This method function extracts the formula associated with a
pdMat
object, in which the column and row names are specified.
USAGE:
formula(object)
REQUIRED ARGUMENTS:
object
an object inheriting from class
pdMat, representing
a positive definite matrix.
VALUE:
if
object has a
formula attribute, its value is
returned, else
NULL is returned.
NOTE: Because factors may be present in
formula(object), 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.