Academic literature on the topic 'Nombre chromatique de packing'
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Journal articles on the topic "Nombre chromatique de packing":
Jammes, Pierre. "Multiplicité du spectre de Steklov sur les surfaces et nombre chromatique." Pacific Journal of Mathematics 282, no. 1 (February 24, 2016): 145–71. http://dx.doi.org/10.2140/pjm.2016.282.145.
Alminaite, Agne, Vera Backström, Antti Vaheri, and Alexander Plyusnin. "Oligomerization of hantaviral nucleocapsid protein: charged residues in the N-terminal coiled-coil domain contribute to intermolecular interactions." Journal of General Virology 89, no. 9 (September 1, 2008): 2167–74. http://dx.doi.org/10.1099/vir.0.2008/004044-0.
Cifuentes, Diego. "On the degree-chromatic polynomial of a tree." Discrete Mathematics & Theoretical Computer Science DMTCS Proceedings vol. AR,..., Proceedings (January 1, 2012). http://dx.doi.org/10.46298/dmtcs.3020.
Bohn, Adam. "Chromatic roots as algebraic integers." Discrete Mathematics & Theoretical Computer Science DMTCS Proceedings vol. AR,..., Proceedings (January 1, 2012). http://dx.doi.org/10.46298/dmtcs.3061.
Jammes, Pierre. "Plongements polyédraux tendus et nombre chromatique relatif des surfaces à bord." Canadian Mathematical Bulletin, December 28, 2020, 1–13. http://dx.doi.org/10.4153/s0008439520001010.
Schultz, Carsten. "The equivariant topology of stable Kneser graphs." Discrete Mathematics & Theoretical Computer Science DMTCS Proceedings vol. AO,..., Proceedings (January 1, 2011). http://dx.doi.org/10.46298/dmtcs.2960.
Dissertations / Theses on the topic "Nombre chromatique de packing":
Tarhini, Batoul. "Oriented paths in digraphs and the S-packing coloring of subcubic graph." Electronic Thesis or Diss., Bourgogne Franche-Comté, 2023. http://www.theses.fr/2023UBFCK079.
This PhD thesis is divided into two principal parts: Part I delves into the existenceof oriented paths in digraphs, aiming to establish a connection between a digraph'schromatic number and the existence of specific oriented paths within it as subdigraphs. Digraphs contained in any n-chromatic digraph are called n-universal. We consider two conjectures: Burr's conjecture, which states that every oriented tree of order n is (2n-2)-universal, and El Sahili's conjeture which states that every oriented path of order n is n-universal. For oriented paths in general, the best bound is given by Burr, that is every oriented path of order n is (n − 1)^2-universal. Our objective is to study the existence of an integer k such that any digraph with a chromatic number k, contains a copy of a given oriented path with three blocks as its subdigraph. To achieve our goals, we rely significantly on fundamental concepts, including, induction on the order of a given digraph, final forests, leveling techniques, and strategic digraph decomposition methods. A path P (k1, k2, k3) is an oriented path consisting of k1 forward arcs, followed by k2 backward arcs, and then by k3 forward arcs. For the path P(k,1,l), we have confirmed El Sahili's conjecture in Hamiltonian digraphs. More clearly, we have established the existence of any path P (k, 1, l) of order n in any n-chromatic Hamiltonian digraph. And depending on this result concerning Hamiltonian digraphs, we proved the correctness of El Sahili's conjecture on a more general class of digraphs which is digraphs containing a Hamiltonian directed path. We introduce a new technique which is represented by a decomposition of the digraph into subdigraphs defined by a series of successive operations applied to the digraph relying on the famous theorem of Roy which establishes the existence of a directed path of order n in any n-chromatic digraph. This technique has proven to be instrumental in establishing new linear bounds for the chromatic number of digraphs that lack an oriented path with three blocks. In deed, using this technique, we proved that the path P(k,1,l) satisfies Burr's conjecture.Moreover, for any path with three blocks, P(k,l,r) we establish a linear bound for the chromatic number which improves all the previously reached bounds. In Part II we study the problem of S-packing coloring in graphs. Given a non-decreasing sequence S = (s1, s2, . . . , sk) of positive integers, an S-packing coloring of a graph G is a partition of the vertex set of G into k subsets{V1, V2, . . . , Vk} such that for each 1 ≤ i ≤ k, the distance between any two dis-tinct vertices u and v in Vi is at least si + 1. Our focus is centered on an intriguing conjecture proposed by Brešar et al., which states that packing chromatic number of the subdivision of any subcubic graph is at most 5. Our desired aim is to provide a confirmation of this conjecture for specific classes of subcubic graphs, and to address the unresolved issues raised within this subject matter. An observation for Gastineau and Togni states that if a graph G is (1, 1, 2, 2)-packing colorable, then the chromatic number of its subdivision graph S(G) is at most 5, and hence it satisfies the conjecture. Depending on this observation, and in order to prove the correctness of the conjecture for the class of cubic Halin graphs, we studied its S-packing coloring aiming to prove that it admits a (1, 1, 2, 2)- packing coloring. We proved that a cubic Halin graph is (1, 1, 2, 3)-packing colorable, then it is (1, 1, 2, 2)-packing colorable, and so we confirm the conjecture for this class. Moreover, Gastineau and Togni, after proving that every subcubic graph is (1, 2, 2, 2, 2, 2, 2)-packing colorbale, have posed an open problem on whether every subcubic graph is (1, 2, 2, 2, 2, 2)-packing colorable. We answer this question in affirmative in the particular class we worked on; we proved that cubic Halin graphs are (1, 2, 2, 2, 2, 2)-packing colorable
Mortada, Maidoun. "The b-chromatic number of regular graphs." Thesis, Lyon 1, 2013. http://www.theses.fr/2013LYO10116.
Two problems are considered in this thesis: the b-coloring problem and the graph packing problem. 1. The b-Coloring Problem : A b-coloring of a graph G is a proper coloring of the vertices of G such that there exists a vertex in each color class joined to at least a vertex in each other color class. The b-chromatic number of a graph G, denoted by b(G), is the maximum number t such that G admits a b-coloring with t colors. El Sahili and Kouider asked whether it is true that every d-regular graph G with girth at least 5 satisfies b(G) = d + 1. Blidia, Maffray and Zemir proved that the conjecture is true for d ≤ 6. Also, the question was solved for d-regular graphs with supplementary conditions. We study El Sahili and Kouider conjecture by determining when it is possible and under what supplementary conditions it is true. We prove that b(G) = d+1 if G is a d-regular graph containing neither a cycle of order 4 nor of order 6. Then, we provide specific conditions on the vertices of a d-regular graph G with no cycle of order 4 so that b(G) = d + 1. Cabello and Jakovac proved that if v(G) ≥ 2d3 - d2 + d, then b(G) = d + 1, where G is a d-regular graph. We improve this bound by proving that if v(G) ≥ 2d3 - 2d2 + 2d, then b(G) = d+1 for a d-regular graph G. 2. Graph Packing Problem : Graph packing problem is a classical problem in graph theory and has been extensively studied since the early 70's. Consider a permutation σ : V (G) → V (Kn), the function σ* : E(G) → E(Kn) such that σ *(xy) = σ *(x) σ *(y) is the function induced by σ. We say that there is a packing of k copies of G into the complete graph Kn if there exist k permutations σ i : V (G) → V (Kn), where i = 1,…, k, such that σ*i (E(G)) ∩ σ*j (E(G)) = ɸ for I ≠ j. A packing of k copies of a graph G will be called a k-placement of G. The kth power Gk of a graph G is the supergraph of G formed by adding an edge between all pairs of vertices of G with distance at most k. Kheddouci et al. proved that for any non-star tree T there exists a 2-placement σ on V (T). We introduce a new variant of graph packing problem, called the labeled packing of a graph into its power graph
Moustrou, Philippe. "Geometric distance graphs, lattices and polytopes." Thesis, Bordeaux, 2017. http://www.theses.fr/2017BORD0802/document.
A distance graph G(X;D) is a graph whose set of vertices is the set of points X of a metric space (X; d), and whose edges connect the pairs fx; yg such that d(x; y) 2 D. In this thesis, we consider two problems that may be interpreted in terms of distance graphs in Rn. First, we study the famous sphere packing problem, in relation with thedistance graph G(Rn; (0; 2r)) for a given sphere radius r. Recently, Venkatesh improved the best known lower bound for lattice sphere packings by a factor log log n for infinitely many dimensions n. We prove an effective version of this result, in the sense that we exhibit, for the same set of dimensions, finite families of lattices containing a lattice reaching this bound. Our construction uses codes over cyclotomic fields, lifted to lattices via Construction A. We also prove a similar result for families of symplectic lattices. Second, we consider the unit distance graph G associated with a norm k _ k. The number m1 (Rn; k _ k) is defined as the supremum of the densities achieved by independent sets in G. If the unit ball corresponding with k _ k tiles Rn by translation, then it is easy to see that m1 (Rn; k _ k) > 1 2n . C. Bachoc and S. Robins conjectured that the equality always holds. We show that this conjecture is true for n = 2 and for several Voronoï cells of lattices in higher dimensions, by solving packing problems in discrete graphs
Benchetrit, Yohann. "Propriétés géométriques du nombre chromatique : polyèdres, structures et algorithmes." Thesis, Université Grenoble Alpes (ComUE), 2015. http://www.theses.fr/2015GREAM049/document.
Computing the chromatic number and finding an optimal coloring of a perfect graph can be done efficiently, whereas it is an NP-hard problem in general. Furthermore, testing perfection can be carried- out in polynomial-time. Perfect graphs are characterized by a minimal structure of their sta- ble set polytope: the non-trivial facets are defined by clique-inequalities only. Conversely, does a similar facet-structure for the stable set polytope imply nice combinatorial and algorithmic properties of the graph ? A graph is h-perfect if its stable set polytope is completely de- scribed by non-negativity, clique and odd-circuit inequalities. Statements analogous to the results on perfection are far from being understood for h-perfection, and negative results are missing. For ex- ample, testing h-perfection and determining the chromatic number of an h-perfect graph are unsolved. Besides, no upper bound is known on the gap between the chromatic and clique numbers of an h-perfect graph. Our first main result states that the operations of t-minors keep h- perfection (this is a non-trivial extension of a result of Gerards and Shepherd on t-perfect graphs). We show that it also keeps the Integer Decomposition Property of the stable set polytope, and use this to answer a question of Shepherd on 3-colorable h-perfect graphs in the negative. The study of minimally h-imperfect graphs with respect to t-minors may yield a combinatorial co-NP characterization of h-perfection. We review the currently known examples of such graphs, study their stable set polytope and state several conjectures on their structure. On the other hand, we show that the (weighted) chromatic number of certain h-perfect graphs can be obtained efficiently by rounding-up its fractional relaxation. This is related to conjectures of Goldberg and Seymour on edge-colorings. Finally, we introduce a new parameter on the complexity of the matching polytope and use it to give an efficient and elementary al- gorithm for testing h-perfection in line-graphs
Silva, Ana. "Le nombre b-chromatique de quelques classes de graphes généralisant les arbres." Grenoble, 2010. http://www.theses.fr/2010GRENM078.
Une coloration des sommets de G s'appelle une b-coloration si chaque classe de couleur contient au moins un sommet qui a un voisin dans toutes les autres classes de couleur. Le nombre b-chromatique b(G) de G est le plus grand entier k pour lequel G a une b-coloration avec k couleurs. Ces notions ont été introduites par Irving et Manlove en 1999. Elles permettent d'évaluer les performances de certains algorithmes de coloration. Irving et Manlove ont montré que le calcul du nombre b-chromatique d'un graphe est un problème NP-difficile et qu'il peut être résolu en temps polynomial pour les arbres. Une question qui se pose naturellement est donc d'enquêter sur les graphes qui ont une structure proche des arbres : cactus, graphes triangulés, graphes série-parallèles, "block" graphes, etc. Dans cette thèse, nous généralisons le résultat d'Irving et Manlove pour les cactus dont le "m-degré" est au moins 7 et pour les graphes planaires extérieurs dont la maille est au moins 8. (Le m-degré m(G) est le plus grand entier d tel que G a au moins d sommets de degré au moins d −1. ) Nous démontrons un résultat semblable pour le produit cartésien d'un arbre par une chaîne, un cycle ou une étoile. Pour ce qui concerne les graphes dont les blocs sont des cliques, nous montrons que le problème avec un nombre de couleurs fixé peut être résolu en temps polynomial et nous présentons des cas où le problème de décision peut être résolu. Toutefois, nous avons constaté que la différence m(G)−b(G) peut être arbitrairement grande pour les graphes blocs, ce qui montre qu'avoir une structure arborescence n'est pas suffisant pour que le graphe satisfasse b(G)>= m(G) − 1
Aboulker, Pierre. "Excluding slightly more than a cycle." Paris 7, 2013. http://www.theses.fr/2013PA077136.
This thesis is concerned with structural graph theory. It contains several results, algorithmics and structural, on classes of graphs defined by forbidding induced subgraphs. Graphs that are excluded are variations around the so-called "Truemper configurations". These last might be seen as generalization of the cycle
Passuello, Alberto. "Semidefinite programming in combinatorial optimization with applications to coding theory and geometry." Phd thesis, Université Sciences et Technologies - Bordeaux I, 2013. http://tel.archives-ouvertes.fr/tel-00948055.
Guignard, Adrien. "Jeux de coloration de graphes." Thesis, Bordeaux 1, 2011. http://www.theses.fr/2011BOR14391/document.
Part 1: Domination Game and its variantsDomination game is a combinatorial game that consists in marking vertices of a graph so that a marked vertex has no marked neighbors. The first player unable to mark a vertex loses the game.Since the computing of winning strategies is an NP-hard problem for any graphs, we examine some specific families of graphs such as complete k-partite graphs, paths or saws. For these families, we establish the set of losing elements. For other families, such as caterpillars, we prove that exists a polynomial algorithm for the computation of outcome and winning strategies. No polynomial algorithm has been found to date for more general families, such as trees.We also study 28 variants of Domination game, including the 12 variants defined by J. Conway for any combinatorial game. Using game functions, we find the set of losing paths for 10 of these 12 variants. We also investigate 16 variants called diameter, for instance when rules require to play on the component that has the largest diameter.Part 2: The game chromatic number of treesThis parameter is computed from a coloring game: Alice and Bob alternatively color the vertices of a graph G, using one of the k colors in the color set. Alice has to achieve the coloring of the entire graph whereas Bob has to prevent this. Faigle and al. proved that the game chromatic number of a tree is at most 4. We undertake characterization of trees with a game chromatic number of 3. Since this problem seems difficult for general trees, we focus on sub-families: 1-caterpillars and caterpillars without holes.For these families we provide the characterization and also compute winning strategies for Alice and Bob. In order to do so, we are led to define a new notion, the bitype, that for a partially-colored graph G associates two letters indicating who has a winning strategy respectively on G and G with an isolated vertex. Bitypes allow us to demonstrate several properties, in particular to compute the game chromatic number of a graph from the bitypes of its connected components
Ferreira, Da Silva Ana Shirley. "Le nombre b-chromatique de quelques classes de graphes généralisant les arbres." Phd thesis, 2010. http://tel.archives-ouvertes.fr/tel-00544757.
Book chapters on the topic "Nombre chromatique de packing":
Aigner, Martin, and Günter M. Ziegler. "Le nombre chromatique des graphes de Kneser." In Raisonnements divins, 281–86. Paris: Springer Paris, 2013. http://dx.doi.org/10.1007/978-2-8178-0400-2_38.