Hi all, I am encountered a weird thing (bug?) and I am having trouble to understand it. Maybe someone has an idea:
I am trying to solve a simple elliptic problem (imagine some sort of a simple Laplace problem for now) with pure Neumann BCs, say -\Delta u = f, n\grad u = g. Now theory tells me that the volume average over f must be the same as the boundary average over g. If I solve that problem (with deal.ii) in the standard form above the Neumann condition is natural and enters the right hand side. I solve and I see what I expect. Fine, intuition confirmed. Now I am solving it in mixed form with RT0-DGQ0 elements which are stable. My Neumann BC becomes essential and enters as hard constraint into the system but the compatibility condition should be the same. When I solve that system now I see things that totally do not match what I see in the standard form and I do not have a clue why. I can see from tests that also the standard form is very sensitive to little mismatches in the compatibility condition so I was wondering if this issue becomes more of a problem in mixed form. (Btw, if I regularize the problem slightly by changing the left hand side -\Delta u to -\Delta u + \epsilon u and setting f to zero (compatibility is not necessary then) I see something that is close to what I would expect in the pure Laplace case.) Best, Konrad -- The deal.II project is located at http://www.dealii.org/ For mailing list/forum options, see https://groups.google.com/d/forum/dealii?hl=en --- You received this message because you are subscribed to the Google Groups "deal.II User Group" group. To unsubscribe from this group and stop receiving emails from it, send an email to [email protected]. For more options, visit https://groups.google.com/d/optout.
