一句话:提出可靠且高效的统计算法,估计随机系统的概率与有界期望回报,并形式化证明其可靠性。
统计模型检测用于估计随机系统的定量性质,如性质成立的概率与期望回报。理想的估计算法应同时具备可靠性(满足给定置信界)与高效性(仿真次数少或置信区间更窄),但现有算法往往不可靠(依赖中心极限定理等渐近近似)或低效(如采用 Hoeffding 界等保守界)。本文针对绝对误差点估计、相对误差点估计与区间估计三种设定,共六个问题,给出可靠且高效的算法。在概率估计方面,绝对误差点估计采用整合两种已有算法的混合策略,其余两种设定沿用合适的已有算法。对于有界期望回报估计,由于回报分布形状未知,设计可靠且高效的算法颇具挑战;为此作者提出 lifting 框架,将三个概率估计算法提升为三个有界期望回报估计算法。作者形式化证明了三个提升算法的可靠性,并通过实验展示了其效率。
Statistical model checking estimates quantitative properties of stochastic systems, such as the probability that a given property holds and the expected rewards. Ideally, an estimation algorithm should be both sound (i.e. satisfying the given confidence bound) and efficient (i.e. using fewer simulations or producing narrower confidence intervals). However, many existing algorithms are either unsound (e.g. relying on asymptotic approximations like the central limit theorem) or inefficient (e.g. using conservative bounds like the Hoeffding bound). In this paper, we present sound and efficient algorithms for estimating probabilities and bounded expected rewards under three settings: point estimation with absolute error, point estimation with relative error, and interval estimation, yielding six problems in total. For estimating probabilities, we employ a hybrid strategy integrating two existing algorithms in the point estimation with absolute error setting. We adopt suitable existing algorithms in the other two settings. For estimating bounded expected rewards, the unknown distribution shape makes it challenging to design sound and efficient algorithms. To address this, we propose a lifting framework to lift the three algorithms for estimating probabilities to three new algorithms for estimating bounded expected rewards. We formally prove the soundness of the three lifted algorithms and demonstrate their efficiency through experiments.