Poor performance with BoomerAMG?

[Barry Smith]

   Run with the DMMG solver with the option -pc_type hypre
What happens? Then run again with the additional option -ksp_type  
richardson

Is hypre taking many, many iterations which is causing the slow speed?

I expect there is something wrong with your code that does not use DMMG.
Be careful how you handle boundary conditions; you need to make sure
they have the same scaling as the other equations.

    Barry



On Feb 15, 2008, at 8:36 AM, knutert at stud.ntnu.no wrote:

> Hi Ben,
>
> Thank you for answering. With gmres and boomeramg I get a run time of
> 2s, so that is much better. However, if I increase the grid size to
> 513x513, I get a run time of one minute. With richardson, it fails  
> to converge.
> LU gives 6 seconds, CG and ICC gives 7s, and the DMMG solver 3s for  
> the 513x513 problem.
>
> When using the DMMG framework, I just used the default solvers.
> I use the Galerkin process to generate the coarse matrices for
> the multigrid cycle.
>
> Best,
> Knut
>
> Siterer Ben Tay <zonexo at gmail.com>:
>
>> Hi Knut,
>>
>> I'm currently using boomeramg to solve my poisson eqn too. I'm  
>> using it
>> on my structured C-grid. I found it to be faster than LU,  
>> especially as
>> the grid size increases. However I use it as a preconditioner with
>> GMRES as the solver. Have you tried this option? Although it's  
>> faster,
>> the speed increase is usually less than double. It seems to be  
>> worse if
>> there is a lot of stretching in the grid.
>>
>> Btw, your mention using the DMMG framework and it takes less than a
>> sec. What solver or preconditioner did you use? It's 4 times faster
>> than GMRES...
>>
>> thanks!
>>
>> knutert at stud.ntnu.no wrote:
>>> Hello,
>>>
>>> I am trying to use the hypre multigrid solver to solve a Poisson  
>>> equation.
>>> However, on a test case with grid size 257x257 it takes 40  
>>> seconds  to converge
>>> on one processor when I run with
>>> ./run -ksp_type richardson -pc_type hypre -pc_type_hypre boomeramg
>>>
>>> Using the DMMG framework, the same problem takes less than a second,
>>> and the default gmres solver uses only four seconds.
>>>
>>> Am I somehow using the solver the wrong way, or is this  
>>> performance  expected?
>>>
>>> Regards
>>> Knut Erik Teigen
>>>
>>>
>
>
>