100 строки
3.6 KiB
Plaintext
100 строки
3.6 KiB
Plaintext
.\" Copyright 2010 Cisco Systems, Inc. All rights reserved.
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.\" Copyright 2006-2008 Sun Microsystems, Inc.
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.\" Copyright (c) 1996 Thinking Machines Corporation
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.TH MPI_Graph_neighbors 3 "#OMPI_DATE#" "#PACKAGE_VERSION#" "#PACKAGE_NAME#"
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.SH NAME
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\fBMPI_Graph_neighbors \fP \- Returns the neighbors of a node associated with a graph topology.
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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_Graph_neighbors(MPI_Comm \fIcomm\fP, int\fI rank\fP, int\fI maxneighbors\fP,
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int\fI *neighbors\fP)
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.fi
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.SH Fortran Syntax
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.nf
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INCLUDE 'mpif.h'
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MPI_GRAPH_NEIGHBORS(\fICOMM, RANK, MAXNEIGHBORS, NEIGHBORS, IERROR\fP)
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INTEGER \fICOMM, RANK, MAXNEIGHBORS, NEIGHBORS(*), IERROR\fP
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.fi
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.SH C++ Syntax
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.nf
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#include <mpi.h>
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void Graphcomm::Get_neighbors(int \fIrank\fP, int \fImaxneighbors\fP,
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int \fIneighbors\fP[]) const
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.fi
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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 graph topology (handle).
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.TP 1i
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rank
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Rank of process in group of comm (integer).
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.TP 1i
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maxneighbors
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Size of array neighbors (integer).
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.SH OUTPUT PARAMETERS
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.ft R
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.TP 1i
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neighbors
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Ranks of processes that are neighbors to specified process (array of integers).
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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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\fBExample:\fP Suppose that comm is a communicator with a shuffle-exchange
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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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.sp
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.nf
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exchange shuffle unshuffle
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node neighbors(1) neighbors(2) neighbors(3)
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0(000) 1 0 0
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1(001) 0 2 4
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2(010) 3 4 1
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3(011) 2 6 5
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4(100) 5 1 2
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5(101) 4 3 6
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6(110) 7 5 3
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7(111) 6 7 7
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.fi
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.sp
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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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.sp
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.nf
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C assume: each process has stored a real number A.
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C extract neighborhood information
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CALL MPI_COMM_RANK(comm, myrank, ierr)
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CALL MPI_GRAPH_NEIGHBORS(comm, myrank, 3, neighbors, ierr)
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C perform exchange permutation
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CALL MPI_SENDRECV_REPLACE(A, 1, MPI_REAL, neighbors(1), 0,
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+ neighbors(1), 0, comm, status, ierr)
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C perform shuffle permutation
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CALL MPI_SENDRECV_REPLACE(A, 1, MPI_REAL, neighbors(2), 0,
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+ neighbors(3), 0, comm, status, ierr)
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C perform unshuffle permutation
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CALL MPI_SENDRECV_REPLACE(A, 1, MPI_REAL, neighbors(3), 0,
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+ neighbors(2), 0, comm, status, ierr)
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.fi
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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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.SH SEE ALSO
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.ft R
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.sp
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MPI_Graph_neighbors_count
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