Add Flower snark generator.

src/org/graphstream/algorithm/generator/FlowerSnarkGenerator.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;
+
+/**
+ * In the mathematical field of graph theory, the flower snarks form an infinite
+ * family of snarks introduced by Rufus Isaacs in 1975. As snarks, the flower
+ * snarks are a connected, bridgeless cubic graphs with chromatic index equal to
+ * 4. The flower snarks are non-planar and non-hamiltonian.
+ * 
+ * Source : <a href="http://en.wikipedia.org/wiki/Flower_snark">Wikipedia</a>
+ */
+public class FlowerSnarkGenerator extends BaseGenerator {
+
+	private int nextStarNumber = 1;
+
+	/*
+	 * (non-Javadoc)
+	 * 
+	 * @see org.graphstream.algorithm.generator.Generator#begin()
+	 */
+	public void begin() {
+		addStar();
+		addStar();
+		addStar();
+
+		addEdge(N.B, 1, N.B, 2);
+		addEdge(N.B, 2, N.B, 3);
+		addEdge(N.B, 3, N.B, 1);
+
+		addEdge(N.C, 1, N.C, 2);
+		addEdge(N.C, 2, N.C, 3);
+		addEdge(N.C, 3, N.D, 1);
+		addEdge(N.D, 1, N.D, 2);
+		addEdge(N.D, 2, N.D, 3);
+		addEdge(N.D, 3, N.C, 1);
+
+		flushCoords();
+	}
+
+	/*
+	 * (non-Javadoc)
+	 * 
+	 * @see org.graphstream.algorithm.generator.Generator#nextEvents()
+	 */
+	public boolean nextEvents() {
+		delEdge(N.B, nextStarNumber - 1, N.B, 1);
+		delEdge(N.C, nextStarNumber - 1, N.D, 1);
+		delEdge(N.D, nextStarNumber - 1, N.C, 1);
+
+		addStar();
+
+		addEdge(N.B, nextStarNumber - 2, N.B, nextStarNumber - 1);
+		addEdge(N.B, nextStarNumber - 1, N.B, 1);
+		addEdge(N.C, nextStarNumber - 2, N.C, nextStarNumber - 1);
+		addEdge(N.C, nextStarNumber - 1, N.D, 1);
+		addEdge(N.D, nextStarNumber - 2, N.D, nextStarNumber - 1);
+		addEdge(N.D, nextStarNumber - 1, N.C, 1);
+
+		flushCoords();
+
+		return true;
+	}
+
+	private void addStar() {
+		int i = nextStarNumber++;
+
+		addNode(N.A, i);
+		addNode(N.B, i);
+		addNode(N.C, i);
+		addNode(N.D, i);
+
+		addEdge(N.A, i, N.B, i);
+		addEdge(N.A, i, N.C, i);
+		addEdge(N.A, i, N.D, i);
+	}
+
+	protected static enum N {
+		A, B, C, D
+	}
+
+	private void addNode(N n, int i) {
+		addNode(getNodeId(n, i));
+	}
+
+	protected String getNodeId(N n, int i) {
+		return String.format("%s%04d", n, i);
+	}
+
+	private void addEdge(N n1, int i1, N n2, int i2) {
+		addEdge(getEdgeId(n1, i1, n2, i2), getNodeId(n1, i1), getNodeId(n2, i2));
+	}
+
+	private void delEdge(N n1, int i1, N n2, int i2) {
+		delEdge(getEdgeId(n1, i1, n2, i2));
+	}
+
+	protected String getEdgeId(N n1, int i1, N n2, int i2) {
+		return String.format("%s%s", getNodeId(n1, i1), getNodeId(n2, i2));
+	}
+
+	protected void flushCoords() {
+		double d = 2 * Math.PI / (nextStarNumber - 1);
+
+		for (int i = 1; i < nextStarNumber; i++) {
+			sendNodeAttributeChanged(sourceId, getNodeId(N.B, i), "x", null,
+					Math.cos((i - 1) * d));
+			sendNodeAttributeChanged(sourceId, getNodeId(N.B, i), "y", null,
+					Math.sin((i - 1) * d));
+
+			sendNodeAttributeChanged(sourceId, getNodeId(N.A, i), "x", null,
+					2 * Math.cos((i - 1) * d));
+			sendNodeAttributeChanged(sourceId, getNodeId(N.A, i), "y", null,
+					2 * Math.sin((i - 1) * d));
+
+			sendNodeAttributeChanged(sourceId, getNodeId(N.C, i), "x", null,
+					3 * Math.cos((i - 1) * d - d / 4.0));
+			sendNodeAttributeChanged(sourceId, getNodeId(N.C, i), "y", null,
+					3 * Math.sin((i - 1) * d - d / 4.0));
+
+			sendNodeAttributeChanged(sourceId, getNodeId(N.D, i), "x", null,
+					3 * Math.cos((i - 1) * d + d / 4.0));
+			sendNodeAttributeChanged(sourceId, getNodeId(N.D, i), "y", null,
+					3 * Math.sin((i - 1) * d + d / 4.0));
+		}
+	}
+}