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Characterizations of inner product spaces via angular distances and Cauchy–Schwarz inequality

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Abstract

We study some interesting characterizations of real inner product spaces expressed in terms of angular distances. We first discuss the equivalence of characterizing an inner product space via the usual angular distance and the p-angular distance. Then, we establish a parametric family of upper bounds for the usual angular distance which also serves as a characterization of an inner product space. As an application, bounds for the usual angular distance are utilized in obtaining improvements of the real Cauchy–Schwarz inequality. Finally, we give several comparative relations for angular distances in inner product spaces.

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Acknowledgements

The authors would like to thank the referee for some valuable comments and useful suggestions.

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Authors and Affiliations

  1. Faculty of Electrical Engineering and Computing, University of Zagreb, Unska 3, 10000, Zagreb, Croatia

    Mario Krnić

  2. Transilvania University of Braşov, Iuliu Maniu Street, No. 50, 500091, Brasov, Romania

    Nicuşor Minculete

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  1. Mario Krnić
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  2. Nicuşor Minculete
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Correspondence to Mario Krnić.

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Krnić, M., Minculete, N. Characterizations of inner product spaces via angular distances and Cauchy–Schwarz inequality. Aequat. Math. 95, 147–166 (2021). https://doi.org/10.1007/s00010-020-00735-0

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  • DOI: https://doi.org/10.1007/s00010-020-00735-0

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