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Java > Open Source Codes > org > apache > commons > math > special > Erf


1 /*
2  * Copyright 2004 The Apache Software Foundation.
3  *
4  * Licensed under the Apache License, Version 2.0 (the "License");
5  * you may not use this file except in compliance with the License.
6  * You may obtain a copy of the License at
7  *
8  * http://www.apache.org/licenses/LICENSE-2.0
9  *
10  * Unless required by applicable law or agreed to in writing, software
11  * distributed under the License is distributed on an "AS IS" BASIS,
12  * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
13  * See the License for the specific language governing permissions and
14  * limitations under the License.
15  */
16 package org.apache.commons.math.special;
17
18 import java.io.Serializable JavaDoc;
19
20 import org.apache.commons.math.MathException;
21
22 /**
23  * This is a utility class that provides computation methods related to the
24  * error functions.
25  *
26  * @version $Revision$ $Date: 2005-02-26 05:11:52 -0800 (Sat, 26 Feb 2005) $
27  */
28 public class Erf implements Serializable JavaDoc {
29
30     /**
31      * Default constructor. Prohibit instantiation.
32      */
33     private Erf() {
34         super();
35     }
36
37     /**
38      * Returns the error function erf(x).
39      *
40      * The implementation of this method is based on:
41      * <ul>
42      * <li>
43      * <a HREF="http://mathworld.wolfram.com/Erf.html">
44      * Erf</a>, equation (3).</li>
45      * </ul>
46      *
47      * @param x the value.
48      * @return the error function erf(x)
49      * @throws MathException if the algorithm fails to converge.
50      */
51     public static double erf(double x) throws MathException {
52         double ret = Gamma.regularizedGammaP(0.5, x * x, 1.0e-15, 10000);
53         if (x < 0) {
54             ret = -ret;
55         }
56         return ret;
57     }
58 }
59
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