On 2011-04-11 13:29, Felix Nensa wrote:
Hi,
I am using nls to fit a non linear function to some data but R keeps giving
me "singular gradient matrix at initial parameter estimates" errors.
For testing purposes I am doing this:
### R code ###
x<- 0:140
y<- 200 / (1 + exp(17 - x)/2) * exp(-0.02*x) # creating 'perfect' samples
with fitting model
yeps<- y + rnorm(length(y), sd = 2) # adding noise
# results in above error
fit = nls(yeps ~ p1 / (1 + exp(p2 - x) / p3) * exp(p4 * x))
###
From what I've found in this list I think that my model is over-parameterized.
How can I work around that?
Take out p3; it's redundant.
Peter Ehlers
Thanks,
Felix
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