Ah thanks for that! Sorry I had incorrectly assumed the preconditioner on S
would be as it was previously. I'll take a look.
Thanks again for all the help.
Best,
Colton
On Thu, May 30, 2024 at 3:25 PM Barry Smith wrote:
>
>Preconditioner for the Schur complement formed from A11
>
>But
Preconditioner for the Schur complement formed from A11
But
PC Object: (fieldsplit_pressure_) 1 MPI process
>
> type: ilu
> out-of-place factorization
> 0 levels of fill
> tolerance for zero pivot 2.22045e-14
> matrix ordering: natural
>
Hi Barry,
Yes, each index set has the correct entries when I checked manually on a
small example.
For the nullspace I was trying to manually build the constant basis on a
compatible DMStag containing just the pressure nodes and creating the
nullspace from that but that does not seem to work. Usin
> On May 30, 2024, at 3:15 PM, Colton Bryant
> wrote:
>
> Hi Barry,
>
> Do you know of an example that demonstrates this approach? I have tried
> implementing this using DMStagCreateISFromStencils and then calling
> PCFieldSplitSetIS with fields named "velocity" and "pressure" respectively,
Hi Barry,
Do you know of an example that demonstrates this approach? I have tried
implementing this using DMStagCreateISFromStencils and then calling
PCFieldSplitSetIS with fields named "velocity" and "pressure" respectively,
but when I look at -ksp_view the fields are being set to "fieldsplit_fac
It is true if A is nonsingular. if it is singular I never did the algebra;
you need to use generalized Schur complements with pseudo-inverses
Il giorno ven 24 mag 2024 alle ore 00:04 Barry Smith ha
scritto:
>
>
> On May 23, 2024, at 3:48 PM, Stefano Zampini
> wrote:
>
> the null space of the Sc
I put in stuff to propagate the nullspace if you use DM.
Matt
On Thu, May 23, 2024 at 11:04 PM Barry Smith wrote:
> On May 23, 2024, at 3: 48 PM, Stefano Zampini com> wrote: the null space of the Schur complement is the restriction of
> the original null space. I guess if fieldsplit is Schu
> On May 23, 2024, at 3:48 PM, Stefano Zampini
> wrote:
>
> the null space of the Schur complement is the restriction of the original
> null space. I guess if fieldsplit is Schur type then we could in principle
> extract the sub vectors and renormalize them
Is this true if A is singular?
the null space of the Schur complement is the restriction of the original
null space. I guess if fieldsplit is Schur type then we could in principle
extract the sub vectors and renormalize them
On Thu, May 23, 2024, 22:13 Jed Brown wrote:
> Barry Smith writes: > Unfortunately it cannot
> autom
Barry Smith writes: > Unfortunately it cannot automatically because -pc_fieldsplit_detect_saddle_point just grabs part of the matrix (having no concept of "what part" so doesn't know to grab the null space information.
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Hi Barry,
Thanks so much for the information. I will get working on that! Thanks
again for all your help.
-Colton
On Thu, May 23, 2024 at 12:55 PM Barry Smith wrote:
>
>Unfortunately it cannot automatically because
> -pc_fieldsplit_detect_saddle_point just grabs part of the matrix (having
Unfortunately it cannot automatically because
-pc_fieldsplit_detect_saddle_point just grabs part of the matrix (having no
concept of "what part" so doesn't know to grab the null space information.
It would be possible for PCFIELDSPLIT to access the null space of the larger
matrix direct
Yes, the original operator definitely has a constant null space
corresponding to the constant pressure mode. I am currently handling this
by using the MatSetNullSpace function when the matrix is being created.
Does this information get passed to the submatrices of the fieldsplit?
-Colton
On Thu,
Ok,
So what is happening is that GMRES with a restart of 30 is running on the
Schur complement system with no preconditioning and LU (as a direct solver) is
being used in the application of S (the Schur complement). The convergence of
GMRES is stagnating after getting about 8 digits of
Hi Barry,
I saw that was reporting as an unused option and the error message I sent
was run with -fieldsplit_0_ksp_type preonly.
-Colton
On Thu, May 23, 2024 at 12:13 PM Barry Smith wrote:
>
>
>Sorry I gave the wrong option. Use -fieldsplit_0_ksp_type preonly
>
> Barry
>
> On May 23, 2024
Sorry I gave the wrong option. Use -fieldsplit_0_ksp_type preonly
Barry
> On May 23, 2024, at 12:51 PM, Colton Bryant
> wrote:
>
> That produces the error:
>
> [0]PETSC ERROR: Residual norm computed by GMRES recursion formula 2.68054e-07
> is far from the computed residual norm 6.8630
That produces the error:
[0]PETSC ERROR: Residual norm computed by GMRES recursion formula
2.68054e-07 is far from the computed residual norm 6.86309e-06 at restart,
residual norm at start of cycle 2.68804e-07
The rest of the error is identical.
On Thu, May 23, 2024 at 10:46 AM Barry Smith wrot
Use -pc_fieldsplit_0_ksp_type preonly
> On May 23, 2024, at 12:43 PM, Colton Bryant
> wrote:
>
> That produces the following error:
>
> [0]PETSC ERROR: Residual norm computed by GMRES recursion formula 2.79175e-07
> is far from the computed residual norm 0.000113154 at restart, residual
Run the failing case with also -ksp_error_if_not_converged so we see exactly
where the problem is first detected.
> On May 23, 2024, at 11:51 AM, Colton Bryant
> wrote:
>
> Hi Barry,
>
> Thanks for letting me know about the need to use fgmres in this case. I ran a
> smaller problem (12
Hi Barry,
Thanks for letting me know about the need to use fgmres in this case. I ran
a smaller problem (1230 in the first block) and saw similar behavior in the
true residual.
I also ran the same problem with the options -fieldsplit_0_pc_type svd
-fieldsplit_0_pc_svd_monitor and get the followin
Thanks for the info. I see you are using GMRES inside the Schur complement
solver, this is ok but when you do you need to use fgmres as the outer solver.
But this is unlikely to be the cause of the exact problem you are seeing.
I'm not sure why the Schur complement KSP is suddenly seeing a
Hi Barry,
I have not used any other solver parameters in the code and the full set of
solver related command line options are those I mentioned in the previous
email.
Below is the output from -ksp_view:
KSP Object: (back_) 1 MPI process
type: gmres
restart=30, using Classical (unmodified)
Are you using any other command line options or did you hardwire any solver
parameters in the code with, like, KSPSetXXX() or PCSetXXX() Please send all of
them.
Something funky definitely happened when the true residual norms jumped up.
Could you run the same thing with -ksp_view and do
Hello,
I am solving the Stokes equations on a MAC grid discretized by finite
differences using a DMSTAG object. I have tested the solver quite
extensively on manufactured problems and it seems to work well. As I am
still just trying to get things working and not yet worried about speed I
am using
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