{{alias}}( [mean] )
    Returns an accumulator function which incrementally computes an unbiased
    sample variance.

    If provided a value, the accumulator function returns an updated unbiased
    sample variance. If not provided a value, the accumulator function returns
    the current unbiased sample variance.

    If provided `NaN` or a value which, when used in computations, results in
    `NaN`, the accumulated value is `NaN` for all future invocations.

    Parameters
    ----------
    mean: number (optional)
        Known mean.

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

    Examples
    --------
    > var accumulator = {{alias}}();
    > var s2 = accumulator()
    null
    > s2 = accumulator( 2.0 )
    0.0
    > s2 = accumulator( -5.0 )
    24.5
    > s2 = accumulator()
    24.5

    See Also
    --------