[petsc-dev] DM not propagating into Fieldsplit when using external DMShell?

Boris Boutkov borisbou at buffalo.edu
Mon Sep 24 17:21:32 CDT 2018

Thanks for the prompt reply and clarifications!

2) Could you be more specific about what should be different? It sounds
> like you want "your" DM attached to the (0,0) block so that
>     you can do GMG on the Laplacian there.

Exactly. This works if I use pc_type gamg on the (0,0) block, but if I swap
to pc_type mg which should use my DM info I end up in this situation.

> 3) We do not actually attach the DM proper. Rather DMCreateSubDM() is
> called to create a new DM with only the fields in the 0 block present. It is
>     likely that your DMShell does not implement this, and so something
> default is being done which does not work.
> What is not getting propagated properly for you?

Right, we do not currently implement this, and as it stands it looks like
the coarsen/refine, createinterpolation/createrestriction pointers are all
empty for the DM at:


while setting up MG at in the first iteration at :

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