Many thanks for your concrete replies. They are very helpful.
Best Wishes,
Xiaofeng
On Sep 27, 2022, at 20:01, Mark Adams mailto:mfad...@lbl.gov>>
wrote:
Shells can be pretty hard.
Start with an easy problem with well-shaped elements and probably best to start
with a well-supported structure
Composed preconditioners (like field split) have multiple moving parts and
you need to "tune" them for each part separately; you cannot just run the
entire preconditioner, get slow convergence on the entire problem and then give
up.
So step one is to get a good preconditioner for
Shells can be pretty hard.
Start with an easy problem with well-shaped elements and probably best to
start with a well-supported structure (eg, not a long cantilever).
You should also configure with hypre and try that. I don't know if they
deal with shells, but it is a well developed solver.
Hello,
A00 comes from shell structures and discretized by FEM.
Thanks,
Xiaofeng
On Sep 27, 2022, at 17:48, Mark Adams mailto:mfad...@lbl.gov>>
wrote:
what equations and discetizations are in A00?
On Tue, Sep 27, 2022 at 1:45 AM 晓峰 何
mailto:tlan...@hotmail.com>> wrote:
Hi Barry,
A00 is
what equations and discetizations are in A00?
On Tue, Sep 27, 2022 at 1:45 AM 晓峰 何 wrote:
> Hi Barry,
>
> A00 is formed from elliptic operator.
>
> I tried GAMG with A00, but it was extremely slow to solve the system with
> field-split preconditioner(I’m not sure I did it with the right way).
>
Hi Barry,
A00 is formed from elliptic operator.
I tried GAMG with A00, but it was extremely slow to solve the system with
field-split preconditioner(I’m not sure I did it with the right way).
Thanks,
Xiaofeng
On Sep 26, 2022, at 23:11, Barry Smith
mailto:bsm...@petsc.dev>> wrote:
What is
What is your A00 operator? ILU is almost never a good choice for large scale
problems. If it is an elliptic operator that using a PC of gamg may work well
for the A00 preconditioner instead of ILU.
Barry
For moderate size problems you can use a PC type LU for AOO to help you
Hello Matt,
Many thanks for your suggestion.
BR,
Xiaofeng
On Sep 26, 2022, at 20:29, Matthew Knepley
mailto:knep...@gmail.com>> wrote:
Another option are the PCPATCH solvers for multigrid, as shown in this paper:
https://arxiv.org/abs/1912.08516
which I believe solves incompressible
Hello Jed,
The saddle point is due to Lagrange multipliers, thus the size of A11 is much
smaller than A00.
Best Regards,
Xiaofeng
On Sep 26, 2022, at 21:03, Jed Brown
mailto:j...@jedbrown.org>> wrote:
Lagrange multipliers
Xiaofeng, is your saddle point due to incompressibility or other constraints
(like Lagrange multipliers for contact or multi-point constraints)? If
incompressibility, are you working on structured or unstructured/non-nested
meshes?
Matthew Knepley writes:
> Another option are the PCPATCH
Another option are the PCPATCH solvers for multigrid, as shown in this
paper: https://arxiv.org/abs/1912.08516
which I believe solves incompressible elasticity. There is an example in
PETSc for Stokes I believe.
Thanks,
Matt
On Mon, Sep 26, 2022 at 5:20 AM 晓峰 何 wrote:
> Are there other
Are there other approaches to solve this kind of systems in PETSc except for
field-split methods?
Thanks,
Xiaofeng
On Sep 26, 2022, at 14:13, Jed Brown
mailto:j...@jedbrown.org>> wrote:
This is the joy of factorization field-split methods. The actual Schur
complement is dense, so we
This is the joy of factorization field-split methods. The actual Schur
complement is dense, so we represent it implicitly. A common strategy is to
assemble the mass matrix and drop it in the 11 block of the Pmat. You can check
out some examples in the repository for incompressible flow (Stokes
If assigned a preconditioner to A11 with this cmd options:
-fieldsplit_0_ksp_type gmres -fieldsplit_0_pc_type ilu
-fieldsplit_1_ksp_type gmres -fieldsplit_1_pc_type ilu
Then I got this error:
"Could not locate a solver type for factorization type ILU and matrix type
schurcomplement"
How
The usual issue is that you need a preconditioner for the Schur complement S =
A11 - A01 A00^{-1} A10. For incompressible elasticity, this S is spectrally
equivalent to a scaled mass matrix.
晓峰 何 writes:
> Hi all,
>
> I have a linear system formed from structural mechanics, and there exists
Hi all,
I have a linear system formed from structural mechanics, and there exists zero
in the diagonal entries:
A = (A00 A01
A10 A11), where A00 has inverse and the diagonal entries in A11 are all
zero.
The GMRES method with ILU preconditioner in PETSc was carried out to solve this
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