Programming and Graphics

9.5 Transferring data fromMatlabto the C++ domain 309

/* --------

Use matlab to compute the eigenvalues

and eigenvectors of a matrix

-----------*/

#include <iostream>

#include <iomanip>

#include "engine.h"

using namespace std;

int main()

{

//--- Define a matrix in C++:

const shortN=4;//size of the data matrix

double x[N][N] ={{1.0, 2.0, 3.0, 4.0},

{-4.0,-3.0, 5.0, 6.0},

{8.0,-5.0, 5.0,-6.0},

{-0.8,-3.0,-5.0, 6.0},

};

//--- Start an engine session:

Engine * bouboulina = engOpen("matlab -nojvm -nosplash");

//--- Establish a buffer:

const int BSZ=1024;

char BuFFer[BSZ];

engOutputBuffer(bouboulina, BuFFer, BSZ);

//--- Transfer x to matlab as xm:

mxArray * xmat = mxCreateDoubleMatrix(N, N, mxREAL);

memcpy(mxGetPr(xmat), x, sizeof(x));

engPutVariable(bouboulina, "matrix", xmat);

//--- Compute the eigenvalues:

engEvalString(bouboulina, "[V,D]=eig(matrix)");

//--- Display the eigenvalues:

cout << BuFFer;

//--- Retrieve the eigenvector matrix: