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.TH "MPI_GET_ACCUMULATE" "3" "May 30, 2025" "" "Open MPI"
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.sp
\fI\%MPI_Get_accumulate\fP, \fI\%MPI_Rget_accumulate\fP \- Combines the contents of the
origin buffer with that of a target buffer and returns the target buffer
value.
.SH SYNTAX
.SS C Syntax
.INDENT 0.0
.INDENT 3.5
.sp
.nf
.ft C
#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)
.ft P
.fi
.UNINDENT
.UNINDENT
.SS Fortran Syntax
.INDENT 0.0
.INDENT 3.5
.sp
.nf
.ft C
USE MPI
! or the older form: INCLUDE \(aqmpif.h\(aq

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
.ft P
.fi
.UNINDENT
.UNINDENT
.SS Fortran 2008 Syntax
.INDENT 0.0
.INDENT 3.5
.sp
.nf
.ft C
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
.ft P
.fi
.UNINDENT
.UNINDENT
.SH INPUT PARAMETERS
.INDENT 0.0
.IP \(bu 2
\fBorigin_addr\fP : Initial address of buffer (choice).
.IP \(bu 2
\fBorigin_count\fP : Number of entries in buffer (nonnegative integer).
.IP \(bu 2
\fBorigin_datatype\fP : Data type of each buffer entry (handle).
.IP \(bu 2
\fBresult_addr\fP : Initial address of result buffer (choice).
.IP \(bu 2
.INDENT 2.0
.TP
.B \fBresult_count\fP
Number of entries in result buffer (nonnegative
integer).
.UNINDENT
.IP \(bu 2
\fBresult_datatype\fP : Data type of each result buffer entry (handle).
.IP \(bu 2
\fBtarget_rank\fP : Rank of target (nonnegative integer).
.IP \(bu 2
.INDENT 2.0
.TP
.B \fBtarget_disp\fP
Displacement from start of window to beginning of
target buffer (nonnegative integer).
.UNINDENT
.IP \(bu 2
.INDENT 2.0
.TP
.B \fBtarget_count\fP
Number of entries in target buffer (nonnegative
integer).
.UNINDENT
.IP \(bu 2
\fBtarget_datatype\fP : Data type of each entry in target buffer (handle).
.IP \(bu 2
\fBop\fP : Reduce operation (handle).
.IP \(bu 2
\fBwin\fP : Window object (handle).
.UNINDENT
.SH OUTPUT PARAMETER
.INDENT 0.0
.IP \(bu 2
\fI\%MPI_Rget_accumulate\fP: RMA request
.IP \(bu 2
\fBierror\fP : Fortran only: Error status (integer).
.UNINDENT
.SH DESCRIPTION
.sp
\fI\%MPI_Get_accumulate\fP 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. \fI\%MPI_Get_accumulate\fP returns in the result buffer result_addr the
contents of the target buffer before the accumulation.
.sp
Any of the predefined operations for \fI\%MPI_Reduce\fP, 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.
.sp
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.
.sp
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.
.sp
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.
.sp
\fI\%MPI_Rget_accumulate\fP is similar to \fI\%MPI_Get_accumulate\fP, 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 \fI\%MPI_Rget_accumulate\fP 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.
.SH NOTES
.sp
The generic functionality of \fI\%MPI_Get_accumulate\fP might limit the
performance of fetch\-and\-increment or fetch\-and\-add calls that might be
supported by special hardware operations. \fI\%MPI_Fetch_and_op\fP thus allows
for a fast implementation of a commonly used subset of the functionality
of \fI\%MPI_Get_accumulate\fP\&.
.sp
\fI\%MPI_Get\fP is a special case of \fI\%MPI_Get_accumulate\fP, with the operation
MPI_NO_OP. Note, however, that \fI\%MPI_Get\fP and \fI\%MPI_Get_accumulate\fP have
different constraints on concurrent updates.
.sp
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 \fI\%MPI_Get_accumulate\fP function.
.SH ERRORS
.sp
Almost all MPI routines return an error value; C routines as the return result
of the function and Fortran routines in the last argument.
.sp
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
\fI\%MPI_Init\fP/\fI\%MPI_Init_thread\fP, after \fI\%MPI_Finalize\fP, or when using the Sessions
Model exclusively) the error raises the initial error handler. The initial
error handler can be changed by calling \fI\%MPI_Comm_set_errhandler\fP on
MPI_COMM_SELF when using the World model, or the mpi_initial_errhandler CLI
argument to mpiexec or info key to \fI\%MPI_Comm_spawn\fP/\fI\%MPI_Comm_spawn_multiple\fP\&.
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.
.sp
Open MPI includes three predefined error handlers that can be used:
.INDENT 0.0
.IP \(bu 2
\fBMPI_ERRORS_ARE_FATAL\fP
Causes the program to abort all connected MPI processes.
.IP \(bu 2
\fBMPI_ERRORS_ABORT\fP
An error handler that can be invoked on a communicator,
window, file, or session. When called on a communicator, it
acts as if \fI\%MPI_Abort\fP was called on that communicator. If
called on a window or file, acts as if \fI\%MPI_Abort\fP 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.
.IP \(bu 2
\fBMPI_ERRORS_RETURN\fP
Returns an error code to the application.
.UNINDENT
.sp
MPI applications can also implement their own error handlers by calling:
.INDENT 0.0
.IP \(bu 2
\fI\%MPI_Comm_create_errhandler\fP then \fI\%MPI_Comm_set_errhandler\fP
.IP \(bu 2
\fI\%MPI_File_create_errhandler\fP then \fI\%MPI_File_set_errhandler\fP
.IP \(bu 2
\fI\%MPI_Session_create_errhandler\fP then \fI\%MPI_Session_set_errhandler\fP or at \fI\%MPI_Session_init\fP
.IP \(bu 2
\fI\%MPI_Win_create_errhandler\fP then \fI\%MPI_Win_set_errhandler\fP
.UNINDENT
.sp
Note that MPI does not guarantee that an MPI program can continue past
an error.
.sp
See the \fI\%MPI man page\fP for a full list of \fI\%MPI error codes\fP\&.
.sp
See the Error Handling section of the MPI\-3.1 standard for
more information.
.sp
\fBSEE ALSO:\fP
.INDENT 0.0
.INDENT 3.5
\fI\%MPI_Put\fP \fI\%MPI_Reduce\fP
.UNINDENT
.UNINDENT
.SH COPYRIGHT
2003-2025, The Open MPI Community
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