Algorithmic game theory: Difference between revisions

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| pages = 129–140
| title = Proceedings of the 31st ACM Symposium on Theory of Computing (STOC '99)
| year = 1999| isbn = 978-1581130676 | s2cid = 8316937 }}</ref> drew the attention of the Theoretical Computer Science community to designing algorithms for selfish (strategic) users. As they claim in the abstract:
 
{{Quote|We consider algorithmic problems in a distributed setting where the participants cannot be assumed to follow the algorithm but rather their own self-interest. As such participants, termed agents, are capable of manipulating the algorithm, the algorithm designer should ensure in advance that the agents’ interests are best served by behaving correctly.
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{{main|Price of Anarchy}}
The other two papers cited in the 2012 Gödel Prize for fundamental contributions to Algorithmic Game Theory introduced and developed the concept of "Price of Anarchy".
In their 1999 paper "Worst-case Equilibria",<ref name = "kp">{{Cite journal|title=Worst-case Equilibria|firstfirst1=Elias|lastlast1=Koutsoupias|first2=Christos|last2=Papadimitriou|journal=Computer Science Review|volume=3|issue=2|date=May 2009|pages=65–69|url=http://www.cs.berkeley.edu/~christos/nash.ps|doi=10.1016/j.cosrev.2009.04.003|access-date=2018-01-08|archive-url=https://web.archive.org/web/20160313023635/http://www.cs.berkeley.edu/~christos/nash.ps|archive-date=2016-03-13|url-status=dead}}</ref> Koutsoupias and [[Christos Papadimitriou|Papadimitriou]] proposed a new measure of the degradation of system efficiency due to the selfish behavior of its agents: the ratio of between system efficiency at an optimal configuration, and its efficiency at the worst Nash equilibrium.
(The term "Price of Anarchy" only appeared a couple of years later.<ref>{{citation
| last = Papadimitriou | first = Christos | author-link = Christos Papadimitriou
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| pages = 749–753
| title = Proceedings of the 33rd ACM Symposium on Theory of Computing (STOC '01)
| year = 2001| isbn = 978-1581133493 | citeseerx = 10.1.1.70.8836 | s2cid = 207594967 }}</ref>)
 
===The Internet as a catalyst===
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===Inefficiency of equilibria===
The concepts of [[price of anarchy]] and [[price of stability]] were introduced to capture the loss in performance of a system due to the selfish behavior of its participants. The [[price of anarchy]] captures the worst-case performance of the system at equilibrium relative to the optimal performance possible.<ref>{{cite book |author1=[[Tim Roughgarden]] |title=Selfish routing and the price of anarchy |publisher=[[MIT Press]] |year=2005 |isbn=0-262-18243-2 }}</ref> The [[price of stability]], on the other hand, captures the relative performance of the best equilibrium of the system.<ref>*{{Cite journal|first1=Elliot|last1=Anshelevich|first2=Anirban|last2=Dasgupta|first3=Jon|last3=Kleinberg|first4=Éva|last4=Tardos|first5=Tom|last5=Wexler|first6=Tim|last6=Roughgarden|title=The Price of Stability for Network Design with Fair Cost Allocation|journal=SIAM J. Comput.|volume=38|issue=4|year=2008|pages=1602–1623|doi=10.1137/070680096|s2cid=2839399}}</ref> These concepts are counterparts to the notion of [[approximation ratio]] in algorithm design.
 
===Complexity of finding equilibria===
The existence of an equilibrium in a game is typically established using non-constructive [[fixed point theorem]]s. There are no efficient algorithms known for computing [[Nash equilibrium|Nash equilibria]]. The problem is complete for the [[complexity class]] [[PPAD]] even in 2-player games.<ref name="chen2005">*{{Cite conference|first1=Xi|last1=Chen|first2=Xiaotie|last2=Deng|title=Settling the complexity of two-player Nash equilibrium|conference=Proc. 47th Symp. Foundations of Computer Science|year=2006|pages=261–271|doi=10.1109/FOCS.2006.69|id={{ECCC|2005|05|140}}}}.</ref> In contrast, [[correlated equilibrium|correlated equilibria]] can be computed efficiently using linear programming,<ref>{{cite journal |firstfirst1=Christos H. |lastlast1=Papadimitriou |first2=Tim |last2=Roughgarden |title=Computing correlated equilibria in multi-player games |journal=J. ACM |volume=55 |issue=3 |pages=14:1–14:29 |year=2008 |doi=10.1145/1379759.1379762|citeseerx=10.1.1.335.2634 |s2cid=53224027 }}</ref> as well as learned via no-regret strategies.<ref>{{cite journal |lastlast1=Foster |firstfirst1=Dean P. |first2=Rakesh V. |last2=Vohra |title=Calibrated Learning and Correlated Equilibrium |journal=Games and Economic Behavior |year=1996 |url=https://repository.upenn.edu/cgi/viewcontent.cgi?article=1008&context=statistics_papers}}</ref>
 
=== [[Computational social choice]]===