Mutually inverse series relating Ferrers and associated Legendre functions and generating functions pertaining to them (2306.05158v1)

Abstract: This article deals with three types of mutually inverse series relating Ferrers and associated Legendre functions of arbitrary complex indexes and orders established on the base of integral representations by using a number of generating functions (some of them are novel) for polynomials expressed in terms of hypergeometric or generalized hypergeometric polynomials. High-order asymptotics of above-mentioned polynomials are indicated. In particular, a uniform asymptotics for Gegenbauer polynomials of degree n and index a-n is obtained for large n. In special cases, the inverse series turn into novel mutually inverse finite sums relating Gegenbauer or associated Legendre polynomials of different arguments as well as into novel connection formulas for Gegenbauer and associated Legendre polynomials.