Note on the HOMO-LUMO Index of Graphs ∗

Abstract

Let G be a simple, connected graph of order n with eigenvalues λ1 ≥ λ2 ≥ · ·· ≥ λn . The median eigenvalues λH ,λ L ,f orH = �(n +1 )/2� and L = �(n +1 )/2� are considered. These play an important