NAME¶
MPI_Accumulate - Combines the contents of the origin buffer with that of
a target buffer.
SYNTAX¶
C Syntax¶
#include <mpi.h>
int MPI_Accumulate(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)
Fortran Syntax (see FORTRAN 77 NOTES)¶
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
C++ Syntax¶
#include <mpi.h>
void MPI::Win::Accumulate(const void* origin_addr, int origin_count,
const MPI::Datatype& origin_datatype, int target_rank,
MPI::Aint target_disp, int target_count, const MPI::Datatype&
target_datatype, const MPI::Op& op) const
- 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¶
- IERROR
- Fortran only: Error status (integer).
DESCRIPTION¶
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 MPI_Put, except
that data is combined into the target area instead of overwriting it.
Any of the predefined operations for 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.
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¶
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.
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.
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.
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_Reduce