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      1 /*
      2  * Licensed to the Apache Software Foundation (ASF) under one or more
      3  * contributor license agreements.  See the NOTICE file distributed with
      4  * this work for additional information regarding copyright ownership.
      5  * The ASF licenses this file to You under the Apache License, Version 2.0
      6  * (the "License"); you may not use this file except in compliance with
      7  * the License.  You may obtain a copy of the License at
      8  *
      9  *      http://www.apache.org/licenses/LICENSE-2.0
     10  *
     11  * Unless required by applicable law or agreed to in writing, software
     12  * distributed under the License is distributed on an "AS IS" BASIS,
     13  * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
     14  * See the License for the specific language governing permissions and
     15  * limitations under the License.
     16  */
     17 
     18 package org.apache.commons.math.optimization.general;
     19 
     20 /**
     21  * Available choices of update formulas for the β parameter
     22  * in {@link NonLinearConjugateGradientOptimizer}.
     23  * <p>
     24  * The &beta; parameter is used to compute the successive conjugate
     25  * search directions. For non-linear conjugate gradients, there are
     26  * two formulas to compute &beta;:
     27  * <ul>
     28  *   <li>Fletcher-Reeves formula</li>
     29  *   <li>Polak-Ribi&egrave;re formula</li>
     30  * </ul>
     31  * On the one hand, the Fletcher-Reeves formula is guaranteed to converge
     32  * if the start point is close enough of the optimum whether the
     33  * Polak-Ribi&egrave;re formula may not converge in rare cases. On the
     34  * other hand, the Polak-Ribi&egrave;re formula is often faster when it
     35  * does converge. Polak-Ribi&egrave;re is often used.
     36  * <p>
     37  * @see NonLinearConjugateGradientOptimizer
     38  * @version $Revision: 758059 $ $Date: 2009-03-24 23:16:21 +0100 (mar. 24 mars 2009) $
     39  * @since 2.0
     40  */
     41 public enum ConjugateGradientFormula {
     42 
     43     /** Fletcher-Reeves formula. */
     44     FLETCHER_REEVES,
     45 
     46     /** Polak-Ribi&egrave;re formula. */
     47     POLAK_RIBIERE
     48 
     49 }
     50