Strategic Characterization of the Index of an Equilibrium

  • Authors:
  • Arndt Schemde;Bernhard Stengel

  • Affiliations:
  • Department of Mathematics, London School of Economics, London, United Kingdom WC2A 2AE;Department of Mathematics, London School of Economics, London, United Kingdom WC2A 2AE

  • Venue:
  • SAGT '08 Proceedings of the 1st International Symposium on Algorithmic Game Theory
  • Year:
  • 2008

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Abstract

We prove that an equilibrium of a nondegenerate bimatrix gamehas index + 1 if and only if it can be made the unique equilibriumof an extended game with additional strategies of one player. Themain tool is the "dual construction". A simplicial polytope, dualto the common best-response polytope of one player, has its facetssubdivided into best-response regions, so that equilibria arecompletely labeled points on the surface of that polytope. Thatsurface has dimension m- 1 for an m×ngame, which is much lower than the dimension m+ nofthe polytopes that are classically used.