[petsc-users] Regarding P4est

[MUKKUND SUNJII]

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.


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 <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 
>  
> 

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