Every non-reflexive subspace of K(H), the space of compact operators on a Hilbert space H, contains an asymptotically isometric copy of c 0 . This, along with a result of Besbes, shows that a subspace of K(H) has the fixed point property if and only if it is reflexive.
Computability of compact operators on computable Banach spaces with bases
โ Scribed by Vasco Brattka; Ruth Dillhage
- Publisher
- John Wiley and Sons
- Year
- 2007
- Tongue
- English
- Weight
- 210 KB
- Volume
- 53
- Category
- Article
- ISSN
- 0044-3050
No coin nor oath required. For personal study only.
โฆ Synopsis
Abstract
We develop some parts of the theory of compact operators from the point of view of computable analysis. While computable compact operators on Hilbert spaces are easy to understand, it turns out that these operators on Banach spaces are harder to handle. Classically, the theory of compact operators on Banach spaces is developed with the help of the nonโconstructive tool of sequential compactness. We demonstrate that a substantial amount of this theory can be developed computably on Banach spaces with computable Schauder bases that are wellโbehaved. The conditions imposed on the bases are such that they generalize the Hilbert space case. In particular, we prove that the space of compact operators on Banach spaces with monotone, computably shrinking, and computable bases is a computable Banach space itself and operations such as composition with bounded linear operators from left are computable. Moreover, we provide a computable version of the Theorem of Schauder on adjoints in this framework and we discuss a nonโuniform result on composition with bounded linear operators from right. (ยฉ 2007 WILEYโVCH Verlag GmbH & Co. KGaA, Weinheim)
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