[petsc-users] DMShellSetCreateRestriction

[Boris Kaus]

> On Mar 11, 2016, at 8:53 PM, Matthew Knepley <knepley at gmail.com> wrote:
> 
> On Fri, Mar 11, 2016 at 12:26 PM, Dave May <dave.mayhem23 at gmail.com <mailto:dave.mayhem23 at gmail.com>> wrote:
> On 11 March 2016 at 18:11, anton <popov at uni-mainz.de <mailto:popov at uni-mainz.de>> wrote:
> Hi team,
> 
> I'm implementing staggered grid in a PETSc-canonical way, trying to build a custom DM object, attach it to SNES, that should later transfered it further to KSP and PC.
> 
> Yet, the Galerking coarsening for staggered grid is non-symmetric. The question is how possible is it that DMShellSetCreateRestriction can be implemented and included in 3.7 release?
> 
> It's a little more work than just adding a new method within the DM and a new APIs for DMCreateRestriction() and DMShellSetCreateRestriction().
> PCMG needs to be modified to call DMCreateRestriction(). 
> 
> Dave is correct. Currently, PCMG only calls DMCreateInterpolation(). We would need to add a DMCreateRestriction() call.
The PCMG object already uses a restriction operator that is different from the interpolation parameter if it is specified with PCMGSetRestriction <http://www.mcs.anl.gov/petsc/petsc-current/docs/manualpages/PC/PCMGSetRestriction.html#PCMGSetRestriction>. 
For consistency, one would expect a similar DMCreateRestriction object, not? I realize that this is not relevant for FEM codes, but for staggered FD it makes quite some difference. 

Other suggestions on how to best integrate staggered finite differences within the current PETSc framework are ofcourse also highly welcome. 
Our current thinking was to pack it into a DMSHELL (which has the problem of not having a restriction interface). 

thanks,
Boris




>   Thanks,
> 
>     Matt
>  
> Please, please.
> 
> Thanks,
> Anton
> 
> 
> -- 
> What most experimenters take for granted before they begin their experiments is infinitely more interesting than any results to which their experiments lead.
> -- Norbert Wiener

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