org.jgrapht.generate.ScaleFreeGraphGenerator Maven / Gradle / Ivy
The newest version!
/*
* (C) Copyright 2008-2023, by Ilya Razenshteyn and Contributors.
*
* JGraphT : a free Java graph-theory library
*
* See the CONTRIBUTORS.md file distributed with this work for additional
* information regarding copyright ownership.
*
* This program and the accompanying materials are made available under the
* terms of the Eclipse Public License 2.0 which is available at
* http://www.eclipse.org/legal/epl-2.0, or the
* GNU Lesser General Public License v2.1 or later
* which is available at
* http://www.gnu.org/licenses/old-licenses/lgpl-2.1-standalone.html.
*
* SPDX-License-Identifier: EPL-2.0 OR LGPL-2.1-or-later
*/
package org.jgrapht.generate;
import org.jgrapht.*;
import java.util.*;
/**
* 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.
*
* @param the graph vertex type
* @param the graph edge type
*
* @author Ilya Razenshteyn
*/
public class ScaleFreeGraphGenerator
implements GraphGenerator
{
private final int size;
private final Random rng;
/**
* Constructor
*
* @param size number of vertices to be generated
*/
public ScaleFreeGraphGenerator(int size)
{
this(size, new Random());
}
/**
* Constructor
*
* @param size number of vertices to be generated
* @param seed initial seed for the random generator
*/
public ScaleFreeGraphGenerator(int size, long seed)
{
this(size, new Random(seed));
}
/**
* Constructor
*
* @param size number of vertices to be generated
* @param rng the random number generator
*/
public ScaleFreeGraphGenerator(int size, Random rng)
{
if (size < 0) {
throw new IllegalArgumentException("invalid size: " + size + " (must be non-negative)");
}
this.size = size;
this.rng = Objects.requireNonNull(rng, "Random number generator cannot be null");
}
/**
* Generates scale-free network with size
passed to the constructor.
*
* @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 resultMap unused parameter, can be null
*/
@Override
public void generateGraph(Graph target, Map resultMap)
{
List vertexList = new ArrayList<>();
List degrees = new ArrayList<>();
int degreeSum = 0;
for (int i = 0; i < size; i++) {
V newVertex = target.addVertex();
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) || (rng.nextInt(degreeSum) < degrees.get(j))) {
degrees.set(j, degrees.get(j) + 1);
newDegree++;
degreeSum += 2;
if (rng.nextBoolean()) {
target.addEdge(vertexList.get(j), newVertex);
} else {
target.addEdge(newVertex, vertexList.get(j));
}
}
}
}
vertexList.add(newVertex);
degrees.add(newDegree);
}
}
}