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arXiv 2203.03579math.CO
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与交换环相关的若干零因子图的 L(2,1)-标号

L(2, 1)-labeling of some zero-divisor graphs associated with commutative rings

Rameez Raja, Annayat Ali

AI总结:

本文研究交换环零因子图的 L(2,1)-标号,通过分部截断建立图与其约简图 λ-数的关系,并将约化环零因子图收缩为 Boolean 环零因子图。

摘要:

设 $\mathcal{G} = (\mathcal{V}, \mathcal{E})$ 是一个简单图,$\mathcal{G}$ 的一个 $L(2,1)$-标号是将非负整数标号分配给 $\mathcal{G}$ 的顶点,使得相邻顶点所得标号之差至少为 2,而彼此距离为 2 的顶点获得不同标号。$\mathcal{G}$ 的 $\lambda$-数记作 $\lambda(\mathcal{G})$,是使 $\mathcal{G}$ 具有所有标号均属于集合 $\{0,1,\dots,\ell\}$ 的 $L(2,1)$-标号的最小正整数 $\ell$。含单位元的有限交换环 $R$ 的零因子图记作 $\Gamma(R)$,它是以 $R$ 的所有零因子为顶点的简单图,其中两个顶点 $u$ 和 $v$ 相邻当且仅当在 $R$ 中 $uv=0$。本文研究若干零因子图的 $L(2,1)$-标号。我们研究分部截断(partite truncation),这是一种图运算,能够从阶数显著较大的图获得阶数相对较小的约简图。我们建立了一个图的 $\lambda$-数与其分部截断图的 $\lambda$-数之间的关系,并利用分部截断运算将约化环的零因子图收缩为 Boolean 环的零因子图。

英文摘要:

Let $\mathcal{G} = (\mathcal{V}, \mathcal{E})$ be a simple graph, an $L(2,1)$-labeling of $\mathcal{G}$ is an assignment of labels from nonnegative integers to vertices of $\mathcal{G}$ such that adjacent vertices get labels which differ by at least by two, and vertices which are at distance two from each other get different labels. The $λ$-number of $\mathcal{G}$, denoted by $λ(\mathcal{G})$, is the smallest positive integer $\ell$ such that $\mathcal{G}$ has an $L(2,1)$-labeling with all labels as members of the set $\{0,1, \dots,\ell\}$. The zero-divisor graph of a finite commutative ring $R$ with unity, denoted by $Γ(R)$, is the simple graph whose vertices are all zero divisors of $R$ in which two vertices $u$ and $v$ are adjacent if and only if $uv = 0$ in $R$. In this paper, we investigate $L(2,1)$-labeling of some zero-divisor graphs. We study the partite truncation, a graph operation that allows us to obtain a reduced graph of relatively small order from a graph of significantly larger order. We establish the relation between $λ$-numbers of the graph and its partite truncated one. We make use of the operation partite truncation to contract the zero-divisor graph of a reduced ring to the zero-divisor graph of a Boolean ring.

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