Signed graphs with two eigenvalues and vertex degree five
Keywords:Regular signed graph, adjacency matrix, weighing matrix, bipartite double
AbstractIt is known that a signed graph with exactly 2 eigenvalues must be regular, and all those whose vertex degree does not exceed 4 are known. In this paper we characterize all signed graphs with 2 eigenvalues and vertex degree 5. We also determine all signed graphs with 2 eigenvalues and 12 or 13 vertices, which is a natural step since those with a fewer number of vertices are known.
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