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


       #include <mpi.h>
       int MPI_Scan(void *sbuf, void *rbuf, int count,
                    MPI_Datatype dtype, MPI_Op op, MPI_Comm comm)


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


       rbuf   - starting address of receive buffer (choice)


       LAM/MPI does not yet support invoking this function on  a  communicator
       that contains ranks that are non-local IMPI procs.


       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


       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  (e.g.,
       MPI_ERRORS_RETURN ), then no error may be indicated.

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


       If an error occurs in an MPI function, the current MPI error handler is
       called to handle it.  By default, this error  handler  aborts  the  MPI
       job.   The  error  handler may be changed with MPI_Errhandler_set ; the
       predefined error handler MPI_ERRORS_RETURN may be used to  cause  error
       values  to  be  returned  (in C and Fortran; this error handler is less
       useful in with the C++ MPI  bindings.   The  predefined  error  handler
       MPI::ERRORS_THROW_EXCEPTIONS  should  be used in C++ if the error value
       needs to be recovered).  Note that MPI does not guarantee that  an  MPI
       program can continue past an error.

       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.   The  C++  bindings  for  MPI do not return error
       values; instead, error values are communicated by  throwing  exceptions
       of  type  MPI::Exception  (but  not  by  default).  Exceptions are only
       thrown if the error value is not MPI::SUCCESS .

       Note that if the MPI::ERRORS_RETURN handler is set in  C++,  while  MPI
       functions  will  return  upon an error, there will be no way to recover
       what the actual error value was.
              - No error; MPI routine completed successfully.
              - Invalid communicator.   A  common  error  is  to  use  a  null
              communicator in a call (not even allowed in MPI_Comm_rank ).
              - A collective implementation was not able to be located at run-
              time for this communicator.
              - A communicator that contains some  non-local  IMPI  procs  was
              used for some function which has not yet had the IMPI extensions
              implemented  yet.   For  example,  most  collectives   on   IMPI
              communicators have not been implemented yet.
              - Invalid count argument.  Count arguments must be non-negative;
              a count of zero is often valid.
              - Invalid datatype argument.  May be an uncommitted MPI_Datatype
              (see MPI_Type_commit ).
              -  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  .   Additionally, only certain
              datatypes are alloed  with  given  predefined  operations.   See
              MPI-1, section 4.9.2.
              -  Invalid  buffer  pointer.  Usually a null buffer where one is
              not valid.
              - 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).


       For more information, please see the official MPI Forum web site, which
       contains  the  text  of  both  the  MPI-1  and  MPI-2 standards.  These
       documents contain detailed information about each MPI function (most of
       which is not duplicated in these man pages).


       The  LAM Team would like the thank the MPICH Team for the handy program
       to       generate        man        pages        ("doctext"        from     ),    the    initial
       formatting, and some initial text for most of the MPI-1 man pages.