Sorry. There is a typo in my previous email. It should be ksp_pc_side.
Regards, Rama On Sun, May 1, 2022 at 9:23 PM Ramakrishnan Thirumalaisamy < [email protected]> wrote: > Thank you. I have a couple of questions. I am solving the low Mach > Navier-Stokes system using a projection preconditioner (pc_shell type) with > GMRES being the outer solver and Richardson being the Krylov > preconditioner. The solver diverges when ksp_pc_type is "right”: > > Linear stokes_ solve did not converge due to DIVERGED_NANORINF iterations 0 > > and it converges when ksp_pc_type is "left": > > Residual norms for stokes_ solve. > 0 KSP preconditioned resid norm 8.829128536017e+04 true resid norm > -nan ||r(i)||/||b|| -nan > 1 KSP preconditioned resid norm 1.219313641627e+00 true resid norm > -nan ||r(i)||/||b|| -nan > 2 KSP preconditioned resid norm 8.547033285706e-12 true resid norm > -nan ||r(i)||/||b|| -nan > Linear stokes_ solve converged due to CONVERGED_RTOL iterations 2 > > I am curious to know why this is happening. The solver also diverges with > "FGMRES" as the outer solver (which supports only right preconditioning). > > 2. Is it also possible to not get "-nan" when || b || = 0? > > > Regards, > Rama > > On Sun, May 1, 2022 at 12:12 AM Dave May <[email protected]> wrote: > >> >> >> On Sun 1. May 2022 at 07:03, Amneet Bhalla <[email protected]> wrote: >> >>> How about using a fixed number of Richardson iterations as a Krylov >>> preconditioner to a GMRES solver? >>> >> >> That is fine. >> >> Would that lead to a linear operation? >>> >> >> Yes. >> >> >> >>> On Sat, Apr 30, 2022 at 8:21 PM Jed Brown <[email protected]> wrote: >>> >>>> In general, no. A fixed number of Krylov iterations (CG, GMRES, etc.) >>>> is a nonlinear operation. >>>> >>>> A fixed number of iterations of a method with a fixed polynomial, such >>>> as Chebyshev, is a linear operation so you don't need a flexible outer >>>> method. >>>> >>>> Ramakrishnan Thirumalaisamy <[email protected]> writes: >>>> >>>> > Hi, >>>> > >>>> > I have a Krylov solver with a preconditioner that is also a Krylov >>>> solver. >>>> > I know I can use "fgmres" for the outer solver but can I use gmres >>>> for the >>>> > outer solver with a fixed number of iterations in the Krylov >>>> > preconditioners? >>>> > >>>> > >>>> > Thanks, >>>> > Rama >>>> >>> -- >>> --Amneet >>> >>> >>> >>>
