docs: def _getHessian(self):
          """
          Internal function for estimating parameter uncertainty
          COMPUTES OF HESSIAN OF E(\theta) = - log L(\theta | X, y)
          """
          assert self.init,        'GP not initialised'
          assert self.fast==False, 'Not supported for fast implementation'
  
          if self.cache['Hessian'] is None:
              ParamMask=self.gp.getParamMask()['covar']
              std=sp.zeros(ParamMask.sum())
              H=self.gp.LMLhess_covar()
              It= (ParamMask[:,0]==1)
              self.cache['Hessian']=H[It,:][:,It]
  
          return self.cache['Hessian']