English

First and second kind paraorthogonal polynomials and their zeros

Classical Analysis and ODEs 2007-05-23 v1

Abstract

Given a probability measure μ\mu with infinite support on the unit circle D={z:z=1}\partial\mathbb{D}=\{z:|z|=1\}, we consider a sequence of paraorthogonal polynomials \hn(z,λ)\h_n(z,\lambda) vanishing at z=λz=\lambda where λ\T\lambda \in \T is fixed. We prove that for any fixed z0∉\supp(dμ)z_0 \not \in \supp(d\mu) distinct from λ\lambda, we can find an explicit ρ>0\rho>0 independent of nn such that either \hn\h_n or \hn+1\h_{n+1} (or both) has no zero inside the disk B(z0,ρ)B(z_0, \rho), with the possible exception of λ\lambda. Then we introduce paraorthogonal polynomials of the second kind, denoted \sn(z,λ)\s_n(z,\lambda). We prove three results concerning \sn\s_n and \hn\h_n. First, we prove that zeros of \sn\s_n and \hn\h_n interlace. Second, for z0z_0 an isolated point in \supp(dμ)\supp(d\mu), we find an explicit radius \rt\rt such that either \sn\s_n or \sn+1\s_{n+1} (or both) have no zeros inside B(z0,\rt)B(z_0,\rt). Finally we prove that for such z0z_0 we can find an explicit radius such that either \hn\h_n or \hn+1\h_{n+1} (or both) has at most one zero inside the ball B(z0,\rt)B(z_0,\rt).

Keywords

Cite

@article{arxiv.math/0703242,
  title  = {First and second kind paraorthogonal polynomials and their zeros},
  author = {Manwah Lilian Wong},
  journal= {arXiv preprint arXiv:math/0703242},
  year   = {2007}
}

Comments

To appear in the Journal of Approximation Theory

R2 v1 2026-07-22T17:52:22.636Z