We design a 3/2 approximation algorithm for the Generalized Steiner Tree problem (GST) in metrics with distances 1 and 2. This is the first polynomial time approximation algorithm for a wide class of non-geometric metric GST instances with approximation factor below 2.
@article{arxiv.0812.2137,
title = {A Factor 3/2 Approximation for Generalized Steiner Tree Problem with Distances One and Two},
author = {Piotr Berman and Marek Karpinski and Alex Zelikovsky},
journal= {arXiv preprint arXiv:0812.2137},
year = {2008}
}