[petsc-users] issues with VecSetValues in petsc 3.19

[Jed Brown]

Edoardo alinovi <edoardo.alinovi at gmail.com> writes:

> Hello Barry,
>
> Welcome to the party! Thank you guys for your precious suggestions, they
> are really helpful!
>
> It's been a while since I am messing around and I have tested many
> combinations. Schur + selfp is the best preconditioner, it converges within
> 5 iters using gmres for inner solvers but it is not very fast and sometimes
> multiplicative it's a better option as the inner iterations looks lighter.
> If I tune the relative tolerance I get a huge speed up, but I am a bit less
> confident about the results. The funny thing is that the default relative
> tolerance if commercial CFD solver is huge, very often 0.1 -.-

This depends on time step size and tolerances for quantities of interest.

> If I may borrow your brain guys for a while, I would like to ask your
> opinion about the multigrid they use in this paper:
> https://www.aub.edu.lb/msfea/research/Documents/CFD-P18.pdf.
> At some point they say: " The algorithm used in this work is a combination
> of the ILU(0) [28] algorithm with an additive corrective multigrid method
> [29] ", 29: https://www.tandfonline.com/doi/abs/10.1080/10407788608913491

It looks like this is a coupled solver with collocated dofs and thus I don't know how they stabilize in the incompressible limit (an inf-sup requirement is needed for stability). (This is based on a cursory read.)