Using ML and options

[Ben Tay]

Hi,

Sorry I made a mistake. The ex2f uses default pc and ksp and hence it is 
actually using GMRES. I've tested some other options of ml like 
-pc_ml_CoarsenScheme, -pc_mg_cycles, -pc_ml_maxNlevels but the answer 
(if there's one) is much slower. Also, for the CoarsenScheme, if I use 
METIS, I also get the error msg:

*ML*WRN* This function has been compiled without the configure
*ML*WRN* option --with-ml_metis
*ML*WRN* I will put all the nodes in the same aggregate, this time...
*ML*WRN* (file ./Coarsen/ml_agg_METIS.c, line 954)

Thanks

Barry Smith wrote:
> On Fri, 17 Aug 2007, Ben Tay wrote:
>
>   
>> Hi,
>>
>> I tried to test ml using "-pc_type ml" on my problem. It was working ok using
>> LU or hypre/boomeramg. However I got the warning:
>>
>> Gen_Prolongator warning : max eigen <= 0.0
>> Gen_Prolongator warning : max eigen <= 0.0
>> Gen_Prolongator warning : max eigen <= 0.0
>> Gen_Prolongator warning : max eigen <= 0.0
>> Gen_Prolongator warning : max eigen <= 0.0
>>
>> When I use hypre, I used "-pc_type hypre -pc_hypre_type boomeramg which gives
>> good and fast result for solving my poisson eqn. Is there a recommendation for
>> ml as well?
>>
>> Moreover, although I got answers from ml, my answer using ml differs from LU
>> and hypre from the 3 sig. fig. When I run the example ex2f, I get different
>> norms of error:
>>
>> LU: Norm of error 0.1192E-05 iterations     4
>>     
>
>   Huh? Why is this not 1.e-14, since LU is a direct solver, do you mean ILU?
>
>   
>> hypre: Norm of error < 1.e-12,iterations     1
>>
>> ml: Norm of error 0.2098E-03 iterations     2
>>     
>
>    You may need to play around with the -ksp_rtol <rtol> value or options
> in ml to (run with -pc_type ml -help to see ML options). Run with 
> -ksp_monitor_true_residual and send us the results, We don't have
> a lot of experience with ML on real problems.
>
>   Barry
>
>   
>> It seems that norm of error for ml is a bit too high. How can I make it lower?
>>
>> Thank you.
>>
>>
>>
>> Hong Zhang wrote:
>>     
>>> On Thu, 16 Aug 2007, Ben Tay wrote:
>>>
>>>   
>>>       
>>>> Btw, is the file to download
>>>> ftp://ftp.mcs.anl.gov/pub/petsc/externalpackages/ml-5.0.tar.gz?
>>>>     
>>>>         
>>> Yes. You can simply use '--download-ml=1' during configuration.
>>>
>>> Run your program with '-help' to see all options for using ml.
>>> See ~petsc/src/ksp/ksp/examples/tests/ex26.c on how to use ML.
>>>
>>> Hong
>>>
>>>   
>>>       
>>>> Thanks
>>>>
>>>> Matthew Knepley wrote:
>>>>     
>>>>         
>>>>> The multigrid PC needs information about the grid and discretization. If
>>>>> you
>>>>> cannot provide this, use AMG through Hypre or ML. Or if you have a
>>>>> structured grid, consider using DMMG.
>>>>>
>>>>>   Thanks,
>>>>>
>>>>>     Matt
>>>>>
>>>>> On 8/15/07, Ben Tay <zonexo at gmail.com> wrote:
>>>>>
>>>>>       
>>>>>           
>>>>>> Hi,
>>>>>>
>>>>>> I found that there's a multigrid option in the manual which can be
>>>>>> used
>>>>>> by adding -pctype mg -pcmgtype PC_MG_MULTIPLICATIVE.
>>>>>>
>>>>>> However, it seems that I am actually just using LU since with or
>>>>>> without
>>>>>> this option, I got exactly the same answer. Am I using multigrid the
>>>>>> wrong way?
>>>>>>
>>>>>> Thanks
>>>>>>
>>>>>>
>>>>>>
>>>>>>         
>>>>>>             
>>>>>       
>>>>>           
>>>>     
>>>>         
>>>   
>>>       
>>     
>
>
>