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MPI_Intercomm_create(3)               MPI              MPI_Intercomm_create(3)


NAME

       MPI_Intercomm_create -  Creates an intercommuncator from two
       intracommunicators


SYNOPSIS

       int MPI_Intercomm_create(MPI_Comm local_comm, int local_leader,
                              MPI_Comm peer_comm, int remote_leader, int tag,
                              MPI_Comm *newintercomm)


INPUT PARAMETERS

       local_comm
              - Local (intra)communicator
       local_leader
              - Rank in local_comm of leader (often 0)
       peer_comm
              - Communicator used to communicate between a designated process
              in the other communicator.  Significant only at the process in
              local_comm with rank local_leader .

       remote_leader
              - 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

       comm_out
              - Created intercommunicator


NOTES

       peer_comm is significant only for the process designated the
       local_leader in the local_comm .

       The MPI 1.1 Standard contains two mutually exclusive comments on the
       input intercommunicators.  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.


THREAD AND INTERRUPT SAFETY

       This routine is thread-safe.  This means that this routine may be
       safely used by multiple threads without the need for any user-provided
       thread locks.  However, the routine is not interrupt safe.  Typically,
       this is due to the use of memory allocation routines such as malloc or
       other non-MPICH runtime routines that are themselves not interrupt-
       safe.


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

       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.  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 MPI_Comm_set_errhandler (for
       communicators), MPI_File_set_errhandler (for files), and
       MPI_Win_set_errhandler (for RMA windows).  The MPI-1 routine
       MPI_Errhandler_set may be used but its use is deprecated.  The
       predefined error handler MPI_ERRORS_RETURN may be used to cause error
       values to be returned.  Note that MPI does not guarentee that an MPI
       program can continue past an error; however, MPI implementations will
       attempt to continue whenever possible.

       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_INTERN
              - This error is returned when some part of the MPICH
              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


LOCATION

       src/mpi/comm/intercomm_create.c

                                   9/20/2012           MPI_Intercomm_create(3)

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