Boost Graph Library, Erdos Renyi Generator. Graphs always have same number of edges

问题

I'm trying to generate Erdos-Renyi graphs using boost graph library.

In the code below, which is taken from The Boost 1.72 documentation

the networks always have the same number of edges (they should not, for particular p values). I have tried using different random seeds to no avail.

Thanks for any help.

#include <boost/graph/adjacency_list.hpp>
#include <boost/graph/erdos_renyi_generator.hpp>
#include <boost/random/linear_congruential.hpp>
#include <iostream>

using namespace std;

typedef boost::adjacency_list<> Graph;
typedef boost::sorted_erdos_renyi_iterator<boost::minstd_rand, Graph> ERGen;

int main()
{
  boost::minstd_rand gen;
  // Create graph with 100 nodes and edges with probability 0.05
  Graph g(ERGen(gen, 100, 0.05), ERGen(), 100);
  cout << num_edges(g)<<endl;
  return 0;
}

回答1:

You should use a randomized seed:

boost::minstd_rand gen(std::random_device{}());

The nature of PRNG is that they generate deterministic output from a given state.

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#include <boost/graph/adjacency_list.hpp>
#include <boost/graph/erdos_renyi_generator.hpp>
#include <boost/random/linear_congruential.hpp>
#include <iostream>
#include <random>

using namespace std;

typedef boost::adjacency_list<> Graph;
typedef boost::sorted_erdos_renyi_iterator<boost::minstd_rand, Graph> ERGen;

int main() {
    boost::minstd_rand gen(std::random_device{}());
    // Create graph with 100 nodes and edges with probability 0.05
    Graph g(ERGen(gen, 100, 0.05), ERGen(), 100);
    cout << num_edges(g) << endl;
}

Prints, e.g.

515
491
518
511

来源：https://stackoverflow.com/questions/61294969/boost-graph-library-erdos-renyi-generator-graphs-always-have-same-number-of-ed