In this note we study some properties of the spectrum of a connected graph G with four different eigenvalues, and (spectrally maximum) diameter three. When G is regular, this is the case, for instance, when G is a distance-regular graph. © 2006 Elsevier B.V. All rights reserved.
Fiol, M. A., & Garriga, E. (2006). On the spectrum of an extremal graph with four eigenvalues. Discrete Mathematics, 306(18), 2241–2244. https://doi.org/10.1016/j.disc.2006.05.010