{"title":"将 $\\ell_1$ 中的球缩回到其简单的球帽上","authors":"J. Intrakul, S. Iampiboonvatana","doi":"10.12775/tmna.2024.005","DOIUrl":null,"url":null,"abstract":"In this article, a notion and classification of spherical caps in the sequence space $\\ell_1$ are introduced, and the least Lipschitz constant of Lipschitz retractions from the unit ball onto a spherical cap is defined.\nIn addition, an approximation of this value for the specific spherical cap, the simple spherical cap, is calculated. This approximation reveals a rough relation between these values, denoted by $\\kappa(\\alpha)$, and the answer of the optimal retraction problem for the space $\\ell_1$, denoted by $k_0(\\ell_1)$.\nTo be precise, there exists $-1< \\mu< 0$ such that $k_0(\\ell_1)\\leq\\kappa(\\alpha)\\leq2+k_0(\\ell_1)$ whenever $-1< \\alpha< \\mu$; here $\\alpha$ is the level of spherical cap.","PeriodicalId":23130,"journal":{"name":"Topological Methods in Nonlinear Analysis","volume":null,"pages":null},"PeriodicalIF":0.7000,"publicationDate":"2024-03-19","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":"0","resultStr":"{\"title\":\"Retracting a ball in $\\\\ell_1$ onto its simple spherical cap\",\"authors\":\"J. Intrakul, S. Iampiboonvatana\",\"doi\":\"10.12775/tmna.2024.005\",\"DOIUrl\":null,\"url\":null,\"abstract\":\"In this article, a notion and classification of spherical caps in the sequence space $\\\\ell_1$ are introduced, and the least Lipschitz constant of Lipschitz retractions from the unit ball onto a spherical cap is defined.\\nIn addition, an approximation of this value for the specific spherical cap, the simple spherical cap, is calculated. This approximation reveals a rough relation between these values, denoted by $\\\\kappa(\\\\alpha)$, and the answer of the optimal retraction problem for the space $\\\\ell_1$, denoted by $k_0(\\\\ell_1)$.\\nTo be precise, there exists $-1< \\\\mu< 0$ such that $k_0(\\\\ell_1)\\\\leq\\\\kappa(\\\\alpha)\\\\leq2+k_0(\\\\ell_1)$ whenever $-1< \\\\alpha< \\\\mu$; here $\\\\alpha$ is the level of spherical cap.\",\"PeriodicalId\":23130,\"journal\":{\"name\":\"Topological Methods in Nonlinear Analysis\",\"volume\":null,\"pages\":null},\"PeriodicalIF\":0.7000,\"publicationDate\":\"2024-03-19\",\"publicationTypes\":\"Journal Article\",\"fieldsOfStudy\":null,\"isOpenAccess\":false,\"openAccessPdf\":\"\",\"citationCount\":\"0\",\"resultStr\":null,\"platform\":\"Semanticscholar\",\"paperid\":null,\"PeriodicalName\":\"Topological Methods in Nonlinear Analysis\",\"FirstCategoryId\":\"100\",\"ListUrlMain\":\"https://doi.org/10.12775/tmna.2024.005\",\"RegionNum\":4,\"RegionCategory\":\"数学\",\"ArticlePicture\":[],\"TitleCN\":null,\"AbstractTextCN\":null,\"PMCID\":null,\"EPubDate\":\"\",\"PubModel\":\"\",\"JCR\":\"Q2\",\"JCRName\":\"MATHEMATICS\",\"Score\":null,\"Total\":0}","platform":"Semanticscholar","paperid":null,"PeriodicalName":"Topological Methods in Nonlinear Analysis","FirstCategoryId":"100","ListUrlMain":"https://doi.org/10.12775/tmna.2024.005","RegionNum":4,"RegionCategory":"数学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":null,"EPubDate":"","PubModel":"","JCR":"Q2","JCRName":"MATHEMATICS","Score":null,"Total":0}
Retracting a ball in $\ell_1$ onto its simple spherical cap
In this article, a notion and classification of spherical caps in the sequence space $\ell_1$ are introduced, and the least Lipschitz constant of Lipschitz retractions from the unit ball onto a spherical cap is defined.
In addition, an approximation of this value for the specific spherical cap, the simple spherical cap, is calculated. This approximation reveals a rough relation between these values, denoted by $\kappa(\alpha)$, and the answer of the optimal retraction problem for the space $\ell_1$, denoted by $k_0(\ell_1)$.
To be precise, there exists $-1< \mu< 0$ such that $k_0(\ell_1)\leq\kappa(\alpha)\leq2+k_0(\ell_1)$ whenever $-1< \alpha< \mu$; here $\alpha$ is the level of spherical cap.
期刊介绍:
Topological Methods in Nonlinear Analysis (TMNA) publishes research and survey papers on a wide range of nonlinear analysis, giving preference to those that employ topological methods. Papers in topology that are of interest in the treatment of nonlinear problems may also be included.