Biclique aresta-coloração por listas

Orientador : Prof. Dr. André Luiz Pires GuedesCoorientadora : Profª. Drª. Marina GroshausDissertação (mestrado) - Universidade Federal do Paraná, Setor de Ciências Exatas, Programa de Pós-Graduação em Informática. Defesa: Curitiba, 05/06/2017Inclui referências : f. 41-42Resumo: Na coloração de grafos existem algumas versões dos problemas de coloração de vértices e de coloração de arestas. Eles podem ser definidos a partir de conceitos como coloração por listas (colorir os elementos do grafo dados subconjuntos do conjunto de cores) ou colorir os elementos do grafo de forma que não existe uma estrutura monocromática. Um grafo G _e dito k-biclique aresta-selecionável se para qualquer atribuição de listas de cores para as arestas, onde cada lista tem tamanho k, existe uma coloração de E(G), onde cada aresta só pode usar as cores de sua lista, tal que não existe uma biclique (subgrafo induzido bipartido completo maximal) monocromática. Se k é o menor valor tal que G é k-biclique aresta-selecionável então k é o biclique índice de seleção de G. Assim nós podemos definir o k-biclique aresta-selecionabilidade como o problema de decidir se um grafo é k-biclique aresta-selecionável ou não. Nessa dissertação estudamos esse problema por provar que os grafos sem triangulo não isomorfo a um ciclo ímpar são 2-estrela aresta-selecionáveis (estrelas não monocromáticas), os bipartidos cordais são 2-biclique aresta-selecionáveis e mostramos um limite inferior do biclique índice de seleção dos grafos potencias de ciclos e potências de caminhos. E também apresentamos algoritmos polinomiais para computar uma 2-biclique (estrela) aresta-coloração das classes de grafos sem triangulo não isomorfo a um ciclo ímpar e bipartido cordal. Palavras-chave: Coloração por listas, Biclique, Coloração de arestas.Abstract: In graph coloring there are some versions of the vertex coloring and edge coloring problems. They can be defined using concepts like list coloring (to color graph elements given subsets of the set of colors) or coloring the elements of a graph such that there is no monochromatic structure. A graph G is said to be k-biclique edge-choosable if for any list assignment of colors to graph edges, which each list has size k, there is a coloring of E(G), that the edges can only use colors from theirs lists, such that there is no monochromatic biclique (maximal induced complete bipartite subgraph). If k is the smallest value such that G is k-biclique edge-choosable then k is the biclique choice index of G. Therefore we can define the k-biclique edge-choosability as the problem to decide if a given graph is k-biclique edge-choosable or not. In this dissertation we studied this problem by proving that triangle-free graphs not isomorphic to odd cycle are 2-star edge-choosable, the chordal bipartite are 2-biclique edge-choosable and showing a lower bound for the biclique choice index of power of cycles and power of paths. And we also show polynomial algorithms to compute a 2-biclique (star) edge-coloring for the graph classes triangle-free not isomorphic to odd cycle and chordal bipartite. Keywords: List coloring, biclique, edge coloring

On star and biclique edge-colorings

A biclique of G is a maximal set of vertices that induces a complete bipartite subgraph Kp,q of G with at least one edge, and a star of a graph G is a maximal set of vertices that induces a complete bipartite graph K1,q. A biclique (resp. star) edge-coloring is a coloring of the edges of a graph with no monochromatic bicliques (resp. stars). We prove that the problem of determining whether a graph G has a biclique (resp. star) edgecoloring using two colors is NP-hard. Furthermore, we describe polynomial time algorithms for the problem in restricted classes: K3-free graphs, chordal bipartite graphs, powers of paths, and powers of cycles

Generalized Colorings of Graphs

A graph coloring is an assignment of labels called “colors” to certain elements of a graph subject to certain constraints. The proper vertex coloring is the most common type of graph coloring, where each vertex of a graph is assigned one color such that no two adjacent vertices share the same color, with the objective of minimizing the number of colors used. One can obtain various generalizations of the proper vertex coloring problem, by strengthening or relaxing the constraints or changing the objective. We study several types of such generalizations in this thesis. Series-parallel graphs are multigraphs that have no K4-minor. We provide bounds on their fractional and circular chromatic numbers and the defective version of these pa-rameters. In particular we show that the fractional chromatic number of any series-parallel graph of odd girth k is exactly 2k/(k − 1), confirming a conjecture by Wang and Yu. We introduce a generalization of defective coloring: each vertex of a graph is assigned a fraction of each color, with the total amount of colors at each vertex summing to 1. We define the fractional defect of a vertex v to be the sum of the overlaps with each neighbor of v, and the fractional defect of the graph to be the maximum of the defects over all vertices. We provide results on the minimum fractional defect of 2-colorings of some graphs. We also propose some open questions and conjectures. Given a (not necessarily proper) vertex coloring of a graph, a subgraph is called rainbow if all its vertices receive different colors, and monochromatic if all its vertices receive the same color. We consider several types of coloring here: a no-rainbow-F coloring of G is a coloring of the vertices of G without rainbow subgraph isomorphic to F ; an F -WORM coloring of G is a coloring of the vertices of G without rainbow or monochromatic subgraph isomorphic to F ; an (M, R)-WORM coloring of G is a coloring of the vertices of G with neither a monochromatic subgraph isomorphic to M nor a rainbow subgraph isomorphic to R. We present some results on these concepts especially with regards to the existence of colorings, complexity, and optimization within certain graph classes. Our focus is on the case that F , M or R is a path, cycle, star, or clique

Proceedings of the 8th Cologne-Twente Workshop on Graphs and Combinatorial Optimization

International audienceThe Cologne-Twente Workshop (CTW) on Graphs and Combinatorial Optimization started off as a series of workshops organized bi-annually by either Köln University or Twente University. As its importance grew over time, it re-centered its geographical focus by including northern Italy (CTW04 in Menaggio, on the lake Como and CTW08 in Gargnano, on the Garda lake). This year, CTW (in its eighth edition) will be staged in France for the first time: more precisely in the heart of Paris, at the Conservatoire National d’Arts et Métiers (CNAM), between 2nd and 4th June 2009, by a mixed organizing committee with members from LIX, Ecole Polytechnique and CEDRIC, CNAM

Graph Colouring with Input Restrictions

In this thesis, we research the computational complexity of the graph colouring problem and its variants including precolouring extension and list colouring for graph classes that can be characterised by forbidding one or more induced subgraphs. We investigate the structural properties of such graph classes and prove a number of new properties. We then consider to what extent these properties can be used for efficiently solving the three types of colouring problems on these graph classes. In some cases we obtain polynomial-time algorithms, whereas other cases turn out to be NP-complete. We determine the computational complexity of k-COLOURING, k-PRECOLOURING EXTENSION and LIST k-COLOURING on $P_k$-free graphs. In particular, we prove that k-COLOURING on $P_8$-free graphs is NP-complete, 4-PRECOLOURING EXTENSION $P_7$-free graphs is NP-complete, and LIST 4-COLOURING on $P_6$-free graphs is NP-complete. In addition, we show the existence of an integer r such that k-COLOURING is NP-complete for $P_r$-free graphs with girth 4. In contrast, we determine for any fixed girth $g\geq 4$ a lower bound $r(g)$ such that every $P_{r(g)}$-free graph with girth at least $g$ is 3-colourable. We also prove that 3-LIST COLOURING is NP-complete for complete graphs minus a matching. We present a polynomial-time algorithm for solving 4-PRECOLOURING EXTENSION on $(P_2+P_3)$-free graphs, a polynomial-time algorithm for solving LIST 3-Colouring on $(P_2+P_4)$-free graphs, and a polynomial-time algorithm for solving LIST 3-COLOURING on $sP_3$-free graphs. We prove that LIST k-COLOURING for $(K_{s,t},P_r)$-free graphs is also polynomial-time solvable. We obtain several new dichotomies by combining the above results with some known results

The Star and Biclique Coloring and Choosability Problems

A biclique of a graph G is an induced complete bipartite graph. A star of G is a biclique contained in the closed neighborhood of a vertex. A star (biclique) k-coloring of G is a k-coloring of G that contains no monochromatic maximal stars (bicliques). Similarly, for a list assignment L of G, a star (biclique) L-coloring is an L-coloring of G in which no maximal star (biclique) is monochromatic. If G admits a star (biclique) L-coloring for every k-list assignment L, then G is said to be star (biclique) k-choosable. In this article we study the computational complexity of the star and biclique coloring and choosability problems. Specifically, we prove that the star (biclique) k-coloring and k-choosability problems are Σp2-complete and Π p 3-complete for k> 2, respectively, even when the input graph contains no induced C4 or Kk+2. Then, we study all these problems in some related classes of graphs, including H-free graphs for every H on three vertices, graphs with restricted diamonds, split graphs, and threshold graphs