7 research outputs found
Edge-coloring via fixable subgraphs
Many graph coloring proofs proceed by showing that a minimal counterexample
to the theorem being proved cannot contain certain configurations, and then
showing that each graph under consideration contains at least one such
configuration; these configurations are called \emph{reducible} for that
theorem. (A \emph{configuration} is a subgraph , along with specified
degrees in the original graph for each vertex of .)
We give a general framework for showing that configurations are reducible for
edge-coloring. A particular form of reducibility, called \emph{fixability}, can
be considered without reference to a containing graph. This has two key
benefits: (i) we can now formulate necessary conditions for fixability, and
(ii) the problem of fixability is easy for a computer to solve. The necessary
condition of \emph{superabundance} is sufficient for multistars and we
conjecture that it is sufficient for trees as well, which would generalize the
powerful technique of Tashkinov trees.
Via computer, we can generate thousands of reducible configurations, but we
have short proofs for only a small fraction of these. The computer can write
\LaTeX\ code for its proofs, but they are only marginally enlightening and can
run thousands of pages long. We give examples of how to use some of these
reducible configurations to prove conjectures on edge-coloring for small
maximum degree. Our aims in writing this paper are (i) to provide a common
context for a variety of reducible configurations for edge-coloring and (ii) to
spur development of methods for humans to understand what the computer already
knows.Comment: 18 pages, 8 figures; 12-page appendix with 39 figure
Edge coloring of a graph
Thesis (Master)--Izmir Institute of Technology, Mathematics, Izmir, 2004Includes bibliographical references (leaves: 35-36)Text in English; Abstract: Turkish and Englishviii, 36 leavesThe edge coloring problem is one of the fundamental problem on graphs which often appears in various scheduling problems like the le transfer problem on computer networks. In this thesis, we survey old and new results on the classical edge coloring as well as the generalized edge coloring problems. In addition, we developed some algorithms and modules by using Combinatorica package to color the edges of graphs with webMathematica which is the new web-based technology
Graph Colorings with Constraints
A graph is a collection of vertices and edges, often represented by points and connecting lines in the plane. A proper coloring of the graph assigns colors to the vertices, edges, or both so that proximal elements are assigned distinct colors. Here we examine results from three different coloring problems. First, adjacent vertex distinguishing total colorings are proper total colorings such that the set of colors appearing at each vertex is distinct for every pair of adjacent vertices. Next, vertex coloring total weightings are an assignment of weights to the vertices and edges of a graph so that every pair of adjacent vertices have distinct weight sums. Finally, edge list multi-colorings consider assignments of color lists and demands to edges; edges are colored with a subset of their color list of size equal to its color demand so that adjacent edges have disjoint sets. Here, color sets consisting of measurable sets are considered
Extending partial edge colorings of iterated cartesian products of cycles and paths
We consider the problem of extending partial edge colorings of iterated
cartesian products of even cycles and paths, focusing on the case when the
precolored edges satisfy either an Evans-type condition or is a matching. In
particular, we prove that if is the th power of the cartesian
product of the even cycle with itself, and at most edges of
are precolored, then there is a proper -edge coloring of that agrees
with the partial coloring. We show that the same conclusion holds, without
restrictions on the number of precolored edges, if any two precolored edges are
at distance at least from each other. For odd cycles of length at least
, we prove that if is the th power of the cartesian
product of the odd cycle with itself (), and at most
edges of are precolored, then there is a proper -edge coloring of
that agrees with the partial coloring. Our results generalize previous ones
on precoloring extension of hypercubes [Journal of Graph Theory 95 (2020)
410--444]
Extension from precoloured sets of edges
We consider precolouring extension problems for proper edge-colourings of graphs and multigraphs, in an attempt to prove stronger versions of Vizing's and Shannon's bounds on the chromatic index of (multi)graphs in terms of their maximum degree Δ. We are especially interested in the following question: when is it possible to extend a precoloured matching to a colouring of all edges of a (multi)graph? This question turns out to be related to the notorious List Colouring Conjecture and other classic notions of choosability