Advanced Search

Return to Snippet

Revision: 19734
at October 29, 2009 16:13 by benjamin
Initial Code 
#include "mex.h"
#include "math.h"
#include<armadillo>

using namespace arma;

void matlab2arma(mat& A, const mxArray *mxdata){
// delete [] A.mem; // don't do this!
access::rw(A.mem)=mxGetPr(mxdata);
access::rw(A.n_rows)=mxGetM(mxdata); // transposed!
access::rw(A.n_cols)=mxGetN(mxdata);
access::rw(A.n_elem)=A.n_rows*A.n_cols;
};

void freeVar(mat& A, const double *ptr){
access::rw(A.mem)=ptr;
access::rw(A.n_rows)=1; // transposed!
access::rw(A.n_cols)=1;
access::rw(A.n_elem)=1;
};

void mexFunction(int nlhs, mxArray *plhs[], int nrhs, const mxArray *prhs[])
{
if (nrhs != 2)
mexErrMsgTxt("Incorrect number of input arguments");
if (nlhs != 1)
mexErrMsgTxt("Incorrect number of output arguments");

mat D1(1,1);
const double* D1mem=access::rw(D1.mem);
matlab2arma(D1,prhs[0]); // First create the matrix, then change it to point to the matlab data.

mat D2(1,1);
const double* D2mem=access::rw(D2.mem);
matlab2arma(D2,prhs[1]);

// check if the input corresponds to what you are expecting
if( D1.n_rows != D2.n_rows )
mexErrMsgTxt("Columns of D1 and D2 must be of equal length!");

if( D1.n_cols != D2.n_cols )
mexErrMsgTxt("Rows of D1 and D2 must be of equal length!");

plhs[0] = mxCreateDoubleMatrix(D1.n_rows, D1.n_cols, mxREAL);
mat output(1,1);
const double* outputmem=access::rw(output.mem);
matlab2arma(output,plhs[0]);

output=D1+D2;
// output.print();

freeVar(D1,D1mem); // Change back the pointers!!
freeVar(D2,D2mem);
freeVar(output,outputmem);
return;
}
Initial URL 
http://www.myoutsourcedbrain.com/2009/08/fast-scientific-computation-in-mex.html
Initial Description 
This code is a demonstration of how to do fast scientific computation in mex functions using the armadillo library. See my blog post for details and leave comments there.
Initial Title 
Fast Scientific Computation in Mex Functions Using Armadillo
Initial Tags 
c
Initial Language 
C++