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

[Mark F. Adams]

Well this is probably my "bizarre coarse grid solver".  I explicitly create the solver after reducing the processor to one proc.  PETSc seems to make it a GMRES solver in PCSetUp_MG and I explicitly set it back to PREONLY but it looks like GMRES slipped in anyway.

Mark

On Sep 14, 2012, at 7:17 PM, Matthew Knepley <knepley at gmail.com> wrote:

> 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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