{{alias}}()
    Returns an accumulator function which incrementally computes a weighted
    arithmetic mean.

    If provided arguments, the accumulator function returns an updated weighted
    mean. If not provided arguments, the accumulator function returns the
    current weighted mean.

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

    The accumulator function accepts two arguments:

    - x: value
    - w: weight

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

    Examples
    --------
    > var accumulator = {{alias}}();
    > var mu = accumulator()
    null
    > mu = accumulator( 2.0, 1.0 )
    2.0
    > mu = accumulator( 2.0, 0.5 )
    2.0
    > mu = accumulator( 3.0, 1.5 )
    2.5
    > mu = accumulator()
    2.5

    See Also
    --------