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