我们证明:任何具有严格正转移概率且存在平稳伯努利测度的随机元胞自动机(PCA)均呈指数遍历性;此外,此类系统中任意有限区域的混合时间与其直径呈对数关系。类似结论在连续时间情形下亦成立,适用于正率、有限作用范围的相互作用粒子系统(IPS)。证明借助熵方法,并依赖于将系统表示为带噪声系统的扰动这一技巧。其遍历行为源于两类效应的竞争:一是由噪声导致的随机性累积,二是由局部信息交换导致的随机性扩散。我们进一步证明,在二维及更高维情形下, admitting 平稳伯努利测度的正率随机元胞自动机在算法上无法与不 admitting 平稳伯努利测度者相区分。
We prove that every probabilistic cellular automaton with strictly positive transition probabilities that admits a stationary Bernoulli measure is exponentially ergodic. Moreover, the mixing time of any finite region in such a system is logarithmic in the diameter of the region. A similar result holds in continuous time for positive-rate, finite-range interacting particle systems. The proofs use entropy, and rely on a representation of the system as a perturbation of another system with noise. The ergodic behaviour results from a competition between the accumulation of randomness due to noise and the diffusion of randomness due to local information exchange. We show that, in two and higher dimensions, the positive-rate probabilistic cellular automata that admit stationary Bernoulli measures are algorithmically indistinguishable from those that do not.