Abstract

Let G be a graph on n vertices and lambda(1), lambda(2), . . . , lambda(n) its eigenvalues. The Estrada index of G is an invariant that is calculated from the eigenvalues of the adjacency matrix of a graph. In this paper, we present some new lower bounds for the Estrada index of graphs and in particular of bipartite graphs that only depend on the number of vertices, the number of edges, Randic index, maximum and minimum degree and diameter. (C) 2021 Elsevier B.V. All rights reserved.