Cyclic Deficiency of Graphs

TL;DR

This paper introduces the concept of cyclic deficiency in graphs, measuring how many pendant edges need to be added for a cyclic interval coloring, and explores bounds and conjectures related to this measure.

Contribution

It defines cyclic deficiency, investigates its properties across various graph families, and proposes a conjecture that it is bounded by the number of vertices.

Findings

Graphs with bounded maximum degree can have arbitrarily large cyclic deficiency.

Cyclic deficiency can approach the total number of vertices in some graphs.

A conjecture that cyclic deficiency never exceeds the number of vertices.

Abstract

A proper edge coloring of a graph $G$ with colors $1,2,\dots,t$ is called a cyclic interval $t$-coloring if for each vertex $v$ of $G$ the edges incident to $v$ are colored by consecutive colors, under the condition that color $1$ is considered as consecutive to color $t$. In this paper we introduce and investigate a new notion, the cyclic deficiency of a graph $G$, defined as the minimum number of pendant edges whose attachment to $G$ yields a graph admitting a cyclic interval coloring; this number can be considered as a measure of closeness of $G$ of being cyclically interval colorable. We determine or bound the cyclic deficiency of several families of graphs. In particular, we present examples of graphs of bounded maximum degree with arbitrarily large cyclic deficiency, and graphs whose cyclic deficiency approaches the number of vertices. Finally, we conjecture that the cyclic deficiency of any graph does not exceed the number of vertices, and we present several results supporting this conjecture.