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

[Barry Smith]

  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 <mailto:jed at jedbrown.org>> wrote:
>> 
>> Lagrange multipliers
> 

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