01: /*
02: * Copyright 2004 The Apache Software Foundation.
03: *
04: * Licensed under the Apache License, Version 2.0 (the "License");
05: * you may not use this file except in compliance with the License.
06: * You may obtain a copy of the License at
07: *
08: * http://www.apache.org/licenses/LICENSE-2.0
09: *
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;
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: 155427 $ $Date: 2005-02-26 06:11:52 -0700 (Sat, 26 Feb 2005) $
27: */
28: public class Erf implements Serializable {
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
53: .regularizedGammaP(0.5, x * x, 1.0e-15, 10000);
54: if (x < 0) {
55: ret = -ret;
56: }
57: return ret;
58: }
59: }
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