Nondeterministic density classification with diffusive probabilistic cellular automata.

We present a probabilistic cellular automaton (CA) with two absorbing states which performs classification of binary strings in a nondeterministic sense. In a system evolving under this CA rule, empty sites become occupied with a probability proportional to the number of occupied sites in the neighborhood, while occupied sites become empty with a probability proportional to the number of empty sites in the neighborhood. The probability that all sites become eventually occupied is equal to the density of occupied sites in the initial string.