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83 lines
3.0 KiB
83 lines
3.0 KiB
//======================================================================= |
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// Copyright 1997, 1998, 1999, 2000 University of Notre Dame. |
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// Authors: Andrew Lumsdaine, Lie-Quan Lee, Jeremy G. Siek, |
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// |
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// Distributed under the Boost Software License, Version 1.0. (See |
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// 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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#ifndef BOOST_GRAPH_RELAX_HPP |
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#define BOOST_GRAPH_RELAX_HPP |
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#include <functional> |
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#include <boost/limits.hpp> // for numeric limits |
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#include <boost/graph/graph_traits.hpp> |
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#include <boost/property_map/property_map.hpp> |
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namespace boost { |
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// The following version of the plus functor prevents |
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// problems due to overflow at positive infinity. |
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template <class T> |
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struct closed_plus |
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{ |
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const T inf; |
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closed_plus() : inf((std::numeric_limits<T>::max)()) { } |
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closed_plus(T inf) : inf(inf) { } |
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T operator()(const T& a, const T& b) const { |
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using namespace std; |
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if (a == inf) return inf; |
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if (b == inf) return inf; |
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return a + b; |
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} |
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}; |
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template <class Graph, class WeightMap, |
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class PredecessorMap, class DistanceMap, |
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class BinaryFunction, class BinaryPredicate> |
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bool relax(typename graph_traits<Graph>::edge_descriptor e, |
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const Graph& g, const WeightMap& w, |
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PredecessorMap& p, DistanceMap& d, |
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const BinaryFunction& combine, const BinaryPredicate& compare) |
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{ |
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typedef typename graph_traits<Graph>::directed_category DirCat; |
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bool is_undirected = is_same<DirCat, undirected_tag>::value; |
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typedef typename graph_traits<Graph>::vertex_descriptor Vertex; |
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Vertex u = source(e, g), v = target(e, g); |
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typedef typename property_traits<DistanceMap>::value_type D; |
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typedef typename property_traits<WeightMap>::value_type W; |
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D d_u = get(d, u), d_v = get(d, v); |
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W w_e = get(w, e); |
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// The redundant gets in the return statements are to ensure that extra |
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// floating-point precision in x87 registers does not lead to relax() |
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// returning true when the distance did not actually change. |
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if ( compare(combine(d_u, w_e), d_v) ) { |
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put(d, v, combine(d_u, w_e)); |
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put(p, v, u); |
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return compare(get(d, v), d_v); |
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} else if (is_undirected && compare(combine(d_v, w_e), d_u)) { |
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put(d, u, combine(d_v, w_e)); |
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put(p, u, v); |
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return compare(get(d, u), d_u); |
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} else |
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return false; |
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} |
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template <class Graph, class WeightMap, |
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class PredecessorMap, class DistanceMap> |
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bool relax(typename graph_traits<Graph>::edge_descriptor e, |
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const Graph& g, WeightMap w, PredecessorMap p, DistanceMap d) |
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{ |
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typedef typename property_traits<DistanceMap>::value_type D; |
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typedef closed_plus<D> Combine; |
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typedef std::less<D> Compare; |
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return relax(e, g, w, p, d, Combine(), Compare()); |
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} |
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} // namespace boost |
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#endif /* BOOST_GRAPH_RELAX_HPP */
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