115 lines
3.4 KiB
C++
115 lines
3.4 KiB
C++
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// Copyright 2004 The Trustees of Indiana University.
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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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// Authors: Douglas Gregor
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// Andrew Lumsdaine
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#ifndef BOOST_GRAPH_SMALL_WORLD_GENERATOR_HPP
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#define BOOST_GRAPH_SMALL_WORLD_GENERATOR_HPP
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#include <iterator>
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#include <utility>
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#include <boost/random/uniform_01.hpp>
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#include <boost/random/uniform_int.hpp>
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namespace boost {
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// Assumes undirected
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template<typename RandomGenerator, typename Graph>
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class small_world_iterator
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{
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typedef typename graph_traits<Graph>::vertices_size_type
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vertices_size_type;
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public:
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typedef std::input_iterator_tag iterator_category;
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typedef std::pair<vertices_size_type, vertices_size_type> value_type;
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typedef const value_type& reference;
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typedef const value_type* pointer;
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typedef void difference_type;
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small_world_iterator() : gen(0) {}
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small_world_iterator(RandomGenerator& gen, vertices_size_type n,
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vertices_size_type k, double prob = 0.0,
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bool allow_self_loops = false)
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: gen(&gen), n(n), k(k), prob(prob), source(0),
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target(allow_self_loops? 0 : 1),
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allow_self_loops(allow_self_loops),
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current(0, allow_self_loops? 0 : 1)
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{ }
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reference operator*() const { return current; }
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pointer operator->() const { return ¤t; }
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small_world_iterator& operator++()
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{
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target = (target + 1) % n;
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if (target == (source + k/2 + 1) % n) {
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++source;
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if (allow_self_loops) target = source;
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else target = (source + 1) % n;
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}
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current.first = source;
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uniform_01<RandomGenerator, double> rand01(*gen);
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uniform_int<vertices_size_type> rand_vertex_gen(0, n-1);
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double x = rand01();
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*gen = rand01.base(); // GRRRR
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if (x < prob) {
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vertices_size_type lower = (source + n - k/2) % n;
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vertices_size_type upper = (source + k/2) % n;
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do {
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current.second = rand_vertex_gen(*gen);
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} while ((current.second >= lower && current.second <= upper)
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|| (upper < lower
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&& (current.second >= lower || current.second <= upper)));
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} else {
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current.second = target;
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}
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return *this;
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}
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small_world_iterator operator++(int)
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{
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small_world_iterator temp(*this);
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++(*this);
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return temp;
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}
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bool operator==(const small_world_iterator& other) const
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{
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if (!gen && other.gen) return other == *this;
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else if (gen && !other.gen) return source == n;
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else if (!gen && !other.gen) return true;
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return source == other.source && target == other.target;
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}
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bool operator!=(const small_world_iterator& other) const
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{ return !(*this == other); }
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private:
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void next()
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{
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uniform_int<vertices_size_type> rand_vertex(0, n-1);
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current.first = rand_vertex(*gen);
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do {
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current.second = rand_vertex(*gen);
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} while (current.first == current.second && !allow_self_loops);
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}
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RandomGenerator* gen;
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vertices_size_type n;
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vertices_size_type k;
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double prob;
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vertices_size_type source;
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vertices_size_type target;
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bool allow_self_loops;
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value_type current;
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};
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} // end namespace boost
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#endif // BOOST_GRAPH_SMALL_WORLD_GENERATOR_HPP
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