Returns the absolute energy of the time series which is the sum over the squared values

    .. math::

        E = \\sum_{i=1,\ldots, n} x_i^2

    :param x: the time series to calculate the feature of
    :type x: numpy.ndarray
    :return: the value of this feature
    :return type: float

def abs_energy(x):
    """
    Returns the absolute energy of the time series which is the sum over the squared values

    .. math::

        E = \\sum_{i=1,\ldots, n} x_i^2

    :param x: the time series to calculate the feature of
    :type x: numpy.ndarray
    :return: the value of this feature
    :return type: float
    """
    if not isinstance(x, (np.ndarray, pd.Series)):
        x = np.asarray(x)
    return np.dot(x, x)