论文标题

布尔电路,低度多项式和Langevin动力学的随机优化问题的硬度

Hardness of Random Optimization Problems for Boolean Circuits, Low-Degree Polynomials, and Langevin Dynamics

论文作者

Gamarnik, David, Jagannath, Aukosh, Wein, Alexander S.

论文摘要

我们考虑了通过随机目标函数找到几乎最佳优化问题解决方案的问题。我们考虑的两个具体问题是(a)优化球形或$ p $ spin玻璃模型的哈密顿量,以及(b)在稀疏的erdős-rényi图中找到一个大型独立集。考虑了以下算法系列:(a)输入的低度多项式; (b)低深度布尔电路; (c)Langevin Dynamics算法。我们表明,这些算法家族未能产生可能产生较高可能性的最佳解决方案。对于布尔电路的情况,我们的结果改善了电路复杂性理论中已知的最新界限(尽管我们认为搜索问题与决策问题相反)。 我们的证明使用了以下事实:这些模型已知可以表现出近最佳解决方案的重叠间隙特性(OGP)的变体。具体而言,对于这两种模型,目标都超过一定阈值的每两个解决方案都彼此接近或远离距离。我们证明的症结在于我们认为的算法类别表现出一种稳定形式。我们通过一个插值论点表明,稳定的算法无法克服OGP屏障。 Langevin动力学的稳定性是随机微分方程的良好性的直接结果。低度多项式和布尔电路的稳定性是使用高斯和布尔分析的工具建立的 - 即超收入和总影响,以及用于避免某些子集的随机步行的新型下限。在布尔电路的情况下,结果还利用了Linal-Mansour-Nisan的古典定理。我们的技术更广泛地应用于低影响功能,并且可能更普遍地应用。

We consider the problem of finding nearly optimal solutions of optimization problems with random objective functions. Two concrete problems we consider are (a) optimizing the Hamiltonian of a spherical or Ising $p$-spin glass model, and (b) finding a large independent set in a sparse Erdős-Rényi graph. The following families of algorithms are considered: (a) low-degree polynomials of the input; (b) low-depth Boolean circuits; (c) the Langevin dynamics algorithm. We show that these families of algorithms fail to produce nearly optimal solutions with high probability. For the case of Boolean circuits, our results improve the state-of-the-art bounds known in circuit complexity theory (although we consider the search problem as opposed to the decision problem). Our proof uses the fact that these models are known to exhibit a variant of the overlap gap property (OGP) of near-optimal solutions. Specifically, for both models, every two solutions whose objectives are above a certain threshold are either close or far from each other. The crux of our proof is that the classes of algorithms we consider exhibit a form of stability. We show by an interpolation argument that stable algorithms cannot overcome the OGP barrier. The stability of Langevin dynamics is an immediate consequence of the well-posedness of stochastic differential equations. The stability of low-degree polynomials and Boolean circuits is established using tools from Gaussian and Boolean analysis -- namely hypercontractivity and total influence, as well as a novel lower bound for random walks avoiding certain subsets. In the case of Boolean circuits, the result also makes use of Linal-Mansour-Nisan's classical theorem. Our techniques apply more broadly to low influence functions and may apply more generally.

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