MPI_GROUP_INCL(3)				     Open MPI					 MPI_GROUP_INCL(3)

MPI_Group_incl — Produces a group by reordering an existing group and taking only listed members.

SYNTAX
   C Syntax
	  #include <mpi.h>

	  int MPI_Group_incl(MPI_Group group, int n, const int ranks[],
	      MPI_Group *newgroup)

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

	  MPI_GROUP_INCL(GROUP, N, RANKS, NEWGROUP, IERROR)
	      INTEGER GROUP, N, RANKS(*), NEWGROUP, IERROR

   Fortran 2008 Syntax
	  USE mpi_f08

	  MPI_Group_incl(group, n, ranks, newgroup, ierror)
	      TYPE(MPI_Group), INTENT(IN) :: group
	      INTEGER, INTENT(IN) :: n, ranks(n)
	      TYPE(MPI_Group), INTENT(OUT) :: newgroup
	      INTEGER, OPTIONAL, INTENT(OUT) :: ierror

INPUT PARAMETERS
       • group : Group (handle).

       •

	 n (Number of elements in array ranks (and size of)
		newgroup)(integer).

       •

	 ranks (Ranks of processes in group to appear in newgroup (array of)
		integers).

OUTPUT PARAMETERS
       •

	 newgroup (New group derived from above, in the order defined by)
		ranks (handle).

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

DESCRIPTION
       The  function MPI_Group_incl creates a group group_out that consists of the n processes in group with ranks
       rank[0], …, rank[n-1]; the process with rank i in group_out is the process with	rank  ranks[i]	in  group.
       Each  of	 the  n elements of ranks must be a valid rank in group and all elements must be distinct, or else
       the program is erroneous. If n = 0, then group_out is MPI_GROUP_EMPTY. This function can, for instance,	be
       used to reorder the elements of a group.

NOTE
       This implementation does not currently check to ensure that there are no duplicates in the list of ranks.

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_Group_compare <#mpi-group-compare>

Copyright
       2003-2026, The Open MPI Community

						   Mar 05, 2026					 MPI_GROUP_INCL(3)
