code: def gradients_X(self, dL_dK, X, X2, target):
          
          if X2==None or X2 is X:
              dL_dKdiag = dL_dK.flat[::dL_dK.shape[0]+1]
              self.dKdiag_dX(dL_dKdiag, X, target)
docs: Derivative of the covariance matrix with respect to X.