lme function, inheriting from class
lme and representing a fitted linear mixed-effects
model. Objects of this class have methods for the generic functions
anova, coef, fitted, fixed.effects,
formula, getGroups, getResponse,
intervals, logLik, pairs, plot,
predict, print, random.effects, residuals,
sigma, summary, update, and vcov.lme
object.lme, lmeStruct