Classes in this File | Line Coverage | Branch Coverage | Complexity | ||||||||
GeometricMean |
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1 | /* |
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2 | * Copyright 2003-2004 The Apache Software Foundation. |
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3 | * |
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4 | * Licensed under the Apache License, Version 2.0 (the "License"); |
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5 | * you may not use this file except in compliance with the License. |
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6 | * You may obtain a copy of the License at |
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7 | * |
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8 | * http://www.apache.org/licenses/LICENSE-2.0 |
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9 | * |
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10 | * Unless required by applicable law or agreed to in writing, software |
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11 | * distributed under the License is distributed on an "AS IS" BASIS, |
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12 | * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied. |
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13 | * See the License for the specific language governing permissions and |
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14 | * limitations under the License. |
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15 | */ |
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16 | package org.apache.commons.math.stat.descriptive.moment; |
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17 | ||
18 | import org.apache.commons.math.stat.descriptive.AbstractStorelessUnivariateStatistic; |
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19 | import org.apache.commons.math.stat.descriptive.summary.SumOfLogs; |
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20 | ||
21 | /** |
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22 | * Returns the <a href="http://www.xycoon.com/geometric_mean.htm"> |
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23 | * geometric mean </a> of the available values. |
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24 | * <p> |
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25 | * Uses a {@link SumOfLogs} instance to compute sum of logs and returns |
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26 | * <code> exp( 1/n (sum of logs) ).</code> Therefore, |
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27 | * <ul> |
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28 | * <li>If any of values are < 0, the result is <code>NaN.</code></li> |
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29 | * <li>If all values are non-negative and less than |
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30 | * <code>Double.POSITIVE_INFINITY</code>, but at least one value is 0, the |
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31 | * result is <code>0.</code></li> |
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32 | * <li>If both <code>Double.POSITIVE_INFINITY</code> and |
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33 | * <code>Double.NEGATIVE_INFINITY</code> are among the values, the result is |
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34 | * <code>NaN.</code></li> |
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35 | * </ul> |
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36 | * <p> |
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37 | * <strong>Note that this implementation is not synchronized.</strong> If |
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38 | * multiple threads access an instance of this class concurrently, and at least |
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39 | * one of the threads invokes the <code>increment()</code> or |
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40 | * <code>clear()</code> method, it must be synchronized externally. |
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41 | * |
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42 | * |
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43 | * @version $Revision$ $Date: 2005-02-26 05:11:52 -0800 (Sat, 26 Feb 2005) $ |
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44 | */ |
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45 | public class GeometricMean extends AbstractStorelessUnivariateStatistic { |
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46 | ||
47 | /** Serializable version identifier */ |
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48 | static final long serialVersionUID = -8178734905303459453L; |
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49 | ||
50 | /** Wrapped SumOfLogs instance */ |
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51 | private SumOfLogs sumOfLogs; |
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52 | ||
53 | /** |
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54 | * Create a GeometricMean instance |
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55 | */ |
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56 | 10210 | public GeometricMean() { |
57 | 10210 | sumOfLogs = new SumOfLogs(); |
58 | 10210 | } |
59 | ||
60 | /** |
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61 | * @see org.apache.commons.math.stat.descriptive.StorelessUnivariateStatistic#increment(double) |
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62 | */ |
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63 | public void increment(final double d) { |
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64 | 131576 | sumOfLogs.increment(d); |
65 | 131576 | } |
66 | ||
67 | /** |
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68 | * @see org.apache.commons.math.stat.descriptive.StorelessUnivariateStatistic#getResult() |
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69 | */ |
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70 | public double getResult() { |
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71 | 606 | if (sumOfLogs.getN() > 0) { |
72 | 430 | return Math.exp(sumOfLogs.getResult() / (double) sumOfLogs.getN()); |
73 | } else { |
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74 | 176 | return Double.NaN; |
75 | } |
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76 | } |
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77 | ||
78 | /** |
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79 | * @see org.apache.commons.math.stat.descriptive.StorelessUnivariateStatistic#clear() |
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80 | */ |
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81 | public void clear() { |
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82 | 40 | sumOfLogs.clear(); |
83 | 40 | } |
84 | ||
85 | /** |
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86 | * Returns the geometric mean of the entries in the specified portion |
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87 | * of the input array. |
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88 | * <p> |
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89 | * See {@link GeometricMean} for details on the computing algorithm. |
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90 | * <p> |
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91 | * Throws <code>IllegalArgumentException</code> if the array is null. |
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92 | * |
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93 | * @param values input array containing the values |
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94 | * @param begin first array element to include |
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95 | * @param length the number of elements to include |
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96 | * @return the geometric mean or Double.NaN if length = 0 or |
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97 | * any of the values are <= 0. |
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98 | * @throws IllegalArgumentException if the input array is null or the array |
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99 | * index parameters are not valid |
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100 | */ |
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101 | public double evaluate( |
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102 | final double[] values, final int begin, final int length) { |
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103 | 34 | return Math.exp( |
104 | sumOfLogs.evaluate(values, begin, length) / (double) length); |
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105 | } |
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106 | ||
107 | /** |
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108 | * @see org.apache.commons.math.stat.descriptive.StorelessUnivariateStatistic#getN() |
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109 | */ |
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110 | public long getN() { |
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111 | 58 | return sumOfLogs.getN(); |
112 | } |
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113 | ||
114 | } |