[R] nls singular gradient ..as always..

[pakoun]

Hi all. Sorry for posting again such a topic but I went through previous 
posts but couldn't find a solution.

I use the following code to fit an exponential model to my data. I have 4
different datasets. For 3 datasets nls seems to work fine and I have no
error messages. But for 1 dataset I am getting the "world known" singular
gradient error.
 
   xfit.dNEE <-
nls(vario.dNEE~V*(1-exp(-1*dist/L)),data=ndat,start=list(V=vstart,L=lstart),trace=T)
     
I tried also with different starting values but still the same error...
Any help would be highly welcome.

Thank you in advance.



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