[petsc-users] SNES question

[Milan Mitrovic]

Hello everyone,

I have a problem trying to use snes. I'm using it in a simulation to
compute an implicit time stepping scheme.

I'm trying to validate my implementation by testing everything on the
heat equation. When I use ksp with the analytic jacobian I get great
results, but when I try to switch back to snes I notice that when I
try to increase the resolution there is a lower limit on dt below
which snes won't converge... It works fine with ksp, but snes fails
with LS_FAILURE.

I also wrote an fd approximation and tested the jacobian and the two
are equal up to machine precision. And the fact that it works with ksp
tells me that it is correct...

What could be the problem with snes so that it fails to solve a linear
equation with a very small dt?

Thanks in advance,
Milan