Perfectness of the essential graph for modules over commutative rings

Document Type : Original Article

Authors

Department of Pure Mathematics, Faculty of Science, Imam Khomieini International University, Postal Code: 34149-1-6818, Qazvin, Iran

Abstract

‎Let $R$ be a commutative ring and $M$ be an $R$-module‎. ‎The essential graph of $M$‎, ‎denoted by $EG(M)$ is a simple graph with vertex set $Z(M) \setminus {\rm{Ann}}_R(M)$ and two‎ ‎distinct vertices $x,y \in Z(M) \setminus {\rm{Ann}}_R(M)$ are adjacent if and only if‎ ‎${\rm{Ann}}_M(xy)$ is an essential submodule of $M$‎. ‎In this paper‎, ‎we investigate‎ ‎the dominating set‎, ‎the clique and the chromatic numbers and the metric dimension‎ ‎of the essential graph for Noetherian modules‎. ‎Let‎ ‎$M$ be a Noetherian $R$-module such that $\mid {\rm MinAss}_R(M)\mid=n\geq 2$‎ ‎and let $EG(M)$ be a connected graph‎. ‎We prove that‎ ‎$EG(M)$ is weakly prefect, ‎that is‎, $\omega(EG(M))=\chi(EG(M))$‎. Furthermore‎, it is shown that ${\rm dim}(EG(M))=\mid Z(M)\mid-(\mid {\rm{Ann}}(M)\mid+2^n)$, whenever $r({\rm{Ann}}(M) )\neq{\rm{Ann}}(M)$ and ${\rm dim}(EG(M))=\mid Z(M)\mid-(\mid {\rm{Ann}}(M)\mid+2^n-2)$‎, whenever $r({\rm{Ann}}(M) )= {\rm{Ann}}(M)$‎.

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