MPI_Reduce

Reduces values on all processes to a single value.

Syntax

• r = MPI_Reduce(Value, Operation, Root)
• r = MPI_Reduce(Value, Operation, Root, Comm)

Input argument

• Value - value to send: numeric or logical array (sparse not supported).
• Operation - a string: MPI_SUM, MPI_MAX, MPI_MIN, MPI_SUM, MPI_PROD, MPI_LAND, MPI_LOR, MPI_BAND, MPI_BOR, MPI_LXOR or MPI_BXOR
• Root - a integer value: rank of root process.
• Comm - a MPI_Comm object.

Output argument

• r - received value

Description

Reduces values on all processes to a single value.

Nelson does not check to ensure that the reduction operation are all the same size across the various processes in the group.

Please be sure that each process passes the same sized array to the MPI_Allreduce operation.

See also

MPI_Allreduce.

Example

mpiexec([modulepath('mpi'), '/examples/help_examples/MPI_Reduce.m'], 4)

if ~MPI_Initialized()
  MPI_Init();
end
my_rank = MPI_Comm_rank ();
num_ranks = MPI_Comm_size();

A = [1 + my_rank:3 + my_rank]
B = MPI_Reduce(A, 'MPI_SUM', 0);
if (my_rank == 0)
  disp('Result:')
  B
end
if MPI_Initialized()
  MPI_Finalize();
end

History

Author

Allan CORNET