def gradients_XX_diag(self, dL_dK, X):
        return np.ones(X.shape) * self.variance/self.lengthscale**2
Given the derivative of the objective K(dL_dK), compute the second derivative of K wrt X and X2:
dataset/ETHPy150Open SheffieldML/GPy/GPy/kern/src/stationary.py/Stationary.gradients_XX_diag