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| <Head> |
| <Title>Boost Graph Library: Breadth-First Visit</Title> |
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| <H1><A NAME="sec:bfv"><img src="figs/python.gif" alt="(Python)"/> |
| <TT>breadth_first_visit</TT> |
| </H1> |
| |
| <P> |
| <PRE> |
| template <class <a href="./IncidenceGraph.html">IncidenceGraph</a>, class P, class T, class R> |
| void breadth_first_visit(IncidenceGraph& G, |
| typename graph_traits<IncidenceGraph>::vertex_descriptor s, |
| const bgl_named_params<P, T, R>& params); |
| |
| template <class <a href="./IncidenceGraph.html">IncidenceGraph</a>, class <a href="./Buffer.html">Buffer</a>, class <a href="./BFSVisitor.html">BFSVisitor</a>, class ColorMap> |
| void breadth_first_visit |
| (const IncidenceGraph& g, |
| typename graph_traits<IncidenceGraph>::vertex_descriptor s, |
| Buffer& Q, BFSVisitor vis, ColorMap color) |
| </PRE> |
| |
| This function is basically the same as <tt>breadth_first_search()</tt> |
| except that the color markers are not initialized in the |
| algorithm. The user is responsible for making sure the color for every |
| vertex is white before calling the algorithm. With this difference, |
| the graph type is only required to be an <a |
| href="./IncidenceGraph.html">Incidence Graph</a> instead of a <a |
| href="./VertexListGraph.html">Vertex List Graph</a>. Also, this |
| difference allows for more flexibility in the color property map. For |
| example, one could use a map that only implements a partial function |
| on the vertices, which could be more space efficient when the search |
| only reaches a small portion of the graph. |
| |
| <H3>Where Defined</H3> |
| |
| <P> |
| <a href="../../../boost/graph/breadth_first_search.hpp"><TT>boost/graph/breadth_first_search.hpp</TT></a> |
| |
| |
| <h3>Parameters</h3> |
| |
| IN: <tt>IncidenceGraph& g</tt> |
| <blockquote> |
| A directed or undirected graph. The graph type must |
| be a model of <a href="./IncidenceGraph.html">Incidence Graph</a>.<br> |
| |
| <b>Python</b>: The parameter is named <tt>graph</tt>. |
| </blockquote> |
| |
| IN: <tt>vertex_descriptor s</tt> |
| <blockquote> |
| The source vertex where the search is started.<br> |
| |
| <b>Python</b>: The parameter is named <tt>root_vertex</tt>. |
| </blockquote> |
| |
| |
| <h3>Named Parameters</h3> |
| |
| IN: <tt>visitor(BFSVisitor vis)</tt> |
| <blockquote> |
| A visitor object that is invoked inside the algorithm at the |
| event-points specified by the <a href="BFSVisitor.html">BFS |
| Visitor</a> concept. The visitor object is passed by value <a |
| href="#1">[1]</a>.<br> <b>Default:</b> |
| <tt>bfs_visitor<null_visitor></tt><br> |
| |
| <b>Python</b>: The parameter should be an object that derives from |
| the <a href="BFSVisitor.html#python"><tt>BFSVisitor</tt></a> type of the graph. |
| </blockquote> |
| |
| UTIL/OUT: <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> <tt>get(vertex_color, g)</tt><br> |
| |
| <b>Python</b>: The color map must be a <tt>vertex_color_map</tt> for |
| the graph. |
| </blockquote> |
| |
| UTIL: <tt>buffer(Buffer& Q)</tt> |
| <blockquote> |
| The queue used to determine the order in which vertices will be |
| discovered. If a FIFO queue is used, then the traversal will |
| be according to the usual BFS ordering. Other types of queues |
| can be used, but the traversal order will be different. |
| For example Dijkstra's algorithm can be implemented |
| using a priority queue. The type <tt>Buffer</tt> must be a model of |
| <a href="./Buffer.html">Buffer</a>.<br> |
| <b>Default:</b> <tt>boost::queue</tt><br> |
| |
| <b>Python</b>: The buffer must derive from the <a |
| href="./Buffer.html">Buffer</a> type for the graph. |
| </blockquote> |
| |
| |
| <H3><A NAME="SECTION001330300000000000000"> |
| Complexity</A> |
| </H3> |
| |
| <P> |
| The time complexity is <i>O(E)</i>. |
| |
| <P> |
| |
| <h3>Visitor Event Points</h3> |
| |
| <ul> |
| <li><b><tt>vis.examine_vertex(u, g)</tt></b>r is invoked in each |
| vertex as it is removed from the queue. |
| |
| <li><b><tt>vis.examine_edge(e, g)</tt></b> is invoked on every out-edge |
| of each vertex immediately after the vertex is removed from the queue. |
| |
| <li><b><tt>vis.tree_edge(e, g)</tt></b> is invoked (in addition to |
| <tt>examine_edge()</tt>) if the edge is a tree edge. The |
| target vertex of edge <tt>e</tt> is discovered at this time. |
| |
| <li><b><tt>vis.discover_vertex(u, g)</tt></b> is invoked the first time the |
| algorithm encounters vertex <i>u</i>. All vertices closer to the |
| source vertex have been discovered, and vertices further from the |
| source have not yet been discovered. |
| |
| <li><b><tt>vis.non_tree_edge(e, g)</tt></b> is invoked (in addition to |
| <tt>examine_edge()</tt>) if the edge is not a tree edge. |
| |
| <li><b><tt>vis.gray_target(e, g)</tt></b> is invoked (in addition to |
| <tt>non_tree_edge()</tt>) if the target vertex is colored gray at the |
| time of examination. The color gray indicates that |
| the vertex is currently in the queue. |
| |
| <li><b><tt>vis.black_target(e, g)</tt></b> is invoked (in addition to |
| <tt>non_tree_edge()</tt>) if the target vertex is colored black at the |
| time of examination. The color black indicates that the |
| vertex is no longer in the queue. |
| |
| <li><b><tt>vis.finish_vertex(u, g)</tt></b> is invoked after all of the out |
| edges of <i>u</i> have been examined and all of the adjacent vertices |
| have been discovered. |
| |
| </ul> |
| |
| <h3>See Also</h3> |
| |
| <a href="./breadth_first_search.html"><tt>breadth_first_search()</tt></a>, |
| <a href="./bfs_visitor.html"><tt>bfs_visitor</tt></a>, and |
| <a href="./depth_first_search.html"><tt>depth_first_search()</tt></a> |
| |
| <h3>Notes</h3> |
| |
| <p><a name="1">[1]</a> |
| Since the visitor parameter is passed by value, if your visitor |
| contains state then any changes to the state during the algorithm |
| will be made to a copy of the visitor object, not the visitor object |
| passed in. Therefore you may want the visitor to hold this state by |
| pointer or reference. |
| |
| <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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