PERTURBATION-METHODS FOR THE MATRIX EIGENPROBLEM

Some computational experiments are reported on the solution of the eigenproblem for a matrix H by using an iterative sequence of transformations of type H --> S-1 HS, where S is trivially invertible and is usually calculated from a first-order perturbation formula. Simple improved methods of constructing S are reported; these methods greatly improve the convergence properties of the eigenvalue calculations.