001 /* ===========================================================
002 * JFreeChart : a free chart library for the Java(tm) platform
003 * ===========================================================
004 *
005 * (C) Copyright 2000-2009, 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 * [Java is a trademark or registered trademark of Sun Microsystems, Inc.
025 * in the United States and other countries.]
026 *
027 * ---------------------------------
028 * NormalDistributionFunction2D.java
029 * ---------------------------------
030 * (C)opyright 2004-2009, by Object Refinery Limited.
031 *
032 * Original Author: David Gilbert (for Object Refinery Limited);
033 * Contributor(s): -;
034 *
035 * Changes
036 * -------
037 * 25-May-2004 : Version 1 (DG);
038 * 21-Nov-2005 : Added getters for the mean and standard deviation (DG);
039 * 12-Feb-2009 : Precompute some constants from the function - see bug
040 * 2572016 (DG);
041 *
042 */
043
044 package org.jfree.data.function;
045
046 /**
047 * A normal distribution function. See
048 * http://en.wikipedia.org/wiki/Normal_distribution.
049 */
050 public class NormalDistributionFunction2D implements Function2D {
051
052 /** The mean. */
053 private double mean;
054
055 /** The standard deviation. */
056 private double std;
057
058 /** Precomputed factor for the function value. */
059 private double factor;
060
061 /** Precomputed denominator for the function value. */
062 private double denominator;
063
064 /**
065 * Constructs a new normal distribution function.
066 *
067 * @param mean the mean.
068 * @param std the standard deviation (> 0).
069 */
070 public NormalDistributionFunction2D(double mean, double std) {
071 if (std <= 0) {
072 throw new IllegalArgumentException("Requires 'std' > 0.");
073 }
074 this.mean = mean;
075 this.std = std;
076 // calculate constant values
077 this.factor = 1 / (std * Math.sqrt(2.0 * Math.PI));
078 this.denominator = 2 * std * std;
079 }
080
081 /**
082 * Returns the mean for the function.
083 *
084 * @return The mean.
085 */
086 public double getMean() {
087 return this.mean;
088 }
089
090 /**
091 * Returns the standard deviation for the function.
092 *
093 * @return The standard deviation.
094 */
095 public double getStandardDeviation() {
096 return this.std;
097 }
098
099 /**
100 * Returns the function value.
101 *
102 * @param x the x-value.
103 *
104 * @return The value.
105 */
106 public double getValue(double x) {
107 double z = x - this.mean;
108 return this.factor * Math.exp(-z * z / this.denominator);
109 }
110
111 }