[petsc-users] Preconditioned residuals for FGMRES

[Jed Brown]

Matthew Knepley <knepley at gmail.com> writes:

> On Fri, Jun 22, 2018 at 1:47 PM Boyce Griffith <griffith at cims.nyu.edu>
> wrote:
>
>> Can you set up the preconditioner so that you can just use GMRES?
>>
>
> So I think what Boyce is saying is, can't you fix the number of iterates in
> the inner Krylov solvers so that it becomes a linear
> operator and you can use GMRES?

A fixed number of Krylov iterations is not a linear operation.

A fixed number of Chebyshev iterations (or other method that applies a
constant polynomial) is linear.