{{alias}}()
    Returns an accumulator function which incrementally computes the mean error
    (ME).

    If provided input values, the accumulator function returns an updated mean
    error. If not provided input values, the accumulator function returns the
    current mean error.

    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 m = accumulator()
    null
    > m = accumulator( 2.0, 3.0 )
    1.0
    > m = accumulator( -5.0, 2.0 )
    4.0
    > m = accumulator()
    4.0

    See Also
    --------