oracular (3) MPI_Comm_create.openmpi.3.gz

NAME

       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

C++ Syntax

       #include <mpi.h>
       MPI::Intercomm MPI::Intercomm::Create(const Group& group) const

       MPI::Intracomm MPI::Intracomm::Create(const Group& group) const

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.

ERRORS

       Almost  all  MPI  routines  return  an  error  value; C routines as the value of the function and Fortran
       routines in the last argument. C++ functions do not return errors. If the default error handler is set to
       MPI::ERRORS_THROW_EXCEPTIONS,  then  on  error  the  C++  exception  mechanism  will  be used to throw an
       MPI::Exception object.

       Before the error value is returned, the current MPI error handler  is  called.  By  default,  this  error
       handler  aborts  the  MPI  job,  except  for  I/O  function errors. The error handler may be changed with
       MPI_Comm_set_errhandler; the predefined error handler MPI_ERRORS_RETURN may be used to cause error values
       to be returned. Note that MPI does not guarantee that an MPI program can continue past an error.

SEE ALSO

       MPI_Comm_split

       MPI_Intercomm_create MPI_Comm_create_group