Example 23 and essential dofs

[mdeuse]

Hi MFEM community, I have a few questions about example 23.

In WaveOperator::ImplicitSolve, in order to compute z from u, Kmat0 is used instead of Kmat, why is that? And why is it different in WaveOperator::Mult, where Kmat is used? If I understand correctly, Kmat and Kmat0 differ in the way the essential dofs are handled, but I do not understand why both are needed.

Also, how could I adapt the example to use time dependent boundary conditions? I have tried to update the value of the essential dofs in u before each Step, but it does no seem to propagate in the solution.

Finally, what is the point of WaveOperator::SetParameters? Is it really necessary to delete and reconstruct T after each Step?

Final comment: the lines 33 to 35 of ex23.cpp seem to be outdated. Nowhere else is the "temperature" referred to in this example.

Thanks in advance for your help!