Chris@16: // Copyright 2004-2006 The Trustees of Indiana University.
Chris@16: 
Chris@16: // Distributed under the Boost Software License, Version 1.0.
Chris@16: // (See accompanying file LICENSE_1_0.txt or copy at
Chris@16: // http://www.boost.org/LICENSE_1_0.txt)
Chris@16: 
Chris@16: //  Authors: Douglas Gregor
Chris@16: //           Andrew Lumsdaine
Chris@16: #ifndef BOOST_GRAPH_PLOD_GENERATOR_HPP
Chris@16: #define BOOST_GRAPH_PLOD_GENERATOR_HPP
Chris@16: 
Chris@16: #include <iterator>
Chris@16: #include <utility>
Chris@16: #include <boost/random/uniform_int.hpp>
Chris@16: #include <boost/shared_ptr.hpp>
Chris@16: #include <boost/graph/graph_traits.hpp>
Chris@16: #include <vector>
Chris@16: #include <map>
Chris@16: #include <boost/config/no_tr1/cmath.hpp>
Chris@16: #include <boost/mpl/if.hpp>
Chris@16: 
Chris@16: namespace boost {
Chris@16:   template<typename RandomGenerator>
Chris@16:   class out_directed_plod_iterator 
Chris@16:   {
Chris@16:   public:
Chris@16:     typedef std::forward_iterator_tag            iterator_category;
Chris@16:     typedef std::pair<std::size_t, std::size_t>  value_type;
Chris@16:     typedef const value_type&                    reference;
Chris@16:     typedef const value_type*                    pointer;
Chris@16:     typedef std::ptrdiff_t                       difference_type;
Chris@16: 
Chris@16:     out_directed_plod_iterator() : gen(0), at_end(true) { }
Chris@16: 
Chris@16:     out_directed_plod_iterator(RandomGenerator& gen, std::size_t n,  
Chris@16:                                double alpha, double beta, 
Chris@16:                                bool allow_self_loops)
Chris@16:       : gen(&gen), n(n), alpha(alpha), beta(beta), 
Chris@16:         allow_self_loops(allow_self_loops), at_end(false), degree(0),
Chris@16:         current(0, 0)
Chris@16:     {
Chris@16:       using std::pow;
Chris@16: 
Chris@16:       uniform_int<std::size_t> x(0, n-1);
Chris@16:       std::size_t xv = x(gen);
Chris@16:       degree = (xv == 0? 0 : std::size_t(beta * pow(xv, -alpha)));
Chris@16:     }
Chris@16: 
Chris@16:     reference operator*() const { return current; }
Chris@16:     pointer operator->() const { return &current; }
Chris@16: 
Chris@16:     out_directed_plod_iterator& operator++()
Chris@16:     { 
Chris@16:       using std::pow;
Chris@16: 
Chris@16:       uniform_int<std::size_t> x(0, n-1);
Chris@16: 
Chris@16:       // Continue stepping through source nodes until the
Chris@16:       // (out)degree is > 0
Chris@16:       while (degree == 0) {
Chris@16:         // Step to the next source node. If we've gone past the
Chris@16:         // number of nodes we're responsible for, we're done.
Chris@16:         if (++current.first >= n) {
Chris@16:           at_end = true;
Chris@16:           return *this;
Chris@16:         }
Chris@16: 
Chris@16:         std::size_t xv = x(*gen);
Chris@16:         degree = (xv == 0? 0 : std::size_t(beta * pow(xv, -alpha)));      
Chris@16:       }
Chris@16: 
Chris@16:       do {
Chris@16:         current.second = x(*gen);
Chris@16:       } while (current.first == current.second && !allow_self_loops);
Chris@16:       --degree;
Chris@16: 
Chris@16:       return *this;
Chris@16:     }
Chris@16: 
Chris@16:     out_directed_plod_iterator operator++(int)
Chris@16:     {
Chris@16:       out_directed_plod_iterator temp(*this);
Chris@16:       ++(*this);
Chris@16:       return temp;
Chris@16:     }
Chris@16: 
Chris@16:     bool operator==(const out_directed_plod_iterator& other) const
Chris@16:     { 
Chris@16:       return at_end == other.at_end; 
Chris@16:     }
Chris@16: 
Chris@16:     bool operator!=(const out_directed_plod_iterator& other) const
Chris@16:     { 
Chris@16:       return !(*this == other); 
Chris@16:     }
Chris@16: 
Chris@16:   private:    
Chris@16:     RandomGenerator* gen;
Chris@16:     std::size_t n;
Chris@16:     double alpha;
Chris@16:     double beta;
Chris@16:     bool allow_self_loops;
Chris@16:     bool at_end;
Chris@16:     std::size_t degree;
Chris@16:     value_type current;
Chris@16:   };
Chris@16: 
Chris@16:   template<typename RandomGenerator>
Chris@16:   class undirected_plod_iterator 
Chris@16:   {
Chris@16:     typedef std::vector<std::pair<std::size_t, std::size_t> > out_degrees_t;
Chris@16: 
Chris@16:   public:
Chris@16:     typedef std::input_iterator_tag              iterator_category;
Chris@16:     typedef std::pair<std::size_t, std::size_t>  value_type;
Chris@16:     typedef const value_type&                    reference;
Chris@16:     typedef const value_type*                    pointer;
Chris@16:     typedef std::ptrdiff_t                       difference_type;
Chris@16: 
Chris@16:     undirected_plod_iterator() 
Chris@16:       : gen(0), out_degrees(), degrees_left(0), allow_self_loops(false) { }
Chris@16: 
Chris@16:     undirected_plod_iterator(RandomGenerator& gen, std::size_t n,  
Chris@16:                              double alpha, double beta, 
Chris@16:                              bool allow_self_loops = false)
Chris@16:       : gen(&gen), n(n), out_degrees(new out_degrees_t),
Chris@16:         degrees_left(0), allow_self_loops(allow_self_loops)
Chris@16:     {
Chris@16:       using std::pow;
Chris@16: 
Chris@16:       uniform_int<std::size_t> x(0, n-1);
Chris@16:       for (std::size_t i = 0; i != n; ++i) {
Chris@16:         std::size_t xv = x(gen);
Chris@16:         std::size_t degree = (xv == 0? 0 : std::size_t(beta * pow(xv, -alpha)));
Chris@16:         if (degree == 0) degree = 1;
Chris@16:         else if (degree >= n) degree = n-1;
Chris@16:         out_degrees->push_back(std::make_pair(i, degree));
Chris@16:         degrees_left += degree;
Chris@16:       }
Chris@16: 
Chris@16:       next();
Chris@16:     }
Chris@16: 
Chris@16:     reference operator*() const { return current; }
Chris@16:     pointer operator->() const { return &current; }
Chris@16: 
Chris@16:     undirected_plod_iterator& operator++()
Chris@16:     { 
Chris@16:       next();
Chris@16:       return *this;
Chris@16:     }
Chris@16: 
Chris@16:     undirected_plod_iterator operator++(int)
Chris@16:     {
Chris@16:       undirected_plod_iterator temp(*this);
Chris@16:       ++(*this);
Chris@16:       return temp;
Chris@16:     }
Chris@16: 
Chris@16:     bool operator==(const undirected_plod_iterator& other) const
Chris@16:     { 
Chris@16:       return degrees_left == other.degrees_left; 
Chris@16:     }
Chris@16: 
Chris@16:     bool operator!=(const undirected_plod_iterator& other) const
Chris@16:     { return !(*this == other); }
Chris@16: 
Chris@16:   private:
Chris@16:     void next()
Chris@16:     {
Chris@16:       std::size_t source, target;
Chris@16:       while (true) {
Chris@16:         /* We may get to the point where we can't actually find any
Chris@16:            new edges, so we just add some random edge and set the
Chris@16:            degrees left = 0 to signal termination. */
Chris@16:         if (out_degrees->size() < 2) {
Chris@16:           uniform_int<std::size_t> x(0, n-1);
Chris@16:           current.first  = x(*gen);
Chris@16:           do {
Chris@16:             current.second = x(*gen);
Chris@16:           } while (current.first == current.second && !allow_self_loops);
Chris@16:           degrees_left = 0;
Chris@16:           out_degrees->clear();
Chris@16:           return;
Chris@16:         }
Chris@16: 
Chris@16:         uniform_int<std::size_t> x(0, out_degrees->size()-1);
Chris@16: 
Chris@16:         // Select source vertex
Chris@16:         source = x(*gen);
Chris@16:         if ((*out_degrees)[source].second == 0) {
Chris@16:           (*out_degrees)[source] = out_degrees->back();
Chris@16:           out_degrees->pop_back();
Chris@16:           continue;
Chris@16:         } 
Chris@16: 
Chris@16:         // Select target vertex
Chris@16:         target = x(*gen);
Chris@16:         if ((*out_degrees)[target].second == 0) {
Chris@16:           (*out_degrees)[target] = out_degrees->back();
Chris@16:           out_degrees->pop_back();
Chris@16:           continue;
Chris@16:         } else if (source != target 
Chris@16:                    || (allow_self_loops && (*out_degrees)[source].second > 2)) {
Chris@16:           break;
Chris@16:         }
Chris@16:       }
Chris@16: 
Chris@16:       // Update degree counts
Chris@16:       --(*out_degrees)[source].second;
Chris@16:       --degrees_left;
Chris@16:       --(*out_degrees)[target].second;
Chris@16:       --degrees_left;
Chris@16:       current.first  = (*out_degrees)[source].first;
Chris@16:       current.second = (*out_degrees)[target].first;
Chris@16:     }
Chris@16: 
Chris@16:     RandomGenerator* gen;
Chris@16:     std::size_t n;
Chris@16:     shared_ptr<out_degrees_t> out_degrees;
Chris@16:     std::size_t degrees_left;
Chris@16:     bool allow_self_loops;
Chris@16:     value_type current;
Chris@16:   };
Chris@16: 
Chris@16: 
Chris@16:   template<typename RandomGenerator, typename Graph>
Chris@16:   class plod_iterator
Chris@16:     : public mpl::if_<is_convertible<
Chris@16:                         typename graph_traits<Graph>::directed_category,
Chris@16:                         directed_tag>,
Chris@16:                       out_directed_plod_iterator<RandomGenerator>,
Chris@16:                       undirected_plod_iterator<RandomGenerator> >::type
Chris@16:   {
Chris@16:     typedef typename mpl::if_<
Chris@16:                        is_convertible<
Chris@16:                          typename graph_traits<Graph>::directed_category,
Chris@16:                          directed_tag>,
Chris@16:                         out_directed_plod_iterator<RandomGenerator>,
Chris@16:                         undirected_plod_iterator<RandomGenerator> >::type
Chris@16:       inherited;
Chris@16: 
Chris@16:   public:
Chris@16:     plod_iterator() : inherited() { }
Chris@16: 
Chris@16:     plod_iterator(RandomGenerator& gen, std::size_t n,  
Chris@16:                   double alpha, double beta, bool allow_self_loops = false)
Chris@16:       : inherited(gen, n, alpha, beta, allow_self_loops) { }
Chris@16:   };
Chris@16: 
Chris@16: } // end namespace boost
Chris@16: 
Chris@16: #endif // BOOST_GRAPH_PLOD_GENERATOR_HPP