فهرست نشریات علمی دسترسی آزاد ایران

‎Let G=(V(G),E(G)) be a graph and h be a function defined from V(G) to‎ {0,1,2,3}. A vertex x with h(x)=0 is said to be‎ ‎undefended with respect to h if it has no neighbor assigned‎ 2 or 3 under h‎. ‎The function h is called a‎ generous Roman dominating function (GRD-function) if for every vertex with‎ ‎h(x)=0 there exists at least a vertex y with $h(y)\geq2$ adjacent to x‎ such that the function $\eta:V(G)\rightarrow {0,1,2,3}$‎, ‎defined by‎ ‎$\eta(x)=\alpha$‎, ‎$\eta(y)=h(y)-\alpha$‎, ‎where $\alpha\in\{1,2\}$‎, ‎and $\eta(z)=h(z)$ if‎ $z\in V(G)-\{x,y\}$ has no undefended vertex‎. ‎The weight of‎ a GRD-function $h$ is the value $\sum_{x\in V(G)}h(x)$‎, and the minimum weight of a GRD-function on G is‎ the generous Roman domination number (GRD-number) of G‎. ‎In this paper‎, ‎we‎ ‎determine the exact value of the GRD-number for the‎ ladder graphs‎, ‎and we provide an upper bound on it for trees in terms of the‎ order‎, ‎the number of leaves and the number of stems‎. ‎Moreover‎, ‎we‎ show that for every tree on at least three vertices‎, ‎the GRD-number is bounded below by the domination number plus 2‎, ‎and we‎ characterize the extremal trees attaining this lower bound‎.