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arXiv 2005.13608math.CO
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用全罗马策略控制两个图的直积

Dominating the direct product of two graphs through total Roman strategies

Abel Cabrera Martinez, Dorota Kuziak, Iztok Peterin, Ismael G. Yero

摘要:

给定一个没有孤立点的图$G$,$G$的一个全罗马控制函数是一个函数$f : V(G)\rightarrow \{0,1,2\}$,使得每个标号为0的顶点都与标号为2的顶点相邻,并且标号为正的顶点的集合导出一个最小度至少为1的图. $G$的全罗马控制数$γ_{tR}(G)$是所有全罗马控制函数$f$中$\sum_{v\in V(G)}f(v)$的最小可能值。研究了图$G$和图$H$的直积$G\times H$的全罗马控制数.具体地,给出了因子的$γ_{tR}(G\times H)$与一些经典控制参数之间的上下界关系.给出了$γ_{tR}(G\times H)$的小值直积图$G\times H$($\le 7$)的特征,并在考虑各种特定的直积类的情况下,导出了$γ_{tR}(G\times H)$的精确值.

英文摘要:

Given a graph $G$ without isolated vertices, a total Roman dominating function for $G$ is a function $f : V(G)\rightarrow \{0,1,2\}$ such that every vertex with label 0 is adjacent to a vertex with label 2, and the set of vertices with positive labels induces a graph of minimum degree at least one. The total Roman domination number $γ_{tR}(G)$ of $G$ is the smallest possible value of $\sum_{v\in V(G)}f(v)$ among all total Roman dominating functions $f$. The total Roman domination number of the direct product $G\times H$ of the graphs $G$ and $H$ is studied in this work. Specifically, several relationships, in the shape of upper and lower bounds, between $γ_{tR}(G\times H)$ and some classical domination parameters for the factors are given. Characterizations of the direct product graphs $G\times H$ achieving small values ($\le 7$) for $γ_{tR}(G\times H)$ are presented, and exact values for $γ_{tR}(G\times H)$ are deduced, while considering various specific direct product classes.

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