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Correct integration in time of the mesh forces

Matthieu Schaller requested to merge mesh_forces into master

Complete rewrite of the time integration of the gravity mesh forces. This fixes the accuracy issues seen in the large-scale power-spectrum in cosmological runs.

This includes:

  • Removing the mesh_force task.
  • Introduce a global time-step for the mesh calculation.
  • Compute the mesh forces when that time-step happens and not when we rebuild.
  • Rewrite the operations in the kick tasks to simplify the with/without cosmology logic.
  • Add the mesh accelerations to the gpart, remove the gravity acceleration from the xpart.
  • Remove the alignment constraint on the gparts to reduce the memory footprint.
  • Add an option to not compute the potentials.
  • Remove the option to dither the particles at tree rebuilds. This was not the solution to the problem and was not implemented in an efficient way.

Todo:

  • Clean-up the mesh time-step calculation.
  • Deal with exact gravity force checks.
  • Interpolation of the hydro velocities in snapshot.
  • Deal with the time-step limiter.
  • Deal with the time-step synchronization.
  • Deal with the potential.
  • Deal with star formation.
  • Fix statistics.
  • Documentation of the whole gravity scheme parameters.
Edited by Matthieu Schaller

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