[petsc-users] rtol meaning

[Danny Lathouwers - TNW]

Dear users,

I have a problem where I step time and repeatedly solve a system with differing rhs.
At some time step petsc solver returns that initial solution is good enough (converged reason = 2 with 0 iterations done).
I do not expect this behaviour. I use rtol = 0.001, atol=0 and dtol =large number.



The manual seems to suggest the criterion is: rnorm < MAX (rtol * rnorm_0, abstol) (probably based on preconditioned residual).

How could this lead to zero iterations being done? Or is the criterion based on rnorm/bnorm instead (which I found in some reference on the internet concerning petsc and would explain the observed behaviour).



Thanks,

Danny.



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