/* ===========================================================
* 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);
}
}