AbstractWardsLinkageTreeBuilder.java

/*
 * Copyright 2004-2010 Information & Software Engineering Group (188/1)
 *                     Institute of Software Technology and Interactive Systems
 *                     Vienna University of Technology, Austria
 *
 * Licensed under the Apache License, Version 2.0 (the "License");
 * you may not use this file except in compliance with the License.
 * You may obtain a copy of the License at
 *
 *     http://www.ifs.tuwien.ac.at/dm/somtoolbox/license.html
 *
 * Unless required by applicable law or agreed to in writing, software
 * distributed under the License is distributed on an "AS IS" BASIS,
 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
 * See the License for the specific language governing permissions and
 * limitations under the License.
 */
package at.tuwien.ifs.somtoolbox.visualization.clustering;

import at.tuwien.ifs.somtoolbox.layers.metrics.L2Metric;
import at.tuwien.ifs.somtoolbox.util.VectorTools;

/**
 * @author Rudolf Mayer
 * @version $Id: AbstractWardsLinkageTreeBuilder.java 3583 2010-05-21 10:07:41Z mayer $
 */
public abstract class AbstractWardsLinkageTreeBuilder extends TreeBuilder {

    public AbstractWardsLinkageTreeBuilder() {
        super();
    }

    /**
     * Calculates the increase of the Error Sum of Squares if the two Clusters are united. To get the "real" Error Sum
     * of Squares increase one must take the square root of the returned value. This step is left out of here to save
     * computation time, as it changes nothing in the order of the distances if this calculation is left out for all
     * distances.
     * 
     * @return the 'distance' value
     */
    protected double calcESSincrease(ClusterNode n1, ClusterNode n2) {
        int length1 = n1.getNodes().length;
        int length2 = n2.getNodes().length;

        L2Metric l2 = new L2Metric();

        double dist = l2.norm(VectorTools.subtract(n1.getMeanVector(), n2.getMeanVector()));
        double result = dist * dist / (length1 + length2) * length1 * length2;

        return result;
    }

}