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

    The `W` parameter defines the number of values over which to compute the
    moving statistical summary.

    If provided a value, the accumulator function returns an updated moving
    statistical summary. If not provided a value, the accumulator function
    returns the current moving statistical summary.

    The returned summary is an object containing the following fields:

    - window: window size.
    - sum: sum.
    - mean: arithmetic mean.
    - variance: unbiased sample variance.
    - stdev: corrected sample standard deviation.
    - min: minimum value.
    - max: maximum value.
    - range: range.
    - midrange: arithmetic mean of the minimum and maximum values.

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

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

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

    Examples
    --------
    > var accumulator = {{alias}}( 3 );
    > var s = accumulator()
    {}
    > s = accumulator( 2.0 )
    {...}
    > s = accumulator( -5.0 )
    {...}
    > s = accumulator()
    {...}

    See Also
    --------