[petsc-users] Solving Poisson equation with multigrid

[Michele Rosso]

Thank you very much. I will try and let you know.

Michele

On 05/17/2013 07:01 PM, Jed Brown wrote:
> Michele Rosso <mrosso at uci.edu> writes:
>
>> I noticed that the problem appears even if I use CG with the default
>> preconditioner: commenting KSPSetDM() solves the problem.
> Okay, this issue can't show up if you use SNES, but it's a consequence
> of making geometric multigrid work with a pure KSP interface.  You can
> either use KSPSetComputeOperators() to put your assembly in a function
> (which will also be called on coarse levels if you use -pc_type mg
> without Galerkin coarse operators) or you can can provide the Jacobian
> using KSPSetOperators() as usual, but also call KSPSetDMActive() so that
> the DM is not used for computing/updating the Jacobian.
>
> The logic is cleaner in petsc-3.4 and I think it just does the right
> thing in your case.
>
>> So basically without a proper grid (it seems no grid with an even
>> numbers of nodes qualifies) and with my own system matrix, I cannot use
>> any type of multigrid
>> pre-conditioner?
> You can use all the AMG methods without setting a DM.
>

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