[petsc-users] Regarding P4est

[Stefano Zampini]

Also, when using p4est, the orientation of the cells are different than the
one generated when refining with DMPlex alone. I would double-check the
code if you are not making any assumption ons it

Il giorno gio 18 giu 2020 alle ore 23:24 Matthew Knepley <knepley at gmail.com>
ha scritto:

> On Wed, Jun 17, 2020 at 3:21 PM MUKKUND SUNJII <mukkundsunjii at gmail.com>
> wrote:
>
>> Yes, precisely! I am not sure how I can replicate using the original
>> version of ex11.c because it does not support bathymetry.
>>
>> Regardless, to demonstrate the discrepancy, I have uploaded three plots.
>> The scenario is a lake at rest. Essentially, you have a varying bathymetry
>> but a level water surface. If the model is well balanced, then the water
>> surface height must not change. The description of the files are below
>>
>> 1) Bathymetry.png : It shows you the bathymetry profile (z(x)) and the
>> water surface height (H = h+z(x)) at t = 0.
>>
>
> Hmm, that does look like a bug. The purpose of TransferVec is to preserve
> moments when transferring from one grid to another. Here it looks like it
> is artificially diffusive, but I do not
> see a reason for this pattern if you did the refinement initially, and not
> with p4est, since then the base grid is the same as the Plex. Is that
> what your code does?
>
>   Thanks,
>
>     Matt
>
>
>>
>> 2) Plex.png : This is the water surface height after 1 time step (0.007055
>> sec)  and the dm type is Plex. As you can see, the water surface height
>> is undisturbed as expected.
>>
>> 3) P4est.png : This is the result after 1 time step (same final time) if
>> I set the dm type as p4est. The noise is in the order of 1e-3 to be a
>> little more specific. Since its not specifically at the boundaries and more
>> or less spread throughout, it could indeed be noise introduced. But of
>> course I could be wrong.
>>
>> Maybe this paints a better picture.
>>
>> Regards,
>>
>> Mukkund
>>
>> For your reference, the Riemann Solver is a modified version of the HLL
>> solver: *A simple well-balanced and positive numerical scheme for the
>> shallow-water system by **Emmanuel Audusse, Christophe Chalons, Philippe
>> Ung. *
>> (
>> https://www.intlpress.com/site/pub/files/_fulltext/journals/cms/2015/0013/0005/CMS-2015-0013-0005-a011.pdf
>> )
>>
>> On 17 Jun 2020, at 20:47, Mark Adams <mfadams at lbl.gov> wrote:
>>
>> So you get this noise with a regular grid in p4est. So the same grid as
>> will Plex, and you are not getting the same results.
>>
>> I don't know of any difference from p4est on a non-adapted grid. Can you
>> reproduce this with ex11?
>>
>> Matt and Toby could answer this better.
>>
>>
>> On Wed, Jun 17, 2020 at 1:33 PM MUKKUND SUNJII <mukkundsunjii at gmail.com>
>> wrote:
>> Greetings,
>>
>> I am a master’s student working on the shallow water model of the TS
>> example 'ex11.c' as part of my thesis. Therefore, I am working with
>> DMForest for the implementation of adaptive grids. I have a question and an
>> observation.
>>
>> I am trying to find relevant information about interpolation that takes
>> place through the routine DMForestTransferVec. Perhaps it could be my
>> inability to find it, but I am unable to locate the implementation of the
>> routine
>>
>> (forest->transfervec)(dmIn,vecIn,dmOut,vecOut,useBCs,time).
>>
>> Any information on this particular routine is highly appreciated.
>>
>> Furthermore, I have developed a well balanced Riemann Solver that
>> includes topography in the model. In the process of testing both the
>> non-adaptive and adaptive version, I found that my results differed when I
>> changed the type of DM. For instance, when I run a scenario in a fixed,
>> non-adaptive grid  with a DM of type 'P4est', I find that the well balanced
>> nature is lost due to small perturbations all across the domain. However,
>> this does not occur when I use a DM of type ‘plex’. Is there a radical
>> change in the routines between the two DM’s? This is not as much of a
>> question as it is an observation.
>>
>> Thank you for all of your suggestions!
>>
>> Regards,
>>
>> Mukkund
>>
>>
>>
>>
>
> --
> 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
>
> https://www.cse.buffalo.edu/~knepley/
> <http://www.cse.buffalo.edu/~knepley/>
>


-- 
Stefano
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