Imposing a discontinuity at interface using DG method

[dokken]

I would suggest searching on the forum for your error message, as it is already covered at:

Linear Elasticity Tutorial w/ Quadratic Tetrahedrals

Use dolfinx.io.VTXWriter instead of xdmffile if you are not using isoparametric elements.

and

Cannot write function to XDMF with DG elements

This is an explicit change to highlight the limitations of the XDMF file format, as in comparison to VTX. In DOLFINx<0.7.0 any function was interpolated into the function space of the mesh geometry (N-th order Lagrange space, N usually 1). Now you have to interpolate this function into (“CG”, 1) explicitly to save it to xdmf, or use the VTXWriter, which supports arbitrary order “CG”/“DG” elements.