Nodal point swarm not working on cubed sphere mesh

[chenxi-kong]

Hi! When I was trying to solve the advection-diffusion equation on a cubed sphere mesh (which by default is using the semi Lagrangian method), I found that the nodal point swarm can not be constructed if its tracked variable is defined on this type of mesh. This issue can be reproduced by running:

import underworld3 as uw
import numpy as np
import sympy

mesh = uw.meshing.uw.meshing.CubedSphere(
    radiusOuter=1.0,
    radiusInner=0.547,
    numElements=10,
    refinement=0,
    simplex=False,
    verbose=False,
)

t_soln = uw.discretisation.MeshVariable("T", mesh, 1, degree=3)
nswarm = uw.swarm.NodalPointSwarm(t_soln, True)

and it says:

ValueError                                Traceback (most recent call last)
Cell In[39], line 1
----> 1 nswarm = uw.swarm.NodalPointSwarm(t_soln, True)

File [~/miniconda3/envs/uw3p/lib/python3.11/site-packages/underworld3/swarm.py:2035](http://localhost:8083/home/ckong/miniconda3/envs/uw3p/lib/python3.11/site-packages/underworld3/swarm.py#line=2034), in NodalPointSwarm.__init__(self, trackedVariable, verbose)
   2032 nswarm.dm.migrate(remove_sent_points=True)
   2034 with nswarm.access(nX0, nI0):
-> 2035     nX0.data[:, :] = coords
   2036     nI0.data[:, 0] = range(0, coords.shape[0])
   2038 self._nswarm = nswarm

ValueError: could not broadcast input array from shape (50442,3) into shape (43710,3)

I am wondering if there is an problem with using semi Lagrangian method for variables on cubed sphere mesh, or it is just because I am not doing it right somewhere?

Thanks!!

[bknight1]

Hi @chenxi-kong,

I've moved this to an issue, as the number of particles from tracked field is larger than the created swarm.

I'm able to reproduce this error for this mesh, and it also occurs on other meshes. I'll update further on the issue