Basic HTML version of Foils prepared 10 Oct 1995

Foil 29 Collective Computation

From Fox Presentation Fall 1995 CPS615 Basic Simulation Track for Computational Science -- Fall Semester 95. by Geoffrey C. Fox
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 labelled 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 as MPI_REDUCE but 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

© on Tue Oct 7 1997