HL-index of a graph

Gašper Jaklič, Patrick W. Fowler, Tomaž Pisanski


Let G be a simple, connected graph with n vertices and eigenvalues λ1 > λ2 ≥ … ≥ λn. If n is even, define H = n/2 and L = H + 1. If n is odd, define H = L = (n + 1)/2. Define the HL-index of G to be R(G) = max(|λH|, |λL|). The eigenvalues λH and λL appear in chemical graph theory in the study of molecular stability. In this paper, bounds on HL-index for chemical and general graphs are studied. It is shown that there exist graphs with arbitrarily large HL-index.


HL-index, graph spectrum, HOMO-LUMO map

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DOI: https://doi.org/10.26493/1855-3974.180.65e

ISSN: 1855-3974

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