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JOURNALS // Trudy Matematicheskogo Instituta imeni V.A. Steklova // Archive

Trudy Mat. Inst. Steklova, 2018 Volume 303, Pages 17–25 (Mi tm3939)

This article is cited in 3 papers

Selections of the best and near-best approximation operators and solarity

A. R. Alimovab

a Faculty of Mechanics and Mathematics, Moscow State University, Moscow, 119991 Russia
b Steklov Mathematical Institute of Russian Academy of Sciences, ul. Gubkina 8, Moscow, 119991 Russia

Abstract: In a finite-dimensional Banach space, a closed set with lower semicontinuous metric projection is shown to have a continuous selection of the near-best approximation operator. Such a set is known to be a sun. In the converse question of the stability of best approximation by suns, it is proved that a strict sun in a finite-dimensional Banach space of dimension at most $3$ is a $P$-sun, has a contractible set of nearest points, and admits a continuous $\varepsilon $-selection from the operator of near-best approximation for any $\varepsilon >0$. A number of approximative and geometric properties of sets with lower semicontinuous metric projection are obtained.

Keywords: lower semicontinuity of the metric projection, selection of the metric projection, sun, strict sun, near-best approximation.

UDC: 517.982.256+517.982.252

Received: October 1, 2017

DOI: 10.1134/S0371968518040027


 English version:
Proceedings of the Steklov Institute of Mathematics, 2018, 303, 10–17

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