NAME

       MPI_Reduce_scatter -  Combines values and scatters the results

SYNOPSIS

       int MPI_Reduce_scatter(const void *sendbuf, void *recvbuf, const int recvcounts[],
                             MPI_Datatype datatype, MPI_Op op, MPI_Comm comm)

INPUT PARAMETERS

       sendbuf
              - starting address of send buffer (choice)
       recvcounts
              -  integer  array  specifying the number of elements in result distributed to each process.  Array
              must be identical on all calling processes.
       datatype
              - data type of elements of input buffer (handle)
       op     - operation (handle)
       comm   - communicator (handle)

OUTPUT PARAMETERS

       recvbuf
              - starting address of receive buffer (choice)

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.

NOTES ON COLLECTIVE OPERATIONS

       The reduction functions ( MPI_Op ) do not return an error value.  As a result, if the functions detect an
       error, all they can do is either call MPI_Abort or silently skip the problem.  Thus, if  you  change  the
       error handler from MPI_ERRORS_ARE_FATAL to something else, for example, MPI_ERRORS_RETURN , then no error
       may be indicated.

       The reason for this is the performance problems in ensuring that all collective routines return the  same
       error value.

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.

       MPI_SUCCESS
              - No error; MPI routine completed successfully.
       MPI_ERR_COMM
              - Invalid communicator.  A common error is to use a null communicator in a call (not even  allowed
              in MPI_Comm_rank ).
       MPI_ERR_COUNT
              - Invalid count argument.  Count arguments must be non-negative; a count of zero is often valid.
       MPI_ERR_TYPE
              -  Invalid  datatype  argument.  Additionally, this error can occur if an uncommitted MPI_Datatype
              (see MPI_Type_commit ) is used in a communication call.
       MPI_ERR_BUFFER
              - Invalid buffer pointer.  Usually a null buffer where one is not valid.
       MPI_ERR_OP
              - Invalid operation.  MPI operations (objects  of  type  MPI_Op  )  must  either  be  one  of  the
              predefined operations (e.g., MPI_SUM ) or created with MPI_Op_create .

       MPI_ERR_BUFFER
              -  This error class is associcated with an error code that indicates that two buffer arguments are
              aliased ; that is, the describe overlapping storage (often  the  exact  same  storage).   This  is
              prohibited  in  MPI  (because  it  is  prohibited  by the Fortran standard, and rather than have a
              separate case for C and Fortran, the MPI  Forum  adopted  the  more  restrictive  requirements  of
              Fortran).

                                                   11/12/2016                              MPI_Reduce_scatter(3)