Example: Why MPI Datatypes

• Handling non-contiguous data

• Assume must pack/unpack on each end

  • cn + (s + r n) + cn

• Can move directly

  • s + r’ n
  • r’ probably > r but < (2c+r)

• MPI implementation must copy data anyway (into network buffer or shared memory); having the datatype permits removing 2 copies

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