def cloud_func(x, a):
    """Function for fitting the mean of wet and dry cloud to the mean of all
    cloud

    This function returns y with

    .. math::
        y = ((-a - 1) / (a^2 x - a^2 - a)) - \\frac{1}{a}

    Parameters
    ----------
    x: np.ndarray
        The x input data
    a: float
        The parameter as mentioned in the equation above"""
    return (-a - 1) / (a * a * x - a * a - a) - 1 / a
