From: Benjamin Kirk <benjamin.kirk@na...>  20080829 13:16:15

> Is there a way to tell Libmesh that certain variables are neither > timeevolving or constraints, so that they are not accounted for in the > factorization? So I would start with a FEMsystem with all of the tensor > components, eigenvalues, and eigenvector components in the same system. Since they are computed as a postprocessing step from the tensor components you definitely do not want them coupled in the linear system, so that calls for another system. I have a somewhat similar issue in my compressible NS stuff. I solve a large implicit system for (rho, rho*u, rho*v, rho*w, rho*E)  the socalled conserved variables. But other places in the code, and for visualization, I really want access to (P, u, v, T, M)  primitive variables + Mach number. And I don't want them making my linear system any bigger. > Would I then just implement the postprocessing functions and use the Gnu > Scientific Library to compute the eigenvalues/vectors based upon the > tensor components computed from the current solution. > > Please give me a few pointers... What I do is add an ExplicitSystem to my EquationSystems. I then fill it with these "auxiliary variables." The benefit of this approach is (i) there is no matrix allocation for these explicit variables, and (ii) they can be output to visualization formats in the usual way. You can either provide your own assemble function for the auxiliary system which does the processing you want, or do it at the beginning/end of the assemble of the primary system. Ben 