What does your error distribution look like? Have you tried any time series analysis on your data? Your information is too little for us to give any concrete directions.

Regards,
Indrajit



________________________________
 From: rch4 <rch4@geneseo.edu>
To: r-help@r-project.org 
Sent: Wednesday, November 30, 2011 8:37 AM
Subject: Re: [R] Negative exponential fit
 
Thank you for your suggestions. We are currently working with an the nls
function, but are having trouble getting a curve that fits our data. We have
tried using the following formula:

mod1 = nls(time~a*exp(b*(date)), start=list(a=4.178,b=-1.18))
av=mdate
bv=predict(mod1,list(mdate=av))
length(av)
length(bv)
lines(av,bv)

We've been trying to work with your suggestions but aren't having any luck
thus far. We've also tried to exponentiate the times in hopes they would
produce a better fit, but can't seem to produce a formula without getting
errors. 

Any further help/explanations would be appreciated. 

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