'Loglikelihood of Generalized Poisson model
Parameters
params : array-like
The parameters of the model.
Returns
loglike : float
The log-likelihood function of the model evaluated at `params`.
See notes.
Notes
.. math:: \ln L=\sum_{i=1}^{n}\left[\mu_{i}+(y_{i}-1)*ln(\mu_{i}+
\alpha*\mu_{i}^{p-1}*y_{i})-y_{i}*ln(1+\alpha*\mu_{i}^{p-1})-
ln(y_{i}!)-\frac{\mu_{i}+\alpha*\mu_{i}^{p-1}*y_{i}}{1+\alpha*
\mu_{i}^{p-1}}\right]'

def loglike(self, params):

    return np.sum(self.loglikeobs(params))
