As usual, the Firedrake person in the best position to answer your question is Lawrence, but he's currently on holiday. I won't try to answer your question, but in an old email <http://mailman.ic.ac.uk/pipermail/firedrake/2015-July/000953.html>, Lawrence suggested you try using multigrid on the blocks; e.g. 'fieldsplit_0_pc_type': 'gamg', 'fieldsplit_1_pc_type': 'gamg', My linear solver knowledge is pretty dire, so I'll stop talking here :) Andrew On 15 October 2015 at 13:58, Justin Chang <jychang48@gmail.com> wrote:
I did ask them, but it went unanswered for the last 1.5 months...
Let me clarify my question a bit though, I tried using -ksp_type cg -pc_type hypre -pc_hypre_type boomeramg, but it is not supported for matnest. I added nest=False but it seems to break my solver somehow.
The only thing that works for me is -ksp_type cg -pc_type bjacobi plus MixedVectorSpaceBasis(W, ...) but the number of solver iterations increases with problem size...
Thanks, Justin
On Thu, Oct 15, 2015 at 6:50 AM, Andrew McRae <A.T.T.McRae@bath.ac.uk> wrote:
I think the PETSc mailing list is a much better place to ask questions like this?
On 15 October 2015 at 13:47, Justin Chang <jychang48@gmail.com> wrote:
Hi all,
I am attempting to solve Darcy's equation:
u + grad[p] = 0 div[u] = f
The weak form under the least-squares finite element method (LSFEM) looks like this:
(u + grad[p]; v + grad[q]) + div[u]*div[v] = (f; div[v])
For H(div) elements like RT0, these options worked nicely:
-ksp_type gmres -pc_type fieldsplit -pc_fieldsplit_type schur -pc_fieldsplit_schur_precondition selfp -fieldsplit_0_ksp_type preonly -fieldsplit_0_pc_type bjacobi -fieldsplit_0_sub_pc_type ilu -fieldsplir_1_ksp_type preonly -fieldsplit_1_pc_type hypre
but for the above LSFEM, it does not work (get a DIVERGED_MAX_IT error). I heard multigrid methods are good for these types of problems, so how do I tweak the above parameters?
Thanks, Justin
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