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_OTHER
              -  A  collective  implementation  was  not  able to be located at run-time for this
              communicator.
       MPI_ERR_OTHER
              - A communicator that contains some non-local IMPI procs was used for some function
              which  has  not  yet  had  the  IMPI extensions implemented 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/sowing/sowing.tar.gz  ),  the  initial
       formatting, and some initial text for most of the MPI-1 man pages.

LOCATION

       alltoall.c