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