[Trilinos-Users] AztecOO conjugate gradient

[Bart Janssens]

On Thu, May 9, 2013 at 6:33 PM, C.S. Natarajan <csnataraj at gmail.com> wrote:

>                Bart I have run across the same issue. Out of curiosity,
> is this with periodic BC’s in any of the directions? I have had a similar
> problem (using both 2nd order FD and FE) when using Belos+ML (IFPACK IC)
> on a 3D anisotropic(from the coefficients) poisson problem. Does SGS
> smoothing work when using Belos+ML?
>


Hi,

I poked around a little more, and with these settings I can solve the
system with Belos Block CG:
 ML ->
  Reuse Fine Level Smoother = 0
  Base Method Defaults = SA   [default]
  ML Settings ->
   default values = SA
   max levels = 10
   prec type = MGV
   increasing or decreasing = increasing
   aggregation: type = Uncoupled
   aggregation: damping factor = 1.333
   eigen-analysis: type = cg
   eigen-analysis: iterations = 10
   smoother: sweeps = 2
   smoother: damping factor = 1
   smoother: pre or post = both
   smoother: type = Chebyshev
   coarse: type = Amesos-KLU
   coarse: max size = 128
   coarse: pre or post = post
   coarse: sweeps = 1

Changing to symmetric GS seems to blow things up (same error as in the
first mail) although it appears to depend on the number of CPUs. I'm not
sure if there's an optimal set of parameters for the 3D Poisson problem?
Right now I a system with 5594877 is taking 15s (71 CG iterations) to solve
on 64 CPU cores (2.2GHz Xeon, 8 cores/machine, gigabit ethernet
interconnect). I'm not sure if it's realistic to expect much faster?

Kind regards,

Bart
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