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Ural Math. J., 2024 Volume 10, Issue 2, Pages 121–130 (Mi umj239)

On widths of some classes of analytic functions in a circle

Mirgand Sh. Shabozova, Muqim S. Saidusajnovb

a Tajik National University
b University of Central Asia

Abstract: We calculate exact values of some $n$-widths of the class $W_{q}^{(r)}(\Phi),$ $r\in\mathbb{Z}_{+},$ in the Banach spaces $\mathscr{L}_{q,\gamma}$ and $B_{q,\gamma},$ $1\leq q\leq\infty,$ with a weight $\gamma$. These classes consist of functions $f$ analytic in the unit circle, their $r$th order derivatives $f^{(r)}$ belong to the Hardy space $H_{q},$ $1\leq q\leq\infty,$ and the averaged moduli of smoothness of boundary values of $f^{(r)}$ are bounded by a given majorant $\Phi$ at the system of points $\{\pi/(2k)\}_{k\in\mathbb{N}}$; more precisely,
$$ \frac{k}{\pi-2}\int_{0}^{\pi/(2k)}\omega_{2}(f^{(r)},2t)_{H_{q,\rho}}dt\leq \Phi\left(\frac{\pi}{2k}\right) $$
for all $k\in\mathbb{N}$, $k>r.$

Keywords: Modulus of smoothness, The best approximation, $n$-widths, The best linear method of approximation

Language: English

DOI: 10.15826/umj.2024.2.011



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© Steklov Math. Inst. of RAS, 2025