doc/snippets/Tutorial_commainit_01b.cpp

// SPDX-FileCopyrightText: The Eigen Authors
// SPDX-License-Identifier: MPL-2.0

Matrix3f m;
m.row(0) << 1, 2, 3;
m.block(1, 0, 2, 2) << 4, 5, 7, 8;
m.col(2).tail(2) << 6, 9;
std::cout << m;