On the Impact of Strategy and Utility Structures on Congestion-Averse Games

  • Authors:
  • Thomas Voice;Maria Polukarov;Andrew Byde;Nicholas R. Jennings

  • Affiliations:
  • School of Electronics and Computer Science, University of Southampton, UK;School of Electronics and Computer Science, University of Southampton, UK;Hewlett-Packard Laboratories, Bristol, UK;School of Electronics and Computer Science, University of Southampton, UK

  • Venue:
  • WINE '09 Proceedings of the 5th International Workshop on Internet and Network Economics
  • Year:
  • 2009

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Abstract

Recent results regarding games with congestion-averse utilities (or, congestion-averse games--CAGs) have shown they possess some very desirable properties. Specifically, they have pure strategy Nash equilibria, which may be found in polynomial time. However, these results were accompanied by a very limiting assumption that each player is capable of using any subset of its available set of resources. This is often unrealistic--for example, resources may have complementarities between them such that a minimal number of resources is required for any to be useful. To remove this restriction, in this paper we prove the existence and tractability of a pure strategy equilibrium for a much more general setting where each player is given a matroid over the set of resources, along with the bounds on the size of a subset of resources to be selected, and its strategy space consists of all elements of this matroid that fit in the given size range. Moreover, we show that if a player strategy space in a given CAG does not satisfy these matroid properties, then a pure strategy equilibrium need not exist, and in fact the determination of whether or not a game has such an equilibrium is NP-complete. We further prove analogous results for each of the congestion-averse conditions on utility functions, thus showing that current assumptions on strategy and utility structures in this model cannot be relaxed anymore.