MPI_CART_SHIFT(3)				     Open MPI					 MPI_CART_SHIFT(3)

MPI_Cart_shift — Returns the shifted source and destination ranks, given a shift direction and amount.

SYNTAX
   C Syntax
	  #include <mpi.h>

	  int MPI_Cart_shift(MPI_Comm comm, int direction, int disp,
	      int *rank_source, int *rank_dest)

   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

   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

INPUT PARAMETERS
       • comm : Communicator with Cartesian structure (handle).

       • direction : Coordinate dimension of shift (integer).

       •

	 disp (Displacement ( > 0: upward shift, < 0: downward shift))
		(integer).

OUTPUT PARAMETERS
       • rank_source : Rank of source process (integer).

       • rank_dest : Rank of destination process (integer).

       • ierror : Fortran only: Error status (integer).

DESCRIPTION
       If the process topology is a Cartesian structure, an MPI_Sendrecv <#mpi-sendrecv> operation is likely to be
       used  along a coordinate direction to perform a shift of data. As input, MPI_Sendrecv <#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  <#mpi-sendrecv>.	 The  user  specifies  the
       coordinate direction and the size of the step (positive or negative). The function is local.

       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.

	  ! 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)

NOTE
       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].

ERRORS
       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>/MPI_Init_thread <#mpi-init-thread>,
       after MPI_Finalize <#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 <#
       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  <#mpi-comm-spawn>/MPI_Comm_spawn_multiple	<#
       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.

       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 <#mpi-abort> was called on that communicator. If called
	 on  a window or file, acts as if MPI_Abort <#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 by calling:

       • MPI_Comm_create_errhandler	<#mpi-comm-create-errhandler>	  then	   MPI_Comm_set_errhandler	<#
	 mpi-comm-set-errhandler>

       • MPI_File_create_errhandler	 <#mpi-file-create-errhandler>	   then	    MPI_File_set_errhandler	<#
	 mpi-file-set-errhandler>

       • MPI_Session_create_errhandler	 <#mpi-session-create-errhandler>   then   MPI_Session_set_errhandler	<#
	 mpi-session-set-errhandler> or at MPI_Session_init <#mpi-session-init>

       • MPI_Win_create_errhandler	<#mpi-win-create-errhandler>	  then	    MPI_Win_set_errhandler	<#
	 mpi-win-set-errhandler>

       Note that MPI does not guarantee that an MPI program can continue past an error.

       See the MPI man page <#open-mpi> for a full list of MPI error codes <#open-mpi-errors>.

       See the Error Handling section of the MPI-3.1 standard for more information.

Copyright
       2003-2026, The Open MPI Community

						   Mar 05, 2026					 MPI_CART_SHIFT(3)
