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 * https://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
18 /*
19 * This is not the original file distributed by the Apache Software Foundation
20 * It has been modified by the Hipparchus project
21 */
22 package org.hipparchus.stat.descriptive.summary;
23
24 import java.io.Serializable;
25
26 import org.hipparchus.exception.MathIllegalArgumentException;
27 import org.hipparchus.exception.NullArgumentException;
28 import org.hipparchus.stat.descriptive.AbstractStorelessUnivariateStatistic;
29 import org.hipparchus.stat.descriptive.AggregatableStatistic;
30 import org.hipparchus.util.FastMath;
31 import org.hipparchus.util.MathArrays;
32 import org.hipparchus.util.MathUtils;
33
34 /**
35 * Returns the sum of the natural logs for this collection of values.
36 * <p>
37 * Uses {@link org.hipparchus.util.FastMath#log(double)} to compute the logs.
38 * Therefore,
39 * <ul>
40 * <li>If any of values are < 0, the result is <code>NaN.</code></li>
41 * <li>If all values are non-negative and less than
42 * <code>Double.POSITIVE_INFINITY</code>, but at least one value is 0, the
43 * result is <code>Double.NEGATIVE_INFINITY.</code></li>
44 * <li>If both <code>Double.POSITIVE_INFINITY</code> and
45 * <code>Double.NEGATIVE_INFINITY</code> are among the values, the result is
46 * <code>NaN.</code></li>
47 * </ul>
48 * <p>
49 * <strong>Note that this implementation is not synchronized.</strong> If
50 * multiple threads access an instance of this class concurrently, and at least
51 * one of the threads invokes the <code>increment()</code> or
52 * <code>clear()</code> method, it must be synchronized externally.
53 */
54 public class SumOfLogs extends AbstractStorelessUnivariateStatistic
55 implements AggregatableStatistic<SumOfLogs>, Serializable {
56
57 /** Serializable version identifier */
58 private static final long serialVersionUID = 20150412L;
59
60 /** Number of values that have been added */
61 private int n;
62
63 /** The currently running value */
64 private double value;
65
66 /**
67 * Create a SumOfLogs instance.
68 */
69 public SumOfLogs() {
70 value = 0d;
71 n = 0;
72 }
73
74 /**
75 * Copy constructor, creates a new {@code SumOfLogs} identical
76 * to the {@code original}.
77 *
78 * @param original the {@code SumOfLogs} instance to copy
79 * @throws NullArgumentException if original is null
80 */
81 public SumOfLogs(SumOfLogs original) throws NullArgumentException {
82 MathUtils.checkNotNull(original);
83 this.n = original.n;
84 this.value = original.value;
85 }
86
87 /** {@inheritDoc} */
88 @Override
89 public void increment(final double d) {
90 value += FastMath.log(d);
91 n++;
92 }
93
94 /** {@inheritDoc} */
95 @Override
96 public double getResult() {
97 return value;
98 }
99
100 /** {@inheritDoc} */
101 @Override
102 public long getN() {
103 return n;
104 }
105
106 /** {@inheritDoc} */
107 @Override
108 public void clear() {
109 value = 0d;
110 n = 0;
111 }
112
113 /** {@inheritDoc} */
114 @Override
115 public void aggregate(SumOfLogs other) {
116 MathUtils.checkNotNull(other);
117 if (other.n > 0) {
118 this.n += other.n;
119 this.value += other.value;
120 }
121 }
122
123 /**
124 * Returns the sum of the natural logs of the entries in the specified portion of
125 * the input array, or <code>Double.NaN</code> if the designated subarray
126 * is empty.
127 *
128 * @param values the input array
129 * @param begin index of the first array element to include
130 * @param length the number of elements to include
131 * @return the sum of the natural logs of the values or 0 if
132 * length = 0
133 * @throws MathIllegalArgumentException if the array is null or the array index
134 * parameters are not valid
135 */
136 @Override
137 public double evaluate(final double[] values, final int begin, final int length)
138 throws MathIllegalArgumentException {
139
140 double sumLog = Double.NaN;
141 if (MathArrays.verifyValues(values, begin, length, true)) {
142 sumLog = 0.0;
143 for (int i = begin; i < begin + length; i++) {
144 sumLog += FastMath.log(values[i]);
145 }
146 }
147 return sumLog;
148 }
149
150 /** {@inheritDoc} */
151 @Override
152 public SumOfLogs copy() {
153 return new SumOfLogs(this);
154 }
155
156 }