{{alias}}()
    Returns an accumulator function which incrementally computes the mean
    arctangent absolute percentage error (MAAPE).

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

    Note that, unlike the mean absolute percentage error (MAPE), the mean
    arctangent absolute percentage error is expressed in radians on the interval
    [0,π/2].

    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 )
    ~0.3218
    > m = accumulator( 5.0, 2.0 )
    ~0.6523
    > m = accumulator()
    ~0.6523

    See Also
    --------