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1 | /* | |
2 | * Copyright (c) 2003, the JUNG Project and the Regents of the University | |
3 | * of California | |
4 | * All rights reserved. | |
5 | * | |
6 | * This software is open-source under the BSD license; see either | |
7 | * "license.txt" or | |
8 | * http://jung.sourceforge.net/license.txt for a description. | |
9 | */ | |
10 | package edu.uci.ics.jung.algorithms.importance; | |
11 | ||
12 | import java.util.Iterator; | |
13 | ||
14 | import cern.colt.matrix.DoubleMatrix2D; | |
15 | import edu.uci.ics.jung.algorithms.GraphMatrixOperations; | |
16 | import edu.uci.ics.jung.graph.UndirectedGraph; | |
17 | import edu.uci.ics.jung.graph.Vertex; | |
18 | import edu.uci.ics.jung.graph.decorators.Indexer; | |
19 | ||
20 | /** | |
21 | * /** | |
22 | * Computes s-t betweenness centrality for each vertex in the graph. The betweenness values in this case | |
23 | * are based on random walks, measuring the expected number of times a node is traversed by a random walk | |
24 | * from s to t. The result is that each vertex has a UserData element of type | |
25 | * MutableDouble whose key is 'centrality.RandomWalkBetweennessCentrality' | |
26 | * | |
27 | * A simple example of usage is: <br> | |
28 | * RandomWalkSTBetweenness ranker = new RandomWalkBetweenness(someGraph,someSource,someTarget); <br> | |
29 | * ranker.evaluate(); <br> | |
30 | * ranker.printRankings(); <p> | |
31 | * | |
32 | * Running time is: O(n^3). | |
33 | * @see "Mark Newman: A measure of betweenness centrality based on random walks, 2002." | |
34 | ||
35 | * @author Scott White | |
36 | */ | |
37 | public class RandomWalkSTBetweenness extends AbstractRanker { | |
38 | ||
39 | public static final String CENTRALITY = "centrality.RandomWalkSTBetweennessCentrality"; | |
40 | private DoubleMatrix2D mVoltageMatrix; | |
41 | private Indexer mIndexer; | |
42 | Vertex mSource; | |
43 | Vertex mTarget; | |
44 | ||
45 | /** | |
46 | * Constructor which initializes the algorithm | |
47 | * @param g the graph whose nodes are to be analyzed | |
48 | * @param s the source vertex | |
49 | * @param t the target vertex | |
50 | */ | |
51 | 1 | public RandomWalkSTBetweenness(UndirectedGraph g, Vertex s, Vertex t) { |
52 | 1 | initialize(g, true, false); |
53 | 1 | mSource = s; |
54 | 1 | mTarget = t; |
55 | 1 | } |
56 | ||
57 | protected Indexer getIndexer() { | |
58 | 1210 | return mIndexer; |
59 | } | |
60 | ||
61 | protected DoubleMatrix2D getVoltageMatrix() { | |
62 | 0 | return mVoltageMatrix; |
63 | } | |
64 | ||
65 | protected void setUp() { | |
66 | 1 | mVoltageMatrix = GraphMatrixOperations.computeVoltagePotentialMatrix((UndirectedGraph) getGraph()); |
67 | 1 | mIndexer = Indexer.getIndexer(getGraph()); |
68 | 1 | } |
69 | ||
70 | protected void computeBetweenness() { | |
71 | 0 | setUp(); |
72 | ||
73 | 0 | for (Iterator iIt = getGraph().getVertices().iterator();iIt.hasNext();) { |
74 | 0 | Vertex ithVertex = (Vertex) iIt.next(); |
75 | ||
76 | 0 | setRankScore(ithVertex,computeSTBetweenness(ithVertex,mSource, mTarget)); |
77 | } | |
78 | 0 | } |
79 | ||
80 | public double computeSTBetweenness(Vertex ithVertex, Vertex source, Vertex target) { | |
81 | 605 | if (ithVertex == source || ithVertex == target) return 1; |
82 | 495 | if (mVoltageMatrix == null) { |
83 | 0 | setUp(); |
84 | } | |
85 | 495 | int i = mIndexer.getIndex(ithVertex); |
86 | 495 | int s = mIndexer.getIndex(source); |
87 | 495 | int t = mIndexer.getIndex(target); |
88 | ||
89 | 495 | double betweenness = 0; |
90 | 495 | for (Iterator vIt = ithVertex.getSuccessors().iterator();vIt.hasNext();) { |
91 | 2070 | Vertex jthVertex = (Vertex) vIt.next(); |
92 | 2070 | int j = mIndexer.getIndex(jthVertex); |
93 | 2070 | double currentFlow = 0; |
94 | 2070 | currentFlow += mVoltageMatrix.get(i,s); |
95 | 2070 | currentFlow -= mVoltageMatrix.get(i,t); |
96 | 2070 | currentFlow -= mVoltageMatrix.get(j,s); |
97 | 2070 | currentFlow += mVoltageMatrix.get(j,t); |
98 | 2070 | betweenness += Math.abs(currentFlow); |
99 | } | |
100 | ||
101 | 495 | return betweenness/2.0; |
102 | ||
103 | } | |
104 | ||
105 | /** | |
106 | * the user datum key used to store the rank scores | |
107 | * @return the key | |
108 | */ | |
109 | public String getRankScoreKey() { | |
110 | 0 | return CENTRALITY; |
111 | } | |
112 | ||
113 | protected double evaluateIteration() { | |
114 | 0 | computeBetweenness(); |
115 | 0 | return 0; |
116 | } | |
117 | } |
this report was generated by version 1.0.5 of jcoverage. |
copyright © 2003, jcoverage ltd. all rights reserved. |