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NAME

MPI_Cart_shift - Returns ranks displaced along a coordinate direction in the cartesian communicator

SYNOPSIS

#include <mpi.h> int MPI_Cart_shift(MPI_Comm comm , int direction , int disp , int *rsource , int *rdest );

#include <pmpi.h> int PMPI_Cart_shift(MPI_Comm comm , int direction , int disp , int *rsource , int *rdest );

#include <mpi.h> void MPI::Cartcomm::Shift(int direction , int disp , int &rsource , int &rdest ) const;

INCLUDE 'mpif.h' MPI_CART_SHIFT(comm , direction , disp , rsource , rdest , ierr ) INTEGER comm , direction , disp , rsource , rdest , ierr

INPUT PARAMETERS

comm - cartesian communicator (handle)

direction - which dimension to displace along (integer)

disp - displacement (integer)

OUTPUT PARAMETERS

rsource - the source rank in this direction and displacement (integer).

rdest - the destination rank in this direction and displacement (integer).

DESCRIPTION

The MPI_Cart_shift() function is used to obtain ranks displaced from the current process along a particular direction within a given cartesian communicator comm . This is useful because in a cartesian communicator, MPI_Sendrecv() is typically used to shift data. The outputs rsource and rdest are the source and destination ranks for that function.

Note that the displacement, disp may be negative, which simply shifts in the opposite direction.

If the displacement overflows outside the cartesian box, then the result depends on the periodicity of the underlying coordinates. Periodic coordinates will wrap. Otherwise, the output ranks will become MPI_PROC_NULL on overflow.

The communicator must be a valid one (not MPI_COMM_NULL). PMPI_Cart_shift() 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_ARG - Invalid arguments.

SEE ALSO

MPI_Cart_create (3) MPI_Cart_rank (3) MPI_Sendrecv (3)

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