eigen/doc/examples/tut_arithmetic_add_sub.cpp

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

int main() {
  Eigen::Matrix2d a;
  a << 1, 2, 3, 4;
  Eigen::MatrixXd b(2, 2);
  b << 2, 3, 1, 4;
  std::cout << "a + b =\n" << a + b << std::endl;
  std::cout << "a - b =\n" << a - b << std::endl;
  std::cout << "Doing a += b;" << std::endl;
  a += b;
  std::cout << "Now a =\n" << a << std::endl;
  Eigen::Vector3d v(1, 2, 3);
  Eigen::Vector3d w(1, 0, 0);
  std::cout << "-v + w - v =\n" << -v + w - v << std::endl;
}