EigenSolver<MatrixXf>es;MatrixXfA=MatrixXf::Random(4,4);es.compute(A,/* computeEigenvectors = */false);cout<<"The eigenvalues of A are: "<<es.eigenvalues().transpose()<<endl;es.compute(A+MatrixXf::Identity(4,4),false);// re-use es to compute eigenvalues of A+Icout<<"The eigenvalues of A+I are: "<<es.eigenvalues().transpose()<<endl;