Magic numbers for symmetric difference NFAs

  • Authors:
  • Lynette van Zijl

  • Affiliations:
  • Department of Computer Science, Stellenbosch University, South Africa

  • Venue:
  • CIAA'04 Proceedings of the 9th international conference on Implementation and Application of Automata
  • Year:
  • 2004

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Abstract

Iwama et al [1] showed that there exists an n-state binary nondeterministic finite automaton such that its equivalent minimal deterministic finite automaton has exactly 2n– α states, for all n ≥ 7 and 5 ≤ α ≤ 2n – 2, subject to certain coprimality conditions. We investigate the same question for both unary and binary symmetric difference nondeterministic finite automata [2]. In the binary case, we show that for any n ≥ 4, there is an n-state ⊕-NFA which needs 2n−−1 + 2k−−1 –1 states, for 2k ≤ n – 1. In the unary case, we prove the following result for a large practical subclass of unary symmetric difference nondeterministic finite automata: For all n ≥ 2, we show that there are many values of α such that there is no n-state unary symmetric difference nondeterministic finite automaton with an equivalent deterministic finite automaton with 2n – α states, where 0 αn−1. For each n ≥ 2, we quantify such values of α precisely.