[petsc-users] Questions about PCEXOTIC

[Edoardo Centofanti]

Dear Stefano,

Very nice, that was exactly what I was looking for. Also the possibility of
turning on adaptivity with MATIS seems an interesting option.

Best,
Edoardo

Il giorno gio 22 mag 2025 alle ore 10:33 Stefano Zampini <
stefano.zampini at gmail.com> ha scritto:

> GDSW is algebraic, not restricted to DMDA. Here is an example command
> line.
>
> -pc_type mg -pc_mg_levels 2 -pc_mg_adapt_interp_coarse_space *gdsw*
> -pc_mg_galerkin -mg_levels_pc_type jacobi
>
>
> If you have a MATIS matrix, you can also turn on adaptivity (see for
> example these tests).
>
>
>
> https://urldefense.us/v3/__https://gitlab.com/petsc/petsc/-/blob/main/src/ksp/ksp/tutorials/ex71.c*L727__;Iw!!G_uCfscf7eWS!Z06Y5N-tG2d-bTV_5UgqncaOVFzjv3GVertAowz01EIeSx2WIgHrNtv_gI26zxcuxrh6IaMuDaQe0Vx6FO3MYaMxOWXsQvfTFv9HGTisNCo$ 
>
> https://urldefense.us/v3/__https://gitlab.com/petsc/petsc/-/blob/main/src/snes/tutorials/ex12.c*L1799__;Iw!!G_uCfscf7eWS!Z06Y5N-tG2d-bTV_5UgqncaOVFzjv3GVertAowz01EIeSx2WIgHrNtv_gI26zxcuxrh6IaMuDaQe0Vx6FO3MYaMxOWXsQvfTFv9HS314Dc0$ 
>
>
>
> Code setup is here
> https://urldefense.us/v3/__https://gitlab.com/petsc/petsc/-/blob/main/src/ksp/pc/impls/mg/gdsw.c__;!!G_uCfscf7eWS!Z06Y5N-tG2d-bTV_5UgqncaOVFzjv3GVertAowz01EIeSx2WIgHrNtv_gI26zxcuxrh6IaMuDaQe0Vx6FO3MYaMxOWXsQvfTFv9H9bF7URM$ 
>
>
>
>
> Il giorno gio 22 mag 2025 alle ore 10:59 Edoardo Centofanti <
> edoardo.centofanti01 at universitadipavia.it> ha scritto:
>
>> Dear all,
>>
>> Thank you for your answers.
>> Do you know which options are required for a typical use case of GDSW in
>> PCMG? However, I imagine that only structured DMDA meshes can be employed
>> with it.
>>
>> Best,
>> Edoardo
>>
>> Il giorno mer 21 mag 2025 alle ore 16:52 Barry Smith <bsmith at petsc.dev>
>> ha scritto:
>>
>>>
>>>   Thanks for your interest in this type of algorithm.
>>>
>>>   As Pierre notes, the code is implemented only as a simple tutorial on
>>> one particular "exotic" wire basket-type algorithm. We don't recommend this
>>> implementation for more general algorithms or geometries.
>>>
>>>   The face dof represents some sort of "average" of the face solution,
>>> it is not a point value.
>>>
>>>   Barry
>>>
>>>
>>> On May 21, 2025, at 4:51 AM, Pierre Jolivet <pierre at joliv.et> wrote:
>>>
>>>
>>>
>>> On 21 May 2025, at 10:41 AM, Edoardo Centofanti <
>>> edoardo.centofanti01 at universitadipavia.it> wrote:
>>>
>>> 
>>> Dear all,
>>>
>>> I have some questions about the PCEXOTIC preconditioner:
>>>
>>> 1- While the type "wirebasket" seems clear to me, I do not understand
>>> what is meant as "one dof per face" in the documentation referring to
>>> "face" type. Is it intended as the interpolation on the centre of the face
>>> or some mean value?
>>>
>>> 2- Is it possible to change the overlap between the subdomains?
>>>
>>> 3- Are there any plans of extending the implementation to unstructured
>>> grids (DMPlex-like)? The current one seems to rely heavily on DMDA
>>>
>>> 4- Running some preliminary tests on GPU with a code of mine that works
>>> on CPU, I got the following error:
>>>
>>>  ** On entry to cusparseSpMM_bufferSize(): dimension mismatch,
>>> matA.num_rows (15405) != matC.num_rows (44955) with opA =
>>> CUSPARSE_OPERATION_NON_TRANSPOSE
>>>
>>> Is the preconditioner intended to run also on GPU or the error above
>>> comes from the fact that this feature has yet to be tested/fully
>>> implemented?
>>>
>>>
>>> This preconditioner is very old and the code is barely maintained.
>>> There is a newer implementation of the GDSW preconditioner in PCMG, see
>>> https://urldefense.us/v3/__https://petsc.org/release/manualpages/PC/PCMGSetAdaptCoarseSpaceType/__;!!G_uCfscf7eWS!Z06Y5N-tG2d-bTV_5UgqncaOVFzjv3GVertAowz01EIeSx2WIgHrNtv_gI26zxcuxrh6IaMuDaQe0Vx6FO3MYaMxOWXsQvfTFv9HS4XKaQc$ 
>>> <https://urldefense.us/v3/__https://petsc.org/release/manualpages/PC/PCMGSetAdaptCoarseSpaceType/__;!!G_uCfscf7eWS!ZDnv3udGFNlZEC_MRfLAqwvcvCObnaAjMCeyaW__UaecBvN3MkXrzOPwJJUSHXo80-xOQdLNnSf_nLmUd7bZxg$>
>>>
>>> Thanks,
>>> Pierre
>>>
>>> Thank you in advance,
>>> Best,
>>> Edoardo
>>>
>>>
>>>
>>
>> --
>> Edoardo Centofanti
>> Dipartimento di Matematica 'Felice Casorati'
>> Università degli Studi di Pavia
>>
>> Tel. 0382985608  |  Ufficio A14  |  Via Ferrata 5, 27100 Pavia, Italy
>> <https://urldefense.us/v3/__https://maps.google.com/?q=Via*20Ferrata*205,*2027100*20Pavia,*20Italy__;JSUlJSU!!G_uCfscf7eWS!Zmi6sdgeoCOMy1lkVGYn-ac5wvH3QEcOkYQ2VzdQgCqLY8nIVkX1oi_yt5S2vJDcF5BT8mmzOLmOUEK483D0v9_aZe01iy1b20hMoN_kNHg$>
>>
>
>
> --
> Stefano
>


-- 
Edoardo Centofanti
Dipartimento di Matematica 'Felice Casorati'
Università degli Studi di Pavia

Tel. 0382985608  |  Ufficio A14  |  Via Ferrata 5, 27100 Pavia, Italy
<https://urldefense.us/v3/__https://maps.google.com/?q=Via*20Ferrata*205,*2027100*20Pavia,*20Italy__;JSUlJSU!!G_uCfscf7eWS!Z06Y5N-tG2d-bTV_5UgqncaOVFzjv3GVertAowz01EIeSx2WIgHrNtv_gI26zxcuxrh6IaMuDaQe0Vx6FO3MYaMxOWXsQvfTFv9Ha7BdO-s$ >
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