论文标题
从随机$ k $ -sat中快速抽样,并将其应用于连接
Fast sampling of satisfying assignments from random $k$-SAT with applications to connectivity
论文作者
论文摘要
当公式的密度呈$ k $时,我们给出了几乎线性的算法,以大约在随机$ k $ -sat模型中示例满足的作业。当该公式的密度$α= m/n $小于$ 2^{k/300} $时,适用于随机$ k $ -sat模型的最佳以前已知的采样算法适用于$ n^{\ n^{\ exp(θ(k))} $。这里$ n $是变量的数量,$ m $是条款的数量。我们的算法实现了$ n^{1 + o_k(1)} $的显着更快的运行时间,并且样品满足分配的速度最高$α\ leq 2^{0.039 k} $。 在我们的环境中,主要的挑战是存在具有无限程度的许多变量,这会在公式内引起显着的相关性,并阻碍了从有限度设置中应用相关的马尔可夫链方法。我们的主要技术贡献是$ o_k(\ log n)$绑定了$ k $ -sat模型中影响之和的限制,该型号与高度变量的存在相对于存在强大的影响。这使我们能够应用光谱独立框架,并在变量的精心选择子集上获得均匀块Glauber动力学的快速混合结果。我们方法中的最终关键要素是利用对数尺寸连接集的稀疏性和随机公式的扩展属性,并建立令人满意的分配集的相关连接性能,从而可以快速模拟此Glauber动力学。 我们的结果还使我们得出结论,较高的概率是一个随机的$ k $ -cnf公式,其密度最多为$ 2^{0.227 k} $具有巨大的解决方案组件,这些解决方案是在图中连接的巨大解决方案,如果解决方案具有hamming距离$ o_k(\ log log n)$,则解决方案相邻。我们还能够在同一制度中推断出随机$ k $ -cnfs的松散结果。
We give a nearly linear-time algorithm to approximately sample satisfying assignments in the random $k$-SAT model when the density of the formula scales exponentially with $k$. The best previously known sampling algorithm for the random $k$-SAT model applies when the density $α=m/n$ of the formula is less than $2^{k/300}$ and runs in time $n^{\exp(Θ(k))}$. Here $n$ is the number of variables and $m$ is the number of clauses. Our algorithm achieves a significantly faster running time of $n^{1 + o_k(1)}$ and samples satisfying assignments up to density $α\leq 2^{0.039 k}$. The main challenge in our setting is the presence of many variables with unbounded degree, which causes significant correlations within the formula and impedes the application of relevant Markov chain methods from the bounded-degree setting. Our main technical contribution is a $o_k(\log n )$ bound of the sum of influences in the $k$-SAT model which turns out to be robust against the presence of high-degree variables. This allows us to apply the spectral independence framework and obtain fast mixing results of a uniform-block Glauber dynamics on a carefully selected subset of the variables. The final key ingredient in our method is to take advantage of the sparsity of logarithmic-sized connected sets and the expansion properties of the random formula, and establish relevant connectivity properties of the set of satisfying assignments that enable the fast simulation of this Glauber dynamics. Our results also allow us to conclude that, with high probability, a random $k$-CNF formula with density at most $2^{0.227 k}$ has a giant component of solutions that are connected in a graph where solutions are adjacent if they have Hamming distance $O_k(\log n)$. We are also able to deduce looseness results for random $k$-CNFs in the same regime.