MPI_COMM_CREATE_FROM_GROUP(3)			     Open MPI			     MPI_COMM_CREATE_FROM_GROUP(3)

MPI_Comm_create_from_group — Creates a new communicator from a group and stringtag

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 <#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 <#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>/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_group <#mpi-comm-create-group>

Copyright
       2003-2026, The Open MPI Community

						   Mar 05, 2026			     MPI_COMM_CREATE_FROM_GROUP(3)
