normaldistributionfunction2d.java

jfreechart安装程序和使用说明

/* ===========================================================
 * JFreeChart : a free chart library for the Java(tm) platform
 * ===========================================================
 *
 * (C) Copyright 2000-2004, 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., 59 Temple Place, Suite 330,
 * Boston, MA 02111-1307, USA.
 *
 * [Java is a trademark or registered trademark of Sun Microsystems, Inc. 
 * in the United States and other countries.]
 *
 * ---------------------------------
 * NormalDistributionFunction2D.java
 * ---------------------------------
 * (C)opyright 2004, by Object Refinery Limited.
 *
 * Original Author:  David Gilbert (for Object Refinery Limited);
 * Contributor(s):   -;
 *
 * $Id: NormalDistributionFunction2D.java,v 1.1 2004/08/31 15:25:00 mungady Exp $
 *
 * Changes
 * -------
 * 25-May-2004 : Version 1(DG);
 * 
 */

package org.jfree.data.function;


/**
 * A normal distribution function.
 */
public class NormalDistributionFunction2D implements Function2D {

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

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

    /**
     * Constructs a new normal distribution function.
     *
     * @param mean  the mean.
     * @param std  the standard deviation.
     */
    public NormalDistributionFunction2D(final double mean, final double std) {
        this.mean = mean;
        this.std = std;
    }

    /**
     * Returns the function value.
     *
     * @param x  the x-value.
     *
     * @return The value.
     */
    public double getValue(final double x) {
        return Math.exp(-1.0 * (x - this.mean) * (x - this.mean) / (2 * this.std * this.std))
               / Math.sqrt(2 * Math.PI * this.std * this.std);
    }

}