[petsc-users] Using DMCOMPOSITE with TS

[Ellen Price]

Hi fellow PETSc users!

I am attempting to use a DMCOMPOSITE alongside TS and have run into some
trouble. I'm attaching a MWE demonstrating the problem. The goal is to
combine a DMDA3d for spatial data and a DMREDUNDANT for non-spatial,
time-dependent fields. In the attached example, this additional field is
temperature.

The DMDA data is currently just temperature-dependent, and the temperature
is supposed to increase linearly. Unfortunately, no matter how I integrate
(explicitly, using Euler or RK, or implicitly, using backward Euler or
BDF), I get the wrong final temperature. The integration proceeds for 100
timesteps and then stops (verified by -ts_monitor). At a heating rate of 1,
and an initial temperature of 150, I should get a final temperature of 250
very easily. However, I get something closer to 200 (not exact, which makes
me think this isn't a simple missing-a-factor-of-2 error).

I'm currently using TSSetDM with the composite DM to let PETSc compute the
Jacobian. Having checked all the inputs and outputs as well as I can, this
is the only step that seems like it may be causing a problem; yet even
explicit integration doesn't work, and that shouldn't need the Jacobian at
all. I'm at a loss.

Run using:
./mwe -implicit yes -ts_type beuler -ts_monitor OR ./mwe -implicit no
-ts_type euler -ts_monitor

Thanks in advance for any help,
Ellen Price
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