To compare the values of 𝜆 obtained from each parameter selection method to 𝜆 opt in , the absolute error on 𝜆, abs 𝜆 , the normalized absolute error on 𝜆, abs norm,𝜆 , and the mean squared error on 𝜆, MSE 𝜆 , were introduced: , and 𝜆 CV is the 𝜆 selected using a given parameter regularization method.