.\"Copyright 2006, Sun Microsystems, Inc.
.\" Copyright (c) 1996 Thinking Machines Corporation
.TH MPI_Comm_create 3OpenMPI "September 2006" "Open MPI 1.2" " "
.SH NAME
\fBMPI_Comm_create\fP \- Creates a new communicator.

.SH SYNTAX
.ft R
.SH C Syntax
.nf
#include <mpi.h>
int MPI_Comm_create(MPI_Comm \fIcomm\fP, MPI_Group\fI group\fP, MPI_Comm\fI *newcomm\fP)

.SH Fortran Syntax
.nf
INCLUDE 'mpif.h'
MPI_COMM_CREATE(\fICOMM, GROUP, NEWCOMM, IERROR\fP)
	INTEGER	\fICOMM, GROUP, NEW, IERROR\fP

.SH C++ Syntax
.nf
#include <mpi.h>
MPI::Intercomm MPI::Intercomm::Create(const Group& \fIgroup\fP) const

MPI::Intracomm MPI::Intracomm::Create(const Group& \fIgroup\fP) const

.SH INPUT PARAMETER
.ft R
.TP 1i
comm
Communicator (handle).
.TP 1i
group
Group, which is a subset of the group of comm (handle).

.SH OUTPUT PARAMETERS
.ft R
.TP 1i
newcomm
New communicator (handle).
.ft R
.TP 1i
IERROR
Fortran only: Error status (integer). 

.SH DESCRIPTION
.ft R
This function creates a new communicator newcomm with communication group
defined by group and a new context. The function sets \fInewcomm\fR to a new communicator that spans all the processes that are in the group.   It sets \fInewcomm\fR to MPI_COMM_NULL for processes that are not in the group.   The call is erroneous if not all group arguments have the same value, or if group is not a subset of the group associated with comm. Note that the call must be executed by all processes in comm, even if they do not belong to the new group. 
.sp
.LP

.SH NOTES
MPI_Comm_create provides a means of making a subset of processes for the purpose of separate MIMD computation, with separate communication space. \fInewcomm\fR, 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. 

.SH 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.
.sp
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.  

.SH SEE ALSO
.ft R
.sp
MPI_Comm_split
.sp
MPI_Intercomm_create