[petsc-users] force KSP to perform at least a single iteration

[Jed Brown]

Rolf Kuiper <kuiper at mpia.de> writes:
> I need this to e.g. solve a linear system of equations several times
> (as the physical system proceeds in time); during a single call /
> timestep, the system, might not change stronger than the RTOL in use,
> but in the long-run (several hundreds to thousands of calls), the
> system will actually change by several RTOL; nonetheless, the default
> KSP solver stops without doing any iteration (= 0), i.e. the system
> does not change at all.

When you use -ksp_converged_reason, is it completing due to RTOL or
ATOL?  For transient problems, it's often good to set an absolute
tolerance.
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