更多关于$\mathbb{R}^n$和Hilbert空间中凸集的露点和极值点

Stoyu T.  Barov
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引用次数: 0

摘要

设${\mathbb{V}}$为可分离实数希尔伯特空间,$k \in {\mathbb{N}}$与$k < \dim {\mathbb{V}}$,并设$B$为${\mathbb{V}}$中的凸闭空间。设${\mathcal{P}}$是${\mathbb{V}}$的线性$k$ -子空间的集合。如果有$P \in {\mathcal{P}}$点,则称为${\mathcal{P}}$暴露点$w \in B$,以便$(w + P) \cap B =\{w\}$。我们证明,在某些自然条件下,当${\mathcal{P}}$是致密的和$G_{\delta}$时,$B$可以被重构为其所有暴露于${\mathcal{P}}$点的闭合的凸包。此外,我们还讨论了一些${\mathcal{P}}$点暴露的集合何时构成$G_{\delta}$ -集合的问题。
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More on exposed points and extremal points of convex sets in $\mathbb{R}^n$ and Hilbert space
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.
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