should also be studied as they are widely used . Second, other hyperparameters aside from 𝜆, namely the parameter 𝛽 of the hyperprior distribution, the number 𝑁 of collocation points, the derivative order q of the differentiation matrix 𝑳 in (2), the partitioning parameter k of the kf-CV, and the minimum 𝜏 min and maximum 𝜏 max timescales, could be "optimally" selected. Third, other methods could be studied, including strong robust CV , generalized maximum likelihood ,