mpi_accumulate.3

MPI stands for the Message Passing Interface. Written by the MPI Forum (a large committee comprising

.\"Copyright 2006, Sun Microsystems, Inc.
.\" Copyright (c) 1996 Thinking Machines Corporation
.TH MPI_Accumulate 3OpenMPI "September 2006" "Open MPI 1.2" " "
.SH NAME
\fBMPI_Accumulate \fP \- Combines the contents of the origin buffer with that of a target buffer. 

.SH SYNTAX
.ft R
.SH C Syntax
.nf
#include <mpi.h>
int MPI_Accumulate(void *\fIorigin_addr\fP, int \fIorigin_count\fP, 
	MPI_Datatype \fIorigin_datatype\fP, int \fItarget_rank\fP, 
	MPI_Aint \fItarget_disp\fP, int \fItarget_count\fP, 
	MPI_Datatype \fItarget_datatype\fP, MPI_Op \fIop\fP, MPI_Win \fIwin\fP)

.SH Fortran Syntax (see FORTRAN 77 NOTES)
.nf
INCLUDE 'mpif.h'
MPI_ACCUMULATE(\fIORIGIN_ADDR, ORIGIN_COUNT, ORIGIN_DATATYPE, TARGET_RANK, 
	TARGET_DISP, TARGET_COUNT, TARGET_DATATYPE, OP, WIN, IERROR\fP) 
	<type> \fIORIGIN_ADDR\fP(*) 
	INTEGER(KIND=MPI_ADDRESS_KIND) \fITARGET_DISP\fP 
	INTEGER \fIORIGIN_COUNT, ORIGIN_DATATYPE, TARGET_RANK, TARGET_COUNT, 
	TARGET_DATATYPE, OP, WIN, IERROR \fP

.SH C++ Syntax
.nf
#include <mpi.h>
void MPI::Win::Accumulate(const void* \fIorigin_addr\fP, int \fIorigin_count\fP, 
	const MPI::Datatype& \fIorigin_datatype\fP, int \fItarget_rank\fP, 
	MPI::Aint \fItarget_disp\fP, int \fItarget_count\fP, const MPI::Datatype& 
	\fItarget_datatype\fP, const MPI::Op& \fIop\fP) const 

.SH INPUT PARAMETERS
.ft R
.TP 1i
origin_addr
Initial address of buffer (choice).
.ft R
.TP 1i
origin_count
Number of entries in buffer (nonnegative integer).
.ft R
.TP 1i
origin_datatype
Data type of each buffer entry (handle).
.ft R
.TP 1i
target_rank
Rank of target (nonnegative integer).
.ft R
.TP 1i
target_disp
Displacement from start of window to beginning of target buffer (nonnegative integer). 
.ft R
.TP 1i
target_count
Number of entries in target buffer (nonnegative integer). 
.ft R
.TP 1i
target_datatype
Data type of each entry in target buffer (handle).
.ft R
.TP 1i
op
Reduce operation (handle). 
.ft R
.TP 1i
win
Window object (handle). 

.SH OUTPUT PARAMETER
.ft R
.TP 1i
IERROR
Fortran only: Error status (integer). 

.SH DESCRIPTION
.ft R
MPI_Accumulate is a function used for one-sided MPI communication that adds the contents of the origin buffer (as defined by \fIorigin_addr\fP, \fIorigin_count\fP, and \fIorigin_datatype\fP) to the buffer specified by the arguments \fItarget_count\fP and \fItarget_datatype\fP, at offset \fItarget_disp\fP, in the target window specified by \fItarget_rank\fP and \fIwin\fP, using the operation \fIop\fP. 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. 
.sp
Any of the predefined operations for MPI_Reduce can be used. User-defined functions cannot be used. For example, if \fIop\fP 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 \fIop\fP applies to elements of that predefined type. The \fItarget_datatype\fP 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. 


.SH FORTRAN 77 NOTES
.ft R
The MPI standard prescribes portable Fortran syntax for
the \fITARGET_DISP\fP argument only for Fortran 90.  FORTRAN 77
users may use the non-portable syntax
.sp
.nf
     INTEGER*MPI_ADDRESS_KIND \fITARGET_DISP\fP
.fi
.sp
where MPI_ADDRESS_KIND is a constant defined in mpif.h
and gives the length of the declared integer in bytes.

.SH 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. 
.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 MPI_Accumulate function.

.SH 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.
.sp
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. 

.SH SEE ALSO
.ft R
.sp
MPI_Put 
.br
MPI_Reduce
' @(#)MPI_Accumulate.3 1.15 06/03/09