General neighbour-distinguishing index via chromatic number

AbstractAn edge colouring of a graph G without isolated edges is neighbour-distinguishing if any two adjacent vertices have distinct sets consisting of colours of their incident edges. The general neighbour-distinguishing index of G is the minimum number gndi(G) of colours in a neighbour-distinguishing edge colouring of G. Győri et al. [E. Győri, M. Horňák, C. Palmer, M. Woźniak, General neighbour-distinguishing index of a graph, Discrete Math. 308 (2008) 827–831] proved that gndi(G)∈{2,3} provided G is bipartite and gave a complete characterisation of bipartite graphs according to their general neighbour-distinguishing index. The aim of this paper is to prove that if χ(G)≥3, then ⌈log2χ(G)⌉+1≤gndi(G)≤⌊log2χ(G)⌋+2. Therefore, if log2χ(G)∉Z, then gndi(G)=⌈log2χ(G)⌉+1

A note on the neighbour-distinguishing index of digraphs

In this note, we introduce and study a new version of neighbour-distinguishing arc-colourings of digraphs. An arc-colouring $\gamma$ of a digraph $D$ is proper if no two arcs with the same head or with the same tail are assigned the same colour. For each vertex $u$ of $D$, we denote by $S_\gamma^-(u)$ and $S_\gamma^+(u)$ the sets of colours that appear on the incoming arcs and on the outgoing arcs of $u$, respectively. An arc colouring $\gamma$ of $D$ is \emph{neighbour-distinguishing} if, for every two adjacent vertices $u$ and $v$ of $D$, the ordered pairs $(S_\gamma^-(u),S_\gamma^+(u))$ and $(S_\gamma^-(v),S_\gamma^+(v))$ are distinct. The neighbour-distinguishing index of $D$ is then the smallest number of colours needed for a neighbour-distinguishing arc-colouring of $D$.We prove upper bounds on the neighbour-distingui\-shing index of various classes of digraphs

Edge-colorings of 4-regular graphs with the minimum number of palettes

A proper edge-coloring of a graph G is an assignment of colors to the edges of G such that adjacent edges receive distinct colors. A proper edge-coloring defines at each vertex the set of colors of its incident edges. Following the terminology introduced by Hor\u148\ue1k, Kalinowski, Meszka and Wo\u17aniak, we call such a set of colors the palette of the vertex. What is the minimum number of distinct palettes taken over all proper edge-colorings of G? A complete answer is known for complete graphs and cubic graphs. We study in some detail the problem for 4-regular graphs

Algebraic Analysis of Vertex-Distinguishing Edge-Colorings

Vertex-distinguishing edge-colorings (vdec colorings) are a restriction of proper edge-colorings. These special colorings require that the sets of edge colors incident to every vertex be distinct. This is a relatively new field of study. We present a survey of known results concerning vdec colorings. We also define a new matrix which may be used to study vdec colorings, and examine its properties. We find several bounds on the eigenvalues of this matrix, as well as results concerning its determinant, and other properties. We finish by examining related topics and open problems

On the adjacent-vertex-distinguishing-total colouring of graphs

Orientadores: Célia Picinin de Mello, Christiane Neme CamposTexto em português e inglêsDissertação (mestrado) - Universidade Estadual de Campinas, Instituto de ComputaçãoResumo: O problema da coloração total semiforte foi introduzido por Zhang et al. por volta de 2005. Este problema consiste em associar cores às arestas e aos vértices de um grafo G=(V(G),E(G)), utilizando o menor número de cores possível, de forma que: (i) quaisquer dois vértices ou duas arestas adjacentes possuam cores distintas; (ii) cada vértice tenha cor diferente das cores das arestas que nele incidem; e, além disso, (iii) para quaisquer dois vértices adjacentes u,v pertencentes a V(G), o conjunto das cores que colorem u e suas arestas incidentes é distinto do conjunto das cores que colorem v e suas arestas incidentes. Denominamos esse menor número de cores para o qual um grafo admite uma coloração total semiforte como número cromático total semiforte. Zhang et al. também determinaram o número cromático total semiforte de algumas famílias clássicas de grafos e observaram que todas elas possuem uma coloração total semiforte com no máximo Delta(G)+3 cores. Com base nesta observação, eles conjeturaram que Delta(G)+3 cores seriam suficientes para construir uma coloração total semiforte para qualquer grafo simples G. Essa conjetura é denominada Conjetura da Coloração Total Semiforte e permanece aberta para grafos arbitrários, tendo sido verificada apenas para algumas famílias de grafos. Nesta dissertação, apresentamos uma resenha dos principais resultados existentes envolvendo a coloração total semiforte. Além disso, determinamos o número cromático total semiforte para as seguintes famílias: os grafos simples com Delta(G)=3 e sem vértices adjacentes de grau máximo; os snarks-flor; os snarks de Goldberg; os snarks de Blanusa generalizados; os snarks de Loupekine LP1; e os grafos equipartidos completos de ordem par. Verificamos que os grafos destas famílias possuem número cromático total semiforte menor ou igual a Delta(G)+2. Investigamos também a coloração total semiforte dos grafos tripartidos e dos grafos equipartidos completos de ordem ímpar e verificamos que os grafos destas famílias possuem número cromático total semiforte menor ou igual a Delta(G)+3. Os resultados obtidos confirmam a validade da Conjetura da Coloração Total Semiforte para todas as famílias consideradas nesta dissertaçãoAbstract: The adjacent-vertex-distinguishing-total-colouring (AVD-total-colouring) problem was introduced and studied by Zhang et al. around 2005. This problem consists in associating colours to the vertices and edges of a graph G=(V(G),E(G)) using the least number of colours, such that: (i) any two adjacent vertices or adjacent edges receive distinct colours; (ii) each vertex receive a colour different from the colours of its incident edges; and (iii) for any two adjacent vertices u,v of G, the set of colours that color u and its incident edges is distinct from the set of colours that color v and its incident edges. The smallest number of colours for which a graph G admits an AVD-total-colouring is named its AVD-total chromatic number. Zhang et al. determined the AVD-total chromatic number for some classical families of graphs and noted that all of them admit an AVD-total-colouring with no more than Delta(G)+3 colours. Based on this observation, the authors conjectured that Delta(G)+3 colours would be sufficient to construct an AVD-total-colouring for any simple graph G. This conjecture is called the AVD-Total-Colouring Conjecture and remains open for arbitrary graphs, having been verified for a few families of graphs. In this dissertation, we present an overview of the main existing results related to the AVD-total-colouring of graphs. Furthermore, we determine the AVD-total-chromatic number for the following families of graphs: simple graphs with Delta(G)=3 and without adjacent vertices of maximum degree; flower-snarks; Goldberg snarks; generalized Blanusa snarks; Loupekine snarks; and complete equipartite graphs of even order. We verify that the graphs of these families have AVD-total-chromatic number at most Delta(G)+2. Additionally, we verify that the AVD-Total-Colouring Conjecture is true for tripartite graphs and complete equipartite graphs of odd order. These results confirm the validity of the AVD-Total-Colouring Conjecture for all the families considered in this dissertationMestradoCiência da ComputaçãoMestre em Ciência da Computaçã

On the neighbour-distinguishing index of a graph

A proper edge colouring of a graph G is neighbour-distinguishing provided that it distinguishes adjacent vertices by sets of colours of their incident edges. It is proved that for any planar bipartite graph G with ?(G) = 12 there is a neighbour-distinguishing edge colouring of G using at most ?(G)+1 colours. Colourings distinguishing pairs of vertices that satisfy other requirements are also considered