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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_PLOD_GENERATOR_HPP
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#define BOOST_GRAPH_PLOD_GENERATOR_HPP
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#include <iterator>
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#include <utility>
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#include <boost/random/uniform_int.hpp>
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#include <boost/shared_ptr.hpp>
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#include <boost/graph/graph_traits.hpp>
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#include <vector>
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#include <map>
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#include <cmath>
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namespace boost {
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template<typename RandomGenerator, typename Graph>
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class plod_iterator
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{
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typedef std::vector<std::pair<std::size_t, std::size_t> > out_degrees_t;
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typedef typename graph_traits<Graph>::directed_category directed_category;
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public:
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typedef std::input_iterator_tag iterator_category;
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typedef std::pair<std::size_t, std::size_t> 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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plod_iterator()
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: gen(0), out_degrees(), degrees_left(0), allow_self_loops(false) { }
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plod_iterator(RandomGenerator& gen, std::size_t n,
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double alpha, double beta, bool allow_self_loops = false)
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: gen(&gen), n(n), out_degrees(new out_degrees_t),
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degrees_left(0), allow_self_loops(allow_self_loops)
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{
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using std::pow;
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uniform_int<std::size_t> x(0, n-1);
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for (std::size_t i = 0; i != n; ++i) {
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std::size_t xv = x(gen);
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std::size_t degree = (xv == 0? 0 : std::size_t(beta * pow(xv, -alpha)));
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if (degree != 0) {
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out_degrees->push_back(std::make_pair(i, degree));
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}
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degrees_left += degree;
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}
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next(directed_category());
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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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plod_iterator& operator++()
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{
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next(directed_category());
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return *this;
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}
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plod_iterator operator++(int)
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{
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plod_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 plod_iterator& other) const
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{
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return degrees_left == other.degrees_left;
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}
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bool operator!=(const plod_iterator& other) const
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{ return !(*this == other); }
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private:
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void next(directed_tag)
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{
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uniform_int<std::size_t> x(0, out_degrees->size()-1);
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std::size_t source;
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do {
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source = x(*gen);
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} while ((*out_degrees)[source].second == 0);
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current.first = (*out_degrees)[source].first;
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do {
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current.second = x(*gen);
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} while (current.first == current.second && !allow_self_loops);
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--degrees_left;
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if (--(*out_degrees)[source].second == 0) {
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(*out_degrees)[source] = out_degrees->back();
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out_degrees->pop_back();
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}
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}
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void next(undirected_tag)
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{
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std::size_t source, target;
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while (true) {
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/* We may get to the point where we can't actually find any
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new edges, so we just add some random edge and set the
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degrees left = 0 to signal termination. */
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if (out_degrees->size() < 2) {
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uniform_int<std::size_t> x(0, n);
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current.first = x(*gen);
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do {
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current.second = x(*gen);
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} while (current.first == current.second && !allow_self_loops);
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degrees_left = 0;
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out_degrees->clear();
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return;
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}
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uniform_int<std::size_t> x(0, out_degrees->size()-1);
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// Select source vertex
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source = x(*gen);
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if ((*out_degrees)[source].second == 0) {
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(*out_degrees)[source] = out_degrees->back();
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out_degrees->pop_back();
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continue;
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}
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// Select target vertex
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target = x(*gen);
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if ((*out_degrees)[target].second == 0) {
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(*out_degrees)[target] = out_degrees->back();
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out_degrees->pop_back();
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continue;
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} else if (source != target
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|| (allow_self_loops && (*out_degrees)[source].second > 2)) {
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break;
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}
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}
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// Update degree counts
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--(*out_degrees)[source].second;
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--degrees_left;
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--(*out_degrees)[target].second;
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--degrees_left;
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current.first = (*out_degrees)[source].first;
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current.second = (*out_degrees)[target].first;
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}
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RandomGenerator* gen;
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std::size_t n;
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shared_ptr<out_degrees_t> out_degrees;
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std::size_t degrees_left;
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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_PLOD_GENERATOR_HPP
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