Abstract of a paper by Miguel Martin, Javier Meri and Rafael Paya
This is an announcement for the paper "On the intrinsic and the spatial numerical range" by Miguel Martin, Javier Meri and Rafael Paya. Abstract: For a bounded function $f$ from the unit sphere of a closed subspace $X$ of a Banach space $Y$, we study when the closed convex hull of its spatial numerical range $W(f)$ is equal to its intrinsic numerical range $V(f)$. We show that for every infinite-dimensional Banach space $X$ there is a superspace $Y$ and a bounded linear operator $T:X\longrightarrow Y$ such that $\ecc W(T)\neq V(T)$. We also show that, up to renormig, for every non-reflexive Banach space $Y$, one can find a closed subspace $X$ and a bounded linear operator $T\in L(X,Y)$ such that $\ecc W(T)\neq V(T)$. Finally, we introduce a sufficient condition for the closed convex hull of the spatial numerical range to be equal to the intrinsic numerical range, which we call the Bishop-Phelps-Bollobas property, and which is weaker than the uniform smoothness and the finite-dimensionality. We characterize strong subdifferentiability and uniform smoothness in terms of this property. Archive classification: Functional Analysis Mathematics Subject Classification: 46B20; 47A12 Remarks: 12 pages The source file(s), MartinMeriPaya.tex: 40725 bytes, is(are) stored in gzipped form as 0503076.gz with size 13kb. The corresponding postcript file has gzipped size 70kb. Submitted from: mmartins@ugr.es The paper may be downloaded from the archive by web browser from URL http://front.math.ucdavis.edu/math.FA/0503076 or http://arXiv.org/abs/math.FA/0503076 or by email in unzipped form by transmitting an empty message with subject line uget 0503076 or in gzipped form by using subject line get 0503076 to: math@arXiv.org.
participants (1)
-
Dale Alspach