Michael J. Schlosser

Bilateral q-ultraspherical functions

(46 pages)

Abstract. We introduce the bilateral q-ultraspherical functions, a bilateral-series extension of the continuous q-ultraspherical polynomials. They are defined by specific bilateral basic hypergeometric 2Ψ2 series, are analytic in the variable x = cos θ, and depend on two parameters β and γ and on a base q. We derive a product formula for their bilateral generating function, a three-term recurrence relation, their transformation under the Askey–Wilson divided difference operator, three weight-based Rodrigues-type formulae, and explicit large-order asymptotic expansions. The main results are full orthogonality relations with respect to explicit orthogonality functionals involving analytic mass aggregates. We also obtain shifted orthogonality relations and a bilateral Chen–Liu type mixed orthogonality formula. In the limit γ→1 the construction and identities reduce to the classical results for the continuous q-ultraspherical polynomials.

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