/*
 * 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.math4.optim;

/**
 * This interface specifies how to check if an optimization algorithm has
 * converged.
 * <br>
 * Deciding if convergence has been reached is a problem-dependent issue. The
 * user should provide a class implementing this interface to allow the
 * optimization algorithm to stop its search according to the problem at hand.
 * <br>
 * For convenience, three implementations that fit simple needs are already
 * provided: {@link SimpleValueChecker}, {@link SimpleVectorValueChecker} and
 * {@link SimplePointChecker}. The first two consider that convergence is
 * reached when the objective function value does not change much anymore, it
 * does not use the point set at all.
 * The third one considers that convergence is reached when the input point
 * set does not change much anymore, it does not use objective function value
 * at all.
 *
 * @param <PAIR> Type of the (point, objective value) pair.
 *
 * @see org.apache.commons.math4.optim.SimplePointChecker
 * @see org.apache.commons.math4.optim.SimpleValueChecker
 * @see org.apache.commons.math4.optim.SimpleVectorValueChecker
 *
 * @since 3.0
 */
public interface ConvergenceChecker<PAIR> {
    /**
     * Check if the optimization algorithm has converged.
     *
     * @param iteration Current iteration.
     * @param previous Best point in the previous iteration.
     * @param current Best point in the current iteration.
     * @return {@code true} if the algorithm is considered to have converged.
     */
    boolean converged(int iteration, PAIR previous, PAIR current);
}