Article

# Equistable graphs

Journal of Graph Theory (Impact Factor: 0.67). 10/2006; 18(3):281 - 299. DOI: 10.1002/jgt.3190180307

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**ABSTRACT:**In this paper we examine the connections between equistable graphs, general partition graphs and triangle graphs. While every general partition graph is equistable and every equistable graph is a triangle graph, not every triangle graph is equistable, and a conjecture due to Jim Orlin states that every equistable graph is a general partition graph. The conjecture holds within the class of chordal graphs; if true in general, it would provide a combinatorial characterization of equistable graphs.Exploiting the combinatorial features of triangle graphs and general partition graphs, we verify Orlin’s conjecture for several graph classes, including AT-free graphs and various product graphs. More specifically, we obtain a complete characterization of the equistable graphs that are non-prime with respect to the Cartesian or the tensor product, and provide some necessary and sufficient conditions for the equistability of strong, lexicographic and deleted lexicographic products. We also show that the general partition graphs are not closed under the strong product, answering a question by McAvaney et al.Discrete Applied Mathematics 07/2011; 159(11):1148–1159. · 0.68 Impact Factor - [Show abstract] [Hide abstract]

**ABSTRACT:**We verify the conjectures of Mahadev–Peled–Sun and of Orlin, both related to equistable graphs, for the classes of simplicial, very well-covered and line graphs. Our results are based on the combinatorial features of triangle graphs and general partition graphs. In particular, we obtain several equivalent characterizations of equistable simplicial graphs, equistable very well-covered graphs, and equistable line graphs, some of which imply polynomial time recognition algorithms for graphs in these classes.Discrete Applied Mathematics 01/2014; 165:205–212. · 0.68 Impact Factor -
##### Conference Paper: On the recognition of k -equistable graphs

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**ABSTRACT:**A graph G=(V,E) is called equistable if there exist a positive integer t and a weight function $w:V \longrightarrow \mathbb{N}$ such that S⊆V is a maximal stable set of G if and only if w(S)=t. The function w, if exists, is called an equistable function of G. No combinatorial characterization of equistable graphs is known, and the complexity status of recognizing equistable graphs is open. It is not even known whether recognizing equistable graphs is in NP. Let k be a positive integer. An equistable graph G=(V,E) is said to be k-equistable if it admits an equistable function which is bounded by k. For every constant k, we present a polynomial time algorithm which decides whether an input graph is k-equistable.Proceedings of the 38th international conference on Graph-Theoretic Concepts in Computer Science; 06/2012

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