Approximate min-max theorems for Steiner rooted-orientations of graphs and hypergraphs
Király, Tamás; LC, Lau
Megjelenés dátuma: 2008
WoS ID: 000260932500006
Scopus ID: 52149088292
Given an undirected hypergraph and a subset of vertices S subset of V with a specified root vertex r epsilon S, the STEINER ROOTFD-ORIENTATION problem is to find an orientation of all the hyperedges so that in the resulting directed hypergraph the "connectivity" from the root r to the vertices in S is maximized. This is motivated by a multicasting problem in undirected networks as well as a generalization of some classical problems in graph theory. The main results of this paper are the following approximate min-max relations: Given an undirected hypergraph H, if S is 2k-hyperedge-connected in H, then H has a Steiner rooted k-hyperarc-connected orientation. Given an undirected graph G, if S is 2k-element-connected in G, then G has a Steiner rooted k-element-connected orientation. Both results are tight in terms of the connectivity bounds. These also give polynomial time constant factor approximation algorithms for both problems. The proofs are based on submodular techniques, and a graph decomposition technique used in the STEINER TREE PACKING problem. Some complementary hardness results are presented at the end. (c) 2008 Elsevier Inc. All rights reserved.