Tricyclic graph with maximal Estrada index

Let G be a simple connected graph on n vertices and λ1,λ2,…,λn be the eigenvalues of the adjacency matrix of G. The Estrada index of G is defined as EE(G)=∑i=1neλi. Let Tn be the class of tricyclic graphs G on n vertices. In this paper, the graphs in Tn with the maximal Estrada index is characterized.