Zeev Ditzian

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For trigonometric polynomials on [− , ] ≡ T , the classical Jackson inequalityEn(f )p C r (f, 1/n)p was sharpened by M. Timan for 1<p<∞ to yield n−r { n ∑ k=1 ksr−1Ek(f )p }1/s C r (f, n−1)p where s =max(p, 2). In this paper a general result on the relations between systems or sequences of best approximation and appropriate measures of smoothness is given.(More)
About twenty years ago the measure of smoothness ω φ (f, t) was introduced and related to the rate of polynomial approximation. In this article we survey developments about this and related concepts since that time. MSC: 41A10, 41A17, 41A25, 41A27, 41A30, 41A36, 41A40, 41A50, 41A63, 26A15, 26B35, 26B05, 42C05, 26A51, 26A33, 46E35 keywords: Moduli of(More)
About twenty years ago the measure of smoothness ω φ (f, t) was introduced and related to the rate of polynomial approximation. In this article we survey developments about this and related concepts since that time. MSC: 41A10, 41A17, 41A25, 41A27, 41A30, 41A36, 41A40, 41A50, 41A63, 26A15, 26B35, 26B05, 42C05, 26A51, 26A33, 46E35 keywords: Moduli of(More)
Rate of approximation of combinations of averages on the spheres is shown to be equivalent to K-functionals yielding higher degree of smoothness. Results relating combinations of averages on rims of caps of spheres are also achieved. © 2004 Elsevier Inc. All rights reserved. MSC: 41A17; 41A63; 26B33; 46E35