Broadcast seed to all ranks

[joaander]

Original report by me.

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Subtle correlations may occur when the seed is different on different ranks of an MPI simulation. HOOMD should protect users who use things like the system time, pid, job id, or other means to set their seed. The solution is to broadcast the seed from rank 0 to all other ranks.

See pull request #298 which implements this for DPD, where different seeds leads to worse problems.

We should also do the same thing for all other places in hoomd that use seeds (if they don't already take care of this). Namely, HPMC integrators, hpmc.compute.free_volume, hpmc.update.boxmc, hpmc.update.wall, hpmc.update.muvt, md.force.active, md.integrate.langevin, and md.integrate.brownian.

[joaander]

Merged in alexchunha/hoomd-blue/fix_langevin_seed_mpi (pull request #315)

refs #233

Fixed RNG seeding issues with the Langevin/Brownian integrators when MPI is enabled

Approved-by: Joshua Anderson joaander@umich.edu

[joaander]

Still to do:

• HPMC integrators
  • hpmc.compute.free_volume
  • hpmc.update.boxmc
  • hpmc.update.wall
  • hpmc.update.muvt
  • md.force.active

[joaander]

Broadcast seed to all ranks in remaining methods

This brodcast is needed because hoomd assumes that the seed is identical across all ranks, and users sometimes provide different seeds to different ranks.

refs #233

[joaander]

Merged in broadcast-seed (pull request #338)

Broadcast seed to all ranks in remaining methods

fixes #233