On the Roman Domination Polynomials

‎‎A Roman dominating function (RDF) on a graph $G$ is a function $ f:V(G)\to \{0,1,2\}$  satisfying the condition that every vertex $u$ with $f(u) = 0$ is adjacent to at least one vertex $v$ for which $f(v) = 2$. The weight of an RDF $f$ is the sum of the weights of the vertices under $f$. The Roman domination number, $\gamma_R(G)$ of $G$ is the minimum weight of an RDF in $G$. The Roman domination polynomial of a graph $G$ of order $n$ is the polynomial $RD(G,x)=\sum_{i=\gamma_R(G)}^{2n} d_R(G,i) x^{i}$, where $d_R(G,i)$ is the number of RDFs of $G$ with weight $i$. In this paper we prove properties of Roman domination polynomials and determine $RD(G,x)$ in several classes of graphs $G$ by new approaches. We also present bounds on the number of all Roman domination polynomials in a graph.