'on_diagonals' diffusion missing grid attribute

I’m experimenting with the diffusion to all adjacent cells in landlab, and I’ve run into an issue.

Instantiating LinearDiffuser with method ‘on_diagonals’ is possible but calling run_one_step gives AttributeError: 'RasterModelGrid' object has no attribute _diag_activelink_tonode.

I searched in the whole code repository, and line 552 in diffusion.py appears to be the only place where this attribute exists. This seems to be similar for _diag_activelink_fromnode too. Maybe these were orphaned somewhere in the LL2.0 process? I would be interested in helping if there is a simple fix.

Furthermore, there are no component tests for methods other than ‘simple’. Seems like this would be useful.

Here is an example:

from landlab import RasterModelGrid
from landlab.components import LinearDiffuser

grid = RasterModelGrid((10, 10), xy_spacing=10)
z = grid.add_ones('node', 'topographic__elevation')

ld = LinearDiffuser(grid, 0.001, method='on_diagonals')
ld.run_one_step(1)

[SiccarPoint]

Yes, I too was struggling with conflict between D8 flow and D4 diffusion. Do feel free just to remove it. Can always reinstate later. I was never totally happy that the scheme I had going for this was justified, and couldn’t justify sinking any more time into it after a certain point. This was long enough ago that our modern QC processes weren’t in place!

[gregtucker]

I’m surprised to hear that you got slower performance with hex. In principle, you do have ~50% more links in a hex grid (not counting diagonals), but that shouldn’t be a huge hit. One area where hex grids are notably slower is in imshow_grid plotting.