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Commit 2fe540ea authored by gsavin's avatar gsavin
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Add a Petersen graph generator.

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/*
* 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));
}
}
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