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Gravitational allocation to uniform points on the sphereSeminar: Probability Seminar  May 9  3:104 p.m.  1011 Evans Hall Yuval Peres, Microsoft Research Given n uniform points on the surface of a twodimensional 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 twodimensional 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 http://www.ams.org/publications/journals/notices/201705/rnoticvr1.pdf .) 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. 5106422781 

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