92 строки
4.3 KiB
Groff
92 строки
4.3 KiB
Groff
.\"Copyright 2006, Sun Microsystems, Inc. All rights reserved. Use is subject to license terms.
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.\"Copyright (c) 1996 Thinking Machines Corporation
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.TH MPI_Cart_shift 3OpenMPI "September 2006" "Open MPI 1.2" " "
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.SH NAME
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\fBMPI_Cart_shift \fP \- Returns the shifted source and destination ranks, given a shift direction and amount.
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.SH SYNTAX
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.ft R
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.SH C Syntax
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.nf
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#include <mpi.h>
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int MPI_Cart_shift(MPI_Comm \fIcomm\fP, int\fI direction\fP, int\fI disp\fP,
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int\fI *rank_source\fP, int\fI *rank_dest\fP)
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.SH Fortran Syntax
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.nf
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INCLUDE 'mpif.h'
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MPI_CART_SHIFT(\fICOMM, DIRECTION, DISP, RANK_SOURCE,
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RANK_DEST, IERROR\fP)
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INTEGER \fICOMM, DIRECTION, DISP, RANK_SOURCE\fP
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INTEGER \fIRANK_DEST, IERROR\fP
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.SH C++ Syntax
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.nf
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#include <mpi.h>
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void Cartcomm::Shift(int \fIdirection\fP, int \fIdisp\fP, int& \fIrank_source\fP,
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int& \fIrank_dest\fP) const
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.SH INPUT PARAMETERS
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.ft R
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.TP 1i
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comm
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Communicator with Cartesian structure (handle).
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.TP 1i
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direction
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Coordinate dimension of shift (integer).
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.TP 1i
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disp
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Displacement ( > 0: upward shift, < 0: downward shift) (integer).
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.SH OUTPUT PARAMETERS
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.ft R
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.TP 1i
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rank_source
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Rank of source process (integer).
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.TP 1i
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rank_dest
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Rank of destination process (integer).
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.ft R
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.TP 1i
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IERROR
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Fortran only: Error status (integer).
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.SH DESCRIPTION
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.ft R
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If the process topology is a Cartesian structure, an MPI_Sendrecv operation is likely to be used along a coordinate direction to 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.
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.sp
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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.
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.sp
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\fBNote:\fP The direction argument is in the range [0, n-1] for an n-dimensional Cartesian mesh.
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.sp
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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.
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.sp
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\fBExample:\fP 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.
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.sp
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.nf
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\&....
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C find process rank
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CALL MPI_COMM_RANK(comm, rank, ierr))
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C find Cartesian coordinates
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CALL MPI_CART_COORDS(comm, rank, maxdims, coords,
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ierr)
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C compute shift source and destination
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CALL MPI_CART_SHIFT(comm, 0, coords(2), source,
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dest, ierr)
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C skew array
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CALL MPI_SENDRECV_REPLACE(A, 1, MPI_REAL, dest, 0,
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source, 0, comm, status,
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ierr)
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.fi
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.SH NOTE
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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].
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.SH ERRORS
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Almost all MPI routines return an error value; C routines as the value of the function and Fortran routines in the last argument. C++ functions do not return errors. If the default error handler is set to MPI::ERRORS_THROW_EXCEPTIONS, then on error the C++ exception mechanism will be used to throw an MPI:Exception object.
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.sp
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Before the error value is returned, the current MPI error handler is
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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.
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' @(#)MPI_Cart_shift.3 1.20 06/03/09
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