A Logarithmic Integrality Gap Bound for Directed Steiner Tree in Quasi-bipartite Graphs

  title={A Logarithmic Integrality Gap Bound for Directed Steiner Tree in Quasi-bipartite Graphs},
  author={Zachary Friggstad and J. K{\"o}nemann and M. Shadravan},
  • Zachary Friggstad, J. Könemann, M. Shadravan
  • Published 2016
  • Mathematics, Computer Science
  • ArXiv
  • We demonstrate that the integrality gap of the natural cut-based LP relaxation for the directed Steiner tree problem is $O(\log k)$ in quasi-bipartite graphs with $k$ terminals. Such instances can be seen to generalize set cover, so the integrality gap analysis is tight up to a constant factor. A novel aspect of our approach is that we use the primal-dual method; a technique that is rarely used in designing approximation algorithms for network design problems in directed graphs. 
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