I'm fitting some exponential data using nls
.
The code I'm using is:
fit <- nls(y ~ expFit(times, A, tau, C), start = c(A=100, tau=-3, C=0))
expFit
is defined as
expFit <- function(t, A, tau, C)
{
expFit <- A*(exp(-t/tau))+C
}
This works well for most of my data, for which the starting parameters provided (100, -3 and 0) work well. Sometimes, though, I have data that doesn't go well with those parameters and I get errors from nls
(e.g. "singular gradient" or things like that). How do I "catch" these errors?
I tried to do something like
fit <- NULL
fit <- nls(...)
if (is.null(fit))
{
// Try nls with other starting parameters
}
But this won't work because nls
seems to stop the execution and the code after nls
will not execute...
Any ideas?
Thanks nico