[R] cross-classified random factors in lme without blocking

[Gordon Smyth]

Many thanks for help from Peter Dalgaard, Douglas Bates and Bill Venables. 
As a result of their help, here is a working example of using lme to fit an 
additive random effects model. The model here is effectively y~a+b with a 
and b random:

y <- rnorm(12)
a <- gl(4,1,12)
b <- gl(3,4,12)
u <- gl(1,1,12)
library(nlme)
fm <- lme(y~1,random=list(u=pdBlocked(list(pdIdent(~a-1),pdIdent(~b-1)))))
summary(fm)

I still can't see though how to extract the three variance components (for 
a and b and for the residual) from the fitted object 'fm'.

Thanks
Gordon