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MPI_Cart_sub

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