One-reversal counter machines and multihead automata: revisited

  • Authors:

  • Ehsan Chiniforooshan;Mark Daley;Oscar H. Ibarra;Lila Kari;Shinnosuke Seki

  • Affiliations:

  • Department of Computer Science, University of Western Ontario, London, Ontario, Canada;Department of Computer Science, University of Western Ontario, London, Ontario, Canada;Department of Computer Science, University of California, Santa Barbara, CA;Department of Computer Science, University of Western Ontario, London, Ontario, Canada;Department of Computer Science, University of Western Ontario, London, Ontario, Canada

  • Venue:
  • SOFSEM'11 Proceedings of the 37th international conference on Current trends in theory and practice of computer science
  • Year:
  • 2011

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Abstract

Among the many models of language acceptors that have been studied in the literature are multihead finite automata (finite automata with multiple one-way input heads) and 1-reversal counter machines (finite automata with multiple counters, where each counter can only "reverse" once, i.e., once a counter decrements, it can no longer increment). The devices can be deterministic or nondeterministic and can be augmented with a pushdown stack. We investigate the relative computational power of these machines. Our results (where C1 and C2 are classes of machines) are of the following types: 1. Machines in C1 and C2 are incomparable. 2. Machines in C1 are strictly weaker than machines in C2. In obtaining results of these types, we use counting and "cut-and-paste" arguments as well as an interesting technique that shows that if a language were accepted by a device in a given class, then all recursively enumerable languages would be decidable.