[R] Envelope curve for scatterplot

[frauke]

Hi, 

to be concise, let me start with my problem: I have a scatterplot that I
want to fit an envelope curve to. The picture of the scatterplot is below. 
<http://r.789695.n4.nabble.com/file/n4673965/day_DryPond1_1_rid03.jpg> 

I have 140 of these plots that I need to compare. Rather than to visually
compare all the plots, I would like to compare the parameters of the curves
enveloping them. 
Possible parameters could be the x-value when the curves starts dropping
down, the y-value that is the asymptote of the enveloping curve and some
parameter describing the curve itself. 

After some googling, I still have no idea how to approach this. Could
anybody please give me a hint where to start?

I attached the data. The plot was generated using the code below(I plotted
the 2nd column against columns 15, 16, 17. )
  plot(output[,2],(1-output[,15]),xlab="Precip [inch]",
ylab="Eff.",ylim=c(-1,1),xlim=c(0,8),pch=18)
  points(output[,2],(1-output[,16]),col=2,pch=18)
  points(output[,2],(1-output[,17]),col=3,pch=18)
DryPond1_1_rid03_24.txt
<http://r.789695.n4.nabble.com/file/n4673965/DryPond1_1_rid03_24.txt>  

Any help would be much appreciated. 

Thank you! Frauke





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