Remove Langevin noise correlation

[jngrad]

Fixes #3343

Description of changes:

• decoupled translational and rotational Langevin RNG seeds
• add a test for Langevin noise correlation
• cleanup docs

[jngrad]

@RudolfWeeber I can't get rotational-diffusion-aniso.py to pass on my machine without noise correlation, even after restoring the test to its state before your speed-up modifications. The outcome of the test also seems to be very sensitive on the numpy seed. You might want to have a look if CI fails.

[bindgens1]

I also had problems with the rotation tests in the modifications that @fweik did in #2957
More samples for the histogram didn't help solving the problem. However, I have no idea, if the issues are related to one another or if this is an independent issue.

[RudolfWeeber]

Please use kT <=1.5
@psci2195, do you know why the test doesn't work for higher temperatures?
Is there an assumption about Peclet numbers in the theory?

[jngrad]

@RudolfWeeber the failing dpd.py test does not fail on my machine, even within a docker container. The test is also extremely sensitive to the seed of the Langevin thermostat.

[fweik]

The failure is due to bad statistics. See #3360, there is no problem. Also this is just thermalized degrees of freedom friction-coupled to other thermalized degrees of freedom, so this should work. This is no different than coupling to a thermalized LB fluid.
I think you can just cherry-pick 05daf01.
I checked multiple seeds, this is all very robust. The test in principle now also passes with 20 loops,
or with a almost tenfold lower error.

[codecov]

Codecov Report

Merging #3355 into python will increase coverage by <1%.
The diff coverage is 100%.

@@           Coverage Diff           @@
##           python   #3355    +/-   ##
=======================================
+ Coverage      86%     86%   +<1%     
=======================================
  Files         537     537            
  Lines       25283   25283            
=======================================
+ Hits        21756   21758     +2     
+ Misses       3527    3525     -2

Impacted Files	Coverage Δ
src/core/random.hpp	70% <ø> (ø)	⬆️
src/core/thermostat.cpp	97% <ø> (ø)	⬆️
src/core/thermostat.hpp	96% <100%> (ø)	⬆️
src/script_interface/accumulators/TimeSeries.hpp	62% <0%> (+6%)	⬆️

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[jngrad]

@fweik @KaiSzuttor Thanks!
@RudolfWeeber Ready for review

[jngrad]

bors r=RudolfWeeber

[bors]

Build succeeded

• ICP GitLab CI