Fej\'{e}r-type positive operator based on Takenaka--Malmquist system on unit circle

TL;DR

This paper investigates convergence criteria and asymptotic behavior of Fejér-type operators based on the Takenaka--Malmquist system on the unit circle, extending classical results to broader function spaces and holomorphic functions.

Contribution

It establishes convergence conditions for Fejér-type operators in Banach spaces and proves a Voronovskaya-type theorem for holomorphic functions, expanding the theoretical understanding of these operators.

Findings

Convergence criteria in L^p and continuous function spaces.

Voronovskaya-type asymptotic theorem for holomorphic functions.

Extension of classical Fejér operator results to Takenaka--Malmquist system.

Abstract

Let $\varphi=\{\varphi_k\}_{k=-\infty}^\infty$ denote the extended Takenaka--Malmquist system on unit circle $\mathbb T$ and let $\sigma_{n,\varphi}(f),$ $f\in L^1(\mathbb T)$, be the Fej\'er-type operator based on $\varphi$, introduced by V. N. Rusak. We give the convergence criteria for $\sigma_{n,\varphi}(f)$ in Banach space $X(\mathbb T):=L^p(\mathbb T)\vee C(\mathbb T)$, $p\ge 1$. Also we prove the Voronovskaya-type theorem for $\sigma_{n,\varphi}(f)$ on class of holomorphic functions representable by Cauchy-type integrals with bounded densities.