eigen-3.3.7.0: eigen3/doc/snippets/LeastSquaresQR.cpp

MatrixXf A = MatrixXf::Random(3, 2);
VectorXf b = VectorXf::Random(3);
cout << "The solution using the QR decomposition is:\n"
     << A.colPivHouseholderQr().solve(b) << endl;