001/* =========================================================== 002 * JFreeChart : a free chart library for the Java(tm) platform 003 * =========================================================== 004 * 005 * (C) Copyright 2000-2014, 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 * NormalDistributionFunction2D.java 029 * --------------------------------- 030 * (C)opyright 2004-2014, 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 * 28-May-2009 : Implemented equals() and hashCode(), and added serialization 042 * support (DG); 043 * 044 */ 045 046package org.jfree.data.function; 047 048import java.io.Serializable; 049 050import org.jfree.chart.HashUtilities; 051 052/** 053 * A normal distribution function. See 054 * http://en.wikipedia.org/wiki/Normal_distribution. 055 */ 056public class NormalDistributionFunction2D implements Function2D, Serializable { 057 058 /** The mean. */ 059 private double mean; 060 061 /** The standard deviation. */ 062 private double std; 063 064 /** Precomputed factor for the function value. */ 065 private double factor; 066 067 /** Precomputed denominator for the function value. */ 068 private double denominator; 069 070 /** 071 * Constructs a new normal distribution function. 072 * 073 * @param mean the mean. 074 * @param std the standard deviation (> 0). 075 */ 076 public NormalDistributionFunction2D(double mean, double std) { 077 if (std <= 0) { 078 throw new IllegalArgumentException("Requires 'std' > 0."); 079 } 080 this.mean = mean; 081 this.std = std; 082 // calculate constant values 083 this.factor = 1 / (std * Math.sqrt(2.0 * Math.PI)); 084 this.denominator = 2 * std * std; 085 } 086 087 /** 088 * Returns the mean for the function. 089 * 090 * @return The mean. 091 */ 092 public double getMean() { 093 return this.mean; 094 } 095 096 /** 097 * Returns the standard deviation for the function. 098 * 099 * @return The standard deviation. 100 */ 101 public double getStandardDeviation() { 102 return this.std; 103 } 104 105 /** 106 * Returns the function value. 107 * 108 * @param x the x-value. 109 * 110 * @return The value. 111 */ 112 @Override 113 public double getValue(double x) { 114 double z = x - this.mean; 115 return this.factor * Math.exp(-z * z / this.denominator); 116 } 117 118 /** 119 * Tests this function for equality with an arbitrary object. 120 * 121 * @param obj the object (<code>null</code> permitted). 122 * 123 * @return A boolean. 124 */ 125 @Override 126 public boolean equals(Object obj) { 127 if (!(obj instanceof NormalDistributionFunction2D)) { 128 return false; 129 } 130 NormalDistributionFunction2D that = (NormalDistributionFunction2D) obj; 131 if (this.mean != that.mean) { 132 return false; 133 } 134 if (this.std != that.std) { 135 return false; 136 } 137 return true; 138 } 139 140 /** 141 * Returns a hash code for this instance. 142 * 143 * @return A hash code. 144 */ 145 @Override 146 public int hashCode() { 147 int result = 29; 148 result = HashUtilities.hashCode(result, this.mean); 149 result = HashUtilities.hashCode(result, this.std); 150 return result; 151 } 152 153}