ABSTRACT
This chapter describes three methods for the calculation of matrix eigenvalues and eigencolumns. The method jolly is of recent origin and so its characteristics have not been fully explored. The method of matrix eigenvalue calculation described has been developed from one which was first described by Jolicard and Grosjean in terms of a formalism based on perturbation theory and an adiabatic switching process. Some of the traditional matrix eigenvalue techniques, such as the Jacobi one, are specifically designed for use with real symmetric matrices, which give only real eigenvalues. The folding algorithm used in folder has its origins in the ideas of perturbation theory and the relevant formulae are often presented in a form in which they resemble traditional perturbation formulae. Feenberg and Feshbach proposed a version of perturbation theory which includes special rules for calculating higher-order terms in the energy perturbation series.
