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  • Fast 4x4 matrix multiplication in Java with NIO float buffers

    - by kayahr
    I know there are LOT of questions like that but I can't find one specific to my situation. I have 4x4 matrices implemented as NIO float buffers (These matrices are used for OpenGL). Now I want to implement a multiply method which multiplies Matrix A with Matrix B and stores the result in Matrix C. So the code may look like this: class Matrix4f { private FloatBuffer buffer = FloatBuffer.allocate(16); public Matrix4f multiply(Matrix4f matrix2, Matrix4f result) { {{{result = this * matrix2}}} <-- I need this code return result; } } What is the fastest possible code to do this multiplication? Some OpenGL implementations (Like the OpenGL ES stuff in Android) provide native code for this but others doesn't. So I want to provide a generic multiplication method for these implementations.

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  • An algorithm for converting a base-10 number to a base-N number.

    - by roja
    Guys, I am looking for a way to convert a base-10 number into a base-N number where N can be large. Specifically i am looking at converting to base-85 and back again. Does anyone know a simple algorithm to perform the conversion? Ideally it would provide something like: to_radix(83992, 85) - [11, 53, 12] Any ideas are appreciated! Roja

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  • Curve fitting: Find a CDF (or any function) that satisfies a list of constraints.

    - by dreeves
    I have some constraints on a CDF in the form of a list of x-values and for each x-value, a pair of y-values that the CDF must lie between. We can represent that as a list of {x,y1,y2} triples such as constraints = {{0, 0, 0}, {1, 0.00311936, 0.00416369}, {2, 0.0847077, 0.109064}, {3, 0.272142, 0.354692}, {4, 0.53198, 0.646113}, {5, 0.623413, 0.743102}, {6, 0.744714, 0.905966}} Graphically that looks like this: And since this is a CDF there's an additional implicit constraint of {Infinity, 1, 1} Ie, the function must never exceed 1. Also, it must be monotone. Now, without making any assumptions about its functional form, we want to find a curve that respects those constraints. For example: (I cheated to get that one: I actually started with a nice log-normal distribution and then generated fake constraints based on it.) One possibility is a straight interpolation through the midpoints of the constraints: mids = ({#1, Mean[{#2,#3}]}&) @@@ constraints f = Interpolation[mids, InterpolationOrder->0] Plotted, f looks like this: That sort of technically satisfies the constraints but it needs smoothing. We can increase the interpolation order but now it violates the implicit constraints (always less than one, and monotone): How can I get a curve that looks as much like the first one above as possible? Note that NonLinearModelFit with a LogNormalDistribution will do the trick in this example but is insufficiently general as sometimes there will sometimes not exist a log-normal distribution satisfying the constraints.

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  • What's a good matrix manipulation library available for C ?

    - by banister
    Hi, I am doing a lot of image processing in C and I need a good, reasonably lightweight, and above all FAST matrix manipulation library. I am mostly focussing on affine transformations and matrix inversions, so i do not need anything too sophisticated or bloated. Primarily I would like something that is very fast (using SSE perhaps?), with a clean API and (hopefully) prepackaged by many of the unix package management systems. Note this is for C not for C++. Thanks :)

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  • Evaluating a function at a particular value in parallel

    - by Gaurav Kalra
    Hi. The question may seem vague, but let me explain it. Suppose we have a function f(x,y,z ....) and we need to find its value at the point (x1,y1,z1 .....). The most trivial approach is to just replace (x,y,z ...) with (x1,y1,z1 .....). Now suppose that the function is taking a lot of time in evaluation and I want to parallelize the algorithm to evaluate it. Obviously it will depend on the nature of function, too. So my question is: what are the constraints that I have to look for while "thinking" to parallelize f(x,y,z...)? If possible, please share links to study.

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  • Is there any sense in performing binary AND with a number where all bits are set to 1

    - by n535
    Greetings everybody. I have seen examples of such operations for so many times that I begin to think that I am getting something wrong with binary arithmetic. Is there any sense to perform the following: byte value = someAnotherByteValue & 0xFF; I don't really understand this, because it does not change anything anyway. Thanks for help. P.S. I was trying to search for information both elsewhere and here, but unsuccessfully. EDIT: Well, off course i assume that someAnotherByteValue is 8 bits long, the problem is that i don't get why so many people ( i mean professionals ) use such things in their code. For example in Jon Skeet's MiscUtil there is: uint s1 = (uint)(initial & 0xffff); where initial is int.

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  • Looking for a function that will split profits/loss equally between 2 business partners.

    - by Hamish Grubijan
    This is not homework, for I am not a student. This is for my general curiosity. I apologize if I am reinventing the wheel here.The function I seek can be defined as follows (language agnostic): int getPercentageOfA(double moneyA, double workA, double moneyB, double workB) { // Perhaps you may assume that workA == 0 // Compute result return result; } Suppose Alice and Bob want to do business together ... such as ... selling used books. Alice is only interested in investing money in it and nothing else. Bob might invest some money, but he might have no $ available to invest. He will, however, put in the effort in finding a seller, a buyer, and doing maintenance. There are no tools, education, health insurance costs, or other expenses to consider. Both Alice and Bob wish to split the profits "equally" (A different weight like 40/60 for advanced users). Both are entrepreneurs, so they deal with low ROI/wage, and high income alike. There is no fixed wage, minimum wage, fixed ROI, or minimum ROI. They try to find the best deal possible, assume risks and go for it. Now, let's stick with the 50/50 model. If Alice invests $100, Bob invests work, and they will end up with a profit (or loss) of $60, they will split it equally - either both get $30 for their efforts/investments, or Bob ends up owing $30 to Alice. A second possibility: Both Alice and Bob invest 100, then Bob does all the work, and they end up splitting $60 profit. It looks like Alice should get only $15, because $30 of that profit came from Bob's investment and Bob's effort, so Alice shall have none of it, and the other $30 is to be split 50/50. Both of the examples above are trivial even when A and B want to split it 35/65 or what have you. Now it gets more complicated: What if Alice invests $70, and Bob invests $30 + does all of the work. It appears simple: (70,30) = (30,30) + (40,0) ... but, if only we knew how to weigh the two parts relative to each other. Another complicated (I think) example: what if Alice and Bob invest $70 and $30 respectively, and also put in an equal amount of work? I have a few data points: When A and B put in the same amount of work and the same $ - 50/50. When A puts in 100% of the money, and B does 100% of the work - 50/50. When A does all of the work and puts in all of the money - 100 for A / 0 for B (and vice-versa). When A puts in 50% of the money, and B puts in 50% of the money as well as does all of the work - 25 for A, and 75 for B (and vice-versa). If I fix things such that always workA = 0%, workB = 100% of the total work, then getPercentageOfA becomes a function: height z given x and y. The question is - how do you extrapolate this function between these several points? What is this function? If you can cover the cases when workA does not have to be 0% of the total work, and when investment vs work is split as 85/15 or using some other model, then what would the new function be?

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  • emacs: Inferior-mode python-shell appears "lagged"

    - by Begbie00
    Hi all - I'm a Python(3.1.2)/emacs(23.2) newbie teaching myself tkinter using the pythonware tutorial found here. Relevant code is pasted below the question. Question: when I click the Hello button (which should call the say_hi function) why does the inferior python shell (i.e. the one I kicked off with C-c C-c) wait to execute the say_hi print function until I either a) click the Quit button or b) close the root widget down? When I try the same in IDLE, each click of the Hello button produces an immediate print in the IDLE python shell, even before I click Quit or close the root widget. Is there some quirk in the way emacs runs the Python shell (vs. IDLE) that causes this "lagged" behavior? I've noticed similar emacs lags vs. IDLE as I've worked through Project Euler problems, but this is the clearest example I've seen yet. FYI: I use python.el and have a relatively clean init.el... (setq python-python-command "d:/bin/python31/python") is the only line in my init.el. Thanks, Mike === Begin Code=== from tkinter import * class App: def __init__(self,master): frame = Frame(master) frame.pack() self.button = Button(frame, text="QUIT", fg="red", command=frame.quit) self.button.pack(side=LEFT) self.hi_there = Button(frame, text="Hello", command=self.say_hi) self.hi_there.pack(side=LEFT) def say_hi(self): print("hi there, everyone!") root = Tk() app = App(root) root.mainloop()

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  • WPF ListView in GridView mode Highlighting problem

    - by xenik
    While reskining GridView (ListView with more columns), I ran into a problem, that I couldn't change the color of the Highlighted row. I searched the internet and found out, that adding this can help. <SolidColorBrush x:Key="{x:Static SystemColors.HighlightBrushKey}" Color="Transparent" /> <SolidColorBrush x:Key="{x:Static SystemColors.ControlBrushKey}" Color="Transparent" /> This solved the issue for some people but it didnt help me. The Highlight color was still in system default. I finally managed to change the color of the selected row, but the highlight is still visible around the border of the row plus i need to get rid of the Highlight in the ColumnHeaders. Heres the code, where my approach doesn't work. sth sthelse

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  • Code computing the cross-product

    - by WizardOfOdds
    This is not a dupe of my question: http://stackoverflow.com/questions/2532810/detecting-one-points-location-compared-to-two-other-points If I have the following piece of pseudo-C/Java/C# code: int a[]= { 30, 20 }; int b[] = { 40, 50 }; int c[] = {12, 12}; How do I compute the sign of the cross-product ABxAC? I'm only interested in the sign, so I have: boolean signABxAC = ? Now concretely what do I write to get the sign of the cross-product ABxAC?

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  • How to play sounds in locked mode on iPhone

    - by Joe Mallik
    Everybody knows the standard procedure to keep your app alive, after the user pressed the lock button (silent sound). If I start a sound with AVAudioPlayer (before the iphone is locked), the sound plays till it's end (after locking). The app is still running. If I try to start another sound while the iPhone is locked, it will never get played. All the other things work as well but the sound doesn't. How can I play a sound while the iphone is locked?

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  • evaluating buffer in emacs python-mode on remote host

    - by Adrian
    Hello, I'm using emacs23 with tramp to modify python scripts on a remote host. I found that when I start the python shell within emacs it starts up python on the remote host. My problem is that when I then try to call python-send-buffer via C-c C-c it comes up with the error Traceback (most recent call last): File "", line 1, in ? ImportError: No module named emacs Traceback (most recent call last): File "", line 1, in ? NameError: name 'emacs' is not defined Now, I must admit that I don't really know what's going on here. Is there a way for me to configure emacs so that I can evaluate the buffer on the remote host? Many thanks.

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  • Java Polynomial Multiplication with ArrayList

    - by user1506919
    I am having a problem with one of my methods in my program. The method is designed to take 2 arraylists and the perform multiplication between the two like a polynomial. For example, if I was to say list1={3,2,1} and list2={5,6,7}; I am trying to get a return value of 15,28,38,20,7. However, all I can get is an error message that says: Exception in thread "main" java.lang.IndexOutOfBoundsException: Index: 0, Size: 0. I have provided the method below: private static ArrayList<Integer> multiply(ArrayList<Integer> list1,ArrayList<Integer> list2) { ArrayList<Integer> array =new ArrayList<Integer>(list1.size()+list2.size()); for (int i=0;i<array.size();i++) array.add(i, 0); for (int i = 0; i < list1.size(); i++) for (int j = 0; j < list2.size(); j++) array.set(i+j, ((list1.get(i) * list2.get(j))+array.get(i+j))); return array; } Any help with solving this problem is greatly appreciated.

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  • Access Edit Mode Values of BindingSource Control

    - by Christopher Edwards
    I have a BindingSource control (http://msdn.microsoft.com/en-us/library/system.windows.forms.bindingsource.aspx) with a datasource of a (single) Linq object. If I change any of the properties of the underlying Linq-to-Sql object then all the other changes on the bound controls on the form are lost. Does anyone now why and how I work around it? I don't want to call EndEdit because this will commit the changes to the underlying object. I think this might be because my underlying object linq-to-sql object does not implement IEditableObject so the potental new values for the object fields are sort of stored in the forms controls. Can anyone either clarify what is going on and/or suggest a work around. Thanks!

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  • Using JavaCC to infer semantics from a Composite tree

    - by Skice
    Hi all, I am programming (in Java) a very limited symbolic calculus library that manages polynomials, exponentials and expolinomials (sums of elements like "x^n * e^(c x)"). I want the library to be extensible in the sense of new analytic forms (trigonometric, etc.) or new kinds of operations (logarithm, domain transformations, etc.), so a Composite pattern that represent the syntactic structure of an expression, together with a bunch of Visitors for the operations, does the job quite well. My problem arise when I try to implement operations that depends on the semantics more than on the syntax of the Expression (like integrals, for instance: there are a lot of resolution methods for specific classes of functions, but these same classes can be represented with more than a single syntax). So I thought I need something to "parse" the Composite tree to infer its semantics in order to invoke the right integration method (if any). Someone pointed me to JavaCC, but all the examples I've seen deal only with string parsing; so, I don't know if I'm digging in the right direction. Some suggestions? (I hope to have been clear enough!)

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  • How to set the Windows Mobile 6 IME mode (to numbers only)

    - by Daniel Crenna
    In Windows Mobile 5 one of the following methods works to set an input to numbers only: // Managed InputModeEditor.SetInputMode(textBox, InputMode.Numeric); // Native Wrapper InputModeSupport.SHSetImeMode(textBox.Handle, InputModeSupport.SHIME_MODE.SHIME_MODE_NUMBERS); In Windows Mobile 6, neither works. How do you set the IME to "Numbers Only" in WM 6.0 / .NET CF 3.5?

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