Simple Mex function to take in two Matlab matrices and return their matrix product. R = MatrixProductMEX( X, Y); same as R = X*Y;

MatrixProductMEX.cpp

#include "Eigen/Dense"
#include "mex.h"
#include <iostream>
using namespace Eigen;
using namespace std;

typedef Map<MatrixXd> MexMat;

void mexFunction(int nlhs, mxArray *plhs[], int nrhs, const mxArray *prhs[]) 
{
 	if ( nrhs != 2 ) {
  		mexErrMsgTxt("Needs 2 arguments -- X (NxD), Y (DxM)");
		return;
  	}	

	int N = mxGetM( prhs[0] );
	int D = mxGetN( prhs[0] );
	
	int D2 = mxGetM( prhs[1] );
	int M = mxGetN( prhs[1] );
	
	if (D != D2 ) {
		mexErrMsgTxt("X #cols needs to match Y #rows!");
		return;
	}

	MexMat X ( mxGetPr(prhs[0]), N, D);
	MexMat Y ( mxGetPr(prhs[1]), D, M);
	
 	// Create output matrix (using Matlab's alloc)
	plhs[0] = mxCreateDoubleMatrix(N, M, mxREAL);
  	MexMat R ( mxGetPr(plhs[0]), N, M );
  
 	R = X * Y;
}