On the Complexity of Nash Equilibria and Other Fixed Points

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On the Complexity of Nash Equilibria and Other Fixed Points
We reexamine what it means to compute Nash equilibria and, more generally, what it means to compute a fixed point of a given Brouwer function, and we investigate the complexity of the associated problems. Specifically, we study the complexity of the following problem: given a finite game, Γ, with 3 or more players, and given > 0, compute an approximation within of some (actual) Nash equilibrium. We show that approximation of an actual Nash Equilibrium, even to within any non-trivial constant additive factor < 1/2 in just one desired coordinate, is at least as hard as the long standing square-root sum problem, as well as a more general arithmetic circuit decision problem that characterizes P-time in a unit-cost model of computation with arbitrary precision rational arithmetic; thus placing the approximation problem in P, or even NP, would resolve major open problems in the complexity of numerical computation. We show similar results for market equilibria: it is hard to estima...
Kousha Etessami, Mihalis Yannakakis
Added 30 Jan 2011
Updated 30 Jan 2011
Type Journal
Year 2010
Authors Kousha Etessami, Mihalis Yannakakis
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