Class SumOfSquares

  • All Implemented Interfaces:
    java.util.function.DoubleConsumer, java.util.function.DoubleSupplier, java.util.function.IntSupplier, java.util.function.LongSupplier, DoubleStatistic, StatisticAccumulator<SumOfSquares>, StatisticResult

    public final class SumOfSquares
    extends java.lang.Object
    implements DoubleStatistic, StatisticAccumulator<SumOfSquares>
    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 NaN if any of the values is NaN.
    • The result is +infinity if any of the values is infinity, or the sum overflows.

    This class is designed to work with (though does not require) 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 accept or combine method, it must be synchronized externally.

    However, it is safe to use accept and combine as accumulator and combiner functions of Collector on a parallel stream, because the parallel instance of Stream.collect() provides the necessary partitioning, isolation, and merging of results for safe and efficient parallel execution.

    Since:
    1.1
    • Field Summary

      Fields 
      Modifier and Type Field Description
      private double ss
      Sum of squares of all values.
    • Constructor Summary

      Constructors 
      Modifier Constructor Description
      private SumOfSquares()
      Create an instance.
    • Field Detail

      • ss

        private double ss
        Sum of squares of all values.
    • Constructor Detail

      • SumOfSquares

        private SumOfSquares()
        Create an instance.
    • Method Detail

      • create

        public static SumOfSquares create()
        Creates an instance.

        The initial result is zero.

        Returns:
        SumOfSquares instance.
      • of

        public static SumOfSquares of​(double... values)
        Returns an instance populated using the input values.

        The result is NaN if any of the values is NaN or the product at any point is a NaN.

        When the input is an empty array, the result is zero.

        Parameters:
        values - Values.
        Returns:
        SumOfSquares instance.
      • accept

        public void accept​(double value)
        Updates the state of the statistic to reflect the addition of value.
        Specified by:
        accept in interface java.util.function.DoubleConsumer
        Parameters:
        value - Value.
      • getAsDouble

        public double getAsDouble()
        Gets the sum of squares of all input values.

        When no values have been added, the result is zero.

        Specified by:
        getAsDouble in interface java.util.function.DoubleSupplier
        Returns:
        sum of squares of all values.