[Rd] Windows crash in confint() with nls fit (PR#8428)

[P Ehlers]

You don't actually need Ben's example. The problem occurs
also for the first example in ?nls if algorithm = "port" is
used.

Peter Ehlers

bolker at zoo.ufl.edu wrote:

> Duncan Murdoch wrote:
> 
>>I've found the problem, but someone who knows more about nls() will have 
>>to fix it.
>>
>>The problem is that in the demo code below, n1 ends up being an nls 
>>object, but n1$call$control is NULL.  profiler.nls() assumed that the 
>>nls object passed to it has a non-NULL element there, and doesn't check.
>>
>>I've fixed the code so now it doesn't crash, but it now dies with this 
>>error instead:
>>
>> > confint(n1)  ## boom
>>Waiting for profiling to be done...
>>Error in prof$getProfile() : 'control$maxiter' absent
>>
>>I'll commmit my change to R-devel and R-patched shortly.
>>
>>Duncan Murdoch
>>
> 
> 
>    thank you for the quick response!
> 
>     actually, I discovered I'm wrong -- bug affects Linux as well,
> gives a segmentation fault
> (I must have tried it without the algorithm="port" argument by
> accident.)  I've looked at the code but I regretfully concur
> that someone else will have to work on this -- I can hack nls
> so it reinserts a "control" element in n1$call, but $tol
> and $minFactor are explicitly deleted from the control list,
> and so we only get one step farther.  I don't know what assumptions
> nls_iter is really making and whether it's safe to make them
> when the port algorithm is being used or not ...
> 
>    My best guess at this point, poking around, is that profiler.nls
> in src/library/stats/R/nls-profile.R has to be changed in parallel
> with nls to call port_nlsb instead of nls_iter when the port
> algorithm is being used, but this is all getting a bit deep for
> me ...
> 
>     Ben
> 
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-- 
Peter Ehlers
Department of Mathematics and Statistics
University of Calgary