Default Formula for Response Surface Design
DESCRIPTION:
Returns a model formula for a quadratic response surface in the rsm.factors of the rsm object. This function is used to generate the default formula in a typical call to rsm.lm.
USAGE: 
formula.rsm.design(object, response)
REQUIRED ARGUMENTS:
object:
an object of class "rsm.design" typically created using either as.rsm.design or rsm.design.
OPTIONAL ARGUMENTS:
response:
name of the response variable. The default is to use the first non rsm.factor in the rsm.design object. A response variable can be supplied which is not part of the rsm.design object (e.g., a response on another scale). This is not a character string.
VALUE:
an object of class "formula" that typically will specify a quadratic response surface model for the rsm.design object.
DETAILS:
Experimental factors in an rsm design have class "rsm.factor". The formula returned has all linear quadratic and interaction terms for these factors, i.e., for the factor design

(A+B+C)^2 + A^2 + B^2 + C^2

SEE ALSO:
as.rsm.design , rsm.design , rsm.lm .
EXAMPLES: 
a.design <- rsm.design(3)
a.df <- cbind(a.design, y = rnorm(18))
formula(a.df)


# the following two statements are equivalent
rsm.lm(formula(a.df), data = a.df)
rsm.lm(a.df)