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