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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.rng.sampling.distribution;
18  
19  /**
20   * Sampling from a log-normal distribution.
21   *
22   * @since 1.1
23   */
24  public class LogNormalSampler implements ContinuousSampler {
25      /** Scale. */
26      private final double scale;
27      /** Shape. */
28      private final double shape;
29      /** Gaussian sampling. */
30      private final NormalizedGaussianSampler gaussian;
31  
32      /**
33       * @param gaussian N(0,1) generator.
34       * @param scale Scale of the log-normal distribution.
35       * @param shape Shape of the log-normal distribution.
36       */
37      public LogNormalSampler(NormalizedGaussianSampler gaussian,
38                              double scale,
39                              double shape) {
40          this.scale = scale;
41          this.shape = shape;
42          this.gaussian = gaussian;
43      }
44  
45      /** {@inheritDoc} */
46      @Override
47      public double sample() {
48          return Math.exp(scale + shape * gaussian.sample());
49      }
50  
51      /** {@inheritDoc} */
52      @Override
53      public String toString() {
54          return "Log-normal deviate [" + gaussian.toString() + "]";
55      }
56  }