[Rd] can this happen?
Peter Dalgaard BSA
Wed Dec 4 18:24:05 2002
Thomas Lumley <firstname.lastname@example.org> writes:
> This is basically a question about where to start looking for a problem.
> I have a program that gives slightly different results on two Windows
> computers. It is a reasonably complicated numerical optimisation, with
> iterative calls to optim().
> The two computers both run Windows 2000. On each computer I get the same
> results in two different versions of R (1.5.1 and 1.6.0 on one, 1.5.1 and
> 1.6.1 on the other, the standard binaries), and the results are stable
> from run to run on each machine. There's nothing lurking in the workspace.
> One computer has a 2GHz Pentium 4 cpu, the other has a 0.75GHz Pentium 3.
> I think the problem is with the Pentium 4 machine, since it's giving
> occasional errors due to NaNs in internal parts of optim that I don't
> understand, but the fault could quite possibly be in my understanding. A
> good-quality dual Pentium 4 Linux system doesn't give these internal
> errors in optim and seems to give the same results as the Pentium 3
> machine (I haven't checked that they are all identical).
I believe that there's a lot of FP activity inside msvcrt.dll (if I
remember the name correctly) so if that isn't the same between the
machines, it might explain things.
O__ ---- Peter Dalgaard Blegdamsvej 3
c/ /'_ --- Dept. of Biostatistics 2200 Cph. N
(*) \(*) -- University of Copenhagen Denmark Ph: (+45) 35327918
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