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• How do people prove the correctness of Computer Vision methods?

  - by solvingPuzzles

  I'd like to pose a few abstract questions about computer vision research. I haven't quite been able to answer these questions by searching the web and reading papers. How does someone know whether a computer vision algorithm is correct? How do we define "correct" in the context of computer vision? Do formal proofs play a role in understanding the correctness of computer vision algorithms? A bit of background: I'm about to start my PhD in Computer Science. I enjoy designing fast parallel algorithms and proving the correctness of these algorithms. I've also used OpenCV from some class projects, though I don't have much formal training in computer vision. I've been approached by a potential thesis advisor who works on designing faster and more scalable algorithms for computer vision (e.g. fast image segmentation). I'm trying to understand the common practices in solving computer vision problems.

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• How to catch FTP errors? e.g., socket.error: [Errno 10060]

  - by Johnson

  I'm using the ftplib module to upload files: files = [ a.txt , b.txt , c.txt ] s = ftplib.FTP(ftp_server , ftp_user , ftp_pw) # Connect to FTP for i in range(len(files)): f = open(files[i], 'rb') stor = 'stor ' + files[i] s.storbinary(stor, f) f.close() # close file s.quit() # close ftp How do I catch the following error? socket.error: [Errno 10060] A connection attempt failed because the connected party did not properly respond after a period of time, or established connection failed because connected host has failed to respond And what other errors are common when using the FTP module that I should also catch? Thanks for any help or pointers.

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• Game Programming - GUIs

  - by Spencer

  I've been coding for a while now and would like to start looking into programming games. I know the industry's standard language is C++, for 3D graphics the main choice is between Direct 3D and OpenGL, but what is the most widely used GUI framework? I'm currently on a Mac so if native Windows API is the answer, then what is the cross platform choice? To be clear, I'm not looking for people's favourites but simply what the common or standard game industry's choice is so that I can learn and familiarize myself with it. Thanks, Spencer

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• Rails uniqueness constraint and matching db unique index for null column

  - by Dave

  I have the following in my migration file def self.up create_table :payment_agreements do |t| t.boolean :automatic, :default => true, :null => false t.string :payment_trigger_on_order t.references :supplier t.references :seller t.references :product t.timestamps end end I want to ensure that if a product_id is specified it is unique but I also want to allow null so I have the following in my model: validates :product_id, :uniqueness => true, :allow_nil => true Works great but I should then add an index to the migration file add_index :payment_agreements, :product_id, :unique => true Obviously this will throw an exception when two null values are inserted for product_id. I could just simply omit the index in the migration but then there's the chance that I'll get two PaymentAgreements with the same product_id as shown here: Concurrency and integrity My question is what is the best/most common way to deal with this problem

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• Bejeweled Blitz - How does it assert there is always a move?

  - by EvilTeach

  I have been playing Bejeweled Blitz for a while now. Yes, it is an addiction. In thinking about the game, I have observed that on some boards, the bottom runs dry (no moves) leaving only the top part of the board playable. Frequently that part of the board drys up, and one is left with moves in area cleared by the last move. The board never runs completely dry, so clearly the program is doing some sorts of calculation that allows it to choose what to drop to prevent it from running dry. I have noticed in this 'mode' that it is very common for the algorithm to drop jewels which causes more non-dry area to appear in the horizontal area. Perhaps less frequent is a drop which seems designed to open up the bottom part of the board again. So my question is "How would one go about designing an algorithm guarantee that there is always a move available.?"

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• navigateToUrl AS3 is not opening a web browser

  - by Ronnie

  I have a textField on my stage named 'adBuy', which when clicked I want to open up my browser with the defined in URL request. However when I click on the 'adBuy' textField on my SWF it opens Coda, the piece of software I'm using to write this small piece of code? I am puzzled. Here is my code: adBuy.defaultTextFormat = adFormat; adBuy.textColor = 0xFF65CB; adBuy.x = 640; adBuy.y = 455; adBuy.text = "Buy Now"; parent.addChild(adBuy); adBuy.addEventListener(MouseEvent.CLICK, buyAdvert); var request:URLRequest = new URLRequest("http://www.google.co.uk"); function buyAdvert(event:MouseEvent):void { navigateToURL(request, "_blank"); trace("link clicked"); } Is there an error in my code, or is this a common problem for which there is an answer?

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• Practical non-Turing-complete languages?

  - by Kyle Cronin

  Nearly all programming languages used are Turing Complete, and while this affords the language to represent any computable algorithm, it also comes with its own set of problems. Seeing as all the algorithms I write are intended to halt, I would like to be able to represent them in a language that guarantees they will halt. Regular expressions used for matching strings and finite state machines are used when lexing, but I'm wondering if there's a more general, broadly language that's not Turing complete? edit: I should clarify, by 'general purpose' I don't necessarily want to be able to write all halting algorithms in the language (I don't think that such a language would exist) but I suspect that there are common threads in halting proofs that can be generalized to produce a language in which all algorithms are guaranteed to halt. There's also another way to tackle this problem - eliminate the need for theoretically infinite memory. Once you limit the amount of memory the machine is allowed, the number of states the machine is in is finite and countable, and therefore you can determine if the algorithm will halt (by not allowing the machine to move into a state it's been in before).

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• Add jar to EAR in Eclipse

  - by Gerard

  I have several projects in an EAR in Eclipse. These projects themselves have dependency jar's on the build path marked as "do not export, do not contribute to others". Now in Eclipse I add jar's to the EAR via the EAR properties "Java EE Module Dependencies". I browse to the jar (add jar) and click ok. The jar is added to the list. When I click apply, the added jar is gone from the list, it cannot be found in other properties, it is contained in the hidden folder .settings in the file org.eclipse.wst.common.component. This behaviour does not make much sense to me, what am I missing?

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• Which processors can run CIL

  - by JonnyBoats

  Which processors are capable of running Common Intermediate Language(CIL), formerly known as Microsoft Intermediate Language (MSIL)? Clearly any machine that can run Microsoft Windows with .net qualifies as well as machines targeted by the Mono project. It would appear that the .NET Micro Framework has the ability to target other processors not covered by the above, but it is not clear to me that it uses CIL. Does anyone have a list of which processors are capable of running a program in CIL and or interpreting C# directly (as the .NET Micro Framework appears to do)?

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• python: iif or (x ? a : b)

  - by Albert

  If Python would support the (x ? a : b) syntax from C/C++, I would write: print paid ? ("paid: " + str(paid) + " €") : "not paid" I really don't want to have an if-check and two independent prints here (because that is only an example above, in my code, it looks much more complicated and would really be stupid to have almost the same code twice). However, Python does not support this operator or any similar operator (afaik). What is the easiest/cleanest/most common way to do this? I have searched a bit and seen someone defining an iif(cond,iftrue,iffalse) function, inspired from Visual Basic. I wondered if I really have to add that code and if/why there is no such basic function in the standard library.

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• Visual Studio: Design a UserControl class that derives from an abstract base class

  - by Marcel

  Hi All, I want to have an abstract base class for some of my custom UserControl's. The reason is obvious: they share some common properties and methods (a basic implementation of some elements of an interface actually), and I want to implement them only once. I have done this by defining my abstract base class: public abstract class ViewBase : UserControl, ISomeInterface Then I went to implement one of my views, as usual, with the designer: public partial class SpecialView : UserControl //all OK Up to here all is fine. Now I replace the derivation of my SpecialView class with the abstract base class: public partial class SpecialView : ViewBase //disrupts the designer Now, the designer in Visual Studio 2008 won't work anymore, stating: The designer must create an instance of type 'ViewBase' but it cannot because the type is declared as abstract. How can I circumvent this? I just do not want to have the same code copied for all those views. Info: there is a question question with virtual methods, instead of abstract classes, but there is no suitable solution for me.

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• Is perl's each function worth using?

  - by eugene y

  From perldoc -f each we read: There is a single iterator for each hash, shared by all each, keys, and values function calls in the program; it can be reset by reading all the elements from the hash, or by evaluating keys HASH or values HASH. The iterator is not reset when you leave the scope containing the each(), and this can lead to bugs: my %h = map { $_, 1 } qw(1 2 3); while (my $k = each %h) { print "1: $k\n"; last } while (my $k = each %h) { print "2: $k\n" } Output: 1: 1 2: 3 2: 2 What are the common workarounds for this behavior? And is it worth using each in general?

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• Is perl's each function worth using?

  - by eugene y

  From perldoc -f each we read: There is a single iterator for each hash, shared by all each, keys, and values function calls in the program; it can be reset by reading all the elements from the hash, or by evaluating keys HASH or values HASH. The iterator is not reset when you leave the scope containing the each(), and this can lead to bugs: my %h = map { $_, 1 } qw(1 2 3); while (my $k = each %h) { print "1: $k\n"; last } while (my $k = each %h) { print "2: $k\n" } Output: 1: 1 2: 3 2: 2 What are the common workarounds for this behavior? And is it worth using each in general?

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• Django : proper way to use model, duplicates!

  - by llazzaro

  Hello, I have a question about the proper, best way to manage the model. I am relative newbie to django, so I think I need to read more docs, tutorials,etc (suggestions for this would be cool!). Anyway, this is my question : I have a python web crawler, that is "connected" with django model. Crawling is done once a day, so its really common to find "duplicates". To avoid duplicates I do this : cars = Car.Objects.filter(name=crawledItem['name']) if len(cars) 0: #object already exists, update it car = cars[0] else: car = Car() #some non-relevant code here car.save() I want to know, if this is the proper/correct way to do it or its any "automatic" way to do it. Its possible to put the logic inside the Car() constructor also, should I do that? Thanks a lot!

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• Default value list for pipeline param in Powershell

  - by fatcat1111

  I have a Powershell script that reads values off of the pipeline: PARAM ( [Parameter(ValueFromPipeline = $true)] $s ) PROCESS { echo "* $s" } Works just fine: PS my.ps1 foo * foo I would like the script to have list of default values, as the most common usage will always use the same values and storing them in the default will be most convenient. I did the usual assignment: PARAM ( [Parameter(ValueFromPipeline = $true)] $s = 'bar' ) PROCESS { echo "* $s" } Again, works just fine: PS my.ps1 * bar PS my.ps1 foo * foo However when setting the default to be a list, I get back something entirely reasonable but not at all what I want: PARAM ( [Parameter(ValueFromPipeline = $true)] $s = @('bar', 'bat', 'boy') ) PROCESS { echo "* $s" } Result: PS my.ps1 * bar bat boy I expected: PS my.ps1 * bar * bat * boy How can I get one call in to the Process loop for each default value? (This is somewhat different than getting one call in to Process, and wrapping the current body of in a big foreach loop over $s).

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• Is it ever a bad idea to publish a sitemap for a blog?

  - by mipadi

  I have a blog, and I have been considering publishing a sitemap for it, which would include the index page, archives page, and an entry for each individual blog post. Is this ever a bad idea? Is it a good (or useful) idea? I'm particularly interested in the <changefreq> element: I edit posts from time to time, and while that's not a common occurrence, I don't want to set a particularly infrequent change frequency that prevents search engines like Google from indexing the edits. (The sitemaps protocol says that search engines may still crawl the pages more frequently, but has no further details on the matter.)

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• A regular expression that will allow a string with only one Capital Letter

  - by Phoenix

  The string should be 6 - 20 characters in length. And it should contain 1 Capital letter. I can do this in code using C# string st = "SomeString" Regex rg = new Regex("[A-Z]"); MatchCollection mc = rg.Matches(st); Console.WriteLine("Total Capital Letters: " + mc.Count); if (mc.Count > 1) { return false; } But what i really want is a Regular expression that will match my string if it only contains one capital. The string can start with a common letter and should have only letters. Thanks In advance. (I did look at some of the other RegEx questions but they did not help).

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• Simple image server

  - by Joel

  I have a bunch of images that I need others to browse via a web browser in pretty much the same way as Apache-Gallery. I'd be able to dump all my images in a directory so that users hitting: http://server:port/directory would see small thumbnails and selecting an image would load it full size on a page with options to browse the previous or next image. I'm looking for a non Apache solution, much like the wonderfull Python simple http server, that can be launched anywhere with minimal configuration & fuss e.g. python -m SimpleHTTPServer 8000 In fact, the python solution above is pretty much want I want except it doesn't thumbnail the images but just a simple directory listing. Happy to use an app written in any common language so long as it is self contained and can run on linux on a custom port (and to re-iterate, not an Apache module).

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• extracting secrets from an embedded chip

  - by Will

  I am looking at an embedded system where secrets are stored in flash that is internal to the chip package, and there is no physical interface to get that information out - all access to this flash is policed by program code. All DMA attacks and JTAG and such are disabled. This seems to be a common locked-down configuration for system-on-a-chip. How might an attacker recover the secrets in that Flash? I understand they can fuzz for vulnerabilities in the app code and exploit it, that there could be some indistinct general side channel attack or something. But how would an attacker really go about trying to recover those keys? Are there viable approaches for a determined attacker to somehow shave-down the chip or some kind of microscope attack?

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• What's the best way to calculate similarity between rows in a table based on association?

  - by André Pena

  Suppose each Person has a collection of favorite Books. So I have a table for: Person Book The association between Person and Book (joint table for MxN) I want to fetch the Persons that are similar to a Person1 based on the favorite Books overlaping. That is: The more books they have in common, the more they are similar. I don't have to use only SQL to solve this problem. I could use programming also. I'm using SQL Server 2008 and C#. What solution would you experts use?

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• Computation geometry: find where's the triangle after rotation, tranlastion or reflection in a mirro

  - by newba

  Hi, I have a small contest problem in which is given a set of points, in 2D, that form a triangle. This triangle may be subject to an arbitrary rotation, may be subject to an arbitrary translation (both in the 2D plane) and may be subject to a reflection on a mirror, but its dimensions were kept unchanged. Then, they give me a set of points in the plane, and I have to find 3 points that form my triangle after one or more of those geometric operations. Example: 5 15 8 5 20 10 6 5 17 5 20 20 5 10 5 15 20 15 10 I bet that have to apply some known algorithm, but I don't know which. The most common are: convex hull, sweep plane, triangulation, etc. Can someone give a tip? I don't need the code, only a push, please!

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• Graphical net and text

  - by chesheerkys

  Hello! My task is to make a control, that behaves itself like RichTextBox, but contains a graphical net. The only task, this net is solving, is to be visible. It should be solution in overriding OnPaint method, but it doesn't. This code: protected override void OnPaint(System.Windows.Forms.PaintEventArgs e) { base.OnPaint(e); ...//drawing a line } gives me RichTextBox without of text This code: protected override void WndProc(ref System.Windows.Forms.Message m) { base.WndProc(ref m); if (m.Msg == 15) { Graphics g = this.CreateGraphics(); g.DrawLine(new Pen(Color.White, 1), new Point(0, 0), new Point(400, 400)); } } sometimes draws extra lines Actually since these two ways don't work, I don't know what to try. Waiting for your advices :) BR Dmitry P.S. I’ve heard a lot about great opportunities of WPF, but I’m not really common with this technology and don’t know what to start with. P.P.S. Sorry for my English, it’s not my natural language.

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• Sending most correct mimetype

  - by Roland Franssen

  Hi all, I have a list of extension to mimetype in a INI file. However some extensions have multiple mimetypes, for example; midi[] = "application/x-midi" midi[] = "audio/midi" midi[] = "audio/x-mid" midi[] = "audio/x-midi" midi[] = "music/crescendo" midi[] = "x-music/x-midi" 6 (possible) mimetypes for 1 extension. Whats common practice to determine the correct mimetype? (e.g. i need to set a HTTP content-type header). I know its not ideal; determining mimetypes based on extension.. but i need consistent (cross-server) results (e.g. fileinfo extension in PHP is making terrible guesses*). * Some fileinfo results for example; js - text/plain css - text/c-h

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• asp.net free cms for library

  - by Andrew Florko

  We have library website written in classic ASP that allows to browse and search by multiple (50+) filter criterias (author, publication year, ISSN ... ). There are lots of security holes and we have only one developer who hardly maintain this ASP-site with some minor features for last 3 years. There are two common user groups - administrators (librarians) and students (5000+) who have books on hands and searches for them. We don't want to rewrite it from scratch, just to use standard free CMS (.net based) and migrate library data and user accounts with minimum effort. What CMS will you suggest? Thank you in advance.

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• Django template not loading properly

  - by fmsf

  Hey, When this one runs everything goes fine: (r"^newobject$", "views.myobjects.newobject"), All the CSS + JS files are properly fetched from: static/css/... static/js/... When this one runs: (r"^mybjects/(([a-z]|[A-Z]|[0-9])+)$","views.myobjects.loadobject"), All the css and JS files that are being fetched, are run trough the urlpatterns and are returning my defailt page: (r"", 'views.main.index'), This makes all my CSS and JS code to actualy be HTML. My guess is that i'm giving some noob mistake. Is there any common reason why this should happen? And how to fix it?

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