bionic (3) MPI_Cart_sub.openmpi.3.gz

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