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MPI_Cart_sub(3OpenMPI)                                                                MPI_Cart_sub(3OpenMPI)



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


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




Open MPI 1.2                                   September 2006                         MPI_Cart_sub(3OpenMPI)