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Revision: 19735
at October 29, 2009 16:20 by benjamin
Initial Code 
#include "mex.h"
#include "math.h"
#include<armadillo> 

using namespace arma;

void importMatlab(mat& A, const mxArray *mxdata){
  access::rw(A.mem)=mxGetPr(mxdata);
  access::rw(A.n_rows)=mxGetM(mxdata);
  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;
  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 != 3)
        mexErrMsgTxt("Incorrect number of input arguments");
    if (nlhs != 1)
        mexErrMsgTxt("Incorrect number of D arguments");
    
  mat X(1,1);
  const double* Xmem=access::rw(X.mem);
  importMatlab(X,prhs[0]);

  mat Y(1,1);
  const double* Ymem=access::rw(Y.mem);
  importMatlab(Y,prhs[1]);
  
  mat W(1,1);
  const double* Wmem=access::rw(W.mem);
  importMatlab(W,prhs[2]);

//    check if the input corresponds to what you are expecting
  if(( X.n_cols !=  Y.n_cols ) || (Y.n_cols != W.n_cols ) )
    mexErrMsgTxt("Columns of X, Y, and W must be of equal length!");
   if( W.n_rows !=  W.n_cols )
    mexErrMsgTxt("W must be a square matrix!");

    plhs[0] = mxCreateDoubleMatrix(X.n_rows, Y.n_rows, mxREAL);

    double *out = mxGetPr(plhs[0]);
    mat diff;
    mat M;
    int k=0;
    for(int y=0;y<Y.n_rows;y++)
      for(int x=0;x<X.n_rows;x++){
// (X(x,:)-Y(y,:))*W*((X(x,:)-Y(y,:))')
            diff=X.row(x)-Y.row(y);
            M=diff*W*trans(diff);
            (*out++)=M(0);
        }
          
    
    freeVar(X,Xmem);
    freeVar(Y,Ymem);
    freeVar(W,Wmem);
    return;
}
Initial URL 
http://www.myoutsourcedbrain.com/2009/08/mex-function-for-mahalanobis-function.html
Initial Description 
This code is a demonstration of writing mex functions using the armadillo scientific library. Please see my blog post for more details and leave comments there.
Initial Title 
Mex Function for Mahalanobis Function
Initial Tags 

                                

                                                            

                                    

                                        

                                        Initial Language
                                        

                                    

                                    
C++