[petsc-users] DIVERGED_DTOL

[w_ang_temp]

At 2013-01-16 03:02:32,"Barry Smith" <bsmith at mcs.anl.gov> wrote:
>
>> 1.701448294063e+04  >   1.e4*1.145582415879e+00  hence it declares divergence

  Hello, Barry
  I made some tests and it is true.  Thanks.
 
  But in the mannual, both version 3.2 and 3.3, the rule is:||rk||>dtol*||b||. It is ||b||, not r_0.
My misunderstanding? Or the error in the mannual?
  Besides, in the mannual, both version 3.2 and 3.3, the default dtol=1.0E+5. But from the results
in the example, it is 1.0E+4. I donot know the reason. My petsc version is 3.2-p7.
  Thanks.                            Jim

 

>Note that at iteration 171 the preconditioned residual is 9.348832909193e-13 < 1.e-12 * 1.145582415879e+00  very good convergence.
>
>You seem to have set an unreasonably tight convergence criteria. In double precision you can never realistically expect to use a rtol smaller than e-12. In fact normally it is not reasonable to use more than like 1.e-8. Those extra digits don't mean anything.
>
>   Barry
>
>
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