MPI_Allreduce(3)

NAME
     MPI_Allreduce - Combines values from all processes and distributes the
     result back to all processes

SYNOPSIS
     C:

          #include <mpi.h>

          int MPI_Allreduce ( sendbuf, recvbuf, count,
          datatype, op, comm )
          void             *sendbuf;
          void             *recvbuf;
          int               count;
          MPI_Datatype      datatype;
          MPI_Op            op;
          MPI_Comm          comm;


     C++:

          #include <mpi.h>

          void Intracomm::Allreduce(
          const void*       sendbuf,
          void*             recvbuf,
          int               count,
          const Datatype&   datatype,
          const Op&         op) const


     Fortran:

          INCLUDE "mpif.h" (or USE MPI)

          <type> SENDBUF(*), RECVBUF(*)
          INTEGER count, datatype, op,
          comm, ierror,

          CALL MPI_ALLREDUCE(sendbuf, recvbuf, count,
          datatype, op, comm, ierror,)


STANDARDS
     This release implements the MPI 1.2 standard, as documented by the MPI
     Forum in the spring 1997 release of MPI:  A Message Passing Interface
     Standard.

DESCRIPTION
     The MPI_Allreduce routine combines values from all processes and
     distributes the result back to all processes.  This routine accepts the
     following parameters:
     sendbuf   Specifies the starting address of the send buffer (choice)

     count     Specifies the number of elements in the send buffer (integer)

     datatype  Specifies the data type of elements in the send buffer (handle)

     op        Specifies the operation (handle)

     comm      Specifies the communicator (handle)

     recvbuf   Returns the starting address of the receive buffer (choice)

     ierror    Specifies the return code value for successful completion,
               which is in MPI_SUCCESS.  MPI_SUCCESS is defined in the mpif.h
               file.