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  • how to use random bits to simulate a fair 26-sided die?

    - by Michael Levin
    How do I use a random number generator that gives bits (0 or 1) to simulate a fair 26-sided die? I want to use a bitstream to pick letters of the English alphabet such that the odds of any one letter coming up is the same as the odds of any other letter (I know real words aren't like that and have specific frequency distributions for each letter but it doesn't matter here). What's the best way to use binary 0/1 decisions to pick letters fairly from the set A-Z? I can think of a few ways to map bits onto letters but it's not obvious to me that they won't be biased. Is there a known good way?

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  • GetDeviceGammaRamp to adjust colors

    - by peter
    Hi, I overlay an OpenGL application (c++), this openGL application uses SetDeviceGammaRamp to set the brightness of the desktop to very high (dont know why). This application is fullscreen and looks good, but my overlay is very bright. Instead of the orange color with normal brightness, I get yellow because of the high gamma. What I want to do: Get the gamma that is currently set (using GetDeviceGammaRamp), and then use this to adjust the colors I set. Like; glColor4f(r, g, b, a) becomes glColor4f(r / gamma, g / gamma, b / gamma, a); So if the brightness of the desktop is very high, the r g and b values will be lower (darker) and will look like they should. How can I accomplish this? GetDeviceGammaRamp fills a table, how can I use it to modify my colors? Thanks

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  • Indentation control while developing a small python like language

    - by sap
    Hello, I'm developing a small python like language using flex, byacc (for lexical and parsing) and C++, but i have a few questions regarding scope control. just as python it uses white spaces (or tabs) for indentation, not only that but i want to implement index breaking like for instance if you type "break 2" inside a while loop that's inside another while loop it would not only break from the last one but from the first loop as well (hence the number 2 after break) and so on. example: while 1 while 1 break 2 'hello world'!! #will never reach this. "!!" outputs with a newline end 'hello world again'!! #also will never reach this. again "!!" used for cout end #after break 2 it would jump right here but since I don't have an "anti" tab character to check when a scope ends (like C for example i would just use the '}' char) i was wondering if this method would the the best: I would define a global variable, like "int tabIndex" on my yacc file that i would access in my lex file using extern. then every time i find a tab character on my lex file i would increment that variable by 1. when parsing on my yacc file if i find a "break" keyword i would decrement by the amount typed after it from the tabIndex variable, and when i reach and EOF after compiling and i get a tabIndex != 0 i would output compilation error. now the problem is, whats the best way to see if the indentation got reduced, should i read \b (backspace) chars from lex and then reduce the tabIndex variable (when the user doesn't use break)? another method to achieve this? also just another small question, i want every executable to have its starting point on the function called start() should i hardcode this onto my yacc file? sorry for the long question any help is greatly appreciated. also if someone can provide an yacc file for python would be nice as a guideline (tried looking on Google and had no luck). thanks in advance.

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  • Dynamically changing background color of a UIView

    - by EricM
    Hello- Here's my setup. I have a viewcontroller that I'm creating and adding as a subview. The viewcontroller presents some options that a user can chose from. The viewcontroller is being pushed in response to a "long press" gesture. Within the viewcontroller, I added a child UIView to group some other controls together so I can move them around the screen as a unit and, when they are displayed, center them on the location of the long press. Here is the code that instantiates the view controller, changes its location, and adds it as a subview: UserOptions *opts = [[UserOptions alloc] initWithNibName:@"UserOptions" bundle:nil]; [opts recenterOptions:location]; [self.view addSubview:opts.view]; That bit of code does create and push the viewcontroller, but the call to recenterOptions doesn't do anything. Here is that method: - (void) recenterOptions:(CGPoint)location { CGRect oldFrame = self.optionsView.frame; CGFloat newX = location.x; // + oldFrame.size.width / 2.0; CGFloat newY = location.y; // + oldFrame.size.height / 2.0; CGRect newFrame = CGRectMake(newX, newY, oldFrame.size.width, oldFrame.size.height); self.optionsView.frame = newFrame; } Note that self.optionsView is the child UIView that I added to the viewcontroller's nib. Does anyone know why I'm unable to change the location of the UIView? Regards, Eric

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  • What is the possible benefit (if any) of allowing recursive contructors?

    - by Penang
    In Java, constructors cannot be recursive. Compile time error: "recursive constructor invocation". Let's assume that we did not have this restriction. Things to keep in mind: The return type of a constructor is void. Since it is a void method you can't harness the complete power of recursion. A constructor can invoke itself (or any other constructor) using this(). But a "call to this must be first statement in constructor" We could use non local data between consecutive calls to still have some possible gain from recursive constructors. Would there be any benefit from allowing recursive constructors?

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  • Are mathamatical Algorithms protected by copyright

    - by analogy
    I wish to implement an algorithm which i read in a journal paper in my software (commercial). I want to know if this is allowed or not. The algorithm in question is described in http://arxiv.org/abs/0709.2938 It is a very simple algorithm and a number of implementations exist in python (http://igraph.sourceforge.net/) and java. One of them is in gpl another which i got from a different researcher and had no license attached. There are significant differences in two implementations, e.g. second one uses threads and multiple cores. It is possible to rewrite/ (not translate) the algorithm. So can I use it in my software or on a server for commercial purpose. Thanks

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  • Calculating Divergent Paths on Subtending Rings

    - by Russ
    I need to calculate two paths from A to B in the following graph, with the constraint that the paths can't share any edges: hmm, okay, can't post images, here's a link. All edges have positive weights; for this example I think we can assume that they're equal. My naive approach is to use Djikstra's algorithm to calculate the first path, shown in the second graph in the above image. Then I remove the edges from the graph and try to calculate the second path, which fails. Is there a variation of Djikstra, Bellman-Ford (or anything else) that will calculate the paths shown in the third diagram above? (Without special knowledge and removal of the subtending link, is what I mean)

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  • All minimum spanning trees implementation

    - by russtbarnacle
    I've been looking for an implementation (I'm using networkx library.) that will find all the minimum spanning trees (MST) of an undirected weighted graph. I can only find implementations for Kruskal's Algorithm and Prim's Algorithm both of which will only return a single MST. I've seen papers that address this problem (such as http://fano.ics.uci.edu/cites/Publication/Epp-TR-95-50.html) but my head tends to explode someway through trying to think how to translate it to code. In fact i've not been able to find an implementation in any language!

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  • Evaluation of jQuery function variable value during definition of that function

    - by thesnail
    I have a large number of rows in a table within which I wish to attach a unique colorpicker (jQuery plugin) to each cell in a particular column identified by unique ids. Given this, I want to automate the generation of instances of the colorpicker as follows: var myrows={"a","b","c",.....} var mycolours={"ffffff","fcdfcd","123123"...} for (var i=0;i<myrows.length;i++) { $("#"+myrows[i]+"colour").ColorPicker({flat: false, color: mycolours[i], onChange: function (hsb, hex, rgb) { $("#"+myrows[i]+"currentcolour").css('backgroundColor', '#' + hex); } }); Now this doesn't work because the evaluation of the $("#"+myrows[i]+"currentcolour") component occurs at the time the function is called, not when it is defined (which is want I need). Given that this plugin javascript appends its code to the level and not to the underlying DOM component that I am accessing above so can't derive what id this pertains to, how can I evaluate the variable during function declaration/definition? Thanks for any help/insight anyone can give. Brian.

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  • what does driver program mean?

    - by Tom
    there is a quote from Algorithms for Java (sedgwick 2003) p. 135: "we commonly use driver programs when developing or debugging adt iplementations" what is meant by driver program? google just gives me loads of info about programming drivers, clearly not related

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  • Imagick: gifs, and background color

    - by TheButch3r
    Hi, I have 2 questions about using the php imagick class that I can't get working properly... 1.) I tried resizing / cropping a gif, and treated it as a normal image. It seemed to work, except that a few frames in the middle of the animation contained a small patch of artifacts. Is there a setting that should be used when working with multi-frame gifs? 2.) Is there a simple command to resize images if they are too small by just adding a background? For instance, if an image is 10x10, could I add a white background, and have a 100x100px image with the original in the upper left corner? Thanks for any help!

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  • Find the shortest path in a graph which visits certain nodes.

    - by dmd
    I have a undirected graph with about 100 nodes and about 200 edges. One node is labelled 'start', one is 'end', and there's about a dozen labelled 'mustpass'. I need to find the shortest path through this graph that starts at 'start', ends at 'end', and passes through all of the 'mustpass' nodes (in any order). ( http://3e.org/local/maize-graph.png / http://3e.org/local/maize-graph.dot.txt is the graph in question - it represents a corn maze in Lancaster, PA)

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  • Why state cannot be part of Presenter in MVP?

    - by rFactor
    I read http://www.codeproject.com/KB/architecture/MVC_MVP_MVVM_design.aspx and it said: As powerful as they are, both MVC and MVP have their problems. One of them is persistence of the View’s state. For instance, if the Model, being a domain object, does not know anything about the UI, and the View does not implement any business logic, then where would we store the state of the View’s elements such as selected items? Fowler comes up with a solution in the form of a Presentation Model pattern. I wonder why Presenter can't hold View state? It already holds all View logic. As far as I understand, in MVC and MVP the state is kept in View. In PM and MVVM the state is kept in the Presentation Model. Why can't Presenter follow PM in this particular case and contain the state of the view? Here is another article which says Presenter does not hold View state, instead the view does: http://www.codeproject.com/KB/aspnet/ArchitectureComparison.aspx

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  • Convert image color space and output separate channels in OpenCV

    - by Victor May
    I'm trying to reduce the runtime of a routine that converts an RGB image to a YCbCr image. My code looks like this: cv::Mat input(BGR->m_height, BGR->m_width, CV_8UC3, BGR->m_imageData); cv::Mat output(BGR->m_height, BGR->m_width, CV_8UC3); cv::cvtColor(input, output, CV_BGR2YCrCb); cv::Mat outputArr[3]; outputArr[0] = cv::Mat(BGR->m_height, BGR->m_width, CV_8UC1, Y->m_imageData); outputArr[1] = cv::Mat(BGR->m_height, BGR->m_width, CV_8UC1, Cr->m_imageData); outputArr[2] = cv::Mat(BGR->m_height, BGR->m_width, CV_8UC1, Cb->m_imageData); split(output,outputArr); But, this code is slow because there is a redundant split operation which copies the interleaved RGB image into the separate channel images. Is there a way to make the cvtColor function create an output that is already split into channel images? I tried to use constructors of the _OutputArray class that accepts a vector or array of matrices as an input, but it didn't work.

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  • Fitts Law, applying it to touch screens

    - by Caylem
    Been reading a lot into UI design lately and Fitts Law keeps popping up. Now from what i gather its basically the larger an item is, and the closer it is to your cursor, the easier it is to click on. So what about touch screen devices where the input comes from multiple touches or just single touches. What are the fundamentals to take into account considering this? Should it be something like, the hands of the user are on the sides of the device so the buttons should be close to the left and right hand sides of the device? Thanks

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  • Mutual Information / Entropy Calculation Help

    - by Fillip
    Hi, Hoping someone can give me some pointers with this entropy problem. Say X is chosen randomly from the uniform integer distribution 0-32 (inclusive). I calculate the entropy, H(X) = 32 bits, as each Xi has equal probability of occurring. Now, say the following pseudocode executes. int r = rand(0,1); // a random integer 0 or 1 r = r * 33 + X; How would I work out the mutual information between the two variables r and X? Mutual Information is defined as I(X; Y) = H(X) - H(X|Y) but I don't really understand how to apply the conditional entropy H(X|Y) to this problem. Thanks

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  • Finding contained bordered regions from Excel imports.

    - by dmaruca
    I am importing massive amounts of data from Excel that have various table layouts. I have good enough table detection routines and merge cell handling, but I am running into a problem when it comes to dealing with borders. Namely performance. The bordered regions in some of these files have meaning. Data Setup: I am importing directly from Office Open XML using VB6 and MSXML. The data is parsed from the XML into a dictionary of cell data. This wonks wonderfully and is just as fast as using docmd.transferspreadsheet in Access, but returns much better results. Each cell contains a pointer to a style element which contains a pointer to a border element that defines the visibility and weight of each border (this is how the data is structured inside OpenXML, also). Challenge: What I'm trying to do is find every region that is enclosed inside borders, and create a list of cells that are inside that region. What I have done: I initially created a BFS(breadth first search) fill routine to find these areas. This works wonderfully and fast for "normal" sized spreadsheets, but gets way too slow for imports into the thousands of rows. One problem is that a border in Excel could be stored in the cell you are checking or the opposing border in the adjacent cell. That's ok, I can consolidate that data on import to reduce the number of checks needed. One thing I thought about doing is to create a separate graph that outlines the cells using the borders as my edges and using a graph algorithm to find regions that way, but I'm having trouble figuring out how to implement the algorithm. I've used Dijkstra in the past and thought I could do similar with this. So I can span out using no endpoint to search the entire graph, and if I encounter a closed node I know that I just found an enclosed region, but how can I know if the route I've found is the optimal one? I guess I could flag that to run a separate check for the found closed node to the previous node ignoring that one edge. This could work, but wouldn't be much better performance wise on dense graphs. Can anyone else suggest a better method? Thanks for taking the time to read this.

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  • Can an algorithmic process ever give true random numbers ?

    - by Arkapravo
    I have worked with random functions in python,ruby, MATLAB, Bash and Java. Nearly every programming language has a function to generate Random numbers. However, these apparently random sequences are termed as pseudo-random number sequences as the generation follows a deterministic approach, and the sequence seems to repeat (usually with a very large period). My question, can an algorithmic/programming process ever yield true random numbers ? The questions probably is more of theoretical computer science than just programming !

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