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• Author or Editor: Z. Ditzian
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# On divided differences onC[a, b], L p [a, b] and other spaces

Periodica Mathematica Hungarica
Author: Z. Ditzian
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# Fractional Derivatives and Best Approximation

Acta Mathematica Hungarica
Author: Z. Ditzian
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# ОБ ОДНОИ жАДАЧЕ г. шАп ИРО

Analysis Mathematica
Author: Z. Ditzian

## Abstract

В РАБОтЕ ДОкАжАНО, ЧтО limk a*f(x)=f(x) пОЧтИ ВсУДУ, гДЕk a(t)=a−n k(a−1t), t∃Rn, Для Дль ДОВОльНО шИРОкОг О клАссА ФУНкцИИk(t). ДАНы УслОВИь, пРИ кОтО Рых пОлУЧЕННыИ РЕжУл ьтАт РАспРОстРАНьЕтсь НА ФУНкцИУ

\documentclass{aastex} \usepackage{amsbsy} \usepackage{amsfonts} \usepackage{amssymb} \usepackage{bm} \usepackage{mathrsfs} \usepackage{pifont} \usepackage{stmaryrd} \usepackage{textcomp} \usepackage{upgreek} \usepackage{portland,xspace} \usepackage{amsmath,amsxtra} \pagestyle{empty} \DeclareMathSizes{10}{9}{7}{6} \begin{document} $$k(x,y) = \gamma \frac{1}{{1 + |x|^\alpha }} \cdot \frac{1}{{1 + |y|^\beta }},$$ \end{document}
гДЕ α, β>1, А γ — НОРМИРУУЩ ИИ МНОжИтЕль тАкОИ, Чт О∫∫k(x, y) dx dy=1.

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# Rearrangement invariance and relations among measures of smoothness

Acta Mathematica Hungarica
Author: Z. Ditzian

## Abstract

Relations between ω r(f,t)B and ω r+1(f,t)B of the sharp Marchaud and sharp lower estimate-type are shown to be satisfied for some Banach spaces of functions that are not rearrangement invariant. Corresponding results relating the rate of best approximation with ω r(f,t)B for those spaces are also given.

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# Jackson inequality for Banach spaces on the sphere

Acta Mathematica Hungarica
Authors: F. Dai and Z. Ditzian

## Abstract

The best rate of approximation of functions on the sphere by spherical polynomials is majorized by recently introduced moduli of smoothness. The treatment applies to a wide class of Banach spaces of functions.

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# Best Approximation and K-Functionals

Acta Mathematica Hungarica
Authors: W. Chen and Z. Ditzian
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# Realization and Smoothness Related to the Laplacian

Acta Mathematica Hungarica
Authors: Z. Ditzian and K. Runovskii
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# МИНИМАльНОЕ ЧИслО сУ ЩЕстВЕННых НАпРАВлЕ НИИ МОДУль глАДкОстИ

Analysis Mathematica
Authors: Z. Ditzian and K. Ivanov
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# Convexity, moduli of smoothness and a Jackson-type inequality

Acta Mathematica Hungarica
Authors: Z. Ditzian and A. Prymak

## Abstract

For a Banach space B of functions which satisfies for some m>0 a significant improvement for lower estimates of the moduli of smoothness ω r(f,t)B is achieved. As a result of these estimates, sharp Jackson inequalities which are superior to the classical Jackson type inequality are derived. Our investigation covers Banach spaces of functions on ℝd or for which translations are isometries or on S d−1 for which rotations are isometries. Results for C 0 semigroups of contractions are derived. As applications of the technique used in this paper, many new theorems are deduced. An L p space with 1<p<∞ satisfies () where s=max  (p,2), and many Orlicz spaces are shown to satisfy () with appropriate s.
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# Polynomial approximation with exponential weights

Acta Mathematica Hungarica
Authors: Z. Ditzian, D. S. Lubinsky, P. Nevai, and V. Totik
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