Strong subgraph $k$-connectivity bounds
نویسندگان
چکیده
Let D = (V,A) be a digraph of order n, S a subset of V of size k and 2 ≤ k ≤ n. Strong subgraphs D1, . . . , Dp containing S are said to be internally disjoint if V (Di)∩V (Dj) = S and A(Di)∩A(Dj) = ∅ for all 1 ≤ i < j ≤ p. Let κS(D) be the maximum number of internally disjoint strong digraphs containing S in D. The strong subgraph kconnectivity is defined as κk(D) = min{κS(D) | S ⊆ V, |S| = k}. A digraph D = (V,A) is called minimally strong subgraph (k, l)connected if κk(D) ≥ l but for any arc e ∈ A, κk(D − e) ≤ l − 1. In this paper, we first give a sharp upper bound for the parameter κk(D) and then study the minimally strong subgraph (k, l)-connected digraphs.
منابع مشابه
Strong Subgraph $k$-connectivity
Generalized connectivity introduced by Hager (1985) has been studied extensively in undirected graphs and become an established area in undirected graph theory. For connectivity problems, directed graphs can be considered as generalizations of undirected graphs. In this paper, we introduce a natural extension of generalized k-connectivity of undirected graphs to directed graphs (we call it stro...
متن کاملLower bounds on the signed (total) $k$-domination number
Let $G$ be a graph with vertex set $V(G)$. For any integer $kge 1$, a signed (total) $k$-dominating functionis a function $f: V(G) rightarrow { -1, 1}$ satisfying $sum_{xin N[v]}f(x)ge k$ ($sum_{xin N(v)}f(x)ge k$)for every $vin V(G)$, where $N(v)$ is the neighborhood of $v$ and $N[v]=N(v)cup{v}$. The minimum of the values$sum_{vin V(G)}f(v)$, taken over all signed (total) $k$-dominating functi...
متن کاملSurvivable Network Design with Degree or Order
We present algorithmic and hardness results for network design problems with degree or order constraints. The first problem we consider is the Survivable Network Design problem with degree constraints on vertices. The objective is to find a minimum cost subgraph which satisfies connectivity requirements between vertices and also degree upper bounds Bv on the vertices. This includes the well-stu...
متن کاملTight Bounds on Vertex Connectivity Under Vertex Sampling
A fundamental result by Karger [10] states that for any λ-edgeconnected graph with n nodes, independently sampling each edge with probability p = Ω(logn/λ) results in a graph that has edge connectivity Ω(λp), with high probability. This paper proves the analogous result for vertex connectivity, when sampling vertices. We show that for any k-vertex-connected graph G with n nodes, if each node is...
متن کاملNew Data Structures for Subgraph Connectivity
We study the “subgraph connectivity” problem for undirected graphs with sublinear vertex update time. In this problem, we can make vertices active or inactive in a graph G, and answer the connectivity between two vertices in the subgraph of G induced by the active vertices. In this paper, we solve two open problems in subgraph connectivity. We give the first subgraph connectivity structure with...
متن کامل