const int size = 6; MatrixXd mat1(size, size); mat1.topLeftCorner(size / 2, size / 2) = MatrixXd::Zero(size / 2, size / 2); mat1.topRightCorner(size / 2, size / 2) = MatrixXd::Identity(size / 2, size / 2); mat1.bottomLeftCorner(size / 2, size / 2) = MatrixXd::Identity(size / 2, size / 2); mat1.bottomRightCorner(size / 2, size / 2) = MatrixXd::Zero(size / 2, size / 2); std::cout << mat1 << std::endl << std::endl; MatrixXd mat2(size, size); mat2.topLeftCorner(size / 2, size / 2).setZero(); mat2.topRightCorner(size / 2, size / 2).setIdentity(); mat2.bottomLeftCorner(size / 2, size / 2).setIdentity(); mat2.bottomRightCorner(size / 2, size / 2).setZero(); std::cout << mat2 << std::endl << std::endl; MatrixXd mat3(size, size); mat3 << MatrixXd::Zero(size / 2, size / 2), MatrixXd::Identity(size / 2, size / 2), MatrixXd::Identity(size / 2, size / 2), MatrixXd::Zero(size / 2, size / 2); std::cout << mat3 << std::endl;