'Second derivative of the negative binomial link function.
Parameters
p : array-like
Mean parameters
Returns
g\'\'(p) : array
The second derivative of the negative binomial transform link
function
Notes
g\'\'(x) = -(1+2*alpha*x)/(x+alpha*x^2)^2'

def deriv2(self, p):

    numer = (- (1 + ((2 * self.alpha) * p)))
    denom = ((p + (self.alpha * (p ** 2))) ** 2)
    return (numer / denom)
