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<Title>Boost Graph Library: Cycle Canceling for Min Cost Max Flow</Title>
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<H1><A NAME="sec:cycle_canceling">
<TT>cycle_canceling</TT>
</H1>
<PRE>
<i>// named parameter version</i>
template &lt;class <a href="./Graph.html">Graph</a>, class P, class T, class R&gt;
void cycle_canceling(
Graph &amp;g,
const bgl_named_params&lt;P, T, R&gt; &amp; params = <i>all defaults</i>)
<i>// non-named parameter version</i>
template &lt;class <a href="./Graph.html">Graph</a>, class Pred, class Distance, class Reversed, class ResidualCapacity, class Weight&gt;
void cycle_canceling(const Graph &amp; g, Weight weight, Reversed rev, ResidualCapacity residual_capacity, Pred pred, Distance distance)
</PRE>
<P>
The <tt>cycle_canceling()</tt> function calculates the minimum cost flow of a network with given flow. See Section <a
href="./graph_theory_review.html#sec:network-flow-algorithms">Network
Flow Algorithms</a> for a description of maximum flow.
For given flow values <i> f(u,v)</i> function minimizes flow cost in such a way, that for each <i>v in V</i> the
<i> sum<sub> u in V</sub> f(v,u) </i> is preserved. Particularly if the input flow was the maximum flow, the function produces min cost max flow.
The function calculates the flow values <i>f(u,v)</i> for all <i>(u,v)</i> in
<i>E</i>, which are returned in the form of the residual capacity
<i>r(u,v) = c(u,v) - f(u,v)</i>.
<p>
There are several special requirements on the input graph and property
map parameters for this algorithm. First, the directed graph
<i>G=(V,E)</i> that represents the network must be augmented to
include the reverse edge for every edge in <i>E</i>. That is, the
input graph should be <i>G<sub>in</sub> = (V,{E U
E<sup>T</sup>})</i>. The <tt>ReverseEdgeMap</tt> argument <tt>rev</tt>
must map each edge in the original graph to its reverse edge, that is
<i>(u,v) -> (v,u)</i> for all <i>(u,v)</i> in <i>E</i>.
The <tt>WeightMap</tt> has to map each edge from <i>E<sup>T</sup></i> to <i>-weight</i> of its reversed edge.
Note that edges from <i>E</i> can have negative weights.
<p>
If weights in the graph are nonnegative, the
<a href="./successive_shortest_path_nonnegative_weights.html"><tt>successive_shortest_path_nonnegative_weights()</tt></a>
might be better choice for min cost max flow.
<p>
The algorithm is described in <a
href="./bibliography.html#ahuja93:_network_flows">Network Flows</a>.
<p>
In each round algorithm augments the negative cycle (in terms of weight) in the residual graph.
If there is no negative cycle in the network, the cost is optimized.
<p>
Note that, although we mention capacity in the problem description, the actual algorithm doesn't have to now it.
<p>
In order to find the cost of the result flow use:
<a href="./find_flow_cost.html"><tt>find_flow_cost()</tt></a>.
<H3>Where Defined</H3>
<P>
<a href="../../../boost/graph/successive_shortest_path_nonnegative_weights.hpp"><TT>boost/graph/successive_shortest_path_nonnegative_weights.hpp</TT></a>
<P>
<h3>Parameters</h3>
IN: <tt>Graph&amp; g</tt>
<blockquote>
A directed graph. The
graph's type must be a model of <a
href="./VertexListGraph.html">VertexListGraph</a> and <a href="./IncidenceGraph.html">IncidenceGraph</a> For each edge
<i>(u,v)</i> in the graph, the reverse edge <i>(v,u)</i> must also
be in the graph.
</blockquote>
<h3>Named Parameters</h3>
IN/OUT: <tt>residual_capacity_map(ResidualCapacityEdgeMap res)</tt>
<blockquote>
This maps edges to their residual capacity. The type must be a model
of a mutable <a
href="../../property_map/doc/LvaluePropertyMap.html">Lvalue Property
Map</a>. The key type of the map must be the graph's edge descriptor
type.<br>
<b>Default:</b> <tt>get(edge_residual_capacity, g)</tt>
</blockquote>
IN: <tt>reverse_edge_map(ReverseEdgeMap rev)</tt>
<blockquote>
An edge property map that maps every edge <i>(u,v)</i> in the graph
to the reverse edge <i>(v,u)</i>. The map must be a model of
constant <a href="../../property_map/doc/LvaluePropertyMap.html">Lvalue
Property Map</a>. The key type of the map must be the graph's edge
descriptor type.<br>
<b>Default:</b> <tt>get(edge_reverse, g)</tt>
</blockquote>
IN: <tt>weight_map(WeightMap w)</tt>
<blockquote>
The weight (also know as ``length'' or ``cost'') 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>. The key type for this property map must be the edge
descriptor of the graph. The value type for the weight map must be
<i>Addable</i> with the distance map's value type. <br>
<b>Default:</b> <tt>get(edge_weight, g)</tt><br>
</blockquote>
UTIL: <tt>predecessor_map(PredEdgeMap pred)</tt>
<blockquote>
Use by the algorithm to store augmenting paths. The map must be a
model of mutable <a
href="../../property_map/doc/LvaluePropertyMap.html">Lvalue Property Map</a>.
The key type must be the graph's vertex descriptor type and the
value type must be the graph's edge descriptor type.<br>
<b>Default:</b> an <a
href="../../property_map/doc/iterator_property_map.html">
<tt>iterator_property_map</tt></a> created from a <tt>std::vector</tt>
of edge descriptors of size <tt>num_vertices(g)</tt> and
using the <tt>i_map</tt> for the index map.
</blockquote>
UTIL: <tt>distance_map(DistanceMap d_map)</tt>
<blockquote>
The shortest path weight from the source vertex <tt>s</tt> to each
vertex in the graph <tt>g</tt> is recorded in this property map. The
shortest path weight is the sum of the edge weights along the
shortest path. The type <tt>DistanceMap</tt> must be a model of <a
href="../../property_map/doc/ReadWritePropertyMap.html">Read/Write
Property Map</a>. The vertex descriptor type of the graph needs to
be usable as the key type of the distance map.
<b>Default:</b> <a
href="../../property_map/doc/iterator_property_map.html">
<tt>iterator_property_map</tt></a> created from a
<tt>std::vector</tt> of the <tt>WeightMap</tt>'s value type of size
<tt>num_vertices(g)</tt> and using the <tt>i_map</tt> for the index
map.<br>
</blockquote>
IN: <tt>vertex_index_map(VertexIndexMap i_map)</tt>
<blockquote>
Maps each vertex of the graph to a unique integer in the range
<tt>[0, num_vertices(g))</tt>. This property map is only needed
if the default for the distance or predecessor map is used.
The vertex index map must be a model of <a
href="../../property_map/doc/ReadablePropertyMap.html">Readable Property
Map</a>. The key type of the map must be the graph's vertex
descriptor type.<br>
<b>Default:</b> <tt>get(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>
<h3>Complexity</h3>
In the integer capacity and weight case, if <i>C</i> is the initial cost of the flow, then the complexity is <i> O(C * |V| * |E|)</i>,
where <i>O(|E|* |V|)</i> is the complexity of the bellman ford shortest paths algorithm and <i>C</i> is upper bound on number of iteration.
In many real world cases number of iterations is much smaller than <i>C</i>.
<h3>Example</h3>
The program in <a
href="../example/cycle_canceling_example.cpp"><tt>example/cycle_canceling_example.cpp</tt></a>.
<h3>See Also</h3>
<a href="./successive_shortest_path_nonnegative_weights.html"><tt>successive_shortest_path_nonnegative_weights()</tt></a><br>
<a href="./find_flow_cost.html"><tt>find_flow_cost()</tt></a>.
<br>
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<TABLE>
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<TD nowrap>Copyright &copy; 2013</TD><TD>
Piotr Wygocki, University of Warsaw (<A HREF="mailto:wygos@mimuw.edu.pl">wygos at mimuw.edu.pl</A>)
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