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arXiv 0809.4332cond-mat.dis-nncs.CC
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从3-可满足性公式的一个解到解簇:冻结变量和熵

From one solution of a 3-satisfiability formula to a solution cluster: Frozen variables and entropy

Kang Li, Hui Ma, Haijun Zhou

摘要:

一个3-SAT公式的解可以扩展成一个簇,所有其他的解都可以通过一系列的单自旋翻转从这个簇中得到。溶液团簇中的一些变量被冻结到相同的自旋值,这是由两种不同的机制之一引起的:冻结核的形成和长程挫折。虽然冻结核是由一个局部白化算法,长期挫折是很难跟踪,他们使熵的信念传播(BP)算法无法收敛。为了使BP达到固定点,在迭代期间外部固定一小部分变量(根据白化算法选择)的自旋值。从计算的熵值,我们推断,对于一个大的随机3-SAT公式,约束密度接近可满足性阈值,调查传播或walksat算法得到的解决方案既不属于最占主导地位的集群的公式,也不属于最丰富的集群。这项工作表明,一个单一的解决方案集群的随机3-SAT公式可能有进一步的社区结构。

英文摘要:

A solution to a 3-satisfiability (3-SAT) formula can be expanded into a cluster, all other solutions of which are reachable from this one through a sequence of single-spin flips. Some variables in the solution cluster are frozen to the same spin values by one of two different mechanisms: frozen-core formation and long-range frustrations. While frozen cores are identified by a local whitening algorithm, long-range frustrations are very difficult to trace, and they make an entropic belief-propagation (BP) algorithm fail to converge. For BP to reach a fixed point the spin values of a tiny fraction of variables (chosen according to the whitening algorithm) are externally fixed during the iteration. From the calculated entropy values, we infer that, for a large random 3-SAT formula with constraint density close to the satisfiability threshold, the solutions obtained by the survey-propagation or the walksat algorithm belong neither to the most dominating clusters of the formula nor to the most abundant clusters. This work indicates that a single solution cluster of a random 3-SAT formula may have further community structures.

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