Dear Dr.Bangerth,
   I tried both, first I tried 1e-4*system_rhs.l2_norm(), it failed. Then I
tried with exact precision limits, from 1e-3 to 1e-8, all of them cannot
converge.  If I set the precision level as 1e-4, with or without L2 norm it
stopped at step-42 with the residue 0.0113395.
Best regards,
Yuesu

On Sun, Aug 16, 2020 at 7:20 PM Wolfgang Bangerth <bange...@colostate.edu>
wrote:

> On 8/14/20 9:20 PM, yuesu jin wrote:
> > I tried a few levels of the tolerance, 1e-3, 1e-4 ,1e-6 and 1e-8. 1e-3
> > converged because that is in the same level with the solution. Error
> occurs
> > below 1e-4.  I have tried the Jacobi preconditioner instead of SSOR in
> the
> > single thread CG version, it converged as well.
>
> Is this 1e-4 * system_rhs.l2_norm(), or just 1e-4? If the latter, what is
> the
> size of system_rhs.l2_norm()? You should choose a tolerance that is
> proportional to the norm of the right hand side.
>
> Best
>   W.
>
>
> --
> ------------------------------------------------------------------------
> Wolfgang Bangerth          email:                 bange...@colostate.edu
>                             www: http://www.math.colostate.edu/~bangerth/
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-- 
Yuesu Jin,
Ph.D student,
University of Houston,
College of Natural Sciences and Mathematics,
Department of Earth and Atmospheric Sciences,
Houston, Texas 77204-5008
346-404-2062

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