Specifying pdMat classes in lme

Dear all,

I try to re-specify an lme model using the pdMat classes in order to then be able to remove some restrictions on the variance-covariance matrices.

My model has the following random effects structure: ~time | b/c

(where b and c are different split-plot sizes in an agricultural experiment).

What would be an equivalent formulation of such a random effects structure using pdBlocked, pdCompSymm etc.?

I believe it?s something like

random=list(b=pdCompsymm(~c-1)

but how would I include the different slopes for time here?

Many thanks for any help,
Christoph


(using R 2.13.1 in Windows 7 64 Bit, lme version 3.1-102)