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NAME

MPI_Cart_sub - Construct a subgrid from a cartesian communicator

SYNOPSIS

#include <mpi.h> int MPI_Cart_sub(MPI_Comm comm , int *remain_dims , MPI_Comm *out );

#include <pmpi.h> int PMPI_Cart_sub(MPI_Comm comm , int *remain_dims , MPI_Comm *out );

#include <mpi.h> MPI::Cartcomm MPI::Cartcomm::Sub(const bool *remain_dims ) const;

INCLUDE 'mpif.h' MPI_CART_SUB(comm , remain_dims , out , ierr ) INTEGER comm , remain_dims , out , ierr

INPUT PARAMETERS

comm - cartesian communicator (handle)

remain_dims - array of dimensions to retain (array of boolean)

OUTPUT PARAMETER

out - the resulting cartesian communicator (handle).

DESCRIPTION

The MPI_Cart_sub() function is used to subdivde a cartesian communcator comm into subgrids. By choosing which dimensions to retain within remain_dims it is possible to determine the form of the partitioning. The new cartesian communicator is returned in out .

This function is somewhat similar to the MPI_Comm_split() function. The returned communicator should eventually be freed by the MPI_Comm_free() function.

In C++, the new cartesian communicator out is the return value.

Note that the communicator must be a valid one (not MPI_COMM_NULL). PMPI_Cart_sub() is the profiling version of this function.

ERRORS

All MPI routines except for MPI_Wtime and MPI_Wtick return an error code. The the current MPI error handler is invoked if the return value is not MPI_SUCCESS. The default error handler aborts, but this may be changed with by using the MPI_Errhandler_set() function. The predefined error handler MPI_ERRORS_RETURN may be used to cause error values to be returned instead. Note that MPI does not guarentee that an MPI program can continue past an error. In this implementation, all errors except MPI_ERR_INTERN or MPI_ERR_OTHER should always be recoverable.

In C, the error code is passed as the return value. In FORTRAN, all functions have an parameter ierr which returns the error code. MPI C++ functions do not directly return an error code. However, C++ users may want to use the MPI::ERRORS_THROW_EXCEPTIONS handler. This will throw an MPI::Exception with the corresponding error code. To prevent exceptions from being raised from within C and Fortran code, they will see all error return values as MPI_ERR_PENDING when this handler is chosen. In this implementation, call MPI::throw_exception() to throw the correct exception if this occurs.

MPI_SUCCESS - No error;

MPI_ERR_PENDING - Pending exception;

MPI_ERR_COMM - Invalid communicator;

MPI_ERR_TOPOLOGY - Not a cartesian communicator;

MPI_ERR_DIMS - Invalid dimension array;

MPI_ERR_ARG - Invalid output pointer;

MPI_ERR_INTERN - Out of Memory. This may be fatal.

SEE ALSO

MPI_Comm_create (3) MPI_Comm_split (3) MPI_Comm_free (3) MPI_Cart_create (3)

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