MPI_Cart_sub(3)                    Open MPI                    MPI_Cart_sub(3)



NAME
       MPI_Cart_sub  - Partitions a communicator into subgroups, which form
       lower-dimensional Cartesian subgrids.


SYNTAX
C Syntax
       #include <mpi.h>
       int MPI_Cart_sub(MPI_Comm comm, int *remain_dims, MPI_Comm *comm_new)


Fortran Syntax
       INCLUDE 'mpif.h'
       MPI_CART_SUB(COMM, REMAIN_DIMS, COMM_NEW, IERROR)
            INTEGER   COMM, COMM_NEW, IERROR
            LOGICAL   REMAIN_DIMS(*)


C++ Syntax
       #include <mpi.h>
       Cartcomm Cartcomm::Sub(const bool remain_dims[]) const


INPUT PARAMETERS
       comm      Communicator with Cartesian structure (handle).

       remain_dims
                 The ith entry of remain_dims specifies whether the ith
                 dimension is kept in the subgrid (true) or is dropped (false)
                 (logical vector).


OUTPUT PARAMETERS
       comm_new  Communicator containing the subgrid that includes the calling
                 process (handle).

       IERROR    Fortran only: Error status (integer).


DESCRIPTION
       If a Cartesian topology has been created with MPI_Cart_create, the
       function  MPI_Cart_sub can be used to partition the communicator group
       into subgroups that form lower-dimensional Cartesian subgrids, and to
       build for each subgroup a communicator with the associated subgrid
       Cartesian topology. (This function is closely related to
       MPI_Comm_split.)

       Example: Assume that  MPI_Cart_create( ..., comm) has defined a (2 x 3
       x 4)   grid. Let  remain_dims = (true, false, true). Then a call to

           MPI_Cart_sub(comm, remain_dims, comm_new)

       will create three communicators, each with eight processes in a 2 x 4
       Cartesian topology. If remain_dims = (false, false, true) then the call
       to MPI_Cart_sub(comm, remain_dims, comm_new) will create six
       nonoverlapping communicators, each with four processes, in a one-
       dimensional Cartesian topology.


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_Cart_create
       MPI_Comm_split




1.4.1                            Jan 14, 2010                  MPI_Cart_sub(3)
