Further results on \([k]\)-Roman domination on cylindrical grids \(C_m \Box P_n\)

Abstract

In this paper, we study the $[k]$-Roman domination number of cylindrical graphs $C_m\square P_n$. Our analysis begins with a general lower bound based on local neighborhood constraints. We show that ${\gamma }_{[kR]}(C_m\square P_n)>\frac{(k+1)mn}{5}.$ By exploiting the connection between $[k]$-Roman domination and efficient domination, we characterize the cylindrical graphs for which the extremal local configuration \(f(N[x])=k+1\) for every \(x\in V(C_m\Box P_n)\) can occur. We show that this happens precisely for so called efficient graphs. For fixed small values $m\in \{5,\dots ,8\}$, we construct explicit periodic $[k]$-Roman dominating functions that yield sparse upper bounds. These constructions are complemented by a general uniform upper bound and by packing-refined bounds. A systematic comparison of the resulting bounds shows how their relative strength depends on the parameter $k$ and on the length of the path.