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    import org.apache.commons.math.util.FastMath;
022    
023    /** Harmonic function of the form <code>f (t) = a cos (&omega; t + &phi;)</code>.
024     * @version $Revision: 990655 $ $Date: 2010-08-29 23:49:40 +0200 (dim. 29 ao??t 2010) $
025     * @since 2.0
026     */
027    public class HarmonicFunction implements DifferentiableUnivariateRealFunction {
028    
029        /** Amplitude a. */
030        private final double a;
031    
032        /** Pulsation &omega;. */
033        private final double omega;
034    
035        /** Phase &phi;. */
036        private final double phi;
037    
038        /** Simple constructor.
039         * @param a amplitude
040         * @param omega pulsation
041         * @param phi phase
042         */
043        public HarmonicFunction(double a, double omega, double phi) {
044            this.a     = a;
045            this.omega = omega;
046            this.phi   = phi;
047        }
048    
049        /** {@inheritDoc} */
050        public double value(double x) {
051            return a * FastMath.cos(omega * x + phi);
052        }
053    
054        /** {@inheritDoc} */
055        public HarmonicFunction derivative() {
056            return new HarmonicFunction(a * omega, omega, phi + FastMath.PI / 2);
057        }
058    
059        /** Get the amplitude a.
060         * @return amplitude a;
061         */
062        public double getAmplitude() {
063            return a;
064        }
065    
066        /** Get the pulsation &omega;.
067         * @return pulsation &omega;
068         */
069        public double getPulsation() {
070            return omega;
071        }
072    
073        /** Get the phase &phi;.
074         * @return phase &phi;
075         */
076        public double getPhase() {
077            return phi;
078        }
079    
080    }