122 строки
5.9 KiB
Plaintext
122 строки
5.9 KiB
Plaintext
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.\" -*- nroff -*-
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.\" Copyright 2013 Los Alamos National Security, LLC. All rights reserved.
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.\" 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_Dist_graph_create 3 "#OMPI_DATE#" "#PACKAGE_VERSION#" "#PACKAGE_NAME#"
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.SH NAME
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\fBMPI_Dist_graph_create \fP \- Makes a new communicator to which topology information has been attached.
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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_Dist_graph_create(MPI_Comm \fIcomm_old\fP, int\fI n\fP, const int\fI sources[]\fP,
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const int\fI degrees[]\fP, const int\fI destinations\fP[], const int\fI weights\fP[],
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MPI_Info info, int\fI reorder\fP, MPI_Comm\fI *comm_dist_graph\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_DIST_GRAPH_CREATE(\fICOMM_OLD, N, SOURCES, DEGREES, DESTINATIONS, WEIGHTS,
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INFO, REORDER, COMM_DIST_GRAPH, IERROR\fP)
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INTEGER \fICOMM_OLD, N, SOURCES(*), DEGRES(*), WEIGHTS(*), INFO\fP
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INTEGER \fICOMM_DIST_GRAPH, IERROR\fP
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LOGICAL \fIREORDER\fP
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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_old
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Input communicator without topology (handle).
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.TP 1i
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n
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Number of source nodes for which this process specifies edges (non-negative integer).
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.TP 1i
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sources
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Array containing the \fIn\fP source nodes for which this process species edges (array of non-negative integers).
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.TP 1i
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degrees
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Array specifying the number of destinations for each source node in the source node array (array of non-negative integers).
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.TP 1i
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destinations
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Destination nodes for the source nodes in the source node array (array of non-negative integers).
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.TP 1i
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weights
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Weights for source to destination edges (array of non-negative integers).
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.TP 1i
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Hints on optimization and interpretation of weights (handle).
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.TP 1i
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reorder
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Ranking may be reordered (true) or not (false) (logical).
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.SH OUTPUT PARAMETERS
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.ft R
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.TP 1i
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comm_dist_graph
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Communicator with distibuted graph topology added (handle).
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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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MPI_Dist_graph_create creates a new communicator \fIcomm_dist_graph\fP with distrubuted
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graph topology and returns a handle to the new communicator. The number of processes in
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\fIcomm_dist_graph\fP is identical to the number of processes in \fIcomm_old\fP. Concretely, each process calls the
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constructor with a set of directed (source,destination) communication edges as described below.
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Every process passes an array of \fIn\fP source nodes in the \fIsources\fP array. For each source node, a
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non-negative number of destination nodes is specied in the \fIdegrees\fP array. The destination
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nodes are stored in the corresponding consecutive segment of the \fIdestinations\fP array. More
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precisely, if the i-th node in sources is s, this species \fIdegrees\fP[i] \fIedges\fP (s,d) with d of the j-th
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such edge stored in \fIdestinations\fP[\fIdegrees\fP[0]+...+\fIdegrees\fP[i-1]+j]. The weight of this edge is
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stored in \fIweights\fP[\fIdegrees\fP[0]+...+\fIdegrees\fP[i-1]+j]. Both the \fIsources\fP and the \fIdestinations\fP arrays
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may contain the same node more than once, and the order in which nodes are listed as
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destinations or sources is not signicant. Similarly, different processes may specify edges
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with the same source and destination nodes. Source and destination nodes must be process
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ranks of comm_old. Different processes may specify different numbers of source and
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destination nodes, as well as different source to destination edges. This allows a fully distributed
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specification of the communication graph. Isolated processes (i.e., processes with
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no outgoing or incoming edges, that is, processes that do not occur as source or destination
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node in the graph specication) are allowed. The call to MPI_Dist_graph_create is collective.
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If reorder = false, all processes will have the same rank in comm_dist_graph as in
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comm_old. If reorder = true then the MPI library is free to remap to other processes (of
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comm_old) in order to improve communication on the edges of the communication graph.
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The weight associated with each edge is a hint to the MPI library about the amount or
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intensity of communication on that edge, and may be used to compute a \"best\" reordering.
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.SH WEIGHTS
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.ft R
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Weights are specied as non-negative integers and can be used to influence the process
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remapping strategy and other internal MPI optimizations. For instance, approximate count
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arguments of later communication calls along specic edges could be used as their edge
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weights. Multiplicity of edges can likewise indicate more intense communication between
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pairs of processes. However, the exact meaning of edge weights is not specied by the MPI
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standard and is left to the implementation. An application can supply the special value
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MPI_UNWEIGHTED for the weight array to indicate that all edges have the same (effectively no)
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weight. It is erroneous to supply MPI_UNWEIGHTED for some but not
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all processes of comm_old. If the graph is weighted but \fIn\fP = 0, then MPI_WEIGHTS_EMPTY
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or any arbitrary array may be passed to weights. Note that MPI_UNWEIGHTED and
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MPI_WEIGHTS_EMPTY are not special weight values; rather they are special values for the
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total array argument. In Fortran, MPI_UNWEIGHTED and MPI_WEIGHTS_EMPTY are objects
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like MPI_BOTTOM (not usable for initialization or assignment). See MPI-3 § 2.5.4.
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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.
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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_Dist_graph_create_adjacent
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MPI_Dist_graph_neighbors
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MPI_Dist_graph_neighbors_count
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