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MPI_Accumulate

:ref:`MPI_Accumulate`, :ref:`MPI_Raccumulate` - Combines the contents of the origin buffer with that of a target buffer.

SYNTAX

C Syntax

#include <mpi.h>

int MPI_Accumulate(const 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)

int MPI_Raccumulate(const 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,
     MPI_Request *request)

Fortran Syntax

USE MPI
! or the older form: 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

MPI_RACCUMULATE(ORIGIN_ADDR, ORIGIN_COUNT, ORIGIN_DATATYPE, TARGET_RANK,
     TARGET_DISP, TARGET_COUNT, TARGET_DATATYPE, OP, WIN, REQUEST, IERROR)
     <type> ORIGIN_ADDR(*)
     INTEGER(KIND=MPI_ADDRESS_KIND) TARGET_DISP
     INTEGER ORIGIN_COUNT, ORIGIN_DATATYPE, TARGET_RANK, TARGET_COUNT,
     TARGET_DATATYPE, OP, WIN, REQUEST, IERROR

Fortran 2008 Syntax

USE mpi_f08
MPI_Accumulate(origin_addr, origin_count, origin_datatype, target_rank,
             target_disp, target_count, target_datatype, op, win, ierror)
     TYPE(*), DIMENSION(..), INTENT(IN), ASYNCHRONOUS :: origin_addr
     INTEGER, INTENT(IN) :: origin_count, target_rank, target_count
     TYPE(MPI_Datatype), INTENT(IN) :: origin_datatype, target_datatype
     INTEGER(KIND=MPI_ADDRESS_KIND), INTENT(IN) :: target_disp
     TYPE(MPI_Op), INTENT(IN) :: op
     TYPE(MPI_Win), INTENT(IN) :: win
     INTEGER, OPTIONAL, INTENT(OUT) :: ierror

MPI_Raccumulate(origin_addr, origin_count, origin_datatype, target_rank,
     target_disp, target_count, target_datatype, op, win, request,
             ierror)
     TYPE(*), DIMENSION(..), INTENT(IN), ASYNCHRONOUS :: origin_addr
     INTEGER, INTENT(IN) :: origin_count, target_rank, target_count
     TYPE(MPI_Datatype), INTENT(IN) :: origin_datatype, target_datatype
     INTEGER(KIND=MPI_ADDRESS_KIND), INTENT(IN) :: target_disp
     TYPE(MPI_Op), INTENT(IN) :: op
     TYPE(MPI_Win), INTENT(IN) :: win
     TYPE(MPI_Request), INTENT(OUT) :: request
     INTEGER, OPTIONAL, INTENT(OUT) :: 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).
  • 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_Raccumulate: RMA request
  • ierror: Fortran only: Error status (integer).

DESCRIPTION

:ref:`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 :ref:`MPI_Put`, except that data is combined into the target area instead of overwriting it.

Any of the predefined operations for :ref:`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.

:ref:`MPI_Raccumulate` is similar to :ref:`MPI_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 :ref:`MPI_Raccumulate` operation indicates that the origin_addr buffer is free to be updated. It does not indicate that the operation has completed at the target window.

NOTES

:ref:`MPI_Put` is a special case of :ref:`MPI_Accumulate`, with the operation MPI_REPLACE. Note, however, that :ref:`MPI_Put` and :ref:`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 :ref:`MPI_Accumulate` function.

ERRORS

.. seealso::
   * :ref:`MPI_Put`
   * :ref:`MPI_Get_accumulate`
   * :ref:`MPI_Reduce`