1 #include <Eigen/Core> 2 #include <iostream> 3 using namespace Eigen; 4 using namespace std; 5 6 template<typename Derived> 7 Eigen::Block<Derived, 2, 2> 8 topLeft2x2Corner(MatrixBase<Derived>& m) 9 { 10 return Eigen::Block<Derived, 2, 2>(m.derived(), 0, 0); 11 } 12 13 template<typename Derived> 14 const Eigen::Block<const Derived, 2, 2> 15 topLeft2x2Corner(const MatrixBase<Derived>& m) 16 { 17 return Eigen::Block<const Derived, 2, 2>(m.derived(), 0, 0); 18 } 19 20 int main(int, char**) 21 { 22 Matrix3d m = Matrix3d::Identity(); 23 cout << topLeft2x2Corner(4*m) << endl; // calls the const version 24 topLeft2x2Corner(m) *= 2; // calls the non-const version 25 cout << "Now the matrix m is:" << endl << m << endl; 26 return 0; 27 } 28
