| #include <iostream> | 
 | #include <Eigen/Dense> | 
 |  | 
 | int main() { | 
 |   Eigen::Matrix2f A; | 
 |   A << 1, 2, 2, 3; | 
 |   std::cout << "Here is the matrix A:\n" << A << std::endl; | 
 |   Eigen::SelfAdjointEigenSolver<Eigen::Matrix2f> eigensolver(A); | 
 |   if (eigensolver.info() != Eigen::Success) abort(); | 
 |   std::cout << "The eigenvalues of A are:\n" << eigensolver.eigenvalues() << std::endl; | 
 |   std::cout << "Here's a matrix whose columns are eigenvectors of A \n" | 
 |             << "corresponding to these eigenvalues:\n" | 
 |             << eigensolver.eigenvectors() << std::endl; | 
 | } |