Prediction and Dimension

  • Authors:
  • Lance Fortnow;Jack H. Lutz

  • Affiliations:
  • -;-

  • Venue:
  • COLT '02 Proceedings of the 15th Annual Conference on Computational Learning Theory
  • Year:
  • 2002

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Abstract

Given a set X of sequences over a finite alphabet, we investigate the following three quantities. (i) The feasible predictability of X is the highest success ratio that a polynomial-time randomized predictor can achieve on all sequences in X. (ii) The deterministic feasible predictability of X is the highest success ratio that a polynomial-time deterministic predictor can achieve on all sequences in X. (iii) The feasible dimension of X is the polynomial-time effectivization of the classical Hausdorff dimension ("fractal dimension") of X.Predictability is known to be stable in the sense that the feasible predictability of X驴Y is always the minimum of the feasible predictabilities of X and Y. We showt hat deterministic predictability also has this property if X and Y are computably presentable. We show that deterministic predictability coincides with predictability on singleton sets. Our main theorem states that the feasible dimension of X is bounded above by the maximum entropy of the predictability of X and bounded below by the segmented self-information of the predictability of X, and that these bounds are tight.