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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  }