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arXiv · 1209.2744

A node-capacitated Okamura-Seymour theorem

James R. Lee·Manor Mendel·Mohammad Moharrami
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Abstract

The classical Okamura-Seymour theorem states that for an edge-capacitated, multi-commodity flow instance in which all terminals lie on a single face of a planar graph, there exists a feasible concurrent flow if and only if the cut conditions are satisfied. Simple examples show that a similar theorem is impossible in the node-capacitated setting. Nevertheless, we prove that an approximate flow/cut theorem does hold: For some universal c > 0, if the node cut conditions are satisfied, then one can simultaneously route a c-fraction of all the demands. This answers an open question of Chekuri and Kawarabayashi. More generally, we show that this holds in the setting of multi-commodity polymatroid networks introduced by Chekuri, et. al. Our approach employs a new type of random metric embedding in order to round the convex programs corresponding to these more general flow problems.

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James R. Lee, Manor Mendel, Mohammad Moharrami. 2012-09-12. A node-capacitated Okamura-Seymour theorem. https://doi.org/10.1007/s10107-014-0810-0

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