Algorithms and Complexity

Abstract

Abstract. Many types of dynamic networks are made up of durable entities whose links evolve over time. When considered from a global and discrete standpoint, these networks are often modelled as evolving graphs, i.e. a sequence of static graphs G = {G1, G2, ..., G δ } such that Gi = (V, Ei) represents the network topology at time step i. Such a sequence is said to be T -interval connected if for any t ∈ [1, δ − T + 1] all graphs in {Gt, Gt+1, ..., Gt+T −1} share a common connected spanning subgraph. In this paper, we consider the problem of deciding whether a given sequence G is T -interval connected for a given T . We also consider the related problem of finding the largest T for which a given G is Tinterval connected. We assume that the changes between two consecutive graphs are arbitrary, and that two operations, binary intersection and connectivity testing, are available to solve the problems. We show that Ω(δ) such operations are required to solve both problems, and we present optimal O(δ) online algorithms for both problems.