1 /* 2 * Copyright 2004 The Apache Software Foundation. 3 * 4 * Licensed under the Apache License, Version 2.0 (the "License"); 5 * you may not use this file except in compliance with the License. 6 * You may obtain a copy of the License at 7 * 8 * http://www.apache.org/licenses/LICENSE-2.0 9 * 10 * Unless required by applicable law or agreed to in writing, software 11 * distributed under the License is distributed on an "AS IS" BASIS, 12 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied. 13 * See the License for the specific language governing permissions and 14 * limitations under the License. 15 */ 16 package org.apache.commons.math.special; 17 18 import java.io.Serializable; 19 20 import org.apache.commons.math.MathException; 21 22 /** 23 * This is a utility class that provides computation methods related to the 24 * error functions. 25 * 26 * @version $Revision: 155427 $ $Date: 2005-02-26 06:11:52 -0700 (Sat, 26 Feb 2005) $ 27 */ 28 public class Erf implements Serializable { 29 30 /** 31 * Default constructor. Prohibit instantiation. 32 */ 33 private Erf() { 34 super(); 35 } 36 37 /** 38 * Returns the error function erf(x). 39 * 40 * The implementation of this method is based on: 41 * <ul> 42 * <li> 43 * <a href="http://mathworld.wolfram.com/Erf.html"> 44 * Erf</a>, equation (3).</li> 45 * </ul> 46 * 47 * @param x the value. 48 * @return the error function erf(x) 49 * @throws MathException if the algorithm fails to converge. 50 */ 51 public static double erf(double x) throws MathException { 52 double ret = Gamma.regularizedGammaP(0.5, x * x, 1.0e-15, 10000); 53 if (x < 0) { 54 ret = -ret; 55 } 56 return ret; 57 } 58 }