Add a Petersen graph generator.

src/org/graphstream/algorithm/generator/PetersenGraphGenerator.java

+/*
+ * Copyright 2006 - 2011 
+ *     Julien Baudry	<julien.baudry@graphstream-project.org>
+ *     Antoine Dutot	<antoine.dutot@graphstream-project.org>
+ *     Yoann Pigné		<yoann.pigne@graphstream-project.org>
+ *     Guilhelm Savin	<guilhelm.savin@graphstream-project.org>
+ * 
+ * This file is part of GraphStream <http://graphstream-project.org>.
+ * 
+ * GraphStream is a library whose purpose is to handle static or dynamic
+ * graph, create them from scratch, file or any source and display them.
+ * 
+ * This program is free software distributed under the terms of two licenses, the
+ * CeCILL-C license that fits European law, and the GNU Lesser General Public
+ * License. You can  use, modify and/ or redistribute the software under the terms
+ * of the CeCILL-C license as circulated by CEA, CNRS and INRIA at the following
+ * URL <http://www.cecill.info> or under the terms of the GNU LGPL as published by
+ * the Free Software Foundation, either version 3 of the License, or (at your
+ * option) any later version.
+ * 
+ * This program is distributed in the hope that it will be useful, but WITHOUT ANY
+ * WARRANTY; without even the implied warranty of MERCHANTABILITY or FITNESS FOR A
+ * PARTICULAR PURPOSE.  See the GNU Lesser General Public License for more details.
+ * 
+ * You should have received a copy of the GNU Lesser General Public License
+ * along with this program.  If not, see <http://www.gnu.org/licenses/>.
+ * 
+ * The fact that you are presently reading this means that you have had
+ * knowledge of the CeCILL-C and LGPL licenses and that you accept their terms.
+ */
+package org.graphstream.algorithm.generator;
+
+/**
+ * Generate a Petersen graph.
+ * 
+ * In the mathematical field of graph theory, the Petersen graph is an
+ * undirected graph with 10 vertices and 15 edges. It is a small graph that
+ * serves as a useful example and counterexample for many problems in graph
+ * theory. The Petersen graph is named for Julius Petersen, who in 1898
+ * constructed it to be the smallest bridgeless cubic graph with no
+ * three-edge-coloring. Although the graph is generally credited to Petersen, it
+ * had in fact first appeared 12 years earlier, in a paper by A. B. Kempe
+ * (1886). Donald Knuth states that the Petersen graph is "a remarkable
+ * configuration that serves as a counterexample to many optimistic predictions
+ * about what might be true for graphs in general."
+ * 
+ * Source : <a href="http://en.wikipedia.org/wiki/Petersen_graph">Wikipedia</a>
+ */
+public class PetersenGraphGenerator extends BaseGenerator {
+
+	private int[][] nodes = { { 0, 2, 4, 1, 3 }, { 7, 6, 5, 9, 8 } };
+
+	/*
+	 * (non-Javadoc)
+	 * @see org.graphstream.algorithm.generator.Generator#begin()
+	 */
+	public void begin() {
+		makeCycle(0, 4);
+		makeCycle(5, 9);
+
+		double a = Math.PI / 2.0;
+		double d = 2.0 * Math.PI / 5.0;
+
+		for (int i = 0; i < 5; i++) {
+			String id1 = getNodeId(nodes[0][i]);
+			String id2 = getNodeId(nodes[1][i]);
+
+			addEdge(getEdgeId(nodes[0][i], nodes[1][i]), id1, id2);
+
+			double x = Math.cos(a);
+			double y = Math.sin(a);
+
+			sendNodeAttributeAdded(sourceId, id1, "x", x);
+			sendNodeAttributeAdded(sourceId, id1, "y", y);
+
+			sendNodeAttributeAdded(sourceId, id2, "x", 2 * x);
+			sendNodeAttributeAdded(sourceId, id2, "y", 2 * y);
+
+			a += d;
+		}
+	}
+
+	/*
+	 * (non-Javadoc)
+	 * @see org.graphstream.algorithm.generator.Generator#nextEvents()
+	 */
+	public boolean nextEvents() {
+		return false;
+	}
+
+	protected void makeCycle(int i, int j) {
+		for (int k = i; k <= j; k++) {
+			addNode(getNodeId(k));
+
+			if (k > i)
+				addEdge(getEdgeId(k - 1, k), getNodeId(k - 1), getNodeId(k));
+		}
+
+		addEdge(getEdgeId(i, j), getNodeId(i), getNodeId(j));
+	}
+
+	protected String getNodeId(int i) {
+		return String.format("%02d", i);
+	}
+
+	protected String getEdgeId(int i, int j) {
+		if (i > j) {
+			j += i;
+			i = j - i;
+			j -= i;
+		}
+
+		return String.format("(%s;%s)", getNodeId(i), getNodeId(j));
+	}
+}