This paper is concerned with the convergence rates of two processes \(\left\{A_{x}\right\}\) and \(\left\{B_{x}\right\}\), under the assumption that \(\left\|A_{x}\right\|=O(1)\) and there is a closed operator \(A\) such that \(B_{x} A \subset A B_{x}=I-A_{x},\left\|A A_{x}\right\|=O(e(\alpha))\), a
Non-Optimal Rates of Ergodic Limits and Approximate Solutions
โ Scribed by Sen-Yen Shaw
- Publisher
- Elsevier Science
- Year
- 1998
- Tongue
- English
- Weight
- 294 KB
- Volume
- 94
- Category
- Article
- ISSN
- 0021-9045
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โฆ Synopsis
This paper is concerned with non-optimal rates of convergence for two processes [A : ] and [B : ], which satisfy &A : &=O(1), B : A/AB : =I&A : , &AA : &=O(e(:)), where A is a closed operator and e(:) ร 0. Under suitable conditions, we describe, in terms of K-functionals, those x (resp. y) for which the non-optimal convergence rate of [A : x] (resp. [B : y]) is of the order O( f (:)), where f is a function satisfying e(:) f (:) ร 0. In case that f (:)รe(:) ร , the sharpness of the non-optimal rate of [A : x] is equivalent to that A has non-closed range. The result provides a unified approach to dealing with non-optimal rates for many particular mean ergodic theorems and for various methods of solving the equation Ax= y. We discuss in particular applications to :-times integrated semigroups, n-times integrated cosine functions, and tensor product semigroups.
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