eigen/doc/examples/Tutorial_ArrayClass_interop_matrix.cpp

#include <Eigen/Dense>
#include <iostream>

using Eigen::MatrixXf;

int main()
{
  MatrixXf m(2,2);
  MatrixXf n(2,2);
  MatrixXf result(2,2);

  m << 1,2,
       3,4;
  n << 5,6,
       7,8;

  result = m * n;
  std::cout << "-- Matrix m*n: --\n" << result << "\n\n";
  result = m.array() * n.array();
  std::cout << "-- Array m*n: --\n" << result << "\n\n";
  result = m.cwiseProduct(n);
  std::cout << "-- With cwiseProduct: --\n" << result << "\n\n";
  result = m.array() + 4;
  std::cout << "-- Array m + 4: --\n" << result << "\n\n";
}