From f59b8a93a9956ac46eac24d294f7a26642b995dc Mon Sep 17 00:00:00 2001
From: Johannes Ranke <jranke@uni-bremen.de>
Date: Thu, 14 Sep 2017 12:15:58 +0200
Subject: Convert FOCUS Z vignette to rmarkdown/html

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----
-title: Introduction to mkin
-author: Johannes Ranke
-date: "`r Sys.Date()`"
-output:
-  html_document:
-    toc: true
-    toc_float: true
-    code_folding: hide
-    fig_retina: null
-bibliography: references.bib
-vignette: >
-  %\VignetteEngine{knitr::rmarkdown}
-  %\VignetteIndexEntry{mkin - Kinetic evaluation of chemical degradation data}
-  %\VignetteEncoding{UTF-8}
----
-
-[Wissenschaftlicher Berater, Kronacher Str. 8, 79639 Grenzach-Wyhlen, Germany](http://www.jrwb.de)<br />
-[Privatdozent at the University of Bremen](http://chem.uft.uni-bremen.de/ranke)
-
-```{r, include = FALSE}
-require(knitr)
-opts_chunk$set(engine='R', tidy=FALSE)
-```
-
-# Abstract
-In the regulatory evaluation of chemical substances like plant protection
-products (pesticides), biocides and other chemicals, degradation data play an
-important role. For the evaluation of pesticide degradation experiments,
-detailed guidance has been developed, based on nonlinear optimisation.
-The `R` add-on package `mkin` [@pkg:mkin] implements fitting some of the models
-recommended in this guidance from within R and calculates some statistical
-measures for data series within one or more compartments, for parent and
-metabolites.
-
-```{r, echo = TRUE, cache = TRUE, fig = TRUE, fig.width = 8, fig.height = 7}
-library(mkin)
-# Define the kinetic model
-m_SFO_SFO_SFO <- mkinmod(parent = mkinsub("SFO", "M1"),
-                         M1 = mkinsub("SFO", "M2"),
-                         M2 = mkinsub("SFO"),
-                         use_of_ff = "max", quiet = TRUE)
-
-
-# Produce model predictions using some arbitrary parameters
-sampling_times = c(0, 1, 3, 7, 14, 28, 60, 90, 120)
-d_SFO_SFO_SFO <- mkinpredict(m_SFO_SFO_SFO,
-  c(k_parent = 0.03,
-    f_parent_to_M1 = 0.5, k_M1 = log(2)/100,
-    f_M1_to_M2 = 0.9, k_M2 = log(2)/50),
-  c(parent = 100, M1 = 0, M2 = 0),
-  sampling_times)
-
-# Generate a dataset by adding normally distributed errors with
-# standard deviation 3, for two replicates at each sampling time
-d_SFO_SFO_SFO_err <- add_err(d_SFO_SFO_SFO, reps = 2,
-                             sdfunc = function(x) 3,
-                             n = 1, seed = 123456789 )
-
-# Fit the model to the dataset
-f_SFO_SFO_SFO <- mkinfit(m_SFO_SFO_SFO, d_SFO_SFO_SFO_err[[1]], quiet = TRUE)
-
-# Plot the results separately for parent and metabolites
-plot_sep(f_SFO_SFO_SFO, lpos = c("topright", "bottomright", "bottomright"))
-```
-
-# Background
-
-Many approaches are possible regarding the evaluation of chemical degradation
-data.
-
-The now deprecated `kinfit` package [@pkg:kinfit] in `R` [@rcore2016]
-implements the approach recommended in the kinetics report provided by the
-FOrum for Co-ordination of pesticide fate models and their USe [@FOCUS2006;
--@FOCUSkinetics2014] for simple data series for one parent compound in one
-compartment.
-
-The `mkin` package [@pkg:mkin] extends this approach to data series with
-transformation products, commonly termed metabolites, and to more than one
-compartment. It is also possible to include back reactions, so equilibrium
-reactions and equilibrium partitioning can be specified, although this
-oftentimes leads to an overparameterisation of the model.
-
-When the first `mkin` code was published in 2010, the most commonly used tools for
-fitting more complex kinetic degradation models to experimental data were
-KinGUI [@schaefer2007], a MATLAB based tool with a graphical user
-interface that was specifically tailored to the task and included some output
-as proposed by the FOCUS Kinetics Workgroup, and ModelMaker, a general purpose
-compartment based tool providing infrastructure for fitting dynamic simulation
-models based on differential equations to data.
-
-The code was first uploaded to the BerliOS platform. When this was taken down,
-the version control history was imported into the R-Forge site, where the code
-is still mirrored today (see *e.g.*
-[the initial commit on 11 May 2010](http://cgit.jrwb.de/mkin/commit/?id=30cbb4092f6d2d3beff5800603374a0d009ad770)).
-
-At that time, the R package `FME` (Flexible Modelling Environment)
-[@soetaert2010] was already available, and provided a good basis for
-developing a package specifically tailored to the task. The remaining challenge
-was to make it as easy as possible for the users (including the author of this
-vignette) to specify the system of differential equations and to include the
-output requested by the FOCUS guidance, such as the relative standard deviation
-that has to be assumed for the residuals, such that the $\chi^2$
-goodness-of-fit test as defined by the FOCUS kinetics workgroup would pass
-using an significance level $\alpha$ of 0.05.
-
-Also, `mkin` introduced using analytical solutions for parent only kinetics for
-improved optimization speed. Later, Eigenvalue based solutions were
-introduced to `mkin` for the case of linear differential equations (*i.e.*
-where the FOMC or DFOP models were not used for the parent compound), greatly
-improving the optimization speed for these cases.
-
-The possibility to specify back-reactions and a biphasic model (SFORB) for
-metabolites were present in `mkin` from the very beginning.
-
-## Derived software tools
-
-Soon after the publication of `mkin`, two derived tools were published, namely
-KinGUII (available from Bayer Crop Science) and CAKE (commissioned to Tessella
-by Syngenta), which added a graphical user interface (GUI), and added fitting by
-iteratively reweighted least squares (IRLS) and characterisation of likely
-parameter distributions by Markov Chain Monte Carlo (MCMC) sampling.
-
-CAKE focuses on a smooth use experience, sacrificing some flexibility in the model
-definition, originally allowing only two primary metabolites in parallel.
-The current version 3.2 of CAKE release in March 2016 uses a basic scheme for
-up to six metabolites in a flexible arrangement, but does not support
-back-reactions (non-instantaneous equilibria) or biphasic kinetics for metabolites.
-
-KinGUI offers an even more flexible widget for specifying complex kinetic
-models.  Back-reactions (non-instanteneous equilibria) were supported early on,
-but until 2014,  only simple first-order models could be specified for
-transformation products.  Starting with KinGUII version 2.1, biphasic modelling
-of metabolites was also available in KinGUII.
-
-A further graphical user interface (GUI) that has recently been brought to a decent
-degree of maturity is the browser based GUI named `gmkin`. Please see its
-[documentation page](http://kinfit.r-forge.r-project.org/gmkin_static) and
-[manual](http://kinfit.r-forge.r-project.org/gmkin_static/vignettes/gmkin_manual.html)
-for further information.
-
-## Recent developments
-
-Currently (June 2016), the main features available in `mkin` which are
-not present in KinGUII or CAKE, are the speed increase by using compiled code when
-a compiler is present, parallel model fitting on multicore machines using the
-`mmkin` function, and the estimation of parameter confidence intervals based on
-transformed parameters. These are explained in more detail below.
-
-# Internal parameter transformations
-
-For rate constants, the log
-transformation is used, as proposed by Bates and Watts [-@bates1988, p. 77,
-149]. Approximate intervals are constructed for the transformed rate
-constants [compare @bates1988, p. 135], *i.e.* for their logarithms.
-Confidence intervals for the rate constants are then obtained using the
-appropriate backtransformation using the exponential function.
-
-In the first version of `mkin` allowing for specifying models using
-formation fractions, a home-made reparameterisation was used in order to ensure
-that the sum of formation fractions would not exceed unity.
-
-This method is still used in the current version of KinGUII (v2.1 from April
-2014), with a modification that allows for fixing the pathway to sink to zero.
-CAKE uses penalties in the objective function in order to enforce this
-constraint.
-
-In 2012, an alternative reparameterisation of the formation fractions was
-proposed together with René Lehmann [@ranke2012], based on isometric
-logratio transformation (ILR). The aim was to improve the validity of the
-linear approximation of the objective function during the parameter
-estimation procedure as well as in the subsequent calculation of parameter
-confidence intervals.
-
-## Confidence intervals based on transformed parameters
-
-In the first attempt at providing improved parameter confidence intervals
-introduced to `mkin` in 2013, confidence intervals obtained from
-FME on the transformed parameters were simply all backtransformed one by one
-to yield asymetric confidence intervals for the backtransformed parameters.
-
-However, while there is a 1:1 relation between the rate constants in the model
-and the transformed parameters fitted in the model, the parameters obtained by the
-isometric logratio transformation are calculated from the set of formation
-fractions that quantify the paths to each of the compounds formed from a
-specific parent compound, and no such 1:1 relation exists.
-
-Therefore, parameter confidence intervals for formation fractions obtained with
-this method only appear valid for the case of a single transformation product, where
-only one formation fraction is to be estimated, directly corresponding to one
-component of the ilr transformed parameter.
-
-The confidence intervals obtained by backtransformation for the cases where a
-1:1 relation between transformed and original parameter exist are considered by
-the author of this vignette to be more accurate than those obtained using a
-re-estimation of the Hessian matrix after backtransformation, as implemented
-in the FME package.
-
-## Parameter t-test based on untransformed parameters
-
-The standard output of many nonlinear regression software packages includes
-the results from a test for significant difference from zero for all parameters.
-Such a test is also recommended to check the validity of rate constants in the
-FOCUS guidance [@FOCUSkinetics2014, p.  96ff].
-
-It has been argued that the precondition for this test, *i.e.* normal distribution
-of the estimator for the parameters, is not fulfilled in the case of nonlinear regression
-[@ranke2015]. However, this test is commonly used by industry, consultants and
-national authorities in order to decide on the reliability of parameter estimates, based
-on the FOCUS guidance mentioned above. Therefore, the results of this one-sided
-t-test are included in the summary output from `mkin`.
-
-As it is not reasonable to test for significant difference of the transformed
-parameters (*e.g.* $log(k)$) from zero, the t-test is calculated based on the
-model definition before parameter transformation, *i.e.* in a similar way as in
-packages that do not apply such an internal parameter transformation.  A note
-is included in the `mkin` output, pointing to the fact that the t-test is based
-on the unjustified assumption of normal distribution of the parameter
-estimators.
-
-# References
-
-<!-- vim: set foldmethod=syntax: -->
-- 
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