1 #include <Eigen/Core> 2 #include <iostream> 3 using namespace Eigen; 4 using namespace std; 5 6 template<typename Derived> 7 Eigen::Block<Derived> 8 topLeftCorner(MatrixBase<Derived>& m, int rows, int cols) 9 { 10 return Eigen::Block<Derived>(m.derived(), 0, 0, rows, cols); 11 } 12 13 template<typename Derived> 14 const Eigen::Block<const Derived> 15 topLeftCorner(const MatrixBase<Derived>& m, int rows, int cols) 16 { 17 return Eigen::Block<const Derived>(m.derived(), 0, 0, rows, cols); 18 } 19 20 int main(int, char**) 21 { 22 Matrix4d m = Matrix4d::Identity(); 23 cout << topLeftCorner(4*m, 2, 3) << endl; // calls the const version 24 topLeftCorner(m, 2, 3) *= 5; // calls the non-const version 25 cout << "Now the matrix m is:" << endl << m << endl; 26 return 0; 27 } 28
