I solve Laplacian problem with "-0.5*std::exp(-2.0*0.963740544195800*p(0))" as exact solution, I apply Neumaan bc on all 4 boundaries. the solver feedback the error. no solution is obtained.
On Friday, August 26, 2022 at 8:01:11 PM UTC+8 [email protected] wrote: > What are the data (rhs, Neumann condition,...) of your problem ? > What is the value of the residual ? > > Best, > Marco > > On 26 Aug 2022, at 13:48, [email protected] <[email protected]> wrote: > > 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. >>> >>> > -- > The deal.II project is located at http://www.dealii.org/ > For mailing list/forum options, see > https://groups.google.com/d/forum/dealii?hl=en > --- > You received this message because you are subscribed to a topic in the > Google Groups "deal.II User Group" group. > To unsubscribe from this topic, visit > https://groups.google.com/d/topic/dealii/0KK8UDeFgRg/unsubscribe. > To unsubscribe from this group and all its topics, send an email to > [email protected]. > To view this discussion on the web visit > https://groups.google.com/d/msgid/dealii/8262a85f-01b0-4b9e-b1f8-ee5a0b3361b3n%40googlegroups.com > > <https://groups.google.com/d/msgid/dealii/8262a85f-01b0-4b9e-b1f8-ee5a0b3361b3n%40googlegroups.com?utm_medium=email&utm_source=footer> > . > > > -- The deal.II project is located at http://www.dealii.org/ For mailing list/forum options, see https://groups.google.com/d/forum/dealii?hl=en --- You received this message because you are subscribed to the Google Groups "deal.II User Group" group. To unsubscribe from this group and stop receiving emails from it, send an email to [email protected]. To view this discussion on the web visit https://groups.google.com/d/msgid/dealii/4a49bb38-1d21-4e96-a86f-dd07f965faf9n%40googlegroups.com.
