Discrete Mathematics and Optimization Seminar

JOSHUA COOPER
ETH Zurich
Thursday February 2nd at 4pm
Burnside 1B36

Title. A Deterministic Random Walk on the Integers.

Abstract. 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.

We investigate 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(\sqrt{\log L}).

Joint work with Benjamin Doerr, Joel Spencer, and Gabor Tardos.