matrix-inverse

Three.js: Show world coordinate axes in corner of scene

由 无人久伴 提交于 2019-11-27 04:28:08
问题 This is probably a very basic problem, but I haven't found a solution yet and it's been bugging me. I'd like to show arrows indicating the world coordinate directions (x, y, z) in the bottom right hand corner of the camera like is done in Maya, so that when rotating the camera around an object, or moving through a scene, you can still identify the directions of the world coordinates. I've tried to accomplish this using two different approaches and neither has worked so far. I have an object

Efficient way to solve for X in AX=B in MATLAB when both A and B are big matrices

由 ぐ巨炮叔叔 提交于 2019-11-27 03:32:27
问题 I have this problem which requires solving for X in AX=B . A is of the order 15000 x 15000 and is sparse and symmetric. B is 15000 X 7500 and is NOT sparse. What is the fastest way to solve for X? I can think of 2 ways. Simplest possible way, X = A\B Using for loop, invA = A\speye(size(A)) for i = 1:size(B,2) X(:,i) = invA*B(:,i); end Is there a better way than the above two? If not, which one is best between the two I mentioned? 回答1: First things first - never, ever compute inverse of A.

inverting a 4x4 matrix

由 99封情书 提交于 2019-11-27 02:50:25
i am looking for a sample code implementation on how to invert a 4x4 matrix. i know there is gaussian eleminiation, LU decomposition, etc. but instead of looking at them in detail i am really just looking for the code to do this. language ideally C++, data is available in array of 16 floats in cloumn-major order. thank you! shoosh here: bool gluInvertMatrix(const double m[16], double invOut[16]) { double inv[16], det; int i; inv[0] = m[5] * m[10] * m[15] - m[5] * m[11] * m[14] - m[9] * m[6] * m[15] + m[9] * m[7] * m[14] + m[13] * m[6] * m[11] - m[13] * m[7] * m[10]; inv[4] = -m[4] * m[10] * m

Computing the inverse of a matrix using lapack in C

由 只愿长相守 提交于 2019-11-27 00:17:50
问题 I would like to be able to compute the inverse of a general NxN matrix in C/C++ using lapack. My understanding is that the way to do an inversion in lapack is by using the dgetri function, however, I can't figure out what all of its arguments are supposed to be. Here is the code I have: void dgetri_(int* N, double* A, int* lda, int* IPIV, double* WORK, int* lwork, int* INFO); int main(){ double M [9] = { 1,2,3, 4,5,6, 7,8,9 }; return 0; } How would you complete it to obtain the inverse of the

Why is Matlab's inv slow and inaccurate?

由 此生再无相见时 提交于 2019-11-26 19:01:38
I read at a few places (in the doc and in this blog post : http://blogs.mathworks.com/loren/2007/05/16/purpose-of-inv/ ) that the use of inv in Matlab is not recommended because it is slow and inaccurate. I am trying to find the reason of this inaccuracy. As of now, Google did not give m interesting result, so I thought someone here could guide me. Thanks ! The inaccuracy I mentioned is with the method INV, not MATLAB's implementation of it. You should be using QR, LU, or other methods to solve systems of equations since these methods don't typically require squaring the condition number of

Python Inverse of a Matrix

由 天涯浪子 提交于 2019-11-26 18:49:06
问题 How do I get the inverse of a matrix in python? I've implemented it myself, but it's pure python, and I suspect there are faster modules out there to do it. 回答1: You should have a look at numpy if you do matrix manipulation. This is a module mainly written in C, which will be much faster than programming in pure python. Here is an example of how to invert a matrix, and do other matrix manipulation. from numpy import matrix from numpy import linalg A = matrix( [[1,2,3],[11,12,13],[21,22,23]])

Java inverse matrix calculation

由 我与影子孤独终老i 提交于 2019-11-26 18:21:56
问题 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 result is quickly provided. However, when the matrix is bigger than 12x12 the time it needs to complete the calculation increases exponentially. The matrix I need to

How to compute inverse of a matrix accurately?

由 独自空忆成欢 提交于 2019-11-26 17:09:15
问题 I'm trying to compute an inverse of a matrix P , but if I multiply inv(P)*P , the MATLAB does not return the identity matrix. It's almost the identity (non diagonal values in the order of 10^(-12) ). However, in my application I need more precision. What can I do in this situation? 回答1: Only if you explicitly need the inverse of a matrix you use inv, otherwise you just use the backslash operator \ . The documentation on inv explicitly states: x = A\b is computed differently than x = inv(A)*b

CUBLAS: Incorrect inversion for matrix with zero pivot

由 柔情痞子 提交于 2019-11-26 14:49:07
问题 Since CUDA 5.5, the CUBLAS library contains routines for batched matrix factorization and inversion (cublas<t>getrfBatched and cublas<t>getriBatched respectively). Getting guide from the documentation, I wrote a test code for inversion of an N x N matrix using these routines. The code gives correct output only if the matrix has all non zero pivots. Setting any pivot to zero results in incorrect results. I have verified the results using MATLAB. I realize that I am providing row major matrices

Why is Matlab&#39;s inv slow and inaccurate?

由 故事扮演 提交于 2019-11-26 06:45:01
问题 I read at a few places (in the doc and in this blog post : http://blogs.mathworks.com/loren/2007/05/16/purpose-of-inv/ ) that the use of inv in Matlab is not recommended because it is slow and inaccurate. I am trying to find the reason of this inaccuracy. As of now, Google did not give m interesting result, so I thought someone here could guide me. Thanks ! 回答1: The inaccuracy I mentioned is with the method INV, not MATLAB's implementation of it. You should be using QR, LU, or other methods
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