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MPI_Iallreduce(3)                     MPI                    MPI_Iallreduce(3)


NAME

       MPI_Iallreduce -  Combines values from all processes and distributes
       the result back to all processes in a nonblocking way


SYNOPSIS

       int MPI_Iallreduce(const void *sendbuf, void *recvbuf, int count,
                          MPI_Datatype datatype, MPI_Op op, MPI_Comm comm,
                          MPI_Request *request)


INPUT PARAMETERS

       sendbuf
              - starting address of the send buffer (choice)
       count  - number of elements in send buffer (non-negative integer)
       datatype
              - data type of elements of send buffer (handle)
       op     - operation (handle)
       comm   - communicator (handle)


OUTPUT PARAMETERS

       recvbuf
              - starting address of the receive buffer (choice)
       request
              - communication request (handle)


THREAD AND INTERRUPT SAFETY

       This routine is thread-safe.  This means that this routine may be
       safely used by multiple threads without the need for any user-provided
       thread locks.  However, the routine is not interrupt safe.  Typically,
       this is due to the use of memory allocation routines such as malloc or
       other non-MPICH runtime routines that are themselves not interrupt-
       safe.


NOTES FOR FORTRAN

       All MPI routines in Fortran (except for MPI_WTIME and MPI_WTICK ) have
       an additional argument ierr at the end of the argument list.  ierr is
       an integer and has the same meaning as the return value of the routine
       in C.  In Fortran, MPI routines are subroutines, and are invoked with
       the call statement.

       All MPI objects (e.g., MPI_Datatype , MPI_Comm ) are of type INTEGER in
       Fortran.


ERRORS

       All MPI routines (except MPI_Wtime and MPI_Wtick ) return an error
       value; C routines as the value of the function and Fortran routines in
       the last argument.  Before the value is returned, the current MPI error
       handler is called.  By default, this error handler aborts the MPI job.
       The error handler may be changed with MPI_Comm_set_errhandler (for
       communicators), MPI_File_set_errhandler (for files), and
       MPI_Win_set_errhandler (for RMA windows).  The MPI-1 routine
       MPI_Errhandler_set may be used but its use is deprecated.  The
       predefined error handler MPI_ERRORS_RETURN may be used to cause error
       values to be returned.  Note that MPI does not guarentee that an MPI
       program can continue past an error; however, MPI implementations will
       attempt to continue whenever possible.

                                   11/9/2015                 MPI_Iallreduce(3)

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