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.statistics.descriptive;
18
19 /**
20 * Returns the sum of the {@link Math#log(double) natural logarithm} of available values.
21 *
22 * <ul>
23 * <li>The result is zero if no values are added.
24 * <li>The result is {@code NaN} if any of the values is {@code NaN}.
25 * <li>The result is {@code NaN} if any of the values is negative.
26 * </ul>
27 *
28 * <p>The sum follows the IEEE754 result for summing infinite values:
29 *
30 * <ul>
31 * <li>The result is {@code +infinity} if all values are in the range {@code (0, +infinity]}
32 * and at least one value is {@code +infinity}.
33 * <li>The result is {@code -infinity} if all values are in the range {@code [0, +infinity)}
34 * and at least one value is zero.
35 * <li>The result is {@code NaN} if all values are in the range {@code [0, +infinity]}
36 * and at least one value is zero, and one value is {@code +infinity}.
37 * </ul>
38 *
39 * <p>This class is designed to work with (though does not require)
40 * {@linkplain java.util.stream streams}.
41 *
42 * <p><strong>This instance is not thread safe.</strong>
43 * If multiple threads access an instance of this class concurrently,
44 * and at least one of the threads invokes the {@link java.util.function.DoubleConsumer#accept(double) accept} or
45 * {@link StatisticAccumulator#combine(StatisticResult) combine} method, it must be synchronized externally.
46 *
47 * <p>However, it is safe to use {@link java.util.function.DoubleConsumer#accept(double) accept}
48 * and {@link StatisticAccumulator#combine(StatisticResult) combine}
49 * as {@code accumulator} and {@code combiner} functions of
50 * {@link java.util.stream.Collector Collector} on a parallel stream,
51 * because the parallel instance of {@link java.util.stream.Stream#collect Stream.collect()}
52 * provides the necessary partitioning, isolation, and merging of results for
53 * safe and efficient parallel execution.
54 *
55 * @see org.apache.commons.numbers.core.Sum
56 * @see Math#log(double)
57 * @since 1.1
58 */
59 public final class SumOfLogs implements DoubleStatistic, StatisticAccumulator<SumOfLogs> {
60
61 /** {@link org.apache.commons.numbers.core.Sum Sum} used to compute the sum. */
62 private final org.apache.commons.numbers.core.Sum delegate =
63 org.apache.commons.numbers.core.Sum.create();
64
65 /**
66 * Create an instance.
67 */
68 private SumOfLogs() {
69 // No-op
70 }
71
72 /**
73 * Creates an instance.
74 *
75 * <p>The initial result is zero.
76 *
77 * @return {@code SumOfLogs} instance.
78 */
79 public static SumOfLogs create() {
80 return new SumOfLogs();
81 }
82
83 /**
84 * Returns an instance populated using the input {@code values}.
85 *
86 * <p>The result is {@code NaN} if any of the values is {@code NaN}
87 * or negative; or the sum at any point is a {@code NaN}.
88 *
89 * <p>When the input is an empty array, the result is zero.
90 *
91 * @param values Values.
92 * @return {@code SumOfLogs} instance.
93 */
94 public static SumOfLogs of(double... values) {
95 return Statistics.add(new SumOfLogs(), values);
96 }
97
98 /**
99 * Returns an instance populated using the input {@code values}.
100 *
101 * <p>The result is {@code NaN} if any of the values is negative.
102 *
103 * <p>When the input is an empty array, the result is zero.
104 *
105 * @param values Values.
106 * @return {@code SumOfLogs} instance.
107 */
108 public static SumOfLogs of(int... values) {
109 return Statistics.add(new SumOfLogs(), values);
110 }
111
112 /**
113 * Returns an instance populated using the input {@code values}.
114 *
115 * <p>The result is {@code NaN} if any of the values is negative.
116 *
117 * <p>When the input is an empty array, the result is zero.
118 *
119 * @param values Values.
120 * @return {@code SumOfLogs} instance.
121 */
122 public static SumOfLogs of(long... values) {
123 return Statistics.add(new SumOfLogs(), values);
124 }
125
126 /**
127 * Updates the state of the statistic to reflect the addition of {@code value}.
128 *
129 * @param value Value.
130 */
131 @Override
132 public void accept(double value) {
133 delegate.accept(Math.log(value));
134 }
135
136 /**
137 * Gets the sum of all input values.
138 *
139 * <p>When no values have been added, the result is zero.
140 *
141 * @return sum of all values.
142 */
143 @Override
144 public double getAsDouble() {
145 return delegate.getAsDouble();
146 }
147
148 @Override
149 public SumOfLogs combine(SumOfLogs other) {
150 delegate.add(other.delegate);
151 return this;
152 }
153 }