Prev: problem with symbolic integration
Next: How can I compare 2 surfaces??
From: Bruno Luong on 4 May 2010 06:57
"Michael " <michael.schmittNOSPAM(a)bv.tum.de> wrote in message <hrosth$5r7$1(a)fred.mathworks.com>...
> Simple answer: I have tested this procedure on some small dataset (100 x 100 pixels) and had a speed gain of about 25%. Although I need to test the reliability of the CMEX implementation...

I have doubt if you do the correct timing (which is not trivial to get it right as it seems to be, believe me).

To be certain I have tried my own test of calling a function directly from Matlab and from mex. The timing speak for itself, the overhead of mexEvalString is HUGE.

function bar

tic
for n=1:10000;
r = foo;
end
toc % 0.005447 seconds
clear r

tic
for n=1:10000;
callfoo;
end % Elapsed time is 0.845930 seconds.
toc

end % bar

function r = foo
r = 1.0;
end % foo

// callfoo.c
#include <string.h>
#include "mex.h"

void mexFunction(int nlhs, mxArray *plhs[], int nrhs, const mxArray *prhs[]) {
char text[200];

strcpy(text, "r = foo;");
mexEvalString(text);
return;
} // callfoo.c


Bruno
From: Michael on 4 May 2010 07:51
You may be right - I don't really know whether it's really worthwhile. That's why I wanted to give it a try.

Nevertheless you should be careful with your comparison: I do the for-loop within C/MEX! With for-loops being terrifyingly slow in MATLAB, I would believe you would have better timing using the following test:

#include <string.h>
#include "mex.h"

void mexFunction(int nlhs, mxArray *plhs[], int nrhs, const mxArray *prhs[]) {
char text[200];
int i;

for(i = 0; i<=10000;i++)
{
strcpy(text, "r = foo;");
mexEvalString(text);
}

return;
} // callfoo.c



Nevertheless this wasn't my original problem. ;) Any help on the segmentation violation would be appreciated.
From: Bruno Luong on 4 May 2010 08:00

>
> Nevertheless this wasn't my original problem. ;) Any help on the segmentation violation would be appreciated.

Have you seen my comments on FREE? Those are very wrong.

Bruno
From: Bruno Luong on 4 May 2010 08:17
"Michael " <michael.schmittNOSPAM(a)bv.tum.de> wrote in message <hrp1n9$er5$1(a)fred.mathworks.com>...
> I would believe you would have better timing using the following test:

Why don't you do it yourself?

Bruno
From: Michael on 4 May 2010 09:05
"Bruno Luong" <b.luong(a)fogale.findmycountry> wrote in message <hrp382$o7c$1(a)fred.mathworks.com>...
> "Michael " <michael.schmittNOSPAM(a)bv.tum.de> wrote in message <hrp1n9$er5$1(a)fred.mathworks.com>...
> > I would believe you would have better timing using the following test:
>
> Why don't you do it yourself?
>
> Bruno

Because I already did a tic-toc test and experienced a speed gain of 25% (cf. my previous messages). With my last message I only replied to your (not sufficient) argumentation.
First  |  Prev  |  Next  |  Last
Pages: 1 2 3
Prev: problem with symbolic integration
Next: How can I compare 2 surfaces??