The Organization of Computations for Uniform Recurrence Equations

  • Authors:
  • Richard M. Karp;Raymond E. Miller;Shmuel Winograd

  • Affiliations:
  • IBM Watson Research Center, Yorktown Heights, New York;IBM Watson Research Center, Yorktown Heights, New York;IBM Watson Research Center, Yorktown Heights, New York

  • Venue:
  • Journal of the ACM (JACM)
  • Year:
  • 1967

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Abstract

A set equations in the quantities ai(p), where i = 1, 2, · · ·, m and p ranges over a set R of lattice points in n-space, is called a system of uniform recurrence equations if the following property holds: If p and q are in R and w is an integer n-vector, then ai(p) depends directly on aj(p - w) if and only if ai(q) depends directly on aj(q - w). Finite-difference approximations to systems of partial differential equations typically lead to such recurrence equations. The structure of such a system is specified by a dependence graph G having m vertices, in which the directed edges are labeled with integer n-vectors. For certain choices of the set R, necessary and sufficient conditions on G are given for the existence of a schedule to compute all the quantities ai(p) explicitly from their defining equations. Properties of such schedules, such as the degree to which computation can proceed “in parallel,” are characterized. These characterizations depend on a certain iterative decomposition of a dependence graph into subgraphs. Analogous results concerning implicit schedules are also given.