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