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.rng.sampling.distribution;
018
019/**
020 * Sampling from a log-normal distribution.
021 *
022 * @since 1.1
023 */
024public class LogNormalSampler implements ContinuousSampler {
025    /** Scale. */
026    private final double scale;
027    /** Shape. */
028    private final double shape;
029    /** Gaussian sampling. */
030    private final NormalizedGaussianSampler gaussian;
031
032    /**
033     * @param gaussian N(0,1) generator.
034     * @param scale Scale of the log-normal distribution.
035     * @param shape Shape of the log-normal distribution.
036     */
037    public LogNormalSampler(NormalizedGaussianSampler gaussian,
038                            double scale,
039                            double shape) {
040        this.scale = scale;
041        this.shape = shape;
042        this.gaussian = gaussian;
043    }
044
045    /** {@inheritDoc} */
046    @Override
047    public double sample() {
048        return Math.exp(scale + shape * gaussian.sample());
049    }
050
051    /** {@inheritDoc} */
052    @Override
053    public String toString() {
054        return "Log-normal deviate [" + gaussian.toString() + "]";
055    }
056}