack with methods Add that returns another Stack. Now here is program: Stack stack = new ...; ThreadedMethod() { loop { //Do the loop stack = stack.Add(element); } } this expression stack = stack.Add(element) is not atomic, and you can overwrite new stack from other thread. Thanks, Andrey

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• Add XSLT 2 schema to Visual Studio 2010 for intellisense

  - by David Merrilees

  I'd like to add the XSLT 2 schema to Visual Studio 2010 to provide intellisense. I've added the schema to C:\Program Files\Microsoft Visual Studio 10.0\Xml\Schemas (removing the XSLT 1 schema), but to no avail. The schema seems to have been parsed by Visual Studio, as I can hover my cursor over the namespace declaration in the stylesheet (xmlns:xsl="http://www.w3.org/1999/XSL/Transform") and see the comments from the new schema, however, intellisense still refers to the XSLT 1 implementation. For example the element has a warning that 'xsl:function is not yet available'. Do I need to register the schema in some way? Any suggestions welcome.

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• What exactly is REST architecture and how is it implemented in Rails?

  - by Jagira

  This is what I think of REST architecture. For every resource, there is an unique URI. We can manipulate that object using its URI and HTTP actions [POST, GET, PUT and DELETE]. The HTTP request transfers the representation of the state of that object. In all the texts I have read, REST is explained in a weird and confusing manner. One more thing, RESTFUL implementation in rails produces different urls for different purposes. Like /teams - for 'index' method... /teams/new - for 'new' method and so on. Ain't this moving away from rest, which defines that each resource has one unique URI???

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• Mapping Hilbert values to 3D points

  - by Alexander Gladysh

  I have a set of Hilbert values (length from the start of the Hilbert curve to the given point). What is the best way to convert these values to 3D points? Original Hilbert curve was not in 3D, so I guess I have to pick by myself the Hilbert curve rank I need. I do have total curve length though (that is, the maximum value in the set). Perhaps there is an existing implementation? Some library that would allow me to work with Hilbert curve / values? Language does not matter much.

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• How does one go about understanding GNU source code?

  - by Max Dwayne

  I'm really sorry if this sounds kinda dumb. I just finished reading K&R and I worked on some of the exercises. This summer, for my project, I'm thinking of re-implementing a linux utility to expand my understanding of C further so I downloaded the source for GNU tar and sed as they both seem interesting. However, I'm having trouble understanding where it starts, where's the main implementation, where all the weird macros came from, etc. I have a lot of time so that's not really an issue. Am I supposed to familiarize myself with the GNU toolchain (ie. make, binutils, ..) first in order to understand the programs? Or maybe I should start with something a bit smaller (if there's such a thing) ? I have little bit of experience with Java, C++ and python if that matters. Thanks!

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• How difficult is it to migrate away from Google App Engine?

  - by Ignas Limanauskas

  I am thinking of making an (initially) small Web Application, which would eventually have a potential to grow. All things considered Google App Engine seems like a very attractive option. Say, user base and complexity grows and for one or other reason I needed to leave GAE behind. How difficult would it be to migrate away? 1) Does GAE provide a way to export the database? What format would it be? Would it be difficult to put it under MySQL (or similar)? 2) In which areas (ex. database access, others?) would I have to use GAE API? I.e. which parts of implementation would have to be abstracted away / interfaced? 3) Alternatively, is it even worth to keep GAE API outside, say, if there is nothing much I would need to use.

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