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<head>
<title>Boost Graph Library: Maximum Adjacency Search</Title>
<body>
<img src="../../../boost.png" alt="C++ Boost" width="277" height="86">

<h1><a name="sec:maximum-adjacency-search"></a>
<tt>maximum_adjacency_search</tt>
</h1>

<p>
<pre>
<em>// named parameter versions</em>
template &lt;class Graph, class class P, class T, class R&gt;
void
maximum_adjacency_search(const Graph&amp; g,
       const bgl_named_params&lt;P, T, R&gt;&amp; params);

<i>// non-named parameter versions</i>
template &lt;class Graph, class WeightMap, class MASVisitor&gt;
void
maximum_adjacency_search(const Graph&amp; g, WeightMap weights, MASVisitor vis,
       const typename graph_traits&lt;Graph&gt;::vertex_descriptor start);

</pre>

<p>
The <tt>maximum_adjacency_search()</tt> function performs a traversal
of the vertices in an undirected graph. The next vertex visited is the
vertex that has the most visited neighbors at any time. In the case of
an unweighted, undirected graph, the number of visited neighbors of the
very last vertex visited in the graph is also the number of edge-disjoint
paths between that vertex and the next-to-last vertex visited. These can be
retrieved from a visitor, an example of which is in the test harness
mas_test.cpp.
</p>

<p>
The <tt>maximum_adjacency_search()</tt> function invokes user-defined
actions at certain event-points within the algorithm. This provides a
mechanism for adapting the generic MAS algorithm to the many situations
in which it can be used. In the pseudo-code below, the event points
for MAS are the labels on the right. The user-defined actions must be
provided in the form of a visitor object, that is, an object whose type
meets the requirements for a MAS Visitor.
</p>

<table>
<tr>
<td valign="top">
<pre>
MAS(<i>G</i>)
  <b>for</b> each vertex <i>u in V</i> 
    <i>reach_count[u] := 0</i>
  <b>end for</b>
  // for the starting vertex s
  <i>reach_count[s] := 1</i>
  <b>for</b> each unvisited vertex <i>u in V</i>
    <b>call</b> MAS-VISIT(<i>G</i>, <i>u</i>)
    remove u from the list on unvisited vertices
    <b>for</b> each out edge from <i>u</i> to <i>t</i>
       <b>if</b> <i>t</i> has not yet been visited
         increment <i>reach_count[t]</i>
       <b>end if</b>
    <b>end for</b> each out edge
    <b>call</b> MAS-VISIT(<i>G</i>, <i>u</i>)
  <b>end for</b> each unvisited vertex
<pre>
</td>
<td valign="top">
<pre>
-
-
initialize vertex <i>u</i>
-
-
-
-
examine vertex <i>u</i>
-
examine edge <i>(u,t)</i>
-
-
-
-
finish vertex <i>u</i>
-
</pre>
</td>
</tr>
</table>

<h3>Where Defined</h3>

<p>
<a href="../../../boost/graph/maximum_adjacency_search.hpp"><tt>boost/graph/maximum_adjacency_search.hpp</tt></a></p>

<h3>Parameters</h3>

IN: <tt>const UndirectedGraph&amp; g</tt></p>
<blockquote>
  A connected, directed graph. The graph type must
  be a model of <a href="./IncidenceGraph.html">Incidence Graph</a>
  and <a href="./VertexListGraph.html">Vertex List Graph</a>.<br>
</blockquote>

<h3>Named Parameters</h3>

<p>IN: <tt>WeightMap weights</tt></p>
<blockquote>
  The weight or length of each edge in the graph. The
  <tt>WeightMap</tt> type must be a model of
  <a href="../../property_map/doc/ReadablePropertyMap.html">Readable
  Property Map</a> and its value type must be <a class="external"
  href="http://www.boost.org/sgi/stl/LessThanComparable.html">
  Less Than Comparable</a> and summable. The key type of this map
  needs to be the graph's edge descriptor type.
  <b>Default:</b> <tt>get(edge_weight, g)</tt><br>
</blockquote>

IN: <tt>visitor(MASVisitor vis)</tt></p>
<blockquote>
  A visitor object that is invoked inside the algorithm at the
  event-points specified by the MAS Visitor concept. The visitor
  object is passed by value <a href="#1">[1]</a>. <br>
  <b>Default:</b> <tt>mas_visitor&lt;null_visitor&gt;</tt><br>
</blockquote>

IN: <tt>root_vertex(typename
graph_traits&lt;VertexListGraph&gt;::vertex_descriptor start)</tt></p>
<blockquote>
  This specifies the vertex that the depth-first search should
  originate from. The type is the type of a vertex descriptor for the
  given graph.<br>
  <b>Default:</b> <tt>*vertices(g).first</tt><br>
</blockquote>

<h4>Expert Parameters</h4>

<p>IN: <tt>vertex_index_map(VertexIndexMap vertexIndices)</tt> </p>
<blockquote>
  This maps each vertex to an integer in the range
  [0, <tt>num_vertices(g)</tt>). This is only necessary if the default is
  used for the assignment, index-in-heap, or distance maps.
  <tt>VertexIndexMap</tt> must be a model of <a
  href="../../property_map/doc/ReadablePropertyMap.html">Readable Property
  Map</a>. The value type of the map must be an integer type. The
  key type must be the graph's vertex descriptor type.<br>
  <b>Default:</b> <tt>get(boost::vertex_index, g)</tt>
    Note: if you use this default, make sure your graph has
    an internal <tt>vertex_index</tt> property. For example,
    <tt>adjacency_list</tt> with <tt>VertexList=listS</tt> does
    not have an internal <tt>vertex_index</tt> property.
</blockquote>

<p>UTIL: <tt>vertex_assignment_map(AssignmentMap assignments)</tt></p>
<blockquote>
  <tt>AssignmentMap</tt> must be a model of <a
  href="../../property_map/doc/ReadWritePropertyMap.html">Read/Write Property
  Map</a>. The key and value types must be the graph's vertex descriptor
  type.<br>
  <b>Default:</b> A <tt>boost::iterator_property_map</tt> using a
  <tt>std::vector</tt> of <tt>num_vertices(g)</tt> vertex descriptors and
  <tt>vertexIndices</tt> for the index map.
</blockquote>

<p>UTIL: <tt>max_priority_queue(MaxPriorityQueue&amp; pq)</tt></p>
<blockquote>
  <tt>MaxPriorityQueue</tt> must be a model of <a
  href="./KeyedUpdatableQueue.html">Keyed Updatable Queue</a> and a
  max-<a href="./UpdatableQueue.html#concept%3AUpdatablePriorityQueue">
  Updatable Priority Queue</a>. The value type must be the graph's vertex
  descriptor and the key type must be the weight type.
  <b>Default:</b> A <tt>boost::d_ary_heap_indirect</tt> using a default
  index-in-heap and distance map.
</blockquote>

<p>UTIL: <tt>index_in_heap_map(IndexInHeapMap indicesInHeap)</tt></p>
<blockquote>
  This parameter only has an effect when the default max-priority queue is used.<br>
  <tt>IndexInHeapMap</tt> must be a model of <a
  href="../../property_map/doc/ReadWritePropertyMap.html">Read/Write Property
  Map</a>. The key type must be the graph's vertex descriptor type. The
  value type must be a size type
  (<tt>typename&nbsp;std::vector&lt;vertex_descriptor&gt;::size_type</tt>).<br>
  <b>Default:</b> A <tt>boost::iterator_property_map</tt> using a
  <tt>std::vector</tt> of <tt>num_vertices(g)</tt> size type objects and
  <tt>vertexIndices</tt> for the index map.
</blockquote>

<p>UTIL: <tt>distance_map(DistanceMap wAs)</tt></p>
<blockquote>
  This parameter only has an effect when the default max-priority queue is used.<br>
  <tt>DistanceMap</tt> must be a model of <a
  href="../../property_map/doc/ReadWritePropertyMap.html">Read/Write Property
  Map</a>. The key type must be the graph's vertex descriptor type. The
  value type must be the weight type
  (<tt>typename&nbsp;boost::property_traits&lt;WeightMap&gt;::value_type</tt>).
  <br>
  <b>Default:</b> A <tt>boost::iterator_property_map</tt> using a
  <tt>std::vector</tt> of <tt>num_vertices(g)</tt> weight type objects
  and <tt>vertexIndices</tt> for the index map.
</blockquote>

<h3>Returns</h3>
<p>void</p>

<h3>Throws</h3>

<p><tt>bad_graph</tt>
<blockquote>
  If <tt>num_vertices(g)</tt> is less than 2
</blockquote></p>

<p><tt>std::invalid_argument</tt>
<blockquote>
  If a max-priority queue is given as an argument and it is not empty
</blockquote>.

<h3><a name="SECTION001340300000000000000">
Complexity</a>
</h3>

<p>
The time complexity is <i>O(E + V)</i>.
</p>

<h3>References</h3>
<ul>
<li>David Matula (1993). <q><a href="http://dl.acm.org/citation.cfm?id=313872&dl=ACM&coll=DL&CFID=85991501&CFTOKEN=44461131">A linear time 2 + epsilon approximation algorightm for edge connectivity</a></q>
</li>
<li>Cai, Weiqing and Matula, David W. 
Partitioning by maximum adjacency search of graphs. 
Partitioning Data Sets: Dimacs Workshop, April 19-21, 1993. 
Vol 19. Page 55. 1995. Amer Mathematical Society</li>
}
</ul>

<h3>Visitor Event Points</h3>

<ul>
<li><b><tt>vis.initialize_vertex(s, g)</tt></b> is invoked on every
  vertex of the graph before the start of the graph search.</li>

<li><b><tt>vis.start_vertex(s, g)</tt></b> is invoked on the source
  vertex once before processing its out edges.</li>

<li><b><tt>vis.examine_edge(e, g)</tt></b> is invoked on every out-edge
  of each vertex after it is started.</li>

<li><b><tt>vis.finish_vertex(u, g)</tt></b> is invoked on a vertex after
  all of its out edges have been examined and the reach counts of the
  unvisited targets have been updated.</li>
</ul>

<h3>Notes</h3>

<p><a name="1">[1]</a> 
  Since the visitor parameter is passed by value, if your visitor
  contains state then any changes to the state during the algorithm
  will be made to a copy of the visitor object, not the visitor object
  passed in. Therefore you may want the visitor to hold this state by
  pointer or reference.</p>

<hr>
<table>
<tr valign=top>
<td nowrap>Copyright &copy; 2012</td><td>
Fernando Vilas
</td></tr></table>

</body>
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