org.jgrapht.generate.ScaleFreeGraphGenerator Maven / Gradle / Ivy
/* ==========================================
* JGraphT : a free Java graph-theory library
* ==========================================
*
* Project Info: http://jgrapht.sourceforge.net/
* Project Creator: Barak Naveh (http://sourceforge.net/users/barak_naveh)
*
* (C) Copyright 2003-2008, by Barak Naveh and Contributors.
*
* This program and the accompanying materials are dual-licensed under
* either
*
* (a) the terms of the GNU Lesser General Public License version 2.1
* as published by the Free Software Foundation, or (at your option) any
* later version.
*
* or (per the licensee's choosing)
*
* (b) the terms of the Eclipse Public License v1.0 as published by
* the Eclipse Foundation.
*/
/* -----------------
* ScaleFreeGraphGenerator.java
* -----------------
* (C) Copyright 2008-2008, by Ilya Razenshteyn and Contributors.
*
* Original Author: Ilya Razenshteyn
* Contributor(s): -
*
* $Id$
*
* Changes
* -------
*/
package org.jgrapht.generate;
import java.util.*;
import org.jgrapht.*;
/**
* Generates directed or undirected scale-free network
* of any size. Scale-free network is a connected graph, where degrees of
* vertices are distributed in unusual way. There are many vertices with small
* degrees and only small amount of vertices with big degrees.
*
* @author Ilya Razenshteyn
*/
public class ScaleFreeGraphGenerator
implements GraphGenerator
{
private int size; // size of graphs, generated by this instance of generator
private long seed; // initial seed
private Random random; // the source of randomness
/**
* Constructs a new ScaleFreeGraphGenerator.
*
* @param size number of vertices to be generated
*/
public ScaleFreeGraphGenerator(
int size)
{
if (size < 0) {
throw new IllegalArgumentException(
"invalid size: " + size + " (must be non-negative)");
}
this.size = size;
random = new Random();
seed = random.nextLong();
}
/**
* Constructs a new ScaleFreeGraphGenerator using fixed
* seed for the random generator.
*
* @param size number of vertices to be generated
* @param seed initial seed for the random generator
*/
public ScaleFreeGraphGenerator(
int size,
long seed)
{
if (size < 0) {
throw new IllegalArgumentException(
"invalid size: " + size + " (must be non-negative)");
}
this.size = size;
random = new Random();
this.seed = seed;
}
/**
* Generates scale-free network with size passed to the
* constructor. Each call of this method produces identical output (but if
* target is an undirected graph, the directions of edges will be
* lost).
*
* @param target receives the generated edges and vertices; if this is
* non-empty on entry, the result will be a disconnected graph since
* generated elements will not be connected to existing elements
* @param vertexFactory called to produce new vertices
* @param resultMap unused parameter
*/
@Override public void generateGraph(
Graph target,
VertexFactory vertexFactory,
Map resultMap)
{
random.setSeed(seed);
List vertexList = new ArrayList();
List degrees = new ArrayList();
int degreeSum = 0;
for (int i = 0; i < size; i++) {
V newVertex = vertexFactory.createVertex();
target.addVertex(newVertex);
int newDegree = 0;
while ((newDegree == 0) && (i != 0)) // we want our graph to be
// connected
{
for (int j = 0; j < vertexList.size(); j++) {
if ((degreeSum == 0)
|| (random.nextInt(degreeSum) < degrees.get(j)))
{
degrees.set(j, degrees.get(j) + 1);
newDegree++;
degreeSum += 2;
if (random.nextInt(2) == 0) {
target.addEdge(vertexList.get(j), newVertex);
} else {
target.addEdge(newVertex, vertexList.get(j));
}
}
}
}
vertexList.add(newVertex);
degrees.add(newDegree);
}
}
}
// End ScaleFreeGraphGenerator.java