[petsc-users] On changing the tolerance for SNES and KSP

[Bao Kai]

Hi, all,

I am a little unclear about the exact definition of the relative and exact
tolerance or how the PETSc determines the convergence, while my problem is
as follows.

Generally, all my equations are solved by SNES and I use the physical
units.  The PC and KSP are bjacobi and bicgstab respectively. For the
pressure equation, at the beginning, the domain is not so big, and the
pressure are within a certain range.  The default parameters works.

Then I increase the size of the domain by 10 times, then the range of the
pressure will be about 10 times bigger accordingly due to gravity. Then
with the default parameters, the KSP failed in getting converged with
reaching the maximum iteration No. .

Could you please help to tell me how I should change the tolerance to fit
the change of the domain?

Thank you very much.

Best Regards,
Kai
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