[petsc-users] Fwd: PCGASMSetLocalSubdomains

[Dmitry Karpeev]

On Tue, May 15, 2012 at 11:25 AM, Hui Zhang <mike.hui.zhang at hotmail.com>wrote:

>
> On May 15, 2012, at 6:20 PM, Jed Brown wrote:
>
> On Tue, May 15, 2012 at 10:11 AM, Hui Zhang <mike.hui.zhang at hotmail.com>wrote:
>
>> Yes, see Mandel & Dorhamann' paper
>> http://ccm.ucdenver.edu/reports/rep194.pdf ,
>>
>
> BDDC needs to solve pinned Neumann problems to build the coarse space.
> There is no way to obtain those Neumann problems from an assembled matrix,
> and neither PCASM or PCGASM is set up to handle that.
>
> There is a BDDC implementation from Stefano Zampini in petsc-dev, but the
> code is still not mature so you have to configure --with-pcbddc to activate
> it.
>
>
> Yes, thanks!
>
>
>
>> but this is for non-overlapping. For overlapping we can see Leong &
>> Widlund
>> http://cs.nyu.edu/web/Research/TechReports/TR2008-914/TR2008-914.pdf
>>
>
> This solves non-overlapping Dirichlet problems to construct the coarse
> basis, then uses overlapping Dirichlet problems for the smoother. Again,
> these problems are different, so it's not useful to extract the subdomain
> problems from PC(G)ASM.
>
>
> Yes, but I want to modify it a bit to just use the overlapping subdomains
> for coarse basis.
> I think my choice is more natural because we avoid factorization on the
> non-overlapping subdomains.
>
As far as I can see, you can only reuse the scatters from PCASM, which are
easy enough to construct on your own.
PCGASM doesn't have the individual scatters, so that's of even less help
for you.

Dmitry.
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