Model factorization with `factorize()` decomposes an `FDboost` model into two objects of class `FDboost_fac` - one for the response and one for the covariate predictor. The first is essentially an `FDboost` object and the second an `mboost` object, however, in a 'read-only' mode and slightly adjusted methods (method defaults).
[factorize(), factorize.FDboost()]