C Syntax

       2003-2025, The Open MPI Community

                                                  Jun 07, 2025                                MPI_COMM_CREATE(3)

       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.

       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 MPImanpage for a full list of MPIerrorcodes.

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

       SEEALSO:

          • MPI_Comm_split

       • comm : Communicator (handle).

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

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.

       • newcomm : New communicator (handle).

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

CSyntax
          #include <mpi.h>

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

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

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

   Fortran2008Syntax
          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