[R] curve fitting to data

[Peter Ehlers]

Pascale,

If you do want an nls fit with the associated error structure
assumptions, check ?SSlogis.

  fm <- nls(y ~ SSlogis(x, Asy, xmid, scal))
  summary(fm)
  xx <- seq(123, 248, length = 101)
  yy <- predict(fm, list(x = xx))
  plot(x, y)
  lines(xx, yy)

  -Peter Ehlers

Gabor Grothendieck wrote:
> A simple y vs log(x) fit seems to work pretty well here:
> 
> fit <- lm(y ~ log(x))
> summary(fit)
> 
> plot(y ~ log(x))
> abline(fit)
> 
> On Fri, Dec 4, 2009 at 9:06 AM, Pascale Weber <pascale.weber at wsl.ch> wrote:
> 
>> Hi to all
>>
>> This is the first time I am quoting a question and I hope, my question is
>> not too basic...
>>
>> For the following data, I wish to draw a fitted curve.
>>
>> x <- c(123,129,141,144,144,145,149,150,158,159,163,174,183,187,242,248)
>>
>> y <-
>> c(14.42,26.96,31.3,19.95,36.36,15.4,24.76,35.39,28.07,40.97,26.23,42.83,46.53,14.79,49.18,48.08)
>>
>> If I plot the data, it looks somehow that a logistic function would render
>> good results.
>>
>> My questions are:
>>
>> How do I use
>>  nls and/or SSlogis (or other)
>> to fit the curve?
>>
>> How can I see the summary statistics of the fit?
>>
>> How do I finally draw the line to my x,y (untransformed data) plot?
>>
>> Any help would be highly appreciated.
>>
>> Thank you and cheers
>>
>> Pascale
>>
>> --
>> ____________________________________..___________________
>>
>> Dr. Pascale Weber
>> Swiss Federal Research Institute WSL
>> Zuercherstrasse 111
>> CH-8903 Birmensdorf
>> Switzerland
>>
>> ______________________________________________
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>>
> 
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> 
> ______________________________________________
> R-help at r-project.org mailing list
> https://stat.ethz.ch/mailman/listinfo/r-help
> PLEASE do read the posting guide http://www.R-project.org/posting-guide.html
> and provide commented, minimal, self-contained, reproducible code.
> 
>