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#include <Eigen/Core>
USING_PART_OF_NAMESPACE_EIGEN
using namespace std;
template<typename Scalar, typename Derived>
Eigen::Block<Derived>
topLeftCorner(MatrixBase<Scalar, Derived>& m, int rows, int cols)
{
return Eigen::Block<Derived>(m.ref(), 0, 0, rows, cols);
}
template<typename Scalar, typename Derived>
const Eigen::Block<Derived>
topLeftCorner(const MatrixBase<Scalar, Derived>& m, int rows, int cols)
{
return Eigen::Block<Derived>(m.ref(), 0, 0, rows, cols);
}
int main(int, char**)
{
Matrix4d m = Matrix4d::identity();
cout << topLeftCorner(4*m, 2, 3) << endl; // calls the const version
topLeftCorner(m, 2, 3) *= 5; // calls the non-const version
cout << "Now the matrix m is:" << endl << m << endl;
return 0;
}
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