% Generated by roxygen2: do not edit by hand
% Please edit documentation in R/tffm0.R
\name{tffm0}
\alias{tffm0}
\alias{invtffm0}
\title{Transform formation fractions as in the first published mkin version}
\usage{
tffm0(ff)

invtffm0(ff_trans)
}
\arguments{
\item{ff}{Vector of untransformed formation fractions. The sum
must be smaller or equal to one}

\item{ff_trans}{Vector of transformed formation fractions that can be
restricted to the interval from 0 to 1}
}
\value{
A vector of the transformed formation fractions

A vector of backtransformed formation fractions for natural use in degradation models
}
\description{
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 \link{ilr} transformation because the ilr transformed
fractions can assumed to follow normal distribution. As the ilr
transformation is not available in \link{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 \link{nlmixr_model}. However, this
implementation cannot be used there, as it is not accessible from RxODE.
}
\details{
If the transformed formation fractions are restricted to the interval
between 0 and 1, the sum of backtransformed values is restricted
to this interval.
}
\examples{
ff_example <- c(
  0.10983681, 0.09035905, 0.08399383
)
ff_example_trans <- tffm0(ff_example)
invtffm0(ff_example_trans)
}