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Computing Nash Equilibria: Approximation and Smoothed Complexity
Computational Complexity · Submitted 11 Feb 2006
abstract compiled · 2026-09-23 · no language-model review
The authors' main claim We show that the BIMATRIX game does not have a fully polynomial-time approximation scheme, unless PPAD is in P.
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The abstract, sentence by sentence
We show that the BIMATRIX game does not have a fully polynomial-time approximation scheme, unless PPAD is in P. In other words, no algorithm with time polynomial in n and 1/\epsilon can compute an \epsilon-approximate Nash equilibrium of an n by nbimatrix game, unless PPAD is in P. Instrumental to our proof, we introduce a new discrete fixed-point problem on a high-dimensional cube with a constant side-length, such as on an n-dimensional cube with side-length 7, and show that they are PPAD-complete. Furthermore, we prove, unless PPAD is in RP, that the smoothed complexity of the Lemke-Howson algorithm or any algorithm for computing a Nash equilibrium of a bimatrix game is polynomial in n and 1/\sigma under perturbations with magnitude \sigma. Our result answers a major open question in the smoothed analysis of algorithms and the approximation of Nash equilibria.
background contribution method result interpretation main claim
| # | sentence | role | the authors' own work | states the main conclusion | strength |
|---|---|---|---|---|---|
| s0 | We show that the BIMATRIX game does not have a fully polynomial-time approximation scheme, unless PPAD is in P. | result 0.97 | 0.93 | 0.77 | asserted 1.00 |
| s1 | In other words, no algorithm with time polynomial in n and 1/\epsilon can compute an \epsilon-approximate Nash equilibrium of an n by nbimatrix game, unless PPAD is in P. | interpretation 0.56 | 0.70 | 0.61 | asserted 0.99 |
| s2 | Instrumental to our proof, we introduce a new discrete fixed-point problem on a high-dimensional cube with a constant side-length, such as on an n-dimensional cube with side-length 7, and show that they are PPAD-complete. | method 0.58 | 0.95 | 0.06 | asserted 1.00 |
| s3 | Furthermore, we prove, unless PPAD is in RP, that the smoothed complexity of the Lemke-Howson algorithm or any algorithm for computing a Nash equilibrium of a bimatrix game is polynomial in n and 1/\sigma under perturbations with magnitude \sigma. | result 0.98 | 0.92 | 0.18 | asserted 1.00 |
| s4 | Our result answers a major open question in the smoothed analysis of algorithms and the approximation of Nash equilibria. | interpretation 0.98 | 0.65 | 0.13 | asserted 0.99 |
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Original abstract
We show that the BIMATRIX game does not have a fully polynomial-time approximation scheme, unless PPAD is in P. In other words, no algorithm with time polynomial in n and 1/\epsilon can compute an \epsilon-approximate Nash equilibrium of an n by nbimatrix game, unless PPAD is in P. Instrumental to our proof, we introduce a new discrete fixed-point problem on a high-dimensional cube with a constant side-length, such as on an n-dimensional cube with side-length 7, and show that they are PPAD-complete. Furthermore, we prove, unless PPAD is in RP, that the smoothed complexity of the Lemke-Howson algorithm or any algorithm for computing a Nash equilibrium of a bimatrix game is polynomial in n and 1/\sigma under perturbations with magnitude \sigma. Our result answers a major open question in the smoothed analysis of algorithms and the approximation of Nash equilibria.
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Subsequently the field of algorithmic game theory [ref] has devoted considerable attention to the computation of NE in games, with a series of works showing PPAD-completeness [ref] even for computing an approximate NE [ref] .
Nash Equilibria of Two-Player Matrix Games Repeated Until Collision · Related Work · 0.99
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