On 01/09/2014 11:19 AM, Jan Blechta wrote: >> So if I understand correctly, I don't need to do anything special for >> > the boundary conditions because Dolfin assumes Neumann by default, and >> > Neumann conditions are only reflected in L. > This is not true - DOLFIN does not assume. It is a property of this > variational problem.
Huh? Maybe we misunderstood each other, but http://fenicsproject.org/documentation/dolfin/1.3.0/python/demo/documented/neumann-poisson/python/documentation.html says: "Since we have natural (Neumann) boundary conditions in this problem, we don´t have to implement boundary conditions. This is because Neumann boundary conditions are default in DOLFIN." which seems to be the same as what I said above. It seems to me that Dolfin could just as well use e.g. Dirichlet conditions with a constant value on the boundary if no BC's are specified, so how is using Neumann conditions in this situation anything but an assumption by Dolfin that this what is most commonly wanted? > However, even after going through the example, I'm not sure how I can > tell FEniCS to use only trial functions satisfying Laplace's equation. > In the example, the constraint on the test functions seems to fix just > the constant offset. It's not clear to me to extend this to something > more complicated, where the constraint itself takes the form of a PDE. > Do you think you could explain in a bit more detail? > You change the constraint to Laplace problem, and the space R for > Lagrange multiplier and corresponding test function to some appropriate > FE subspace of Sobolev space W_0^{1,2}. Hint: > http://en.wikipedia.org/wiki/Lagrange_multipliers_on_Banach_spaces I'll look into that. Thanks! Best, Nikolaus -- Nikolaus Rath, Ph.D. Senior Scientist Tri Alpha Energy, Inc. +1 949 830 2117 ext 211 _______________________________________________ fenics mailing list [email protected] http://fenicsproject.org/mailman/listinfo/fenics
