[R] lme vs. lmer results

[Dimitri Liakhovitski]

Hello,
and sorry for asking a question without the data - hope it can still
be answered:

I've run two things on the same data:

# Using lme:
mix.lme <- lme(DV ~a+b+c+d+e+f+h+i, random = random = ~ e+f+h+i|
group, data = mydata)

# Using lmer
mix.lmer <- lmer(DV
~a+b+c+d+(1|group)+(e|group)+(f|group)+(h|group)+(i|group), data =
mydata)

lme provided an output (fixed effects and random effects coefficients).
lmer gave me an error: Error in mer_finalize(ans) : Downdated X'X is
not positive definite, 10.
I've rerun lmer with - but specifying the random effects for 2 fewer
predictors. This time it ran and provided an output. (BTW, the random
effects of lmer with 2 fewer predictors specified as random were very
close to the output of lme).

Question:
Looks like lmer could not invert the matrix, right? But how come lme
(which I thought was an earlier version of lmer) COULD invert it?
Greatly appreciate a clarification!


-- 
Dimitri Liakhovitski
Ninah Consulting
www.ninah.com