Hi Younghigh,
a quick try of computing the jump ||[\nabla u_h \cdot n]|| via
Code:
Integrate((grad(gfu)-grad(gfu).Other())*n*dx(skeleton=True), mesh)
led to the exception
netgen.libngpy._meshing.NgException: other mir not set, pls report to developers.
But with the exact solution at hand the following code should do the job (might not work for older NGSolve versions)
Code:
Integrate( (gfu-u_ex)**2*dx(element_boundary=True), mesh)
Note, that you get two values at each inner edge as a loop over elements and then over each element boundary is done.
Best
Michael