#include <mpi.h> int MPI_Cart_shift(MPI_Comm comm, int direction, int disp, int *rank_source, int *rank_dest)
INCLUDE 'mpif.h' MPI_CART_SHIFT(COMM, DIRECTION, DISP, RANK_SOURCE, RANK_DEST, IERROR) INTEGER COMM, DIRECTION, DISP, RANK_SOURCE INTEGER RANK_DEST, IERROR
#include <mpi.h> void Cartcomm::Shift(int direction, int disp, int& rank_source, int& rank_dest) const
The direction argument indicates the dimension of the shift, i.e., the coordinate whose value is modified by the shift. The coordinates are numbered from 0 to ndims-1, where ndims is the number of dimensions.
Note: The direction argument is in the range [0, n-1] for an n-dimensional Cartesian mesh.
Depending on the periodicity of the Cartesian group in the specified coordinate direction, MPI_Cart_shift provides the identifiers for a circular or an end-off shift. In the case of an end-off shift, the value MPI_PROC_NULL may be returned in rank_source or rank_dest, indicating that the source or the destination for the shift is out of range.
Example: The communicator, comm, has a two-dimensional, periodic, Cartesian topology associated with it. A two-dimensional array of REALs is stored one element per process, in variable A. One wishes to skew this array, by shifting column i (vertically, i.e., along the column) by i steps.
.... C find process rank CALL MPI_COMM_RANK(comm, rank, ierr)) C find Cartesian coordinates CALL MPI_CART_COORDS(comm, rank, maxdims, coords, ierr) C compute shift source and destination CALL MPI_CART_SHIFT(comm, 0, coords(2), source, dest, ierr) C skew array CALL MPI_SENDRECV_REPLACE(A, 1, MPI_REAL, dest, 0, source, 0, comm, status, ierr)
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.