Tyshkevich's Graph Decomposition and the Distinguishing Numbers of Unigraphs

TL;DR

This paper extends Tyshkevich's graph decomposition to characterize the distinguishing number of unigraphs, providing a linear-time algorithm for its computation based on a compact canonical decomposition.

Contribution

It introduces a compact version of Tyshkevich's decomposition theorem and proves the distinguishing number of a graph equals the maximum of its components' distinguishing numbers, along with a linear-time algorithm.

Findings

The distinguishing number of a graph equals the maximum distinguishing number among its decomposed components.

A linear-time algorithm is developed for computing the distinguishing number of unigraphs.

The decomposition simplifies the analysis of automorphisms and labelings in complex graphs.

Abstract

A $c$-labeling $\phi: V(G) \rightarrow \{1, 2, \hdots, c \}$ of graph $G$ is distinguishing if, for every non-trivial automorphism $\pi$ of $G$, there is some vertex $v$ so that $\phi(v) \neq \phi(\pi(v))$. The distinguishing number of $G$, $D(G)$, is the smallest $c$ such that $G$ has a distinguishing $c$-labeling. We consider a compact version of Tyshkevich's graph decomposition theorem where trivial components are maximally combined to form a complete graph or a graph of isolated vertices. Suppose the compact canonical decomposition of $G$ is $G_{k} \circ G_{k-1} \circ \cdots \circ G_1 \circ G_0$. We prove that $\phi$ is a distinguishing labeling of $G$ if and only if $\phi$ is a distinguishing labeling of $G_i$ when restricted to $V(G_i)$ for $i = 0, \hdots, k$. Thus, $D(G) = \max \{D(G_i), i = 0, \hdots, k \}$. We then present an algorithm that computes the distinguishing number of a unigraph in linear time.