[petsc-users] ML options

[Jed Brown]

Could we get an example matrix exhibiting this behavior? If you run with
-ksp_view_binary, the solver will write out the matrix to a file called
'binaryoutput' (and 'binaryoutput.info') when KSPSolve() returns. I suppose
it could be a "math" reason of the inodes somehow causing an incorrect
near-null space to be passed to ML, but the interface is not supposed to
work like this. If you are serious about smoothed aggregation for
elasticity, you should use MatSetNearNullSpace() to provide the rigid body
modes.

As a related matter, does -pc_type gamg -pc_gamg_agg_nsmooths 1
-mg_levels_ksp_type richardson -mg_levels_pc_type sor converge well?


On Mon, Jan 7, 2013 at 12:55 AM, Sanjay Govindjee <s_g at berkeley.edu> wrote:

>
> I am adding ML as an option to our FEA code and was looking for a bit of
> guidance on
> options.  Generally we solve 1,2, and 3D solids problems (nonlinear
> elasticity) but
> we also treat shells, thermal, problems, coupled problems, etc. etc.
>
> My basic run line looks like:
>
> -@${MPIEXEC} -n $(NPROC) $(MY_PROGRAM) -ksp_type cg -ksp_monitor -pc_type
> ml  -log_summary  -ksp_view  -options_left
>
> but this does not work very well at all with 3D elasticity for example --
> in fact it fails to converge after 10K iterations on a rather
> modest problem.  However following ex26 in the ksp tutorials I also tried:
>
> -@${MPIEXEC} -n $(NPROC) $(FEAPRUN) -ksp_type cg -ksp_monitor -pc_type ml
> -mat_no_inode -log_summary  -ksp_view  -options_left
>
> And this worked very very much better -- converged in about 10 iterations.
>  What exactly is -mat_no_inode doing for me? and are there other
> 'important' options
> that I should be aware of when using ML.
>
> -sanjay
>
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