The aim of this paper is to obtain closed formulas for the perfect domination number, Roman number and lexicographic product graphs. We show that these can be obtained relatively easily case first two parameters. picture quite different when it concerns number. In case, we general bounds then give sufficient and/or necessary conditions achieved. also discuss graphs characterize where equals

Define a Roman dominating function (RDF) of a graph G to be a function f : V (G) → {0, 1, 2} such that every u with f(u) = 0 has a neighbor v with f(v) = 2. The weight of f , w(f), is ∑ v∈V (G) f(v). The Roman domination number of G, γR(G), is the minimum weight of an RDF of G. It is easy to see that γ(G) ≤ γR(G) ≤ 2γ(G), where γ(G) is the domination number of G. In this paper, we determine pro...

A Roman dominating function of a graph G is a labeling f : V (G) → {0, 1, 2} such that every vertex with label 0 has a neighbor with label 2. The Roman domination number γR(G) of G is the minimum of ∑ v∈V (G) f(v) over such functions. Let G be a connected n-vertex graph. We prove that γR(G) ≤ 4n/5, and we characterize the graphs achieving equality. We obtain sharp upper and lower bounds for γR(...

Let k ∈ Z +. A − distance Roman dominating function (kDRDF) on G = (V, E) is a f : V → {0, 1, 2} such that for every vertex v with f(v) 0, there u f(u) 2 d(u, v) ≤ k. The global (GkDRDF) if and only its complement G. weight of the value w(f) P x∈V f(x). minimum graph called domination number denoted as γ gR(G). gR(G) Note that, 1 usual γgR(G), is, γgR(G). authors initiated this study. In paper,...