{"title":"A note on the positivity of inverse operators acting on C⋆-algebras","authors":"Jochen Glück , Ulrich Groh","doi":"10.1016/j.laa.2024.12.006","DOIUrl":null,"url":null,"abstract":"<div><div>For a positive and invertible linear operator <em>T</em> acting on a C<sup>⋆</sup>-algebra, we give necessary and sufficient criteria for the inverse operator <span><math><msup><mrow><mi>T</mi></mrow><mrow><mo>−</mo><mn>1</mn></mrow></msup></math></span> to be positive, too. Moreover, a simple counterexample shows that <span><math><msup><mrow><mi>T</mi></mrow><mrow><mo>−</mo><mn>1</mn></mrow></msup></math></span> need not be positive even if <em>T</em> is unital and its spectrum is contained in the unit circle.</div></div>","PeriodicalId":18043,"journal":{"name":"Linear Algebra and its Applications","volume":"708 ","pages":"Pages 337-354"},"PeriodicalIF":1.0000,"publicationDate":"2024-12-16","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":"0","resultStr":null,"platform":"Semanticscholar","paperid":null,"PeriodicalName":"Linear Algebra and its Applications","FirstCategoryId":"100","ListUrlMain":"https://www.sciencedirect.com/science/article/pii/S0024379524004786","RegionNum":3,"RegionCategory":"数学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":null,"EPubDate":"","PubModel":"","JCR":"Q1","JCRName":"MATHEMATICS","Score":null,"Total":0}
引用次数: 0
Abstract
For a positive and invertible linear operator T acting on a C⋆-algebra, we give necessary and sufficient criteria for the inverse operator to be positive, too. Moreover, a simple counterexample shows that need not be positive even if T is unital and its spectrum is contained in the unit circle.
期刊介绍:
Linear Algebra and its Applications publishes articles that contribute new information or new insights to matrix theory and finite dimensional linear algebra in their algebraic, arithmetic, combinatorial, geometric, or numerical aspects. It also publishes articles that give significant applications of matrix theory or linear algebra to other branches of mathematics and to other sciences. Articles that provide new information or perspectives on the historical development of matrix theory and linear algebra are also welcome. Expository articles which can serve as an introduction to a subject for workers in related areas and which bring one to the frontiers of research are encouraged. Reviews of books are published occasionally as are conference reports that provide an historical record of major meetings on matrix theory and linear algebra.