|
This article is cited in 1 scientific paper (total in 1 paper)
Polynomial and rational approximation of functions of several variables with convex
derivatives in the $L_p$-metric $(0<p\leqslant\infty)$
A. Khatamov
Abstract:
Let $\operatorname{Conv}_n^{(l)}(\mathscr G)$ be the set of all functions $f$ such that for every $n$-dimensional unit vector $\mathbf e$ the $l$th derivative in the direction of $\mathbf e$, $D^{(l)}(\mathbf e)f$, is continuous on a convex bounded domain $\mathscr G\subset\mathbf R^n$ $(n\geqslant 2)$ and convex (upwards or downwards) on the nonempty intersection of every line $L\subset\mathbf R^n$ with the domain $\mathscr G$, and let $M^{(l)}(f,\mathscr G)\colon=\sup\{\|D^{(l)}(\mathbf e)f\|_{C(\mathscr G)}\colon\mathbf e\in \mathbf R^n$, $\|\mathbf e\|=1\}<\infty$.
Sharp, in the sense of order of smallness, estimates of best simultaneous polynomial approximations of the functions $f\in\operatorname{Conv}_n^{(l)}(\mathscr G)$ for which $D^{(l)}(\mathbf e)f\in\operatorname{Lip}_K1$ for every $\mathbf e$, and their derivatives in the metrics of $L_p(\mathscr G)$ $(0<p\leqslant\infty)$ are obtained. It is proved that the corresponding parts of these estimates are preserved for best rational approximations, on any $n$-dimensional parallelepiped $Q$, of functions $f\in\operatorname{Conv}_n^{(l)}(Q)$ in the metrics of $L_p(Q)$ $(0<p<\infty)$ and it is shown that they are sharp in the sense of order of smallness for $0<p\leqslant 1$.
Received: 15.10.1992
Citation:
A. Khatamov, “Polynomial and rational approximation of functions of several variables with convex
derivatives in the $L_p$-metric $(0<p\leqslant\infty)$”, Russian Acad. Sci. Izv. Math., 44:1 (1995), 165–179
Linking options:
https://www.mathnet.ru/eng/im820https://doi.org/10.1070/IM1995v044n01ABEH001587 https://www.mathnet.ru/eng/im/v58/i1/p167
|
Statistics & downloads: |
Abstract page: | 286 | Russian version PDF: | 124 | English version PDF: | 15 | References: | 47 | First page: | 2 |
|