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 (handle)
       local_leader
              - rank of local group leader in local_comm (integer)
       peer_comm
              - `peer communicator; significant only at the local_leader (handle)
       remote_leader
              -  rank  of  remote group leader in peer_comm; significant only at the local_leader
              (integer)
       tag    - tag (integer)

OUTPUT PARAMETERS

       newintercomm
              - new inter-communicator (handle)

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 respective 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 guarantee 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_ARG
              -  Invalid  argument.  Some argument is invalid and is not identified by a specific
              error class (e.g., MPI_ERR_RANK ).
       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_OTHER
              - Other error; use MPI_Error_string to get more information about this error code.

SEE ALSO

       MPI_Intercomm_merge, MPI_Comm_free, MPI_Comm_remote_group, MPI_Comm_remote_size

                                            2/22/2022                     MPI_Intercomm_create(3)