#' Double First-Order in Parallel kinetics #' #' Function describing decline from a defined starting value using the sum of #' two exponential decline functions. #' #' @param t Time. #' @param parent.0 Starting value for the response variable at time zero. #' @param k1 First kinetic constant. #' @param k2 Second kinetic constant. #' @param g Fraction of the starting value declining according to the first #' kinetic constant. #' @return The value of the response variable at time \code{t}. #' @references FOCUS (2006) \dQuote{Guidance Document on Estimating Persistence #' and Degradation Kinetics from Environmental Fate Studies on Pesticides in #' EU Registration} Report of the FOCUS Work Group on Degradation Kinetics, #' EC Document Reference Sanco/10058/2005 version 2.0, 434 pp, #' \url{http://esdac.jrc.ec.europa.eu/projects/degradation-kinetics} #' @examples #' #' plot(function(x) DFOP.solution(x, 100, 5, 0.5, 0.3), 0, 4, ylim = c(0,100)) #' #' @export DFOP.solution <- function(t, parent.0, k1, k2, g) { parent = g * parent.0 * exp(-k1 * t) + (1 - g) * parent.0 * exp(-k2 * t) }