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