Very well-covered graphs with log-concave independence polynomials

Vadim E. Levit, Eugen Mâ ndrescu

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14 Scopus citations

Abstract

If sk equals the number of stable sets of cardinality k in the graph G, then I(G; x) = σα (G) k=0 skxk is the independence polynomial of G (Gutman and Harary, 1983). Alavi, Malde, Schwenk and Erdös (1987) conjectured that I(G; x) is unimodal whenever G is a forest, while Brown, Dilcher and Nowakowski (2000) conjectured that I(G; x) is unimodal for any well- covered graph G. Michael and Traves (2002) showed that the assertion is false for well-covered graphs with (G) ≤ 4, while for very well-covered graphs the conjecture is still open. In this paper we give support to both conjectures by demonstrating that if α(G) ≤ 3, or G {K1,n, Pn : n ≥ 1}, then I(G* x) is log-concave, and, hence, unimodal (where G* is the very well-covered graph obtained from G by appending a single pendant edge to each vertex).

Original languageEnglish
Pages (from-to)73-80
Number of pages8
JournalCarpathian Journal of Mathematics
Volume20
Issue number1
StatePublished - 2004
Externally publishedYes

Keywords

  • Claw-free graph
  • Independence polynomial
  • Log-concavity
  • Stable set
  • Tree
  • Unimodality
  • Well-covered graph

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