Localized locally convex topologies

Abstract

Motivated by ill-posed PDEs such as $\mathrm{div}(v)=F$ we study locally convex topologies ${\mathcal{T}}_{\mathcal{C}}$ on real vector spaces $X$ that are a ``localized'' version of a locally convex topology $\mathcal{T}$ to members of a family $\mathcal{C}$ of convex subsets of $X$. The distributions $F$ arising as $\mathrm{div}(v)$ are expected to be the members of the dual of well-chosen $X$ with respect to an appropriate localized topology ${\mathcal{T}}_{\mathcal{C}}$. In this work, the emphasis is on studying the functional analytic properties of ${\mathcal{T}}_{\mathcal{C}}$, according to those of $\mathcal{T}$ and $\mathcal{C}$. For instance, we show that in all foreseen applications, ${\mathcal{T}}_{\mathcal{C}}$ is sequential but none of Fréchet-Urysohn, barrelled, and bornological. These awkward phenomena are illustrated explicitly on a specific example corresponding to the distributional divergence of continuous vector fields in ${\mathbb{R}}^m$. We also show that, essentially, ${\mathcal{T}}_{\mathcal{C}}$ is semireflexive if and only if members of $\mathcal{C}$ are $\mathcal{T}$-compact. This leads to an abstract existence theorem, thereby establishing a general scheme for characterizing those $F$ such that $\mathrm{div}(v)=F$ for various classes of regularity of $v$, various classes of domains, and various boundary conditions.