1 Matrix2f M = Matrix2f::Random(); 2 Matrix2f m; 3 m = M; 4 cout << "Here is the matrix m:" << endl << m << endl; 5 cout << "Now we want to copy a column into a row." << endl; 6 cout << "If we do m.col(1) = m.row(0), then m becomes:" << endl; 7 m.col(1) = m.row(0); 8 cout << m << endl << "which is wrong!" << endl; 9 cout << "Now let us instead do m.col(1) = m.row(0).eval(). Then m becomes" << endl; 10 m = M; 11 m.col(1) = m.row(0).eval(); 12 cout << m << endl << "which is right." << endl; 13