English

Zeros of linear combinations of orthogonal polynomials

Classical Analysis and ODEs 2025-05-20 v1

Abstract

Given a sequence of orthogonal polynomials (pn)n(p_n)_n with respect to a positive measure in the real line, we study the real zeros of finite combinations of K+1K+1 consecutive orthogonal polynomials of the form qn(x)=j=0Kγjpnj(x),nK, q_n(x)=\sum_{j=0}^K\gamma_jp_{n-j}(x),\quad n\ge K, where γj\gamma_j, j=0,,Kj=0,\cdots ,K, are real numbers with γ0=1\gamma_0=1, γK0\gamma_K\not =0 (which do not depend on nn). We prove that for every positive measure μ\mu there always exists a sequence of orthogonal polynomials with respect to μ\mu such that all the zeros of the polynomial qnq_n above are real and simple for nn0n\ge n_0, where n0n_0 is a positive integer depending on KK and the γj\gamma_j's.

Keywords

Cite

@article{arxiv.2505.11956,
  title  = {Zeros of linear combinations of orthogonal polynomials},
  author = {Antonio J. Durán},
  journal= {arXiv preprint arXiv:2505.11956},
  year   = {2025}
}