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MPI_Cart_sub(3) man page (version 1.8)

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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

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