001 /* 002 * Licensed to the Apache Software Foundation (ASF) under one or more 003 * contributor license agreements. See the NOTICE file distributed with 004 * this work for additional information regarding copyright ownership. 005 * The ASF licenses this file to You under the Apache License, Version 2.0 006 * (the "License"); you may not use this file except in compliance with 007 * the License. You may obtain a copy of the License at 008 * 009 * http://www.apache.org/licenses/LICENSE-2.0 010 * 011 * Unless required by applicable law or agreed to in writing, software 012 * distributed under the License is distributed on an "AS IS" BASIS, 013 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied. 014 * See the License for the specific language governing permissions and 015 * limitations under the License. 016 */ 017 package org.apache.commons.math.special; 018 019 import org.apache.commons.math.MathException; 020 021 /** 022 * This is a utility class that provides computation methods related to the 023 * error functions. 024 * 025 * @version $Revision: 811685 $ $Date: 2009-09-05 13:36:48 -0400 (Sat, 05 Sep 2009) $ 026 */ 027 public class Erf { 028 029 /** 030 * Default constructor. Prohibit instantiation. 031 */ 032 private Erf() { 033 super(); 034 } 035 036 /** 037 * Returns the error function erf(x). 038 * 039 * The implementation of this method is based on: 040 * <ul> 041 * <li> 042 * <a href="http://mathworld.wolfram.com/Erf.html"> 043 * Erf</a>, equation (3).</li> 044 * </ul> 045 * 046 * @param x the value. 047 * @return the error function erf(x) 048 * @throws MathException if the algorithm fails to converge. 049 */ 050 public static double erf(double x) throws MathException { 051 double ret = Gamma.regularizedGammaP(0.5, x * x, 1.0e-15, 10000); 052 if (x < 0) { 053 ret = -ret; 054 } 055 return ret; 056 } 057 }