Thanks, Wolfgang. I'll look into it some more and eventually try with a larger problem.
On Tuesday, January 30, 2024 at 11:18:01 PM UTC-5 Wolfgang Bangerth wrote: > > Alex: > > > I am running a solid-mechanics job where I import a large mesh and run > using > > parallel fullydistributed with MPI. I had been trying to run my job > using a CG > > solver with the BoomerAMG > > preconditioner (based on the example in step-40). > > > > I ran my mesh with 116,000 nodes and the solver took about 700 seconds > and > > used around 18GB of RAM. I then tried to run another version of the > same > > problem with a finer 1.5M node mesh. This one never finished because > > it's memory requirements exceeded the resources of my small cluster. > > > > Eventually, I decided to test out some different solvers and > preconditioners. > > I switched the preconditioner to Jacobi and suddenly the 116k job ran in > 40 > > seconds and only needed ~4GB of memory. > > This is too small a problem to be indicative of much. Jacobi is good for > small > problems, see also here: > > https://dealii.org/developer/doxygen/deal.II/step_6.html#step_6-Solversandpreconditioners > But it is not effective for large problems because the effort to solve > linear > problems is not O(N) with this preconditioner. AMG typically is, but it is > only better on large problems. > > I do wonder about your memory usage. A good order of magnitude for 2d > problems > is 1 kB per DoF. Perhaps twice that in 3d. You are using 30 kB. > > > > - Maybe it's because my mesh is generated externally and not refined > using the > > deal.ii mesh refinement approach? > > - Maybe it's related to the use of p:f:t instead of p:d:t? > > - Maybe I have some issue with my PETSc install? > > - Maybe I didn't properly set the parameters for the AMG preconditioner? > > All possibilities. But hard to tell on such a small problem. > > 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/a5263d6d-b2ef-4c2b-8313-7c4bbdc5870an%40googlegroups.com.
