A universal theory of switching for combinatorial objects, and applications to complex Hadamard matrices
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arXiv
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| Format: | Preprint |
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2025
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| _version_ | 1866909036998295552 |
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| author | Crnković, Dean Egan, Ronan Švob, Andrea |
| author_facet | Crnković, Dean Egan, Ronan Švob, Andrea |
| contents | The concept of switching has arisen in several different areas within combinatorics. The act of switching usually transforms a combinatorial object into a non-isomorphic object of the same type, in a way that some key property is preserved. Godsil-McKay switching of graphs preserves the spectrum, switching of designs preserves their parameters, and switching of binary codes preserves the minimum distance. For Hadamard matrices, the switching techniques introduced by Orrick proved to be an incredibly powerful tool in generating inequivalent Hadamard matrices. In this paper, we introduce a universal definition of switching that can be adapted to incorporate these known types of switching. Through this language, we extend Orrick's methods to Butson Hadamard and complex Hadamard matrices. We introduce switchings of these matrices that can be used to construct new, inequivalent matrices. We also consider the concept of trades in complex Hadamard matrices in this terminology, and address an open problem on the permissible size of a trade. |
| format | Preprint |
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arxiv_https___arxiv_org_abs_2511_07020 |
| institution | arXiv |
| publishDate | 2025 |
| record_format | arxiv |
| spellingShingle | A universal theory of switching for combinatorial objects, and applications to complex Hadamard matrices Crnković, Dean Egan, Ronan Švob, Andrea Combinatorics 05B05, 05B20 The concept of switching has arisen in several different areas within combinatorics. The act of switching usually transforms a combinatorial object into a non-isomorphic object of the same type, in a way that some key property is preserved. Godsil-McKay switching of graphs preserves the spectrum, switching of designs preserves their parameters, and switching of binary codes preserves the minimum distance. For Hadamard matrices, the switching techniques introduced by Orrick proved to be an incredibly powerful tool in generating inequivalent Hadamard matrices. In this paper, we introduce a universal definition of switching that can be adapted to incorporate these known types of switching. Through this language, we extend Orrick's methods to Butson Hadamard and complex Hadamard matrices. We introduce switchings of these matrices that can be used to construct new, inequivalent matrices. We also consider the concept of trades in complex Hadamard matrices in this terminology, and address an open problem on the permissible size of a trade. |
| title | A universal theory of switching for combinatorial objects, and applications to complex Hadamard matrices |
| topic | Combinatorics 05B05, 05B20 |
| url | https://arxiv.org/abs/2511.07020 |