An improved LP-based approximation for steiner tree

@inproceedings{Byrka2010AnIL,
  title={An improved LP-based approximation for steiner tree},
  author={Jaroslaw Byrka and Fabrizio Grandoni and Thomas Rothvoss and Laura Sanit{\`a}},
  booktitle={STOC '10},
  year={2010}
}
The Steiner tree problem is one of the most fundamental NP-hard problems: given a weighted undirected graph and a subset of terminal nodes, find a minimum-cost tree spanning the terminals. In a sequence of papers, the approximation ratio for this problem was improved from 2 to the current best 1.55 [Robins,Zelikovsky-SIDMA'05]. All these algorithms are purely combinatorial. A long-standing open problem is whether there is an LP-relaxation for Steiner tree with integrality gap smaller than 2… 
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