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Lineability of the set of supporting vectors
Revista de la Real Academia de Ciencias Exactas, Físicas y Naturales. Serie A. Matemáticas ( IF 2.9 ) Pub Date : 2021-01-05 , DOI: 10.1007/s13398-020-00981-6
Francisco Javier García-Pacheco

The set of supporting vectors of a continuous linear operator \(T:X\rightarrow Y\) between normed spaces, denoted by \(\mathrm {suppv}(T)\) since 2017, is defined as \(\mathrm {suppv}(T):=\{x\in X:\Vert T(x)\Vert =\Vert T\Vert \Vert x\Vert \}\). In this manuscript, we study the lineability and coneability properties of \(\mathrm {suppv}(T)\), reaching both positive and negative results depending on T. For instance, if T is a functional, then \(\mathrm {suppv}(T)\) is 1-lineable and this result cannot be improved. However, if T is a (1, 1)-projection and X is infinite dimensional, then either \(\mathrm {suppv}(T)\) or \(\mathrm {suppv}(I-T)\) is lineable. Other general sufficient conditions for \(\mathrm {suppv}(T)\) to be lineable and coneable are provided. Special attention is given to the case where X and Y are Hilbert spaces, obtaining a characterization of unitary operators. The particular case of operators on \(\ell _1\) and \(c_0\) is also studied.



中文翻译:

支持向量集的线性

自2017年以来以\(\ mathrm {suppv}(T)\)表示的规范空间之间的连续线性算子\(T:X \ rightarrow Y \)的支持向量集定义为\(\ mathrm {suppv }(T):= \ {x \ in X:\ Vert T(x)\ Vert = \ Vert T \ Vert \ Vert x \ Vert \} \)。在本手稿中,我们研究\(\ mathrm {suppv}(T)\)的可线性性和圆锥性,根据T达到正和负结果。例如,如果T是一个函数,则\(\ mathrm {suppv}(T)\)是1线的,此结果无法改善。但是,如果T是(1,1)投影而X是无限维,则\(\ mathrm {suppv}(T)\)\(\ mathrm {suppv}(IT)\)是可排列的。为\(\ mathrm {suppv}(T)\)提供可线化和可锥化的其他一般充分条件。特别注意XY是希尔伯特空间的情况,获得obtaining算子的特征。还研究了\(\ ell _1 \)\(c_0 \)上运算符的特殊情况。

更新日期:2021-01-06
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