[R] general mixed model statement

[brook@biology.nmsu.edu]

I am trying to analyze a general mixed model, but am confused about
the model statement to use.  The structure of the problem is the
following:

	y = X b + Z u + e

where X and Z are known incidence matrices for fixed and random
effects respectively, b is a vector of fixed effects to be estimated,
u is a vector of random effects, and e is a vector of error terms.
Additionally, the covariance matrices of the random effects and error
terms are given by

       G = g A, and
       R = r E

where A and E are known matrices and g and r must be estimated.

Presumably there is a way to specify in a model statement the known
covariance structure for the random and error terms, but I cannot find
the documentation I need.  Please either clarify for me how to write
this out or point me to the appropriate documentation that outlines
the full range of model statements that are possible.

Thank you very much for your help.

Cheers,
Brook