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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.fitting;
19  
20  import org.apache.commons.math.analysis.DifferentiableUnivariateRealFunction;
21  
22  /** Harmonic function of the form <code>f (t) = a cos (&omega; t + &phi;)</code>.
23   * @version $Revision: 786479 $ $Date: 2009-06-19 08:36:16 -0400 (Fri, 19 Jun 2009) $
24   * @since 2.0
25   */
26  public class HarmonicFunction implements DifferentiableUnivariateRealFunction {
27  
28      /** Amplitude a. */
29      private final double a;
30  
31      /** Pulsation &omega;. */
32      private final double omega;
33  
34      /** Phase &phi;. */
35      private final double phi;
36  
37      /** Simple constructor.
38       * @param a amplitude
39       * @param omega pulsation
40       * @param phi phase
41       */
42      public HarmonicFunction(double a, double omega, double phi) {
43          this.a     = a;
44          this.omega = omega;
45          this.phi   = phi;
46      }
47  
48      /** {@inheritDoc} */
49      public double value(double x) {
50          return a * Math.cos(omega * x + phi);
51      }
52  
53      /** {@inheritDoc} */
54      public HarmonicFunction derivative() {
55          return new HarmonicFunction(a * omega, omega, phi + Math.PI / 2);
56      }
57  
58      /** Get the amplitude a.
59       * @return amplitude a;
60       */
61      public double getAmplitude() {
62          return a;
63      }
64  
65      /** Get the pulsation &omega;.
66       * @return pulsation &omega;
67       */
68      public double getPulsation() {
69          return omega;
70      }
71  
72      /** Get the phase &phi;.
73       * @return phase &phi;
74       */
75      public double getPhase() {
76          return phi;
77      }
78  
79  }