Upper case mpi4py communication in convergence controllers

[brownbaerchen]

I am starting to merge back some of the changes I have in a development branch of mine, so expect some PRs in the upcoming days with random small things. This is one of them.

I ran into issues with the pipeline on GitHub behaving differently from my local machine and going to upper case communication in mpi4py solved that. It is a few more lines, but also should be faster because it does not pickle everything before sending because you have to specify a buffer yourself. There is still the option to do the lower case stuff and I believe it is still used in some places as well.
The tests for which this was relevant are not part of this PR and I don't actually know if the issue persists or has been solved by some updates. Anyways, I guess forgoing the pickling is enough to merit doing this.

The second small change is a different initial guess for RK methods. Instead of the initial conditions, they now use the last stage as recommended by Daniel.

[pancetta]

Could you please encapsulate the additional lines of code in the send and recv functions? I just cleaned up the controller a bit to make it more readable (hahahaha)..

[brownbaerchen]

I don't think I can because different convergence controllers will need different buffers. And the same convergence controller will need different buffers when communicating different things. The controller, I believe, only communicates the solution so there everything is the same, but here this is not the case.
I could overload the functions in some convergence controllers to streamline it a bit, but honestly I am afraid that would be even more mess.
Maybe I misunderstood and you can elaborate?

[codecov]

Codecov Report

Patch coverage: 92.50% and project coverage change: -0.01% ⚠️

Comparison is base (65195b3) 73.51% compared to head (c475623) 73.51%.

Additional details and impacted files

@@            Coverage Diff             @@
##           master     #343      +/-   ##
==========================================
- Coverage   73.51%   73.51%   -0.01%     
==========================================
  Files         266      266              
  Lines       22301    22322      +21     
==========================================
+ Hits        16395    16409      +14     
- Misses       5906     5913       +7     

Files Changed	Coverage Δ
...SDC/implementations/sweeper_classes/Runge_Kutta.py	94.97% <ø> (ø)
pySDC/core/ConvergenceController.py	88.42% <81.81%> (-9.41%)	⬇️
...convergence_controller_classes/basic_restarting.py	97.02% <92.85%> (-0.80%)	⬇️
...onvergence_controller_classes/check_convergence.py	85.18% <100.00%> (+1.85%)	⬆️
...entations/convergence_controller_classes/hotrod.py	92.10% <100.00%> (+0.67%)	⬆️

... and 1 file with indirect coverage changes

☔ View full report in Codecov by Sentry.
📢 Have feedback on the report? Share it here.

[pancetta]

No, no, I understand. Since you're not touching the controller directly, I'm ok with this.

[brownbaerchen]

I am excited to see the new clean controller by the way! :D

[pancetta]

There is none besides the one that is already in the master branch. The "cleanup" was done many weeks ago and didn't help much. So, no excitement here.