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A universal theory of switching for combinatorial objects, and applications to complex Hadamard matrices

Egan, Ronan orcid logoORCID: 0000-0001-6010-116X, Švob, Andrea orcid logoORCID: 0000-0001-6558-5167 and Crnković, Dean orcid logoORCID: 0000-0002-3299-7859 (2026) A universal theory of switching for combinatorial objects, and applications to complex Hadamard matrices. Journal of Algebraic Combinatorics, 63 (64). p. 64. ISSN 1572-9192

Abstract
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.
Metadata
Item Type:Article (Published)
Refereed:Yes
Uncontrolled Keywords:Switching of combinatorial objects; complex Hadamard matrices
Subjects:Mathematics > Algebra
DCU Faculties and Centres:DCU Faculties and Schools > Faculty of Science and Health > School of Mathematical Sciences
Publisher:Springer US
Official URL:https://link.springer.com/article/10.1007/s10801-0...
Copyright Information:Authors
ID Code:33507
Deposited On:23 Sep 2026 13:15 by Eimear Maher . Last Modified 23 Sep 2026 13:15
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