it seems I cann't get a converged solution . which Solver should i use
to treat this situation?The error message is as follows .
This error message can indicate that you have simply not allowed a
sufficiently large number of iterations for your iterative solver to
converge. This often happens when you increase the size of your
problem. In such cases, the last residual will likely still be very
small, and you can make the error go away by increasing the allowed
number of iterations when setting up the SolverControl object that
determines the maximal number of iterations you allow.
The other situation where this error may occur is when your matrix is
not invertible (e.g., your matrix has a null-space), or if you try to
apply the wrong solver to a matrix (e.g., using CG for a matrix that
is not symmetric or not positive definite). In these cases, the
residual in the last iteration is likely going to be large.
On Wednesday, August 24, 2022 at 12:56:59 AM UTC+8 [email protected]
wrote:
> Actually, it turns out there's a tutorial program doing precisely what you
> are looking for: step-11 (
> https://www.dealii.org/developer/doxygen/deal.II/step_11.html)
>
> Best,
> Marco
>
> Il giorno martedì 23 agosto 2022 alle 18:54:24 UTC+2 Marco Feder ha
> scritto:
>
>>
>> Hi,
>>
>> step-7 (https://www.dealii.org/current/doxygen/deal.II/step_7.html)
>> shows this procedure. Be careful that if you apply Neumann BCs on all your
>> boundary, then the solution is determined up to a constant and you need to
>> add an additional constraint to your solution. Also, you need to satisfy a
>> compatibility condition between the r.h.s. and the neumann data.
>>
>> Best,
>> Marco
>> Il giorno martedì 23 agosto 2022 alle 15:54:19 UTC+2 [email protected]
>> ha scritto:
>>
>>> In step 3 , I want to implemente the Neumann bc for all the boundary
>>> condition. which tutorial show this procedure.
>>
>>
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