| /* |
| * Copyright 2004 The Apache Software Foundation. |
| * |
| * Licensed under the Apache License, Version 2.0 (the "License"); |
| * you may not use this file except in compliance with the License. |
| * You may obtain a copy of the License at |
| * |
| * http://www.apache.org/licenses/LICENSE-2.0 |
| * |
| * Unless required by applicable law or agreed to in writing, software |
| * distributed under the License is distributed on an "AS IS" BASIS, |
| * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied. |
| * See the License for the specific language governing permissions and |
| * limitations under the License. |
| */ |
| package org.apache.commons.math.special; |
| |
| import java.io.Serializable; |
| |
| import org.apache.commons.math.MathException; |
| |
| /** |
| * This is a utility class that provides computation methods related to the |
| * error functions. |
| * |
| * @version $Revision$ $Date$ |
| */ |
| public class Erf implements Serializable { |
| |
| /** |
| * Default constructor. Prohibit instantiation. |
| */ |
| private Erf() { |
| super(); |
| } |
| |
| /** |
| * Returns the error function erf(x). |
| * |
| * The implementation of this method is based on: |
| * <ul> |
| * <li> |
| * <a href="http://mathworld.wolfram.com/Erf.html"> |
| * Erf</a>, equation (3).</li> |
| * </ul> |
| * |
| * @param x the value. |
| * @return the error function erf(x) |
| * @throws MathException if the algorithm fails to converge. |
| */ |
| public static double erf(double x) throws MathException { |
| double ret = Gamma.regularizedGammaP(0.5, x * x, 1.0e-15, 10000); |
| if (x < 0) { |
| ret = -ret; |
| } |
| return ret; |
| } |
| } |