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ls1mardyn / ls1-mardyn

ls1-MarDyn is a massively parallel Molecular Dynamics (MD) code for large systems. Its main target is the simulation of thermodynamics and nanofluidics. ls1-MarDyn is designed with a focus on performance and easy extensibility.
http://www.ls1-mardyn.de
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Slightly different results for SEQ and PAR #335

Open HomesGH opened 2 months ago

HomesGH commented 2 months ago

Describe the bug

Different results (e.g. Epot or p) are computed depending on the number of ranks used. OpenMP does not have any effect on the result (as expected).

To Reproduce

Steps to reproduce the behavior:

  1. Choose e.g. adios/write/config_mix.xml example
  2. Run simulation for 10 steps with SEQ/PAR and different ranks
The values after 10 steps: Version Epot p
SEQ -15068.6 -3.72075
PAR 1 rank -15068.6 -3.72075
PAR 1 rank + OMP -15068.6 -3.72075
PAR 2 ranks -15071.4 -3.72071
PAR 2 ranks + OMP -15071.4 -3.72071
PAR 4 ranks -15071.4 -3.72071
PAR 8 ranks -15071.9 -3.72142

Additional context

Maybe this is no proper bug but due to inaccuracies in the communication plus the chaotic system.