[petsc-users] Solve Linear System with Field Split Preconditioner

[Mark Adams]

what equations and discetizations are in A00?

On Tue, Sep 27, 2022 at 1:45 AM 晓峰 何 <tlanyan at hotmail.com> wrote:

> Hi Barry,
>
> A00 is formed from elliptic operator.
>
> I tried GAMG with A00, but it was extremely slow to solve the system with
> field-split preconditioner(I’m not sure I did it with the right way).
>
> Thanks,
> Xiaofeng
>
> On Sep 26, 2022, at 23:11, Barry Smith <bsmith at petsc.dev> wrote:
>
>
>   What is your A00 operator? ILU is almost never a good choice for large
> scale problems. If it is an elliptic operator that using a PC of gamg may
> work well for the A00 preconditioner instead of ILU.
>
>   Barry
>
>   For moderate size problems you can use a PC type LU for AOO to help you
> understand the best preconditioner to use for the A11 (the Schur complement
> block), once you have a good preconditioner for the A11 block you would
> then go back and determine a good preconditioner for the A00 block.
>
> On Sep 26, 2022, at 10:08 AM, 晓峰 何 <tlanyan at hotmail.com> wrote:
>
> Hello Jed,
>
> The saddle point is due to Lagrange multipliers, thus the size of A11 is
> much smaller than A00.
>
>
>
> Best Regards,
>
> Xiaofeng
>
>
> On Sep 26, 2022, at 21:03, Jed Brown <jed at jedbrown.org> wrote:
>
> Lagrange multipliers
>
>
>
>
>
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