Consider those graphs \(G\) of size \(2n\) that have an eigenvalue \(\lambda\) of multiplicity \(n\) and where the edges between the star set and its complement is a matching. We show that \(\lambda\) must be either \(0\) or \(1\) and completely characterize the corresponding graphs.
Citation
N.E. Clarke, W.D. Garraway, C.A. Hickman, R.J. Nowakowski. Graphs Where Star Sets Are Matched to Their Complements[J], Journal of Combinatorial Mathematics and Combinatorial Computing, Volume 037. 177-185. .