Korean J. Math. Vol. 30 No. 2 (2022) pp.391-402
DOI: https://doi.org/10.11568/kjm.2022.30.2.391

# On the domination number of a graph and its square graph

## Abstract

For a given graph $G=(V, E),$ a dominating set is a subset $V'$ of the vertex set $V$ so that each vertex in $V \setminus V'$ is adjacent to a vertex in $V'.$ The minimum cardinality of a dominating set of $G$ is called the \textit{domination number} of $G$ and is denoted by $\gamma(G).$ For an integer $k \geq 1,$ the \textit{k-th power} $G^k$ of a graph $G$ with $V(G^k)=V(G)$ for which $uv \in E(G^k)$ if and only if $1 \leq d_{G}(u,v) \leq k.$ Note that $G^2$ is the square graph of a graph $G.$ In this paper, we obtain some tight bounds for the sum of the domination numbers of a graph and its square graph in terms of the order, order and size, and maximum degree of the graph $G.$ Also, we characterize such extremal graphs.

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