001/* ===========================================================
002 * JFreeChart : a free chart library for the Java(tm) platform
003 * ===========================================================
004 *
005 * (C) Copyright 2000-present, by David Gilbert and Contributors.
006 *
007 * Project Info:  http://www.jfree.org/jfreechart/index.html
008 *
009 * This library is free software; you can redistribute it and/or modify it
010 * under the terms of the GNU Lesser General Public License as published by
011 * the Free Software Foundation; either version 2.1 of the License, or
012 * (at your option) any later version.
013 *
014 * This library is distributed in the hope that it will be useful, but
015 * WITHOUT ANY WARRANTY; without even the implied warranty of MERCHANTABILITY
016 * or FITNESS FOR A PARTICULAR PURPOSE. See the GNU Lesser General Public
017 * License for more details.
018 *
019 * You should have received a copy of the GNU Lesser General Public
020 * License along with this library; if not, write to the Free Software
021 * Foundation, Inc., 51 Franklin Street, Fifth Floor, Boston, MA  02110-1301,
022 * USA.
023 *
024 * [Oracle and Java are registered trademarks of Oracle and/or its affiliates. 
025 * Other names may be trademarks of their respective owners.]
026 *
027 * --------------------
028 * PowerFunction2D.java
029 * --------------------
030 * (C) Copyright 2002-present, by David Gilbert.
031 *
032 * Original Author:  David Gilbert;
033 * Contributor(s):   -;
034 *
035 */
036
037package org.jfree.data.function;
038
039import java.io.Serializable;
040import org.jfree.chart.HashUtils;
041
042/**
043 * A function of the form y = a * x ^ b.
044 */
045public class PowerFunction2D implements Function2D, Serializable {
046
047    /** The 'a' coefficient. */
048    private double a;
049
050    /** The 'b' coefficient. */
051    private double b;
052
053    /**
054     * Creates a new power function.
055     *
056     * @param a  the 'a' coefficient.
057     * @param b  the 'b' coefficient.
058     */
059    public PowerFunction2D(double a, double b) {
060        this.a = a;
061        this.b = b;
062    }
063
064    /**
065     * Returns the 'a' coefficient that was specified in the constructor.
066     *
067     * @return The 'a' coefficient.
068     */
069    public double getA() {
070        return this.a;
071    }
072
073    /**
074     * Returns the 'b' coefficient that was specified in the constructor.
075     *
076     * @return The 'b' coefficient.
077     */
078    public double getB() {
079        return this.b;
080    }
081
082    /**
083     * Returns the value of the function for a given input ('x').
084     *
085     * @param x  the x-value.
086     *
087     * @return The value.
088     */
089    @Override
090    public double getValue(double x) {
091        return this.a * Math.pow(x, this.b);
092    }
093
094    /**
095     * Tests this function for equality with an arbitrary object.
096     *
097     * @param obj  the object ({@code null} permitted).
098     *
099     * @return A boolean.
100     */
101    @Override
102    public boolean equals(Object obj) {
103        if (!(obj instanceof PowerFunction2D)) {
104            return false;
105        }
106        PowerFunction2D that = (PowerFunction2D) obj;
107        if (this.a != that.a) {
108            return false;
109        }
110        if (this.b != that.b) {
111            return false;
112        }
113        return true;
114    }
115
116    /**
117     * Returns a hash code for this instance.
118     *
119     * @return A hash code.
120     */
121    @Override
122    public int hashCode() {
123        int result = 29;
124        result = HashUtils.hashCode(result, this.a);
125        result = HashUtils.hashCode(result, this.b);
126        return result;
127    }
128
129}