MPI_Get_accumulate(3)

NAME
MPI_Get_accumulate, MPI_Rget_accumulate - Combines the contents of the origin buffer with that of a target buffer and returns the target buffer value.

SYNTAX

C Syntax
#include <mpi.h>
int MPI_Get_accumulate(const void *origin_addr, int origin_count,
	MPI_Datatype origin_datatype, void *result_addr,
	int result_count, MPI_Datatype result_datatype,
	int target_rank, MPI_Aint target_disp, int target_count,
	MPI_Datatype target_datatype, MPI_Op op, MPI_Win win)
int MPI_Rget_accumulate(const void *origin_addr, int origin_count,
	MPI_Datatype origin_datatype, void *result_addr,
	int result_count, MPI_Datatype result_datatype,
	int target_rank, MPI_Aint target_disp, int target_count,
	MPI_Datatype target_datatype, MPI_Op op, MPI_Win win,
	MPI_Request *request)

Fortran Syntax (see FORTRAN 77 NOTES)
INCLUDE 'mpif.h'
MPI_GET_ACCUMULATE(ORIGIN_ADDR, ORIGIN_COUNT, ORIGIN_DATATYPE, RESULT_ADDR,
        RESULT_COUNT, RESULT_DATATYPE, TARGET_RANK, TARGET_DISP, TARGET_COUNT,
        TARGET_DATATYPE, OP, WIN, IERROR)
	<type> ORIGIN_ADDR, RESULT_ADDR(*)
	INTEGER(KIND=MPI_ADDRESS_KIND) TARGET_DISP
	INTEGER ORIGIN_COUNT, ORIGIN_DATATYPE, TARGET_COUNT, TARGET_DATATYPE,
        TARGET_RANK, TARGET_COUNT, TARGET_DATATYPE, OP, WIN, IERROR
MPI_RGET_ACCUMULATE(ORIGIN_ADDR, ORIGIN_COUNT, ORIGIN_DATATYPE, RESULT_ADDR,
        RESULT_COUNT, RESULT_DATATYPE, TARGET_RANK, TARGET_DISP, TARGET_COUNT,
        TARGET_DATATYPE, OP, WIN, REQUEST, IERROR)
	<type> ORIGIN_ADDR, RESULT_ADDR(*)
	INTEGER(KIND=MPI_ADDRESS_KIND) TARGET_DISP
	INTEGER ORIGIN_COUNT, ORIGIN_DATATYPE, TARGET_COUNT, TARGET_DATATYPE,
        TARGET_RANK, TARGET_COUNT, TARGET_DATATYPE, OP, WIN, REQUEST, IERROR

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).

result_addr
    Initial address of result buffer (choice).

result_count
    Number of entries in result buffer (nonnegative integer).

result_datatype
    Data type of each result 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

MPI_Rget_accumulate: RMA request

IERROR
    Fortran only: Error status (integer).

DESCRIPTION
MPI_Get_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. MPI_Get_accumulate returns in the result buffer result_addr the contents of the target buffer before the accumulation.

Any of the predefined operations for MPI_Reduce, as well as MPI_NO_OP, 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.

A new predefined operation, MPI_NO_OP, is defined. It corresponds to the assiciative function f(a, b) = a; that is the current value in the target memory is returned in the result buffer at the origin and no operation is performed on the target buffer.

MPI_Rget_accumulate is similar to MPI_Get_accumulate, except that it allocates a communication request object and associates it with the request handle (the argument request) that can be used to wait or test for completion. The completion of an MPI_Rget_accumulate operation indicates that the data is available in the result buffer and the origin buffer is free to be updated. It does not indicate that the operation has been completed at the target window.

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
The generic functionality of MPI_Get_accumulate might limit the performance of fetch-and-increment or fetch-and-add calls that might be supported by special hardware operations. MPI_Fetch_and_op thus allows for a fast implementation of a commonly used subset of the functionality of MPI_Get_accumulate.

MPI_Get is a special case of MPI_Get_accumulate, with the operation MPI_NO_OP. Note, however, that MPI_Get and MPI_Get_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_Get_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.

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_Get MPI_Accumulate MPI_Fetch_and_op
MPI_Reduce