MPI_COMM_CREATE(3)				     Open MPI					MPI_COMM_CREATE(3)

MPI_Comm_create — Creates a new communicator.

SYNTAX
   C Syntax
	  #include <mpi.h>

	  int MPI_Comm_create(MPI_Comm comm, MPI_Group group, MPI_Comm *newcomm)

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

	  MPI_COMM_CREATE(COMM, GROUP, NEWCOMM, IERROR)
	      INTEGER COMM, GROUP, NEWCOMM, IERROR

   Fortran 2008 Syntax
	  USE mpi_f08

	  MPI_Comm_create(comm, group, newcomm, ierror)
	      TYPE(MPI_Comm), INTENT(IN) :: comm
	      TYPE(MPI_Group), INTENT(IN) :: group
	      TYPE(MPI_Comm), INTENT(OUT) :: newcomm
	      INTEGER, OPTIONAL, INTENT(OUT) :: ierror

INPUT PARAMETER
       • comm : Communicator (handle).

       • group : Group, which is a subset of the group of comm (handle).

OUTPUT PARAMETERS
       • newcomm : New communicator (handle).

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

DESCRIPTION
       This  function  creates	a  new	communicator  newcomm  with communication group defined by group and a new
       context. The function sets newcomm to a new communicator that spans all	the  processes	that  are  in  the
       group.  It  sets	 newcomm to MPI_COMM_NULL for processes that are not in the group.  Each process must call
       with a group argument that is a subgroup of the group associated with comm; this could be  MPI_GROUP_EMPTY.
       The  processes  may  specify  different	values for the group argument. If a process calls with a non-empty
       group, then all processes in that group must call the function with the same group as  argument,	 that  is:
       the same processes in the same order. Otherwise the call is erroneous.

NOTES
       MPI_Comm_create	provides  a  means  of	making	a  subset  of  processes  for the purpose of separate MIMD
       computation, with separate communication space.	newcomm, which is created by MPI_Comm_create, can be  used
       in  subsequent  calls  to  MPI_Comm_create  (or	other  communicator  constructors)  to further subdivide a
       computation into parallel sub-computations. A  more  general  service  is  provided  by	MPI_Comm_split	<#
       mpi-comm-split>.

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_split <#mpi-comm-split>

Copyright
       2003-2026, The Open MPI Community

						   Mar 05, 2026					MPI_COMM_CREATE(3)
