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Discrete Applied Mathematics 160, 10-11 (2012) 1532-1546
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On the size of identifying codes in triangle-free graphs
Florent Foucaud ( ) 1, Ralf Klasing 1, 2, Adrian Kosowski 1, 2, 3, André Raspaud 1
(01/07/2012)

In an undirected graph $G$, a subset $C\subseteq V(G)$ such that $C$ is a dominating set of $G$, and each vertex in $V(G)$ is dominated by a distinct subset of vertices from $C$, is called an identifying code of $G$. The concept of identifying codes was introduced by Karpovsky, Chakrabarty and Levitin in 1998. For a given identifiable graph $G$, let $\M(G)$ be the minimum cardinality of an identifying code in $G$. In this paper, we show that for any connected identifiable triangle-free graph $G$ on $n$ vertices having maximum degree $\Delta\geq 3$, $\M(G)\le n-\tfrac{n}{\Delta+o(\Delta)}$. This bound is asymptotically tight up to constants due to various classes of graphs including $(\Delta-1)$-ary trees, which are known to have their minimum identifying code of size $n-\tfrac{n}{\Delta-1+o(1)}$. We also provide improved bounds for restricted subfamilies of triangle-free graphs, and conjecture that there exists some constant $c$ such that the bound $\M(G)\le n-\tfrac{n}{\Delta}+c$ holds for any nontrivial connected identifiable graph $G$.
1 :  Laboratoire Bordelais de Recherche en Informatique (LaBRI)
CNRS : UMR5800 – Université Sciences et Technologies - Bordeaux I – École Nationale Supérieure d'Électronique, Informatique et Radiocommunications de Bordeaux (ENSEIRB) – Université Victor Segalen - Bordeaux II
2 :  CEPAGE (INRIA Bordeaux - Sud-Ouest)
INRIA – CNRS : UMR5800 – Université Sciences et Technologies - Bordeaux I – École Nationale Supérieure d'Électronique, Informatique et Radiocommunications de Bordeaux (ENSEIRB)
3 :  Department of Algorithms and System Modeling [Gdansk]
Gdansk University of Technology
Informatique/Mathématique discrète

Mathématiques/Combinatoire
Identifying code – Dominating set – Triangle-free graph – Maximum degree
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