    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 * PolynomialFunction2D.java
    029 * -------------------------
    030 * (C) Copyright 2009, by Object Refinery Limited.
    031 *
    032 * Original Author:  Peter Kolb;
    033 * Contributor(s):   David Gilbert (for Object Refinery Limited);
    034 *
    035 * Changes:
    036 * --------
    037 * 23-Mar-2009 : Version 1, patch 2795746 (PK);
    038 * 28-May-2009 : Integrated in JFreeChart with modifications (DG);
    039 *
    040 */
    041
    042package org.jfree.data.function;
    043
    044import java.io.Serializable;
    045import java.util.Arrays;
    046import org.jfree.chart.HashUtilities;
    047
    048/**
    049 * A function in the form <code>y = a0 + a1 * x + a2 * x^2 + ... + an *
    050 * x^n</code>.  Instances of this class are immutable.
    051 *
    052 * @since 1.0.14
    053 */
    054public class PolynomialFunction2D implements Function2D, Serializable {
    055
    056    /** The coefficients. */
    057    private double[] coefficients;
    058
    059    /**
    060     * Constructs a new polynomial function <code>y = a0 + a1 * x + a2 * x^2 +
    061     * ... + an * x^n</code>
    062     *
    063     * @param coefficients  an array with the coefficients [a0, a1, ..., an]
    064     *         (<code>null</code> not permitted).
    065     */
    066    public PolynomialFunction2D(double[] coefficients) {
    067        if (coefficients == null) {
    068            throw new IllegalArgumentException("Null 'coefficients' argument");
    069        }
    070        this.coefficients = (double[]) coefficients.clone();
    071    }
    072
    073    /**
    074     * Returns a copy of the coefficients array that was specified in the
    075     * constructor.
    076     *
    077     * @return The coefficients array.
    078     */
    079    public double[] getCoefficients() {
    080        return (double[]) this.coefficients.clone();
    081    }
    082
    083    /**
    084     * Returns the order of the polynomial.
    085     *
    086     * @return The order.
    087     */
    088    public int getOrder() {
    089        return this.coefficients.length - 1;
    090    }
    091
    092    /**
    093     * Returns the function value.
    094     *
    095     * @param x  the x-value.
    096     *
    097     * @return The value.
    098     */
    099    public double getValue(double x) {
    100        double y = 0;
    101        for(int i = 0; i < coefficients.length; i++){
    102            y += coefficients[i] * Math.pow(x, i);
    103        }
    104        return y;
    105    }
    106
    107    /**
    108     * Tests this function for equality with an arbitrary object.
    109     *
    110     * @param obj  the object (<code>null</code> permitted).
    111     *
    112     * @return A boolean.
    113     */
    114    public boolean equals(Object obj) {
    115        if (!(obj instanceof PolynomialFunction2D)) {
    116            return false;
    117        }
    118        PolynomialFunction2D that = (PolynomialFunction2D) obj;
    119        return Arrays.equals(this.coefficients, that.coefficients);
    120    }
    121
    122    /**
    123     * Returns a hash code for this instance.
    124     *
    125     * @return A hash code.
    126     */
    127    public int hashCode() {
    128        return HashUtilities.hashCodeForDoubleArray(this.coefficients);
    129    }
    130
    131}