R help - Feb 2005 - model matrix for random effects (lme)

Greetings. Is it possible to extract the model matrix (Z) for the random effects
from an lme object? For example, assume the model has two levels of random
effects as in:
 
Y = XB + Zu + e
 
model.matrix() gives the matrix X only. For example:
 
> tt<-model.matrix(distance~age, Orthodont, random=~age|Subject)
> tt[1:10,]
   (Intercept) age
1            1   8
2            1  10
3            1  12
4            1  14
5            1   8
6            1  10
7            1  12
8            1  14
9            1   8
10           1  10
 
Thanks.
Harold

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