[petsc-users] Regarding ksp ex42 - Citations

[Barry Smith]

   I'll add support for handling both A and M via Galerkin. It is easy to write the code, picking a good simple API that doesn't break anything is more difficult.   I'm leaning to change PCMGSetGalerkin(PC,PetscBool) to PCMGSetGalerkin(PC, PCMGGalerkinType) where 

typedef enum { PC_MG_GALERKIN_BOTH,PC_MG_GALERKIN_PMAT,PC_MG_GALERKIN_MAT, PC_MG_GALERKIN_NONE
 } PCMGGalerkinType;

Barry



> On Jul 21, 2016, at 6:09 AM, Lawrence Mitchell <lawrence.mitchell at imperial.ac.uk> wrote:
> 
> 
>> On 21 Jul 2016, at 10:55, domenico lahaye <domenico_lahaye at yahoo.com> wrote:
>> 
>> Apologies for being not sufficient clear in my previous message.
>> 
>> I would like to be able to Galerkin coarsen A^h to obtain A^H
>> and to separately Galerkin coarsen M^h to obtain M^H.
>> 
>> So, yes, the way in which I currently (partially) understand your
>> description of the new DMCreateMatrices would do the job.
> 
> If you want to separately coarsen A and M via Galerkin, I think it will be easier to just change the code in PCSetUp_MG to handle the case where A and M are different on the coarse levels.  Effectively you just need to replicate the code that computes the coarse grid "B" matrix to separately compute coarse grid A and B matrices and pass them in to KSPSetOperators.
> 
> Cheers,
> 
> Lawrence
>