The asymptotic complexity of merging networks

  • Authors:
  • Peter Bro Miltersen;Mike Paterson;Jun Tarui

  • Affiliations:
  • Univ. of Toronto, Toronto, Ont., Canada;Univ. of Warwick, Coventry, UK;Univ. of Electro-Communications, Chofu, Tokyo, Japan

  • Venue:
  • Journal of the ACM (JACM)
  • Year:
  • 1996

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Abstract

Let M(m,n) be the minimum number of comparatorsneeded in a comparator network that merges m elements x1≤x2≤&cdots;≤xm and n elements y1≤y2≤&cdots;≤yn , where n≥m . Batcher's odd-even merge yields the following upper bound: Mm,n≤1 2m+nlog 2m+on; in particular, Mn,n≤nlog 2n+On. We prove the following lower bound that matches the upper bound above asymptotically as n≥m→∞: Mm,n≥1 2m+nlog 2m-Om; in particular, Mn,n≥nlog 2n-On. Our proof technique extends to give similarily tight lower bounds for the size of monotone Boolean circuits for merging, and for the size of switching networks capable of realizing the set of permutations that arise from merging.