[petsc-users] Regarding ksp ex42 - Citations

[domenico lahaye]

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. 
What is a sensible way to proceed? 
Thanks, Domenico. 
      From: Lawrence Mitchell <lawrence.mitchell at imperial.ac.uk>
 To: domenico lahaye <domenico_lahaye at yahoo.com> 
Cc: petsc-users at mcs.anl.gov
 Sent: Thursday, July 21, 2016 11:25 AM
 Subject: Re: [petsc-users] Regarding ksp ex42 - Citations
   
[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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