For each b ≥ 5 we construct a pair of cospectral b-regular graphs, where one has a perfect matching and the other one not. This solves a research problem posed by the third author at the 22nd British Combinatorial Conference.

Back in 1983, D. Cvetković posed the conjecture that the components of NEPS of connected bipartite graphs are almost cospectral. In 2000, we showed that this conjecture does not hold for infinitely many bases of NEPS, and we posed a necessary condition on the base of NEPS for NEPS to have almost cospectral components. At the same time, D. Cvetković posed weaker version of his original conjectur...

Let G = (V ,E) be a simple undirected connected graph and let M be a nonempty subset of vertices of G. Using the results we have derived in our previous paper on marker set distance matrix, we define two graphs G1 with a marker set M1 and G2 with a marker set M2 to be marker set cospectral if they have the same marker distance spectrum. In this paper, we obtain the conditions under which two gr...

A tree which has exactly one vertex of degree greater than two is said to be starlike. In spite of seemingly simple structure of these trees, not much is known about their spectral properties. In this paper, we introduce a generalization of the notion of cospectrality called m-cospectrality which turns out to be useful in constructing cospectral graphs. Based on this, we construct cospectral ma...

At some time, in the childhood of spectral graph theory, it was conjectured that non-isomorphic graphs have different spectra, i.e. that graphs are characterized by their spectra. Very quickly this conjecture was refuted and numerous examples and families of non-isomorphic graphs with the same spectrum (cospectral graphs) were found. Still some graphs are characterized by their spectra and seve...