This transformation was used originally in mkin, in order to implement a constraint for the sum of formation fractions to be smaller than 1. It was later replaced by the ilr transformation because the ilr transformed fractions can assumed to follow normal distribution. As the ilr transformation is not available in RxODE and can therefore not be used in the nlmixr modelling language, the original transformation is currently used for translating mkin models with formation fractions to more than one target compartment for fitting with nlmixr in nlmixr_model. However, this implementation cannot be used there, as it is not accessible from RxODE.
tffm0(ff)
invtffm0(ff_trans)Vector of untransformed formation fractions. The sum must be smaller or equal to one
Vector of transformed formation fractions that can be restricted to the interval from 0 to 1
A vector of the transformed formation fractions A vector of backtransformed formation fractions for natural use in degradation models
If the transformed formation fractions are restricted to the interval between 0 and 1, the sum of backtransformed values is restricted to this interval.
ff_example <- c(
0.10983681, 0.09035905, 0.08399383
)
ff_example_trans <- tffm0(ff_example)
invtffm0(ff_example_trans)
#> [1] 0.10983681 0.09035905 0.08399383