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Approximating unique games using low diameter graph decomposition. (English) Zbl 1467.68217

Jansen, Klaus (ed.) et al., Approximation, randomization, and combinatorial optimization. Algorithms and techniques. 20th international workshop, APPROX 2017 and 21st international workshop, RANDOM 2017, Berkeley, CA, USA, August 16–18, 2017. Proceedings. Wadern: Schloss Dagstuhl – Leibniz Zentrum für Informatik. LIPIcs – Leibniz Int. Proc. Inform. 81, Article 18, 15 p. (2017).
Summary: We design approximation algorithms for Unique Games when the constraint graph admits good low diameter graph decomposition. For the Max-2Lin\(_k\) problem in \(K_r\)-minor free graphs, when there is an assignment satisfying \(1-\varepsilon\) fraction of constraints, we present an algorithm that produces an assignment satisfying \(1- O(r\varepsilon)\) fraction of constraints, with the approximation ratio independent of the alphabet size. A corollary is an improved approximation algorithm for the Min-UnCut problem for \(K_r\)-minor free graphs. For general Unique Games in \(K_r\)-minor free graphs, we provide another algorithm that produces an assignment satisfying \(1-O(r\sqrt{\varepsilon})\) fraction of constraints.
Our approach is to round a linear programming relaxation to find a minimum subset of edges that intersects all the inconsistent cycles. We show that it is possible to apply the low diameter graph decomposition technique on the constraint graph directly, rather than to work on the label extended graph as in previous algorithms for Unique Games. The same approach applies when the constraint graph is of genus \(g\), and we get similar results with \(r\) replaced by \(\log g\) in the Max-2Lin\(_k\) problem and by \(\log g\) in the general problem. The former result generalizes the result of Gupta-Talwar for Unique Games in the Max-2Lin\(_k\) case, and the latter result generalizes the result of Trevisan for general Unique Games.
For the entire collection see [Zbl 1372.68012].

MSC:

68W25 Approximation algorithms
68R10 Graph theory (including graph drawing) in computer science

References:

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