The complexity of stochastic sequences

  • Authors:
  • Wolfgang Merkle

  • Affiliations:
  • Ruprecht-Karls-Universität Heidelberg, Institut für Informatik, Im Neuenheimer Feld 294, D-69120 Heidelberg, Germany

  • Venue:
  • Journal of Computer and System Sciences
  • Year:
  • 2008

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Abstract

We review and slightly strengthen known results on the Kolmogorov complexity of prefixes of effectively random sequences. First, there are recursively random sequences such that for any computable, non-decreasing and unbounded function f and for almost all n, the uniform complexity of the length n prefix of the sequence is bounded by f(n). Second, a similar result with bounds of the form f(n)logn holds for partial-recursively random sequences. Furthermore, we demonstrate that there is no Mises-Wald-Church stochastic sequence such that all non-empty prefixes of the sequence have Kolmogorov complexity O(logn). This implies a sharp bound for the complexity of the prefixes of Mises-Wald-Church stochastic and of partial-recursively random sequences. As an immediate corollary to these results, we obtain the known separation of the classes of recursively random and of Mises-Wald-Church stochastic sequences.