MPI_GET_ACCUMULATE(3)				     Open MPI				     MPI_GET_ACCUMULATE(3)

MPI_Get_accumulate,  MPI_Rget_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
	  USE MPI
	  ! or the older form: 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

   Fortran 2008 Syntax
	  USE mpi_f08

	  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(*), DIMENSION(..), INTENT(IN) :: origin_addr
	      TYPE(*), DIMENSION(..) :: result_addr
	      INTEGER, INTENT(IN) :: origin_count, result_count, target_rank, target_count
	      TYPE(MPI_Datatype), INTENT(IN) :: origin_datatype, target_datatype, result_datatype
	      INTEGER(KIND=MPI_ADDRESS_KIND), INTENT(IN) :: target_dist
	      TYPE(MPI_Op), INTENT(IN) :: op
	      TYPE(MPI_Win), INTENT(IN) :: win
	      INTEGER, OPTIONAL, INTENT(OUT) :: 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(*), DIMENSION(..), INTENT(IN) :: origin_addr
	      TYPE(*), DIMENSION(..) :: result_addr
	      INTEGER, INTENT(IN) :: origin_count, result_count, target_rank, target_count
	      TYPE(MPI_Datatype), INTENT(IN) :: origin_datatype, target_datatype, result_datatype
	      INTEGER(KIND=MPI_ADDRESS_KIND), INTENT(IN) :: target_dist
	      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).

       • 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 <#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  <#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  <#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 <#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.

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	<#
       mpi-fetch-and-op>  thus	allows for a fast implementation of a commonly used subset of the functionality of
       MPI_Get_accumulate.

       MPI_Get <#mpi-get> is a special case of MPI_Get_accumulate, with the operation  MPI_NO_OP.  Note,  however,
       that MPI_Get <#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 return result of the function and Fortran
       routines in the last argument.

       Before the error value is returned, the current MPI error handler associated with the communication  object
       (e.g.,  communicator, window, file) is called.  If no communication object is associated with the MPI call,
       then the call is considered attached to MPI_COMM_SELF and will call the associated MPI error handler.  When
       MPI_COMM_SELF  is  not  initialized  (i.e., before MPI_Init <#mpi-init>/MPI_Init_thread <#mpi-init-thread>,
       after MPI_Finalize <#mpi-finalize>, or when using the Sessions Model  exclusively)  the	error  raises  the
       initial	error  handler.	 The  initial  error  handler can be changed by calling MPI_Comm_set_errhandler <#
       mpi-comm-set-errhandler> on MPI_COMM_SELF when using the World model,  or  the  mpi_initial_errhandler  CLI
       argument	  to   mpiexec	 or   info  key	 to  MPI_Comm_spawn  <#mpi-comm-spawn>/MPI_Comm_spawn_multiple	<#
       mpi-comm-spawn-multiple>.  If no other appropriate error handler has been set, then  the	 MPI_ERRORS_RETURN
       error  handler  is  called  for	MPI I/O functions and the MPI_ERRORS_ABORT error handler is called for all
       other MPI functions.

       Open MPI includes three predefined error handlers that can be used:

       • MPI_ERRORS_ARE_FATAL Causes the program to abort all connected MPI processes.

       • MPI_ERRORS_ABORT An error handler that can be invoked on a communicator, window, file, or  session.  When
	 called on a communicator, it acts as if MPI_Abort <#mpi-abort> was called on that communicator. If called
	 on  a window or file, acts as if MPI_Abort <#mpi-abort> was called on a communicator containing the group
	 of processes in the corresponding window or file. If called on a session, aborts only the local process.

       • MPI_ERRORS_RETURN Returns an error code to the application.

       MPI applications can also implement their own error handlers by calling:

       • MPI_Comm_create_errhandler	<#mpi-comm-create-errhandler>	  then	   MPI_Comm_set_errhandler	<#
	 mpi-comm-set-errhandler>

       • MPI_File_create_errhandler	 <#mpi-file-create-errhandler>	   then	    MPI_File_set_errhandler	<#
	 mpi-file-set-errhandler>

       • MPI_Session_create_errhandler	 <#mpi-session-create-errhandler>   then   MPI_Session_set_errhandler	<#
	 mpi-session-set-errhandler> or at MPI_Session_init <#mpi-session-init>

       • MPI_Win_create_errhandler	<#mpi-win-create-errhandler>	  then	    MPI_Win_set_errhandler	<#
	 mpi-win-set-errhandler>

       Note that MPI does not guarantee that an MPI program can continue past an error.

       See the MPI man page <#open-mpi> for a full list of MPI error codes <#open-mpi-errors>.

       See the Error Handling section of the MPI-3.1 standard for more information.

       See also:
	  MPI_Put <#mpi-put> MPI_Reduce <#mpi-reduce>

Copyright
       2003-2026, The Open MPI Community

						   Mar 05, 2026				     MPI_GET_ACCUMULATE(3)
