| 1 | <HTML> |
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| 2 | <!-- |
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| 3 | -- Copyright (c) 2004 Kris Beevers |
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| 4 | -- |
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| 5 | -- Distributed under the Boost Software License, Version 1.0. |
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| 6 | -- (See accompanying file LICENSE_1_0.txt or copy at |
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| 7 | -- http://www.boost.org/LICENSE_1_0.txt) |
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| 8 | --> |
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| 9 | <Head> |
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| 10 | <Title>Boost Graph Library: AStarHeuristic</Title> |
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| 11 | <BODY BGCOLOR="#ffffff" LINK="#0000ee" TEXT="#000000" VLINK="#551a8b" |
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| 12 | ALINK="#ff0000"> |
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| 13 | <IMG SRC="../../../boost.png" |
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| 14 | ALT="C++ Boost" width="277" height="86"> |
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| 15 | |
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| 16 | <BR Clear> |
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| 17 | |
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| 18 | <H1>AStar Heuristic Concept</H1> |
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| 19 | |
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| 20 | This concept defines the interface for the heuristic function of an A* |
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| 21 | search, which is responsible for estimating the remaining cost from |
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| 22 | some vertex to a goal. The user can create a class that matches this |
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| 23 | interface, and then pass objects of the class into <a |
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| 24 | href="./astar_search.html"><tt>astar_search()</tt></a> to guide the |
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| 25 | order of vertex examination of the search. The heuristic instance |
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| 26 | must incorporate any necessary information about goal vertices in the |
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| 27 | graph. |
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| 28 | |
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| 29 | For further discussion of the use of heuristics in an A* search, see |
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| 30 | the documentation of <a |
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| 31 | href="./astar_search.html">astar_search()</a>. |
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| 32 | |
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| 33 | <h3>Refinement of</h3> |
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| 34 | |
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| 35 | <a href="http://www.sgi.com/tech/stl/UnaryFunction.html">Unary |
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| 36 | Function</a> (must take a single argument -- a graph vertex -- and |
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| 37 | return a cost value) and <a |
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| 38 | href="../../utility/CopyConstructible.html">Copy Constructible</a> |
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| 39 | (copying a heuristic should be a lightweight operation). |
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| 40 | |
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| 41 | |
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| 42 | <h3>Notation</h3> |
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| 43 | |
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| 44 | <Table> |
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| 45 | <TR> |
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| 46 | <TD><tt>H</tt></TD> |
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| 47 | <TD>A type that is a model of AStar Heuristic.</TD> |
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| 48 | </TR> |
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| 49 | |
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| 50 | <TR> |
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| 51 | <TD><tt>h</tt></TD> |
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| 52 | <TD>An object of type <tt>H</tt>.</TD> |
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| 53 | </TR> |
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| 54 | |
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| 55 | <TR> |
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| 56 | <TD><tt>G</tt></TD> |
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| 57 | <TD>A type that is a model of Graph.</TD> |
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| 58 | </TR> |
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| 59 | |
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| 60 | <TR> |
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| 61 | <TD><tt>g</tt></TD> |
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| 62 | <TD>An object of type <tt>G</tt>.</TD> |
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| 63 | </TR> |
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| 64 | |
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| 65 | <TR> |
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| 66 | <TD><tt>u</tt></TD> |
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| 67 | <TD>An object of type <tt>boost::graph_traits<G>::vertex_descriptor</tt>.</TD> |
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| 68 | </TR> |
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| 69 | |
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| 70 | <TR> |
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| 71 | <TD><tt>CostType</tt></TD> |
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| 72 | <TD>A type that can be used with the <tt>compare</tt> and |
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| 73 | <tt>combine</tt> functions passed to A*.</TD> |
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| 74 | </TR> |
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| 75 | |
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| 76 | <TR> |
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| 77 | <TD><tt>c</tt></TD> |
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| 78 | <TD>An object of type <tt>CostType</tt>.</TD> |
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| 79 | </TR> |
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| 80 | |
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| 81 | </table> |
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| 82 | |
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| 83 | <h3>Associated Types</h3> |
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| 84 | |
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| 85 | none |
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| 86 | <p> |
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| 87 | |
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| 88 | <h3>Valid Expressions</h3> |
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| 89 | |
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| 90 | <table border> |
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| 91 | <tr> |
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| 92 | <th>Name</th><th>Expression</th><th>Return Type</th><th>Description</th> |
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| 93 | </tr> |
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| 94 | |
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| 95 | <tr> |
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| 96 | <td>Call Heuristic</td> |
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| 97 | <td><tt>CostType c = h(u)</tt></td> |
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| 98 | <td><tt>CostType</tt></td> |
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| 99 | <td> |
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| 100 | Called for the target of every out edge of a vertex being examined. |
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| 101 | </td> |
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| 102 | </tr> |
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| 103 | |
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| 104 | </table> |
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| 105 | |
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| 106 | <h3>Models</h3> |
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| 107 | |
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| 108 | <ul> |
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| 109 | <li><a href="./astar_heuristic.html"><tt>astar_heuristic</tt></a> |
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| 110 | </ul> |
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| 111 | |
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| 112 | <h3>Concept Checking Class</h3> |
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| 113 | |
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| 114 | <pre> |
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| 115 | template <class Heuristic, class Graph> |
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| 116 | struct AStarHeuristicConcept { |
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| 117 | void constraints() |
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| 118 | { |
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| 119 | function_requires< CopyConstructibleConcept<Heuristic> >(); |
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| 120 | h(u); |
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| 121 | } |
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| 122 | Heuristic h; |
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| 123 | typename graph_traits<Graph>::vertex_descriptor u; |
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| 124 | }; |
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| 125 | </pre> |
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| 126 | |
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| 127 | <br> |
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| 128 | <HR> |
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| 129 | <TABLE> |
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| 130 | <TR valign=top> |
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| 131 | <TD nowrap>Copyright © 2004</TD><TD> |
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| 132 | <A HREF="http://www.cs.rpi.edu/~beevek/">Kristopher Beevers</A>, |
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| 133 | Rensselaer Polytechnic Institute (<A |
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| 134 | HREF="mailto:beevek@cs.rpi.edu">beevek@cs.rpi.edu</A>) |
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| 135 | </TD></TR></TABLE> |
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| 136 | |
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| 137 | </BODY> |
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| 138 | </HTML> |
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