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 org.apache.commons.math.MathException; 20 21 /** 22 * This is a utility class that provides computation methods related to the 23 * error functions. 24 * 25 * @version $Revision: 780933 $ $Date: 2009-06-02 00:39:12 -0400 (Tue, 02 Jun 2009) $ 26 */ 27 public class Erf { 28 29 /** 30 * Default constructor. Prohibit instantiation. 31 */ 32 private Erf() { 33 super(); 34 } 35 36 /** 37 * Returns the error function erf(x). 38 * 39 * The implementation of this method is based on: 40 * <ul> 41 * <li> 42 * <a href="http://mathworld.wolfram.com/Erf.html"> 43 * Erf</a>, equation (3).</li> 44 * </ul> 45 * 46 * @param x the value. 47 * @return the error function erf(x) 48 * @throws MathException if the algorithm fails to converge. 49 */ 50 public static double erf(double x) throws MathException { 51 double ret = Gamma.regularizedGammaP(0.5, x * x, 1.0e-15, 10000); 52 if (x < 0) { 53 ret = -ret; 54 } 55 return ret; 56 } 57 }