code: def _build_information(self):
          
          lag_time = float(self.lag_time)
  
          # only the "active set" of variables not at the bounds of the
          # feasible set.
          inds = np.where(self.theta_ != 0)[0]
  
          hessian = _ratematrix.hessian(
              self.theta_, self.countsmat_, t=lag_time, inds=inds)
  
          self.information_ = np.zeros((len(self.theta_), len(self.theta_)))
          self.information_[np.ix_(inds, inds)] = scipy.linalg.pinv(-hessian)
docs: Build the inverse of hessian of the log likelihood at theta_