Giorgos, You can find a discussion for how constraints are handled in deal.II in https://www.dealii.org/developer/doxygen/deal.II/group__constraints.html.

Thank you for your feedback. > I'll try to explain what I try to calculate with the help of a standard > FEM textbook: > > [...] > > In the book the global system is partitioned so that the first row > contains the known U1 dofs and the second row the unknown the dofs U2. > They solve the system for the U2 and then they calculate F1. > In short: we normally don't condense the linear system but use a diagonal matrix for the constrained rows instead (and modify the right-hand side accordingly). > I think that the F1 vector contains, among others, the fluxes from the > imposed BCs. > In case you only have Dirichlet boundary conditions, K11 is diagonal, K12 is zero and F1 contains the (possibly scaled) Dirichlet boundary values. Could you clarify in mathematical terms what you mean by "fluxes"? Maybe, we are just using different terms fo the same thing. In case you are interested in n\cdot In u at the boundary, you can use FEValues::get_function_gradients() and FEValues::get_normal_vectors() with a quadrature formel that contains the points you are interested in on a cell in reference coordinates. This is the approach VectorTools::point_gradient() is using for returning the gradient for a single point in real coordinates. Best, Daniel -- 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 dealii+unsubscr...@googlegroups.com. To view this discussion on the web visit https://groups.google.com/d/msgid/dealii/CAOYDWb%2B0Vj_LTboMTc2Rqo0%2BMLc7VQpNK0QfZFgeqabk_f7qbg%40mail.gmail.com.