Christian, Thank you for the response and hint. This is essentially what I ended up doing but I ran into several problems using nls(). I have since switched to optim() and seem to be having better luck. Again, thank you for your help.
> -----Original Message----- > From: Christian Ritz [mailto:r...@life.ku.dk] > Sent: Saturday, April 17, 2010 2:45 PM > To: Derek Ogle > Cc: r-help@r-project.org > Subject: Re: [R] piecewise nls? > > Hi Derek, > > have a look at the following made-up example: > > f1 <- function(x){2*x} > f2 <- function(x){-10*x+1} > > x<-rnorm(10) > x > (x<0)*f1(x) > (x>=0)*f2(x) > (x<0)*f1(x) + (x>=0)*f2(x) > > > > Therefore I suggest you should specify the model as follows: > > yourNLSmodel <- nls(Y ~ (X<Z) * f(X,a,b,c) + (X>=Z) * g(X,a,d,e), data > = myData, ...) > > > > Christian ______________________________________________ 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.
