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

[Dana C. <dan...@ak...>]

Hi,

Thanks for your assistance.

Switching to BiCGStab (-ksp_type bcgs) doesn't improve convergence and
shows the same symptoms (residual with frequent oscillations).
Using fieldsplit as Jens suggests doesn't help either; residual doesn't go
below 1e-3 even after 1000 iterations.
Using GMRES makes the oscillations disappear, but the residual doesn't
converge either.

Cheers,
Dana


On Sat, Feb 1, 2014 at 4:28 PM, David Knezevic
<dkn...@se...>wrote:

> Thanks Jens, we'll try this next week.
>
>
>
> On 02/01/2014 04:06 AM, Jens Lohne Eftang wrote:
> > Hi,
> >
> > I used these arguments for 3D elasticity and they seemed to work well
> > also in combination with DirichletBoundary (why does that break
> symmetry?)
> >
> > -ksp_type cg
> > -pc_type fieldsplit
> > -pc_fieldsplit_block_size 3
> > -fieldsplit_pc_type hypre
> > -fieldsplit_pc_hypre_type boomeramg
> > -fieldsplit_pc_hypre_boomeramg_strong_threshold 0.7
> > -pc_fieldsplit_0 0,1,2
> > -ksp_atol 1e-11
> > -ksp_rtol 1e-11
> > -pc_fieldsplit_type symmetric_multiplicative
> >
> > It is key to use the fieldsplit preconditioner in order to be able to
> > exploit smoothness within each field component. If it's 2D elasticity I
> > believe you'd have to modify to -pc_fieldsplit_block_size 2 and
> > -pc_fieldsplit_0 0,1.
> >
> > I was able to solve a problem with tens of millions dofs in 90 CG
> > iterations using these parameters.
> >
> > Best,
> > Jens
> >
> > On 01/31/2014 11:11 PM, David Knezevic wrote:
> >> 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
> >>
> >>
> >>
> >>
> >>
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