1 Matrix4i m = Matrix4i::Random(); 2 cout << "Here is the matrix m:" << endl << m << endl; 3 cout << "Here is m.block(1, 1, 2, 2):" << endl << m.block(1, 1, 2, 2) << endl; 4 m.block(1, 1, 2, 2).setZero(); 5 cout << "Now the matrix m is:" << endl << m << endl; 6