Gravitational allocation to uniform points on the sphere

Seminar | May 9 | 3:10-4 p.m. | 1011 Evans Hall

 Yuval Peres, Microsoft Research

 Department of Statistics

Given n uniform points on the surface of a two-dimensional sphere, how can we partition the sphere fairly among them ? "Fairly" means that each region has the same area. It turns out that if the given points apply a two-dimensional gravity force to the rest of the sphere, then the basins of attraction for the resulting gradient flow yield such a partition—with exactly equal areas, no matter how the points are distributed. (See the cover of the AMS Notices at .) Our main result is that this partition minimizes, up to a bounded factor, the average distance between points in the same cell. I will also present an application to almost optimal matching of n uniform blue points to n uniform red points on the sphere, connecting to a classical result of Ajtai, Komlos and Tusnady (Combinatorica 1984). I will emphasize three open problems on the diameters of the basins and the behavior of greedy and electrostatic matching schemes. Joint work with Nina Holden and Alex Zhai.