'Second derivative of the power transform
Parameters
p : array-like
Mean parameters
Returns
g\'\'(p) : array
Second derivative of the power transform of `p`
Notes
g\'\'(`p`) = `power` * (`power` - 1) * `p`**(`power` - 2)'

def deriv2(self, p):

    if (self.power == 1):
        return np.zeros_like(p)
    else:
        return ((self.power * (self.power - 1)) * np.power(p, (self.power - 2)))
