Basic HTML version of Foils prepared 19 September 98

Foil 44 Collective Computation

From MPI Message Passing Interface Computational Science for Simulations -- Fall Semester 1998. by Geoffrey C. Fox, Nancy McCracken
One can often perform computing during a collective communication
MPI_REDUCE performs reduction operation of type chosen from
  • maximum(value or value and location), minimum(value or value and location), sum, product, logical and/or/xor, bit-wise and/or/xor
  • e.g. operation labeled MPI_MAX stores in location result of processor rank the global maximum of original in each processor as in
  • call MPI_REDUCE(original, result, 1, MPI_REAL, MPI_MAX, rank, comm, ierror)
    • One can also supply one's own reduction function
MPI_ALLREDUCE is same as MPI_REDUCE but it stores result in all -- not just one -- processors
MPI_SCAN performs reductions with result for processor r depending on data in processors 0 to r

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