How to vectorize the algebraic multi-level iteration

  • Authors:
  • Lutz Grosz

  • Affiliations:
  • Massey University, Auckland, New Zealand

  • Venue:
  • Computational science, mathematics and software
  • Year:
  • 2002

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Abstract

We consider the algebraic multi-level iteration (AMLI) for the solution of systems of linear equations as they arise from a finite difference discretization on a rectangular grid. Key operation is the matrix-vector product, which can efficiently be executed on vector and parallel-vector computer architectures if the non-zero entries of the matrix are concentrated in a few diagonals. In order to maintain this structure for all matrices on all levels coarsening in alternating directions is used. In some cases it is necessary to introduce additional dummy grid hyperplanes. The data movements in the restriction and prolongation are crucial as they produce massive memory conflicts on vector architectures. By using a simple performance model the best of the possible vectorization strategies is automatically selected at runtime. Examples show that on a Fujitsu VPP300 the presented implementation of AMLI reaches about 85% of the useful performance, and scalability with respect to computing time can be achieved.