English

Polynomials with Zeros on the Unit Circle: Regularity of Leja Sequences

Classical Analysis and ODEs 2021-09-16 v4 Complex Variables

Abstract

Let z1,,zmz_1, \dots, z_m be mm distinct complex numbers, normalized to zk=1|z_k| = 1, and consider the polynomial pm(z)=k=1m(zzk). p_{m}(z) = \prod_{k=1}^{m}{(z-z_k)}. We define a sequence of polynomials in a greedy fashion, pN+1(z)=pN(z)(zz)\mboxwhere z=argmaxz=1pN(z), p_{N+1}(z) = p_{N}(z) \left(z - z^*\right)\qquad \mbox{where}~z^* = \arg\max_{|z|=1} |p_{N}(z)|, and prove that, independently of the initial polynomial pmp_m, the roots of pNp_{N} equidistribute in angle at rate at most (logN)2/N(\log{N})^2/N. This even persists when sometimes adding `adversarial' points by hand. We rephrase the main result in terms of a dynamical system involving the inverse fractional Laplacian (Δ)1/2(-\Delta)^{-1/2} and conjecture that, when phrased in this language, the underlying regularity phenomenon might appear in a very general setting.

Keywords

Cite

@article{arxiv.2006.10708,
  title  = {Polynomials with Zeros on the Unit Circle: Regularity of Leja Sequences},
  author = {Stefan Steinerberger},
  journal= {arXiv preprint arXiv:2006.10708},
  year   = {2021}
}
R2 v1 2026-06-23T16:26:37.193Z