[R-sig-ME] lme4 vs nlme?

[Dominick Samperi]

Hello,

I just read through Bates's excellent notes on lme4a and now I'm trying to
compare what I learned with what is in nlme. The first thing I notice is that
lme4a is not restricted to linear modeling (as its name and the lme4a package
description might suggest).

Second, I do not see the equivalent of pdMatrix, varIdent, etc. in lme4a.
That is, I don't see how to specify different correlation structures for
the random effect, or dependency information for the error terms, like
heteroskedasticity, autocorrelation, etc.

Are the latter missing because lme4a is not finished?

What is the intended scope of lme4a and how does
this compare with nlme?

Thanks,
Dominick