摘要

Let G = (V, E) be a simple graph of order n with m edges and Laplacian eigenvalues mu(1) >= mu(2) >= ... >= mu(n-1) >= mu(n) = 0. The Kirchhoff index and the Laplacian-energy-like invariant of G are defined as Kf(G) = n Sigma(n-1)(k=1) 1/mu(k) and LEL(G) = Sigma(n-1)(k=1) root mu(k), respectively. The Laplacian energy of the graph G is defined as LE(G) = Sigma(n)(i=1) vertical bar mu(i) - 2m/n vertical bar. In this paper, we present an upper bound on Kf of graphs. Also, we obtain some relations between Kf, LEL and first Zagreb index of G. Finally, we give a relation between LEL and LE of G.