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>
topLeft2x2Corner(MatrixBase<Derived> & m)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>
topLeft2x2Corner(const MatrixBase<Derived> & m)15 topLeft2x2Corner(const MatrixBase<Derived>& m)
16 {
17 return Eigen::Block<const Derived, 2, 2>(m.derived(), 0, 0);
18 }
19
main(int,char **)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