An Improved Lower Bound for the Degree Kirchhoff Index of Bipartite Graphs

Abstract

Abstract For a connected graphGwithn vertices andm edges, the degree Kirchhoff index ofG is defined asKf∗ (G) = 2m ∑n−1 i=1 (γi) , where γ1 ≥ γ2 ≥ · · · ≥ γn−1 > γn = 0 are the normalized Laplacian eigenvalues of G. In this paper, a lower bound on the degree Kirchhoff index of bipartite graphs is established. Also, it is proved that the obtained bound is stronger than a lower bound derived by Zhou and Trinajstić in [J. Math. Chem. 46 (2009) 283–289].