{{alias}}( W[, mean] )
    Returns an accumulator function which incrementally computes a moving
    variance-to-mean (VMR).

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

    If provided a value, the accumulator function returns an updated moving
    variance-to-mean ratio. If not provided a value, the accumulator function
    returns the current moving variance-to-mean ratio.

    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.

    mean: number (optional)
        Known mean.

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

    Examples
    --------
    > var accumulator = {{alias}}( 3 );
    > var F = accumulator()
    null
    > F = accumulator( 2.0 )
    0.0
    > F = accumulator( 1.0 )
    ~0.33
    > F = accumulator( 3.0 )
    0.5
    > F = accumulator( 7.0 )
    ~2.55
    > F = accumulator()
    ~2.55

    See Also
    --------