[R] Newbie Question: Shifted Power Fit?

[Uwe Ligges]

Bill Simpson wrote:
> 
>>I have multiple sets of 2D data that are coming from
>>distributions of the form:
>>
>>y = A(x-C)^B     (Eq.1)
>>
>>I am trying to estimate for each set the best values 
>>of A, B, and C so that Eq.1 will be the best fit for
>>the data. I guess that it should be easy to do, but
>>I lack the experience :(
>>
> Do this:
>  library(nls)
>  ?nls
> Here is an example
> x<-3:13
> y<-2*(x-3)^1.5  #fake perfect data
> fit<-nls(y~a*(x-b)^c,start=list(a=2,b=3,c=1.5))
> 
> This gives:
> Error in numericDeriv(form[[3]], names(ind), env) : 
>         Missing value or an Infinity produced when evaluating the model
> Maybe others here can say what is wrong.
> 
> I personally tend to use nlm() and minimize the sum of squared errors...
> 
> Once it works do summary(fit) to see the fit results.
> 
> Bill
> 
> -.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-
> r-help mailing list -- Read http://www.ci.tuwien.ac.at/~hornik/R/R-FAQ.html
> Send "info", "help", or "[un]subscribe"
> (in the "body", not the subject !)  To: r-help-request at stat.math.ethz.ch
> _._._._._._._._._._._._._._._._._._._._._._._._._._._._._._._._._._._._._._._._
> 



-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-
r-help mailing list -- Read http://www.ci.tuwien.ac.at/~hornik/R/R-FAQ.html
Send "info", "help", or "[un]subscribe"
(in the "body", not the subject !)  To: r-help-request at stat.math.ethz.ch
_._._._._._._._._._._._._._._._._._._._._._._._._._._._._._._._._._._._._._._._