Swietanowski Artur writes:
>
> This kind of reasoning goes nowhere. If the rational argument that
> the precision is better, thus the (new) product is also better
> doesn't work in this case, how can you ever add new optimizations
> to the language or, e.g., better precision FPU's?
For models as complicated as our forecasting model, sometimes the only
way to ensure a hardware/compiler upgrade has worked it to get bit
comparibility. For climate work, exact repeatability across many
years is essential. One of the biggest issues of our C90 - T3E
upgrade and MPP conversion was the precision changes due to the
change in number format from Cray to ieee, and the calculation order
changes required for MPP.
This disruption can be accepted for such a major hardware and
design philosophy change, but any suggestion that language changes
would also affect reproducability would worry us a lot, and
disuade us from using new compilers or language features. We are
introducing large Fortran 90 systems into operational use now,
but the main forecast model is still resolutely f77 for this
kind of reason.
John
--
John Bray, Room 337, Numerical Weather Prediction, UK Met Office
Work: [log in to unmask], http://fr0400/~frjb (internal only)
+ 44 (0) 1344 854035 (voice), + 44 (0) 1344 854026 (fax)
Home: http://www.cix.co.uk/~vicarage/
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