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 ε-selection from the operator of near-best approximation for any ε>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.
The work was supported by the Russian Foundation for Basic Research (project nos. 18-01-00333 and 19-01-00332-a) and by a grant of the President of the Russian Federation (project no. NSh-6222.2018.1).
Citation:
A. R. Alimov, “Selections of the best and near-best approximation operators and solarity”, Harmonic analysis, approximation theory, and number theory, Collected papers. Dedicated to Academician Sergei Vladimirovich Konyagin on the occasion of his 60th birthday, Trudy Mat. Inst. Steklova, 303, MAIK Nauka/Interperiodica, Moscow, 2018, 17–25; Proc. Steklov Inst. Math., 303 (2018), 10–17
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\paper Selections of the best and near-best approximation operators and solarity
\inbook Harmonic analysis, approximation theory, and number theory
\bookinfo Collected papers. Dedicated to Academician Sergei Vladimirovich Konyagin on the occasion of his 60th birthday
\serial Trudy Mat. Inst. Steklova
\yr 2018
\vol 303
\pages 17--25
\publ MAIK Nauka/Interperiodica
\publaddr Moscow
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\jour Proc. Steklov Inst. Math.
\yr 2018
\vol 303
\pages 10--17
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Linking options:
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https://doi.org/10.1134/S0371968518040027
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This publication is cited in the following 3 articles:
A. R. Alimov, “Monotone path-connectedness of strict suns”, Lobachevskii J. Math., 43:3 (2022), 519
A. R. Alimov, “Characterization of Sets with Continuous Metric Projection in the Space ℓ∞n”, Math. Notes, 108:3 (2020), 309–317
A. R. Alimov, “Solarity of sets in max-approximation problems”, J. Fixed Point Theory Appl., 21:3 (2019), UNSP 76