Geodesic
$\mathcal{K}$-Functionals and exact values of $n$-widths for some classes of functions in the Hardy space
Trudy Instituta matematiki i mehaniki, Trudy Instituta Matematiki i Mekhaniki UrO RAN, Tome 30 (2024) no. 4, pp. 301-308 Cet article a éte moissonné depuis la source Math-Net.Ru

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In this work, we obtain exact Jackson–Stechkin type inequalities in the Hardy space $H_{q,\rho}$ ($1\le q\le\infty$, $0\rho\le R$), in which the values of the best polynomial approximations are estimated from above in terms of the $\mathcal{K}$-functionals of the $r$th derivatives. For function classes defined by the mentioned characteristics, exact values of Bernstein and Kolmogorov $n$-widths in the space $H_{q,\rho}$ are calculated.
Keywords: Jackson–Stechkin type inequality, best polynomial approximation, $\mathcal{K}$-functional, $n$-widths. 
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M. Sh. Shabozov; R. A. Karimzoda. $\mathcal{K}$-Functionals and exact values of $n$-widths for some classes of functions in the Hardy space. Trudy Instituta matematiki i mehaniki, Trudy Instituta Matematiki i Mekhaniki UrO RAN, Tome 30 (2024) no. 4, pp. 301-308. http://geodesic.mathdoc.fr/item/TIMM_2024_30_4_a23/

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