lme for long.data

Murali Haran <mharan at stat.umn.edu> writes:

I am attempting to fit a model for longitudinal
data with the lme function.

"sim" is a data set with sim$Y as response, sim$time
as times of each observation, sim$id as patient
id's.

I try to do the following :
simcorExp <-corExp(form=(~time|id),nugget=T)
simcorExp <- initialize(simcorExp, data=sim)

I think this should be done automatically in a call to lme.

sim.fit <- lme(fixed = Y~1, data=sim, random =
~1|id,correlation=simcorExp)

Try 

 sim.fit <- lme(Y ~ 1, data = sim, random = ~ 1 | id,
     correlation = corExp(~ time | id, nugget = T))

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