[petsc-users] FIELDSPLIT fields

[Rossi, Simone]

Thanks for clarifying that.

So if I have my subdomain set as

0 —— 1 —— 2  —— 3 —— 4  —— 5 —— 6
 | subdomain 1 | subdomain 2 | subdomain 1 |

Should I actually make sure that I define 3 separate subdomains?
Currently, my subdomains are defined  depending on a parameter of the system of PDEs I’m solving.

Thanks,

Simone

On Sep 5, 2018, at 12:37 PM, Fande Kong <fdkong.jd at gmail.com<mailto:fdkong.jd at gmail.com>> wrote:



On Wed, Sep 5, 2018 at 9:54 AM Smith, Barry F. <bsmith at mcs.anl.gov<mailto:bsmith at mcs.anl.gov>> wrote:

  2 should belong to one of the subdomains, either one is fine.

   Barry


> On Sep 5, 2018, at 10:46 AM, Rossi, Simone <srossi at email.unc.edu<mailto:srossi at email.unc.edu>> wrote:
>
> I’m trying to setup GASM, but I’m probably misunderstanding something.
>
> If I have this mesh
>
> 0 —— 1 —— 2 —— 3 —— 4
> subdomain 1  |   subdomain 2
>

You may need to make a decision which subdomain ``2" belongs to. Most people just let the shared node go to the lower MPI rank. If so, in this example, ``2" belongs to the subdomain one.

iis1 = {0, 1, 2}
ois  = {0, 1, 2, 3}

iis2 = {3, 4}
ois2 = {2, 3, 4}

You consider seriously to use GASM, I would suggest to partition  your problem (using ``hierach") in such a way that multi-rank subdomain is actually connected, otherwise you may end up having a deficient performance.


Thanks,

Fande,



> I create an interior (no overlap) and an outer (with overlap) IS for both subdomains.
>
> In my naive understanding
>
> iis1  = {0, 1}
> ois1 = {0, 1, 2}
>
> and
>
> iis2  = {3, 4}
> ois2 = {2, 3, 4}
>
> but then the node at the interface (node 2) does not belong to any interior IS. Should node 2 belong to both interior IS? Or should it belong only to one of the domains?
>
> Thanks,
> Simone
>
>
> On Aug 15, 2018, at 22:11, Griffith, Boyce Eugene <boyceg at email.unc.edu<mailto:boyceg at email.unc.edu>> wrote:
>
>>
>>
>>> On Aug 15, 2018, at 10:07 PM, Smith, Barry F. <bsmith at mcs.anl.gov<mailto:bsmith at mcs.anl.gov>> wrote:
>>>
>>>
>>> Yes you can have "overlapping fields" with FIELDSPLIT but I don't think you can use FIELDSPLIT for your case. You seem to have a geometric decomposition into regions. ASM and GASM are intended for such decompositions. Fieldsplit is for multiple fields that each live across the entire domain.
>>
>> Basically there is one field the lives on the entire domain, and another field that lives only on a subdomain.
>>
>> Perhaps we could do GASM for the geometric split and FIELDSPLIT within the subdomain with the two fields.
>>
>>> Barry
>>>
>>>
>>>> On Aug 15, 2018, at 7:42 PM, Griffith, Boyce Eugene <boyceg at email.unc.edu<mailto:boyceg at email.unc.edu>> wrote:
>>>>
>>>> Is it permissible to have overlapping fields in FIELDSPLIT? We are specifically thinking about how to handle DOFs living on the interface between two regions.
>>>>
>>>> Thanks!
>>>>
>>>> — Boyce
>>>
>>
>

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