[Rd] nls (with SSlogis model and upper limit) never returns (PR#10544)

[Gabor Grothendieck]

On my Windows Vista system it returns an answer:

> values <- list(x=10:30, y=c(23.85, 28.805, 28.195, 26.23, 25.005, 20.475,
+ 17.33, 14.97, 11.765, 8.857, 5.3725, 5.16, 4.2105, 2.929, 2.174, 1.25, 1.0255,
+ 0.612, 0.556, 0.4025, 0.173))
> y.max <- max(values$y)
> model <- nls(y ~ SSlogis(x, asym, xmid, scal), data=values, algorithm="port",
+ start=c(asym=y.max, xmid=15, scal=-0.5), upper=c(y.max, Inf, Inf))
> model
Nonlinear regression model
  model:  y ~ SSlogis(x, asym, xmid, scal)
   data:  values
  asym   xmid   scal
28.805 17.268 -2.223
 residual sum-of-squares: 32.02

Algorithm "port", convergence message: relative convergence (4)
> R.version.string # Vista
[1] "R version 2.6.1 Patched (2007-12-06 r43610)"


On Jan 4, 2008 9:45 AM,  <hendrik.weisser at gmx.net> wrote:
> Full_Name: Hendrik Weisser
> Version: 2.6.1
> OS: Linux
> Submission from: (NULL) (139.19.102.218)
>
>
> The following computation never finishes and locks R up:
>
> > values <- list(x=10:30, y=c(23.85, 28.805, 28.195, 26.23, 25.005, 20.475,
> 17.33, 14.97, 11.765, 8.857, 5.3725, 5.16, 4.2105, 2.929, 2.174, 1.25, 1.0255,
> 0.612, 0.556, 0.4025, 0.173))
> > y.max <- max(values$y)
> > model <- nls(y ~ SSlogis(x, asym, xmid, scal), data=values, algorithm="port",
> start=c(asym=y.max, xmid=15, scal=-0.5), upper=c(y.max, Inf, Inf))
>
> This used to work with R version 2.5.1 patched.
> The problem does _not_ occur if the parameter "scal=-0.5" in the nls call is
> changed, e. g. to "scal=-0.6" or "scal=-0.4".
> Simply calling "model <- nls(y ~ SSlogis(x, asym, xmid, scal), data=values)"
> also works, but this does not use the upper bound for the asym parameter, which
> was the point.
>
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