classmethod neso_fame.coordinates.CoordMap[C: (neso_fame.coordinates.Coord, neso_fame.coordinates.SliceCoord)]].empty_slicecoord[T](t: type[T], rtol: float = 1e-09, atol: float = 1e-09) → CoordMap[SliceCoord, T] Construct an empty mapping for SliceCoords.