On extremal bipartite bicyclic graphs

Let Bn+ be the set of all connected bipartite bicyclic graphs with n vertices. The Estrada index of a graph G   is defined as EE(G)=∑i=1neλi, where λ1,λ2,…,λnλ1,λ2,…,λn are the eigenvalues of the adjacency matrix of G, and the Kirchhoff index of a graph G   is defined as Kf(G)=∑i