MPI_Cart_shift - Returns the shifted source and destination ranks, given a shift direction and amount.
184.108.40.206.1. C Syntax
#include <mpi.h> int MPI_Cart_shift(MPI_Comm comm, int direction, int disp, int *rank_source, int *rank_dest)
220.127.116.11.2. Fortran Syntax
USE MPI ! or the older form: INCLUDE 'mpif.h' MPI_CART_SHIFT(COMM, DIRECTION, DISP, RANK_SOURCE, RANK_DEST, IERROR) INTEGER COMM, DIRECTION, DISP, RANK_SOURCE INTEGER RANK_DEST, IERROR
18.104.22.168.3. Fortran 2008 Syntax
USE mpi_f08 MPI_Cart_shift(comm, direction, disp, rank_source, rank_dest, ierror) TYPE(MPI_Comm), INTENT(IN) :: comm INTEGER, INTENT(IN) :: direction, disp INTEGER, INTENT(OUT) :: rank_source, rank_dest INTEGER, OPTIONAL, INTENT(OUT) :: ierror
22.214.171.124. INPUT PARAMETERS
comm: Communicator with Cartesian structure (handle).
direction: Coordinate dimension of shift (integer).
disp: Displacement ( > 0: upward shift, < 0: downward shift) (integer).
126.96.36.199. OUTPUT PARAMETERS
rank_source: Rank of source process (integer).
rank_dest: Rank of destination process (integer).
IERROR: Fortran only: Error status (integer).
If the process topology is a Cartesian structure, an MPI_Sendrecv
operation is likely to be used along a coordinate
perform a shift of data. As input, MPI_Sendrecv takes the rank of a
source process for the receive, and the rank of a destination process
for the send. If the function MPI_Cart_shift is called for a
Cartesian process group, it provides the calling process with the above
identifiers, which then can be passed to MPI_Sendrecv. The user
specifies the coordinate
direction and the size of the step
(positive or negative). The function is local.
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.
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
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_dest, indicating that the source or the destination for the
shift is out of range.
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.
! find process rank CALL MPI_COMM_RANK(comm, rank, ierr) ! find Cartesian coordinates CALL MPI_CART_COORDS(comm, rank, maxdims, coords, ierr) ! compute shift source and destination CALL MPI_CART_SHIFT(comm, 0, coords(2), source, dest, ierr) ! skew array CALL MPI_SENDRECV_REPLACE(A, 1, MPI_REAL, dest, 0, source, 0, comm, status, ierr)
In Fortran, the dimension indicated by DIRECTION = i has DIMS(i+1) nodes, where DIMS is the array that was used to create the grid. In C, the dimension indicated by direction = i is the dimension specified by dims[i].
Almost all MPI routines return an error value; C routines as the return result of the function and Fortran routines in the last argument.
Before the error value is returned, the current MPI error handler associated with the communication object (e.g., communicator, window, file) is called. If no communication object is associated with the MPI call, then the call is considered attached to MPI_COMM_SELF and will call the associated MPI error handler. When MPI_COMM_SELF is not initialized (i.e., before MPI_INIT / MPI_INIT_THREAD, after MPI_FINALIZE, or when using the Sessions Model exclusively) the error raises the initial error handler. The initial error handler can be changed by calling MPI_COMM_SET_ERRHANDLER on MPI_COMM_SELF when using the World model, or the mpi_initial_errhandler CLI argument to mpiexec or info key to MPI_COMM_SPAWN[_MULTIPLE]. If no other appropriate error handler has been set, then the MPI_ERRORS_RETURN error handler is called for MPI I/O functions and the MPI_ERRORS_ABORT error handler is called for all other MPI functions.
In the sessions model, the error handler can be set during MPI_Session_init.
Open MPI includes three predefined error handlers that can be used:
MPI_ERRORS_ARE_FATAL: Causes the program to abort all connected MPI processes. MPI_ERRORS_ABORT: An error handler that can be invoked on a communicator, window, file, or session. When called on a communicator, it acts as if MPI_ABORT was called on that communicator. If called on a window or file, acts as if MPI_ABORT was called on a communicator containing the group of processes in the corresponding window or file. If called on a session, aborts only the local process. MPI_ERRORS_RETURN: Returns an error code to the application.
MPI applications can also implement their own error handlers.
Note that MPI does not guarantee that an MPI program can continue past an error.
See the MPI man page for a full list of MPI error codes.
See the Error Handling section of the MPI-3 standard for more information.