package edu.uci.ics.jung.algorithms.generators.random;
/*
* Copyright (c) 2009, 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.
*/
import java.util.HashMap;
import java.util.Map;
import java.util.Random;
import org.apache.commons.collections15.Factory;
import edu.uci.ics.jung.algorithms.generators.Lattice2DGenerator;
import edu.uci.ics.jung.algorithms.util.WeightedChoice;
import edu.uci.ics.jung.graph.Graph;
/**
* Graph generator that produces a random graph with small world properties. The
* underlying model is an mxn (optionally toroidal) lattice. Each node u has
* four local connections, one to each of its neighbors, and in addition 1+ long
* range connections to some node v where v is chosen randomly according to
* probability proportional to d^-alpha where d is the lattice distance between
* u and v and alpha is the clustering exponent.
*
* @see "Navigation in a small world J. Kleinberg, Nature 406(2000), 845."
* @author Joshua O'Madadhain
*/
public class KleinbergSmallWorldGenerator<V, E>
extends Lattice2DGenerator<V, E> {
private double clustering_exponent;
private Random random;
private int num_connections = 1;
/**
* Creates
*
* @param graph_factory
* @param vertex_factory
* @param edge_factory
* @param latticeSize
* @param clusteringExponent
*/
public KleinbergSmallWorldGenerator(
Factory<? extends Graph<V, E>> graph_factory,
Factory<V> vertex_factory, Factory<E> edge_factory, int latticeSize,
double clusteringExponent) {
this(graph_factory, vertex_factory, edge_factory, latticeSize,
latticeSize, clusteringExponent);
}
/**
* @param graph_factory
* @param vertex_factory
* @param edge_factory
* @param row_count
* @param col_count
* @param clusteringExponent
*/
public KleinbergSmallWorldGenerator(
Factory<? extends Graph<V, E>> graph_factory,
Factory<V> vertex_factory, Factory<E> edge_factory, int row_count,
int col_count, double clusteringExponent) {
super(graph_factory, vertex_factory, edge_factory, row_count, col_count,
true);
clustering_exponent = clusteringExponent;
initialize();
}
/**
* @param graph_factory
* @param vertex_factory
* @param edge_factory
* @param row_count
* @param col_count
* @param clusteringExponent
* @param isToroidal
*/
public KleinbergSmallWorldGenerator(
Factory<? extends Graph<V, E>> graph_factory,
Factory<V> vertex_factory, Factory<E> edge_factory, int row_count,
int col_count, double clusteringExponent, boolean isToroidal) {
super(graph_factory, vertex_factory, edge_factory, row_count, col_count,
isToroidal);
clustering_exponent = clusteringExponent;
initialize();
}
private void initialize() {
this.random = new Random();
}
/**
* Sets the {@code Random} instance used by this instance. Useful for unit
* testing.
*/
public void setRandom(Random random) {
this.random = random;
}
/**
* Sets the seed of the internal random number generator. May be used to
* provide repeatable experiments.
*/
public void setRandomSeed(long seed) {
random.setSeed(seed);
}
/**
* Sets the number of new 'small-world' connections (outgoing edges) to be
* added to each vertex.
*/
public void setConnectionCount(int num_connections) {
if (num_connections <= 0) {
throw new IllegalArgumentException(
"Number of new connections per vertex must be >= 1");
}
this.num_connections = num_connections;
}
/**
* Returns the number of new 'small-world' connections to be made to each
* vertex.
*/
public int getConnectionCount() {
return this.num_connections;
}
/**
* Generates a random small world network according to the parameters given
*
* @return a random small world graph
*/
@Override
public Graph<V, E> create() {
Graph<V, E> graph = super.create();
// TODO: For toroidal graphs, we can make this more clever by
// pre-creating the WeightedChoice object
// and using the output as an offset to the current vertex location.
WeightedChoice<V> weighted_choice;
// Add long range connections
for (int i = 0; i < graph.getVertexCount(); i++) {
V source = getVertex(i);
int row = getRow(i);
int col = getCol(i);
int row_offset = row < row_count / 2 ? -row_count : row_count;
int col_offset = col < col_count / 2 ? -col_count : col_count;
Map<V, Float> vertex_weights = new HashMap<V, Float>();
for (int j = 0; j < row_count; j++) {
for (int k = 0; k < col_count; k++) {
if (j == row && k == col) {
continue;
}
int v_dist = Math.abs(j - row);
int h_dist = Math.abs(k - col);
if (is_toroidal) {
v_dist = Math.min(v_dist,
Math.abs(j - row + row_offset));
h_dist = Math.min(h_dist,
Math.abs(k - col + col_offset));
}
int distance = v_dist + h_dist;
if (distance < 2) {
continue;
}
vertex_weights.put(getVertex(j, k),
(float) Math.pow(distance, -clustering_exponent));
}
}
for (int j = 0; j < this.num_connections; j++) {
weighted_choice = new WeightedChoice<V>(vertex_weights, random);
V target = weighted_choice.nextItem();
graph.addEdge(edge_factory.create(), source, target);
}
}
return graph;
}
}