For a mixed element, such as P2/P1 element for velocity (in space Vh) and pressure (in space Ph) pair. If I loop for (i=0; i<Vh.ndof; i++), how can I know which DOF includes pressure and which one does not ?
If I do varf rhs([u,v,p],[uh,vh,ph]) =…, and later do real[int] b = rhs(0, Rh), with Rh=[Vh, Vh, Ph]
How are variables u,v, and p numerated in b ?
Alternatively, if I solve for
w=A^-1 * b
how can I give w to [u, v, p], what’s the order?
Yes, much better. For example, take a [P1, P1]fespace, instead of having a 2-by-2 block matrix [[A, B]; [C, D]], you end up with a sparse matrix A where all unknowns are 2-by-2 dense small blocks. This is coherent, for example, with PETSc MATBAIJ format.