seperateFormula(formula) y ~
clust(time+time2) + pop(sex), here 'time' and 'time2'
will have a different effect according to the cluster,
the 'sex' effect is the same for all the clusters. In the
non-parametric case only one covariate is allowed.Y ~ clust(T1 + T2 +
...) + pop(X1 + X2 + ...) or just Y ~ clust(T1 +
T2 + ...), it returns a list of two or one 'formula' of
the form Y ~ T1 + T2 + ... and ~ X1 + X2 +
... if provided. The first element of the list
correspond to the covariates with a different effects
corresponding to the cluster, the 2nd correspond to
covariates having an identical effect in each cluster.
In the non-parametric case only one covariate is
allowed.