[R] nls: Missing value or an Infinity produced when evaluating the model

[Christian Ritz]

Hi Angel,

I tried reparametrise your model, setting:

BirthMass^0.25=u
MaxMass^0.25=v

and giving the following formula in R:

GrowthModel<-nls(BodyMass~(((1-(1-u/v)*exp(-a*Time/(4*v)))^4)*v^4),data=grow
th,start=c(u=4,v=5,a=1.5),trace=TRUE)

And this works for me, but the u estimate is negative (not significantly
different from 0, though).

Christian

----- Original Message -----
From: "Angel -" <angel_lul at hotmail.com>
To: <r-help at stat.math.ethz.ch>
Sent: Wednesday, April 23, 2003 2:29 PM
Subject: [R] nls: Missing value or an Infinity produced when evaluating the
model


> Hi,
> I am trying to fit a sigmoid curve to some data with nls but I am getting
> into some trouble.
> Seems that the optimization method is getting down to some parameter
> estimates that make the equation unsolvable. This is an example:
>
...