More on Signed Graphs with at Most Three Eigenvalues

Abstract

We consider signed graphs with just 2 or 3 distinct eigenvalues, in particular (i) those with at least one simple eigenvalue, and (ii) those with vertex-deleted subgraphs which themselves have at most 3 distinct eigenvalues. We also construct new examples using weighing matrices and symmetric 3-class association schemes.

Keywords

• adjacency matrix
• simple eigenvalue
• strongly regular signed graph
• vertex-deleted subgraph
• weighing matrix
• association scheme
• 05c22
• 05c50