In R, you can use the "nlme" package to fit mixed-effects models, including the Brody and Bertalanffy growth curve models. The "nlme" package provides the necessary functions for modeling and analyzing longitudinal and repeated measures data with both fixed and random effects. Here are the functions you can use for fitting these growth curve models:

Both the nlme and gnls functions allow you to incorporate random effects in the model to account for individual variation or repeated measures within subjects.

Here is an example of using the gnls function to fit a Brody growth curve model in R:

RCopy codelibrary(nlme) # Define the Brody growth model equation brody_model