On equivalence of moduli of smoothness of polynomials in Lp, 0 < p ≤ ∞

Yingkang Hu, Yongping Liu

Research output: Contribution to journalArticlepeer-review

7 Scopus citations

Abstract

It is well known that ωr (f, t)p ≤ t ωr-1 f′, t)p ≤ t2 ωr-2 f″, t)p ≤ ⋯ for functions f ∈ Wpr, 1 ≤ p ≤ ∞ For general functions f ∈ Lp, it does not hold for 0 < p < 1, and its inverse is not true for any p in general. It has been shown in the literature, however, that for certain classes of functions the inverse is true, and the terms in the inequalities are all equivalent. Recently, Zhou and Zhou proved the equivalence for polynomials with p = ∞ Using a technique by Ditzian, Hristov and Ivanov, we give a simpler proof to their result and extend it to the Lp space for 0 < p ≤ ∞ We then show its analogues for the Ditzian-Totik modulus of smoothness ωφ r (f, t)p and the weighted Ditzian-Totik modulus of smoothness ωφr (f, t)w,p for polynomials with φ (x) = √1 - x2.

Original languageEnglish
Pages (from-to)182-197
Number of pages16
JournalJournal of Approximation Theory
Volume136
Issue number2
DOIs
StatePublished - Oct 2005

Scopus Subject Areas

  • Analysis
  • Numerical Analysis
  • General Mathematics
  • Applied Mathematics

Keywords

  • Equivalence
  • Moduli of smoothness
  • Polynomials
  • Weighted moduli of smoothness

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