Poor performance with BoomerAMG?

[knutert at stud.ntnu.no]

Thank you for the reply, Barry.

The same thing happens if I use hypre with the DMMG solver.
As you say, with hypre, the convergence is extremely slow, requiring
a lot of iterations, 1413 iterations (1820 if I use richardson) for a 257x257
problem, while the default only needs 5.

I use the same way of handling boundary conditions in the two codes.
I've also compared the coeff matrix and rhs, and they are equal.

-Knut Erik-

Siterer Barry Smith <bsmith at mcs.anl.gov>:

>
>   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
>>>>
>>>>
>>
>>
>>