Could exponent of an array be inproved in speed ? Maybe mex file with exp function (reduced accuracy) for windows 64 bit.
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Could this line of code be improved in speed ? MM is an array 512x512^2 elements.
MM =ones(512^2,512); tic; exp(1i*(MM)); toc
Elapsed time is 3.824361 seconds.
I am looking for mex file for 64bit windows of exp function with reduced accuracy ?
#include <stddef.h>
#include <math.h>
#include "mex.h"
#ifndef mwSize
#define mwSize int
#endif
/* these 2 #define lines help make the later code more
readable */
/* Input Arguments */
#define PARAMETER_IN prhs[0]
/* Output Arguments */
#define RESULT_OUT plhs[0]
#define LITTLE_ENDIAN 1
static union
{
double d;
struct {
#ifdef LITTLE_ENDIAN
int j,i;
#else
int i,j;
#endif
} n;
} _eco;
#define EXP_A (1048576/0.69314718055994530942)
#define EXP_C 60801
#define EXP(y) (_eco.n.i = EXP_A*(y) + (1072693248 - EXP_C),_eco.d)
void mexexp(double*y, double*yp, mwSize m) {
while(m--) {
*yp++ = EXP(*y++);
}
}
void mexFunction( int nlhs, mxArray *plhs[],
int nrhs, const mxArray*prhs[] )
{
mwSize numel;
mwSize ndim;
mwSize *dims;
/* Check for proper number of arguments */
if (nrhs != 1) {
mexErrMsgTxt("One input argument required.");
} else if (nlhs > 1) {
mexErrMsgTxt("Too many output arguments.");
} else if ( !mxIsDouble(PARAMETER_IN) ) {
mexErrMsgTxt("Input must be double.");
} else if ( mxIsComplex(PARAMETER_IN) ) {
mexErrMsgTxt("Input cannot be complex.");
}
ndim = mxGetNumberOfDimensions(PARAMETER_IN);
dims = mxGetDimensions(PARAMETER_IN);
numel = mxGetNumberOfElements(PARAMETER_IN);
/* Create a matrix for the return argument */
RESULT_OUT = mxCreateNumericArray(ndim, dims,
mxDOUBLE_CLASS, mxREAL);
/* Do the actual computation*/
mexexp(mxGetPr(PARAMETER_IN),mxGetPr(RESULT_OUT),numel);
return;
}
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回答 (1 件)
James Tursa
2015 年 3 月 14 日
編集済み: James Tursa
2015 年 3 月 14 日
For your particular posed example all the elements are the same, so only compute the exp calculation once and don't do all of those multiplies either. E.g.,
NN = complex(zeros(512^2,512)); tic; NN(:) = exp(1i); toc
Is this the real problem, or is MM not really all 1's in your actual problem?
2 件のコメント
Jan
2015 年 3 月 14 日
@Ole: Usually it is impossible to give suggestions for speed improvements, if only a roughly simplified version of the code is posted. So please post the relevant part of the code.
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