[gmx-users] numerical reproducibility on Gromacs 2018.3 GPU

[Hubert Santuz]

Hi everyone,

I'm trying to get numerical identical results on a test system (di-alanine
in water) with Gromacs 2018.3 version with GPU. I'm doing 100 steps in NVE.

When I'm using GPU (gmx mdrun -nt 1 -nb gpu), I'm not getting exactly the
same results when I launch 2 separated times the same system (same mdp,
same gromacs version). The numerical values start to diverge at step ~1-2.
When I discard GPU (gmx mdrun -nt 1 -nb cpu), I can get the same exactly
results when I launch 2 separated times.

I tried to play with verlet-buffer-tolerance = 0.00000005 or
vdw-modifier/coulomb-modifier = None.
I also tried the "-reprod" option in mdrun.

Is this an expected behavior with GPU? I tried to search for documentation
about that without success.
Can I achieve identical numerical results with GPU in the same way as CPU?

Thanks in advance,
Hubert