[petsc-users] Recommended solver and preconditioner to solve Poisson eqn on win7

[Matthew Knepley]

On Fri, Sep 14, 2012 at 6:14 PM, Jed Brown <jedbrown at mcs.anl.gov> wrote:

> Also, add -pc_gamg_agg_nsmooths 1 as Mark suggested. It will reduce the
> iteration count significantly at the expense of somewhat higher setup cost.


Unless I am reading this wrong, you have a bizarre coarse grid solver. It
should be redundant LU but instead
you have GMRES/BJacobi?

   Matt


>
> On Fri, Sep 14, 2012 at 6:11 PM, Jed Brown <jedbrown at mcs.anl.gov> wrote:
>
>> *
>> *
>> *      ##########################################################*
>> *      #                                                        #*
>> *      #                          WARNING!!!                    #*
>> *      #                                                        #*
>> *      #   This code was compiled with a debugging option,      #*
>> *      #   To get timing results run ./configure                #*
>> *      #   using --with-debugging=no, the performance will      #*
>> *      #   be generally two or three times faster.              #*
>> *      #                                                        #*
>> *      ##########################################################*
>>
>> On Fri, Sep 14, 2012 at 6:08 PM, Zhenglun (Alan) Wei <
>> zhenglun.wei at gmail.com> wrote:
>>
>>>  I'm sorry about that. I attached the output files here with '
>>> -ksp_monitor -ksp_view -log_summary'. They are named after the grid size
>>> and pc-type.
>>>
>>> cheers,
>>> Alan
>>>
>>> On 9/14/2012 5:51 PM, Jed Brown wrote:
>>>
>>> On Fri, Sep 14, 2012 at 5:49 PM, Matthew Knepley <knepley at gmail.com>wrote:
>>>
>>>> On Fri, Sep 14, 2012 at 5:40 PM, Zhenglun (Alan) Wei <
>>>> zhenglun.wei at gmail.com> wrote:
>>>>
>>>>>  Dear folks,
>>>>>     I did some test with -pc_type gamg with
>>>>> /src/ksp/ksp/example/tutorial/ex45.c. It is not as good as default -pc_type
>>>>> when my mesh (Cartisian) is 100*50*50; while it is a little bit better than
>>>>> the default one when the mesh is 200*100*100. Therefore, I guess this type
>>>>> of pc is good for larger problem. Is that ture? or is there any rule of
>>>>> thumb for this type of preconditioner? BTW, I tested it with 8 processes.
>>>>>
>>>>
>>>>  When asking questions about convergence, always always ALWAYS send
>>>> the output of -ksp_monitor -ksp_view. If
>>>> you don't, we are just guessing blindly.
>>>>
>>>
>>>  And -log_summary because this is about performance.
>>>
>>>
>>>
>>
>


-- 
What most experimenters take for granted before they begin their
experiments is infinitely more interesting than any results to which their
experiments lead.
-- Norbert Wiener
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