Arepo_SOLAS version

Modified from the AREPO public version for the SOLAS project.

Details of the physical models implemented can be found in this high level description and in these technical details.

How to contribute

1. Fork from or create a new branch at the official repository.
2. Make your changes in a new, appropriately named branch (e.g. starformation or bh_feedback).
   • All git commit messages should loosely follow the standard format outlined here.
   • Ensure your new code is commented enough so that others can understand what it's doing. If possible, update the wiki as well.
3. Issue a pull request to the official repository.

IMPORTANT

1. Direct pushes to the main have been disabled; one has to merge through a PR. Code review is not enforced but having a PR will help you check whether you had inadvertently changed something.
2. Delete stale branches after merging.