[petsc-users] Usage of AMG as preconditioner

[Jed Brown]

Michael Werner <michael.werner at dlr.de> writes:

>>> >> > It uses unpreconditioned GMRES to estimate spectral bounds for
>>> >> > the operator before using a Chebychev smoother.  

It is GMRES preconditioned by the diagonal.

>> Moreover, in the incompressible limit, the compressible 
>> formulation can
>> become very stiff,
>> leading to failure of solvers. That is why you get the slightly
>> compressible (adiabatic?) formulations.
>
> Ah, too bad, I was already expecting something like that, because 
> most of the applications I found so far were FEM/ elasticity 
> problems. Then I'll have to see if I can find some other suitable 
> solution.

You can implement a low-Mach preconditioner that would use multigrid.
If you're working in conservative variables, then it requires a
nonlinear change of variables to isolate the pressure space.