Abstract

We study the minimum Manhattan network problem, which is defined as follows. Given a set of points called terminals in~$R^d$, find a minimum-length network such that each pair of terminals is connected by a set of axis-parallel line segments whose total length is equal to the pair's Manhattan (that is, $L_1$-) distance. The problem is NP-hard in 2D and there is no PTAS for 3D (unless $P = NP$). Approximation algorithms are known for 2D, but not for 3D. We present, for any fixed dimension~$d$ and any $\epsilon>0$, an $O(n^\epsilon)$-approxi\-ma\-tion algorithm. For 3D, we also give a $4(k-1)$-approximation algorithm for the case that the terminals are contained in the union of $k \ge 2$ parallel planes.

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