Hi Abbas, as you already noticed, standard preconditioners do not yield very good convergence for Maxwell's equations, for more details see Why it is Difficult to Solve Helmholtz Problems with Classical Iterative Methods <https://link.springer.com/chapter/10.1007/978-3-642-22061-6_10>. Since the scalar Helmholtz problem is closely related to the Maxwell's equations, the same arguments from the Helmholtz problem also hold true for the Maxwell's equations. So not even your plan B would work (see Geometric Multigrid Methods for Maxwell’s Equations <https://julianroth.org/res/bachelorarbeit.pdf>, Chapter 6.2).
Therefore you need to apply specially suited preconditioners for the Maxwell's equations. For the problem you are considering, I would recommend the block-preconditioner, which is presented in this paper: Large-scale 3D geoelectromagnetic modeling using parallel adaptive high-order finite element method <https://library.seg.org/doi/10.1190/geo2015-0013.1>. As a starting point for your implementation of that block-preconditioner you can use step-22 <https://www.dealii.org/current/doxygen/deal.II/step_22.html>. An other approach to solve the Maxwell's equations is via domain decomposition method (for example see: A quasi-optimal domain decomposition algorithm for the time-harmonic Maxwell's equations <https://www.sciencedirect.com/science/article/pii/S0021999115001965>). I hope this helps you, best regards Sebastian Abbas schrieb am Mittwoch, 19. Mai 2021 um 15:45:35 UTC+2: > This isn't a dealii problem and I am sorry if this isn't the right place > to post to, but if there is someone who could give me some hints on how I > would approach this then it would be you guys. > > I have been trying to solve the time harmonic maxwell equation discritized > with the use of Nedelec elements. Details are in This stack overflow post > <https://scicomp.stackexchange.com/questions/37447/how-to-create-a-good-preconditioner-for-a-system-of-linear-equations-that-is-cre> > . > > I have an issue with the linear system, since using any black box Trilinos > preconditioner yields no convergence or worse convergence than a simple > Jaccobi or an identity preconditioner and even in that case the restarted > GMRES solver needs more than 400 > vectors to converge and it gets worse with a refined mesh. My system is > broken into 2x2 block matrices much like step-29 by the way. > > Creating a multigrid solver like step-16 might solve this issue but I > would rather use that as plan B. > > Any hint is appreciated. > > Thanx :3 > Abbas > > -- 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/d763b695-dc30-4dc7-870f-352266af1c41n%40googlegroups.com.
