[petsc-dev] API changes in MatIS

[Stefano Zampini]

> Okay. Presumably the change of basis can be done with a MatPtAP if
> desirable.
>

One we have the constraint matrix, we can easily obtain the change of basis
matrix T (as in Klawonn-Widlund papers).
Note that the change of basis approach will be very effective for exact
applications with reduced iterations. I think we should include in the new
matrix class the possibility of doing iterations on the reduced space
instead of the whole space of dofs.


>
>
>> Actually in PCBDDC the local coarse matrix is computed using a
>> theoretical equivalence of the PtAP operation of coarse basis and the
>> unassembled MATIS matrix (coarse basis are continuous only at vertex and
>> constraints dofs). PtAP (where P is dense) is just avoided for its
>> computational costs.
>>
>
> Are you basically just doing a local PtAP or do you use the equivalence
>
> K \Psi = C^T \Lambda   (notation of Dohrmann's Eq 2)
>
> or something else?
>
>

I'm using the equivalence.

You said you would have the new matrix class to support either more
subdomains per core, or more cores per subdomain. In the latter case,
threaded or mpi matrices (on subcomms)?






-- 
Stefano
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