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jfreechart example source code file (NormalDistributionFunction2D.java)

This example jfreechart source code file (NormalDistributionFunction2D.java) is included in the DevDaily.com "Java Source Code Warehouse" project. The intent of this project is to help you "Learn Java by Example" TM.

Java - jfreechart tags/keywords

function2d, function2d, illegalargumentexception, illegalargumentexception, normaldistributionfunction2d, normaldistributionfunction2d, requires, requires

The jfreechart NormalDistributionFunction2D.java source code

/* ===========================================================
 * JFreeChart : a free chart library for the Java(tm) platform
 * ===========================================================
 *
 * (C) Copyright 2000-2009, by Object Refinery Limited and Contributors.
 *
 * Project Info:  http://www.jfree.org/jfreechart/index.html
 *
 * This library is free software; you can redistribute it and/or modify it
 * under the terms of the GNU Lesser General Public License as published by
 * the Free Software Foundation; either version 2.1 of the License, or
 * (at your option) any later version.
 *
 * This library is distributed in the hope that it will be useful, but
 * WITHOUT ANY WARRANTY; without even the implied warranty of MERCHANTABILITY
 * or FITNESS FOR A PARTICULAR PURPOSE. See the GNU Lesser General Public
 * License for more details.
 *
 * You should have received a copy of the GNU Lesser General Public
 * License along with this library; if not, write to the Free Software
 * Foundation, Inc., 51 Franklin Street, Fifth Floor, Boston, MA  02110-1301,
 * USA.
 *
 * [Java is a trademark or registered trademark of Sun Microsystems, Inc.
 * in the United States and other countries.]
 *
 * ---------------------------------
 * NormalDistributionFunction2D.java
 * ---------------------------------
 * (C)opyright 2004-2009, by Object Refinery Limited.
 *
 * Original Author:  David Gilbert (for Object Refinery Limited);
 * Contributor(s):   -;
 *
 * Changes
 * -------
 * 25-May-2004 : Version 1 (DG);
 * 21-Nov-2005 : Added getters for the mean and standard deviation (DG);
 * 12-Feb-2009 : Precompute some constants from the function - see bug
 *               2572016 (DG);
 *
 */

package org.jfree.data.function;

/**
 * A normal distribution function.  See
 * http://en.wikipedia.org/wiki/Normal_distribution.
 */
public class NormalDistributionFunction2D implements Function2D {

    /** The mean. */
    private double mean;

    /** The standard deviation. */
    private double std;

    /** Precomputed factor for the function value. */
    private double factor;

    /** Precomputed denominator for the function value. */
    private double denominator;

    /**
     * Constructs a new normal distribution function.
     *
     * @param mean  the mean.
     * @param std  the standard deviation (> 0).
     */
    public NormalDistributionFunction2D(double mean, double std) {
        if (std <= 0) {
            throw new IllegalArgumentException("Requires 'std' > 0.");
        }
        this.mean = mean;
        this.std = std;
        // calculate constant values
        this.factor = 1 / (std * Math.sqrt(2.0 * Math.PI));
        this.denominator = 2 * std * std;
    }

    /**
     * Returns the mean for the function.
     *
     * @return The mean.
     */
    public double getMean() {
        return this.mean;
    }
    
    /**
     * Returns the standard deviation for the function.
     *
     * @return The standard deviation.
     */
    public double getStandardDeviation() {
        return this.std;
    }

    /**
     * Returns the function value.
     *
     * @param x  the x-value.
     *
     * @return The value.
     */
    public double getValue(double x) {
        double z = x - this.mean;
        return this.factor * Math.exp(-z * z / this.denominator);
    }

}

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