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260 lines
10 KiB
C++
260 lines
10 KiB
C++
// The contents of this file are in the public domain. See LICENSE_FOR_EXAMPLE_PROGRAMS.txt
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/*
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This is an example illustrating the use of the graph_labeler and
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structural_graph_labeling_trainer objects.
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Suppose you have a bunch of objects and you need to label each of them as true or
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false. Suppose further that knowing the labels of some of these objects tells you
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something about the likely label of the others. This is common in a number of domains.
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For example, in image segmentation problems you need to label each pixel, and knowing
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the labels of neighboring pixels gives you information about the likely label since
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neighboring pixels will often have the same label.
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We can generalize this problem by saying that we have a graph and our task is to label
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each node in the graph as true or false. Additionally, the edges in the graph connect
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nodes which are likely to share the same label. In this example program, each node
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will have a feature vector which contains information which helps tell if the node
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should be labeled as true or false. The edges also contain feature vectors which give
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information indicating how strong the edge's labeling consistency constraint should be.
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This is useful since some nodes will have uninformative feature vectors and the only
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way to tell how they should be labeled is by looking at their neighbor's labels.
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Therefore, this program will show you how to learn two things using machine learning.
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The first is a linear classifier which operates on each node and predicts if it should
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be labeled as true or false. The second thing is a linear function of the edge
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vectors. This function outputs a penalty for giving two nodes connected by an edge
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differing labels. The graph_labeler object puts these two things together and uses
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them to compute a labeling which takes both into account. In what follows, we will use
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a structural SVM method to find the parameters of these linear functions which minimize
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the number of mistakes made by a graph_labeler.
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Finally, you might also consider reading the book Structured Prediction and Learning in
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Computer Vision by Sebastian Nowozin and Christoph H. Lampert since it contains a good
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introduction to machine learning methods such as the algorithm implemented by the
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structural_graph_labeling_trainer.
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*/
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#include <dlib/svm_threaded.h>
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#include <iostream>
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using namespace std;
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using namespace dlib;
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// ----------------------------------------------------------------------------------------
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// The first thing we do is define the kind of graph object we will be using.
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// Here we are saying there will be 2-D vectors at each node and 1-D vectors at
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// each edge. (You should read the matrix_ex.cpp example program for an introduction
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// to the matrix object.)
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typedef matrix<double,2,1> node_vector_type;
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typedef matrix<double,1,1> edge_vector_type;
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typedef graph<node_vector_type, edge_vector_type>::kernel_1a_c graph_type;
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// ----------------------------------------------------------------------------------------
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template <
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typename graph_type,
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typename labels_type
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>
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void make_training_examples(
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dlib::array<graph_type>& samples,
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labels_type& labels
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)
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{
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/*
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This function makes 3 graphs we will use for training. All of them
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will contain 4 nodes and have the structure shown below:
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(0)-----(1)
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(3)-----(2)
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In this example, each node has a 2-D vector. The first element of this vector
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is 1 when the node should have a label of false while the second element has
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a value of 1 when the node should have a label of true. Additionally, the
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edge vectors will contain a value of 1 when the nodes connected by the edge
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should share the same label and a value of 0 otherwise.
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We want to see that the machine learning method is able to figure out how
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these features relate to the labels. If it is successful it will create a
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graph_labeler which can predict the correct labels for these and other
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similarly constructed graphs.
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Finally, note that these tools require all values in the edge vectors to be >= 0.
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However, the node vectors may contain both positive and negative values.
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*/
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samples.clear();
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labels.clear();
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std::vector<bool> label;
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graph_type g;
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// ---------------------------
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g.set_number_of_nodes(4);
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label.resize(g.number_of_nodes());
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// store the vector [0,1] into node 0. Also label it as true.
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g.node(0).data = 0, 1; label[0] = true;
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// store the vector [0,0] into node 1.
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g.node(1).data = 0, 0; label[1] = true; // Note that this node's vector doesn't tell us how to label it.
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// We need to take the edges into account to get it right.
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// store the vector [1,0] into node 2.
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g.node(2).data = 1, 0; label[2] = false;
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// store the vector [0,0] into node 3.
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g.node(3).data = 0, 0; label[3] = false;
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// Add the 4 edges as shown in the ASCII art above.
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g.add_edge(0,1);
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g.add_edge(1,2);
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g.add_edge(2,3);
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g.add_edge(3,0);
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// set the 1-D vector for the edge between node 0 and 1 to the value of 1.
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edge(g,0,1) = 1;
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// set the 1-D vector for the edge between node 1 and 2 to the value of 0.
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edge(g,1,2) = 0;
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edge(g,2,3) = 1;
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edge(g,3,0) = 0;
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// output the graph and its label.
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samples.push_back(g);
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labels.push_back(label);
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// ---------------------------
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g.set_number_of_nodes(4);
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label.resize(g.number_of_nodes());
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g.node(0).data = 0, 1; label[0] = true;
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g.node(1).data = 0, 1; label[1] = true;
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g.node(2).data = 1, 0; label[2] = false;
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g.node(3).data = 1, 0; label[3] = false;
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g.add_edge(0,1);
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g.add_edge(1,2);
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g.add_edge(2,3);
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g.add_edge(3,0);
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// This time, we have strong edges between all the nodes. The machine learning
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// tools will have to learn that when the node information conflicts with the
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// edge constraints that the node information should dominate.
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edge(g,0,1) = 1;
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edge(g,1,2) = 1;
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edge(g,2,3) = 1;
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edge(g,3,0) = 1;
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samples.push_back(g);
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labels.push_back(label);
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// ---------------------------
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g.set_number_of_nodes(4);
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label.resize(g.number_of_nodes());
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g.node(0).data = 1, 0; label[0] = false;
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g.node(1).data = 1, 0; label[1] = false;
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g.node(2).data = 1, 0; label[2] = false;
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g.node(3).data = 0, 0; label[3] = false;
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g.add_edge(0,1);
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g.add_edge(1,2);
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g.add_edge(2,3);
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g.add_edge(3,0);
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edge(g,0,1) = 0;
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edge(g,1,2) = 0;
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edge(g,2,3) = 1;
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edge(g,3,0) = 0;
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samples.push_back(g);
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labels.push_back(label);
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// ---------------------------
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}
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// ----------------------------------------------------------------------------------------
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int main()
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{
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try
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{
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// Get the training samples we defined above.
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dlib::array<graph_type> samples;
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std::vector<std::vector<bool> > labels;
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make_training_examples(samples, labels);
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// Create a structural SVM trainer for graph labeling problems. The vector_type
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// needs to be set to a type capable of holding node or edge vectors.
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typedef matrix<double,0,1> vector_type;
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structural_graph_labeling_trainer<vector_type> trainer;
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// This is the usual SVM C parameter. Larger values make the trainer try
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// harder to fit the training data but might result in overfitting. You
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// should set this value to whatever gives the best cross-validation results.
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trainer.set_c(10);
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// Do 3-fold cross-validation and print the results. In this case it will
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// indicate that all nodes were correctly classified.
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cout << "3-fold cross-validation: " << cross_validate_graph_labeling_trainer(trainer, samples, labels, 3) << endl;
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// Since the trainer is working well. Let's have it make a graph_labeler
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// based on the training data.
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graph_labeler<vector_type> labeler = trainer.train(samples, labels);
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/*
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Let's try the graph_labeler on a new test graph. In particular, let's
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use one with 5 nodes as shown below:
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(0 F)-----(1 T)
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(3 T)-----(2 T)------(4 T)
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I have annotated each node with either T or F to indicate the correct
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output (true or false).
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*/
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graph_type g;
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g.set_number_of_nodes(5);
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g.node(0).data = 1, 0; // Node data indicates a false node.
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g.node(1).data = 0, 1; // Node data indicates a true node.
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g.node(2).data = 0, 0; // Node data is ambiguous.
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g.node(3).data = 0, 0; // Node data is ambiguous.
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g.node(4).data = 0.1, 0; // Node data slightly indicates a false node.
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g.add_edge(0,1);
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g.add_edge(1,2);
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g.add_edge(2,3);
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g.add_edge(3,0);
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g.add_edge(2,4);
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// Set the edges up so nodes 1, 2, 3, and 4 are all strongly connected.
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edge(g,0,1) = 0;
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edge(g,1,2) = 1;
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edge(g,2,3) = 1;
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edge(g,3,0) = 0;
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edge(g,2,4) = 1;
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// The output of this shows all the nodes are correctly labeled.
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cout << "Predicted labels: " << endl;
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std::vector<bool> temp = labeler(g);
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for (unsigned long i = 0; i < temp.size(); ++i)
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cout << " " << i << ": " << temp[i] << endl;
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// Breaking the strong labeling consistency link between node 1 and 2 causes
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// nodes 2, 3, and 4 to flip to false. This is because of their connection
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// to node 4 which has a small preference for false.
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edge(g,1,2) = 0;
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cout << "Predicted labels: " << endl;
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temp = labeler(g);
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for (unsigned long i = 0; i < temp.size(); ++i)
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cout << " " << i << ": " << temp[i] << endl;
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}
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catch (std::exception& e)
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{
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cout << "Error, an exception was thrown!" << endl;
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cout << e.what() << endl;
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}
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}
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