17.2.48. MPI_Comm_create

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

! or the older form: INCLUDE 'mpif.h'


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. 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