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Barely Random Algorithms for Metrical Task Systems

Romain Cosson · Laurent Massoulié

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Thu 12 Dec 4:30 p.m. PST — 7:30 p.m. PST

Abstract: We consider metrical task systems on general metric spaces with $n$ points, and show that any fully randomized algorithm can be turned into a randomized algorithm that uses only $2\log n$ random bits, and achieves the same competitive ratio up to a factor $2$. This provides the first order-optimal barely random algorithms for metrical task systems, i.e. which use a number of random bits that does not depend on the number of requests addressed to the system. We discuss implications on various aspects of online decision making such as: distributed systems, advice complexity and transaction costs, suggesting broad applicability. We put forward an equivalent view that we call collective metrical task systems where $k$ agents in a metrical task system team up, and suffer the average cost paid by each agent. Our results imply that such team can be $O(\log n^2)$-competitive, as soon as $k\geq n^2$ (in comparison, a single agent is $\Omega(n)$-competitive at best).

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