I adapted a selfStart function and the lower bounds are not working. The parameter "b" is negative, whereas I would like the lower bound to be zero. Any ideas? Thanks.
Here is my code (I am still figuring out how to easily make replicable examples): A<-1.75 mu<-.2 l<-2 b<-0 x<-seq(0,18,.25) create.y<-function(x){ y<-b+A/(1+exp(4*mu/A*(l-x)+2)) return(y) } ys<-create.y(x) yvec<-(rep(ys,5))*(.95+runif(length(x)*5)/10) Trt<-factor(c(rep("A1",length(x)),rep("A2",length(x)),rep("A3",length(x)),rep("A4",length(x)),rep("A5",length(x)))) Data<-data.frame(Trt,rep(x,5),yvec) names(Data)<-c("Trt","x","y") NewData<-groupedData(y~x|Trt,data=Data) powrDpltInit <- function(mCall, LHS, data) { xy <- sortedXyData(mCall[["x"]],LHS,data) A.s <- max(xy$y)-min(xy$y) mu.s <- A.s/7.5 l.s <- 0 b.s <- max(min(xy$y),0.00001) value <- c(A.s, l.s, mu.s, b.s) #function to optimize func1 <- function(value) { A.s <- value[1] mu.s <- value[2] l.s <- value[3] b.s <- value[4] y1<-rep(0,length(xy$x)) # generate vector for predicted y (y1) to evaluate against observed y for(cnt in 1:length(xy$x)){ y1[cnt]<- b.s+A.s/(1+exp(4*mu.s/A.s*(l.s-x[cnt])+2))} #predicting y1 for values of y evl<-sum((xy$y-y1)^2) #sum of squares is function to minimize return(evl)} #optimizing oppar<-optim(c(A.s , mu.s , l.s , b.s),func1,method="L-BFGS-B", lower=c(0.0001,0.0,0.0,0.0), control=list(maxit=2000,trace=TRUE)) #saving optimized parameters value<-c(oppar$par[1L],oppar$par[2L],oppar$par[3L],oppar$par[4L]) names(value) <- mCall[c("A","mu","l","b")] value } SSpowrDplt<-selfStart(~b+A/(1+exp(4*mu/A*(l-x)+2)),initial=powrDpltInit, parameters=c("A","mu","l","b")) test1<-nlsList(SSpowrDplt,NewData) coef(test1) ----- In theory, practice and theory are the same. In practice, they are not - Albert Einstein -- View this message in context: http://r.789695.n4.nabble.com/Lower-bounds-on-selfStart-function-not-working-tp3999231p3999231.html Sent from the R help mailing list archive at Nabble.com. ______________________________________________ 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.