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 (&omega; t + &phi;)</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 &omega;. */
032        private final double omega;
033    
034        /** Phase &phi;. */
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 &omega;.
066         * @return pulsation &omega;
067         */
068        public double getPulsation() {
069            return omega;
070        }
071    
072        /** Get the phase &phi;.
073         * @return phase &phi;
074         */
075        public double getPhase() {
076            return phi;
077        }
078    
079    }