[petsc-users] Is it possible to use -snes_ksp_ew in the framework of KSP?

[Jed Brown]

Song Gao <song.gao2 at mail.mcgill.ca> writes:

> We modified the codes, used SNES to control the newton iteration and
> changed the code to matrix free fashion. But the legacy codes did a lot of
> other things between two newton iterations (such as output solution, update
> variables....). I know we could use linesearchpostcheck but it is
> difficulty to do that correctly.

It shouldn't be difficult and I still recommend this (SNES with monitors
and pre/post checks if necessary).

> Therefore, we decide to go back to the KSP framework but still use
> matrix free.
>
> When using SNES, we always use the runtime option -snes_ksp_ew, we observe
> that for some test cases, the residual stalls without -snes_ksp_ew, but
> converges with-snes_ksp_ew. So I'm thinking if it is possible to
> use -snes_ksp_ew in KSP? Thanks in advance.

KSP doesn't know about the nonlinear solve so it has no way of doing
this on its own.  You can implement the equivalent algorithm yourself if
you want.
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