NAME

       MPI_Intercomm_create -  Creates an intercommuncator from two intracommunicators

SYNOPSIS

       #include <mpi.h>
       int MPI_Intercomm_create(MPI_Comm lcomm, int lleader,
                              MPI_Comm pcomm, int pleader, int tag,
                              MPI_Comm *newcomm)

INPUT PARAMTERS

       lcomm  - Local (intra)communicator
       lleader
              - Rank in local_comm of leader (often 0)
       pcomm  - Remote communicator
       pleader
              - Rank in peer_comm of remote leader (often 0)
       tag    -   Message   tag   to   use   in   constructing   intercommunicator;  if  multiple
              MPI_Intercomm_creates  are  being  made,  they  should  use  different  tags  (more
              precisely,  ensure  that  the local and remote leaders are using different tags for
              each MPI_intercomm_create ).

OUTPUT PARAMETER

       newcomm
              - Created intercommunicator

NOTES

       The  MPI  1.1  Standard  contains  two  mutually   exclusive   comments   on   the   input
       intracommunicators.  One says that their repective groups must be disjoint; the other that
       the leaders can be the same process.  After some discussion by the MPI Forum, it has  been
       decided  that  the  groups  must  be disjoint.  Note that the reason given for this in the
       standard  is  not  the  reason  for  this  choice;  rather,  the   other   operations   on
       intercommunicators  (like  MPI_Intercomm_merge  )  do not make sense if the groups are not
       disjoint.

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_TAG
              -  Invalid tag argument.  Tags must be non-negative; tags in a receive ( MPI_Recv ,
              MPI_Irecv , MPI_Sendrecv , etc.)  may also be MPI_ANY_TAG .  The largest tag  value
              is available through the the attribute MPI_TAG_UB .

       MPI_ERR_ARG
              -  Invalid  argument.  Some argument is invalid and is not identified by a specific
              error class.  This is typically a NULL pointer or other such error.
       MPI_ERR_OTHER
              - This error is returned when some part of the LAM/MPI implementation is unable  to
              acquire memory.
       MPI_ERR_RANK
              -  Invalid  source or destination rank.  Ranks must be between zero and the size of
              the  communicator  minus  one;  ranks  in  a  receive  (  MPI_Recv  ,  MPI_Irecv  ,
              MPI_Sendrecv , etc.) may also be MPI_ANY_SOURCE .

SEE ALSO

       MPI_Intercomm_merge, MPI_Comm_free, MPI_Comm_remote_group,
       MPI_Comm_remote_size

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

       iccreate.c