nmle: gnls freezes on difficult case
On Thu, 18 Oct 2007, Nicholas Lewin-Koh wrote:
Hi, Following up on my own post, if in gnlsControl I specify opt='optim' gnls exits quite nicely, with an error, which is what I would expect. Is this a bug in nlminb?
Possibly, but complex algorithms can loop for non-bug reasons. I don't feel motivated to explore it in detail, but if you want/are able to, please let us know what you find. I have always found optim to work better in package nlme than nlminb (and I know others who have the same experience).
Nicholas tt<-gnls(response~SSllogis(conc,A,B,xmid,scal),tdat,start=start,weights=varPower(),verbose=TRUE,control=gnlsControl(opt='optim')) **Iteration 1 GLS step: Objective: 29.04254varStruct parameters: power 0.3373206 NLS step: RSS = 0 model parameters:-0.799941 8.99983 -0.522623 212.314 iterations: 2 Convergence: params varStruct 1.172208 1.000000 Error in optim(c(coef(gnlsSt)), function(gnlsPars) -logLik(gnlsSt, gnlsPars), : initial value in 'vmmin' is not finite In addition: Warning messages: 1: In log(xmid) : NaNs produced 2: In log(xmid) : NaNs produced 3: In log(xmid) : NaNs produced
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