Compute power and sample size for linear models of longitudinal
data. Supported models include mixed-effects models and models fit by
generalized least squares and generalized estimating equations. The package
is described in Iddi and Donohue (2022) . Relevant
formulas are derived by Liu and Liang (1997) ,
Diggle et al (2002) , and Lu, Luo, and Chen (2008)
.