Compositions of Cospectrality Graphs of Smith Graphs

Abstract

Graphs whose spectrum belongs to the interval [−2, 2] are called Smith graphs. Vertices of the cospectrality graph C(H) of a Smith graph H are all graphs cospectral with H with two vertices adjacent if there exists a certain transformation transforming one to another. We study how the cospectrality graph of the union of two Smith graphs can be composed starting from cospectrality graphs of starting graphs.