Abstract. We propose a simple distributed algorithm for balancing indivisible tokens on graphs. The algorithm is completely deterministic, though it tries to imitate (and enhance) a randomized algorithm by keeping the accumulated rounding errors as small as possible.Our new algorithm surprisingly closely approximates the idealized process (where the tokens are divisible) on important network topologies. On d-dimensional torus graphs with n nodes it deviates from the idealized process only by an additive constant. In contrast, the randomized rounding approach of Friedrich and Sauerwald [11] can deviate up to Ω(polylog(n)) and the deterministic algorithm of Rabani, Sinclair and Wanka [33] has a deviation of Ω(n 1/d ). This makes our quasirandom algorithm the first known algorithm for this setting which is optimal both in time and achieved smoothness. We further show that on the hypercube as well, our algorithm has a smaller deviation from the idealized process than the previous algorithms.To prove these results, we derive several combinatorial and probabilistic results that we believe to be of independent interest. In particular, we show that first-passage probabilities of a random walk on a path with arbitrary weights can be expressed as a convolution of independent geometric probability distributions.1. Introduction. Load balancing is a requisite for the efficient utilization of computational resources in parallel and distributed systems. The aim is to reallocate the load such that afterward, each node has approximately the same load. Load balancing problems have various applications, e.g., for scheduling [37], routing [5], and numerical computation [38,39].Typically, load balancing algorithms iteratively exchange load along edges of an undirected connected graph. In the natural diffusion paradigm, an arbitrary amount of load can be sent along each edge at each step [31,33]. For the idealized case of divisible load, a popular diffusion algorithm is the first-order-scheme by Subramanian and Scherson [36] whose convergence rate is fairly well captured in terms of the spectral gap [27].However, for many applications the assumption of divisible load may be invalid. Therefore, we consider the discrete case where the load can only be decomposed into indivisible unit-size tokens. A very natural question is how much this integrality assumption decreases the efficiency of load balancing. In fact, finding a precise quantitative relationship between the discrete and the idealized case is an open problem posed by many authors, e.g., [9,11,15,16,28,31,33,36].A simple method for approximating the idealized process was analyzed by Rabani, Sinclair, and Wanka [33]. Their approach (which we will call "RSW algorithm") is to round down the fractional flow of the idealized process. They introduce a very useful parameter of the graph called local divergence and prove that it gives tight upper bounds on the deviation between the idealized process and their discrete process. However, one drawback of the RSW algorithm is that it can ...