rsm (version 1.40)

FO: Response-surface model components

Description

Use of one of these functions in a model is how you specify the portion of the model that is to be regarded as a response-surface component.

Usage

FO (...)
TWI (...)
PQ (...)
SO (...)
PE (...)

Arguments

...

The numerical predictors for the response surface, separated by commas.

Value

• The functions FO, TWI, PQ, and SO return a matrix whose columns are the required predictors. PE returns a factor whose levels are all the distinct combinations of arguments provided to the function.

Details

Use FO() in the model formula in rsm to specify a first-order response surface (i.e., a linear function) in its arguments. Use TWI() to generate two-way interactions, and PQ() to generate pure quadratic terms (squares of the FO() terms). A call to SO() creates all terms in FO(), TWI(), and PQ() (in that order) for those variables. However, specifying SO() in a model formula in rsm will be replaced by the explicit sum of model terms, so that the anova table shows separate sums of squares. Other variables (such as blocks or factors) may be included in the model but should nevel be included in the arguments to FO or SO. PE is used for fitting pure-error models. It should not be used in response-surface models. This function exists primarily for use by loftest, but could be useful in other linear-model contexts for fitting a model that interpolates the means at each distinct combination of argument values.

References

Lenth RV (2009). ``Response-Surface Methods in R, Using rsm'', Journal of Statistical Software, 32(7), 1--17. http://www.jstatsoft.org/v32/i07/.

See Also

rsm

Examples

### See 'rsm' help for more examples
  
  library(rsm)
  ### Test LOF for a regression model
  ChemReact.lm = lm(Yield ~ Time*Temp, data=ChemReact, subset=1:7)
  PureError.lm = update (ChemReact.lm, . ~ PE(Time,Temp))
  anova (ChemReact.lm, PureError.lm)