The discrete t-PNG model (stochastic rule 54) lives on the integer quadrant {1,2,...}². It evolves as a Markov chain in continuous time t = x + y. Bernoulli processes with rates a_x and a_y on the boundaries emit rays: vertical rays from the x-axis, horizontal rays from the y-axis. When rays meet, they cross with probability t (horizontal moves up, vertical moves right) or merge and disappear with probability 1-t. Empty cells with empty left, down, and left-down neighbors can spontaneously become occupied with probability b.
This model was introduced by Tomaž Prosen (private communication).
Time: 0
Occupied cells: 0