From: James Salsman <james_at_bovik.org>

Date: Sat 23 Apr 2005 - 18:04:20 EST

R-help@stat.math.ethz.ch mailing list

https://stat.ethz.ch/mailman/listinfo/r-help PLEASE do read the posting guide! http://www.R-project.org/posting-guide.html Received on Sat Apr 23 18:10:27 2005

Date: Sat 23 Apr 2005 - 18:04:20 EST

I'm trying to fit a Gompertz sigmoid as follows:

gm <- nls(y ~ a+b*exp(-exp(-c*(x-d))), start=c(a=?, b=?, c=?, d=?))

How can I pick starting values that don't result in singular gradients?

step factor 0.000488281 reduced below `minFactor' of 0.000976563

And this:

> getInitial(y ~ SSgompertz(x,a,b,c),data=data.frame(x=x,y=y))

Error in nls(y ~ cbind(1, 1 - exp(-exp(lrc) * x)), data = xy, start =
list(lrc = as.vector(log(-coef(lm(log(abs(y - :

singular gradient

Thanks for any help.

Sincerely,

James Salsman

R-help@stat.math.ethz.ch mailing list

https://stat.ethz.ch/mailman/listinfo/r-help PLEASE do read the posting guide! http://www.R-project.org/posting-guide.html Received on Sat Apr 23 18:10:27 2005

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