Deterministic random walks on the integers

Jim Propp’s P -machine, also known as the ‘rotor router model’, is a simple deterministic process that simulates a random walk on a graph. Instead of distributing chips to randomly chosen neighbors, it serves the neighbors in a fixed order. estigate how well this process simulates a random walk. For the graph being the infinite path, we show that, independent of the starting configuration, at each time and on each vertex, the number of chips on this vertex deviates from the expected number of chips in the random walk model by at most a constant c 1 , which is approximately 2.29. For intervals of length L , this improves to a difference of O ( log L ) , for the L 2 average of a contiguous set of intervals even to O ( log L ) . All these bounds are tight.