English

Very well-covered graphs with log-concave independence polynomials

Combinatorics 2011-01-25 v1 Discrete Mathematics

Abstract

If for any kk the kk-th coefficient of a polynomial I(G;x)I(G;x) is equal to the number of stable sets of cardinality kk in the graph GG, then it is called the independence polynomial of GG (Gutman and Harary, 1983). Alavi, Malde, Schwenk and Erdos (1987) conjectured that I(G;x)I(G;x) is unimodal, whenever GG is a forest, while Brown, Dilcher and Nowakowski (2000) conjectured that I(G;x)I(G;x) is unimodal for any well-covered graph G. Michael and Traves (2003) showed that the assertion is false for well-covered graphs with a(G)a(G) > 3 (a(G)a(G) is the size of a maximum stable set of the graph GG), while for very well-covered graphs the conjecture is still open. In this paper we give support to both conjectures by demonstrating that if a(G)a(G) < 4, or GG belongs to K1,n,Pn:n>0{K_{1,n}, P_{n}: n > 0}, then I(G;x)I(G*;x) is log-concave, and, hence, unimodal (where GG* is the very well-covered graph obtained from GG by appending a single pendant edge to each vertex).

Keywords

Cite

@article{arxiv.math/0411239,
  title  = {Very well-covered graphs with log-concave independence polynomials},
  author = {Vadim E. Levit and Eugen Mandrescu},
  journal= {arXiv preprint arXiv:math/0411239},
  year   = {2011}
}

Comments

8 pages, 4 figures