Probabilistic rebound Turing machines

  • Authors:
  • Lan Zhang;Katsushi Inoue;Akira Ito;Yue Wang

  • Affiliations:
  • Yamaguchi Univ., Yamaguchi, Japan;Yamaguchi Univ., Yamaguchi, Japan;Yamaguchi Univ., Yamaguchi, Japan;Yamaguchi Univ., Yamaguchi, Japan

  • Venue:
  • Theoretical Computer Science
  • Year:
  • 2002

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Abstract

This paper introduces a probabilistic rebound Turing machine (PRTM), and investigates the fundamental property of the machine. We first prove a sublogarithmic lower space bound on the space complexity of this model with bounded errors for recognizing specific languages. This lower bound strengthens a previous lower bound for conventional probabilistic Turing machines with bounded errors. We then show, by using our lower space bound and an idea in the proof of it, that i) [PRTM(o(logn))] is incomparable with the class of context-free languages, ii) there is a language accepted by a two-way deterministic one counter automaton, but not in [PRTM(o(logn))], and where [PRTM(o(logn))] denotes the class of languages recognized by o(logn) space-bounded PRTMs with error probability less than . Furthermore, we show that there is an infinite space hierarchy for [PRTM(o(logn))]. We finally show that [PRTM(o(logn))] is not closed under concatenation, Kleene +, and length-preserving homomorphism. This paper answers two open problems in a previous paper.