How to obtain the element-wise stiffness matrix?

dokken · March 30, 2021, 8:23pm

As the first part of the question is a duplicate of:

I’ll just supply you with a reference on how to compute the midpoint of all cells local to a process:

FEniCS/dolfinx/blob/cd7361f2ea43ca976100923ffa75280a4a8d082a/python/demo/pyvista/demo_pyvista.py#L178


      
          
          
          def in_circle(x):
              # Mark sphere with radius < sqrt(2)
              return np.array((x.T[0] - 0.5)**2 + (x.T[1] - 0.5)**2 < 0.2**2, dtype=np.int32)
          
          
          # Create a dolfinx.MeshTag for all cells. If midpoint is inside the
          # circle, it gets value 1, otherwise 0.
          num_cells = mesh.topology.index_map(mesh.topology.dim).size_local
          midpoints = dolfinx.cpp.mesh.midpoints(mesh, mesh.topology.dim, list(np.arange(num_cells, dtype=np.int32)))
          cell_tags = dolfinx.MeshTags(mesh, mesh.topology.dim, np.arange(num_cells), in_circle(midpoints))
          
          # As the dolfinx.MeshTag contains a value for every cell in the
          # geometry, we can attach it directly to the grid
          grid.cell_arrays["Marker"] = cell_tags.values
          grid.set_active_scalars("Marker")
          
          # We create a plotter consisting of two windows, and add a plot of the
          # Meshtags to the first window.
          subplotter = pyvista.Plotter(shape=(1, 2))

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How to obtain the element-wise stiffness matrix?

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