[petsc-users] Problem with TS and SNES VI

[Huck, Moritz]

Hi,
I think I am missing something here.
How would events help to constrain the states.
Do you mean to use the event to "pause" to integration an adjust the state manually?
Or are the events to enforce smaller timesteps when the state come close to the constraints?

Thank you,
Moritz
________________________________________
Von: Abhyankar, Shrirang G <shrirang.abhyankar at pnnl.gov>
Gesendet: Montag, 5. August 2019 17:21:41
An: Huck, Moritz; petsc-users at mcs.anl.gov
Betreff: Re: [petsc-users] Problem with TS and SNES VI

For problems with constraints on the states, I would recommend trying the event functionality, TSEvent, that allows detection and location of discrete events, such as one that you have in your problem.
https://www.mcs.anl.gov/petsc/petsc-current/docs/manualpages/TS/TSSetEventHandler.html.

An example using TSEvent functionality:  https://www.mcs.anl.gov/petsc/petsc-current/src/ts/examples/tutorials/ex40.c.html

A brief intro to TSEvent can be found here<https://www.mcs.anl.gov/petsc/petsc-20/conference/Abhyankar_S.pdf>.

Thanks,
Shri


From: petsc-users <petsc-users-bounces at mcs.anl.gov> on behalf of "Huck, Moritz via petsc-users" <petsc-users at mcs.anl.gov>
Reply-To: "Huck, Moritz" <Moritz.Huck at rwth-aachen.de>
Date: Monday, August 5, 2019 at 5:18 AM
To: "petsc-users at mcs.anl.gov" <petsc-users at mcs.anl.gov>
Subject: [petsc-users] Problem with TS and SNES VI

Hi,
I am trying to solve a DAE with the ARKIMEX solver, which works mostly fine.
The problem arises when some states go to unphysical values. I try to constrain my states with SNESVISetVariableBounds (through the petsc4py interface).
But TS seems not respect this e.g. I have a state with is usually between 1 and 1e3 for which I set a lower bound of 1, but the state goes t0 -0.8 at some points.
Are there some tolerances I have to set for VI or something like this?

Best Regards,
Moritz