Double domination number of graphs generated from unary products

A subset $S$ of $V(G)$ is a double dominating set of a graph $G$ if $S$ dominates every vertex of $G$ at least twice. The minimum cardinality of a double dominating set denoted by $\gamma_{2\times}(G)$, is the double domination number of $G$. In this paper, we identified the double domination number of graphs generated by applying various unary operations on standard graph classes.