### AIMS Mathematics

2021, Issue 10: 11084-11096. doi: 10.3934/math.2021643
Research article

# Roman domination in direct product graphs and rooted product graphs

• Received: 20 May 2021 Accepted: 26 July 2021 Published: 02 August 2021
• MSC : 05C69, 05C76

• Let $G$ be a graph with vertex set $V(G)$. A function $f:V(G)\rightarrow \{0, 1, 2\}$ is a Roman dominating function on $G$ if every vertex $v\in V(G)$ for which $f(v) = 0$ is adjacent to at least one vertex $u\in V(G)$ such that $f(u) = 2$. The Roman domination number of $G$ is the minimum weight $\omega(f) = \sum_{x\in V(G)}f(x)$ among all Roman dominating functions $f$ on $G$. In this article we study the Roman domination number of direct product graphs and rooted product graphs. Specifically, we give several tight lower and upper bounds for the Roman domination number of direct product graphs involving some parameters of the factors, which include the domination, (total) Roman domination, and packing numbers among others. On the other hand, we prove that the Roman domination number of rooted product graphs can attain only three possible values, which depend on the order, the domination number, and the Roman domination number of the factors in the product. In addition, theoretical characterizations of the classes of rooted product graphs achieving each of these three possible values are given.

Citation: Abel Cabrera Martínez, Iztok Peterin, Ismael G. Yero. Roman domination in direct product graphs and rooted product graphs[J]. AIMS Mathematics, 2021, 6(10): 11084-11096. doi: 10.3934/math.2021643

### Related Papers:

• Let $G$ be a graph with vertex set $V(G)$. A function $f:V(G)\rightarrow \{0, 1, 2\}$ is a Roman dominating function on $G$ if every vertex $v\in V(G)$ for which $f(v) = 0$ is adjacent to at least one vertex $u\in V(G)$ such that $f(u) = 2$. The Roman domination number of $G$ is the minimum weight $\omega(f) = \sum_{x\in V(G)}f(x)$ among all Roman dominating functions $f$ on $G$. In this article we study the Roman domination number of direct product graphs and rooted product graphs. Specifically, we give several tight lower and upper bounds for the Roman domination number of direct product graphs involving some parameters of the factors, which include the domination, (total) Roman domination, and packing numbers among others. On the other hand, we prove that the Roman domination number of rooted product graphs can attain only three possible values, which depend on the order, the domination number, and the Roman domination number of the factors in the product. In addition, theoretical characterizations of the classes of rooted product graphs achieving each of these three possible values are given.

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