[Wrf-users] reproducing identical results on different machines/compilers

[HONG]

Hi Marc

You are experiencing the famous chaotic nature of the atmosphere caused by the software system dependency 
, which was noted earlier by Prof. Lorenz. Bit-wise exact output for different number of CPUs on a MPI platform would 
be a necessary condition for bug-free. Object measure of the tolerance in differences due to dissimilar software 
could be rather difficult in regional models due to another factor in lateral boundary forcing.
The attached is a paper dealing with this issue in a global model.

Cheers,

songyou



2014. 3. 22., 오전 1:30, "Marcella, Marc" <MMarcella at AIR-WORLDWIDE.COM> 작성:

> Hi all,
> 
> I had a question about wrf and compiler/machine differences that I was hoping to get some clarity on.  I am trying to run the same set of wps/wrf compiled executables on two different machines (the libraries for the machine in which the .exe’s were not compiled on were placed in the exact same location as those on the machine in which the .exe’s were configured/compiled on, hence they run just fine).  So essentially, the only difference is the actual machine hardware being used. 
>  
> For metgrid.exe and real.exe, the results between the two machines are identical, however even with identical met_ems and wrfinput/wrfbdy files, the wrf results are different.  By day 58 or so the average  differences in TA and especially precipitation, are quite large (on the order of 1-2mm/day).  I am trying to run this over Southeast Asia where there is a lot of cumulus convection.  But, I wanted to check if this is to be expected to observe such large differences?   I did do a quick internet and forum search but couldn’t find specific work documenting this.  And, I wanted to see if there was a way in the compiling of the code (via a flag, etc that one can add) to get identical results across machines or even compilers?  I ask because what is interesting is that running an identical CCSM.exe on the two machines will yield identical CAM results on the two different machines. 
> 
> Any help or insight you could lend would be greatly appreciated.
> 
> Thanks,
> Marc
>  
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