Magdalini, The problem only appears with inhomogeneous boundary conditions, but periodic boundary conditions don't set any inhomogeneity.
Best, Daniel Am Do., 5. März 2020 um 16:13 Uhr schrieb Magdalini Ntetsika < ntets...@berkeley.edu>: > Hi Wolfgang, > > thank you for the prompt reply. I see, I'll look up both. But I have a > quick question: what if I have periodic boundary conditions all around my > domain? It seems to be working in that case, even if the boundary values > are nonzero, I get to have the correct system_rhs vector. I guess will need > first to watch the topic on Dirichlet Boundary conditions to understand > better, but it will be very helpful if I could get some feedback on that > specific observation from you. > > Best, > Magda > > On Thursday, March 5, 2020 at 9:41:11 AM UTC-8, Wolfgang Bangerth wrote: >> >> On 3/5/20 9:24 AM, Magdalini Ntetsika wrote: >> > >> > but I don't seem to get the same *system_rhs *when >> > *assemble_system=false* as when *assemble_system=true*. To be more >> > specific, it seems that there is something wrong with how >> > constraints.distribute_local_to_global(local_rhs, local_dof_indices, >> > system_rhs) creates the system_rhs from local_rhs and >> > local_dofs_indices. I don't change anything about constraints etc >> > throughout the time steps since I set those things up at the very >> > beginning and then I just run several times without updating anything. >> > Any idea about what the problem could be? >> >> Magdalini, >> it's not in the function you point to, but in your understanding. In >> order to compute the correct values of the right hand side when you have >> non-zero constraints (e.g., when you have nonzer boundary values), the >> function you call needs to have access to the matrix elements. >> >> The issue is a bit complicated to understand, but you may want to look >> up the video lectures on the topic of Dirichlet boundary conditions. >> >> As for your case, take a look at step-26, which deals with exactly this >> problem by building the matrix only once, but then using it for several >> time steps. >> >> Best >> W. >> >> -- >> ------------------------------------------------------------------------ >> Wolfgang Bangerth email: bang...@colostate.edu >> www: http://www.math.colostate.edu/~bangerth/ >> > -- > 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 dealii+unsubscr...@googlegroups.com. > To view this discussion on the web visit > https://groups.google.com/d/msgid/dealii/a320a562-6800-4650-871f-83a5eff9b79a%40googlegroups.com > <https://groups.google.com/d/msgid/dealii/a320a562-6800-4650-871f-83a5eff9b79a%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 dealii+unsubscr...@googlegroups.com. To view this discussion on the web visit https://groups.google.com/d/msgid/dealii/CAOYDWbKXD1Oijy5YKX71b7vWeT7_%3Dzcu58gK_Es5BYBsHiZc-w%40mail.gmail.com.
