[petsc-users] unexpected behavior of the snes solver

[Dominik Szczerba]

Hi,

I am implementing both FormFunction and FormJacobian for the SNES
solver. It seems to start off correctly, with the 2 functions being
called one after another in a loop, and with ||Ax-b|| decreasing about
3 orders of magnitude. But then only the FormFunction is being called
several times, without subsequent calls to FormJacobian and obviously
the residue is not being reduced any further, because there are no
calls to the underlying ksp. If I inspect the solution it looks
qualitatively "on the way" to the expected one, but the values are not
correct, just as if the iterations were prematurely stopped. What sort
of a problem can such a behavior indicate?

Regards,
Dominik