Array nodal bcs for eigenproblem

[xieeeect]

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Question

Hello,

I'm working on a array nodal boundary condition for eigenvalue problems, it describes like: M * U = 0 , M is an n*n matrix, and U is an array variable. However, I didn't find any BCS about it, and when developing a new bcs with 'ArrayNodalBC', I got an error:
"Invalid NodalBC for eigenvalue problems, please use homogeneous (array) Dirichlet."

Thanks for your time,

xieeeect

[GiudGiud]

@YaqiWang I think we have had this conversation before.
Do you recall the conclusions? What kind of BCs can be used for eigenvalue problems?

[GiudGiud]

or @lindsayad I think you know exactly what's up here considering your latest work

[lindsayad]

The short answer is that I do not know the theory well enough to say what BCs can theoretically be used for eigenvalue problems. I can only speak to the implementation which is that we only allow homogeneous BCs in MOOSE.

From the libMesh side we now allow solving eigenproblems with arbitrary constraints in which we condense out the constrained degrees of freedom when performing the eigensolve. We then enforce the constraints post-eigensolve on the requested eigenvector

[xieeeect]

Thanks for the answer, I have a general understanding of the rules for handling BCs for eigenvalue problems, and next I will study the idea you said. : )