Derivative of the power transform

        Parameters
        ----------
        p : array-like
            Mean parameters

        Returns
        --------
        g'(p) : array
            Derivative of power transform of `p`

        Notes
        -----
        g'(`p`) = `power` * `p`**(`power` - 1)

def deriv(self, p):
        """
        Derivative of the power transform

        Parameters
        ----------
        p : array-like
            Mean parameters

        Returns
        --------
        g'(p) : array
            Derivative of power transform of `p`

        Notes
        -----
        g'(`p`) = `power` * `p`**(`power` - 1)
        """
        return self.power * np.power(p, self.power - 1)