org.apache.commons.statistics.descriptive.SumOfSquares Maven / Gradle / Ivy
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* Licensed to the Apache Software Foundation (ASF) under one or more
* contributor license agreements. See the NOTICE file distributed with
* this work for additional information regarding copyright ownership.
* The ASF licenses this file to You under the Apache License, Version 2.0
* (the "License"); you may not use this file except in compliance with
* the License. You may obtain a copy of the License at
*
* http://www.apache.org/licenses/LICENSE-2.0
*
* Unless required by applicable law or agreed to in writing, software
* distributed under the License is distributed on an "AS IS" BASIS,
* WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
* See the License for the specific language governing permissions and
* limitations under the License.
*/
package org.apache.commons.statistics.descriptive;
/**
* Returns the sum of the squares of the available values. Uses the following definition:
*
* \[ \sum_{i=1}^n x_i^2 \]
*
*
where \( n \) is the number of samples.
*
*
* - The result is zero if no values are observed.
*
- The result is {@code NaN} if any of the values is {@code NaN}.
*
- The result is {@code +infinity} if any of the values is {@code infinity},
* or the sum overflows.
*
*
* This class is designed to work with (though does not require)
* {@linkplain java.util.stream streams}.
*
*
This instance is not thread safe.
* If multiple threads access an instance of this class concurrently,
* and at least one of the threads invokes the {@link java.util.function.DoubleConsumer#accept(double) accept} or
* {@link StatisticAccumulator#combine(StatisticResult) combine} method, it must be synchronized externally.
*
*
However, it is safe to use {@link java.util.function.DoubleConsumer#accept(double) accept}
* and {@link StatisticAccumulator#combine(StatisticResult) combine}
* as {@code accumulator} and {@code combiner} functions of
* {@link java.util.stream.Collector Collector} on a parallel stream,
* because the parallel instance of {@link java.util.stream.Stream#collect Stream.collect()}
* provides the necessary partitioning, isolation, and merging of results for
* safe and efficient parallel execution.
*
* @since 1.1
*/
public final class SumOfSquares implements DoubleStatistic, StatisticAccumulator {
/** Sum of squares of all values. */
private double ss;
/**
* Create an instance.
*/
private SumOfSquares() {
// No-op
}
/**
* Creates an instance.
*
* The initial result is zero.
*
* @return {@code SumOfSquares} instance.
*/
public static SumOfSquares create() {
return new SumOfSquares();
}
/**
* Returns an instance populated using the input {@code values}.
*
*
The result is {@code NaN} if any of the values is {@code NaN}
* or the product at any point is a {@code NaN}.
*
*
When the input is an empty array, the result is zero.
*
* @param values Values.
* @return {@code SumOfSquares} instance.
*/
public static SumOfSquares of(double... values) {
return Statistics.add(new SumOfSquares(), values);
}
/**
* Updates the state of the statistic to reflect the addition of {@code value}.
*
* @param value Value.
*/
@Override
public void accept(double value) {
ss += value * value;
}
/**
* Gets the sum of squares of all input values.
*
*
When no values have been added, the result is zero.
*
* @return sum of squares of all values.
*/
@Override
public double getAsDouble() {
return ss;
}
@Override
public SumOfSquares combine(SumOfSquares other) {
ss += other.ss;
return this;
}
}