## Abstract

Graph defined by Birkhoff–James orthogonality relation in normed spaces is studied. It is shown that (i) in a normed space of sufficiently large dimension there always exists a nonzero vector which is mutually Birkhoff–James orthogonal to each among a fixed number of given vectors, and (ii) in nonsmooth norms the cardinality of the set of pairwise Birkhoff–James orthogonal vectors may exceed the dimension of the vector space, but this cardinality is always bounded above by a function of the dimension. It is further shown that any given pair of elements in a normed space can be extended to a finite tuple such that each consecutive elements are mutually Birkhoff–James orthogonal; the exact minimal length of the tuple is also determined.

Original language | English |
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Article number | 125203 |

Journal | Journal of Mathematical Analysis and Applications |

Volume | 502 |

Issue number | 1 |

DOIs | |

State | Published - 1 Oct 2021 |

Externally published | Yes |

### Bibliographical note

Publisher Copyright:© 2021 Elsevier Inc.

## Keywords

- Birkhoff–James orthogonality
- Clique number
- Graph diameter
- Normed vector space