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 PARAMETERS

       newintercomm
              - 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

                                            11/12/2016                    MPI_Intercomm_create(3)