This method function extracts the formula associated with a
corStruct
object, in which the covariate and the grouping
factor, if any is present, are defined.
USAGE:
formula(object)
REQUIRED ARGUMENTS:
object
an object inheriting from class
corStruct
representing a correlation structure.
VALUE:
an object of class
formula specifying the covariate and the
grouping factor, if any is present, associated with
object.