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benjamin on 10/29/09

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Fast Scientific Computation in Mex Functions Using Armadillo

/ Published in: C++

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.

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#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;
}

URL: http://www.myoutsourcedbrain.com/2009/08/fast-scientific-computation-in-mex.html

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