001/*
002 * Licensed to the Apache Software Foundation (ASF) under one or more
003 * contributor license agreements.  See the NOTICE file distributed with
004 * this work for additional information regarding copyright ownership.
005 * The ASF licenses this file to You under the Apache License, Version 2.0
006 * (the "License"); you may not use this file except in compliance with
007 * the License.  You may obtain a copy of the License at
008 *
009 *      http://www.apache.org/licenses/LICENSE-2.0
010 *
011 * Unless required by applicable law or agreed to in writing, software
012 * distributed under the License is distributed on an "AS IS" BASIS,
013 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
014 * See the License for the specific language governing permissions and
015 * limitations under the License.
016 */
017package org.apache.commons.numbers.gamma;
018
019/**
020 * Inverse of the <a href="http://mathworld.wolfram.com/Erf.html">error function</a>.
021 */
022public final class InverseErf {
023    /** Private constructor. */
024    private InverseErf() {
025        // intentionally empty.
026    }
027
028    /**
029     * Returns the inverse error function.
030     *
031     * <p>Special cases:
032     * <ul>
033     * <li>If the argument is 0, then the result is 0.
034     * <li>If the argument is 1, then the result is positive infinity.
035     * <li>If the argument is -1, then the result is negative infinity.
036     * <li>If the argument is outside the interval {@code [-1, 1]}, then the result is nan.
037     * <li>If the argument is nan, then the result is nan.
038     * </ul>
039     *
040     * @param x Value (in {@code [-1, 1]})
041     * @return t such that {@code x =} {@link Erf#value(double) Erf.value(t)}.
042     */
043    public static double value(final double x) {
044        return BoostErf.erfInv(x);
045    }
046}