### Coordinates of Ghost DOFs

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Hi!

Is there any way to get the coordinates of the unowned local dofs (ghost)?

The function tabulate_dof_coordinates() only tabulates owned dof coordinates when it works in parallel!

Thanks a lot!

Ximo

Is there any way to get the coordinates of the unowned local dofs (ghost)?

The function tabulate_dof_coordinates() only tabulates owned dof coordinates when it works in parallel!

Thanks a lot!

Ximo

Community: FEniCS Project

### 1 Answer

1

There is very likely a better way, but below you can find code that I briefly tested for my own purposes and it seems to work.

This is not optimized in any way! It always returns x, y, and z coordinates, also in 2D because that was something I needed

This is not optimized in any way! It always returns x, y, and z coordinates, also in 2D because that was something I needed

```
def all_dof_coordinates(V):
"""
Return coordinates of all dofs, similar to tabulate_dof_coordinates,
but also includes the ghosts dofs. This always returns 3-vectors for
the coordinates, even if the mesh is 2D or 1D.
This has all communication going via the root. Consider rewriting this
by using DofMap.off_process_owner to avoid the root botleneck for
large MPI runs
"""
mesh = V.mesh()
# Get coordinates of regular dofs
gdim = mesh.geometry().dim()
dofs_x = V.tabulate_dof_coordinates().reshape((-1, gdim))
global_dofs = V.dofmap().tabulate_local_to_global_dofs()
Nlocal = len(dofs_x)
# Make sure dof positions are 3-vectors
if gdim != 3:
tmp = numpy.zeros((dofs_x.shape[0], 3), float)
tmp[:, :gdim] = dofs_x
dofs_x = tmp
# Do nothing in serial
comm = mesh.mpi_comm()
if comm.size == 1:
return dofs_x, Nlocal
# Missing and present information
missing_dofs = global_dofs[Nlocal:]
present_dofs = global_dofs[:Nlocal]
# Send list of global dofs which we want to know the coordinates for
# along with the global dofs where we know the coordinates
alldata = comm.gather((missing_dofs, present_dofs, dofs_x))
# Global dof coordinate map, may need to be changed for comm.size >> 1
if comm.rank == 0:
# Build global dof coordinate mapping using each ranks info
global_dofs_x = {}
for _rank_missing_dofs, rank_present_dofs, rank_dofs_x in alldata:
for gdof, coord in zip(rank_present_dofs, rank_dofs_x):
global_dofs_x[gdof] = coord
# Find the missing local data in the global mapping for each rank
ret_data = []
for rank_missing_dofs, _rank_present_dofs, _rank_dofs_x in alldata:
ret = []
ret_data.append(ret)
for gdof in rank_missing_dofs:
ret.append(global_dofs_x[gdof])
else:
ret_data = None
# Get back the missing values
ghost_coords = comm.scatter(ret_data)
# Create dof coordinates with ghost positions
dofs_x_all = numpy.zeros((len(global_dofs), 3), float)
dofs_x_all[:Nlocal] = dofs_x
for i, coord in enumerate(ghost_coords):
dofs_x_all[Nlocal + i] = coord
return dofs_x_all, Nlocal
```

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