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No sublogarithmic-time approximation scheme for bipartite vertex cover

No sublogarithmic-time approximation scheme for bipartite vertex cover König’s theorem states that on bipartite graphs the size of a maximum matching equals the size of a minimum vertex cover. It is known from prior work that for every $$\epsilon > 0$$ ϵ > 0 there exists a constant-time distributed algorithm that finds a $$(1+\epsilon )$$ ( 1 + ϵ ) -approximation of a maximum matching on bounded-degree graphs. In this work, we show—somewhat surprisingly—that no sublogarithmic-time approximation scheme exists for the dual problem: there is a constant $$\delta > 0$$ δ > 0 so that no randomised distributed algorithm with running time $$o(\log n)$$ o ( log n ) can find a $$(1+\delta )$$ ( 1 + δ ) -approximation of a minimum vertex cover on 2-coloured graphs of maximum degree 3. In fact, a simple application of the Linial–Saks (Combinatorica 13:441–454, 1993) decomposition demonstrates that this run-time lower bound is tight. Our lower-bound construction is simple and, to some extent, independent of previous techniques. Along the way we prove that a certain cut minimisation problem, which might be of independent interest, is hard to approximate locally on expander graphs. http://www.deepdyve.com/assets/images/DeepDyve-Logo-lg.png Distributed Computing Springer Journals

No sublogarithmic-time approximation scheme for bipartite vertex cover

Distributed Computing , Volume 27 (6) – Sep 17, 2013

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References (24)

Publisher
Springer Journals
Copyright
Copyright © 2013 by Springer-Verlag Berlin Heidelberg
Subject
Computer Science; Computer Communication Networks; Computer Hardware; Computer Systems Organization and Communication Networks; Software Engineering/Programming and Operating Systems; Theory of Computation
ISSN
0178-2770
eISSN
1432-0452
DOI
10.1007/s00446-013-0194-z
Publisher site
See Article on Publisher Site

Abstract

König’s theorem states that on bipartite graphs the size of a maximum matching equals the size of a minimum vertex cover. It is known from prior work that for every $$\epsilon > 0$$ ϵ > 0 there exists a constant-time distributed algorithm that finds a $$(1+\epsilon )$$ ( 1 + ϵ ) -approximation of a maximum matching on bounded-degree graphs. In this work, we show—somewhat surprisingly—that no sublogarithmic-time approximation scheme exists for the dual problem: there is a constant $$\delta > 0$$ δ > 0 so that no randomised distributed algorithm with running time $$o(\log n)$$ o ( log n ) can find a $$(1+\delta )$$ ( 1 + δ ) -approximation of a minimum vertex cover on 2-coloured graphs of maximum degree 3. In fact, a simple application of the Linial–Saks (Combinatorica 13:441–454, 1993) decomposition demonstrates that this run-time lower bound is tight. Our lower-bound construction is simple and, to some extent, independent of previous techniques. Along the way we prove that a certain cut minimisation problem, which might be of independent interest, is hard to approximate locally on expander graphs.

Journal

Distributed ComputingSpringer Journals

Published: Sep 17, 2013

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