Re: [Libmesh-users] BoomerAMG/hypre with CG for elasticity

[David K. <dkn...@se...>]

On 01/31/2014 12:36 PM, John Peterson wrote:
>> Hello,
>>
>> I'm trying to solve a linear elasticity problem based on a tetraheadral
>> mesh with over a million degrees of freedom.
>>
>> I've been using the LU solver in MUMPS but I'm now forced to switch to an
>> iterative solver because of the memory requirements of that solver.
>>
>> CG and BoomerAMG in hypre seem to be a good combination, but I've not been
>> able to achieve convergence. The residual never goes below 1 even after
>> several thousand iterations and shows high oscillations.
>>
>> The parameters I'm using are
>> -ksp_type cg
>> -ksp_monitor
>> -ksp_converged_reason
>> -pc_type hypre
>> -pc_hypre_type boomeramg
>> -pc_hypre_boomeramg_strong_threshold 0.7
>> -log_summary
>>
> First thing I would think of is that the problem isn't actually symmetric
> even though logically it should be?
>
> Does it work any better with -ksp_type bcgs?
>
>
>
>> -eps_monitor
>> -st_type sinvert
>>
> Is this an eigenvalue problem too?

Dana is working with me on this. It's not an eigenproblem, so 
"-eps_monitor -st_type sinvert" isn't meant to be there (but it those 
options would've just been ignored I believe).

Regarding symmetry: That's a good thought. The PDE is linear elasticity, 
hence it's symmetric. But we enforce boundary conditions using 
DirchletBoundary, so that'll ruin symmetry on the Dirichlet rows/cols. 
Not sure if that's the problem here or not, but Dana will try "-ksp_type 
bcgs" to see if that helps convergence.

Thanks,
David