1 SelfAdjointEigenSolver<MatrixXf> es(4); 2 MatrixXf X = MatrixXf::Random(4,4); 3 MatrixXf A = X + X.transpose(); 4 es.compute(A); 5 cout << "The eigenvalues of A are: " << es.eigenvalues().transpose() << endl; 6 es.compute(A + MatrixXf::Identity(4,4)); // re-use es to compute eigenvalues of A+I 7 cout << "The eigenvalues of A+I are: " << es.eigenvalues().transpose() << endl; 8