The model m1 is fit to the data. Using
the fitted values of the parameters, nsim new data vectors from
this model are simulated. Both m1 and m2 are fit by
maximum likelihood (ML) and/or by restricted maximum likelihood (REML)
to each of the simulated data vectors.
an object of class simulate.lme with components null and
alt. Each of these has components ML and/or REML
which are matrices. An attribute called Random.seed contains
the seed that was used for the random number generator.