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.TH MPI_Reduce_scatter 3 "1/6/1997" " " "MPI"
.SH NAME
MPI_Reduce_scatter \- Combines values and scatters the results
.SH SYNOPSIS
.nf
#include "mpi.h"
int MPI_Reduce_scatter ( sendbuf, recvbuf, recvcnts, datatype, op, comm )
void *sendbuf;
void *recvbuf;
int *recvcnts;
MPI_Datatype datatype;
MPI_Op op;
MPI_Comm comm;
.fi
.SH INPUT PARAMETERS
.PD 0
.TP
.B sendbuf
- starting address of send buffer (choice)
.PD 1
.PD 0
.TP
.B recvcounts
- integer array specifying the
number of elements in result distributed to each process.
Array must be identical on all calling processes.
.PD 1
.PD 0
.TP
.B datatype
- data type of elements of input buffer (handle)
.PD 1
.PD 0
.TP
.B op
- operation (handle)
.PD 1
.PD 0
.TP
.B comm
- communicator (handle)
.PD 1
.SH OUTPUT PARAMETER
.PD 0
.TP
.B recvbuf
- starting address of receive buffer (choice)
.PD 1
.SH NOTES FOR FORTRAN
All MPI routines in Fortran (except for
.I MPI_WTIME
and
.I MPI_WTICK
) have
an additional argument
.I ierr
at the end of the argument list.
.I ierr
is an integer and has the same meaning as the return value of the routine
in C. In Fortran, MPI routines are subroutines, and are invoked with the
.I call
statement.
All MPI objects (e.g.,
.I MPI_Datatype
,
.I MPI_Comm
) are of type
.I INTEGER
in Fortran.
.SH NOTES ON COLLECTIVE OPERATIONS
The reduction functions (
.I MPI_Op
) do not return an error value. As a result,
if the functions detect an error, all they can do is either call
.I MPI_Abort
or silently skip the problem. Thus, if you change the error handler from
.I MPI_ERRORS_ARE_FATAL
to something else, for example,
.I MPI_ERRORS_RETURN
,
then no error may be indicated.
The reason for this is the performance problems in ensuring that
all collective routines return the same error value.
.SH ERRORS
All MPI routines (except
.I MPI_Wtime
and
.I MPI_Wtick
) return an error value;
C routines as the value of the function and Fortran routines in the last
argument. Before the value is returned, the current MPI error handler is
called. By default, this error handler aborts the MPI job. The error handler
may be changed with
.I MPI_Errhandler_set
; the predefined error handler
.I MPI_ERRORS_RETURN
may be used to cause error values to be returned.
Note that MPI does
.B not
guarentee that an MPI program can continue past
an error.
.PD 0
.TP
.B MPI_SUCCESS
- No error; MPI routine completed successfully.
.PD 1
.PD 0
.TP
.B MPI_ERR_COMM
- Invalid communicator. A common error is to use a null
communicator in a call (not even allowed in
.I MPI_Comm_rank
).
.PD 1
.PD 0
.TP
.B MPI_ERR_COUNT
- Invalid count argument. Count arguments must be
non-negative; a count of zero is often valid.
.PD 1
.PD 0
.TP
.B MPI_ERR_TYPE
- Invalid datatype argument. May be an uncommitted
.PD 1
MPI_Datatype (see
.I MPI_Type_commit
).
.PD 0
.TP
.B MPI_ERR_BUFFER
- Invalid buffer pointer. Usually a null buffer where
one is not valid.
.PD 1
.PD 0
.TP
.B MPI_ERR_OP
- Invalid operation. MPI operations (objects of type
.I MPI_Op
)
must either be one of the predefined operations (e.g.,
.I MPI_SUM
) or
created with
.I MPI_Op_create
.
.PD 1
.PD 0
.TP
.B MPI_ERR_BUFFER
- This error class is associcated with an error code that
indicates that two buffer arguments are
.B aliased
; that is, the
describe overlapping storage (often the exact same storage). This
is prohibited in MPI (because it is prohibited by the Fortran
standard, and rather than have a separate case for C and Fortran, the
.PD 1
MPI Forum adopted the more restrictive requirements of Fortran).
.SH LOCATION
red_scat.c
|
