/*
 * Licensed to the Apache Software Foundation (ASF) under one or more
 * contributor license agreements.  See the NOTICE file distributed with
 * this work for additional information regarding copyright ownership.
 * The ASF licenses this file to You under the Apache License, Version 2.0
 * (the "License"); you may not use this file except in compliance with
 * the License.  You may obtain a copy of the License at
 *
 *      http://www.apache.org/licenses/LICENSE-2.0
 *
 * Unless required by applicable law or agreed to in writing, software
 * distributed under the License is distributed on an "AS IS" BASIS,
 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
 * See the License for the specific language governing permissions and
 * limitations under the License.
 */

package org.apache.commons.math.optimization.fitting;

import org.apache.commons.math.analysis.DifferentiableUnivariateRealFunction;

/**
 * Harmonic function of the form <code>f (t) = a cos (&omega; t + &phi;)</code>.
 * 
 * @version $Revision$ $Date$
 * @since 2.0
 */
public class HarmonicFunction implements DifferentiableUnivariateRealFunction {

	/** Amplitude a. */
	private final double a;

	/** Pulsation &omega;. */
	private final double omega;

	/** Phase &phi;. */
	private final double phi;

	/**
	 * Simple constructor.
	 * 
	 * @param a
	 *            amplitude
	 * @param omega
	 *            pulsation
	 * @param phi
	 *            phase
	 */
	public HarmonicFunction(double a, double omega, double phi) {
		this.a = a;
		this.omega = omega;
		this.phi = phi;
	}

	/** {@inheritDoc} */
	public double value(double x) {
		return a * Math.cos(omega * x + phi);
	}

	/** {@inheritDoc} */
	public HarmonicFunction derivative() {
		return new HarmonicFunction(a * omega, omega, phi + Math.PI / 2);
	}

	/**
	 * Get the amplitude a.
	 * 
	 * @return amplitude a;
	 */
	public double getAmplitude() {
		return a;
	}

	/**
	 * Get the pulsation &omega;.
	 * 
	 * @return pulsation &omega;
	 */
	public double getPulsation() {
		return omega;
	}

	/**
	 * Get the phase &phi;.
	 * 
	 * @return phase &phi;
	 */
	public double getPhase() {
		return phi;
	}

}
