Project HDiv function to L2 FacetFESpace


In the stabilization for the diffusion operator in Navier-Stokes equation, if we use Raviart-Thomas HDiv basis, the projection of functions in HDiv (say order ‘k’) to the L2 space (order ‘k-1’) on facets is needed. How do we get this projection in ngsolve?

Thank you.


I just updated the tutorials to explain how we implement the projection, see
2.8 Discontinuous Galerkin Methods — NGS-Py 6.2.2302-87-ga5a5eff3b documentation,
section Projected Jumps.

Try also help(FacetFESpace).

The same works for H(div)-conforming HDG, with a TangentialFacetFESpace.

The theory behind is in Lehrenfeld-Schöberl: High order exactly divergence-free Hybrid Discontinuous Galerkin Methods for unsteady incompressible flows, CMAME, Vol 307, p 339-361, 2016.

best, Joachim