From: John Peterson <peterson@cf...>  20040524 18:42:16

Michael Schindler writes: > Hello, > > I am trying to implement boundary conditions (for the NavierStokes > equation of example 13) via Lagrange multipliers. > > For this I need extra degreesoffreedom for every boundaryside of an > element. > One possibility, that already works, is to define an extra variable. > But this has then DOFs at all elements of the mesh  far too many. > This makes the System unnecessary large. > > Therefore, I would like to know: > > 1. Is there a readymade way to implement Lagrange multipliers? > or > 2. Can I "throw away" DOFs of one specified variable where I do not > want to calculate its solution? > 3. Can I add DOFs to a System without adding a variable? Hi, Yes that seems like a reasonable and general thing to have. I hope Ben will comment on this, since he was working with a constrained system at some point in which he only activated the extra DOF on elements which required it. In that case, I believe the lagrange multiplier was used to enforce positivity of the solution in each element... John 