NAME

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

SYNOPSIS

       int MPI_Exscan(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 PARAMETERS

       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

                                            4/24/2013                               MPI_Exscan(3)