Lax Pairs and Rational Solutions of Similarity Reductions for Kupershmidt and Sawada – Kotera Hierarchies

Self-similar reductions for equations of the Kupershmidt and Sawada – Kotera hierarchies are considered. Algorithms for constructing a Lax pair for equations of these hierarchies are presented. Lax pairs for ordinary differential equations of the fifth, seventh and eleventh orders corresponding to the Kupershmidt and the Sawada – Kotera hierarchies are given. The Lax pairs allow us to solve these equations by means of the inverse monodromy transform method. The application of the Painlevé test to the seventh order of the similarity reduction for the Kupershmidt hierarchy is demonstrated. It is shown that special solutions of the similarity reductions for the Kupershnmidt and Sawada – Kotera hierarchies are determined via the transcendents of the $K_1$ and $K_2$ hierarchies. Rational solutions of the similarity reductions of the modified Kupershmidt and Sawada – Kotera hierarchies are given. Special polynomials associated with the self-similar reductions of the Kupershmidt and Sawada – Kotera hierarchies are presented. Rational solutions of some hierarchies are calculated by means of the Miura transformations and taking into account special polynomials.