[petsc-dev] Discussion about time-dependent optimization moved from PR

[Stefano Zampini]

> >> have you thought about how to fix this?
> >>
> >> https://lists.mcs.anl.gov/pipermail/petsc-dev/2017-October/021387.html
>
> I feel like I'm missing context.  I know I failed to follow up in a
> thread at some time in the past, but I don't really understand the
> problem or what is being attempted.  What is the failing test case?
>
>
There's no failing test; however, you can see considerable slow downs when
calling TSSolve on the same ts multiple times. Just copying and paste the
original mail message below: it seems clear to me the code path. However,
what it's not clear is why we need to call DMCoarsenHookAdd so many times.
Cannot be set once?

Every time you call TSGetRHSMats_Private, TSGetIJacobian gets called,
which in turns calls SNESSetUpMatrices, that adds the entry in the linked
list of hooks via DMCoarsenHookAdd. This causes a considerable slow down
when using the RHS interface with an implicit solver, as you can see from
running the patched code.
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