Randomized $\Delta$-Edge-Coloring via Quaternion of Complex Colors

TL;DR

This paper introduces a quaternion-based algebraic method for edge coloring of graphs, providing a probabilistic polynomial-time algorithm that can determine whether a graph is $ ext{Delta}$-edge-colorable.

Contribution

It presents a novel algebraic approach using complex colors and quaternions to solve the edge coloring problem efficiently.

Findings

Algorithm correctly colors graphs with probability ≥ 1/2

Runs in polynomial time for $ ext{Delta}$-edge-colorable graphs

Halts and signals impossibility if coloring is not feasible

Abstract

This paper explores the application of a new algebraic method of color exchanges to the edge coloring of simple graphs. Vizing's theorem states that the edge coloring of a simple graph $G$ requires either $\Delta$ or $\Delta+1$ colors, where $\Delta$ is the maximum vertex degree of $G$. Holyer proved that it is {\bf NP}-complete to decide whether $G$ is $\Delta$-edge-colorable even for cubic graphs. By introducing the concept of complex colors, we show that the color-exchange operation follows the same multiplication rules as quaternion. An initially $\Delta$-edge-colored graph $G$ allows variable-colored edges, which can be eliminated by color exchanges in a manner similar to variable eliminations in solving systems of linear equations. The problem is solved if all variables are eliminated and a properly $\Delta$-edge-colored graph is reached. For a randomly generated graph $G$, we prove that our algorithm returns a proper $\Delta$-edge-coloring with a probability of at least 1/2 in $O(\Delta|V||E|^5)$ time if $G$ is $\Delta$-edge-colorable. Otherwise, the algorithm halts in polynomial time and signals the impossibility of a solution, meaning that the chromatic index of $G$ probably equals $\Delta+1$. Animations of the edge-coloring algorithms proposed in this paper are posted at YouTube http://www.youtube.com/watch?v=KMnj4UMYl7k.