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JOURNALS // Matematicheskie Zametki // Archive

Mat. Zametki, 2018 Volume 104, Issue 1, Pages 3–10 (Mi mzm11666)

This article is cited in 3 papers

Approximation by Sums of the Form $\sum_k\lambda_kh(\lambda_kz)$ in the Disk

P. A. Borodin

Lomonosov Moscow State University

Abstract: Given a function $h$ analytic in the unit disk $D$, we study the density in the space $A(D)$ of functions analytic inside $D$ of the set $S(h,E)$ of sums of the form $\sum_k\lambda_kh(\lambda_kz)$ with parameters $\lambda_k\in E$, where $E$ is a compact subset of $\overline D$. It is proved, in particular, that if the compact set $E$ “surrounds” the point $0$ and all Taylor coefficients of the function $h$ are nonzero, then $S(h,E)$ is dense in $A(D)$.

Keywords: approximation, analytic function, density, $h$-sum.

UDC: 517.538.5

Received: 06.05.2017
Revised: 16.10.2017

DOI: 10.4213/mzm11666


 English version:
Mathematical Notes, 2018, 104:1, 3–9

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© Steklov Math. Inst. of RAS, 2025