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The docs for staggered grids (https://bout-dev.readthedocs.io/en/latest/user_docs/differential_operators.html#staggered-grids) say:
Several things are not currently implemented, which probably should be:
- Only 3D fields currently have a cell location attribute. The location (cell centre etc) of 2D fields is ignored at the moment. The rationale for this is that 2D fields are assumed to be slowly-varying equilibrium quantities for which it won’t matter so much. Still, needs to be improved in future
- Twist-shift and X shifting still treat all quantities as cell-centred.
- No boundary condition functions yet account for cell location.
I don't think any of these are true any more (X-shifting is not done since BOUT++ v4, replaced by 'shifted metric' and 'aligned transform'), but someone should probably check and update the docs.
It would probably also be useful to list which derivative methods have staggered-grid implementations.