MPI_Cart_sub(3) Open MPI MPI_Cart_sub(3)
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
USE MPI
! or the older form: INCLUDE 'mpif.h'
MPI_CART_SUB(COMM, REMAIN_DIMS, COMM_NEW, IERROR)
INTEGER COMM, COMM_NEW, IERROR
LOGICAL REMAIN_DIMS(*)
Fortran 2008 Syntax
USE mpi_f08
MPI_Cart_sub(comm, remain_dims, newcomm, ierror)
TYPE(MPI_Comm), INTENT(IN) :: comm
LOGICAL, INTENT(IN) :: remain_dims(*)
TYPE(MPI_Comm), INTENT(OUT) :: newcomm
INTEGER, OPTIONAL, INTENT(OUT) :: ierror
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 dimen-
sion 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 nonover-
lapping 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++ func-
tions 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
4.1.2 Nov 24, 2021 MPI_Cart_sub(3)
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