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

[Anush Krishnan]

Hi Jed,

Is there any reason why ATOL needs to be set for transient problems? Are
there any references you can point me to? I've been experiencing some
issues with transient problems where sometimes the flow stops evolving and
the linear solvers exit after zero iterations, and was wondering if this
might help.

Thanks,
Anush


On 28 July 2014 11:37, Jed Brown <jed at jedbrown.org> wrote:

> 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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