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 }