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MPI_Exscan(3)                         MPI                        MPI_Exscan(3)


NAME

       MPI_Exscan -  Computes the exclusive scan (partial reductions) of data
       on a  collection of processes


SYNOPSIS

       int MPI_Exscan(MPICH2_CONST void *sendbuf, void *recvbuf, int count, MPI_Datatype datatype,
                      MPI_Op op, MPI_Comm comm)


INPUT PARAMETERS

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


OUTPUT PARAMETER

       recvbuf
              - starting address of receive buffer (choice)


NOTES

       MPI_Exscan is like MPI_Scan , except that the contribution from the
       calling process is not included in the result at the calling process
       (it is contributed to the subsequent processes, of course).


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_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

       src/mpi/coll/exscan.c

                                   9/20/2012                     MPI_Exscan(3)

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