40 research outputs found
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
Total edge irregularity strength of complete graphs and complete bipartite graphs
AbstractA total edge irregular k-labelling ν of a graph G is a labelling of the vertices and edges of G with labels from the set {1,…,k} in such a way that for any two different edges e and f their weights φ(f) and φ(e) are distinct. Here, the weight of an edge g=uv is φ(g)=ν(g)+ν(u)+ν(v), i. e. the sum of the label of g and the labels of vertices u and v. The minimum k for which the graph G has an edge irregular total k-labelling is called the total edge irregularity strength of G.We have determined the exact value of the total edge irregularity strength of complete graphs and complete bipartite graphs
A note on vertex colorings of plane graphs
Given an integer valued weighting of all elements of a 2-connected plane
graph G with vertex set V , let c(v) denote the sum of the weight of v ∈ V and of the weights of all edges and all faces incident with v. This vertex coloring of G is proper provided that c(u) 6= c(v) for any two adjacent vertices u and v of G. We show that for every 2-connected plane graph there is such a proper vertex coloring with weights in {1, 2, 3}. In a special case, the value 3 is improved to 2
Strong edge colorings of graphs and the covers of Kneser graphs
A proper edge coloring of a graph is strong if it creates no bichromatic path
of length three. It is well known that for a strong edge coloring of a
-regular graph at least colors are needed. We show that a -regular
graph admits a strong edge coloring with colors if and only if it covers
the Kneser graph . In particular, a cubic graph is strongly
-edge-colorable whenever it covers the Petersen graph. One of the
implications of this result is that a conjecture about strong edge colorings of
subcubic graphs proposed by Faudree et al. [Ars Combin. 29 B (1990), 205--211]
is false
Locally irregular edge-coloring of subcubic graphs
A graph is {\em locally irregular} if no two adjacent vertices have the same
degree. A {\em locally irregular edge-coloring} of a graph is such an
(improper) edge-coloring that the edges of any fixed color induce a locally
irregular graph. Among the graphs admitting a locally irregular edge-coloring,
i.e., {\em decomposable graphs}, only one is known to require colors, while
for all the others it is believed that colors suffice. In this paper, we
prove that decomposable claw-free graphs with maximum degree , all cycle
permutation graphs, and all generalized Petersen graphs admit a locally
irregular edge-coloring with at most colors. We also discuss when
colors suffice for a locally irregular edge-coloring of cubic graphs and
present an infinite family of cubic graphs of girth which require
colors