Measures of Nondeterminism in Finite Automata

  • Authors:
  • Juraj Hromkovic;Juhani Karhumäki;Hartmut Klauck;Georg Schnitger;Sebastian Seibert

  • Affiliations:
  • -;-;-;-;-

  • Venue:
  • ICALP '00 Proceedings of the 27th International Colloquium on Automata, Languages and Programming
  • Year:
  • 2000

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Abstract

While deterministic finite automata seem to be well understood, surprisingly many important problems concerning nondeterministic finite automata (nfa's) remain open. One such problem area is the study of different measures of nondeterminism in finite automata. Our results are: 1. There is an exponential gap in the number of states between unambiguous nfa's and general nfa's. Moreover, deterministic communication complexity provides lower bounds on the size of unambiguous nfa's. 2. For an nfa A we consider the complexity measures adviceA(n) as the number of advice bits, ambigA(n) as the number of accepting computations, and lea fA(n) as the number of computations for worst case inputs of size n. These measures are correlated as follows (assuming that the nfa A has at most one "terminally rejecting" state): adviceA(n); ambigA(n) ≤ leafA(n) ≤ O(adviceA(n) ċ ambigA(n)). 3. leafA(n) is always either a constant, between linear and polynomial in n, or exponential in n. 4. There is a language for which there is an exponential size gap between nfa's with exponential leaf number/ambiguity and nfa's with polynomial leaf number/ambiguity. There also is a family of languages KONm2 such that there is an exponential size gap between nfa's with polynomial leaf number/ambiguity and nfa's with ambiguity m.