    001    /*
    002     * Licensed to the Apache Software Foundation (ASF) under one or more
    003     * contributor license agreements.  See the NOTICE file distributed with
    004     * this work for additional information regarding copyright ownership.
    005     * The ASF licenses this file to You under the Apache License, Version 2.0
    006     * (the "License"); you may not use this file except in compliance with
    007     * the License.  You may obtain a copy of the License at
    008     *
    009     *      http://www.apache.org/licenses/LICENSE-2.0
    010     *
    011     * Unless required by applicable law or agreed to in writing, software
    012     * distributed under the License is distributed on an "AS IS" BASIS,
    013     * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
    014     * See the License for the specific language governing permissions and
    015     * limitations under the License.
    016     */
    017
    018    package org.apache.commons.math.optimization.general;
    019
    020    /**
    021     * Available choices of update formulas for the &beta; parameter
    022     * in {@link NonLinearConjugateGradientOptimizer}.
    023     * <p>
    024     * The &beta; parameter is used to compute the successive conjugate
    025     * search directions. For non-linear conjugate gradients, there are
    026     * two formulas to compute &beta;:
    027     * <ul>
    028     *   <li>Fletcher-Reeves formula</li>
    029     *   <li>Polak-Ribi&egrave;re formula</li>
    030     * </ul>
    031     * On the one hand, the Fletcher-Reeves formula is guaranteed to converge
    032     * if the start point is close enough of the optimum whether the
    033     * Polak-Ribi&egrave;re formula may not converge in rare cases. On the
    034     * other hand, the Polak-Ribi&egrave;re formula is often faster when it
    035     * does converge. Polak-Ribi&egrave;re is often used.
    036     * <p>
    037     * @see NonLinearConjugateGradientOptimizer
    038     * @version $Revision: 758059 $ $Date: 2009-03-24 23:16:21 +0100 (mar. 24 mars 2009) $
    039     * @since 2.0
    040     */
    041    public enum ConjugateGradientFormula {
    042
    043        /** Fletcher-Reeves formula. */
    044        FLETCHER_REEVES,
    045
    046        /** Polak-Ribi&egrave;re formula. */
    047        POLAK_RIBIERE
    048
    049    }