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MPI_Scan(3)				     LAM/MPI				      MPI_Scan(3)

       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 argu-
       ment 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.

       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 excep-
       tions 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 ).
	      -  Invalid  communicator.   LAM/MPI  does  not  yet support invoking collectives on
	      - 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 col-
	      lectives 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_com-
	      mit ).
	      - 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 opera-
	      tions.  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 ftp://ftp.mcs.anl.gov/pub/sowing/sowing.tar.gz ), the initial for-
       matting, and some initial text for most of the MPI-1 man pages.


LAM/MPI 6.5.8				    11/10/2002				      MPI_Scan(3)
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