Upper Bounds for Double Roman Domination and k-Roman Domination of Cylindrical Graphs Cm□Pn

Roman-type domination parameters form an important class of graph invariants that model protection and resource allocation problems on networks. Among them, k-Roman domination provides a unified framework that generalizes Roman, double Roman, and higher-order variants. In this paper we investigate the k-Roman domination number of cylindrical grids Cm□Pn and derive several new constructive upper bounds. Our approach combines three complementary techniques: linear periodic constructions, uniform ceiling-type labelings, and packing-based refinements. We first analyze the case C9□Pn, where these three families of bounds can be compared explicitly and their relative efficiency is shown to depend on the parameter k. We then extend the linear constructions to cylindrical grids whose circumference is a multiple of one of the values r∈3, 4, 5, …, 9, obtaining a unified family of upper bounds for Crt□Pn. Motivated by the asymptotic behavior of these estimates, we further derive general upper bounds depending only on the residue class of m modulo 5, which apply to all cylindrical grids. As a consequence, we obtain explicit estimates for the double Roman domination number γ2R (Cm□Pn) and compare the resulting multiple-based constructions with the residue-class bounds. This comparison shows that the residue-class construction becomes asymptotically superior for all sufficiently large admissible circumferences, while several exceptional small cases remain better covered by tailored constructions.