English

Two families of orthogonal polynomials on the unit circle from basic hypergeometric functions

Classical Analysis and ODEs 2018-01-30 v4

Abstract

The sequence {2ϕ1(qk,qb+1;qbk+1;q,qb+1/2z)}k0\{\,_2\phi_1(q^{-k},q^{b+1};\,q^{-\overline{b}-k+1};\, q, q^{-\overline{b}+1/2} z)\}_{k \geq 0} of basic hypergeometric polynomials is known to be orthogonal on the unit circle with respect to the weight function (q1/2eiθ;q)/(qb+1/2eiθ;q)2|(q^{1/2}e^{i\theta};\,q)_{\infty}/(q^{b+1/2}e^{i\theta};\,q)_{\infty}|^2. This result, where one must take the parameters qq and bb to be 0<q<10 < q < 1 and (b)>1/2\Re(b) > -1/2, is due to P.I. Pastro \cite{Pastro-1985}. In the present manuscript we deal with the orthogonal polynomials Φ^n(b;.)\hat{\Phi}_{n}(b;.) and Φˇn(b;.)\check{\Phi}_{n}(b;.) on the unit circle with respect to the two parametric families of weight functions ω^(b;θ)=(eiθ;q)/(qbeiθ;q)2\hat{\omega}(b; \theta) = |(e^{i\theta};\,q)_{\infty}/(q^{b}e^{i\theta};\,q)_{\infty}|^2 and ωˇ(b;θ)=(qeiθ;q)/(qbeiθ;q)2\check{\omega}(b;\theta) = |(qe^{i\theta};\,q)_{\infty}/(q^{b}e^{i\theta};\,q)_{\infty}|^2, where 0<q<10 < q < 1 and (b)>0\Re(b) > 0. With the use of the basic hypergeometric polynomials 2ϕ1(qk,qb;qbk+1;q,qb+1z) _2\phi_1(q^{-k},q^{b};\,q^{-\overline{b}-k+1};\, q, q^{-\overline{b}+1} z), k0k \geq 0, which have zeros on the unit circle when (b)>0\Re(b) > 0, simple expressions for the (monic) polynomials Φ^n(b;.)\hat{\Phi}_{n}(b;.) and Φˇn(b;.)\check{\Phi}_{n}(b;.), their norms, the associated Verblunsky coefficients and also the respective Szeg\H{o} functions are found.

Keywords

Cite

@article{arxiv.1611.08064,
  title  = {Two families of orthogonal polynomials on the unit circle from basic hypergeometric functions},
  author = {A. Sri Ranga},
  journal= {arXiv preprint arXiv:1611.08064},
  year   = {2018}
}
R2 v1 2026-06-22T17:03:06.145Z