getCovariate.varFunc          package:nlme          R Documentation

Extract varFunc Covariate

Description:

     This method function extracts the covariate(s) associated with the
     variance function represented by 'object', if any is present.

Usage:

     ## S3 method for class 'varFunc':
     getCovariate(object, form, data)

Arguments:

  object: an object inheriting from class 'varFunc', representing a
          variance function structure.

    form: an optional formula specifying the covariate to be evaluated
          in 'object'. Defaults to 'formula(object)'.

    data: some methods for this generic require a 'data' object.  Not
          used in this method.

Value:

     if 'object' has a 'covariate' attribute, its value is returned;
     else 'NULL' is returned.

Author(s):

     Jose Pinheiro Jose.Pinheiro@pharma.novartis.com and Douglas Bates
     bates@stat.wisc.edu

See Also:

     'covariate<-.varFunc'

Examples:

     data(Orthodont)
     vf1 <- varPower(1.1, form = ~age)
     covariate(vf1) <- Orthodont[["age"]]
     getCovariate(vf1)

