> Take a look at the predicted values at your starting fit: there's a > discontinuity at 0.4, which sure makes it look as though overflow is > occurring. I'd recommend expanding tanh() in terms of exponentials and > rewrite the prediction in a way that won't overflow. > > Duncan Murdoch
Hi Duncan, Thank you for your suggestion. I wrote a function "mytanh" and nls terminates a bit later with another error message: Error in nls(data = dd, y ~ 1/2 * (1 - mytanh((x - ttt)/1e-04) * exp(-x/tau2)), : number of iterations exceeded maximum of 50 How can i fix that? Kind regards, Jonas ============================ R CODE STARTS HERE ======= mytanh <- function(x){ return(x - x^3/3 + 2*x^5 /15 - 17 * x^7/315) } t <- seq(0,1,0.001) t0 <- 0.5 tau1 <- 0.02 yy <- 1/2 * ( 1- tanh((t - t0)/0.0001) * exp(-t / tau1) ) + rnorm(length(t))*0.001 plot(x=t, y=yy, pch=18) dd <- data.frame(y=yy, x=t) nlsfit <- nls(data=dd, y ~ 1/2 * ( 1- mytanh((x - ttt)/0.0001) * exp(-x / tau2) ), start=list(ttt=0.5, tau2=0.02) , trace=TRUE) ============================ R CODE ENDS HERE ======= -- Jonas Stein <n...@jonasstein.de> ______________________________________________ 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.