Unbounded fan-in circuits and associative functions

  • Authors:
  • Ashok K. Chandra;Steven Fortune;Richard Lipton

  • Affiliations:
  • -;-;-

  • Venue:
  • STOC '83 Proceedings of the fifteenth annual ACM symposium on Theory of computing
  • Year:
  • 1983

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Abstract

We consider the computation of finite semigroups using unbounded fan-in circuits. There are constant-depth, polynomial size circuits for semigroup product iff the semigroup does not contain a nontrivial group as a subset. In the case that the semigroup in fact does not contain a group, then for any primitive recursive function f, circuits of size O(nf−1(n)) and constant depth exist for the semigroup product of n elements. The depth depends upon the choice of the primitive recursive function f. The circuits not only compute the semigroup product, but every prefix of the semigroup product. A consequence is that the same bounds apply for circuits computing the sum of two n-bit numbers.