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    
042    package org.jfree.data.function;
043    
044    import java.io.Serializable;
045    import java.util.Arrays;
046    import 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     */
054    public 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    }