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Unboundedness of the Lipschitz Constants of Best Polynomial Approximation

Unboundedness of the Lipschitz constants of best polynomial approximation
Authors: Gehlen, Wolfgang;

Unboundedness of the Lipschitz Constants of Best Polynomial Approximation

Abstract

This paper is a proof of a single noteworthy theorem that confirms a conjecture of \textit{M. S. Henry} and \textit{J. A. Roulier} [J. Approximation Theory 22, 85-94 (1978; Zbl 0428.41003)]. For \(f\in C[-1,1]\), let \(q_n(f)\) be the best uniform approximation to \(f\) from \(P_n\) -- the algebraic polynomials of degree \(n\) or less. It is known that there is a finite number \(L_nf\) such that for all \(g\in C[-1,1]\); \[ \|q_n(f)-q_n(g)\|\leq (L_nf) \|f-g\|. \] It is also easy to show that if \(f\in P_n\) then for all \(g\in C[-1,1]\); \[ \|q_n(f)-q_n(g)\|\leq 2 \|f-g\|. \] This work shows that if there is a finite number \(B\) such that for all \(g\in C[-1,1]\); \[ \|q_n(f)-q_n(g)\|\leq B \|f-g\|, \] then \(f\) is a polynomial.

Related Organizations
Keywords

Best approximation, Chebyshev systems, Mathematics(all), Numerical Analysis, uniform approximation, Applied Mathematics, Analysis

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selected citations
These citations are derived from selected sources.
This is an alternative to the "Influence" indicator, which also reflects the overall/total impact of an article in the research community at large, based on the underlying citation network (diachronically).
BIP!Citations provided by BIP!
popularity
This indicator reflects the "current" impact/attention (the "hype") of an article in the research community at large, based on the underlying citation network.
BIP!Popularity provided by BIP!
influence
This indicator reflects the overall/total impact of an article in the research community at large, based on the underlying citation network (diachronically).
BIP!Influence provided by BIP!
impulse
This indicator reflects the initial momentum of an article directly after its publication, based on the underlying citation network.
BIP!Impulse provided by BIP!
2
Average
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