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, const 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