Function describing two exponential decline functions with a break point between them.
1 
t 
Time. 
parent.0 
Starting value for the response variable at time zero. 
k1 
First kinetic constant. 
k2 
Second kinetic constant. 
tb 
Break point. Before this time, exponential decline according
to 
The value of the response variable at time t
.
Johannes Ranke
FOCUS (2006) “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, http://focus.jrc.ec.europa.eu/dk
1  ## Not run: plot(function(x) HS(x, 100, 2, 0.3, 0.5), 0, 2, ylim=c(0,100))

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