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.
--
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Wolfgang Bangerth email: bange...@colostate.edu
www: http://www.math.colostate.edu/~bangerth/
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