'Hessian matrix computed by second-order complex-step differentiation
on the `loglike` function.'

def _hessian_complex_step(self, params, **kwargs):

    epsilon = _get_epsilon(params, 3.0, None, len(params))
    kwargs['transformed'] = True
    kwargs['complex_step'] = True
    hessian = approx_hess_cs(params, self.loglike, epsilon=epsilon, kwargs=kwargs)
    return (hessian / (self.nobs - self.ssm.loglikelihood_burn))
