DOI

We investigate the possibility of approximating a function on a compact set K of the complex plane in such a way that the rate of approximation is almost optimal on K, and the rate inside the interior of K is faster than on the whole of K. We show that if K has an external angle smaller than π at some point zo∈δK, then geometric convergence inside K is possible only for functions that are analytic at zo. We also consider the possibility of approximation rates of the form exp(-cnβ), for approximation inside K, where β is related to the largest external angle of K. It is also shown that no matter how slowly the sequence {γn} tends to zero, there is a K and a Lip β, β<1, function f such that approximation inside K cannot have order {γn}.

Original languageEnglish
Pages (from-to)145-152
Number of pages8
JournalConstructive Approximation
Volume10
Issue number2
DOIs
StatePublished - Jun 1994
Externally publishedYes

    Scopus subject areas

  • Analysis
  • Mathematics(all)
  • Computational Mathematics

    Research areas

  • AMS classification: 30E10, 41A10, Key words and phrases, Polynomial approximation, Complex domain

ID: 86661982