1 files changed, 29 insertions, 6 deletions
diff --git a/R/HS.solution.R b/R/HS.solution.R
index 4651a6a8..890ad8ff 100644
--- a/R/HS.solution.R
+++ b/R/HS.solution.R
@@ -1,6 +1,29 @@
-HS.solution <- function(t, parent.0, k1, k2, tb)
-{
-	parent = ifelse(t <= tb, 
-		parent.0 * exp(-k1 * t),
-		parent.0 * exp(-k1 * tb) * exp(-k2 * (t - tb)))
-}
+#' Hockey-Stick kinetics
+#' 
+#' Function describing two exponential decline functions with a break point
+#' between them.
+#' 
+#' @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 tb Break point. Before this time, exponential decline according to
+#'   \code{k1} is calculated, after this time, exponential decline proceeds
+#'   according to \code{k2}.
+#' @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) HS.solution(x, 100, 2, 0.3, 0.5), 0, 2, ylim=c(0,100))
+#' 
+#' @export
+HS.solution <- function(t, parent.0, k1, k2, tb)
+{
+	parent = ifelse(t <= tb, 
+		parent.0 * exp(-k1 * t),
+		parent.0 * exp(-k1 * tb) * exp(-k2 * (t - tb)))
+}