Dear support, I’m a new lammps user and I analyzed some examples; I found some difference between scalar and parallel version, why the output of simulations are different?
Regard.
Nicola Varini
There could be many reasons - initialization of velocites, application
of a Langevin thermostat with different random numbers, round-off,
drift of 2 systems apart over long times. LAMMPS makes no guarantee
that 2 simulations on different numbers of procs will give identical
answers.
Steve
There could be many reasons - initialization of velocites, application
of a Langevin thermostat with different random numbers, round-off,
drift of 2 systems apart over long times. LAMMPS makes no guarantee
that 2 simulations on different numbers of procs will give identical
answers.
... not to mention the fact that floating point numbers are
_not_ associative. in general, (a+b)+c != a+(b+c)
thus whenever you have a different distribution of
atoms and therefore sum up contributions of forces and
energies in a different order, you will not get
the exact same numbers, which in turn will lead
to (exponentially) diverging trajectories.
cheers,
axel.
Hi.
Could you be more specific about what outputs are different? Are any
Physical quantities at equilibrium different from the expected
statistical variance?
Regards,
Manoj
The top of the doc/Section_errors.html page has a brief
discussion of this. Everything should be statistically the
same at equilibrium.
Steve