eigen/doc/examples/Tutorial_ArrayClass_mult.cpp

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

int main() {
  Eigen::ArrayXXf a(2, 2);
  Eigen::ArrayXXf b(2, 2);
  a << 1, 2, 3, 4;
  b << 5, 6, 7, 8;
  std::cout << "a * b = " << std::endl << a * b << std::endl;
}