168 lines
4.6 KiB
HTML
168 lines
4.6 KiB
HTML
<HTML>
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<!--
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Copyright (c) Jeremy Siek 2000
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Distributed under the Boost Software License, Version 1.0.
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(See accompanying file LICENSE_1_0.txt or copy at
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http://www.boost.org/LICENSE_1_0.txt)
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-->
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<Head>
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<Title>AdjacencyGraph</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="../../../boost.png"
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ALT="C++ Boost" width="277" height="86">
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<BR Clear>
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<H2><A NAME="concept:AdjacencyGraph"></A>
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AdjacencyGraph
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</H2>
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The AdjacencyGraph concept provides and interface for efficient access
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of the adjacent vertices to a vertex in a graph. This is quite similar
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to the <a href="./IncidenceGraph.html">IncidenceGraph</a> concept (the
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target of an out-edge is an adjacent vertex). Both concepts are
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provided because in some contexts there is only concern for the
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vertices, whereas in other contexts the edges are also important.
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<H3>Refinement of</H3>
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<a href="Graph.html">Graph</a>
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<h3>Notation</h3>
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<Table>
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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>v</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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</table>
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<H3>Associated Types</H3>
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<Table border>
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<tr>
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<td><tt>boost::graph_traits<G>::traversal_category</tt><br><br>
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This tag type must be convertible to <tt>adjacency_graph_tag</tt>.
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</td>
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</tr>
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<TR>
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<TD><pre>boost::graph_traits<G>::adjacency_iterator</pre>
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An adjacency iterator for a vertex <i>v</i> provides access to the
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vertices adjacent to <i>v</i>. As such, the value type of an
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adjacency iterator is the vertex descriptor type of its graph. An
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adjacency iterator must meet the requirements of <a
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href="../../utility/MultiPassInputIterator.html">MultiPassInputIterator</a>.
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</TD>
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</TR>
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</table>
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<h3>Valid Expressions</h3>
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<table border>
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<tr>
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<td><a name="sec:adjacent-vertices"><TT>adjacent_vertices(v, g)</TT></a></TD>
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<TD>
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Returns an iterator-range providing access to the vertices adjacent to
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vertex <TT>v</TT> in graph <TT>g</TT>.<a
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href="#1">[1]</a>
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<br> Return type:
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<TT>std::pair<adjacency_iterator, adjacency_iterator></TT>
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</TD>
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</TR>
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</table>
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<H3>Complexity guarantees</H3>
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The <TT>adjacent_vertices()</TT> function must return in constant time.
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<H3>See Also</H3>
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<a href="./graph_concepts.html">Graph concepts</a>,
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<a href="./adjacency_iterator.html"><tt>adjacency_iterator</tt></a>
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<H3>Concept Checking Class</H3>
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<PRE>
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template <class G>
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struct AdjacencyGraphConcept
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{
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typedef typename boost::graph_traits<G>::adjacency_iterator
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adjacency_iterator;
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void constraints() {
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BOOST_CONCEPT_ASSERT(( MultiPassInputIteratorConcept<adjacency_iterator> ));
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p = adjacent_vertices(v, g);
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v = *p.first;
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const_constraints(g);
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}
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void const_constraints(const G& g) {
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p = adjacent_vertices(v, g);
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}
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std::pair<adjacency_iterator,adjacency_iterator> p;
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typename boost::graph_traits<G>::vertex_descriptor v;
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G g;
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};
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</PRE>
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<h3>Design Rationale</h3>
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The AdjacencyGraph concept is somewhat frivolous since <a
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href="./IncidenceGraph.html">IncidenceGraph</a> really covers the same
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functionality (and more). The AdjacencyGraph concept exists because
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there are situations when <tt>adjacent_vertices()</tt> is more
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convenient to use than <tt>out_edges()</tt>. If you are constructing a
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graph class and do not want to put in the extra work of creating an
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adjacency iterator, have no fear. There is an adaptor class named <a
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href="./adjacency_iterator.html"> <tt>adjacency_iterator</tt></a> that
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you can use to create an adjacency iterator out of an out-edge
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iterator.
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<h3>Notes</h3>
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<a name="1">[1]</a> The case of a
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<I>multigraph</I> (where multiple edges can connect the same two
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vertices) brings up an issue as to whether the iterators returned by
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the <TT>adjacent_vertices()</TT> function access a range that
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includes each adjacent vertex once, or whether it should match the
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behavior of the <TT>out_edges()</TT> function, and access a
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range that may include an adjacent vertex more than once. For now the
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behavior is defined to match that of <TT>out_edges()</TT>,
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though this decision may need to be reviewed in light of more
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experience with graph algorithm implementations.
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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 © 2000-2001</TD><TD>
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<A HREF="http://www.boost.org/people/jeremy_siek.htm">Jeremy Siek</A>, Indiana University (<A HREF="mailto:jsiek@osl.iu.edu">jsiek@osl.iu.edu</A>)
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</TD></TR></TABLE>
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</BODY>
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</HTML>
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