[petsc-dev] obscure changes in TSGetStages_Theta

[Matthew Knepley]

On Sun, Jan 24, 2021 at 11:48 AM Zhang, Hong via petsc-dev <
petsc-dev at mcs.anl.gov> wrote:

> Some TS methods such as TSRK do have an array of vectors like this to
> store the stage values. But not all TS methods have it. I am fine adding
> the scratch for TSTheta and any other method missing it. A little drawback
> is that it is used only by TSGetStages and the TSStep implementation does
> not necessarily need it. So I like the idea to return a temporary array
> with GetStages and free it with RestoreStages when the TS method does not
> have an array for stages internally.
>

This array is just a few pointers, so incredibly small. Why make the user
mess around with restore? It seems easier to just give access.

  Thanks,

     Matt


> Hong
>
> On Jan 24, 2021, at 1:08 AM, Stefano Zampini <stefano.zampini at gmail.com>
> wrote:
>
> You actually do not need a RestoreStages if you use a scratch
>
> Vec stages[2];
>
> in TS_theta, and pass it back with TSGetStages_Theta. I understand PETSc
> philosophy is that every Get should have a Restore method, but is this
> really necessary for TSGetStages?
>
> Il giorno sab 23 gen 2021 alle ore 21:05 Zhang, Hong <hongzhang at anl.gov>
> ha scritto:
>
>> Done. Please check https://gitlab.com/petsc/petsc/-/merge_requests/3583
>>
>> Sorry for any disturbance it caused. It was for the convenience of the
>> adjoint implementation. The stages returned by TSGetStages_Theta currently
>> do not reflect the true stages associated with these methods. The endpoint
>> variant actually has two stages. This will be changed in a separate
>> forthcoming MR, where TSRestoreStages() will be added and TSGetStages will
>> return an array of vectors for the endpoint variant.
>>
>> Hong
>>
>> On Jan 21, 2021, at 4:16 AM, Stefano Zampini <stefano.zampini at gmail.com>
>> wrote:
>>
>> Hong,
>>
>> I do not understand why you changed the behavior of TSGetStages_Theta
>> https://gitlab.com/petsc/petsc/-/merge_requests/3500/diffs#a582bbaec75f4ae14bbf97d1d0404073ca89ff09_1194_1209
>> with this MR https://gitlab.com/petsc/petsc/-/merge_requests/3500
>>
>> Now, the non-endpoint variant does no longer use th->X as stage!
>>
>> Please revert this change
>> Thanks
>> --
>> Stefano
>>
>>
>>
>
> --
> Stefano
>
>
>

-- 
What most experimenters take for granted before they begin their
experiments is infinitely more interesting than any results to which their
experiments lead.
-- Norbert Wiener

https://www.cse.buffalo.edu/~knepley/ <http://www.cse.buffalo.edu/~knepley/>
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