/*
 *  RapidMiner
 *
 *  Copyright (C) 2001-2011 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.performance;

import com.rapidminer.tools.Tools;

/**
 * The average relative error in a strict way of calculation: 
 * <i>Sum(|label-predicted|/min(|label|, |predicted|))/#examples</i>.
 * The relative error of label 0 and prediction 0 is defined as 0.
 * If the minimum of label and prediction is 0, the relative error is
 * defined as infinite.
 * 
 * @author Ingo Mierswa
 */
public class StrictRelativeError extends SimpleCriterion {

	private static final long serialVersionUID = 8055914052886853327L;

	public StrictRelativeError() {}

	public StrictRelativeError(StrictRelativeError sc) {
		super(sc);
	}

	@Override
	public double countExample(double label, double predictedLabel) {
		double diff = Math.abs(label - predictedLabel);
		double absLabel = Math.abs(label);
		double absPrediction = Math.abs(predictedLabel);
		if (Tools.isZero(diff)) {
			return 0.0d;
		} else {
			double min = Math.min(absLabel, absPrediction);
			if (Tools.isZero(min)) {
				return Double.POSITIVE_INFINITY;
			} else {
				return diff / min;
			}
		}
	}

	/**
	 * Indicates whether or not percentage format should be used in the
	 * {@link #toString} method. The default implementation returns false.
	 */
	@Override
	public boolean formatPercent() {
		return true;
	}
	
	@Override
	public String getName() {
		return "relative_error_strict";
	}

	@Override
	public String getDescription() {
		return "Average strict relative error (average of absolute deviation of the prediction from the actual value divided by minimum of the actual value and the prediction)";
	}
}