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143 lines
3.4 KiB
HTML
<HTML>
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<!--
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-- Copyright (c) 2004 Kris Beevers
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--
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-- Permission to use, copy, modify, distribute and sell this software
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-- and its documentation for any purpose is hereby granted without fee,
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-- provided that the above copyright notice appears in all copies and
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-- that both that copyright notice and this permission notice appear
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-- in supporting documentation. We make no
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-- representations about the suitability of this software for any
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-- purpose. It is provided "as is" without express or implied warranty.
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-->
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<Head>
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<Title>Boost Graph Library: AStarHeuristic</Title>
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<BODY BGCOLOR="#ffffff" LINK="#0000ee" TEXT="#000000" VLINK="#551a8b"
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ALINK="#ff0000">
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<IMG SRC="../../../c++boost.gif"
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ALT="C++ Boost" width="277" height="86">
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<BR Clear>
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<H1>AStar Heuristic Concept</H1>
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This concept defines the interface for the heuristic function of an A*
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search, which is responsible for estimating the remaining cost from
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some vertex to a goal. The user can create a class that matches this
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interface, and then pass objects of the class into <a
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href="./astar_search.html"><tt>astar_search()</tt></a> to guide the
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order of vertex examination of the search. The heuristic instance
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must incorporate any necessary information about goal vertices in the
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graph.
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For further discussion of the use of heuristics in an A* search, see
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the documentation of <a
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href="./astar_search.html">astar_search()</a>.
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<h3>Refinement of</h3>
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<a href="http://www.sgi.com/tech/stl/UnaryFunction.html">Unary
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Function</a> (must take a single argument -- a graph vertex -- and
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return a cost value) and <a
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href="../../utility/CopyConstructible.html">Copy Constructible</a>
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(copying a heuristic should be a lightweight operation).
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<h3>Notation</h3>
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<Table>
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<TR>
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<TD><tt>H</tt></TD>
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<TD>A type that is a model of AStar Heuristic.</TD>
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</TR>
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<TR>
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<TD><tt>h</tt></TD>
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<TD>An object of type <tt>H</tt>.</TD>
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</TR>
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<TR>
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<TD><tt>G</tt></TD>
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<TD>A type that is a model of Graph.</TD>
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</TR>
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<TR>
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<TD><tt>g</tt></TD>
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<TD>An object of type <tt>G</tt>.</TD>
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</TR>
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<TR>
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<TD><tt>u</tt></TD>
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<TD>An object of type <tt>boost::graph_traits<G>::vertex_descriptor</tt>.</TD>
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</TR>
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<TR>
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<TD><tt>CostType</tt></TD>
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<TD>A type that can be used with the <tt>compare</tt> and
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<tt>combine</tt> functions passed to A*.</TD>
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</TR>
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<TR>
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<TD><tt>c</tt></TD>
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<TD>An object of type <tt>CostType</tt>.</TD>
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</TR>
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</table>
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<h3>Associated Types</h3>
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none
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<p>
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<h3>Valid Expressions</h3>
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<table border>
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<tr>
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<th>Name</th><th>Expression</th><th>Return Type</th><th>Description</th>
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</tr>
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<tr>
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<td>Call Heuristic</td>
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<td><tt>CostType c = h(u)</tt></td>
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<td><tt>CostType</tt></td>
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<td>
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Called for the target of every out edge of a vertex being examined.
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</td>
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</tr>
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</table>
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<h3>Models</h3>
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<ul>
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<li><a href="./astar_heuristic.html"><tt>astar_heuristic</tt></a>
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</ul>
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<h3>Concept Checking Class</h3>
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<pre>
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template <class Heuristic, class Graph>
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struct AStarHeuristicConcept {
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void constraints()
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{
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function_requires< CopyConstructibleConcept<Heuristic> >();
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h(u);
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}
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Heuristic h;
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typename graph_traits<Graph>::vertex_descriptor u;
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};
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</pre>
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<br>
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<HR>
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<TABLE>
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<TR valign=top>
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<TD nowrap>Copyright © 2004</TD><TD>
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<A HREF="http://www.cs.rpi.edu/~beevek/">Kristopher Beevers</A>,
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Rensselaer Polytechnic Institute (<A
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HREF="mailto:beevek@cs.rpi.edu">beevek@cs.rpi.edu</A>)
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</TD></TR></TABLE>
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</BODY>
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</HTML>
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