def dKdiag_dX(self, dL_dKdiag, X, target):
        """Gradient of diagonal of covariance with respect to X"""
        self._K_diag_computations(X)
        arg = self._K_diag_poly_arg
        target += 2.*self.weight_variance*self.degree*self.variance*X*dL_dKdiag[:, None]*(arg**(self.degree-1))[:, None]
Gradient of diagonal of covariance with respect to X