what equations and discetizations are in A00? On Tue, Sep 27, 2022 at 1:45 AM 晓峰 何 <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> 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> 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> wrote: > > Lagrange multipliers > > > > >
