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MPI_Cart_sub(3) man page (version 5.0.0rc2)

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Name

C]MPI_Cart_subR] - Partitions a communicator into subgroups, which form lower-dimensional Cartesian subgrids.

Syntax

C Syntax



C]#include <mpi.h>int MPI_Cart_sub(MPI_Comm comm, const int remain_dims[], MPI_Comm *comm_new)R]Fortran Syntax



C]USE MPI! or the older form: INCLUDE [aq]mpif.h[aq]MPI_CART_SUB(COMM, REMAIN_DIMS, COMM_NEW, IERROR) INTEGER COMM, COMM_NEW, IERROR LOGICAL REMAIN_DIMS(*)R]Fortran 2008 Syntax



C]USE mpi_f08MPI_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) :: ierrorR]Input Parameters

[bu]
C]commR] : Communicator with Cartesian structure (handle).
[bu]
C]remain_dimsR] : The ith entry of C]remain_dimsR] specifies whether the ith dimension is kept in the subgrid (true) or is dropped (false) (logical vector).

Output Parameters

[bu]
C]comm_newR] : Communicator containing the subgrid that includes the calling process (handle).
[bu]
C]IERRORR] : Fortran only: Error status (integer).

Description

If a Cartesian topology has been created with C]MPI_Cart_createR], the function C]MPI_Cart_subR] 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 C]MPI_Comm_splitR].)

Example: Assume that C]MPI_Cart_create( ..., comm)R] has defined a (2 x 3 x 4) grid. Let C]remain_dimsR] = (true, false, true). Then a call to


C]MPI_Cart_sub(comm, remain_dims, comm_new)R]will create three communicators, each with eight processes in a 2 x 4
Cartesian topology. If C]remain_dims = (false, false, true)R] then the call to C]MPI_Cart_sub(comm, remain_dims, comm_new)R] 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. 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 C]MPI_Comm_set_errhandlerR]; the predefined error handler C]MPI_ERRORS_RETURNR] 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

C]MPI_Cart_createR](3) C]MPI_Comm_splitR](3)


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