clustered_ba.cpp

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#include <boost/numeric/conversion/cast.hpp>
#include <boost/random/uniform_int.hpp>
#include <cstddef>
#include <iterator>
#include <sstream>
#include <string>
#include <utility>


#include "../exceptions.h"
#include "../rng.h"
#include "clustered_ba.h"
#include "base.h"

namespace pagmo { namespace topology {


clustered_ba::clustered_ba(int m0, int m, double p):
        m_m0(boost::numeric_cast<std::size_t>(m0)),m_m(boost::numeric_cast<std::size_t>(m)), m_p(double(p)),
        m_drng(rng_generator::get<rng_double>()),m_urng(rng_generator::get<rng_uint32>())
{
        if (m0 < 2 || m < 1 || m > m0) {
                pagmo_throw(value_error,"the value of m and m0 must be at least 1 and 2, and m must not be greater than m0");
        }
        if(p < 0 || p > 1) {
                pagmo_throw(value_error,"the value of p must be between 0 and 1");
        }
}

base_ptr clustered_ba::clone() const
{
        return base_ptr(new clustered_ba(*this));
}

void clustered_ba::connect(const vertices_size_type &idx)
{
        pagmo_assert(get_number_of_vertices() > 0);
        const vertices_size_type prev_size = get_number_of_vertices() - 1;
        if (prev_size < m_m0) {
                // If we had not built the initial m0 nodes, do it.
                // We want to connect the newcomer island with high probability, and make sure that
                // at least one connection exists (otherwise the island stays isolated).
                // NOTE: is it worth to make it a user-tunable parameter?
                const double prob = 0.0;
                // Flag indicating if at least 1 connection was added.
                bool connection_added = false;
                // Main loop.
                for (std::pair<v_iterator,v_iterator> vertices = get_vertices(); vertices.first != vertices.second; ++vertices.first) {
                        // Do not consider the new vertex itself.
                        if (*vertices.first != idx) {
                                if (m_drng() < prob) {
                                        connection_added = true;
                                        // Add the connections
                                        add_edge(*vertices.first,idx);
                                        add_edge(idx,*vertices.first);
                                }
                        }
                }
                // If no connections were established and this is not the first island being inserted,
                // establish at least one connection with a random island other than n.
                if ((!connection_added) && (prev_size != 0)) {
                        // Get a random vertex index between 0 and n_vertices - 1. Keep on repeating the procedure if by
                        // chance we end up on idx again.
                        boost::uniform_int<vertices_size_type> uni_int(0,get_number_of_vertices() - 1);
                        vertices_size_type rnd;
                        do {
                                rnd = uni_int(m_urng);
                        } while (rnd == idx);
                        // Add connections to the random vertex.
                        add_edge(rnd,idx);
                        add_edge(idx,rnd);
                }
        } else {
                // Now we need to add j edges, choosing the nodes with a probability
                // proportional to their number of connections. We keep track of the
                // connection established in order to avoid connecting twice to the same
                // node.
                // j is a random integer in the range 1 to m.
                boost::uniform_int<edges_size_type> uni_int2(1,m_m);
                std::size_t i = 0;
                std::size_t j = uni_int2(m_urng);
                std::pair<v_iterator,v_iterator> vertices;
                std::pair<a_iterator,a_iterator> adj_vertices;
                while (i < j) {
                        // Let's find the current total number of edges.
                        const edges_size_type n_edges = get_number_of_edges();
                        pagmo_assert(n_edges > 0);
                        boost::uniform_int<edges_size_type> uni_int(0,n_edges - 1 - i);
                        // Here we choose a random number between 0 and n_edges - 1 - i.
                        const edges_size_type rn = uni_int(m_urng);
                        edges_size_type n = 0;
                        // Iterate over all vertices and accumulate the number of edges for each of them. Stop when the accumulated number of edges is greater
                        // than rn. This is equivalent to giving a chance of connection to vertex v directly proportional to the number of edges departing from v.
                        // You can think of this process as selecting a random edge among all the existing edges and connecting to the vertex from which the
                        // selected edge departs.
                        vertices = get_vertices();
                        for (; vertices.first != vertices.second; ++vertices.first) {
                                // Do not consider it_n.
                                if (*vertices.first != idx) {
                                        adj_vertices = get_adjacent_vertices(*vertices.first);
                                        n += boost::numeric_cast<edges_size_type>(std::distance(adj_vertices.first,adj_vertices.second));
                                        if (n > rn) {
                                                break;
                                        }
                                }
                        }
                        pagmo_assert(vertices.first != vertices.second);
                        // If the candidate was not already connected, then add it.
                        if (!are_adjacent(idx,*vertices.first)) {
                                // Connect to nodes that are already adjacent to idx with probability p.
                                // This step increases clustering in the network.
                                adj_vertices = get_adjacent_vertices(idx);
                                for(;adj_vertices.first != adj_vertices.second; ++adj_vertices.first) {
                                    if(m_drng() < m_p && *adj_vertices.first != *vertices.first && !are_adjacent(*adj_vertices.first,*vertices.first)) {
                                        add_edge(*adj_vertices.first, *vertices.first);
                                        add_edge(*vertices.first, *adj_vertices.first);
                                    }
                                }
                                // Connect to idx
                                add_edge(*vertices.first,idx);
                                add_edge(idx,*vertices.first);
                                ++i;
                        }
                }
        }
}


std::string clustered_ba::human_readable_extra() const
{
        std::ostringstream oss;
        oss << "\tm0 = " << m_m0 << '\n';
        oss << "\tm = " << m_m << '\n';
        oss << "\tp = " << m_p << '\n';
        return oss.str();
}

std::string clustered_ba::get_name() const
{
        return "Clustered Barabasi-Albert";
}

}} //namespaces

BOOST_CLASS_EXPORT_IMPLEMENT(pagmo::topology::clustered_ba)