[R] Can someone Help in nls() package

[Spencer Graves]

	  When I tried to run your example, I got the following:

Error in func(times[1], y, parms) : object "Cum2" not found

	  While I couldn't replicate your error, I can tell you that the reason 
"print(coef(fit))" gave the error it did was because "nls" refuses to 
return anything when it encounters an error.

	  If it were my problem, I might write a least-squares wrapper and give 
it to "optim(..., hessian=T)", as optim will still return an answer when 
it seems overparameterized, etc.;  in that case, computing the 
eigenvalues and vectors of the hessian can help identify the problem. 
If "optim" also generated an error like "Missing value or an infinity 
produced", I might modify 'f' to print its arguments and output.  From 
that, I can usually figure out what I want to do about that.

	  hope this helps.
	  spencer graves

Raja Jayaraman wrote:

> Hello R-Community,
> we are running aprogram to fit Non-linear differential equations to Aphid
> population Data and to estimate the birth and death parameters,
> here is the code:
> 
> dat<-data.frame(Time=c(0:60),Cur=c(5,6.2,59,39,38,44,20.4,19.4,34.2,35.4,38.2,48.2,55.4,113.2,
> 97,112,115,126,136.6,140.6,147.2,151.6,157.8,170,202,210.4,221.2,224.4,248.2,266,
> 277,291.4,392,461.2,470,418,410.8,395.6,365.2,189.4,43.4,33.2,32,29,26,26,25.6,24.6,
> 24,23.4,18.4,17.6,15.8,13.6,10.6,8.4,6.4,5.4,4.2,3.6,2.7))
> 
> times<-c(0:60)
> f <- function(t,xx,pars){
>  Cur<- xx[1]
>  Cum<- xx[2]
>  a <- pars[1]
>  b <- pars[2]
>  dCur <- a*Cur-b*Cur*Cum^2
>  dCum <- Cur
>  list(c(dCur,dCum))
> }
> 
> 
> require(nls)
> fit <- nls(Cur ~ lsoda(c(Cur=1,Cum=1), times, f, c(a=a, b=b))[,2],
>            data=dat,
>            start=list(a=2.5, b=.01),
>            trace=T
>            )
> print(coef(fit))
> 
> It runs the first iterations and shows the output, after the intial
> eveluation it send the following error message:
> 
> 92 :  2.50 0.01
> Error in numericDeriv(form[[3]], names(ind), env) :
>         Missing value or an infinity produced when evaluating the model
> In addition: There were 50 or more warnings (use warnings() to see the first 50)
> 
>>print(coef(fit))
> 
> Error in coef(fit) : object "fit" not found
> 
> Looking forward to hear soon
> Thanks
> Raj
> 
> 	[[alternative HTML version deleted]]
> 
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Spencer Graves, PhD
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