Optimized matrix multiplication in C
Hello, I'm trying to compare different methods for matrix multiplication. The first one is normal method: do { for (j = 0; j < i; j++) { for (k = 0; k < i; k++) { suma = 0; for (l = 0; l < i; l...
matrix
MATLAB function for 'does matrix contain value X?' (ala php's in_array())
Is there a built in matlab function to find out if a matrix contains a value? Thanks ...
Strassen's algorithm for matrix multiplication
Can someone please explain strassen's algorithm for matrix multiplication in an intuitive way? I've gone through (well, tried to go through) the explanation in the book and wiki but it's not clicking upstairs. Any links on the web that use a lot of English rather than formal notation etc. would be helpful, too. Are there any analogies wh...
Converting a matlab matrix to a vector
I want to get a vector of elements of a Matlab matrix at predefined locations. For example, I have the following >> i = [1,2,3]; >> j = [1,3,4]; >> A = [1,2,3,4; 5,6,7,8; 9,10,11,12; 13,14,15,16] A = 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 I want a vector that will give me ...
matrix addition skipping NaN values
I would like to do element wise addition over matrices while skipping NaN values. MATLAB and Octave have nansum, but it does column wise addition within a matrix. Let: a = NaN * zeros(3) b = ones(3) I want: c = nan+(a, b) and c = b and: d = nan+(a,a) and d = a ...
Quaternions and Transform Matrices
Tell me if I am wrong. I'm starting using quaternions. Using a rotation matrix 4 x 4 (as used in OpenGL), I can compute model view matrix multiplying the current model view with a rotation matrix. The rotation matrix is derived from the quaternion. The quaternion is a direction vector (even not normalized) and a rotation angle. Resulte...
Is there any method for multiplying matrices having O(n) complexity?
I want to multiply two matrices but the triple loop has O(n3) complexity. Is there any algorithm in dynamic programming to multiply two matrices with O(n) complexity? ...
2D pixel array rotation and scaling
Hi I am working on C# program to process images ( given as int[,] ).. So I have 2D array of pixels, and I need to rotate them around a point, then scale them down to fit the original array.. I already found articles about using matrix to transform to a point and rotate then transform back.. What remains is to scale the resultant image ...
How to generate a function of two variables in matlab without using any loop?
Suppose I have a function y(t,x) = exp(-t)*sin(x) In Matlab, I define t = [0: 0.5: 5]; x = [0: 0.1: 10*2*pi]; y = zeros(length(t), length(x)); % empty matrix init Now, how do I define matrix y without using any loop, such that each element y(i,j) contains the value of desired function y at (t(i), x(j))? Below is how I did it using a ...
getting two matrices in one line
im trying to get these to appear in the same line without any success, my coding is \begin{equation} P^+=\[ \left( \begin{array}{ccc} 1 & 0\\ 0 & 0\end{array} \right)\] P^-=\[ \left( \begin{array}{ccc} 0 & 0\\ 0 & 1\end{array} \right)\] \end{equation} any hints or suggestions would be welcome ...
Comparing 2 elements of a 3x3 matrix to see if element 2 is adjacent to element 1.
Basically, I'm creating a puzzle where you can swap pieces. And I want to make sure that when swapping 2 elements, the selection is valid. Since the puzzle is only 9 pieces (3x3), I am currently using the code: function valid_selection(p1, p2) { if (p1 == 1 && (p2 == 2 || p2 == 4)) return true; if (p1 == 2 && (p2 == 1 || p2 == ...
Fast counting of 2D sub-matrices withing a large, dense 2D matrix?
What's a good algorithm for counting submatrices within a larger, dense matrix? If I had a single line of data, I could use a suffix tree, but I'm not sure if generalizing a suffix tree into higher dimensions is exactly straightforward or the best approach here. Thoughts? My naive solution to index the first element of the dense matrix...
OpenGL Rotations around World Origin when they should be around Local Origin
I'm implementing a simple camera system in OpenGL. I set up gluPerspective under the projection matrix and then use gluLookAt on the ModelView matrix. After this I have my main render loop which checks for keyboard events and, if any of the arrow keys are pressed, modifies angular and forward speeds (I only rotate through the y axis and ...
1067: Implicit coercion of a value of type void to an unrelated type flash.geom:Matrix.
Im confused, I passed a matrix datatype into the this.graphics.beginBitmapFill(); and i get Implicit coercion of a value of type. below is my code. var theMatrix:Matrix; theMatrix = new Matrix(); this.graphics.beginBitmapFill(tileImage,theMatrix.translate(30,0)); this.graphics.endFill(); and the fol...
understanding matrix.transition(); as3
I am trying to understand the method transition that falls in the Matrix Class. I am using it to copy pieces of a bitMapData. But I need to better understand what transitions do. I have a tilesheet that has 3 images on it. all 30x30 pixels. the width of the total bitmap is 90pxs. The first tile is green, the second is brown, and the ...
Smooth animation using MatrixTransform?
I'm trying to do an Matrix animation where I both scale and transpose a canvas at the same time. The only approach I found was using a MatrixTransform and MatrixAnimationUsingKeyFrames. Since there doesnt seem to be any interpolation for matrices built in (only for path/rotate) it seems the only choice is to try and build the interpolati...
Java inverse matrix calculation
Hi, I'm trying to calculate the inverse matrix in Java. I'm following the adjoint method (first calculation of the adjoint matrix, then transpose this matrix and finally, multiply it for the inverse of the value of the determinant). It works when the matrix is not too big. I've checked that for matrixes up to a size of 12x12 the resul...
Calculating scores from incomplete league tables
When I was in high school and learning about matrices, we were shown a technique that would help in a situation like this: There are a number of chess players in a league, and they need to determine a ranking for all of them, but don't have enough time for every player to play every other person. If it ends up that Player A beats Player...
Conversion euler to matrix and matrix to euler
I'm trying to convert a 3D rotation described in term of euler angles into a matrix and then back, using .NET/C#. My conventions are: left handed system (x right, y top, z forward) order of rotations: heading around y, pitch around x, bank around z rotations are positive using the left hand rule (thumb pointing to +infinity) My tria...
Flex container transform matrix problems
I have a Box container that has a label element inside it. When the box is transformed using a Matrix the label element is not visible anymore. How do I make the elements visible? <mx:Script> <![CDATA[ private function onBoxClick(event:MouseEvent):void { var transformMatrix:Matrix = this.box.transform....