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This article is cited in 2 scientific papers (total in 2 papers)
Approximation, by rational functions, of convex functions with given modulus of continuity
A. P. Bulanov
Abstract:
We denote by $R_n[f]$ the least deviation of the continuous function $f(x)$,
$x\in[a,b]$, from the rational functions of order at most $n$.
We establish the following theorems.
Theorem 1. Let $f(x)$ be convex on $[a,b]$ $(-\infty<a<b<+\infty)$
with modulus of continuity $\omega(\delta,f)$. Then
$$
R_n[f]\leqslant c\frac{\ln^6n}{n^2}\max_{(b-a)e^{-n}\leqslant\theta\leqslant
b-a}\biggl\{\omega(\theta)\ln\frac{b-a}{\theta}\biggr\},\qquad n=2,3,\dots,
$$
where $c$ is an absolute constant.
\medskip
Theorem 2. There exist a convex function $f^*(x)$ and a sequence
$n_k\nearrow\infty$ such that 1) $\omega(\delta,f^*)\leqslant(\ln(e/\delta))^{-\gamma}$, $0<\delta\leqslant1$, and 2) $R_{n_k}[f^*]\geqslant c_1\gamma/n^{1-\gamma}_k$, where $c_1$ is an absolute constant.
Bibliography: 8 titles.
Received: 13.05.1977
Citation:
A. P. Bulanov, “Approximation, by rational functions, of convex functions with given modulus of continuity”, Math. USSR-Sb., 34:1 (1978), 1–24
Linking options:
https://www.mathnet.ru/eng/sm2513https://doi.org/10.1070/SM1978v034n01ABEH001041 https://www.mathnet.ru/eng/sm/v147/i1/p3
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