1 /* 2 * Licensed to the Apache Software Foundation (ASF) under one or more 3 * contributor license agreements. See the NOTICE file distributed with 4 * this work for additional information regarding copyright ownership. 5 * The ASF licenses this file to You under the Apache License, Version 2.0 6 * (the "License"); you may not use this file except in compliance with 7 * the License. You may obtain a copy of the License at 8 * 9 * http://www.apache.org/licenses/LICENSE-2.0 10 * 11 * Unless required by applicable law or agreed to in writing, software 12 * distributed under the License is distributed on an "AS IS" BASIS, 13 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied. 14 * See the License for the specific language governing permissions and 15 * limitations under the License. 16 */ 17 package org.apache.commons.math.special; 18 19 import java.io.Serializable; 20 21 import org.apache.commons.math.MathException; 22 23 /** 24 * This is a utility class that provides computation methods related to the 25 * error functions. 26 * 27 * @version $Revision: 506601 $ $Date: 2007-02-12 12:37:49 -0700 (Mon, 12 Feb 2007) $ 28 */ 29 public class Erf implements Serializable { 30 31 /** Serializable version identifier */ 32 private static final long serialVersionUID = 490960015010326571L; 33 34 /** 35 * Default constructor. Prohibit instantiation. 36 */ 37 private Erf() { 38 super(); 39 } 40 41 /** 42 * Returns the error function erf(x). 43 * 44 * The implementation of this method is based on: 45 * <ul> 46 * <li> 47 * <a href="http://mathworld.wolfram.com/Erf.html"> 48 * Erf</a>, equation (3).</li> 49 * </ul> 50 * 51 * @param x the value. 52 * @return the error function erf(x) 53 * @throws MathException if the algorithm fails to converge. 54 */ 55 public static double erf(double x) throws MathException { 56 double ret = Gamma.regularizedGammaP(0.5, x * x, 1.0e-15, 10000); 57 if (x < 0) { 58 ret = -ret; 59 } 60 return ret; 61 } 62 }