[petsc-users] Regarding ksp ex42 - Citations

[Lawrence Mitchell]

[Reintroducing petsc-users in cc]

On 21/07/16 10:18, domenico lahaye wrote:
> Thanks Lauwrence. 
> 
> Does the fact that the coarse level preconditioner M^H should be
> constructed 
> by Galerkin coarse (rather then rediscretization) cause additional
> wrinkles? 

Do you want to rediscretise A, but use a galerkin coarse grid M?

If so, that is currently unsupported in PCMG:  In PCSetUp_MG (mg.c,
line 660 or so):

if (mg->galerkin == 1) {
   /* Currently only handle case where mat and pmat are the same on
coarser levels */
   ...
}

I guess if you're managing the creation of the coarse grid operators
yourself via KSPSetComputeOperators and a putative (new)
DMCreateMatrices then you'd have the flexibility to do separate things
for A and M (including, I think, galerkin coarse M).  Since you have
access to the DM hierarchy inside your compute operators.

Make sense?

Lawrence

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