1 | .\"Copyright 2006-2008 Sun Microsystems, Inc. |
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2 | .\"Copyright (c) 1996 Thinking Machines |
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3 | .TH MPI_Cart_shift 3 "Dec 08, 2009" "1.4" "Open MPI" |
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4 | .SH NAME |
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5 | \fBMPI_Cart_shift \fP \- Returns the shifted source and destination ranks, given a shift direction and amount. |
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6 | |
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7 | .SH SYNTAX |
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8 | .ft R |
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9 | .SH C Syntax |
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10 | .nf |
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11 | #include <mpi.h> |
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12 | int MPI_Cart_shift(MPI_Comm \fIcomm\fP, int\fI direction\fP, int\fI disp\fP, |
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13 | int\fI *rank_source\fP, int\fI *rank_dest\fP) |
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14 | |
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15 | .SH Fortran Syntax |
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16 | .nf |
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17 | INCLUDE 'mpif.h' |
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18 | MPI_CART_SHIFT(\fICOMM, DIRECTION, DISP, RANK_SOURCE, |
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19 | RANK_DEST, IERROR\fP) |
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20 | INTEGER \fICOMM, DIRECTION, DISP, RANK_SOURCE\fP |
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21 | INTEGER \fIRANK_DEST, IERROR\fP |
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22 | |
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23 | .SH C++ Syntax |
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24 | .nf |
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25 | #include <mpi.h> |
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26 | void Cartcomm::Shift(int \fIdirection\fP, int \fIdisp\fP, int& \fIrank_source\fP, |
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27 | int& \fIrank_dest\fP) const |
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28 | |
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29 | .SH INPUT PARAMETERS |
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30 | .ft R |
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31 | .TP 1i |
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32 | comm |
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33 | Communicator with Cartesian structure (handle). |
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34 | .TP 1i |
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35 | direction |
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36 | Coordinate dimension of shift (integer). |
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37 | .TP 1i |
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38 | disp |
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39 | Displacement ( > 0: upward shift, < 0: downward shift) (integer). |
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40 | |
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41 | .SH OUTPUT PARAMETERS |
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42 | .ft R |
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43 | .TP 1i |
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44 | rank_source |
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45 | Rank of source process (integer). |
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46 | .TP 1i |
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47 | rank_dest |
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48 | Rank of destination process (integer). |
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49 | .ft R |
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50 | .TP 1i |
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51 | IERROR |
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52 | Fortran only: Error status (integer). |
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53 | |
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54 | .SH DESCRIPTION |
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55 | .ft R |
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56 | 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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57 | .sp |
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58 | 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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59 | .sp |
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60 | \fBNote:\fP The direction argument is in the range [0, n-1] for an n-dimensional Cartesian mesh. |
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61 | .sp |
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62 | 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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63 | .sp |
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64 | \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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65 | .sp |
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66 | .nf |
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67 | \&.... |
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68 | C find process rank |
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69 | CALL MPI_COMM_RANK(comm, rank, ierr)) |
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70 | C find Cartesian coordinates |
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71 | CALL MPI_CART_COORDS(comm, rank, maxdims, coords, |
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72 | ierr) |
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73 | C compute shift source and destination |
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74 | CALL MPI_CART_SHIFT(comm, 0, coords(2), source, |
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75 | dest, ierr) |
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76 | C skew array |
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77 | CALL MPI_SENDRECV_REPLACE(A, 1, MPI_REAL, dest, 0, |
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78 | source, 0, comm, status, |
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79 | ierr) |
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80 | .fi |
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81 | |
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82 | .SH NOTE |
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83 | 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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84 | |
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85 | .SH ERRORS |
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86 | 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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87 | .sp |
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88 | Before the error value is returned, the current MPI error handler is |
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89 | 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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90 | |
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