On peculiar properties of generating functions of some orthogonal polynomials

Abstract

We prove that for |x|,|t|<1, -1 <q \leq1 and n\geq0: \Sigma_{i\geq0}((t^{i})/((q)_{i}))h_{n+i}(x|q) = h_{n}(x|t,q) \Sigma_{i\geq0}((t^{i})/((q)_{i}))h_{i}(x|q), where h_{n}(x|q) and h_{n}(x|t,q) are respectively the so called q-Hermite and the big q-Hermite polynomials and (q)_{n} denotes the so called q-Pochhammer symbol. We prove similar equalities involving big q-Hermite and Al-Salam---Chihara (ASC) polynomials and ASC and the so called continuous dual q-Hahn (c2h) polynomials. Moreover we are able to relate in this way some other 'ordinary ' orthogonal polynomials such as e.g. Hermite, Chebyshev or Laguerre. These equalities give new interpretation of the polynomials involved and moreover can give rise to a simple method of generating more and more general (i.e. involving more and more parameters) families of orthogonal polynomials. We pose some conjectures concerning Askey--Wilson polynomials and their possible generalizations. We prove that these conjectures are true for the cases q = 1 (classical case) and q = 0 (free case) thus paving the way to generalization of AW polynomials at least in these two cases.