[petsc-dev] Algebraic Multigrid

[Mark Adams]

Ari, I would also check that your operator is not messed up in parallel.
The solver is looking pretty solid.

Also, you can configure PETSc with hypre and use '-pc_type hypre'.  If
hypre is also good in serial but hosed on multi-proc then it is most
probably your operator.


On Tue, Jul 26, 2016 at 6:58 PM, Mark Adams <mfadams at lbl.gov> wrote:

> So remove one of the -mg_levels_pc_type jacobi and add -mg_coarse_ksp_type
> preonly, then verify that this works on one proc and then try two procs.
>
> On Tue, Jul 26, 2016 at 6:56 PM, Mark Adams <mfadams at lbl.gov> wrote:
>
>> Oh, actually this worked.  You have this ...pc_type jacobi in there
>> twice, so one of them was "unused".
>>
>> Try this with 2 processors now.
>>
>> On Tue, Jul 26, 2016 at 6:42 PM, Mark Adams <mfadams at lbl.gov> wrote:
>>
>>>
>>>
>>> On Tue, Jul 26, 2016 at 6:24 PM, Ari Rappaport <arir at vosssci.com> wrote:
>>>
>>>> So I commented out the line PCSetType(pc, PCGAMG). The line
>>>> KSPSetFromOptions(ksp) was already in the code at the end of our
>>>> initialization routine. I also added .petscrc to the working dir. Here is
>>>> the current output. It seems as if Option left: name:-mg_levels_pc_type
>>>> jacobi (no value) is still present in the output..I dunno.
>>>>
>>>
>>> Yea, I dunno either.  If you use -help you will get printout of the
>>> available options.  If you do this you will see stuff like -mg_levels_1_
>>> ... you can also see this in the ksp_view.  There is a shortcut that lets
>>> you _not_ put "_1" in.  Try putting this in for each level like so:
>>>
>>> -mg_levels_1_pc_type jacobi
>>> -mg_levels_2_pc_type jacobi
>>> -mg_levels_3_pc_type jacobi
>>>
>>> I also notice that the coarse grid ksp is GMRES.  This is our fault.  It
>>> should be preonly. Add:
>>>
>>> -mg_coarse_ksp_type preonly
>>>
>>>
>>>
>>>
>>>
>>>
>>>
>>>
>>>>
>>>> -Ari
>>>>
>>>> ----- Original Message -----
>>>> From: "Mark Adams" <mfadams at lbl.gov>
>>>> To: "Ari Rappaport" <arir at vosssci.com>, "For users of the development
>>>> version of PETSc" <petsc-dev at mcs.anl.gov>
>>>> Sent: Tuesday, July 26, 2016 4:03:03 PM
>>>> Subject: Re: [petsc-dev] Algebraic Multigrid
>>>>
>>>>
>>>> At the end of this you have:
>>>>
>>>>
>>>>
>>>> #PETSc Option Table entries:
>>>> -ksp_view
>>>> -mg_levels_pc_type jacobi
>>>> -options_left
>>>> #End of PETSc Option Table entries
>>>> There is one unused database option. It is:
>>>> Option left: name:-mg_levels_pc_type jacobi (no value)
>>>>
>>>>
>>>> So this jacobi parameter is not being used.
>>>>
>>>>
>>>> Do you call KPSSetFromOptions? Do you set solver parameters in the
>>>> code? Like PCGAMG?
>>>>
>>>>
>>>> You should not set anything in the code, it just confuses things at
>>>> this point. Use KSPSetFromOptions(). You can hardwire stuff before this
>>>> call, this just lets you set the defaults, but you should always call this
>>>> last to let command line parameters override the defaults.
>>>>
>>>>
>>>> You can put this in a .petscrc file in the working directory and try
>>>> again.
>>>>
>>>>
>>>>
>>>> -ksp_type cg
>>>> -ksp_max_it 50
>>>>
>>>> -ksp_rtol 1.e-6
>>>> -ksp_converged_reason
>>>> -pc_type gamg
>>>> -pc_gamg_type agg
>>>> -pc_gamg_agg_nsmooths 1
>>>> -pc_gamg_coarse_eq_limit 10
>>>> -pc_gamg_reuse_interpolation true
>>>> -pc_gamg_square_graph 1
>>>> -pc_gamg_threshold -0.05
>>>> -mg_levels_ksp_max_it 2
>>>> -mg_levels_ksp_type chebyshev
>>>> -mg_levels_esteig_ksp_type cg
>>>> -mg_levels_esteig_ksp_max_it 10
>>>> -mg_levels_ksp_chebyshev_esteig 0,.05,0,1.05
>>>> -mg_levels_pc_type jacobi
>>>> -pc_hypre_type boomeramg
>>>> -pc_hypre_boomeramg_no_CF
>>>> -pc_hypre_boomeramg_agg_nl 1
>>>> -pc_hypre_boomeramg_coarsen_type HMIS
>>>> -pc_hypre_boomeramg_interp_type ext+i
>>>>
>>>>
>>>
>>
>
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