projects / ceph.git / blame
| Commit | Line | Data |
|---|---|---|
| 7c673cae FG |
1 | <HTML> |
| 2 | <!-- | |
| 3 | Copyright (c) Jeremy Siek, Lie-Quan Lee, and Andrew Lumsdaine 2000 | |
| 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>DFS Visitor</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><img src="figs/python.gif" alt="(Python)"/>DFS Visitor Concept</H1> | |
| 19 | ||
| 20 | This concept defines the visitor interface for <a | |
| 21 | href="./depth_first_search.html"><tt>depth_first_search()</tt></a>. | |
| 22 | Users can define a class with the DFS Visitor interface and pass an | |
| 23 | object of the class to <tt>depth_first_search()</tt>, thereby | |
| 24 | augmenting the actions taken during the graph search. | |
| 25 | ||
| 26 | <h3>Refinement of</h3> | |
| 27 | ||
| 28 | <a href="../../utility/CopyConstructible.html">Copy Constructible</a> | |
| 29 | (copying a visitor should be a lightweight operation). | |
| 30 | ||
| 31 | <h3>Notation</h3> | |
| 32 | ||
| 33 | <Table> | |
| 34 | <TR> | |
| 35 | <TD><tt>V</tt></TD> | |
| 36 | <TD>A type that is a model of DFS Visitor.</TD> | |
| 37 | </TR> | |
| 38 | ||
| 39 | <TR> | |
| 40 | <TD><tt>vis</tt></TD> | |
| 41 | <TD>An object of type <tt>V</tt>.</TD> | |
| 42 | </TR> | |
| 43 | ||
| 44 | <TR> | |
| 45 | <TD><tt>G</tt></TD> | |
| 46 | <TD>A type that is a model of Graph.</TD> | |
| 47 | </TR> | |
| 48 | ||
| 49 | <TR> | |
| 50 | <TD><tt>g</tt></TD> | |
| 51 | <TD>An object of type <tt>G</tt>.</TD> | |
| 52 | </TR> | |
| 53 | ||
| 54 | <TR> | |
| 55 | <TD><tt>e</tt></TD> | |
| 56 | <TD>An object of type <tt>boost::graph_traits<G>::edge_descriptor</tt>.</TD> | |
| 57 | </TR> | |
| 58 | ||
| 59 | <TR> | |
| 60 | <TD><tt>s,u</tt></TD> | |
| 61 | <TD>An object of type <tt>boost::graph_traits<G>::vertex_descriptor</tt>.</TD> | |
| 62 | </TR> | |
| 63 | ||
| 64 | </table> | |
| 65 | ||
| 66 | <h3>Associated Types</h3> | |
| 67 | ||
| 68 | none | |
| 69 | <p> | |
| 70 | ||
| 71 | <h3>Valid Expressions</h3> | |
| 72 | ||
| 73 | <table border> | |
| 74 | <tr> | |
| 75 | <th>Name</th><th>Expression</th><th>Return Type</th><th>Description</th> | |
| 76 | </tr> | |
| 77 | ||
| 78 | <tr> | |
| 79 | <td>Initialize Vertex</td> | |
| 80 | <td><tt>vis.initialize_vertex(s, g)</tt></td> | |
| 81 | <td><tt>void</tt></td> | |
| 82 | <td> | |
| 83 | This is invoked on every vertex of the graph before the start of the | |
| 84 | graph search. | |
| 85 | </td> | |
| 86 | </tr> | |
| 87 | ||
| 88 | <tr> | |
| 89 | <td>Start Vertex</td> | |
| 90 | <td><tt>vis.start_vertex(s, g)</tt></td> | |
| 91 | <td><tt>void</tt></td> | |
| 92 | <td> | |
| 93 | This is invoked on the source vertex once before the start of the | |
| 94 | search. | |
| 95 | </td> | |
| 96 | </tr> | |
| 97 | ||
| 98 | <tr> | |
| 99 | <td>Discover Vertex</td> | |
| 100 | <td><tt>vis.discover_vertex(u, g)</tt></td> | |
| 101 | <td><tt>void</tt></td> | |
| 102 | <td> | |
| 103 | This is invoked when a vertex is encountered for the first time. | |
| 104 | </td> | |
| 105 | </tr> | |
| 106 | ||
| 107 | <tr> | |
| 108 | <td>Examine Edge</td> | |
| 109 | <td><tt>vis.examine_edge(e, g)</tt></td> | |
| 110 | <td><tt>void</tt></td> | |
| 111 | <td> | |
| 112 | This is invoked on every out-edge of each vertex after it is discovered. | |
| 113 | </td> | |
| 114 | </tr> | |
| 115 | ||
| 116 | ||
| 117 | <tr> | |
| 118 | <td>Tree Edge</td> | |
| 119 | <td><tt>vis.tree_edge(e, g)</tt></td> | |
| 120 | <td><tt>void</tt></td> | |
| 121 | <td> | |
| 122 | This is invoked on each edge as it becomes a member of the edges that | |
| 123 | form the search tree.</td> | |
| 124 | </tr> | |
| 125 | ||
| 126 | <tr> | |
| 127 | <td>Back Edge</td> | |
| 128 | <td><tt>vis.back_edge(e, g)</tt></td> | |
| 129 | <td><tt>void</tt></td> | |
| 130 | <td> | |
| 131 | This is invoked on the back edges in the graph. For an undirected | |
| 132 | graph there is some ambiguity between tree edges and back edges since | |
| 133 | the edge <i>(u,v)</i> and <i>(v,u)</i> are the same edge, but both the | |
| 134 | <tt>tree_edge()</tt> and <tt>back_edge()</tt> functions will be | |
| 135 | invoked. One way to resolve this ambiguity is to record the tree | |
| 136 | edges, and then disregard the back-edges that are already marked as | |
| 137 | tree edges. An easy way to record tree edges is to record | |
| 138 | predecessors at the <tt>tree_edge</tt> event point. | |
| 139 | </td> | |
| 140 | </tr> | |
| 141 | ||
| 142 | <tr> | |
| 143 | <td>Forward or Cross Edge</td> | |
| 144 | <td><tt>vis.forward_or_cross_edge(e, g)</tt></td> | |
| 145 | <td><tt>void</tt></td> | |
| 146 | <td> | |
| 147 | This is invoked on forward or cross edges in the graph. In an | |
| 148 | undirected graph this method is never called. | |
| 149 | </td> | |
| 150 | </tr> | |
| 151 | ||
| 152 | <tr> | |
| 153 | <td>Finish Edge</td> | |
| 154 | <td><tt>vis.finish_edge(e, g)</tt></td> | |
| 155 | <td><tt>void</tt></td> | |
| 156 | <td> | |
| 157 | This is invoked on each non-tree edge as well as on each tree edge after | |
| 158 | <tt>finish_vertex</tt> has been called on its target vertex.</td> | |
| 159 | </tr> | |
| 160 | ||
| 161 | <tr> | |
| 162 | <td>Finish Vertex</td> | |
| 163 | <td><tt>vis.finish_vertex(u, g)</tt></td> | |
| 164 | <td><tt>void</tt></td> | |
| 165 | <td> | |
| 166 | This is invoked on vertex <tt>u</tt> after <tt>finish_vertex</tt> has | |
| 167 | been called for all the vertices in the DFS-tree rooted at vertex | |
| 168 | <tt>u</tt>. If vertex <tt>u</tt> is a leaf in the DFS-tree, then | |
| 169 | the <tt>finish_vertex</tt> function is called on <tt>u</tt> after | |
| 170 | all the out-edges of <tt>u</tt> have been examined. | |
| 171 | </td> | |
| 172 | </tr> | |
| 173 | ||
| 174 | </table> | |
| 175 | ||
| 176 | <h3>Models</h3> | |
| 177 | ||
| 178 | <ul> | |
| 179 | <li><a href="./dfs_visitor.html"><tt>dfs_visitor</tt></a> | |
| 180 | </ul> | |
| 181 | ||
| 182 | <a name="python"></a> | |
| 183 | <h3>Python</h3> | |
| 184 | ||
| 185 | To implement a model of the <tt>DFSVisitor</tt> concept in Python, | |
| 186 | create a new class that derives from the <tt>DFSVisitor</tt> type of | |
| 187 | the graph, which will be | |
| 188 | named <tt><i>GraphType</i>.DFSVisitor</tt>. The events and syntax are | |
| 189 | the same as with visitors in C++. Here is an example for the | |
| 190 | Python <tt>bgl.Graph</tt> graph type: | |
| 191 | ||
| 192 | <pre> | |
| 193 | class count_tree_edges_dfs_visitor(bgl.Graph.DFSVisitor): | |
| 194 | def __init__(self, name_map): | |
| 195 | bgl.Graph.DFSVisitor.__init__(self) | |
| 196 | self.name_map = name_map | |
| 197 | ||
| 198 | def tree_edge(self, e, g): | |
| 199 | (u, v) = (g.source(e), g.target(e)) | |
| 200 | print "Tree edge ", | |
| 201 | print self.name_map[u], | |
| 202 | print " -> ", | |
| 203 | print self.name_map[v] | |
| 204 | </pre> | |
| 205 | ||
| 206 | <br> | |
| 207 | <HR> | |
| 208 | <TABLE> | |
| 209 | <TR valign=top> | |
| 210 | <TD nowrap>Copyright © 2000-2001</TD><TD> | |
| 211 | <A HREF="http://www.boost.org/people/jeremy_siek.htm">Jeremy Siek</A>, | |
| 212 | Indiana University (<A | |
| 213 | HREF="mailto:jsiek@osl.iu.edu">jsiek@osl.iu.edu</A>)<br> | |
| 214 | <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> | |
| 215 | <A HREF="http://www.osl.iu.edu/~lums">Andrew Lumsdaine</A>, | |
| 216 | Indiana University (<A | |
| 217 | HREF="mailto:lums@osl.iu.edu">lums@osl.iu.edu</A>) | |
| 218 | </TD></TR></TABLE> | |
| 219 | ||
| 220 | </BODY> | |
| 221 | </HTML> |