matrix multiplication using provided memory area

mul.cpp

#include <iostream>
#include <Eigen/Dense>
using namespace std;
using namespace Eigen;

// matrix multiplication using provided memory area
// compile with -std=c++11
int main()
{
  const int size = 2;
  float* data = new float[size*size]{1.0,3.0,5.0,7.0};
  Map<Matrix<float, Dynamic, Dynamic, RowMajor> > m(data, size, size);
  cout << m << endl;
  // [1 3; 5 7]
  float* data2 = new float[size*size]{2.0,3.0,4.0,5.0};
  Map<Matrix<float, Dynamic, Dynamic, ColMajor> > m2(data2, size, size);
  cout << m2 << endl;
  // [2 4; 3 5]
  float* data3 = new float[size*size];
  Map<Matrix<float, Dynamic, Dynamic, RowMajor> > m3(data3, size, size);
  m3.noalias() = m * m2;
  cout << m3 << endl;// [11 19; 31 55]
  for (int i = 0; i < size*size; i++) {
    cout << data3[i] << " ";
  }
  cout << endl;
}