[cam-users] pgf90 compiler differences

[Norm Wood]

David,

Thanks for the reply.

On 15 Jul., David Noone wrote:
> 
> I believe one should expect differences to the limit of numerical
> precision (as the intrinsic math libraries, etc., will do the math ever
> so slightly differently) - recall there is some discussion of this in
> the users guide. Does this sound like what you see?

No, I don't think so, but my expectations may be a bit naive.  In many
cases, the differences I'm seeing are in the 6th - 7th decimal place.
That's several decimal places worse than I'd expected with double
precision arithmetic, allowing for some progressive loss of
precision over the course of a calculation.  

> time step will be particularly sensitive. One test might be to use the
> "adiabatic physics" (?).

Yes, that might help isolate the particular calculations that are
contributing to the differences.

Portland Group have also suggested some tests I can do that are supposed to
put the version 4.0-2 and the version 5.0-1 executables on more equal
numerical footing.   Hopefully, this will resolve the differences.

Norm

-- 
Norm Wood

     Department of Atmospheric Science
     Colorado State University
     norm@atmos.colostate.edu
     phone:  970-491-8587