[petsc-users] Question about TSComputeRHSJacobianConstant

[Sajid Ali]

Hi PETSc developers,

I have a question about TSComputeRHSJacobianConstant. If I create a TS (of
type linear) for a problem where the jacobian does not change with time
(set with the aforementioned option) and run it for different number of
time steps, why does the time it takes to evaluate the jacobian change (as
indicated by TSJacobianEval) ?

To clarify, I run with the example with different TSSetTimeStep, but the
same jacobian matrix. I see that the time spent in KSPSolve increases with
increasing number of steps (which is as expected as this is a KSPOnly SNES
solver). But surprisingly, the time spent in TSJacobianEval also increases
with decreasing time-step (or increasing number of steps).

For reference, I attach the log files for two cases which were run with
different time steps and the source code.

Thank You,
Sajid Ali
Applied Physics
Northwestern University
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