A fitted model. Methods are available for models fit by lme and by gls

For models fit by lme a vector of levels of the grouping factor can be specified for the conditional or marginal variance-covariance matrices.

For models fit by gls the only type of variance-covariance matrix provided is the marginal variance-covariance of the responses by group. The optional argument individual specifies the group of responses.

For models fit by lme the type argument specifies the type of variance-covariance matrix, either "random.effects" for the random-effects variance-covariance (the default), or "conditional" for the conditional. variance-covariance of the responses or "marginal" for the the marginal variance-covariance of the responses.

Optional arguments for some methods, as described above