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.fitting;
019
020 import org.apache.commons.math.analysis.DifferentiableUnivariateRealFunction;
021
022 /** Harmonic function of the form <code>f (t) = a cos (ω t + φ)</code>.
023 * @version $Revision: 786479 $ $Date: 2009-06-19 08:36:16 -0400 (Fri, 19 Jun 2009) $
024 * @since 2.0
025 */
026 public class HarmonicFunction implements DifferentiableUnivariateRealFunction {
027
028 /** Amplitude a. */
029 private final double a;
030
031 /** Pulsation ω. */
032 private final double omega;
033
034 /** Phase φ. */
035 private final double phi;
036
037 /** Simple constructor.
038 * @param a amplitude
039 * @param omega pulsation
040 * @param phi phase
041 */
042 public HarmonicFunction(double a, double omega, double phi) {
043 this.a = a;
044 this.omega = omega;
045 this.phi = phi;
046 }
047
048 /** {@inheritDoc} */
049 public double value(double x) {
050 return a * Math.cos(omega * x + phi);
051 }
052
053 /** {@inheritDoc} */
054 public HarmonicFunction derivative() {
055 return new HarmonicFunction(a * omega, omega, phi + Math.PI / 2);
056 }
057
058 /** Get the amplitude a.
059 * @return amplitude a;
060 */
061 public double getAmplitude() {
062 return a;
063 }
064
065 /** Get the pulsation ω.
066 * @return pulsation ω
067 */
068 public double getPulsation() {
069 return omega;
070 }
071
072 /** Get the phase φ.
073 * @return phase φ
074 */
075 public double getPhase() {
076 return phi;
077 }
078
079 }