Hello, A00 comes from shell structures and discretized by FEM.
Thanks, Xiaofeng On Sep 27, 2022, at 17:48, Mark Adams <mfad...@lbl.gov<mailto:mfad...@lbl.gov>> wrote: what equations and discetizations are in A00? On Tue, Sep 27, 2022 at 1:45 AM 晓峰 何 <tlan...@hotmail.com<mailto:tlan...@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 <bsm...@petsc.dev<mailto:bsm...@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 <tlan...@hotmail.com<mailto:tlan...@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 <j...@jedbrown.org<mailto:j...@jedbrown.org>> wrote: Lagrange multipliers
