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 }