/*
 * Licensed to the Apache Software Foundation (ASF) under one or more
 * contributor license agreements.  See the NOTICE file distributed with
 * this work for additional information regarding copyright ownership.
 * The ASF licenses this file to You 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 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 {

	/**
	 * 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;
	}
}
