> 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>
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