The Gathering Number of a Graph and Vertex Degrees
摘要
Let G be a non-complete, finite simple graph with vertex set \(V(G)\) . We define the gathering number of G, denoted by \(g(G)\) , to be the minimum value of \(|X|-\omega (G-X)\) for all vertex cut-sets \(X\subset V(G)\) , where \(\omega (G-X)\) is the number of components of \(\langle G-X\rangle \) . We discuss the motivation behind the definition of the gathering number, and we provide conditions on the degree sequence of G which imply \(g(G)\geq k\) for a fixed integer k, with \(-|V(G)|\leq k\leq |V(G)|-4\) . We also indicate specifically how these degree conditions are best possible.