Linear and sublinear time algorithms for the basis of abelian groups

  • Authors:
  • Li Chen;Bin Fu

  • Affiliations:
  • Department of Computer Science, University of District of Columbia, Washington, DC 20008, USA;Department of Computer Science, University of Texas-Pan American, Edinburg, TX 78539, USA

  • Venue:
  • Theoretical Computer Science
  • Year:
  • 2011

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Abstract

It is well known that every finite abelian group G can be represented as a direct product of cyclic groups: G@?G"1xG"2x...xG"t, where each G"i is a cyclic group of order p^j for some prime p and integer j=1. If a"i generates the cyclic group of G"i, i=1,2,...,t, then the elements a"1,a"2,...,a"t are called a basis of G. We show a randomized algorithm such that given a set of generators M={x"1,...,x"k} for an abelian group G and the prime factorization of order ord(x"i)(i=1,...,k), it computes a basis of G in O(|M|(logn)^2+@?"i"="1^tn"ip"i^n^"^i^/^2) time, where n=|G| has prime factorization p"1^n^"^1p"2^n^"^2...p"t^n^"^t (which is not a part of input). This generalizes Buchmann and Schmidt's algorithm that takes O(|M||G|) time. In another model, all elements in an abelian group are put into a list as a part of input. We obtain an O(n) time deterministic algorithm and a sublinear time randomized algorithm for computing a basis of an abelian group.