MPI_Accumulate(3)                  Open MPI                  MPI_Accumulate(3)



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



1.4.1                            Jan 14, 2010                MPI_Accumulate(3)
