More on exposed points and extremal points of convex sets in $\mathbb{R}^n$ and Hilbert space

Barov, Stoyu T.

Commentationes Mathematicae Universitatis Carolinae, Tome 64 (2023) no. 1, pp. 63-72.

Résumé

Let ${\mathbb{V}}$ be a separable real Hilbert space, $k \in {\mathbb{N}}$ with $k \dim {\mathbb{V}}$, and let $B$ be convex and closed in ${\mathbb{V}}$. Let ${\mathcal{P}}$ be a collection of linear $k$-subspaces of ${\mathbb{V}}$. A point $w \in B$ is called exposed by ${\mathcal{P}}$ if there is a $P \in {\mathcal{P}}$ so that $(w + P) \cap B =\{w\}$. We show that, under some natural conditions, $B$ can be reconstituted as the convex hull of the closure of all its exposed by ${\mathcal{P}}$ points whenever ${\mathcal{P}}$ is dense and $G_{\delta}$. In addition, we discuss the question when the set of exposed by some ${\mathcal{P}}$ points forms a $G_{\delta}$-set.

Détail

DOI : 10.14712/1213-7243.2023.018

Classification : 52A07, 52A20
Keywords: convex set; extremal point; exposed point; Hilbert space; Grassmann manifold