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