org.matsim.contrib.socnetgen.sna.graph.analysis.Degree.java Source code

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Here is the source code for org.matsim.contrib.socnetgen.sna.graph.analysis.Degree.java

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/* *********************************************************************** *
 * project: org.matsim.*
 * Degree.java
 *                                                                         *
 * *********************************************************************** *
 *                                                                         *
 * copyright       : (C) 2009 by the members listed in the COPYING,        *
 *                   LICENSE and WARRANTY file.                            *
 * email           : info at matsim dot org                                *
 *                                                                         *
 * *********************************************************************** *
 *                                                                         *
 *   This program is free software; you can redistribute it and/or modify  *
 *   it under the terms of the GNU General Public License as published by  *
 *   the Free Software Foundation; either version 2 of the License, or     *
 *   (at your option) any later version.                                   *
 *   See also COPYING, LICENSE and WARRANTY file                           *
 *                                                                         *
 * *********************************************************************** */
package org.matsim.contrib.socnetgen.sna.graph.analysis;

import gnu.trove.map.hash.TObjectDoubleHashMap;

import java.util.Set;

import org.apache.commons.math.stat.descriptive.DescriptiveStatistics;
import org.matsim.contrib.socnetgen.sna.graph.Edge;
import org.matsim.contrib.socnetgen.sna.graph.Graph;
import org.matsim.contrib.socnetgen.sna.graph.Vertex;

/**
 * A class that provides functionality to analyze degree related
 * graph-properties.
 * 
 * @author illenberger
 * 
 */
public class Degree extends AbstractVertexProperty {

    private static Degree instance;

    public static Degree getInstance() {
        if (instance == null)
            instance = new Degree();
        return instance;
    }

    /**
     * Returns a descriptive statistics object containing the elements of <tt>vertices</tt>. The
     * graph is treated as undirected.
     * 
     * @param vertices
     *            a collection of vertices.
     *            
     * @return a descriptive statistics object.
     */
    public DescriptiveStatistics statistics(Set<? extends Vertex> vertices) {
        DescriptiveStatistics distribution = new DescriptiveStatistics();
        for (Vertex v : vertices)
            distribution.addValue(v.getEdges().size());

        return distribution;
    }

    /**
     * Returns a Vertex-double-map containing the degree of each vertex.
     * 
     * @param vertices
     *            a set of vertices
     * @return a Vertex-double-map containing the degree of each vertex.
     */
    public TObjectDoubleHashMap<Vertex> values(Set<? extends Vertex> vertices) {
        TObjectDoubleHashMap<Vertex> values = new TObjectDoubleHashMap<Vertex>();
        for (Vertex v : vertices)
            values.put(v, v.getEdges().size());

        return values;
    }

    /**
     * Calculates the degree correlation of graph <tt>graph</tt>.<br>
     * See: M. E. J. Newman. Assortative mixing in networks. Physical Review
     * Letters, 89(20), 2002.
     * 
     * @param g
     *            the graph the degree correlation is to be calculated.
     * @return the degree correlation.
     */
    public double assortativity(Graph graph) {
        double product = 0;
        double sum = 0;
        double squareSum = 0;

        for (Edge e : graph.getEdges()) {
            Vertex v_i = e.getVertices().getFirst();
            Vertex v_j = e.getVertices().getSecond();

            int k_i = v_i.getEdges().size();
            int k_j = v_j.getEdges().size();

            sum += 0.5 * (k_i + k_j);
            squareSum += 0.5 * (Math.pow(k_i, 2) + Math.pow(k_j, 2));
            product += k_i * k_j;
        }

        double norm = 1 / (double) graph.getEdges().size();
        return ((norm * product) - Math.pow(norm * sum, 2)) / ((norm * squareSum) - Math.pow(norm * sum, 2));
    }
}