[97] | 1 | .\"Copyright 2006-2008 Sun Microsystems, Inc. |
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| 2 | .\" Copyright (c) 1996 Thinking Machines Corporation |
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| 3 | .TH MPI_Graph_neighbors 3 "Dec 08, 2009" "1.4" "Open MPI" |
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| 4 | .SH NAME |
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| 5 | \fBMPI_Graph_neighbors \fP \- Returns the neighbors of a node associated with a graph topology. |
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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_Graph_neighbors(MPI_Comm \fIcomm\fP, int\fI rank\fP, int\fI maxneighbors\fP, |
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| 13 | int\fI *neighbors\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_GRAPH_NEIGHBORS(\fICOMM, RANK, MAXNEIGHBORS, NEIGHBORS, IERROR\fP) |
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| 19 | INTEGER \fICOMM, RANK, MAXNEIGHBORS, NEIGHBORS(*), IERROR\fP |
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| 20 | |
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| 21 | .SH C++ Syntax |
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| 22 | .nf |
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| 23 | #include <mpi.h> |
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| 24 | void Graphcomm::Get_neighbors(int \fIrank\fP, int \fImaxneighbors\fP, |
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| 25 | int \fIneighbors\fP[]) const |
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| 26 | |
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| 27 | .SH INPUT PARAMETERS |
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| 28 | .ft R |
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| 29 | .TP 1i |
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| 30 | comm |
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| 31 | Communicator with graph topology (handle). |
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| 32 | .TP 1i |
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| 33 | rank |
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| 34 | Rank of process in group of comm (integer). |
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| 35 | .TP 1i |
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| 36 | maxneighbors |
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| 37 | Size of array neighbors (integer). |
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| 38 | |
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| 39 | .SH OUTPUT PARAMETERS |
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| 40 | .ft R |
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| 41 | .TP 1i |
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| 42 | neighbors |
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| 43 | Ranks of processes that are neighbors to specified process (array of integers). |
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| 44 | .ft R |
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| 45 | .TP 1i |
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| 46 | IERROR |
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| 47 | Fortran only: Error status (integer). |
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| 48 | |
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| 49 | .SH DESCRIPTION |
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| 50 | .ft R |
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| 51 | \fBExample:\fP Suppose that comm is a communicator with a shuffle-exchange |
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| 52 | topology. The group has 2n members. Each process is labeled by a(1),\ ..., a(n) with a(i) E{0,1}, and has three neighbors: exchange (a(1),\ ..., a(n) = a(1),\ ..., a(n-1), a(n) (a = 1 - a), shuffle (a(1),\ ..., a(n)) = a(2),\ ..., a(n), a(1), and unshuffle (a(1),\ ..., a(n)) = a(n), a(1),\ ..., a(n-1). The graph adjacency list is illustrated below for n=3. |
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| 53 | .sp |
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| 54 | .nf |
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| 55 | exchange shuffle unshuffle |
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| 56 | node neighbors(1) neighbors(2) neighbors(3) |
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| 57 | 0(000) 1 0 0 |
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| 58 | 1(001) 0 2 4 |
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| 59 | 2(010) 3 4 1 |
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| 60 | 3(011) 2 6 5 |
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| 61 | 4(100) 5 1 2 |
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| 62 | 5(101) 4 3 6 |
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| 63 | 6(110) 7 5 3 |
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| 64 | 7(111) 6 7 7 |
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| 65 | .fi |
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| 66 | .sp |
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| 67 | Suppose that the communicator comm has this topology associated with it. The following code fragment cycles through the three types of neighbors and performs an appropriate permutation for each. |
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| 68 | .sp |
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| 69 | .nf |
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| 70 | C assume: each process has stored a real number A. |
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| 71 | C extract neighborhood information |
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| 72 | CALL MPI_COMM_RANK(comm, myrank, ierr) |
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| 73 | CALL MPI_GRAPH_NEIGHBORS(comm, myrank, 3, neighbors, ierr) |
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| 74 | C perform exchange permutation |
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| 75 | CALL MPI_SENDRECV_REPLACE(A, 1, MPI_REAL, neighbors(1), 0, |
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| 76 | + neighbors(1), 0, comm, status, ierr) |
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| 77 | C perform shuffle permutation |
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| 78 | CALL MPI_SENDRECV_REPLACE(A, 1, MPI_REAL, neighbors(2), 0, |
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| 79 | + neighbors(3), 0, comm, status, ierr) |
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| 80 | C perform unshuffle permutation |
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| 81 | CALL MPI_SENDRECV_REPLACE(A, 1, MPI_REAL, neighbors(3), 0, |
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| 82 | + neighbors(2), 0, comm, status, ierr) |
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| 83 | |
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| 84 | .SH ERRORS |
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| 85 | 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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| 86 | .sp |
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| 87 | Before the error value is returned, the current MPI error handler is |
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| 88 | 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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| 89 | |
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| 90 | .SH SEE ALSO |
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| 91 | .ft R |
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| 92 | .sp |
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| 93 | MPI_Graph_neighbors_count |
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| 94 | |
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