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96 lines
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<!DOCTYPE html PUBLIC "-//W3C//DTD XHTML 1.0 Transitional//EN" "http://www.w3.org/TR/xhtml1/DTD/xhtml1-transitional.dtd">
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<meta name="generator" content="Docutils 0.6: http://docutils.sourceforge.net/" />
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<title>Parallel BGL Connected Components Parallel Search</title>
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</head>
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<body>
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<div class="document" id="logo-connected-components-parallel-search">
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<h1 class="title"><a class="reference external" href="http://www.osl.iu.edu/research/pbgl"><img align="middle" alt="Parallel BGL" class="align-middle" src="pbgl-logo.png" /></a> Connected Components Parallel Search</h1>
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<!-- Copyright (C) 2004-2009 The Trustees of Indiana University.
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Use, modification and distribution is subject to the Boost Software
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License, Version 1.0. (See accompanying file LICENSE_1_0.txt or copy at
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http://www.boost.org/LICENSE_1_0.txt) -->
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<pre class="literal-block">
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namespace graph { namespace distributed {
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template<typename Graph, typename ComponentMap>
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typename property_traits<ComponentMap>::value_type
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connected_components_ps(const Graph& g, ComponentMap c)
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} }
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</pre>
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<p>The <tt class="docutils literal"><span class="pre">connected_components_ps()</span></tt> function computes the connected
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components of a graph by performing a breadth-first search from
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several sources in parallel while recording and eventually resolving
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the collisions.</p>
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<div class="contents topic" id="contents">
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<p class="topic-title first">Contents</p>
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<ul class="simple">
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<li><a class="reference internal" href="#where-defined" id="id1">Where Defined</a></li>
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<li><a class="reference internal" href="#parameters" id="id2">Parameters</a></li>
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<li><a class="reference internal" href="#complexity" id="id3">Complexity</a></li>
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<li><a class="reference internal" href="#algorithm-description" id="id4">Algorithm Description</a></li>
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</ul>
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</div>
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<div class="section" id="where-defined">
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<h1><a class="toc-backref" href="#id1">Where Defined</a></h1>
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<p><<tt class="docutils literal"><span class="pre">boost/graph/distributed/connected_components_parallel_search.hpp</span></tt>></p>
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</div>
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<div class="section" id="parameters">
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<h1><a class="toc-backref" href="#id2">Parameters</a></h1>
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<dl class="docutils">
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<dt>IN: <tt class="docutils literal"><span class="pre">const</span> <span class="pre">Graph&</span> <span class="pre">g</span></tt></dt>
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<dd>The graph type must be a model of <a class="reference external" href="DistributedGraph.html">Distributed Graph</a>. The graph
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type must also model the <a class="reference external" href="http://www.boost.org/libs/graph/doc/IncidenceGraph.html">Incidence Graph</a> and be directed.</dd>
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<dt>OUT: <tt class="docutils literal"><span class="pre">ComponentMap</span> <span class="pre">c</span></tt></dt>
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<dd>The algorithm computes how many connected components are in the
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graph, and assigns each component an integer label. The algorithm
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then records to which component each vertex in the graph belongs by
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recording the component number in the component property map. The
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<tt class="docutils literal"><span class="pre">ComponentMap</span></tt> type must be a <a class="reference external" href="distributed_property_map.html">Distributed Property Map</a>. The
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value type must be the <tt class="docutils literal"><span class="pre">vertices_size_type</span></tt> of the graph. The key
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type must be the graph's vertex descriptor type.</dd>
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</dl>
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</div>
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<div class="section" id="complexity">
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<h1><a class="toc-backref" href="#id3">Complexity</a></h1>
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<p><em>O(PN^2 + VNP)</em> work, in <em>O(N + V)</em> time, where N is the
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number of mappings and V is the number of local vertices.</p>
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</div>
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<div class="section" id="algorithm-description">
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<h1><a class="toc-backref" href="#id4">Algorithm Description</a></h1>
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<p>Every <em>N</em> th nodes starts a parallel search from the first vertex in
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their local vertex list during the first superstep (the other nodes
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remain idle during the first superstep to reduce the number of
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conflicts in numbering the components). At each superstep, all new
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component mappings from remote nodes are handled. If there is no work
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from remote updates, a new vertex is removed from the local list and
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added to the work queue.</p>
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<p>Components are allocated from the <tt class="docutils literal"><span class="pre">component_value_allocator</span></tt>
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object, which ensures that a given component number is unique in the
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system, currently by using the rank and number of processes to stride
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allocations.</p>
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<p>When two components are discovered to actually be the same component,
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a collision is recorded. The lower component number is prefered in
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the resolution, so component numbering resolution is consistent.
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After the search has exhausted all vertices in the graph, the mapping
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is shared with all processes and they independently resolve the
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comonent mapping. This phase can likely be significantly sped up if a
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clever algorithm for the reduction can be found.</p>
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<hr class="docutils" />
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<p>Copyright (C) 2009 The Trustees of Indiana University.</p>
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<p>Authors: Brian Barrett, Douglas Gregor, and Andrew Lumsdaine</p>
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</div>
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</div>
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Generated on: 2009-05-31 00:21 UTC.
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Generated by <a class="reference external" href="http://docutils.sourceforge.net/">Docutils</a> from <a class="reference external" href="http://docutils.sourceforge.net/rst.html">reStructuredText</a> source.
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