[petsc-users] TS (arkimex) question

[Mark Adams]

Can you recommend a higher order method that I might try?

On Sun, Jan 19, 2020 at 10:37 AM Jed Brown <jed at jedbrown.org> wrote:

> Use -ts_adapt_monitor to see the rationale.
>
> Note that 1bee is backward Euler with an extrapolation error estimator
> (for adaptive control).  It's still only first order accurate, and the
> longer step may be part of your SNES issues.
>
> You can set a maximum time step (-ts_adapt_dt_max) or be more aggressive
> about reducing time step in response to SNES failure
> (-ts_adapt_scale_solve_failed) or remember that failure for longer
> before increasing the step again (-ts_adapt_time_step_increase_delay) or
> more gradually increase time step when permitted (-ts_adapt_clip).
>
> Mark Adams <mfadams at lbl.gov> writes:
>
> > I am using -ts_type arkimex -ts_arkimex_type 1bee -ts_max_snes_failures
> -1
> > -ts_rtol 1e-6 -ts_dt 1.e-7
> >
> > First ,Jed gave me these parameters. This is not a DAE, just a fully
> > implicit solve. Advice on parameters welcome.
> >
> > Second, TS is reporting a large time step (0.0505357) that is wrong.
> >
> > Third, it repeatedly takes this extra one or two (its a 3 step method)
> step
> > due to SNES failure. I wonder if that can be optimized.
> >
> > Thanks,
> > Mark
> >
> >
> > ....
> >     9 SNES Function norm 1.438395286712e-06
> >    10 SNES Function norm 8.050454869525e-07
> >   Nonlinear solve converged due to CONVERGED_SNORM_RELATIVE iterations 10
> > [0] TSAdaptChoose_Basic(): Estimated scaled local truncation error
> > 0.00461254, *accepting step of size 0.00304954*
> > 600 TS *dt 0.0304954* time 0.697817
> >     0 SNES Function norm 1.018387577463e-02
> > ...
> >    23 SNES Function norm 6.583420045281e-05
> >    24 SNES Function norm 5.959294539241e-05
> >    25 SNES Function norm 5.394347124131e-05
> >   Nonlinear solve did not converge due to *DIVERGED_MAX_IT* iterations 25
> >     0 SNES Function norm 1.018387577468e-02
> >   ...
> >    24 SNES Function norm 1.000717662032e-06
> >    25 SNES Function norm 7.741622573808e-07
> >   Nonlinear solve converged due to *CONVERGED_SNORM_RELATIVE* iterations
> 25
> >     0 SNES Function norm 1.014795904701e-02
> > ...
> >    15 SNES Function norm 1.334407891279e-06
> >    16 SNES Function norm 9.148934277015e-07
> >   Nonlinear solve converged due to *CONVERGED_SNORM_RELATIVE* iterations
> 16
> >     0 SNES Function norm 1.016588008759e-02
> >   ...
> >    16 SNES Function norm 9.144418053264e-07
> >   Nonlinear solve converged due to *CONVERGED_SNORM_RELATIVE* iterations
> 16
> > [0] TSAdaptChoose_Basic(): Estimated scaled local truncation error
> > 0.0184347, *accepting step of size 0.00762384*
> > 601 TS *dt 0.0505357 *time 0.705441
> >     0 SNES Function norm 1.014792968017e-02
> >     1 SNES Function norm 1.026477259201e-03
> >     2 SNES Function norm 6.170336507030e-04
> >     3 SNES Function norm 5.433176612554e-04
> >     4 SNES Function norm 5.196626557375e-04
> >     5 SNES Function norm 4.977855046309e-04
>
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