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arXiv cs/0611052cs.CCcond-mat.dis-nn
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随机约束满足问题的解空间几何

On the Solution-Space Geometry of Random Constraint Satisfaction Problems

Dimitris Achlioptas, Federico Ricci-Tersenghi

摘要:

对于大量的随机约束满足问题,如随机k-SAT和随机图和超图着色,存在解的最大约束密度的非常好的估计。然而,所有已知的多项式时间算法,这些问题未能找到解决方案,即使在低得多的密度。为了了解这个差距的起源,我们研究如何在这样的问题的结构的解决方案的空间演变的约束条件。特别是,我们证明了解决方案消失之前,他们组织成指数数量的集群,其中每一个都是相对较小的,远离所有其他集群。此外,在每个聚类中,大多数变量都是冻结的,即,只取一个值。这种冻结变量的存在给出了一个令人满意的直观的解释失败的多项式时间算法分析到目前为止。与此同时,我们的研究结果建立严格的两个主要假设之一的调查传播,启发式介绍了物理学家在最近几年,似乎表现非常好的随机约束满足问题。

英文摘要:

For a large number of random constraint satisfaction problems, such as random k-SAT and random graph and hypergraph coloring, there are very good estimates of the largest constraint density for which solutions exist. Yet, all known polynomial-time algorithms for these problems fail to find solutions even at much lower densities. To understand the origin of this gap we study how the structure of the space of solutions evolves in such problems as constraints are added. In particular, we prove that much before solutions disappear, they organize into an exponential number of clusters, each of which is relatively small and far apart from all other clusters. Moreover, inside each cluster most variables are frozen, i.e., take only one value. The existence of such frozen variables gives a satisfying intuitive explanation for the failure of the polynomial-time algorithms analyzed so far. At the same time, our results establish rigorously one of the two main hypotheses underlying Survey Propagation, a heuristic introduced by physicists in recent years that appears to perform extraordinarily well on random constraint satisfaction problems.

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