From: KIRK, BENJAMIN (JSCEG) (NASA) <benjamin.kirk1@na...>  20050107 14:43:34

It's not clear that you need to use the constraint matrix for this = case... For example, consider Laplace's problem in 2D: =20  div(grad(u)) =3D 0 with u=3Dg on some part of the boundary, du/dn=3Dh on the remainder. In the weak statement you perform integrationbyparts, and the term = du/dn appears in a boundary integral and you can use this to impose a Neumann = BC in the RHS of the system. See, for example, http://cfdlab.ae.utexas.edu/~benkirk/seminar/talk.pdf, Especially page = 4. In a similar way, Robin BCs can be implemented by letting h =3D alpha u = + beta du/dn. In this case you have two boundary terms that contribute to the system matrix. For implementation, you simply need to define a finite element object = that lives on the boundary and can be used to integrate along the edge to = provide the required term. Clear? Unfortunately, none of the examples show this. If you have any more questions let me know, it would be straightforward to modify ex14 to = show this procedure since it has the exact solution's derivative available. Regardless, we should probably do that since it seems silly to have 14 examples, all with Dirichlet BCs! Ben =20 Original Message From: libmeshusersadmin@... [mailto:libmeshusersadmin@...] On Behalf Of Michael Schindler Sent: Friday, January 07, 2005 3:26 AM To: libmeshusers@... Subject: [Libmeshusers] Constraint matrix for boundary conditions Hello, I would like to enforce nonDirichlet boundary conditions via the = constraint matrix. Does someone have an example how to implement this for e.g. = Neumann or Robin BC? Thanks, Michael. =20 "A mathematician is a device for turning coffee into theorems" Paul Erd=F6s.  The SF.Net email is sponsored by: Beat the postholiday blues Get a = FREE limited edition SourceForge.net tshirt from ThinkGeek. It's fun and = FREE  well, almost....http://www.thinkgeek.com/sfshirt _______________________________________________ Libmeshusers mailing list Libmeshusers@... https://lists.sourceforge.net/lists/listinfo/libmeshusers 