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| <Head> |
| <Title>Boost Graph Library: Connected Components</Title> |
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| <H1> |
| <A NAME="sec:connected-components"> |
| <img src="figs/python.gif" alt="(Python)"/> |
| <TT>connected_components</TT></A> |
| </H1> |
| |
| <PRE> |
| <i>// named parameter version</i> |
| template <class VertexListGraph, class ComponentMap, class P, class T, class R> |
| typename property_traits<ComponentMap>::value_type |
| connected_components(VertexListGraph& G, ComponentMap comp, |
| const bgl_named_params<P, T, R>& params = <i>all defaults</i>); |
| |
| <i>// there is not a non-named parameter version of this function</i> |
| </PRE> |
| |
| <P> |
| The <TT>connected_components()</TT> functions compute the connected |
| components of an undirected graph using a DFS-based approach. A |
| <b><I>connected component</I></b> of an undirected graph is a set of |
| vertices that are all reachable from each other. If the connected |
| components need to be maintained while a graph is growing the |
| disjoint-set based approach of function <a |
| href="./incremental_components.html"> |
| <TT>incremental_components()</TT></a> is faster. For ``static'' graphs |
| this DFS-based approach is faster [<A |
| HREF="bibliography.html#clr90">8</A>]. |
| |
| <P> |
| The output of the algorithm is recorded in the component property map |
| <TT>comp</TT>, which will contain numbers giving the component number |
| assigned to each vertex. The total number of components is the return |
| value of the function. |
| |
| <H3>Where Defined</H3> |
| |
| <P> |
| <a href="../../../boost/graph/connected_components.hpp"><TT>boost/graph/connected_components.hpp</TT></a> |
| |
| |
| <h3>Parameters</h3> |
| |
| IN: <tt>const Graph& g</tt> |
| <blockquote> |
| An undirected graph. The graph type must be a model of <a |
| href="VertexListGraph.html">Vertex List Graph</a> and <a |
| href="IncidenceGraph.html">Incidence Graph</a>.<br> |
| |
| <b>Python</b>: The parameter is named <tt>graph</tt>. |
| </blockquote> |
| |
| OUT: <tt>ComponentMap c</tt> |
| <blockquote> |
| The algorithm computes how many connected components are in the graph, |
| and assigning each component an integer label. The algorithm then |
| records which component each vertex in the graph belongs to by |
| recording the component number in the component property map. The |
| <tt>ComponentMap</tt> type must be a model of <a |
| href="../../property_map/doc/WritablePropertyMap.html">Writable Property |
| Map</a>. The value type shouch be an integer type, preferably the same |
| as the <tt>vertices_size_type</tt> of the graph. The key type must be |
| the graph's vertex descriptor type.<br> |
| |
| <b>Python</b>: Must be an <tt>vertex_int_map</tt> for the graph.<br> |
| <b>Python default</b>: <tt>graph.get_vertex_int_map("component")</tt> |
| </blockquote> |
| |
| <h3>Named Parameters</h3> |
| |
| UTIL: <tt>color_map(ColorMap color)</tt> |
| <blockquote> |
| This is used by the algorithm to keep track of its progress through |
| the graph. The type <tt>ColorMap</tt> must be a model of <a |
| href="../../property_map/doc/ReadWritePropertyMap.html">Read/Write |
| Property Map</a> and its key type must be the graph's vertex |
| descriptor type and the value type of the color map must model |
| <a href="./ColorValue.html">ColorValue</a>.<br> |
| <b>Default:</b> an <a |
| href="../../property_map/doc/iterator_property_map.html"> |
| </tt>iterator_property_map</tt></a> created from a |
| <tt>std::vector</tt> of <tt>default_color_type</tt> of size |
| <tt>num_vertices(g)</tt> and using the <tt>i_map</tt> for the index |
| map.<br> |
| <b>Python</b>: The color map must be a <tt>vertex_color_map</tt> for |
| the graph. |
| </blockquote> |
| |
| IN: <tt>vertex_index_map(VertexIndexMap i_map)</tt> |
| <blockquote> |
| This maps each vertex to an integer in the range <tt>[0, |
| num_vertices(g))</tt>. This parameter is only necessary when the |
| default color property map is used. The type <tt>VertexIndexMap</tt> |
| must be a model of <a |
| href="../../property_map/doc/ReadablePropertyMap.html">Readable Property |
| Map</a>. The value type of the map must be an integer type. The |
| vertex descriptor type of the graph needs to be usable as the key |
| type of the map.<br> |
| |
| <b>Default:</b> <tt>get(vertex_index, g)</tt>. |
| Note: if you use this default, make sure your graph has |
| an internal <tt>vertex_index</tt> property. For example, |
| <tt>adjacenty_list</tt> with <tt>VertexList=listS</tt> does |
| not have an internal <tt>vertex_index</tt> property.<br> |
| |
| <b>Python</b>: Unsupported parameter. |
| </blockquote> |
| |
| |
| <H3>Complexity</H3> |
| |
| <P> |
| The time complexity for the connected components algorithm is also |
| <i>O(V + E)</i>. |
| |
| <P> |
| |
| <h3>See Also</h3> |
| |
| <a href="./strong_components.html"><tt>strong_components()</tt></a> |
| and <a href="./incremental_components.html"><tt>incremental_components()</tt></a> |
| |
| <H3>Example</H3> |
| |
| <P> |
| The file <a |
| href="../example/connected_components.cpp"><tt>examples/connected_components.cpp</tt></a> |
| contains an example of calculating the connected components of an |
| undirected graph. |
| |
| <br> |
| <HR> |
| <TABLE> |
| <TR valign=top> |
| <TD nowrap>Copyright © 2000-2001</TD><TD> |
| <A HREF="http://www.boost.org/people/jeremy_siek.htm">Jeremy Siek</A>, Indiana University (<A HREF="mailto:jsiek@osl.iu.edu">jsiek@osl.iu.edu</A>) |
| </TD></TR></TABLE> |
| |
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