parallel for loop in mex

2015 8 4
1 个回答
更新时间：2015 8 4
4 次查看（30 天）

0 个投票

The outer loop in this code should be parallelizable
#include "mex.h"
#include "matrix.h"
#include <math.h>
//[reX imX]=cfrft(rectpuls(t),0.5,linspace(-10,10,2^12),-5:0.01:5);
void mexFunction(int nlhs, mxArray *plhs[],
int nrhs, const mxArray *prhs[]) {
nlhs=2;
const double pi = 3.1415926535897;
double *f= mxGetPr(prhs[0]);
size_t flen=mxGetNumberOfElements(prhs[0]);
double *ap= mxGetPr(prhs[1]);
double p = (*ap)*pi/2; double cscp = 2/sin(p); double cotp = 1/tan(p);
double *t= mxGetPr(prhs[2]);
// size_t tlen=mxGetNumberOfElements(prhs[2]);
double *w= mxGetPr(prhs[3]);
size_t wlen=mxGetNumberOfElements(prhs[3]);
plhs[0]=mxCreateDoubleMatrix(1, static_cast<int>(wlen), mxREAL);
plhs[1]=mxCreateDoubleMatrix(1, static_cast<int>(wlen), mxREAL);
double *reF = mxGetPr(plhs[0]);
double *imF = mxGetPr(plhs[1]);
double dt=t[1]-t[0];
for (int i = 0;i<wlen;i++){ //<<<<< THIS LOOP
double re=0;
double im=0;
double wc=w[i];
double wc2=wc*wc;
for(int j=0;j<flen;j++){
re += cos(pi*(cotp*wc2-cscp*t[j]*wc+cotp*t[j]*t[j]))*f[j];
im += sin(pi*(cotp*wc2-cscp*t[j]*wc+cotp*t[j]*t[j]))*f[j];
}
reF[i]=re*dt;
imF[i]=im*dt;
}
}
How do I use parallel loops in mex? My compiler is Building with 'Microsoft Windows SDK 7.1 (C++)'.

请先登录，再回答此问题。

回答（1 个）

James Tursa
James Tursa 2015-8-4

0 个投票

Some Microsoft compilers support OpenMP, but I don't think the vanilla SDK compiler is one of them. Did you mean using OpenMP, or something else?

6 个评论
显示 4更早的评论 隐藏 4更早的评论

htrh5
htrh5 2015-8-4
Okay, what must I do? matlab itself can run parfor loops. Is this OpenMP something I can simply install? Where would I learn how to make matlab to use that instead of sdk 7.1?
James Tursa
James Tursa 2015-8-4
编辑：James Tursa 2015-8-4
To run MATLAB parfor loops you need to purchase the Parallel Computing Toolbox. But parfor is not something you would use in a mex routine. To use OpenMP in a mex routine, you need to purchase a compiler with that capability. E.g., one of the Microsoft Professional/Ultimate/Etc editions.
Are you simply looking for speed improvements for some critical part of your code?
htrh5
htrh5 2015-8-4
There is no way to write parallel for loops in C++ without paying money for compilers? That doesn't sound right.
James Tursa
James Tursa 2015-8-4
OpenMP is a relatively easy way to do it, but it is not the only way. Another way is to write your own threading code. For that I would suggest looking at some examples in the FEX to see what others have done. E.g., here is one example:
http://www.mathworks.com/matlabcentral/fileexchange/37515-mmx-multithreaded-matrix-operations-on-n-d-matrices
htrh5
htrh5 2015-8-4
if this table is true http://openmp.org/wp/openmp-compilers/
maybe I have access to intel c++ compiler, if I installed that and changed matlab's compiler to that one, would OpenMP work then?
htrh5
htrh5 2015-8-4
I did try writing that code in matlab (and I vectorialized the inner loop using sum()). The function runs about 30% faster when it uses 4 cores. That much difference is not worth keeping 4 extra matlab processes running and waiting about a minute for the first function call to me.

请先登录，再进行评论。

类别

在 帮助中心 和 File Exchange 中查找有关 Call C++ from MATLAB 的更多信息

产品

标签

提问:

htrh5
htrh5
2015-8-4

评论：

htrh5
htrh5
2015-8-4

Community Treasure Hunt

Find the treasures in MATLAB Central and discover how the community can help you!

Start Hunting!

Translated by