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

[晓峰 何]

Hello,

A00 comes from shell structures and discretized by FEM.

Thanks,
Xiaofeng

On Sep 27, 2022, at 17:48, Mark Adams <mfadams at lbl.gov<mailto:mfadams at lbl.gov>> wrote:

what equations and discetizations are in A00?

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

Lagrange multipliers




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