docs: def _check_inference(self, inference):
          """
          Internal method for checking that the selected inference scheme is compatible with the specified model
          """
          if inference=='GP2KronSum':
              assert self.n_randEffs==2, 'VarianceDecomposition: for fast inference number of random effect terms must be == 2'
              assert not sp.isnan(self.Y).any(), 'VarianceDecomposition: fast inference available only for complete phenotype designs'