[petsc-users] SNES without SNESSetJacobian, snes_fd or snes_mf

[Jed Brown]

Florian Kauer <florian.kauer at koalo.de> writes:

> Hi,
> what is the SNES solver actually doing when you do not provide a 
> jacobian and not explicitly select either finite differencing 
> approximation or matrix-free Newton-Krylov method?
>
> I just noticed that I mistakenly did this, but a good solution is found 
> anyway (and fast). So what is actually happening? Simple fixed-point 
> iteration?

Presumably you are using a DM that can provide a coloring, in which case
the sparse Jacobian is assembled using finite differencing with coloring.