formula.pdMat {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

formula(object)

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.

Author(s)

Jose Pinheiro and Douglas Bates

See Also

pdMat

Examples

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