[petsc-users] discontinuous viscosity stokes equation 3D staggered grid

[Matthew Knepley]

On Fri, Jul 19, 2013 at 3:56 AM, Bishesh Khanal <bisheshkh at gmail.com> wrote:

>
>
>
> On Thu, Jul 18, 2013 at 7:59 PM, Matthew Knepley <knepley at gmail.com>wrote:
>
>> On Thu, Jul 18, 2013 at 12:51 PM, Bishesh Khanal <bisheshkh at gmail.com>wrote:
>>
>>> Thanks Jed. I implemented a 2D case which worked when running the
>>> program with the options: -pc_type fieldsplit -pc_fieldsplit_type schur
>>> -pc_fieldsplit_detect_saddle_point
>>>  But I encountered some problems when using following options (this set
>>> of options is based on one of the tutorial slides in the website for
>>> multiphysics problem):
>>> -ksp_type fgmres -pc_type mg -mg_levels_ksp_type fgmres
>>> -mg_levels_ksp_max_it 2 -mg_levels_pc_type fieldsplit
>>> -mg_levels_pc_fieldsplit_detect_saddle_point ‐mg_levels_pc_fieldsplit_type
>>> schur -mg_levels_pc_fieldsplit_factorization_type full
>>> -mg_levels_pc_fieldsplit_schur_precondition user
>>> -mg_levels_fieldsplit_0_ksp_type preonly -mg_levels_fieldsplit_0_pc_type
>>> sor -mg_levels_fieldsplit_0_pc_sor_forward -mg_levels_fieldsplit_0_ksp_type
>>> gmres -mg_levels_fieldsplit_0_pc_type none -mg_levels_fieldsplit_ksp_max_it
>>> 5 -mg_coarse_pc_type svd
>>>
>>> The relevant error messages:
>>> [1]PETSC ERROR: --------------------- Error Message
>>> ------------------------------------
>>> [1]PETSC ERROR: Invalid argument!
>>> [1]PETSC ERROR: Unknown logical value: ‐mg_levels_pc_fieldsplit_type!
>>> [1]PETSC ERROR:
>>> ------------------------------------------------------------------------
>>> [1]PETSC ERROR: Petsc Release Version 3.4.1, Jun, 10, 2013
>>>  ...
>>> [1]PETSC ERROR: PetscOptionsStringToBool() line 173 in
>>> /home/bkhanal/Documents/softwares/petsc-3.4.1/src/sys/objects/options.c
>>> [1]PETSC ERROR: PetscOptionsGetBool() line 1530 in
>>> /home/bkhanal/Documents/softwares/petsc-3.4.1/src/sys/objects/options.c
>>> [1]PETSC ERROR: PCSetFromOptions_FieldSplit() line 1060 in
>>> /home/bkhanal/Documents/softwares/petsc-3.4.1/src/ksp/pc/impls/fieldsplit/fieldsplit.c
>>>
>>
>> These line numbers do not match the source. How did you install?
>>
>>
>> https://bitbucket.org/petsc/petsc/src/160ea6873d9fa631d01b6f8a2d8b12aece7dfb61/src/ksp/pc/impls/fieldsplit/fieldsplit.c?at=maint#cl-1060
>>
>> I had installed it in pretty much a standard way: downloading the tarball
> from the petsc webpage, then using ./configure with a bunch of options.
> I checked the fieldsplit.c file in my local installation, it seemed the
> difference to be in the first line. My local copy the code starts at 2nd
> line with first being just a newline unlike the one in bitbucket.
>

Okay, you have some kind of invisible character in there (maybe \r?) or the
dash is another ASCII character instead of -, so it thinks that
‐mg_levels_pc_fieldsplit_type is the argument. Retype the input by hand.

   Matt


> In any case, I tried to install a newer version: petsc-3.4.2 but I
> encountered some problems! I will send another email regarding installation
> issues at  petsc-maint at mcs.anl.gov while keeping this thread intact for
> my stokes problem!
>
>
>
>
>>    Matt
>>
>>
>>>  [1]PETSC ERROR: PCSetFromOptions() line 174 in
>>> /home/bkhanal/Documents/softwares/petsc-3.4.1/src/ksp/pc/interface/pcset.c
>>> [1]PETSC ERROR: KSPSetFromOptions() line 357 in
>>> /home/bkhanal/Documents/softwares/petsc-3.4.1/src/ksp/ksp/interface/itcl.c
>>> [1]PETSC ERROR: PCSetUp_MG() line 677 in
>>> /home/bkhanal/Documents/softwares/petsc-3.4.1/src/ksp/pc/impls/mg/mg.c
>>> [1]PETSC ERROR: PCSetUp() line 890 in
>>> /home/bkhanal/Documents/softwares/petsc-3.4.1/src/ksp/pc/interface/precon.c
>>> [1]PETSC ERROR: KSPSetUp() line 278 in
>>> /home/bkhanal/Documents/softwares/petsc-3.4.1/src/ksp/ksp/interface/itfunc.c
>>> ...
>>> And the warnings:
>>>
>>> WARNING! There are options you set that were not used!
>>> WARNING! could be spelling mistake, etc!
>>> Option left: name:-mg_coarse_pc_type value: svd
>>> Option left: name:-mg_levels_fieldsplit_0_ksp_type value: gmres
>>> Option left: name:-mg_levels_fieldsplit_0_pc_sor_forward (no value)
>>> Option left: name:-mg_levels_fieldsplit_0_pc_type value: none
>>> Option left: name:-mg_levels_fieldsplit_ksp_max_it value: 5
>>> Option left: name:-mg_levels_ksp_max_it value: 2
>>> Option left: name:-mg_levels_ksp_type value: fgmres
>>> Option left: name:-mg_levels_pc_fieldsplit_factorization_type value: full
>>> Option left: name:-mg_levels_pc_fieldsplit_schur_precondition value: user
>>>
>>> Is it that -mg_levels_pc_fieldsplit_type should be followed by some
>>> "bool" value ? 1 ? true ?
>>> I tried using "true", then it did not give any error but the following
>>> warnings:
>>> WARNING! There are options you set that were not used!
>>> WARNING! could be spelling mistake, etc!
>>> Option left: name:-mg_coarse_pc_type value: svd
>>> Option left: name:-mg_levels_fieldsplit_0_pc_sor_forward (no value)
>>> Option left: name:-mg_levels_pc_fieldsplit_factorization_type value: full
>>>
>>> I ran the program for the small size. Now, before I implement the 3D
>>> case with this approach instead of trying the implementation of Augmented
>>> Lagrangian method (M2 in previous email) my question is:
>>> If I use the Petsc with the method you suggested (PCFieldSplit,
>>> multigrid for momentum etc), tentatively how much of computing resources
>>> and the corresponding time would it require to solve the problem of the
>>> size I want (around 250^3 grid sized domain) ?
>>>
>>>
>>>
>>> On Wed, Jul 17, 2013 at 9:48 PM, Jed Brown <jedbrown at mcs.anl.gov> wrote:
>>>
>>>> Bishesh Khanal <bisheshkh at gmail.com> writes:
>>>>
>>>> > Now, I implemented two different approaches, each for both 2D and 3D,
>>>> in
>>>> > MATLAB. It works for the smaller sizes but I have problems solving it
>>>> for
>>>> > the problem size I need (250^3 grid size).
>>>> > I use staggered grid with p on cell centers, and components of v on
>>>> cell
>>>> > faces. Similar split up of K to cell center and faces to account for
>>>> the
>>>> > variable viscosity case)
>>>>
>>>> Okay, you're using a staggered-grid finite difference discretization of
>>>> variable-viscosity Stokes.  This is a common problem and I recommend
>>>> starting with PCFieldSplit with Schur complement reduction (make that
>>>> work first, then switch to block preconditioner).  You can use PCLSC or
>>>> (probably better for you), assemble a preconditioning matrix containing
>>>> the inverse viscosity in the pressure-pressure block.  This diagonal
>>>> matrix is a spectrally equivalent (or nearly so, depending on
>>>> discretization) approximation of the Schur complement.  The velocity
>>>> block can be solved with algebraic multigrid.  Read the PCFieldSplit
>>>> docs (follow papers as appropriate) and let us know if you get stuck.
>>>>
>>>
>>>
>>
>>
>> --
>> 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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