{"title":"更多关于$\\mathbb{R}^n$和Hilbert空间中凸集的露点和极值点","authors":"Stoyu T. Barov","doi":"10.14712/1213-7243.2023.018","DOIUrl":null,"url":null,"abstract":"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.","PeriodicalId":44396,"journal":{"name":"Commentationes Mathematicae Universitatis Carolinae","volume":"84 12","pages":"0"},"PeriodicalIF":0.2000,"publicationDate":"2023-11-13","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":"0","resultStr":"{\"title\":\"More on exposed points and extremal points of convex sets in $\\\\mathbb{R}^n$ and Hilbert space\",\"authors\":\"Stoyu T. Barov\",\"doi\":\"10.14712/1213-7243.2023.018\",\"DOIUrl\":null,\"url\":null,\"abstract\":\"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.\",\"PeriodicalId\":44396,\"journal\":{\"name\":\"Commentationes Mathematicae Universitatis Carolinae\",\"volume\":\"84 12\",\"pages\":\"0\"},\"PeriodicalIF\":0.2000,\"publicationDate\":\"2023-11-13\",\"publicationTypes\":\"Journal Article\",\"fieldsOfStudy\":null,\"isOpenAccess\":false,\"openAccessPdf\":\"\",\"citationCount\":\"0\",\"resultStr\":null,\"platform\":\"Semanticscholar\",\"paperid\":null,\"PeriodicalName\":\"Commentationes Mathematicae Universitatis Carolinae\",\"FirstCategoryId\":\"1085\",\"ListUrlMain\":\"https://doi.org/10.14712/1213-7243.2023.018\",\"RegionNum\":0,\"RegionCategory\":null,\"ArticlePicture\":[],\"TitleCN\":null,\"AbstractTextCN\":null,\"PMCID\":null,\"EPubDate\":\"\",\"PubModel\":\"\",\"JCR\":\"Q4\",\"JCRName\":\"MATHEMATICS\",\"Score\":null,\"Total\":0}","platform":"Semanticscholar","paperid":null,"PeriodicalName":"Commentationes Mathematicae Universitatis Carolinae","FirstCategoryId":"1085","ListUrlMain":"https://doi.org/10.14712/1213-7243.2023.018","RegionNum":0,"RegionCategory":null,"ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":null,"EPubDate":"","PubModel":"","JCR":"Q4","JCRName":"MATHEMATICS","Score":null,"Total":0}
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.