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## org.apache.commons.math.stat.descriptive.moment
Class GeometricMean

    java.lang.Object
      org.apache.commons.math.stat.descriptive.AbstractUnivariateStatistic
          org.apache.commons.math.stat.descriptive.AbstractStorelessUnivariateStatistic
              org.apache.commons.math.stat.descriptive.moment.GeometricMean

All Implemented Interfaces:
  Serializable, StorelessUnivariateStatistic, UnivariateStatistic

    public class GeometricMean

extends AbstractStorelessUnivariateStatistic
implements 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 Summary
`GeometricMean()` Create a GeometricMean instance
`GeometricMean(GeometricMean original)` Copy constructor, creates a new `GeometricMean` identical to the `original`
`GeometricMean(SumOfLogs sumOfLogs)` Create a GeometricMean instance using the given SumOfLogs instance

Method Summary
`void` | `clear()` Clears the internal state of the Statistic
`GeometricMean` | `copy()` Returns a copy of the statistic with the same internal state.
`static void` | `copy(GeometricMean source, GeometricMean dest)` Copies source to dest.
`double` | `evaluate(double[] values, int begin, int length)` Returns the geometric mean of the entries in the specified portion of the input array.
`long` | `getN()` Returns the number of values that have been added.
`double` | `getResult()` Returns the current value of the Statistic.
`StorelessUnivariateStatistic` | `getSumLogImpl()` Returns the currently configured sum of logs implementation
`void` | `increment(double d)` Updates the internal state of the statistic to reflect the addition of the new value.
`void` | `setSumLogImpl(StorelessUnivariateStatistic sumLogImpl)` Sets the implementation for the sum of logs.

Methods inherited from class org.apache.commons.math.stat.descriptive.AbstractStorelessUnivariateStatistic
`equals, evaluate, hashCode, incrementAll, incrementAll`

Methods inherited from class org.apache.commons.math.stat.descriptive.AbstractUnivariateStatistic
`evaluate, getData, getDataRef, setData, setData, test, test`

Methods inherited from class java.lang.Object
`clone, finalize, getClass, notify, notifyAll, toString, wait, wait, wait`

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

### copy

    public GeometricMean copy()

  Returns a copy of the statistic with the same internal state.

  Specified by:
    `copy` in interface `StorelessUnivariateStatistic`
  Specified by:
    `copy` in interface `UnivariateStatistic`
  Specified by:
    `copy` in class `AbstractStorelessUnivariateStatistic`
  Returns:
    a copy of the statistic

### increment

    public void increment(double d)

  Updates the internal state of the statistic to reflect the addition of the new value.

  Specified by:
    `increment` in interface `StorelessUnivariateStatistic`
  Specified by:
    `increment` in class `AbstractStorelessUnivariateStatistic`
  Parameters:
    `d` - the new value.

### getResult

    public double getResult()

  Returns the current value of the Statistic.

  Specified by:
    `getResult` in interface `StorelessUnivariateStatistic`
  Specified by:
    `getResult` in class `AbstractStorelessUnivariateStatistic`
  Returns:
    value of the statistic, `Double.NaN` if it has been cleared or just instantiated.

### clear

    public void clear()

  Clears the internal state of the Statistic

  Specified by:
    `clear` in interface `StorelessUnivariateStatistic`
  Specified by:
    `clear` in class `AbstractStorelessUnivariateStatistic`

### 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:
    `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:
    `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:
    `NullPointerException` - if either source or dest is null

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