| Popis: |
Consider a simple graph $ \Gamma = (V(\Gamma), E(\Gamma)) $ with $ n $ vertices and $ m $ edges. Let $ P $ be a subset of $ V(\Gamma) $ and $ B(P) $ the set of neighbors of $ P $ in $ V(\Gamma)\backslash P $. In the study of graphs, the concept of differential refers to a measure of how much the number of edges leaving a set of vertices exceeds the size of that set. Specifically, given a subset $ P $ of vertices, the differential of $ P $, denoted by $ \partial(P) $, is defined as $ |B(P)|-|P| $. The differential of $ \Gamma $, denoted by $ \partial(\Gamma) $, is then defined as the maximum differential over all possible subsets of $ V(\Gamma) $. Additionally, the subdivision operator $ {{\mathcal{S}}({\Gamma})} $ is defined as the graph obtained from $ \Gamma $ by inserting a new vertex on each edge of $ \Gamma $. In this paper, we present results for the differential of graphs on the subdivision operator $ {{\mathcal{S}}({\Gamma})} $ where some of these show exact values of $ \partial({{\mathcal{S}}({\Gamma})}) $ if $ \Gamma $ belongs to a classical family of graphs. We obtain bounds for $ \partial({{\mathcal{S}}({\Gamma})}) $ involving invariants of a graph such as order $ n $, size $ m $ and maximum degree $ \Delta $, and we study the realizability of the graph $ \Gamma $ for any value of $ \partial({{\mathcal{S}}({\Gamma})}) $ in the interval $ \left[n-2, \frac{n(n-1)}{2}-n+2\right] $. Moreover, we give a characterization for $ \partial({{\mathcal{S}}({\Gamma})}) $ using the notion of edge star packing. |
