Extract pdMat Formula

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

# 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.

Author

José Pinheiro and Douglas Bates bates@stat.wisc.edu

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.

See also

pdMat

Examples

pd1 <- pdSymm(~Sex*age)
formula(pd1)
#> ~Sex * age
#> <environment: 0x55c54c5c9ae0>