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.