NAME¶
MPI_Gather - Gathers together values from a group of processes
SYNOPSIS¶
#include <mpi.h>
int MPI_Gather(void *sbuf, int scount, MPI_Datatype sdtype,
void *rbuf, int rcount, MPI_Datatype rdtype,
int root, MPI_Comm comm)
- sbuf
- - starting address of send buffer (choice)
- scount
- - number of elements in send buffer (integer)
- sdtype
- - data type of send buffer elements (handle)
- rcount
- - number of elements for any single receive (integer, significant only at
root)
- rdtype
- - data type of recv buffer elements (significant only at root)
(handle)
- root
- - rank of receiving process (integer)
- comm
- - communicator (handle)
OUTPUT PARAMETER¶
- rbuf
- - address of receive buffer (choice, significant only at root )
USAGE WITH IMPI EXTENSIONS¶
LAM/MPI does not yet support invoking this function on a communicator that
contains ranks that are non-local IMPI procs.
NOTES FOR FORTRAN¶
All MPI routines in Fortran (except for
MPI_WTIME and
MPI_WTICK )
have an additional argument
ierr at the end of the argument list.
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
call statement.
All MPI objects (e.g.,
MPI_Datatype ,
MPI_Comm ) are of type
INTEGER in Fortran.
ERRORS¶
If an error occurs in an MPI function, the current MPI error handler is called
to handle it. By default, this error handler aborts the MPI job. The error
handler may be changed with
MPI_Errhandler_set ; the predefined error
handler
MPI_ERRORS_RETURN may be used to cause error values to be
returned (in C and Fortran; this error handler is less useful in with the C++
MPI bindings. The predefined error handler
MPI::ERRORS_THROW_EXCEPTIONS
should be used in C++ if the error value needs to be recovered). Note that MPI
does
not guarantee that an MPI program can continue past an error.
All MPI routines (except
MPI_Wtime and
MPI_Wtick ) return an error
value; C routines as the value of the function and Fortran routines in the
last argument. The C++ bindings for MPI do not return error values; instead,
error values are communicated by throwing exceptions of type
MPI::Exception (but not by default). Exceptions are only thrown if the
error value is not
MPI::SUCCESS .
Note that if the
MPI::ERRORS_RETURN handler is set in C++, while MPI
functions will return upon an error, there will be no way to recover what the
actual error value was.
- MPI_SUCCESS
- - No error; MPI routine completed successfully.
- MPI_ERR_COMM
- - Invalid communicator. A common error is to use a null communicator in a
call (not even allowed in MPI_Comm_rank ).
- MPI_ERR_OTHER
- - A collective implementation was not able to be located at run-time for
this communicator.
- MPI_ERR_COUNT
- - Invalid count argument. Count arguments must be non-negative; a count of
zero is often valid.
- MPI_ERR_TYPE
- - Invalid datatype argument. May be an uncommitted MPI_Datatype (see
MPI_Type_commit ).
- MPI_ERR_BUFFER
- - Invalid buffer pointer. Usually a null buffer where one is not
valid.
- MPI_ERR_ROOT
- - Invalid root. The root must be specified as a rank in the communicator.
Ranks must be between zero and the size of the communicator minus one.
For more information, please see the official MPI Forum web site, which contains
the text of both the MPI-1 and MPI-2 standards. These documents contain
detailed information about each MPI function (most of which is not duplicated
in these man pages).
http://www.mpi-forum.org/
ACKNOWLEDGEMENTS¶
The LAM Team would like the thank the MPICH Team for the handy program to
generate man pages ("doctext" from
ftp://ftp.mcs.anl.gov/pub/sowing/sowing.tar.gz ), the initial
formatting, and some initial text for most of the MPI-1 man pages.
LOCATION¶
gather.c