Partitionnement, recouvrement et colorabilité dans les graphes

Our research are about graph coloring with distance constraints (packing coloring) or neighborhood constraints (Grundy coloring). Let S={si| i in N*} be a non decreasing sequence of integers. An S-packing coloring is a proper coloring such that every set of color i is an si-packing (a set of vertices at pairwise distance greater than si). A graph G is (s1,... ,sk)-colorable if there exists a packing coloring of G with colors 1,... ,k. A Grundy coloring is a proper vertex coloring such that for every vertex of color i, u is adjacent to a vertex of color j, for each ji. These results allow us to determine S-packing coloring of these lattices for several sequences of integers. We examine a class of graph that has never been studied for S-packing coloring: the subcubic graphs. We determine that every subcubic graph is (1,2,2,2,2,2,2)-colorable and (1,1,2,2,3)-colorable. Few results are proven about some subclasses. Finally, we study the Grundy number of regular graphs. We determine a characterization of the cubic graphs with Grundy number 4. Moreover, we prove that every r-regular graph without induced square has Grundy number r+1, for ri. Ces résultats nous permettent de déterminer des S-colorations de packings de ces grilles pour plusieurs séries d’entiers. Nous examinons une classe de graphe jamais étudiée en ce qui concerne la S -coloration de packing: les graphes subcubiques. Nous déterminons que tous les graphes subcubiques sont (1,2,2,2,2,2,2)-colorables et (1,1,2,2,3)-colorables. Un certain nombre de résultats sont prouvés pour certaines sous-classes des graphes subcubiques. Pour finir, nous nous intéressons au nombre de Grundy des graphes réguliers. Nous déterminons une caractérisation des graphes cubiques avec un nombre de Grundy de 4. De plus, nous prouvons que tous les graphes r-réguliers sans carré induit ont pour nombre de Grundy de r+1, pour r<5

On the packing chromatic number of hypercubes

The packing chromatic number χρ(G) of a graph G is the smallest integer k needed to proper color the vertices of G in such a way that the distance in G between any two vertices having color i be at least i + 1. Goddard et al. [8] found an upper bound for the packing chromatic number of hypercubes Qn. Moreover, they compute χρ(Qn) for n ≤ 5 leaving as an open problem the remaining cases. In this paper, we obtain a better upper bound for χρ(Qn) and we compute the exact value of χρ(Qn) for 6 ≤ n ≤ 8.Fil: Torres, Pablo Daniel. Universidad Nacional de Rosario; Argentina. Consejo Nacional de Investigaciones Científicas y Técnicas; ArgentinaFil: Valencia Pabon, Mario. Universite de Paris 13-nord. Laboratoire D'informatique de L'universite Paris-nord; Franci