docs: def _getLaplaceCovar(self):
          """
          Internal function for estimating parameter uncertainty
          Returns:
              the
          """
          assert self.init,        'GP not initialised'
          assert self.fast==False, 'Not supported for fast implementation'
  
          if self.cache['Sigma'] is None:
              self.cache['Sigma'] = sp.linalg.inv(self._getHessian())
          return self.cache['Sigma']