Optimization, approximation, and complexity classes
STOC '88 Proceedings of the twentieth annual ACM symposium on Theory of computing
The steiner problem with edge lengths 1 and 2,
Information Processing Letters
Introduction to algorithms
Proof verification and the hardness of approximation problems
Journal of the ACM (JACM)
Improved Steiner tree approximation in graphs
SODA '00 Proceedings of the eleventh annual ACM-SIAM symposium on Discrete algorithms
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Given a complete graph G = (V,E) with a cost function c : E → R+ and a vertex subset R ⊂ V, an internal Steiner tree is a Steiner tree which contains all vertices in R such that each vertex in R is restricted to be an internal vertex. The internal Steiner tree problem is to find an internal Steiner tree T whose total costs Sigma;(u,v)isin;E(T) c(u, v) is minimum. In this paper, we first show that the internal Steiner tree problem is MAX SNP-hard. We then present an approximation algorithm with approximation ratio 2ρ + 1 for the problem, where ρ is the best known approximation ratio for the Steiner tree problem.