Package org.apache.commons.math.stat.descriptive.moment

Class GeometricMean

  • All Implemented Interfaces:
    java.io.Serializable, StorelessUnivariateStatistic, UnivariateStatistic
    public class GeometricMean
extends AbstractStorelessUnivariateStatistic
implements java.io.Serializable
    Returns the geometric mean of the available values.

    Uses a SumOfLogs instance to compute sum of logs and returns exp( 1/n (sum of logs) ). Therefore,

    • If any of values are < 0, the result is NaN.
    • If all values are non-negative and less than Double.POSITIVE_INFINITY, but at least one value is 0, the result is 0.
    • If both Double.POSITIVE_INFINITY and Double.NEGATIVE_INFINITY are among the values, the result is NaN.

    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.

    Version:
    $Revision: 1006299 $ $Date: 2010-10-10 16:47:17 +0200 (dim. 10 oct. 2010) $
    See Also:
    Serialized Form

    • Constructor Detail

      • GeometricMean

        public GeometricMean()
        Create a GeometricMean instance

      • GeometricMean

        public GeometricMean​(GeometricMean original)
        Copy constructor, creates a new GeometricMean identical to the original
        Parameters:
        original - the GeometricMean instance to copy

      • GeometricMean

        public GeometricMean​(SumOfLogs sumOfLogs)
        Create a GeometricMean instance using the given SumOfLogs instance
        Parameters:
        sumOfLogs - sum of logs instance to use for computation

    • Method Detail

      • evaluate

        public double evaluate​(double[] values,
                       int begin,
                       int length)
        Returns the geometric mean of the entries in the specified portion of the input array.

        See GeometricMean for details on the computing algorithm.

        Throws IllegalArgumentException if the array is null.

        Specified by:
        evaluate in interface UnivariateStatistic
        Overrides:
        evaluate in class AbstractStorelessUnivariateStatistic
        Parameters:
        values - input array containing the values
        begin - first array element to include
        length - the number of elements to include
        Returns:
        the geometric mean or Double.NaN if length = 0 or any of the values are <= 0.
        Throws:
        java.lang.IllegalArgumentException - if the input array is null or the array index parameters are not valid
        See Also:
        UnivariateStatistic.evaluate(double[], int, int)

      • getN

        public long getN()
        Returns the number of values that have been added.
        Specified by:
        getN in interface StorelessUnivariateStatistic
        Returns:
        the number of values.

      • setSumLogImpl

        public void setSumLogImpl​(StorelessUnivariateStatistic sumLogImpl)

        Sets the implementation for the sum of logs.

        This method must be activated before any data has been added - i.e., before increment has been used to add data; otherwise an IllegalStateException will be thrown.

        Parameters:
        sumLogImpl - the StorelessUnivariateStatistic instance to use for computing the log sum
        Throws:
        java.lang.IllegalStateException - if data has already been added (i.e if n > 0)

      • getSumLogImpl

        public StorelessUnivariateStatistic getSumLogImpl()
        Returns the currently configured sum of logs implementation
        Returns:
        the StorelessUnivariateStatistic implementing the log sum

      • copy

        public static void copy​(GeometricMean source,
                        GeometricMean dest)
        Copies source to dest.

        Neither source nor dest can be null.

        Parameters:
        source - GeometricMean to copy
        dest - GeometricMean to copy to
        Throws:
        java.lang.NullPointerException - if either source or dest is null