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
- 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