1 #include <Eigen/Core>
2 #include <iostream>
3 using namespace Eigen;
4 using namespace std;
5
6 template<typename Derived>
7 Eigen::Block<Derived>
topLeftCorner(MatrixBase<Derived> & m,int rows,int cols)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>
topLeftCorner(const MatrixBase<Derived> & m,int rows,int cols)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
main(int,char **)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