Hi,

My question is how to calculate lambda for the original series y(t), if y(t) is negative or has zero's?

Because from forecast (fpp2) forecast source: R/guerrero.R says

guerrero: "Guerrero's method for selecting a Box-Cox parameter (lambda) is given for strictly positive data" and

bcloglik: Modified version of boxcox from MASS package "x must be positive".

And in feasts (fpp3) guerrero is similar feasts source: R/guerrero.R

Thus, I cannot calculate lambda for negative y(t), and use eqn(3.1), eqn(5.2) and eqn(5.3) in fpp3 (which allow for negative values of y(t) provided lambda>0), if y(t) the original series is <=0.

thanks,

Amarjit