Abstract
In this paper we introduce a new distance measure called Busch–Gudder metric on the cone of all positive semidefinite operators acting on a complex Hilbert space. It is defined as the sup-distance between the so-called strength functions corresponding to positive semidefinite operators. We investigate the properties of that metric, among others its relation to the metric induced by the operator norm. We show that in spite of many dissimilarities between the topological features of those two metrics, their isometry groups still coincide.
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The author is grateful to the referee for his/her comments which have helped to improve the presentation of the paper.
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The research was supported by the “Lendület” Program (LP2012-46/2012) of the Hungarian Academy of Sciences and by the National Research, Development and Innovation Office NKFIH, Grant No. K115383.
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Molnár, L. Busch–Gudder metric on the Cone of Positive Semidefinite Operators and Its Isometries. Integr. Equ. Oper. Theory 90, 20 (2018). https://doi.org/10.1007/s00020-018-2443-9
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DOI: https://doi.org/10.1007/s00020-018-2443-9