[petsc-users] Solving Poisson equation with multigrid

[Michele Rosso]

Thank you.
I will ask to update to 3.4 but I am working on a supercomputer thus I 
do not have control on the installed software.
So you suggest to use conjugate gradient + multigrid as preconditioner, 
correct?
If so, I retain

-ksp_type cg

instead of

-ksp_type richardson

correct?

Michele


On 05/17/2013 12:45 PM, Jed Brown wrote:
> Michele Rosso <mrosso at uci.edu> writes:
>
>> Hi,
>>
>> I am successfully using PETSc (v3.3) in parallel to solve the Poisson
>> equation in 3D .
> Please upgrade to petsc-3.4 when you get a chance.
>
>> The discretization is done by using finite difference on a uniform
>> structured grid.  So far I used the conjugate gradient method, but I
>> would like to give a try to multigrid.  The documentation describes
>> multigrid as a preconditioner only, thus I would like to know if it is
>> possible to use multigrid as a solver
>    -ksp_type richardson
>
> will not accelerate your multigrid.  Krylov with preconditioning is
> almost never slower, and a lot more robust.
>
>> and, if so, if you could give my some tips to start.
>    -pc_type mg -pc_mg_levels 3
>
>    -pc_type gamg
>
>    -pc_type ml
>
>    -pc_type hypre
>

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