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							27 lines
						
					
					
						
							697 B
						
					
					
				| #include <Eigen/Core> | |
| #include <iostream> | |
| using namespace Eigen; | |
| using namespace std; | |
| 
 | |
| template<typename Derived> | |
| Eigen::Block<Derived, 2, 2> | |
| topLeft2x2Corner(MatrixBase<Derived>& m) | |
| { | |
|   return Eigen::Block<Derived, 2, 2>(m.derived(), 0, 0); | |
| } | |
| 
 | |
| template<typename Derived> | |
| const Eigen::Block<const Derived, 2, 2> | |
| topLeft2x2Corner(const MatrixBase<Derived>& m) | |
| { | |
|   return Eigen::Block<const Derived, 2, 2>(m.derived(), 0, 0); | |
| } | |
| 
 | |
| int main(int, char**) | |
| { | |
|   Matrix3d m = Matrix3d::Identity(); | |
|   cout << topLeft2x2Corner(4*m) << endl; // calls the const version | |
|   topLeft2x2Corner(m) *= 2;              // calls the non-const version | |
|   cout << "Now the matrix m is:" << endl << m << endl; | |
|   return 0; | |
| }
 |