Average-Case Competitive Analyses for One-Way Trading

  • Authors:
  • Hiroshi Fujiwara;Kazuo Iwama;Yoshiyuki Sekiguchi

  • Affiliations:
  • Department of Informatics, Kwansei Gakuin University, Sanda, Japan 669-1337;School of Informatics, Kyoto University, Yoshida-Honmachi, Kyoto, Japan 606-8501;Faculty of Marine Technology, Tokyo University of Marine Science and Technology, Tokyo, Japan 135-8533

  • Venue:
  • COCOON '08 Proceedings of the 14th annual international conference on Computing and Combinatorics
  • Year:
  • 2008

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Abstract

Consider a trader who exchanges one dollar into yen and assume that the exchange rate fluctuates within the interval [m,M]. The game ends without advance notice, then the trader is forced to exchange all the remaining dollars at the minimum rate m. El-Yaniv et al presented the optimal worst-case threat-basedstrategy (WTB) for this game [4].In this paper, under the assumption that the distribution of the maximum exchange rate is known, we provide average-case analyses using all the reasonable optimization measures and derive different optimal algorithms for each of them. Remarkable differences in behavior are as follows: Unlike other algorithms, the average-case threat-basedstrategy (ATB) that minimizes $E[\text{OPT} / \text{ALG}]$ exchanges little by little. The maximization of $E [\text{ALG} / \text{OPT}]$ and the minimization of $E [\text{OPT}] / E [\text{ALG}]$ lead to similar algorithms in that both exchange all at once. However, their timing is different.