sl@0: //=======================================================================
sl@0: // Copyright 1997, 1998, 1999, 2000 University of Notre Dame.
sl@0: // Authors: Andrew Lumsdaine, Lie-Quan Lee, Jeremy G. Siek,
sl@0: //
sl@0: // Distributed under the Boost Software License, Version 1.0. (See
sl@0: // accompanying file LICENSE_1_0.txt or copy at
sl@0: // http://www.boost.org/LICENSE_1_0.txt)
sl@0: //=======================================================================
sl@0: #ifndef BOOST_GRAPH_RELAX_HPP
sl@0: #define BOOST_GRAPH_RELAX_HPP
sl@0: 
sl@0: #include <functional>
sl@0: #include <boost/limits.hpp> // for numeric limits
sl@0: #include <boost/graph/graph_traits.hpp>
sl@0: #include <boost/property_map.hpp>
sl@0: 
sl@0: namespace boost {
sl@0: 
sl@0:     // The following version of the plus functor prevents
sl@0:     // problems due to overflow at positive infinity.
sl@0: 
sl@0:     template <class T>
sl@0:     struct closed_plus
sl@0:     {
sl@0:       // std::abs just isn't portable :(
sl@0:       template <class X>
sl@0:       inline X my_abs(const X& x) const { return x < 0 ? -x : x; }
sl@0: 
sl@0:       T operator()(const T& a, const T& b) const {
sl@0:         using namespace std;
sl@0:         T inf = (numeric_limits<T>::max)();
sl@0:         if (b > 0 && my_abs(inf - a) < b)
sl@0:           return inf;
sl@0:         return a + b;
sl@0:       }
sl@0:     };
sl@0:     
sl@0:     template <class Graph, class WeightMap, 
sl@0:             class PredecessorMap, class DistanceMap, 
sl@0:             class BinaryFunction, class BinaryPredicate>
sl@0:     bool relax(typename graph_traits<Graph>::edge_descriptor e, 
sl@0:                const Graph& g, const WeightMap& w, 
sl@0:                PredecessorMap& p, DistanceMap& d, 
sl@0:                const BinaryFunction& combine, const BinaryPredicate& compare)
sl@0:     {
sl@0:       typedef typename graph_traits<Graph>::directed_category DirCat;
sl@0:       bool is_undirected = is_same<DirCat, undirected_tag>::value;
sl@0:       typedef typename graph_traits<Graph>::vertex_descriptor Vertex;
sl@0:       Vertex u = source(e, g), v = target(e, g);
sl@0:       typedef typename property_traits<DistanceMap>::value_type D;
sl@0:       typedef typename property_traits<WeightMap>::value_type W;
sl@0:       D d_u = get(d, u), d_v = get(d, v);
sl@0:       W w_e = get(w, e);
sl@0:       
sl@0:       if ( compare(combine(d_u, w_e), d_v) ) {
sl@0:         put(d, v, combine(d_u, w_e));
sl@0:         put(p, v, u);
sl@0:         return true;
sl@0:       } else if (is_undirected && compare(combine(d_v, w_e), d_u)) {
sl@0:         put(d, u, combine(d_v, w_e));
sl@0:         put(p, u, v);
sl@0:         return true;
sl@0:       } else
sl@0:         return false;
sl@0:     }
sl@0:     
sl@0:     template <class Graph, class WeightMap, 
sl@0:       class PredecessorMap, class DistanceMap>
sl@0:     bool relax(typename graph_traits<Graph>::edge_descriptor e,
sl@0:                const Graph& g, WeightMap w, PredecessorMap p, DistanceMap d)
sl@0:     {
sl@0:       typedef typename property_traits<DistanceMap>::value_type D;
sl@0:       typedef closed_plus<D> Combine;
sl@0:       typedef std::less<D> Compare;
sl@0:       return relax(e, g, w, p, d, Combine(), Compare());
sl@0:     }
sl@0: 
sl@0: } // namespace boost
sl@0: 
sl@0: #endif /* BOOST_GRAPH_RELAX_HPP */