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]] > > ______________________________________________ > R-help@stat.math.ethz.ch mailing list > https://stat.ethz.ch/mailman/listinfo/r-help > PLEASE do read the posting guide! http://www.R-project.org/posting-guide.html -- Spencer Graves, PhD Senior Development Engineer PDF Solutions, Inc. 333 West San Carlos Street Suite 700 San Jose, CA 95110, USA [EMAIL PROTECTED] www.pdf.com <http://www.pdf.com> Tel: 408-938-4420 Fax: 408-280-7915 ______________________________________________ R-help@stat.math.ethz.ch mailing list https://stat.ethz.ch/mailman/listinfo/r-help PLEASE do read the posting guide! http://www.R-project.org/posting-guide.html