MPI_Comm_create(3) man page (version 4.0.7)

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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

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

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Table of Contents

• Name
• Syntax
• C Syntax
• Fortran Syntax
• Fortran 2008 Syntax
• Input Parameter
• Output Parameters
• Description
• Notes
• Errors
• See Also

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Page last modified: 16-Nov-2021
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