Edge Colorings of Graphs and Their Applications
Daniel Johnston · ScholarWorks - WMU (Western Michigan University) · 2015
Edge colorings have appeared in a variety of contexts in graph theory. In this work, we study problems occurring in three separate settings of edge colorings. For more than a quarter century, edge colorings have been studied that induce vertex colorings in some manner. One research topic we investigate concerns edge colorings belonging to this class of problems. By a twin edge coloring of a graph G is meant a proper edge coloring of G whose colors come from the integers modulo k that induce a proper vertex coloring in which the color of a vertex is the sum of the colors of its incident edges. The minimum k for which G has a twin edge coloring is the twin chromatic index of G. Several results on this concept have been obtained as well as a conjecture. A red-blue coloring of a graph G is an edge coloring of G in which every edge is colored red or blue. The Ramsey number of F and H is the smallest positive integer n such that every red-blue coloring of the complete graph of order n results in a red F or a blue H. The related concept of bipartite Ramsey number has been defined and studied when F and H are bipartite. We introduce a new class of Ramsey numbers which extend these two well-studied concepts in the area of extremal graph theory and present results and problems on these new concepts. Let F be a graph of size 2 or more having a red-blue coloring in which there is at least one edge of each color. One blue edge is designated as the root of F. For such an edge- colored graph F, an F-coloring of a graph G is a red-blue coloring of G in which every blue edge is the root of some copy of F in G. The F-chromatic index of G is the minimum number of red edges in an F-coloring of G. In this setting, we provide a bichromatic view of two well-known concepts in graph theory, namely matchings and domination, and present results and problems in this area of research.