


MPI_Intercomm_create(3)      LAM/MPI      MPI_Intercomm_create(3)


NAME
       MPI_Intercomm_create  -  Creates an intercommuncator from two intracom-
       municators

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  mul-
              tiple MPI_Intercomm_creates are being made, they should use dif-
              ferent 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



LAM/MPI 6.5.9               1/27/2003                           1





MPI_Intercomm_create(3)      LAM/MPI      MPI_Intercomm_create(3)


       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  val-
       ues;  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 commu-
              nicator 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 identi-
              fied 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 implemen-
              tation 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



LAM/MPI 6.5.9               1/27/2003                           2





MPI_Intercomm_create(3)      LAM/MPI      MPI_Intercomm_create(3)


       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/sow-
       ing/sowing.tar.gz ), the initial formatting, and some initial text  for
       most of the MPI-1 man pages.

LOCATION
       iccreate.c










































LAM/MPI 6.5.9               1/27/2003                           3


