[R] a bug and a question

[Guido Masarotto]

On Wed, Jan 13, 1999 at 11:15:00AM +0100, Peter Dalgaard BSA wrote:
> Jim Lindsey <jlindsey at alpha.luc.ac.be> writes:
> 
> > The question: I am getting various reports that R under MS-Windows and
> > X-Windows/Linux on the same machine behaves very differently for nlm
> > convergence in my libraries. Under Linux, convergence is easy with
> > many starting values, but under MS they have to be very close to the
> > MLE. Does anyone have experience with this and or an explanation?
> > Is the math used different in the two systems?
> >   Jim
> 
> Not entirely unlikely. The FPU should be the same of course, but the C
> and math libraries link to a Microsoft DLL, which I have heard people
> speak badly about before. 
> 
> Particularly the IEEE exception handling could be causing trouble if
> an iterative method wanders near the boundary of a functions domain.
> That is pure speculation, though, I suppose Guido and Brian will know
> more.
  
  I think Peter points to the origin of the problem.
  Consider that under MSWindows: (i) the source is the Unix one
  (at least for  the computational part); 
  (ii) the compiler is one that many of us are using under Unix
  (egcs 1.1); (iii) the assembler is more or less the same used
  under Linux (or other ix386/Unix) BUT the libc and libm
  are  completly different.
  
  Anyway, I would like to get a couple of examples to play with.
  
  g.
  (ps) I have just tested Machine()$double.rounding, but is
  equal to 5 at least on my son's Win95 machine (the one
  from which I am connected in this moment) and, at least in this
  moment.





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