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 }