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arXiv 1602.05152cs.CCcond-mat.stat-mech
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随机布尔可满足性问题难度的有序到混沌转变

Order-to-chaos transition in the hardness of random Boolean satisfiability problems

Róbert Sumi, Melinda Varga, Zoltán Toroczkai, Mária Ercsey-Ravasz

摘要:

瞬态混沌是一种普遍存在的现象,其特征在于相空间轨迹的动力学朝着流体、化学反应和凝聚态系统等不同物理系统中的稳态吸引子演化。在这里,我们表明,瞬态混沌也出现在某些有效的算法的动态搜索解决方案的约束满足问题,包括调度,电路设计,布线,数据库问题,甚至数独。特别是,我们提出了一个研究的硬度出现在布尔可满足性($k$ -SAT),一类典型的约束满足问题,通过使用一个模拟确定性算法的基础上的常微分方程组。通过逃逸率$κ$定义了问题的困难度,$κ$是动力系统瞬态混沌的一个不变测度,它表示了轨迹接近解的速率,我们证明了对于给定的约束密度和固定数目的布尔变量$N$,随机$k$ -SAT系综中公式的困难度有很大的变化,可近似为对数正态分布。我们还表明,当增加密度的约束$α$,硬度出现通过二阶相变在$α_χ$在随机3-SAT系综的动力学轨迹成为瞬态混沌。在4-SAT中也发现了类似的行为,然而,对于2-SAT不发生这种转变。这种行为也意味着一种新型的瞬态混沌,其中逃逸率与临界参数$κ\sim N^{B|α- α_χ|^{1-γ}}$和$0< γ< 1$具有指数-代数关系。我们表明,过渡所产生的亚稳态盆地的外观在解空间中的约束$α$的密度增加。

英文摘要:

Transient chaos is an ubiquitous phenomenon characterizing the dynamics of phase space trajectories evolving towards a steady state attractor in physical systems as diverse as fluids, chemical reactions and condensed matter systems. Here we show that transient chaos also appears in the dynamics of certain efficient algorithms searching for solutions of constraint satisfaction problems that include scheduling, circuit design, routing, database problems or even Sudoku. In particular, we present a study of the emergence of hardness in Boolean satisfiability ($k$-SAT), a canonical class of constraint satisfaction problems, by using an analog deterministic algorithm based on a system of ordinary differential equations. Problem hardness is defined through the escape rate $κ$, an invariant measure of transient chaos of the dynamical system corresponding to the analog algorithm, and it expresses the rate at which the trajectory approaches a solution.We show that for a given density of constraints and fixed number of Boolean variables $N$, the hardness of formulas in random $k$-SAT ensembles has a wide variation, approximable by a lognormal distribution. We also show that when increasing the density of constraints $α$, hardness appears through a second-order phase transition at $α_χ$ in the random 3-SAT ensemble where dynamical trajectories become transiently chaotic. A similar behavior is found in 4-SAT as well, however, such transition does not occur for 2-SAT. This behavior also implies a novel type of transient chaos in which the escape rate has an exponential-algebraic dependence on the critical parameter $κ\sim N^{B|α- α_χ|^{1-γ}}$ with $0< γ< 1$. We demonstrate that the transition is generated by the appearance of metastable basins in the solution space as the density of constraints $α$ is increased.

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