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Jackson Theorems for Erdo&#x030B;s Weights inLp(0<p⩽∞)

✍ Scribed by S.B. Damelin; D.S. Lubinsky


Publisher
Elsevier Science
Year
1998
Tongue
English
Weight
572 KB
Volume
94
Category
Article
ISSN
0021-9045

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✦ Synopsis


An Erdo s weight is of the form W :=e &Q where Q is even and of faster than polynomial growth at . For example, we can take

where exp k denotes the kth iterated exponential. We prove Jackson theorems in weighted L p spaces with norm & fW& L p (R) for all 0<p . These are the first proper Jackson theorems for Erdo s weights even in L . An interesting feature is a Timan Nikolskii Brudnyi effect: The degree of approximation improves towards the endpoints of a certain interval. By contrast, there is no such feature for Freud weights.


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Converse and Smoothness Theorems for Erd
✍ S.B. Damelin 📂 Article 📅 1998 🏛 Elsevier Science 🌐 English ⚖ 529 KB

We prove converse and smoothness theorems of polynomial approximation in weighted L p spaces with norm & fW& L p (R) ( 0<p) for Erdo s weights on the real line. In particular we prove characterization theorems involving realization functionals and thereby establish some interesting properties of our