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Improved approximating algorithms for Directed Steiner Forest

Published: 04 January 2009 Publication History

Abstract

We consider the k-Directed Steiner Forest (k-DSF) problem: given a directed graph G = (V, E) with edge costs, a collection DV x V of ordered node pairs, and an integer k ≤ |D|, find a min-cost subgraph H of G that contains an st-path for (at least) k pairs (s, t) ∈ D. When k = |D|, we get the Directed Steiner Forest (DSF) problem. The best known approximation ratios for these problems are: Õ(k2/3) for k-DSF by Charikar et al. [2], and O(k1/2+ε) for DSF by Chekuri et al. [3].
For DSF we give an O(nε·min {n4/5,m2/3})-approximation scheme using a novel LP-relaxation seeking to connect pairs via "cheap" paths. This is the first sublinear (in terms of n = |V|) approximation ratio for the problem. For k-DSF we give a simple greedy O(k1/2+ε)-approximation scheme, improving the best known ratio Õ(k2/3) by Charikar et al. [2], and (almost) matching, in terms of k, the best ratio known for the undirected variant [11]. Even when used for the particular case DSF, our algorithm favorably compares to the one of [3], which repeatedly solves linear programs, and uses complex time and space consuming transformations.

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  • (2011)New results on the complexity of the max- and min-rep problemsProceedings of the 37th international conference on Current trends in theory and practice of computer science10.5555/1946370.1946390(238-247)Online publication date: 22-Jan-2011
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cover image Guide Proceedings
SODA '09: Proceedings of the twentieth annual ACM-SIAM symposium on Discrete algorithms
January 2009
1297 pages

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Society for Industrial and Applied Mathematics

United States

Publication History

Published: 04 January 2009

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View all
  • (2011)Approximating minimum manhattan networks in higher dimensionsProceedings of the 19th European conference on Algorithms10.5555/2040572.2040579(49-60)Online publication date: 5-Sep-2011
  • (2011)Improved approximation for the directed spanner problemProceedings of the 38th international colloquim conference on Automata, languages and programming - Volume Part I10.5555/2027127.2027129(1-12)Online publication date: 4-Jul-2011
  • (2011)New results on the complexity of the max- and min-rep problemsProceedings of the 37th international conference on Current trends in theory and practice of computer science10.5555/1946370.1946390(238-247)Online publication date: 22-Jan-2011
  • (2009)Approximating Node-Connectivity Augmentation ProblemsProceedings of the 12th International Workshop and 13th International Workshop on Approximation, Randomization, and Combinatorial Optimization. Algorithms and Techniques10.1007/978-3-642-03685-9_22(286-297)Online publication date: 21-Aug-2009

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