/*******************************************************************************
* Copyright (c) 2010 Haifeng Li
*
* 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.apache.org/licenses/LICENSE-2.0
*
* 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 smile.clustering.linkage;
/**
* Weighted Pair Group Method with Arithmetic mean. WPGMA down-weights the
* largest group by giving equal weights to the two branches of the dendrogram
* that are about to fuse.
* <p>
* Note that the terms weighted and unweighted refer to the final result,
* not the math by which it is achieved. Thus the simple averaging in WPGMA
* produces a weighted result, and the proportional averaging in UPGMA produces
* an unweighted result.
*
* @author Haifeng Li
*/
public class WPGMALinkage extends Linkage {
/**
* Constructor.
* @param proximity the proximity matrix to store the distance measure of
* dissimilarity. To save space, we only need the lower half of matrix.
*/
public WPGMALinkage(double[][] proximity) {
this.proximity = proximity;
}
@Override
public String toString() {
return "WPGMA linkage";
}
@Override
public void merge(int i, int j) {
for (int k = 0; k < i; k++) {
proximity[i][k] = (proximity[i][k] + d(j, k)) / 2;
}
for (int k = i+1; k < proximity.length; k++) {
proximity[k][i] = (proximity[k][i] + d(j, k)) / 2;
}
}
}