MPI_INTERCOMM_CREATE_FROM_GROUPS(3)		     Open MPI		       MPI_INTERCOMM_CREATE_FROM_GROUPS(3)

MPI_Intercomm_create_from_groups — Creates a new inter-communicator from a local and remote group and stringtag

SYNTAX
   C Syntax
	  #include <mpi.h>

	  int MPI_Intercomm_create_from_groups(MPI_Group local_group, int local_leader, MPI_Group remote_group, int remote_leader, const char *stringtag, MPI_Info info, MPI_Errhandler errhandler, MPI_Comm *newintercomm)

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

	  MPI_INTERCOMM_CREATE_FROM_GROUPS(LOCAL_GROUP, LOCAL_LEADER, REMOTE_GROUP, REMOTE_LEADER, STRINGTAG, INFO, ERRHANDLER, NEWINTERCOMM, IERROR)
	      INTEGER LOCAL_GROUP, LOCAL_LEADER, REMOTE_GROUP, REMOTE_LEADER, INFO, ERRHANDLER, NEWINTERCOMM, IERROR
	      CHARACTER*(*) STRINGTAG

   Fortran 2008 Syntax
	  USE mpi_f08

	  MPI_Intercomm_create_from_groups(local_group, local_leader, remote_group, remote_leader, stringtag, info, errhandler, newintercomm, ierror)
	      TYPE(MPI_Group), INTENT(IN) :: local_group, remote_group
	      INTEGER, INTENT(IN) :: local_leader, remote_leader
	      CHARACTER(LEN=*), INTENT(IN) :: stringtag
	      TYPE(MPI_Info), INTENT(IN) :: info
	      TYPE(MPI_Errhandler), INTENT(IN) :: errhandler
	      TYPE(MPI_Comm), INTENT(OUT) :: newintercomm
	      INTEGER, OPTIONAL, INTENT(OUT) :: ierror

INPUT PARAMETERS
       • local_group : Local group (handler)

       • local_leader : rank of local group leader in local_group (integer)

       • remote_group : Remote group (handler)

       •

	 remote_leader (rank of remote leader in remote_group, significant)
		only at local_leader (integer)

       • stringtag : Unique identifier for this operation (string)

       • info : info object (handler)

       •

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

OUTPUT PARAMETERS
       • newintercomm : New inter-communicator (handle).

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

DESCRIPTION
       MPI_Intercomm_create_from_groups	   creates   an	  inter-communicator.	Unlike	 MPI_Intercomm_create	<#
       mpi-intercomm-create>, this function uses as input previously defined, disjoint local  and  remote  groups.
       The  calling  MPI process must be a member of the local group. The call is collective over the union of the
       local and remote groups. All involved MPI processes shall provide an  identical	value  for  the	 stringtag
       argument. Within each group, all MPI processes shall provide identical local_group, local_leader arguments.
       Wildcards  are not permitted for the remote_leader or local_leader arguments. The stringtag argument serves
       the same purpose as the stringtag  used	in  the	 MPI_Comm_create_from_group  <#mpi-comm-create-from-group>
       function; it differentiates concurrent calls in a multithreaded environment. The stringtag shall not exceed
       MPI_MAX_STRINGTAG_LEN  characters  in length.  For C, this includes space for a null terminating character.
       In the event that MPI_GROUP_EMPTY is supplied as the local_group or remote_group1 or both, then the call is
       a local operation and MPI_COMM_NULL is returned as the newintercomm.

NOTES
       The errhandler argument specifies an error handler to be attached to the new inter-communicator.	 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>/MPI_Init_thread  <#mpi-init-thread>,
       after  MPI_Finalize  <#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	<#
       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>/MPI_Comm_spawn_multiple	<#
       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 <#mpi-abort> was called on that communicator. If called
	 on a window or file, acts as if MPI_Abort <#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	 <#mpi-comm-create-errhandler>	   then	    MPI_Comm_set_errhandler	<#
	 mpi-comm-set-errhandler>

       • MPI_File_create_errhandler	<#mpi-file-create-errhandler>	  then	   MPI_File_set_errhandler	<#
	 mpi-file-set-errhandler>

       • MPI_Session_create_errhandler	 <#mpi-session-create-errhandler>   then   MPI_Session_set_errhandler	<#
	 mpi-session-set-errhandler> or at MPI_Session_init <#mpi-session-init>

       • MPI_Win_create_errhandler	<#mpi-win-create-errhandler>	  then	    MPI_Win_set_errhandler	<#
	 mpi-win-set-errhandler>

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

       See the MPI man page <#open-mpi> for a full list of MPI error codes <#open-mpi-errors>.

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

       See also:
	  MPI_Comm_create_from_group <#mpi-comm-create-from-group>

Copyright
       2003-2026, The Open MPI Community

						   Mar 05, 2026		       MPI_INTERCOMM_CREATE_FROM_GROUPS(3)
