/*
 *  RapidMiner
 *
 *  Copyright (C) 2001-2014 by RapidMiner and the contributors
 *
 *  Complete list of developers available at our web site:
 *
 *       http://rapidminer.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.tools.math.similarity.divergences;

import Jama.Matrix;

import com.rapidminer.example.ExampleSet;
import com.rapidminer.example.Tools;
import com.rapidminer.operator.OperatorException;
import com.rapidminer.tools.math.matrix.CovarianceMatrix;
import com.rapidminer.tools.math.similarity.BregmanDivergence;

/**
 * The "Mahalanobis distance ".
 * 
 * @author Sebastian Land, Regina Fritsch
 */
public class MahalanobisDistance extends BregmanDivergence {

	private static final long serialVersionUID = -5986526237805285428L;
	private Matrix inverseCovariance;

	@Override
	public double calculateDistance(double[] value1, double[] value2) {

		Matrix x = new Matrix(value1, value1.length);
		Matrix y = new Matrix(value2, value2.length);

		Matrix deltaxy = x.minus(y);

		// compute the mahalanobis distance
		return Math.sqrt(deltaxy.transpose().times(inverseCovariance).times(deltaxy).get(0, 0));
	}

	@Override
	public void init(ExampleSet exampleSet) throws OperatorException {
	    super.init(exampleSet);
	    Tools.onlyNumericalAttributes(exampleSet, "value based similarities");
		inverseCovariance = CovarianceMatrix.getCovarianceMatrix(exampleSet).inverse();
	}

	@Override
	public String toString() {
		return "Mahalanobis distance";
	}
}