Article
Details
Citation
Rowlinson P & Stani? Z (2022) Signed graphs whose spectrum is bounded by ?2. Applied Mathematics and Computation, 423, Art. No.: 126991. https://doi.org/10.1016/j.amc.2022.126991
Abstract
We prove that for every tree T with t vertices (t > 2), the signed line graph ? (Kt) has ? (T) as a star complement for the eigenvalue -2; in other words, T is a foundation for Kt (regarded as a signed graph with all edges positive). In fact, ? (Kt) is, to within switching equivalence, the unique maximal signed line graph having such a star complement. It follows that if t ? {7, 8, 9} then, to within switching equivalence, Kt is the unique maximal signed graph with T as a foundation. We obtain analogous results for a signed unicyclic graph as a foundation, and then provide a classification of signed graphs with spectrum in [-2, ∞). We note various consequences, and review cospectrality and strong regularity in signed graphs with least eigenvalue ≥, -2.
Keywords
Adjacency matrix; Foundation of a signed graph; Signed line graph; Star complement; Star partition
Journal
Applied Mathematics and Computation: Volume 423
Status | Published |
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Publication date | 15/06/2022 |
Publication date online | 14/02/2022 |
Date accepted by journal | 26/01/2022 |
ISSN | 0096-3003 |
People (1)
Emeritus Professor, Mathematics