Robust way of setting an affine constraint on a single point

[blais...@gmail.com]

Dear all,

I hope you are well.

This is most likely a very simple question, but what would be a good way to robustly set an AffineConstraint not on a face, but on a single DOF, while making sure that it is not an hanging node. I'd like to do something equivalent to what is done by VectorTools::interpolate_boundary_values but for an a priori unknown DOF (it could be for example the first non-hanging node DOF or something similar).

This is to set the reference value for a Laplace problem with Neumann Bcs. I know there are alternative ways which are better (such as constraining the zero mean), but this is for a quick test.

Thank you very much :)!
Bruno

[Wolfgang Bangerth]

On 6/22/21 3:12 PM, blais...@gmail.com wrote:
>
> This is most likely a very simple question, but what would be a good way to
> robustly set an AffineConstraint not on a face, but on a single DOF, while
> making sure that it is not an hanging node. I'd like to do something
> equivalent to what is done by VectorTools::interpolate_boundary_values but for
> an a priori unknown DOF (it could be for example the first non-hanging node
> DOF or something similar).

As so often, there is precedent for this kind of thing in ASPECT :-)

https://github.com/geodynamics/aspect/blob/master/source/simulator/nullspace.cc#L112-L209


Best
W.

--
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Wolfgang Bangerth email: bang...@colostate.edu
www: http://www.math.colostate.edu/~bangerth/

[blais...@gmail.com]

Thank you Wolfgang, this is exactly what I needed :)

Best

Bruno