dlib C++ Library - bayes_net_from_disk_ex.cpp

    // The contents of this file are in the public domain. See LICENSE_FOR_EXAMPLE_PROGRAMS.txt
    /*
        This is an example illustrating the use of the Bayesian Network
        inference utilities found in the dlib C++ library.  In this example
        we load a saved Bayesian Network from disk.
    */

    #include <dlib/bayes_utils.h>
    #include <dlib/graph_utils.h>
    #include <dlib/graph.h>
    #include <dlib/directed_graph.h>
    #include <iostream>
    #include <fstream>

    using namespace dlib;
    using namespace std;

    // ----------------------------------------------------------------------------------------

    int main(int argc, char** argv)
    {
        try
        {
            // This statement declares a bayesian network called bn.  Note that a bayesian network
            // in the dlib world is just a directed_graph object that contains a special kind
            // of node called a bayes_node.
            directed_graph<bayes_node>::kernel_1a_c bn;

            if (argc != 2)
            {
                cout << "You must supply a file name on the command line.  The file should "
                     << "contain a serialized Bayesian Network" << endl;
                return 1;
            }

            ifstream fin(argv[1],ios::binary);

            // Note that the saved networks produced by the bayes_net_gui_ex.cpp example can be deserialized
            // into a network.  So you can make your networks using that GUI if you like.
            cout << "Loading the network from disk..." << endl;
            deserialize(bn, fin);

            cout << "Number of nodes in the network: " << bn.number_of_nodes() << endl;

            // Let's compute some probability values using the loaded network using the join tree (aka. Junction
            // Tree) algorithm.

            // First we need to create an undirected graph which contains set objects at each node and
            // edge.  This long declaration does the trick.
            typedef graph<dlib::set<unsigned long>::compare_1b_c, dlib::set<unsigned long>::compare_1b_c>::kernel_1a_c join_tree_type;
            join_tree_type join_tree;

            // Now we need to populate the join_tree with data from our bayesian network.  The next two
            // function calls do this.  Explaining exactly what they do is outside the scope of this
            // example.  Just think of them as filling join_tree with information that is useful
            // later on for dealing with our bayesian network.
            create_moral_graph(bn, join_tree);
            create_join_tree(join_tree, join_tree);

            // Now we have a proper join_tree we can use it to obtain a solution to our
            // bayesian network.  Doing this is as simple as declaring an instance of
            // the bayesian_network_join_tree object as follows:
            bayesian_network_join_tree solution(bn, join_tree);

            // now print out the probabilities for each node
            cout << "Using the join tree algorithm:\n";
            for (unsigned long i = 0; i < bn.number_of_nodes(); ++i)
            {
                // print out the probability distribution for node i.
                cout << "p(node " << i <<") = " << solution.probability(i);
            }
        }
        catch (exception& e)
        {
            cout << "exception thrown: " << e.what() << endl;
            return 1;
        }
    }