On 10/22/21 2:53 AM, richard@gmail.com wrote:
I think I know what it is: the ML guide on p 16 says in footnote 11:
"Note that the hierarchy produced by ReComputePreconditioner() can differ from
that produced by ComputePreconditioner() for non-zero threshold values."
So when the matrix changes too much, the const double aggregation_threshold in
PreconditionAMG::AdditionalData would lead to different matrix entries being
considered.
That is why it was also working for (constant) Laplace and (almost constant
Hyper-) Elasticity, but not so well for Navier-Stokes, since I initialized the
AMG in the first timestep, where convective terms are completely zero starting
from the quiescent state.
Hope someone finds this in the future and updates their AMG every few
timesteps as well!
Richard -- I cannot recall who implemented the AMG preconditioner, but suspect
that that parameter was simply never used. I don't think we use it in ASPECT,
for example.
Since you figured out how to use it, is there a place where one could add a
paragraph that describes what you found out and how one would use this
feature? You might know this one piece of the library better than anyone else
at this time :-) It would be nice to write your experience down in the place
where others might look for it.
Best
Wolfgang
--
Wolfgang Bangerth email: bange...@colostate.edu
www: http://www.math.colostate.edu/~bangerth/
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