{"title":"Approximative Compactness and Acting Points","authors":"A.R. Alimov, N.A. Ilyasov","doi":"10.1134/S1061920825600527","DOIUrl":null,"url":null,"abstract":"<p> It is shown that, in many problems of geometric approximation theory related to min- and max-approximative compactness, it suffices to consider not the entire unit sphere, but rather its only part consisting of acting points (for a given set <span>\\(M\\)</span>) — these being the points of the unit sphere such that <span>\\(M\\)</span> can be touched by an “analog” of such a point on some homothetic copy of the unit ball. CLUR- and VDS-point for a set are introduced, and their relations to points of min- and max- approximative (norm, weak) compactness are studied. In terms of these points, balayage theorems for problems of min- and max- approximative (norm, weak) compactness of suns and max-suns are obtained. </p><p> <b> DOI</b> 10.1134/S1061920825600527 </p>","PeriodicalId":763,"journal":{"name":"Russian Journal of Mathematical Physics","volume":"32 2","pages":"219 - 227"},"PeriodicalIF":1.5000,"publicationDate":"2025-07-29","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":"0","resultStr":null,"platform":"Semanticscholar","paperid":null,"PeriodicalName":"Russian Journal of Mathematical Physics","FirstCategoryId":"101","ListUrlMain":"https://link.springer.com/article/10.1134/S1061920825600527","RegionNum":3,"RegionCategory":"物理与天体物理","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":null,"EPubDate":"","PubModel":"","JCR":"Q2","JCRName":"PHYSICS, MATHEMATICAL","Score":null,"Total":0}
引用次数: 0
Abstract
It is shown that, in many problems of geometric approximation theory related to min- and max-approximative compactness, it suffices to consider not the entire unit sphere, but rather its only part consisting of acting points (for a given set \(M\)) — these being the points of the unit sphere such that \(M\) can be touched by an “analog” of such a point on some homothetic copy of the unit ball. CLUR- and VDS-point for a set are introduced, and their relations to points of min- and max- approximative (norm, weak) compactness are studied. In terms of these points, balayage theorems for problems of min- and max- approximative (norm, weak) compactness of suns and max-suns are obtained.
期刊介绍:
Russian Journal of Mathematical Physics is a peer-reviewed periodical that deals with the full range of topics subsumed by that discipline, which lies at the foundation of much of contemporary science. Thus, in addition to mathematical physics per se, the journal coverage includes, but is not limited to, functional analysis, linear and nonlinear partial differential equations, algebras, quantization, quantum field theory, modern differential and algebraic geometry and topology, representations of Lie groups, calculus of variations, asymptotic methods, random process theory, dynamical systems, and control theory.