Abstract:
The Lorentz space Lp,τ(Tm) of periodic functions of m variables is considered. The Besov space B0,αp,τ,θ of functions with logarithmic smoothness is defined. The aim of the paper is to find the exact order of the best approximation of functions from the class B0,αp,τ,θ under different relations between the parameters p, τ, and θ. The paper consists of three sections. In the first section, known facts necessary for the proof of the main results are given and several auxiliary statements are proved. In the second section, order-exact estimates for the best approximation of functions from the class B0,αp,τ,θ are established in the space Lp,τ(Tm). In the third section, an inequality for different metrics of trigonometric polynomials is proved and a sufficient condition for the belonging of a function f∈Lp,τ1(Tm) to the space Lp,τ2(Tm) in terms of the best approximation is established in the case 1<τ2<τ1. In contrast to anisotropic Lorentz spaces, the condition is independent of the number m of the variables. Order-exact estimates for the best approximation of functions from the Besov class B0,αp,τ1,θ by trigonometric polynomials Lp,τ2(Tm) are obtained in the case 1<τ2<τ1.
Keywords:
Lorentz space, Besov class, best approximation, logarithmic smoothness.
Citation:
G. A. Akishev, “Estimates for best approximations of functions from the logarithmic smoothness class in the Lorentz space”, Trudy Inst. Mat. i Mekh. UrO RAN, 23, no. 3, 2017, 3–21
\Bibitem{Aki17}
\by G.~A.~Akishev
\paper Estimates for best approximations of functions from the logarithmic smoothness class in the Lorentz space
\serial Trudy Inst. Mat. i Mekh. UrO RAN
\yr 2017
\vol 23
\issue 3
\pages 3--21
\mathnet{http://mi.mathnet.ru/timm1433}
\crossref{https://doi.org/10.21538/0134-4889-2017-23-3-3-21}
\elib{https://elibrary.ru/item.asp?id=29937995}
Linking options:
https://www.mathnet.ru/eng/timm1433
https://www.mathnet.ru/eng/timm/v23/i3/p3
This publication is cited in the following 5 articles:
G. Akishev, “On embedding theorems for function spaces with mixed logarithmic smoothness”, Rend. Circ. Mat. Palermo, II. Ser, 74:1 (2025)
G. Akishev, “Estimates of M–term approximations of functions of several variables in the Lorentz space by a constructive method”, Eurasian Math. J., 15:2 (2024), 8–32
G. A. Akishev, “Neravenstva dlya nailuchshego priblizheniya «uglom» i modulya gladkosti funktsii v prostranstve Lorentsa”, Materialy Voronezhskoi mezhdunarodnoi vesennei matematicheskoi shkoly «Sovremennye metody kraevykh zadach. Pontryaginskie chteniya—XXXIV», Voronezh, 3-9 maya 2023 g. Chast 1, Itogi nauki i tekhn. Sovrem. mat. i ee pril. Temat. obz., 230, VINITI RAN, M., 2023, 8–24
G. Akishev, “Estimates of the best approximations of the functions of the Nikol'skii-Besov class in the generalized space of Lorentz”, Adv. Oper. Theory, 6:1 (2021), 15
Gabdolla Akishev, “Estimates of best approximations of functions with logarithmic smoothness in the Lorentz space with anisotropic norm”, Ural Math. J., 6:1 (2020), 16–29