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Zapiski Nauchnykh Seminarov POMI, 2006, Volume 337, Pages 233–237
(Mi znsl190)
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This article is cited in 1 scientific paper (total in 1 paper)
Approximation by entire functions on subsets of a ray
O. V. Sil'vanovich, N. A. Shirokov Saint-Petersburg State University
Abstract:
Let $E\subset\mathbb R^+$ be a set consisting of finitely many intervals and a ray $[a,\infty)$, and let $H_\omega^r(E)$ be the set of functions defined on $E$ for which
$$
|f^{(r)}(x)-f^{(r)}(y)|\le c_f\omega(|x-y|),
$$
where the continuity module $\omega(x)$ satisfies the condition
$$
\int_0^y\frac{\omega(x)}{x}dx+y\int_y^\infty\frac{\omega(x)}{x^2}dx\le C_0\omega(y), \quad y>0.
$$
Let $C_\sigma^{(r,\omega)}$, $\sigma>0$, denote the class of entire functions $F$ of order 1/2 and of type $\sigma$ such that
$$
\sup_{z\in\mathbb C\setminus\mathbb R^+}\frac{|F(z)|e^{-\sigma|\operatorname{Im}\sqrt{z}|}}{1+|z|^r\omega(|z|)+\sigma^{-2r}\omega(\sigma^{-2})}<\infty.
$$
In the paper, given a function $f\in H_\omega^r(E)$, we construct approximating functions $F$ in the class $C_\sigma^{(r,\omega)}$. Approximation by such functions on the set $E$ is analogous to approximation by polynomials on compacts. The analogy involves constructing a scale for measuring approximations and providing a constructive description of the class $H_\omega^r(E)$ in terms of the approximation rate, similar to that of polynomial approximation. Bibliography: 4 titles.
Received: 28.08.2006
Citation:
O. V. Sil'vanovich, N. A. Shirokov, “Approximation by entire functions on subsets of a ray”, Analytical theory of numbers and theory of functions. Part 21, Zap. Nauchn. Sem. POMI, 337, POMI, St. Petersburg, 2006, 233–237; J. Math. Sci. (N. Y.), 143:3 (2007), 3149–3152
Linking options:
https://www.mathnet.ru/eng/znsl190 https://www.mathnet.ru/eng/znsl/v337/p233
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Abstract page: | 293 | Full-text PDF : | 70 | References: | 53 |
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