[petsc-users] User-defined updating function in SNES

[YuSh Lo]

Hi Matthew,

Thank you. I will try setting up custom linesearch.

Thanks,
Josh


Matthew Knepley <knepley at gmail.com> 於 2023年7月6日 週四 下午3:01寫道：

> On Thu, Jul 6, 2023 at 3:42 PM YuSh Lo <ysjosh.lo at gmail.com> wrote:
>
>> Hi,
>>
>> I am using SNES to solve some nonlinear functions.
>> After each iteration, I have an user-defined updating to do.
>> Some values in the solution vectors must be inserted to some different
>> location.
>> I have tried to do it in the beginning of form RHS and form Jacobian, but
>> the vector is read-only. The results are correct although some warnings are
>> thrown with debug build saying that the vector is in wrong state. I also
>> tried setting a function with SNESSetupdate, but the convergence is bad.
>> Is the vector I get using SNESGetSolution the same as the vector that
>> will be used in following forming Jacobian and RHS?, and is it again read
>> only?
>>
>
> For these kinds of things, it might be easiest to put this in the line
> search. I would write a custom line search routine that did your
> modifications. That way you are assured that it does not short circuit
> anything else since the line search is where we are updating the solution
> directly.
>
> It should also work in the Update(), and we could try to determine what is
> wrong here, but that would be more digging. I think making it a line search
> is easier.
>
>   Thanks,
>
>      Matt
>
>
>> Thanks,
>> Josh
>>
>>
>
>
> --
> 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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