Cospectrality results for signed graphs with two eigenvalues unequal to ±1
Haemers,Willem H. Topcu,Hatice
Haemers,Willem H.
Topcu,Hatice
Abstract
Recently, the collection of all signed graphs for which the adjacency matrix has all but at most two eigenvalues equal to +/- 1 have been determined. Here we investigate for cospectral pairs, and for signed graphs determined by their spectrum (up to switching). If the order is at most 20, the outcome is presented in a clear table. If the spectrum is symmetric, we find all signed graphs in determined by their spectrum, and we obtain all signed graphs cospectral with the bipartite double of the complete graph. In addition, we determine all signed graphs cospectral with the friendship graph F & ell; , and show that there is no connected signed graph cospectral but not switching equivalent with F & ell;.
Description
Date
2026
Journal Title
Journal ISSN
Volume Title
Publisher
Research Projects
Organizational Units
Journal Issue
Keywords
Signed graph, Friendship graph, Graph spectrum, Spectral characterization, Symmetric spectrum
Citation
Haemers, W H & Topcu, H 2026, 'Cospectrality results for signed graphs with two eigenvalues unequal to ±1', Turkish Journal of Mathematics, vol. 50, no. 1. https://doi.org/10.55730/1300-0098.3639