Documentation API of the 'org.apache.commons.math3.stat.descriptive.moment.SecondMoment' Java class

Class SecondMoment

  • All Implemented Interfaces:
    Serializable, StorelessUnivariateStatistic, UnivariateStatistic, MathArrays.Function

    public class SecondMomentextends AbstractStorelessUnivariateStatisticimplements Serializable
    Computes a statistic related to the Second Central Moment. Specifically, what is computed is the sum of squared deviations from the sample mean.

    The following recursive updating formula is used:


    • dev = (current obs - previous mean)
    • n = number of observations (including current obs)

    new value = old value + dev^2 * (n -1) / n.

    Returns Double.NaN if no data values have been added and returns 0 if there is just one value in the data set.

    Note that this implementation is not synchronized. If multiple threads access an instance of this class concurrently, and at least one of the threads invokes the increment() or clear() method, it must be synchronized externally.

    See Also:
    Serialized Form

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