Hello. I have a script in which I repeatedly fit a nonlinear regression to
a series of data sets using nls and the port algorithm from within a loop.
The general structure of the loop is:
for(i in 1:n){
extract relevant vectors of dependent and independent variables
estimate starting values for Amax and Q.LCP
fit<-nls(photosynthesis~fit.Mitcherlich(irradiance,Amax,LCP,Q.LCP),data=temp
,
start=list(Amax=Astart,Q.LCP=x,LCP=33),control=list(maxiter=100,tol=5e-4),
na.action=na.omit,trace=T,algorithm="port",lower=c(0,0,0))
}
Despite trying to estimate good starting values, the nls function
occasionally experiences problems with convergence. When this happens the
function stops and prints an error message, thus preventing the loop from
continuing. Is there some what of detecting the convergence problem while
preventing the nls function from stopping when this happens, so that the
loop can continue?
Bill Shipley
North American Editor, Annals of Botany
Département de biologie
Université de Sherbrooke
Sherbrooke (Québec) J1K 2R1
Canada
(819) 821-8000, poste 62079
(819) 821-8049 FAX
http://pages.usherbrooke.ca/jshipley/recherche/
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