SYNTAX

   C Syntax
          #include <mpi.h>

          int MPI_Comm_create_from_group(MPI_Group group, const char *stringtag, MPI_Info info, MPI_Errhandler errhandler, MPI_Comm *newcomm)

   Fortran Syntax
          USE MPI
          ! or the older form: INCLUDE 'mpif.h'

          MPI_COMM_CREATE_FROM_GROUP(GROUP, STRINGTAG, INFO, ERRHANDLER, NEWCOMM, IERROR)
              INTEGER GROUP, INFO, ERRHANDLER, NEWCOMM, IERROR
              CHARACTER*(*) STRINGTAG

   Fortran 2008 Syntax
          USE mpi_f08

          MPI_Comm_create_from_group(group, stringtag, info, errhandler, newcomm, ierror)
              TYPE(MPI_Group), INTENT(IN) :: group
              CHARACTER(LEN=*), INTENT(IN) :: stringtag
              TYPE(MPI_Info), INTENT(IN) :: info
              TYPE(MPI_Errhandler), INTENT(IN) :: errhandler
              TYPE(MPI_Comm), INTENT(OUT) :: newcomm
              INTEGER, OPTIONAL, INTENT(OUT) :: ierror

INPUT PARAMETERS

       • group : Group (handler)

       • stringtag : Unique identifier for this operation (string)

       • info : info object (handler)

       •

         errhandler (error handler to be attached to the new)
                intra-communicator (handle)

OUTPUT PARAMETERS

       • newcomm : New communicator (handle).

       • ierror : Fortran only: Error status (integer).

DESCRIPTION

       MPI_Comm_create_from_group  is  similar  to  MPI_Comm_create_group,  except that the set of MPI processes
       involved in the creation of the new intra-communicator is specified by a group argument, rather than  the
       group  associated  with  a  pre-existing  communicator.  If  a non-empty group is specified, then all MPI
       processes in that group must call the function and each of these MPI  processes  must  provide  the  same
       arguments,  including  a  group  that  contains  the  same  members with the same ordering, and identical
       stringtag value. In the event that MPI_GROUP_EMPTY is supplied as the group argument, then the call is  a
       local  operation and MPI_COMM_NULL is returned as newcomm. The stringtag argument is analogous to the tag
       used  for  MPI_Comm_create_group.  If  multiple  threads  at  a  given  MPI  process  perform  concurrent
       MPI_Comm_create_from_group  operations, the user must distinguish these operations by providing different
       stringtag arguments. The stringtag shall not exceed MPI_MAX_STRINGTAG_LEN characters in  length.  For  C,
       this includes space for a null terminating character.

NOTES

       The  errhandler argument specifies an error handler to be attached to the new intracommunicator. The info
       argument provides hints and assertions, possibly MPI implementation  dependent,  which  indicate  desired
       characteristics and guide communicator creation. MPI_MAX_STRINGTAG_LEN shall have a value of at least 63.

ERRORS

       Almost  all  MPI  routines  return  an  error  value; C routines as the return result of the function and
       Fortran routines in the last argument.

       Before the error value is returned, the current MPI  error  handler  associated  with  the  communication
       object  (e.g.,  communicator, window, file) is called.  If no communication object is associated with the
       MPI call, then the call is considered attached to MPI_COMM_SELF and will call the  associated  MPI  error
       handler.   When   MPI_COMM_SELF   is   not  initialized  (i.e.,  before  MPI_Init/MPI_Init_thread,  after
       MPI_Finalize, or when using the Sessions Model exclusively) the error raises the initial  error  handler.
       The  initial  error handler can be changed by calling MPI_Comm_set_errhandler on MPI_COMM_SELF when using
       the World model, or the mpi_initial_errhandler CLI argument to mpiexec or info  key  to  MPI_Comm_spawn/‐
       MPI_Comm_spawn_multiple.   If no other appropriate error handler has been set, then the MPI_ERRORS_RETURN
       error handler is called for MPI I/O functions and the MPI_ERRORS_ABORT error handler is  called  for  all
       other MPI functions.

       Open MPI includes three predefined error handlers that can be used:

       • MPI_ERRORS_ARE_FATAL Causes the program to abort all connected MPI processes.

       • MPI_ERRORS_ABORT An error handler that can be invoked on a communicator, window, file, or session. When
         called  on  a  communicator,  it  acts  as if MPI_Abort was called on that communicator. If called on a
         window or file, acts as if MPI_Abort was called on a communicator containing the group of processes  in
         the corresponding window or file. If called on a session, aborts only the local process.

       • MPI_ERRORS_RETURN Returns an error code to the application.

       MPI applications can also implement their own error handlers by calling:

       • MPI_Comm_create_errhandler then MPI_Comm_set_errhandler

       • MPI_File_create_errhandler then MPI_File_set_errhandler

       • MPI_Session_create_errhandler then MPI_Session_set_errhandler or at MPI_Session_init

       • MPI_Win_create_errhandler then MPI_Win_set_errhandler

       Note that MPI does not guarantee that an MPI program can continue past an error.

       See the MPI man page for a full list of MPI error codes.

       See the Error Handling section of the MPI-3.1 standard for more information.

       SEE ALSO:

          • MPI_Comm_create_group

COPYRIGHT

       2003-2025, The Open MPI Community

                                                  Feb 17, 2025                     MPI_COMM_CREATE_FROM_GROUP(3)