{"title":"The pointwise James type constant","authors":"M. A. Rincón-Villamizar","doi":"10.1007/s10476-023-0221-7","DOIUrl":null,"url":null,"abstract":"<div><p>In 2008, Takahashi introduced the James type constants. We discuss here the pointwise James type constant: for all <i>x</i> ∈ <i>X</i>, ∥<i>x</i>∥ = 1, </p><div><figure><div><div><picture><source><img></source></picture></div></div></figure></div><p> We show that in almost transitive Banach spaces, the map <i>x</i> ∈ <i>X</i>, ∥<i>x</i>∥ = 1 ↦ <i>J</i>(<i>x, X, t</i>) is constant. As a consequence and having in mind the Mazur’s rotation problem, we prove that for almost transitive Banach spaces, the condition <span>\\(J(x,X,t) = \\sqrt 2 \\)</span> for some unit vector <i>x</i> ∈ <i>X</i> implies that <i>X</i> is Hilbert.</p></div>","PeriodicalId":55518,"journal":{"name":"Analysis Mathematica","volume":"49 2","pages":"651 - 659"},"PeriodicalIF":0.6000,"publicationDate":"2023-06-08","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":"0","resultStr":null,"platform":"Semanticscholar","paperid":null,"PeriodicalName":"Analysis Mathematica","FirstCategoryId":"100","ListUrlMain":"https://link.springer.com/article/10.1007/s10476-023-0221-7","RegionNum":3,"RegionCategory":"数学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":null,"EPubDate":"","PubModel":"","JCR":"Q3","JCRName":"MATHEMATICS","Score":null,"Total":0}
引用次数: 0
Abstract
In 2008, Takahashi introduced the James type constants. We discuss here the pointwise James type constant: for all x ∈ X, ∥x∥ = 1,
We show that in almost transitive Banach spaces, the map x ∈ X, ∥x∥ = 1 ↦ J(x, X, t) is constant. As a consequence and having in mind the Mazur’s rotation problem, we prove that for almost transitive Banach spaces, the condition \(J(x,X,t) = \sqrt 2 \) for some unit vector x ∈ X implies that X is Hilbert.
期刊介绍:
Traditionally the emphasis of Analysis Mathematica is classical analysis, including real functions (MSC 2010: 26xx), measure and integration (28xx), functions of a complex variable (30xx), special functions (33xx), sequences, series, summability (40xx), approximations and expansions (41xx).
The scope also includes potential theory (31xx), several complex variables and analytic spaces (32xx), harmonic analysis on Euclidean spaces (42xx), abstract harmonic analysis (43xx).
The journal willingly considers papers in difference and functional equations (39xx), functional analysis (46xx), operator theory (47xx), analysis on topological groups and metric spaces, matrix analysis, discrete versions of topics in analysis, convex and geometric analysis and the interplay between geometry and analysis.