[petsc-users] Problem with TS and SNES VI

[Zhang, Hong]

Where does your DAE come from? If the DAE does not come from PDE discretization, there are a few things that you might want to try.

1. Use direct solvers (-pc_type lu, some third-party solvers can also be used by specifying -pc_factor_mat_solver_type xxx);
2. Adjust SNES tolerances;
3. Adjust TS tolerances if you use adaptive time stepping or reduce the stepsize with -ts_dt if fixed stepsize is used.

Hong (Mr.) 

> On Aug 5, 2019, at 4:16 AM, Huck, Moritz via petsc-users <petsc-users at mcs.anl.gov> wrote:
> 
> 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