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arXiv · 2302.06720

Summability and duality

Soumitra Ghara·Javad Mashreghi·Thomas Ransford
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Abstract

We formalize the observation that the same summability methods converge in a Banach space $X$ and its dual $X^*$. At the same time we determine conditions under which these methods converge in the weak and weak*-topologies on $X$ and $X^*$ respectively. We also derive a general limitation theorem, which yields a necessary condition for the convergence of a summability method in $X$. These results are then illustrated by applications to a wide variety of function spaces, including spaces of continuous functions, Lebesgue spaces, the disk algebra, Hardy and Bergman spaces, the BMOA space, the Bloch space, and de Branges-Rovnyak spaces. Our approach shows that all these applications flow from just two abstract theorems.

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Soumitra Ghara, Javad Mashreghi, Thomas Ransford. 2023-02-13. Summability and duality. https://arxiv.org/abs/2302.06720

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