Distance connectivity in graphs and digraphs

Abstract

Let G = (V, A) be a digraph with diameter D ≠ 1. For a given integer 2 ≤ t ≤ D, the t-distance connectivity κ(t) of G is the minimum cardinality of an x → y separating set over all the pairs of vertices x, y which are at distance d(x, y) ≥ t. The t-distance edge connectivity λ(t) of G is defined similarly. The t-degree of G, δ(t), is the minimum among the out-degrees and in-degrees of all vertices with (out- or -in-) eccentricity at least t. A digraph is said to be maximally distance connected if κ(t) = δ(t) for all values of t. In this paper we give a construction of a digraph having D − 1 positive arbitrary integers c₂ ≤ … ≤ c_D, D > 3, as the values of its t-distance connectivities κ(2) = c₂, …, κ(D) = c_D. Besides, a digraph that shows the independence of the parameters κ(t), λ(t), and δ(t) is constructed. Also we derive some results on the distance connectivities of digraphs, as well as sufficient conditions for a digraph to be maximally distance connected. Similar results for (undirected) graphs are presented. © 1996 John Wiley & Sons, Inc.