New Grid API

[dpanici]

related to Finite build grid api #1421 #1169 #1807

• _Grid to AbstractGrid
  • rename rho poloidal zeta idx to x1 x2 x3 or something
  • no assumption on periodicity
  • move

    DESC/desc/grid.py

    Line 85 in 0d6bb5f

    def _enforce_symmetry(self):

    to AbstractRTZGrid
• subclass for AbstractRTZGrid
• LinearGrid etc other existing grids will not subclass from this.
• subclass also for AbstractFiniteBuildGrid
  • implements whatever methods required for finite build

Abstract grid classes instead for the topology of the grid (Torus vs Rectangular x circle)

How to keep current flexibility of allowing finite build coils to also compute centerline quantities (centerline curvature, etc) when given a 3D finite build grid?

In transforms, is particular structure assumed in grids?

• FFT assumes something, may need to add extra checks (like only allow FFT for rtz grids for now, could be added later for finite build stuff)

CurveGrid class, which coils should use? is only 1-D instead of 3-D and use zeta as curve coordinate

• would have to in certain places, potentially make changes where a usual nodes (n x 3) array is indexed into the last column

In curve and coil compute stuff

• requirements could be 'z' for only centerline quanitites or just `` if can be computed pointwise without any resolution requirement
• or 'rtz' or 'xsz' or something for things that need finite build

TODO:

• separate PR from Ryan for the ABCs and a concrete filamentary coil grid class (CurveGrid) or something
  • make ABC for flux coords, cylindrical, and finite build (include Abstract in name)
• finite build coil PR Finite Build Coils #1421 then bases off this PR and implements finitebuild, adds warnings when needed
  • change curve compute to check grid types, throw warnings about future errors if wrong grid (rtz grid when curve grid is needed)