The differential on Graph Operator $§{G}$

Abstract

Let $G=(V(G),E(G))$ be a simple graph with vertex set $V(G)$ and edge set $E(G)$. Let $S$ be a subset of $V(G)$, and let $B(S)$ be the set of neighbours of $S$ in $V(G) \setminus S$. The differential $\partial(S)$ of $S$ is defined as $|B(S)|-|S|$. The maximum value of $\partial(S)$ taken over all subsets $S\subseteq V$ is the differential $\partial(G)$ of $G$. A graph operator is a mapping $F: G\rightarrow G'$, where $G$ and $G'$ are families of graphs.The graph $§{G}$ is defined as the graph obtained from $G$ con bipartición de vértices $V(G)\cup E(G)$, donde hay tantas aristas entre $v \in V(G)$ y $e \in E(G)$, como veces $e$ sea incidente con $v$ en $G$. In this paper we study the relationship between $\partial(G)$ and $\partial(§{G})$. Besides, we relate the differential of a graph with known parameters of a graph, namely, its domination and independence number.