[petsc-users] PetscDSSetJacobianPreconditioner causing DIVERGED_LINE_SEARCH for multi-field problem
Sander Arens
Sander.Arens at UGent.be
Thu Mar 3 10:48:20 CST 2016
So is the block size here refering to the dimension of the near-nullspace
or has it something to do with the coarsening?
I would have thought to also see the block size in this part:
Mat Object: 1 MPI processes
type: seqaij
rows=1701, cols=1701
total: nonzeros=109359, allocated nonzeros=109359
total number of mallocs used during MatSetValues calls =0
has attached near null space
using I-node routines: found 567 nodes, limit used is 5
Thanks,
Sander
On 3 March 2016 at 17:29, Matthew Knepley <knepley at gmail.com> wrote:
> You can see the block size in the output
>
> Mat Object: 1 MPI processes
> type: seqaij
> rows=12, cols=12, bs=6
> total: nonzeros=144, allocated nonzeros=144
> total number of mallocs used during MatSetValues calls
> =0
> using I-node routines: found 3 nodes, limit used is 5
> linear system matrix = precond matrix:
> Mat Object: 1 MPI processes
> type: seqaij
> rows=12, cols=12, bs=6
> total: nonzeros=144, allocated nonzeros=144
> total number of mallocs used during MatSetValues calls =0
> using I-node routines: found 3 nodes, limit used is 5
>
> Thanks,
>
> Matt
>
> On Thu, Mar 3, 2016 at 10:28 AM, Sander Arens <Sander.Arens at ugent.be>
> wrote:
>
>> Sure, here it is.
>>
>> Thanks,
>> Sander
>>
>> On 3 March 2016 at 15:33, Matthew Knepley <knepley at gmail.com> wrote:
>>
>>> On Thu, Mar 3, 2016 at 8:05 AM, Sander Arens <Sander.Arens at ugent.be>
>>> wrote:
>>>
>>>> Yes, the matrix is created by one of the assembly functions in Plex, so
>>>> that answers my question. I was confused by this because I couldn't see
>>>> this information when using -snes_view.
>>>>
>>>
>>> Hmm, then something is wrong because the block size should be printed
>>> for the matrix at the end of the solver in -snes_view, Can you
>>> send that to me?
>>>
>>> Thanks,
>>>
>>> Matt
>>>
>>>
>>>> Thanks for the helpful replies,
>>>> Sander
>>>>
>>>> On 3 March 2016 at 14:52, Matthew Knepley <knepley at gmail.com> wrote:
>>>>
>>>>> On Thu, Mar 3, 2016 at 7:49 AM, Sander Arens <Sander.Arens at ugent.be>
>>>>> wrote:
>>>>>
>>>>>> And how can I do this? Because when I look at all the options with
>>>>>> -help I can strangely enough only find -fieldsplit_pressure_mat_block_size
>>>>>> and not -fieldsplit_displacement_mat_block_size.
>>>>>>
>>>>>
>>>>> Maybe I am missing something here. The matrix from which you calculate
>>>>> the preconditioner using GAMG must be created somewhere. Why
>>>>> is the block size not specified at creation time? If the matrix is
>>>>> created by one of the assembly functions in Plex, and the PetscSection has
>>>>> a number of field components, then the block size will already be set.
>>>>>
>>>>> Thanks,
>>>>>
>>>>> Matt
>>>>>
>>>>>
>>>>>> Thanks,
>>>>>> Sander
>>>>>>
>>>>>> On 3 March 2016 at 14:21, Matthew Knepley <knepley at gmail.com> wrote:
>>>>>>
>>>>>>> On Thu, Mar 3, 2016 at 6:20 AM, Sander Arens <Sander.Arens at ugent.be>
>>>>>>> wrote:
>>>>>>>
>>>>>>>> Ok, I forgot to call SNESSetJacobian(snes, J, P, NULL, NULL) with J
>>>>>>>> != P, which caused to write the mass matrix into the (otherwise zero) (1,1)
>>>>>>>> block of the Jacobian and which was the reason for the linesearch to fail.
>>>>>>>> However, after fixing that and trying to solve it with FieldSplit
>>>>>>>> with LU factorization for the (0,0) block it failed because there were zero
>>>>>>>> pivots for all rows.
>>>>>>>>
>>>>>>>> Anyway, I found out that attaching the mass matrix to the Lagrange
>>>>>>>> multiplier field also worked.
>>>>>>>>
>>>>>>>> Another related question for my elasticity problem: after creating
>>>>>>>> the rigid body modes with DMPlexCreateRigidBody and attaching it to the
>>>>>>>> displacement field, does the matrix block size of the (0,0) block still
>>>>>>>> have to be set for good performance with gamg? If so, how can I do this?
>>>>>>>>
>>>>>>>
>>>>>>> Yes, it should be enough to set the block size of the preconditioner
>>>>>>> matrix.
>>>>>>>
>>>>>>> Matt
>>>>>>>
>>>>>>>
>>>>>>>> Thanks,
>>>>>>>> Sander
>>>>>>>>
>>>>>>>> On 2 March 2016 at 12:25, Matthew Knepley <knepley at gmail.com>
>>>>>>>> wrote:
>>>>>>>>
>>>>>>>>> On Wed, Mar 2, 2016 at 5:13 AM, Sander Arens <
>>>>>>>>> Sander.Arens at ugent.be> wrote:
>>>>>>>>>
>>>>>>>>>> Hi,
>>>>>>>>>>
>>>>>>>>>> I'm trying to set a mass matrix preconditioner for the Schur
>>>>>>>>>> complement of an incompressible finite elasticity problem. I tried using
>>>>>>>>>> the command PetscDSSetJacobianPreconditioner(prob, 1, 1, g0_pre_mass_pp,
>>>>>>>>>> NULL, NULL, NULL) (field 1 is the Lagrange multiplier field).
>>>>>>>>>> However, this causes a DIVERGED_LINE_SEARCH due to to Nan or Inf
>>>>>>>>>> in the function evaluation after Newton iteration 1. (Btw, I'm using the
>>>>>>>>>> next branch).
>>>>>>>>>>
>>>>>>>>>> Is this because I didn't use PetscDSSetJacobianPreconditioner for
>>>>>>>>>> the other blocks (which uses the Jacobian itself for preconditioning)? If
>>>>>>>>>> so, how can I tell Petsc to use the Jacobian for those blocks?
>>>>>>>>>>
>>>>>>>>>
>>>>>>>>> 1) I put that code in very recently, and do not even have
>>>>>>>>> sufficient test, so it may be buggy
>>>>>>>>>
>>>>>>>>> 2) If you are using FieldSplit, you can control which blocks come
>>>>>>>>> from A and which come from the preconditioner P
>>>>>>>>>
>>>>>>>>>
>>>>>>>>> http://www.mcs.anl.gov/petsc/petsc-current/docs/manualpages/PC/PCFieldSplitSetDiagUseAmat.html#PCFieldSplitSetDiagUseAmat
>>>>>>>>>
>>>>>>>>> http://www.mcs.anl.gov/petsc/petsc-current/docs/manualpages/PC/PCFieldSplitSetOffDiagUseAmat.html#PCFieldSplitSetOffDiagUseAmat
>>>>>>>>>
>>>>>>>>>
>>>>>>>>>> I guess when using PetscDSSetJacobianPreconditioner the
>>>>>>>>>> preconditioner is recomputed at every Newton step, so for a constant mass
>>>>>>>>>> matrix this might not be ideal. How can I avoid recomputing this at every
>>>>>>>>>> Newton iteration?
>>>>>>>>>>
>>>>>>>>>
>>>>>>>>> Maybe we need another flag like
>>>>>>>>>
>>>>>>>>>
>>>>>>>>> http://www.mcs.anl.gov/petsc/petsc-current/docs/manualpages/SNES/SNESSetLagPreconditioner.html
>>>>>>>>>
>>>>>>>>> or we need to expand
>>>>>>>>>
>>>>>>>>>
>>>>>>>>> http://www.mcs.anl.gov/petsc/petsc-current/docs/manualpages/SNES/SNESSetLagJacobian.html
>>>>>>>>>
>>>>>>>>> to separately cover the preconditioner matrix. However, both
>>>>>>>>> matrices are computed by one call so this would
>>>>>>>>> involve interface changes to user code, which we do not like to
>>>>>>>>> do. Right now it seems like a small optimization.
>>>>>>>>> I would want to wait and see whether it would really be maningful.
>>>>>>>>>
>>>>>>>>> Thanks,
>>>>>>>>>
>>>>>>>>> Matt
>>>>>>>>>
>>>>>>>>>
>>>>>>>>>> Thanks,
>>>>>>>>>> Sander
>>>>>>>>>>
>>>>>>>>>
>>>>>>>>>
>>>>>>>>>
>>>>>>>>> --
>>>>>>>>> What most experimenters take for granted before they begin their
>>>>>>>>> experiments is infinitely more interesting than any results to which their
>>>>>>>>> experiments lead.
>>>>>>>>> -- Norbert Wiener
>>>>>>>>>
>>>>>>>>
>>>>>>>>
>>>>>>>
>>>>>>>
>>>>>>> --
>>>>>>> What most experimenters take for granted before they begin their
>>>>>>> experiments is infinitely more interesting than any results to which their
>>>>>>> experiments lead.
>>>>>>> -- Norbert Wiener
>>>>>>>
>>>>>>
>>>>>>
>>>>>
>>>>>
>>>>> --
>>>>> What most experimenters take for granted before they begin their
>>>>> experiments is infinitely more interesting than any results to which their
>>>>> experiments lead.
>>>>> -- Norbert Wiener
>>>>>
>>>>
>>>>
>>>
>>>
>>> --
>>> What most experimenters take for granted before they begin their
>>> experiments is infinitely more interesting than any results to which their
>>> experiments lead.
>>> -- Norbert Wiener
>>>
>>
>>
>
>
> --
> What most experimenters take for granted before they begin their
> experiments is infinitely more interesting than any results to which their
> experiments lead.
> -- Norbert Wiener
>
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