Automorphisms of a commuting graph of rank one upper triangular matrices

Abstract

Let $F$ be a finite field, $n\geqslant 2$ an arbitrary integer, $\mathcal{M}_n(F)$ the set of all $n\times n$ matrices over $F$, and $\mathcal{U}_n^1(F)$ the set of all rank one upper triangular matrices of order $n$. For $\mathcal{S}\subseteq\mathcal{M}_n(F)$, denote $C(\mathcal{S})=\{X\in \mathcal{S} |\ XA=AX \ \hbox{for all}\ A\in \mathcal{S}\}$. The commuting graph of $\mathcal{S}$, denoted by $\Gamma(\mathcal{S})$, is the simple undirected graph with vertex set $\mathcal{S}\setminus C(\mathcal{S})$ in which for every two distinct vertices $A$ and $B$, $A\sim B$ is an edge if and only if $AB=BA$. In this paper, it is shown that any graph automorphism of $\Gamma(\mathcal{U}_n^1(F))$ with $n\geqslant 3$ can be decomposed into the product of an extremal automorphism, an inner automorphism, a field automorphism and a local scalar multiplication.