MPI_Alltoall(3) 						      LAM/MPI							   MPI_Alltoall(3)

NAME

       MPI_Alltoall -  Sends data from all to all processes

SYNOPSIS

       #include <mpi.h>
       int MPI_Alltoall(void *sbuf, int scount, MPI_Datatype sdtype,
	  void* rbuf, int rcount, MPI_Datatype rdtype,
	  MPI_Comm comm)

INPUT PARAMETERS

       sbuf   - starting address of send buffer (choice)
       scount - number of elements to send to each process (integer)
       sdtype - data type of send buffer elements (handle)
       rcount - number of elements received from any process (integer)
       rdtype - data type of receive buffer elements (handle)
       comm   - communicator (handle)

OUTPUT PARAMETER

       rbuf   - address of receive buffer (choice)

NOTES

       The  rcount parameter is the value to be expected from each process, not the total that is expected from all processes.	The receive buffer
       rbuf , however, needs to be large enough to hold the data that will be received from all processes, however.

       For example, scount and sdtype and typically the same as rcount and rdtype
	.

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_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_COMM
	      - Invalid communicator.  LAM/MPI does not yet support invoking collectives on intercommunicators.
       MPI_ERR_COMM
	      - A communicator that contains some non-local IMPI procs was used for some function which has not yet had the IMPI extensions imple-
	      mented yet.  For example, most collectives on IMPI communicators have not been implemented yet.
       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.

MORE INFORMATION

       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/sow-
       ing/sowing.tar.gz ), the initial formatting, and some initial text for most of the MPI-1 man pages.

LOCATION

       alltoall.c

LAM
/MPI 6.5.8							    11/10/2002							   MPI_Alltoall(3)