    001/* ===========================================================
    002 * JFreeChart : a free chart library for the Java(tm) platform
    003 * ===========================================================
    004 *
    005 * (C) Copyright 2000-2011, by Object Refinery Limited 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 2002-2009, by Object Refinery Limited.
    031 *
    032 * Original Author:  David Gilbert (for Object Refinery Limited);
    033 * Contributor(s):   -;
    034 *
    035 * Changes:
    036 * --------
    037 * 01-Oct-2002 : Version 1 (DG);
    038 * 28-May-2009 : Added accessor methods for co-efficients, implemented
    039 *               equals() and hashCode(), and added Serialization support (DG);
    040 *
    041 */
    042
    043package org.jfree.data.function;
    044
    045import java.io.Serializable;
    046import org.jfree.chart.HashUtilities;
    047
    048/**
    049 * A function of the form y = a * x ^ b.
    050 */
    051public class PowerFunction2D implements Function2D, Serializable {
    052
    053    /** The 'a' coefficient. */
    054    private double a;
    055
    056    /** The 'b' coefficient. */
    057    private double b;
    058
    059    /**
    060     * Creates a new power function.
    061     *
    062     * @param a  the 'a' coefficient.
    063     * @param b  the 'b' coefficient.
    064     */
    065    public PowerFunction2D(double a, double b) {
    066        this.a = a;
    067        this.b = b;
    068    }
    069
    070    /**
    071     * Returns the 'a' coefficient that was specified in the constructor.
    072     *
    073     * @return The 'a' coefficient.
    074     *
    075     * @since 1.0.14
    076     */
    077    public double getA() {
    078        return this.a;
    079    }
    080
    081    /**
    082     * Returns the 'b' coefficient that was specified in the constructor.
    083     *
    084     * @return The 'b' coefficient.
    085     *
    086     * @since 1.0.14
    087     */
    088    public double getB() {
    089        return this.b;
    090    }
    091
    092    /**
    093     * Returns the value of the function for a given input ('x').
    094     *
    095     * @param x  the x-value.
    096     *
    097     * @return The value.
    098     */
    099    public double getValue(double x) {
    100        return this.a * Math.pow(x, this.b);
    101    }
    102
    103    /**
    104     * Tests this function for equality with an arbitrary object.
    105     *
    106     * @param obj  the object (<code>null</code> permitted).
    107     *
    108     * @return A boolean.
    109     */
    110    public boolean equals(Object obj) {
    111        if (!(obj instanceof PowerFunction2D)) {
    112            return false;
    113        }
    114        PowerFunction2D that = (PowerFunction2D) obj;
    115        if (this.a != that.a) {
    116            return false;
    117        }
    118        if (this.b != that.b) {
    119            return false;
    120        }
    121        return true;
    122    }
    123
    124    /**
    125     * Returns a hash code for this instance.
    126     *
    127     * @return A hash code.
    128     */
    129    public int hashCode() {
    130        int result = 29;
    131        result = HashUtilities.hashCode(result, this.a);
    132        result = HashUtilities.hashCode(result, this.b);
    133        return result;
    134    }
    135
    136}