    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    }