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Optimal recovery of a function analytic in a half-plane from approximately given values on a part of the straight-line boundary
R. R. Akopyanab a Ural Federal University named after the First President of Russia B. N. Yeltsin, Ekaterinburg
b Institute of Mathematics and Mechanics, Ural Branch of the Russian Academy of Sciences, Ekaterinburg
Abstract:
Let Hp(Π+,ϕ) be the class of functions analytic in the upper half-plane Π+ and belonging to the universal Hardy class N∗ with boundary values from Lpϕ(R) with a weight ϕ, and let Qp(Π+,I,ϕ) be the class of function f∈Hp(Π+,ϕ) such that ‖f‖Lpϕ(R∖I)⩽1, where I is a finite open interval or a half-line from R and 1⩽p⩽∞. On the class Qp(Π+,I,ϕ), we consider the problem of optimal recovery of the value of a function at a point z0∈Π+ from its approximately given limit boundary values on I in the norm Lpϕ(I) and the related problem of the best approximation of a functional by linear bounded functionals. Explicit solutions of these problems are written: an extremal function, optimal recovery method, and best approximation functional. On the class Qp(Π+,R+,ψ), ψ(z)=1/|z|, we solve the problem of optimal recovery of a function on a ray γ={z:argz=φ0} with respect to the norm Lpψ(γ) from its approximately given limit boundary values on R+ in the norm Lpψ(R+) and the related problem of the best approximation of an operator by linear bounded operators. For f∈Hp(Π+,ψ), we obtain the exact inequality ‖f‖Lpψ(γ)⩽‖f‖φ0/πLpψ(−∞,0)‖f‖1−φ0/πLpψ(0,+∞).
Keywords:
optimal recovery of an operator, best approximation of an unbounded operator by bounded operators, analytic function.
Received: 12.08.2018 Revised: 14.11.2018 Accepted: 19.11.2018
Citation:
R. R. Akopyan, “Optimal recovery of a function analytic in a half-plane from approximately given values on a part of the straight-line boundary”, Trudy Inst. Mat. i Mekh. UrO RAN, 24, no. 4, 2018, 19–33
Linking options:
https://www.mathnet.ru/eng/timm1572 https://www.mathnet.ru/eng/timm/v24/i4/p19
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Abstract page: | 233 | Full-text PDF : | 61 | References: | 52 | First page: | 1 |
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