formula.pdMat              package:nlme              R Documentation

Extract pdMat Formula

Description:

     This method function extracts the formula associated with a
     'pdMat' object, in which the column and row names are specified.

Usage:

     ## S3 method for class 'pdMat':
     formula(x, asList, ...)

Arguments:

       x: an object inheriting from class 'pdMat', representing a
          positive definite matrix.

  asList: logical.  Should the asList argument be applied to each of
          the components?  Never used.

     ...: some methods for this generic require additional arguments. 
          None are used in this method.

Value:

     if 'x' has a 'formula' attribute, its value is returned, else
     'NULL' is returned.

Note:

     Because factors may be present in 'formula(x)', the 'pdMat' object
     needs to have access to a data frame where the variables named in
     the formula can be evaluated, before it can resolve its row and
     column names from the formula.

Author(s):

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

See Also:

     'pdMat'

Examples:

     pd1 <- pdSymm(~Sex*age)
     formula(pd1)

