Integral regular net-balanced signed graphs with vertex degree at most four

Zoran Stanić

Abstract


A signed graph is called integral if its spectrum consists entirely of integers, it is r-regular if its underlying graph is regular of degree r, and it is net-balanced if the difference between positive and negative vertex degree is a constant on the vertex set (this constant is called the net-balance and denoted ρ). We determine all the connected integral 3-regular net-balanced signed graphs. In the next natural step, for r = 4, we consider only those whose net-balance is a simple eigenvalue. There, we complete the list of feasible spectra in bipartite case for ρ ≠ 0 and prove the non-existence for ρ = 0. Certain existence conditions are established and the existence of some 4-regular (simple) graphs is confirmed. In this study we transferred some results from the theory of graph spectra; in particular, we give a counterpart to the Hoffman polynomial.


Keywords


Signed graph, switching equivalent signed graphs, adjacency matrix, net-balanced signed graph

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DOI: https://doi.org/10.26493/1855-3974.1740.803

ISSN: 1855-3974

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