/*
 * Licensed to the Apache Software Foundation (ASF) under one or more
 * contributor license agreements.  See the NOTICE file distributed with
 * this work for additional information regarding copyright ownership.
 * The ASF licenses this file to You 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 org.apache.commons.math.optimization;

import java.io.Serializable;

import org.apache.commons.math.util.MathUtils;

/**
 * Simple implementation of the {@link RealConvergenceChecker} interface using
 * only point coordinates.
 * <p>
 * Convergence is considered to have been reached if either the relative
 * difference between each point coordinate are smaller than a threshold or if
 * either the absolute difference between the point coordinates are smaller than
 * another threshold.
 * </p>
 * 
 * @version $Revision: 757180 $ $Date: 2009-03-22 13:54:45 +0100 (dim., 22 mars
 *          2009) $
 * @since 2.0
 */
public class SimpleRealPointChecker implements RealConvergenceChecker, Serializable {
	// TODO: Add Serializable documentation
	// TODO: Check Serializable implementation

	/** Serializable version identifier. */
	private static final long serialVersionUID = 2490271385513842607L;

	/** Default relative threshold. */
	private static final double DEFAULT_RELATIVE_THRESHOLD = 100 * MathUtils.EPSILON;

	/** Default absolute threshold. */
	private static final double DEFAULT_ABSOLUTE_THRESHOLD = 100 * MathUtils.SAFE_MIN;

	/** Relative tolerance threshold. */
	private final double relativeThreshold;

	/** Absolute tolerance threshold. */
	private final double absoluteThreshold;

	/**
	 * Build an instance with default threshold.
	 */
	public SimpleRealPointChecker() {
		this.relativeThreshold = DEFAULT_RELATIVE_THRESHOLD;
		this.absoluteThreshold = DEFAULT_ABSOLUTE_THRESHOLD;
	}

	/**
	 * Build an instance with a specified threshold.
	 * <p>
	 * In order to perform only relative checks, the absolute tolerance must be
	 * set to a negative value. In order to perform only absolute checks, the
	 * relative tolerance must be set to a negative value.
	 * </p>
	 * 
	 * @param relativeThreshold
	 *            relative tolerance threshold
	 * @param absoluteThreshold
	 *            absolute tolerance threshold
	 */
	public SimpleRealPointChecker(final double relativeThreshold, final double absoluteThreshold) {
		this.relativeThreshold = relativeThreshold;
		this.absoluteThreshold = absoluteThreshold;
	}

	/** {@inheritDoc} */
	public boolean converged(final int iteration, final RealPointValuePair previous, final RealPointValuePair current) {
		final double[] p = previous.getPoint();
		final double[] c = current.getPoint();
		for (int i = 0; i < p.length; ++i) {
			final double difference = Math.abs(p[i] - c[i]);
			final double size = Math.max(Math.abs(p[i]), Math.abs(c[i]));
			if ((difference > (size * relativeThreshold)) && (difference > absoluteThreshold)) {
				return false;
			}
		}
		return true;
	}

}
