NAME

       MPI_Accumulate  - Combines the contents of the origin buffer with that of a target buffer.

SYNTAX

C Syntax

       #include <mpi.h>
       int MPI_Accumulate(void *origin_addr, int origin_count,
            MPI_Datatype origin_datatype, int target_rank,
            MPI_Aint target_disp, int target_count,
            MPI_Datatype target_datatype, MPI_Op op, MPI_Win win)

Fortran Syntax (see FORTRAN 77 NOTES)

       INCLUDE 'mpif.h'
       MPI_ACCUMULATE(ORIGIN_ADDR, ORIGIN_COUNT, ORIGIN_DATATYPE, TARGET_RANK,
            TARGET_DISP, TARGET_COUNT, TARGET_DATATYPE, OP, WIN, IERROR)
            <type> ORIGIN_ADDR(*)
            INTEGER(KIND=MPI_ADDRESS_KIND) TARGET_DISP
            INTEGER ORIGIN_COUNT, ORIGIN_DATATYPE, TARGET_RANK, TARGET_COUNT,
            TARGET_DATATYPE, OP, WIN, IERROR

C++ Syntax

       #include <mpi.h>
       void MPI::Win::Accumulate(const void* origin_addr, int origin_count,
            const MPI::Datatype& origin_datatype, int target_rank,
            MPI::Aint target_disp, int target_count, const MPI::Datatype&
            target_datatype, const MPI::Op& op) const

INPUT PARAMETERS

       origin_addr
                 Initial address of buffer (choice).

       origin_count
                 Number of entries in buffer (nonnegative integer).

       origin_datatype
                 Data type of each buffer entry (handle).

       target_rank
                 Rank of target (nonnegative integer).

       target_disp
                 Displacement  from  start  of  window to beginning of target buffer (nonnegative
                 integer).

       target_count
                 Number of entries in target buffer (nonnegative integer).

       target_datatype
                 Data type of each entry in target buffer (handle).

       op        Reduce operation (handle).

       win       Window object (handle).

OUTPUT PARAMETER

       IERROR    Fortran only: Error status (integer).

DESCRIPTION

       MPI_Accumulate is a function used for one-sided MPI communication that adds  the  contents
       of the origin buffer (as defined by origin_addr, origin_count, and origin_datatype) to the
       buffer specified by the arguments target_count and target_datatype, at offset target_disp,
       in  the target window specified by target_rank and win, using the operation op. The target
       window can only be accessed by processes within the same node. This is similar to MPI_Put,
       except that data is combined into the target area instead of overwriting it.

       Any of the predefined operations for MPI_Reduce can be used. User-defined functions cannot
       be used. For example, if op is MPI_SUM, each element of the origin buffer is added to  the
       corresponding element in the target, replacing the former value in the target.

       Each  datatype  argument  must be a predefined data type or a derived data type, where all
       basic components are of the same predefined data type. Both  datatype  arguments  must  be
       constructed  from  the  same predefined data type. The operation op applies to elements of
       that predefined type. The target_datatype argument must not specify  overlapping  entries,
       and the target buffer must fit in the target window.

       A  new  predefined  operation,  MPI_REPLACE, is defined. It corresponds to the associative
       function f(a, b) =b; that is, the current value in the target memory is  replaced  by  the
       value supplied by the origin.

FORTRAN 77 NOTES

       The  MPI standard prescribes portable Fortran syntax for the TARGET_DISP argument only for
       Fortran 90.  FORTRAN 77 users may use the non-portable syntax

            INTEGER*MPI_ADDRESS_KIND TARGET_DISP

       where MPI_ADDRESS_KIND is a constant defined  in  mpif.h  and  gives  the  length  of  the
       declared integer in bytes.

NOTES

       MPI_Put  is  a  special  case  of  MPI_Accumulate,  with  the operation MPI_REPLACE. Note,
       however, that MPI_Put and MPI_Accumulate have different constraints on concurrent updates.

       It is the user's responsibility to guarantee that, when using  the  accumulate  functions,
       the  target displacement argument is such that accesses to the window are properly aligned
       according to the data type arguments in the call to the MPI_Accumulate function.

ERRORS

       Almost all MPI routines return an error value; C routines as the value of the function and
       Fortran  routines in the last argument. C++ functions do not return errors. If the default
       error handler is set to MPI::ERRORS_THROW_EXCEPTIONS, then  on  error  the  C++  exception
       mechanism will be used to throw an MPI:Exception object.

       Before  the  error value is returned, the current MPI error handler is called. By default,
       this error handler aborts the MPI job, except for I/O function errors. The  error  handler
       may    be   changed   with   MPI_Comm_set_errhandler;   the   predefined   error   handler
       MPI_ERRORS_RETURN may be used to cause error values to be returned. Note that MPI does not
       guarantee that an MPI program can continue past an error.

SEE ALSO

       MPI_Put
       MPI_Reduce