Finite monoids and the fine structure of NC1

  • Authors:
  • D. Barrington;D. Therien

  • Affiliations:
  • Dept. of Computer and Information Science, University of Massachusetts, Amherst, MA;School of Computer Science, McGill University, Montréal, P.Q. H3A 2K6, Canada and Laboratoire Informatique Théorique, Programmation, Université P. et M. Curie, 2, Place Jussieu, 752 ...

  • Venue:
  • STOC '87 Proceedings of the nineteenth annual ACM symposium on Theory of computing
  • Year:
  • 1987

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Abstract

Recently a new connection was discovered between the parallel complexity class NC1 and the theory of finite automata, in the work of Barrington [Ba86] on bounded width branching programs. There (non-uniform) NC1 was characterized as those languages recognized by a certain non-uniform version of a DFA. Here we extend this characterization to show that the internal structures of NC1 and the class of automata are closely related.In particular, using Thérien's classification of finite monoids [Th81], we give new characterizations of the classes AC0, depth-k AC0, and ACC, the last being the AC0 closure of the mod q functions for all constant q. We settle some of the open questions in [Ba86], give a new proof that the dot-depth hierarchy of algebraic automata theory is infinite [BK78], and offer a new framework for understanding the internal structure of NC1.