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NAME

       MPI_Reduce_scatter_block -  Combines values and scatters the results

SYNOPSIS

       int MPI_Reduce_scatter_block(void *sendbuf, void *recvbuf, int recvcount,
                                    MPI_Datatype datatype, MPI_Op op, MPI_Comm comm)

INPUT PARAMETERS

       sendbuf
              - starting address of send buffer (choice)
       recvcount
              - element count per block (non-negative integer)
       datatype
              - datatype of elements of send and receive buffers (handle)
       op     - operation (handle)
       comm   - communicator (handle)

OUTPUT PARAMETER

       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.  May be an uncommitted MPI_Datatype
              (see MPI_Type_commit ).
       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).

LOCATION

       red_scat_block.c

                                  11/14/2009       MPI_Reduce_scatter_block(3)