Message-ID: <x2wump8zqd.fsf@biostat.ku.dk>
Date: 2002-12-04T18:24:05Z
From: Peter Dalgaard
Subject: can this happen?
In-Reply-To: <Pine.A41.4.44.0212040841570.81760-100000@homer37.u.washington.edu>
Thomas Lumley <tlumley@u.washington.edu> 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
~~~~~~~~~~ - (p.dalgaard@biostat.ku.dk) FAX: (+45) 35327907