/**
* Copyright (c) 2008, the JUNG Project and the Regents of the University
* of California
* All rights reserved.
*
* This software is open-source under the BSD license; see either
* "license.txt" or
* http://jung.sourceforge.net/license.txt for a description.
* Created on Jun 7, 2008
*
*/
package edu.uci.ics.jung.algorithms.metrics;
import java.util.ArrayList;
import java.util.HashMap;
import java.util.Map;
import edu.uci.ics.jung.graph.Graph;
/**
* A class consisting of static methods for calculating graph metrics.
*/
public class Metrics {
/**
* Returns a <code>Map</code> of vertices to their clustering coefficients.
* The clustering coefficient cc(v) of a vertex v is defined as follows:
* <ul>
* <li/><code>degree(v) == {0,1}</code>: 0
* <li/><code>degree(v) == n, n >= 2</code>: given S, the set of
* neighbors of <code>v</code>: cc(v) = (the sum over all w in S of the
* number of other elements of w that are neighbors of w) / ((|S| * (|S| -
* 1) / 2). Less formally, the fraction of <code>v</code>'s neighbors that
* are also neighbors of each other.
* <p>
* <b>Note</b>: This algorithm treats its argument as an undirected graph;
* edge direction is ignored.
*
* @param graph
* the graph whose clustering coefficients are to be calculated
* @see "The structure and function of complex networks, M.E.J. Newman, aps.arxiv.org/abs/cond-mat/0303516"
*/
public static <V, E> Map<V, Double> clusteringCoefficients(
Graph<V, E> graph) {
Map<V, Double> coefficients = new HashMap<V, Double>();
for (V v : graph.getVertices()) {
int n = graph.getNeighborCount(v);
if (n < 2) {
coefficients.put(v, new Double(0));
} else {
// how many of v's neighbors are connected to each other?
ArrayList<V> neighbors = new ArrayList<V>(
graph.getNeighbors(v));
double edge_count = 0;
for (int i = 0; i < n; i++) {
V w = neighbors.get(i);
for (int j = i + 1; j < n; j++) {
V x = neighbors.get(j);
edge_count += graph.isNeighbor(w, x) ? 1 : 0;
}
}
double possible_edges = (n * (n - 1)) / 2.0;
coefficients.put(v, new Double(edge_count / possible_edges));
}
}
return coefficients;
}
}