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

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

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

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

    Examples
    --------
    > var accumulator = {{alias}}();
    > var mu = accumulator()
    null
    > mu = accumulator( 2.0 )
    2.0
    > mu = accumulator( -5.0 )
    -1.5
    > mu = accumulator()
    -1.5

    See Also
    --------