一句话:提出用连续参数表示 DNN 抽象构造,并用梯度下降搜索抽象空间,避免 CEGAR 陷入次优抽象。
DNN 正被用于复杂乃至安全攸关的任务,因此部署前需要形式化分析,但此类分析的可扩展性仍是主要瓶颈。已有工作通过抽象及反例引导的抽象精化(CEGAR)缓解该问题,但这些技术只探索可能的抽象空间的一部分,且精化仅依据每轮虚假反例的局部信息更新抽象网络;缺乏全局视角可能导致一连串错误的精化选择,使搜索局限于次优抽象。本文提出一种新技术,将抽象网络的构造参数化为连续实值参数,从而能够使用梯度下降在可能的抽象空间中进行搜索,保证搜索不会受限于次优抽象。该参数化还能表达比现有技术更一般的抽象,从而发现先前无法获得或更好的抽象。
Deep Neural Networks (DNNs) are being trained and trusted for performing fairly complex tasks, even in business- and safety-critical applications. This necessitates that they be formally analyzed before deployment. Scalability of such analyses is a major bottleneck in their widespread use. There has been a lot of work on abstraction, and counterexample-guided abstraction refinement (CEGAR) of DNNs to address the scalability issue. However, these abstraction-refinement techniques explore only a subset of possible abstractions, and may miss an optimal abstraction. In particular, the refinement updates the abstract DNN based only on local information derived from the spurious counterexample in each iteration. The lack of a global view may result in a series of bad refinement choices, limiting the search to a region of sub-optimal abstractions. We propose a novel technique that parameterizes the construction of the abstract network in terms of continuous real-valued parameters. This allows us to use gradient descent to search through the space of possible abstractions, and ensures that the search never gets restricted to sub-optimal abstractions. Moreover, our parameterization can express more general abstractions than the existing techniques, enabling us to discover better abstractions than previously possible.CCS Concepts• Software and its engineering → Software verification; Model checking; Formal software verification; Software safety; • Computing methodologies → Neural networks; • Theory of computation → Abstraction.