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- Copyright (c) 2004 Kris Beevers
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- Distributed under the Boost Software License, Version 1.0.
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- <Head>
- <Title>Boost Graph Library: AStarVisitor</Title>
- <BODY BGCOLOR="#ffffff" LINK="#0000ee" TEXT="#000000" VLINK="#551a8b"
- ALINK="#ff0000">
- <IMG SRC="../../../boost.png"
- ALT="C++ Boost" width="277" height="86">
- <BR Clear>
- <H1>AStar Visitor Concept</H1>
- This concept defines the visitor interface for <a
- href="./astar_search.html"><tt>astar_search()</tt></a>. Users can
- define a class with the AStar Visitor interface and pass an object of
- the class to <tt>astar_search()</tt>, thereby augmenting the actions
- taken during the graph 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 AStar 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>const 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>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/ReadablePropertyMap.html">Readable Property
- Map</a>.</TD>
- </TR>
- <TR>
- <TD><tt>w</tt></TD>
- <TD>An object of type <tt>WeightMap</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 on each vertex of the graph when it is first
- initialized (i.e., when its property maps are initialized).
- </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 first discovered and is added to the
- OPEN list.
- </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 (i.e., it
- has the lowest cost on the OPEN list). 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
- examined.
- </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 (the distance of its target vertex is reduced) and this method
- is invoked:
- <blockquote>
- <pre>
- tie(u, s) = incident(e, g);
- D d_u = get(d, u), d_v = get(d, s);
- W w_e = get(w, e);
- assert(compare(combine(d_u, w_e), d_s));
- </pre>
- </blockquote>
- </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 an edge is not relaxed (see above) then this
- method is invoked.
- </td>
- </tr>
- <tr>
- <td>Black Target</td>
- <td><tt>vis.black_target(e, g)</tt></td>
- <td><tt>void</tt></td>
- <td>
- This is invoked when a vertex that is on the CLOSED list is
- ``rediscovered'' via a more efficient path and is re-added to the
- OPEN list.
- </td>
- </tr>
- <tr>
- <td>Finish Vertex</td>
- <td><tt>vis.finish_vertex(u, g)</tt></td>
- <td><tt>void</tt></td>
- <td>
- This is invoked on a vertex when it is added to the CLOSED list. This
- happens after all of its out-edges have been examined.
- </td>
- </tr>
- </table>
- <h3>Models</h3>
- <ul>
- <li><a href="./astar_visitor.html"><tt>astar_visitor</tt></a>
- </ul>
- <h3>See also</h3>
- <a href="./visitor_concepts.html">Visitor concepts</a>
- <br>
- <HR>
- <TABLE>
- <TR valign=top>
- <TD nowrap>Copyright © 2004</TD><TD>
- <A HREF="http://cs.krisbeevers.com/">Kristopher Beevers</A>,
- Rensselaer Polytechnic Institute (<A
- HREF="mailto:beevek@cs.rpi.edu">beevek@cs.rpi.edu</A>)
- </TD></TR></TABLE>
- </BODY>
- </HTML>
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