[gmx-users] floating point exception in .xtc file

[Mark Abraham]

On 9/06/2012 7:27 AM, Christopher Neale wrote:
> Dear Users:
>
> I have a 500 ns trajectory of 65 GB that gives a floating point 
> exception when I run it through gmxcheck or trjcat (generated and 
> analyzed with gromacs 4.5.5). Has anybody encountered this? I ran 
> mdrun with -append so this is the xtc resulting from months of 
> simulation of a 1,000,000 atom system. If I run trjconv -f md.xtc -b 
> 200000, where the floating point exception occurred around t=180000 ps 
> in gmxcheck, then I can extract the readable frames and repair around 
> the damaged section. Still, I'd rather not lose any data and I had 
> thought that the new default -append option to mdrun checked for these 
> types of problems at runtime.
>

I've no idea what might happen when some file-system transient occurs 
mid-simulation, but if mdrun has managed to compute a checksum on an 
incomplete file and stored that in the checkpoint, then the append 
mechanism can be none the wiser. The check upon restart is that the 
checksum matches, not that the checksum is computed on a file whose 
properties would satisfy gmxcheck.

Note also that some file systems that do not support file locking and 
this is known to cause issues (Redmine 924), but I don't know if this is 
related to your observation.

Mark
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