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| <Head> |
| <Title>Boost Graph Library: Dijkstra Visitor</Title> |
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| <BR Clear> |
| |
| <H1><img src="figs/python.gif" alt="(Python)"/>Dijkstra Visitor Concept</H1> |
| |
| This concept defines the visitor interface for <a |
| href="./dijkstra_shortest_paths.html"><tt>dijkstra_shortest_paths()</tt></a> |
| and related algorithms. The user can create a class that matches this |
| interface, and then pass objects of the class into |
| <tt>dijkstra_shortest_paths()</tt> to augment the actions taken during |
| the search. |
| |
| <h3>Refinement of</h3> |
| |
| <a href="../../utility/CopyConstructible.html">Copy Constructible</a> |
| (copying a visitor should be a lightweight operation). |
| |
| |
| <h3>Notation</h3> |
| |
| <Table> |
| <TR> |
| <TD><tt>V</tt></TD> |
| <TD>A type that is a model of Dijkstra Visitor.</TD> |
| </TR> |
| |
| <TR> |
| <TD><tt>vis</tt></TD> |
| <TD>An object of type <tt>V</tt>.</TD> |
| </TR> |
| |
| <TR> |
| <TD><tt>G</tt></TD> |
| <TD>A type that is a model of Graph.</TD> |
| </TR> |
| |
| <TR> |
| <TD><tt>g</tt></TD> |
| <TD>An object of type <tt>G</tt>.</TD> |
| </TR> |
| |
| <TR> |
| <TD><tt>e</tt></TD> |
| <TD>An object of type <tt>boost::graph_traits<G>::edge_descriptor</tt>.</TD> |
| </TR> |
| |
| <TR> |
| <TD><tt>s,u,v</tt></TD> |
| <TD>An object of type <tt>boost::graph_traits<G>::vertex_descriptor</tt>.</TD> |
| </TR> |
| |
| <TR> |
| <TD><tt>DistanceMap</tt></TD> |
| <TD>A type that is a model of <a href="../../property_map/doc/ReadWritePropertyMap.html">Read/Write Property Map</a>.</TD> |
| </TR> |
| |
| <TR> |
| <TD><tt>d</tt></TD> |
| <TD>An object of type <tt>DistanceMap</tt>.</TD> |
| </TR> |
| |
| <TR> |
| <TD><tt>WeightMap</tt></TD> |
| <TD>A type that is a model of <a href="../../property_map/doc/ReadWritePropertyMap.html">Readable Property Map</a>.</TD> |
| </TR> |
| |
| <TR> |
| <TD><tt>w</tt></TD> |
| <TD>An object of type <tt>DistanceMap</tt>.</TD> |
| </TR> |
| |
| </table> |
| |
| <h3>Associated Types</h3> |
| |
| none |
| <p> |
| |
| <h3>Valid Expressions</h3> |
| |
| <table border> |
| <tr> |
| <th>Name</th><th>Expression</th><th>Return Type</th><th>Description</th> |
| </tr> |
| |
| <tr> |
| <td>Initialize Vertex</td> |
| <td><tt>vis.initialize_vertex(u, g)</tt></td> |
| <td><tt>void</tt></td> |
| <td> |
| This is invoked one each vertex of the graph when it is initialized. |
| </td> |
| </tr> |
| |
| <tr> |
| <td>Examine Vertex</td> |
| <td><tt>vis.examine_vertex(u, g)</tt></td> |
| <td><tt>void</tt></td> |
| <td> |
| This is invoked on a vertex as it is popped from the queue. This |
| happens immediately before <tt>examine_edge()</tt> is invoked |
| on each of the out-edges of vertex <tt>u</tt>. |
| </td> |
| </tr> |
| |
| <tr> |
| <td>Examine Edge</td> |
| <td><tt>vis.examine_edge(e, g)</tt></td> |
| <td><tt>void</tt></td> |
| <td> |
| This is invoked on every out-edge of each vertex after it is discovered. |
| </td> |
| </tr> |
| |
| <tr> |
| <td>Discover Vertex</td> |
| <td><tt>vis.discover_vertex(u, g)</tt></td> |
| <td><tt>void</tt></td> |
| <td> |
| This is invoked when a vertex is encountered for the first time. |
| </td> |
| </tr> |
| |
| <tr> |
| <td>Edge Relaxed</td> |
| <td><tt>vis.edge_relaxed(e, g)</tt></td> |
| <td><tt>void</tt></td> |
| <td> |
| Upon examination, if the following condition holds then the edge |
| is relaxed (its distance is reduced), and this method is invoked.<br> |
| <tt> |
| tie(u,v) = incident(e, g);<br> |
| D d_u = get(d, u), d_v = get(d, v);<br> |
| W w_e = get(w, e);<br> |
| assert(compare(combine(d_u, w_e), d_v));<br> |
| </tt> |
| </td> |
| </tr> |
| |
| <tr> |
| <td>Edge Not Relaxed</td> |
| <td><tt>vis.edge_not_relaxed(e, g)</tt></td> |
| <td><tt>void</tt></td> |
| <td> |
| Upon examination, if the edge is not relaxed (see above) then |
| this method is invoked. |
| </td> |
| </tr> |
| |
| <tr> |
| <td>Finish Vertex</td> |
| <td><tt>vis.finish_vertex(u, g)</tt></td> |
| <td><tt>void</tt></td> |
| <td> |
| This invoked on a vertex after all of its out edges have been added to the |
| search tree and all of the adjacent vertices have been discovered |
| (but before their out-edges have been examined). |
| </td> |
| </tr> |
| |
| </table> |
| |
| <h3>Models</h3> |
| |
| <ul> |
| <li><a href="./dijkstra_visitor.html"><tt>dijkstra_visitor</tt></a> |
| </ul> |
| |
| <a name="python"></a> |
| <h3>Python</h3> |
| |
| To implement a model of the <tt>DijkstraVisitor</tt> concept in Python, |
| create a new class that derives from the <tt>DijkstraVisitor</tt> type of |
| the graph, which will be |
| named <tt><i>GraphType</i>.DijkstraVisitor</tt>. The events and syntax are |
| the same as with visitors in C++. Here is an example for the |
| Python <tt>bgl.Graph</tt> graph type: |
| |
| <pre> |
| class count_tree_edges_dijkstra_visitor(bgl.Graph.DijkstraVisitor): |
| def __init__(self, name_map): |
| bgl.Graph.DijkstraVisitor.__init__(self) |
| self.name_map = name_map |
| |
| def edge_relaxed(self, e, g): |
| (u, v) = (g.source(e), g.target(e)) |
| print "Relaxed edge ", |
| print self.name_map[u], |
| print " -> ", |
| print self.name_map[v] |
| </pre> |
| |
| <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>)<br> |
| <A HREF="http://www.boost.org/people/liequan_lee.htm">Lie-Quan Lee</A>, Indiana University (<A HREF="mailto:llee@cs.indiana.edu">llee@cs.indiana.edu</A>)<br> |
| <A HREF="http://www.osl.iu.edu/~lums">Andrew Lumsdaine</A>, |
| Indiana University (<A |
| HREF="mailto:lums@osl.iu.edu">lums@osl.iu.edu</A>) |
| </TD></TR></TABLE> |
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