English

On the weighted trigonometric Bojanov-Chebyshev extremal problem

Classical Analysis and ODEs 2023-09-13 v1

Abstract

We investigate the weighted Bojanov-Chebyshev extremal problem for trigonometric polynomials, that is, the minimax problem of minimizing Tw,C(T)\|T\|_{w,C({\mathbb T})}, where ww is a sufficiently nonvanishing, upper bounded, nonnegative weight function, the norm is the corresponding weighted maximum norm on the torus T{\mathbb T}, and TT is a trigonometric polynomial with prescribed multiplicities ν1,,νn\nu_1,\ldots,\nu_n of root factors sin(π(tzj))νj|\sin(\pi(t-z_j))|^{\nu_j}. If the νj\nu_j are natural numbers and their sum is even, then TT is indeed a trigonometric polynomial and the case when all the νj\nu_j are 1 covers the Chebyshev extremal problem. Our result will be more general, allowing, in particular, so-called generalized trigonometric polynomials. To reach our goal, we invoke Fenton's sum of translates method. However, altering from the earlier described cases without weight or on the interval, here we find different situations, and can state less about the solutions.

Cite

@article{arxiv.2309.06083,
  title  = {On the weighted trigonometric Bojanov-Chebyshev extremal problem},
  author = {Béla Nagy and Szilárd Gy. Révész},
  journal= {arXiv preprint arXiv:2309.06083},
  year   = {2023}
}
R2 v1 2026-06-28T12:19:01.379Z