PCNN-preconditioner and "floating domains"

[Andreas Grassl]

Barry Smith schrieb:
> 
>    As we have said before the BNN in PETSc is ONLY implemented for a
> scalar PDE with
> a null space of the constant functions. If you shove in linear
> elasticity it isn't really going to work.

Do you have any suggestions to work around this drawback?
Do I understand right, that this issue is problematic, if floating subdomains
appear?
Do I have the possibility to provide the null space from user site?
Or how big would be the effort to change the nn-code to work for this problem
classes?
Is such a work useful at all or do you regard BNN only a rather complicated
method to be done much better by other (even simpler) algorithms?

Cheers,

Ando

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