/*
* RapidMiner
*
* Copyright (C) 2001-2008 by Rapid-I and the contributors
*
* Complete list of developers available at our web site:
*
* http://rapid-i.com
*
* This program is free software: you can redistribute it and/or modify
* it under the terms of the GNU Affero General Public License 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 Affero General Public License for more details.
*
* You should have received a copy of the GNU Affero General Public License
* along with this program. If not, see http://www.gnu.org/licenses/.
*/
package com.rapidminer.operator.validation.clustering.itemdistribution;
/**
* Normalized Gini Coefficient.
*
* @author Michael Wurst
* @version $Id: GiniCoefficient.java,v 1.5 2008/09/12 10:30:05 tobiasmalbrecht Exp $
*
*/
public class GiniCoefficient implements ItemDistributionMeasure {
public double evaluate(int[] x, int n) {
double sum = 0;
for (int i = 0; i < x.length; i++)
sum = sum + x[i];
double mean = sum / n;
sum = 0;
for (int i = 0; i < x.length; i++)
for (int j = 0; j < x.length; j++)
sum = sum + Math.abs(x[i] - x[j]);
if (mean == 0)
return 0.0;
return 1 - (sum / (2 * mean * (n * ((double) n - 1))));
}
}