Hello there,
I am using NLS for fitting a complex model to some data to estimate a couple
of the missing parameters. The model is -
y ~ (C+((log(1-r))*exp(-A*d)*(-1+r+exp(d*(A-B)))/(r*(-A*d+d*B+log(1-r)))))
where A, B and C are unknown.
In order to test the model, I generate data by setting values for all
parameters and add some noise (C).
A <- 20
B <- 500
r <- 0.6881
d <- (1:1000)/1000
y ~
(rnorm(d)*0.005)+(((log(1-r))*exp(-A*d)*(-1+r+exp(d*(A-B)))/(r*(-A*d+d*B+log(1-r)))))
I use Deoptim package to pick the optimum starting values. The model works
fine in most cases, but every now and again, I get the following error -
Error in numericDeriv(form[[3L]], names(ind), env) :
Missing value or an infinity produced when evaluating the model
Any suggestions on how I can resolve this? Can you suggest a better way for
picking the starting parameters?
Thanks,
Diviya
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