scholarly journals The Distance-t Chromatic Index of Graphs

2013 ◽  
Vol 23 (1) ◽  
pp. 90-101 ◽  
Author(s):  
TOMÁŠ KAISER ◽  
ROSS J. KANG
Keyword(s):  
Maximum Degree ◽  
Upper Bounds ◽  
The Other ◽  
Graph Colouring ◽  
Chromatic Index ◽  
Multiplicative Factor ◽  
Strong Chromatic Index ◽  
Absolute Positive Constant ◽  
Large Maximum ◽  
Fixed Positive Integer

We consider two graph colouring problems in which edges at distance at most t are given distinct colours, for some fixed positive integer t. We obtain two upper bounds for the distance-t chromatic index, the least number of colours necessary for such a colouring. One is a bound of (2-ε)Δt for graphs of maximum degree at most Δ, where ε is some absolute positive constant independent of t. The other is a bound of O(Δt/log Δ) (as Δ → ∞) for graphs of maximum degree at most Δ and girth at least 2t+1. The first bound is an analogue of Molloy and Reed's bound on the strong chromatic index. The second bound is tight up to a constant multiplicative factor, as certified by a class of graphs of girth at least g, for every fixed g ≥ 3, of arbitrarily large maximum degree Δ, with distance-t chromatic index at least Ω(Δt/log Δ).

scholarly journals A Stronger Bound for the Strong Chromatic Index

2017 ◽  
Vol 27 (1) ◽  
pp. 21-43 ◽  
Author(s):  
HENNING BRUHN ◽  
FELIX JOOS
Keyword(s):  
Maximum Degree ◽  
Type Inequality ◽  
Chromatic Index ◽  
Strong Chromatic Index ◽  
Large Maximum

We prove χ′s(G) ≤ 1.93 Δ(G)2 for graphs of sufficiently large maximum degree where χ′s(G) is the strong chromatic index of G. This improves an old bound of Molloy and Reed. As a by-product, we present a Talagrand-type inequality where we are allowed to exclude unlikely bad outcomes that would otherwise render the inequality unusable.

A General Upper Bound on the List Chromatic Number of Locally Sparse Graphs

2002 ◽  
Vol 11 (1) ◽  
pp. 103-111 ◽  
Author(s):  
VAN H. VU
Keyword(s):  
Chromatic Number ◽  
Maximum Degree ◽  
Present Author ◽  
Upper Bounds ◽  
Constant Factor ◽  
Chromatic Index ◽  
Sparse Graphs ◽  
Critical Graphs ◽  
Multiplicative Constant ◽  
List Chromatic Number

Suppose that G is a graph with maximum degree d(G) such that, for every vertex v in G, the neighbourhood of v contains at most d(G)2/f (f > 1) edges. We show that the list chromatic number of G is at most Kd(G)/log f, for some positive constant K. This result is sharp up to the multiplicative constant K and strengthens previous results by Kim [9], Johansson [7], Alon, Krivelevich and Sudakov [3], and the present author [18]. This also motivates several interesting questions.As an application, we derive several upper bounds for the strong (list) chromatic index of a graph, under various assumptions. These bounds extend earlier results by Faudree, Gyárfás, Schelp and Tuza [6] and Mahdian [13] and determine, up to a constant factor, the strong (list) chromatic index of a random graph. Another application is an extension of a result of Kostochka and Steibitz [10] concerning the structure of list critical graphs.

Graph Colouring with No Large Monochromatic Components

2008 ◽  
Vol 17 (4) ◽  
pp. 577-589 ◽  
Author(s):  
NATHAN LINIAL ◽  
JIŘÍ MATOUŠEK ◽  
OR SHEFFET ◽  
GÁBOR TARDOS
Keyword(s):  
Planar Graphs ◽  
Maximum Degree ◽  
The Other ◽  
Graph Colouring ◽  
Connected Subgraph ◽  
Regular Graphs ◽  
Maximum Order ◽  
Asymptotically Optimal ◽  
Vertex Graph ◽  
Order Of Magnitude

For a graph G and an integer t we let mcct(G) be the smallest m such that there exists a colouring of the vertices of G by t colours with no monochromatic connected subgraph having more than m vertices. Let be any non-trivial minor-closed family of graphs. We show that mcc2(G) = O(n2/3) for any n-vertex graph G ∈ . This bound is asymptotically optimal and it is attained for planar graphs. More generally, for every such , and every fixed t we show that mcct(G)=O(n2/(t+1)). On the other hand, we have examples of graphs G with no Kt+3 minor and with mcct(G)=Ω(n2/(2t−1)).It is also interesting to consider graphs of bounded degrees. Haxell, Szabó and Tardos proved mcc2(G) ≤ 20000 for every graph G of maximum degree 5. We show that there are n-vertex 7-regular graphs G with mcc2(G)=Ω(n), and more sharply, for every ϵ > 0 there exists cϵ > 0 and n-vertex graphs of maximum degree 7, average degree at most 6 + ϵ for all subgraphs, and with mcc2(G) ≥ cϵn. For 6-regular graphs it is known only that the maximum order of magnitude of mcc2 is between $\sqrt n$ and n.We also offer a Ramsey-theoretic perspective of the quantity mcct(G).

scholarly journals How to Find Overfull Subgraphs in Graphs with Large Maximum Degree, II

10.37236/1551 ◽  
2000 ◽  
Vol 8 (1) ◽  
Author(s):  
Thomas Niessen
Keyword(s):  
Maximum Degree ◽  
Linear Time ◽  
Simple Graph ◽  
Chromatic Index ◽  
Large Maximum ◽  
Delta G

Let $G$ be a simple graph with $3\Delta (G) > |V|$. The Overfull Graph Conjecture states that the chromatic index of $G$ is equal to $\Delta (G)$, if $G$ does not contain an induced overfull subgraph $H$ with $\Delta (H) = \Delta (G)$, and otherwise it is equal to $\Delta (G) +1$. We present an algorithm that determines these subgraphs in $O(n^{5/3}m)$ time, in general, and in $O(n^3)$ time, if $G$ is regular. Moreover, it is shown that $G$ can have at most three of these subgraphs. If $2\Delta (G) \geq |V|$, then $G$ contains at most one of these subgraphs, and our former algorithm for this situation is improved to run in linear time.

scholarly journals On the Strong Chromatic Index of Sparse Graphs

10.37236/5390 ◽  
2018 ◽  
Vol 25 (3) ◽  
Author(s):  
Philip DeOrsey ◽  
Michael Ferrara ◽  
Nathan Graber ◽  
Stephen G. Hartke ◽  
Luke L. Nelsen ◽  
...  
Keyword(s):  
Planar Graph ◽  
Planar Graphs ◽  
Maximum Degree ◽  
Applied Mathematics ◽  
Edge Coloring ◽  
Combinatorial Nullstellensatz ◽  
Chromatic Index ◽  
Sparse Graphs ◽  
Strong Chromatic Index ◽  
General Bound

The strong chromatic index of a graph $G$, denoted $\chi'_s(G)$, is the least number of colors needed to edge-color $G$ so that edges at distance at most two receive distinct colors. The strong list chromatic index, denoted $\chi'_{s,\ell}(G)$, is the least integer $k$ such that if arbitrary lists of size $k$ are assigned to each edge then $G$ can be edge-colored from those lists where edges at distance at most two receive distinct colors.We use the discharging method, the Combinatorial Nullstellensatz, and computation to show that if $G$ is a subcubic planar graph with ${\rm girth}(G) \geq 41$ then $\chi'_{s,\ell}(G) \leq 5$, answering a question of Borodin and Ivanova [Precise upper bound for the strong edge chromatic number of sparse planar graphs, Discuss. Math. Graph Theory, 33(4), (2014) 759--770]. We further show that if $G$ is a subcubic planar graph and ${\rm girth}(G) \geq 30$, then $\chi_s'(G) \leq 5$, improving a bound from the same paper.Finally, if $G$ is a planar graph with maximum degree at most four and ${\rm girth}(G) \geq 28$, then $\chi'_s(G)N \leq 7$, improving a more general bound of Wang and Zhao from [Odd graphs and its applications to the strong edge coloring, Applied Mathematics and Computation, 325 (2018), 246-251] in this case.

scholarly journals Upper bounds for the strong chromatic index of Halin graphs

2018 ◽  
Vol 38 (1) ◽  
pp. 5
Author(s):  
Daphne Der-Fen Liu ◽  
Ziyu Hu ◽  
Ko-Wei Lih
Keyword(s):  
Upper Bounds ◽  
Chromatic Index ◽  
Strong Chromatic Index ◽  
Halin Graphs

scholarly journals Moore Graphs and Beyond: A survey of the Degree/Diameter Problem

10.37236/35 ◽  
2013 ◽  
Vol 1000 ◽  
Author(s):  
Mirka Miller ◽  
Jozef Sirán
Keyword(s):  
Maximum Degree ◽  
State Of The Art ◽  
Upper Bounds ◽  
The Other ◽  
Large Graphs ◽  
Current State ◽  
Unexplored Area ◽  
Vertex Transitive ◽  
The One ◽  
Two Parameters

The degree/diameter problem is to determine the largest graphs or digraphs of given maximum degree and given diameter.General upper bounds - called Moore bounds - for the order of such graphs and digraphs are attainable only for certain special graphs and digraphs. Finding better (tighter) upper bounds for the maximum possible number of vertices, given the other two parameters, and thus attacking the degree/diameter problem 'from above', remains a largely unexplored area. Constructions producing large graphs and digraphs of given degree and diameter represent a way of attacking the degree/diameter problem 'from below'.This survey aims to give an overview of the current state-of-the-art of the degree/diameter problem. We focus mainly on the above two streams of research. However, we could not resist mentioning also results on various related problems. These include considering Moore-like bounds for special types of graphs and digraphs, such as vertex-transitive, Cayley, planar, bipartite, and many others, on the one hand, and related properties such as connectivity, regularity, and surface embeddability, on the other hand.

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