English

Exact values of Kolmogorov widths of classes of analytic functions

Classical Analysis and ODEs 2017-03-21 v1

Abstract

We prove that kernels of analytic functions of kind Hh,β(t)=k=11coshkhcos(ktβπ2)H_{h,\beta}(t)=\sum\limits_{k=1}^{\infty}\frac{1}{\cosh kh}\cos\Big(kt-\frac{\beta\pi}{2}\Big), h>0h>0, βR{\beta\in\mathbb{R}}, satisfies Kushpel's condition Cy,2nC_{y,2n} beginning with some number nhn_h which is explicitly expressed by parameter hh of smoothness of the kernel. As a consequence, for all nnhn\geqslant n_h we obtain lower bounds for Kolmogorov widths d2nd_{2n} of functional classes that are representable as convolutions of kernel Hh,βH_{h,\beta} with functions φ1\varphi\perp1, which belong to the unit ball in the space LL_{\infty}, in the space CC. The obtained estimates coincide with the best uniform approximations by trigonometric polynomials for these classes. As a result, we obtain exact values for widths of mentioned classes of convolutions. Also for all nnhn\geqslant n_h we obtain exact values for Kolmogorov widths d2n1d_{2n-1} of classes of convolutions of functions φ1\varphi\perp1, which belong to the unit ball in the space L1L_1, with kernel Hh,βH_{h,\beta} in the space L1L_1.

Keywords

Cite

@article{arxiv.1410.2966,
  title  = {Exact values of Kolmogorov widths of classes of analytic functions},
  author = {A. S. Serdyuk and V. V. Bodenchuk},
  journal= {arXiv preprint arXiv:1410.2966},
  year   = {2017}
}

Comments

25 pages, in Ukrainian