On Fri, Oct 16, 2009 at 7:09 PM, Michael A. Gilchrist <mi...@utk.edu> wrote: > Hello, > > I'm having problems creating and using a selfStart model with nlme. > Briefly, I've defined the model, a selfStart object, and then combined them > to make a selfStart.default model. > > If I apply getInitial to the selfStart model, I get results. However, if I > try usint it with nls or nlsList, these routines complain about a lack of > initial conditions. > > If someone could point out what I'm doing wrong, I'd greatly appreciate it.
Thanks for providing the code. Could you also provide some data as a test case? > > Details: > ## Nonlinear model I want to fit to the data > const.PBMC.tcell.model <- function(B0, t, aL, aN, T0){ > > Tb0 = B0; > > x = exp(-log(aL) + log(T0*aL+(-1+exp(t * aL))*Tb0 * aN) - t * aL); > > return(x); > } > > > ##Define selfStart routine > const.PBMC.tcell.selfStart<- function(mCall, LHS, data){ > > t0 = 0; > t1 = 24; > t2 = 48; > > ##Get B0 Value > B0 = data[1, "B0"]; > > T0 = mean(data[data$Time==t0, "Count"]); > T1 = mean(data[data$Time==t1, "Count"]); > T2 = mean(data[data$Time==t2, "Count"]); > > if(T0 < T2){ ##increase -- doesn't work > stop(paste("Error in const.PBMC.tcell.start: T0 < T2 for data: ", data[1, > ])); > > } > ##Estimate aL based on exponential decline from t=0 to t=24 > aLVal = -(log(T1) - log(T0))/(t1-t0); > > ##Estimate aNVal based on final value > aNVal = aLVal*T2/B0; > > values = list(aLVal, aNVal, T0); > names(values) <- mCall[c("aL", "aN", "T0")]; #mimic syntax used by P&B > return(values) > } > > > > ##Now create new model with selfStart attributes > const.PBMC.tcell.modelSS<- selfStart(model = const.PBMC.tcell.model, > initial=const.PBMC.tcell.selfStart) > > > ##Test routines using getInitial -- This works >> >> getInitial(Count ~ const.PBMC.tcell.modelSS(B0, Time,aL, aN, T0), data = >> tissueData) > > [1] 0.05720924 > $aL > [1] 0.05720924 > > $aN > [1] 0.1981895 > > $T0 > [1] 1360.292 > > ##Now try to use the SS model -- this doesn't work >> >> nls(Count ~ const.PBMC.tcell.modelSS(B0, Time,aL, aN, T0), data = >> tissueData) > > Error in numericDeriv(form[[3L]], names(ind), env) : > Missing value or an infinity produced when evaluating the model > In addition: Warning message: > In nls(Count ~ const.PBMC.tcell.modelSS(B0, Time, aL, aN, T0), data = > tissueData) : > No starting values specified for some parameters. > Intializing 'aL', 'aN', 'T0' to '1.'. > Consider specifying 'start' or using a selfStart model > > ______________________________________________ > R-help@r-project.org mailing list > https://stat.ethz.ch/mailman/listinfo/r-help > PLEASE do read the posting guide http://www.R-project.org/posting-guide.html > and provide commented, minimal, self-contained, reproducible code. > ______________________________________________ R-help@r-project.org mailing list https://stat.ethz.ch/mailman/listinfo/r-help PLEASE do read the posting guide http://www.R-project.org/posting-guide.html and provide commented, minimal, self-contained, reproducible code.