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							27 lines
						
					
					
						
							673 B
						
					
					
				| #include <Eigen/Core> | |
| #include <iostream> | |
| using namespace Eigen; | |
| using namespace std; | |
| 
 | |
| template<typename Derived> | |
| Eigen::VectorBlock<Derived, 2> | |
| firstTwo(MatrixBase<Derived>& v) | |
| { | |
|   return Eigen::VectorBlock<Derived, 2>(v.derived(), 0); | |
| } | |
| 
 | |
| template<typename Derived> | |
| const Eigen::VectorBlock<const Derived, 2> | |
| firstTwo(const MatrixBase<Derived>& v) | |
| { | |
|   return Eigen::VectorBlock<const Derived, 2>(v.derived(), 0); | |
| } | |
| 
 | |
| int main(int, char**) | |
| { | |
|   Matrix<int,1,6> v; v << 1,2,3,4,5,6; | |
|   cout << firstTwo(4*v) << endl; // calls the const version | |
|   firstTwo(v) *= 2;              // calls the non-const version | |
|   cout << "Now the vector v is:" << endl << v << endl; | |
|   return 0; | |
| }
 |