[petsc-users] TSBDF prr-load higher order solution

[Zhang, Hong]

TSTrajectory supports checkpointing for multistage methods and can certainly be extended to multistep methods. But I doubt it is the best solution to Alfredo’s problem. Alfredo, can you elaborate a bit on what you would like to do? TSBDF_Restart is already using the previous solution to restart the integration with first-order BDF.

Hong(Mr.)

> On Mar 9, 2022, at 4:24 PM, Jed Brown <jed at jedbrown.org> wrote:
> 
> Can you restart using small low-order steps?
> 
> Hong, does (or should) your trajectory stuff support an exact checkpointing scheme for BDF?
> 
> I think we could add an interface to access the stored steps, but there are few things other than checkpointing that would make sense mathematically. Would you be up for making a merge request to add TSBDFGetStepVecs(TS ts, PetscInt *num_steps, const PetscReal **times, const Vec *vecs) and the respective setter? 
> 
> Alfredo J Duarte Gomez <aduarteg at utexas.edu> writes:
> 
>> Good morning PETSC team,
>> 
>> I am currently using a TSBDF object, which is working very well.
>> 
>> However, I am running into trouble restarting higher order BDF methods.
>> 
>> My problem is highly nonlinear, and when restarted for higher order BDF
>> methods (using the TSBDF_Restart function), wiggles appear in a specific
>> region of the solution.
>> 
>> Is there any way I can initialize the higher order BDF restart loading
>> previous solutions from a data file? I took a look at the code, but there
>> is no obvious way to do this.
>> 
>> Thanks,
>> 
>> -Alfredo
>> 
>> -- 
>> Alfredo Duarte
>> Graduate Research Assistant
>> The University of Texas at Austin