Using some delta_t in embedded RK

[Praveen C]

Hello

I am using embedded RK scheme

https://www.dealii.org/current/doxygen/deal.II/classTimeStepping_1_1EmbeddedExplicitRungeKutta.html

which chooses the time step in some adaptive manner.

I also want to save solution to file at some intervals, e.g., at t = 1.0, 2.0, etc for which sometimes I have to use a definite delta_t so I exactly reach the next time I need to save the solution.

I could not figure out how to force evolve_one_time_step to sometimes use the given delta_t.

Do you have any suggestion for this ?

Thanks
praveen

[Wolfgang Bangerth]

I'm not sure these classes were designed for this kind of thing. My suggestion
would be to use the very much more sophisticated interfaces to SUNDIALS and
PETSc's TS sub-system. See also
https://github.com/dealii/dealii/pull/15540

Best
W.

--
------------------------------------------------------------------------
Wolfgang Bangerth email: bang...@colostate.edu
www: http://www.math.colostate.edu/~bangerth/

[Praveen C]

With the embedded RK in dealii, I could still control this by resetting max_delta whenever I want to use a fixed delta_t.

Thanks, I will check out Petsc TS which I have some experience with. I have to still use same method as above, reset max_delta.

Arkode seems to give a output_period variable which can be used to control when solution output is done.

best
praveen

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[Tomas Fernandez Bouvier]

Hi,

Could you share the solution ? I would like to implement timestepping using petsc in step-26 and it doesnt seem trivial to me. I didn't find any example.

Thank you

[Wolfgang Bangerth]

On 6/13/24 03:02, Tomas Fernandez Bouvier wrote:
>
> Could you share the solution ? I would like to implement timestepping using
> petsc in step-26 and it doesnt seem trivial to me. I didn't find any example.

You will be interested in this pull request which I still hope we can get into
the next release:

[Tomas Fernandez Bouvier]

Yes! Cannot wait for the next release. I tried to download and compile the unreleased example but there were errors. Thank you for your help!