An edge grafting theorem on the Estrada index of graphs and its applications

The Estrada index of a graph GG is defined as EE(G)=∑i=1neλi, where λ1,λ2,…,λnλ1,λ2,…,λn are the eigenvalues of the adjacency matrix of GG. It can be used as an efficient measuring tool in a variety of fields. An edge grafting operation on a graph moves a pendent edge between two pendent paths. In this paper, we give an edge grafting theorem on the Estrada index of graphs. We also give some applications of this theorem.