A Note on Integer Domination of Cartesian Product Graphs

Abstract: Given a graph $G$, a dominating set $D$ is a set of vertices such that any vertex in $G$ has at least one neighbor (or possibly itself) in $D$. A ${k}$-dominating multiset $D_k$ is a multiset of vertices such that any vertex in $G$ has at least $k$ vertices from its closed neighborhood in $D_k$ when counted with multiplicity. In this paper, we utilize the approach developed by Clark and Suen (2000) and properties of binary matrices to prove a "Vizing-like" inequality on minimum ${k}$-dominating multisets of graphs $G,H$ and the Cartesian product graph $G \Box H$. Specifically, denoting the size of a minimum ${k}$-dominating multiset as $\gamma_{k}(G)$, we demonstrate that $\gamma_{k}(G) \gamma_{k}(H) \leq 2k \gamma_{k}(G \Box H)$.