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

[Rolf Kuiper]

Hi Jed,

in general, I am using only RTOL with ATOL=0, sometimes (if the range of the physical solution is known a priori) I use both criteria.
Actually, Matthew already helped me to build my own KSPConverged routine including the minimum iteration number.

Thanks a lot for all your effort and great support,
Rolf


Am 28.07.2014 um 17:37 schrieb 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.