Evaluation of grad(u) at a point x_ref for variational formulation

[dokken]

There are various topics on this, see:

How to construct a sparse matrix used for calculating function values at multiple points

What you are searching for is how to create a point source. Following is code for getting the basis functions evaluated at a point in the cell: # Author: Jørgen S. Dokken # # Create a point source import dolfinx from mpi4py import MPI import numpy as np import ufl def compute_cell_contributions(V, points): # Determine what process owns a point and what cells it lies within _, _, owning_points, cells = dolfinx.cpp.geometry.determine_point_ownership( mesh._cpp_object, points, …

and

Eval in Expression freezes in parallel

It freezes as you are not sending in the appropriate MPI communicator to the expression. Since you are not sending in a communicator (which in your case should be MPI.COMM_SELF, it is using the mesh communicator, thus waiting for a sync step between all processes that never happens. See: dolfinx.fem — DOLFINx 0.7.3 documentation i.e. E = Expression(expr, x_ref, comm=MPI.COMM_SELF) does the trick

I think this is also implemented in helmholtx by @Ekrem_Ekici : helmholtz-x/helmholtz_x/flame_matrices.py at 3a20260bb51a48a8c315f6c02277465ddd729e01 · ekremekc/helmholtz-x · GitHub
which I guess is what you want.