{{alias}}( W )
    Returns an accumulator function which incrementally computes a moving
    geometric mean.

    The `W` parameter defines the number of values over which to compute the
    moving geometric mean.

    If provided a value, the accumulator function returns an updated moving
    geometric mean. If not provided a value, the accumulator function returns
    the current moving geometric mean.

    As `W` values are needed to fill the window buffer, the first `W-1` returned
    values are calculated from smaller sample sizes. Until the window is full,
    each returned value is calculated from all provided values.

    Parameters
    ----------
    W: integer
        Window size.

    Returns
    -------
    acc: Function
        Accumulator function.

    Examples
    --------
    > var accumulator = {{alias}}( 3 );
    > var v = accumulator()
    null
    > v = accumulator( 2.0 )
    2.0
    > v = accumulator( 5.0 )
    ~3.16
    > v = accumulator( 3.0 )
    ~3.11
    > v = accumulator( 5.0 )
    ~4.22
    > v = accumulator()
    ~4.22

    See Also
    --------