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Apr 9, 2021 at 8:47 history edited username CC BY-SA 4.0
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Apr 9, 2021 at 8:44 comment added username @JacobLu added a paragraph about regularity
Apr 9, 2021 at 7:55 history edited username CC BY-SA 4.0
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Apr 9, 2021 at 4:13 vote accept Jacob Lu
Apr 9, 2021 at 4:11 comment added Jacob Lu Many thanks for the detailed answer! This is very helpful! I understand that in general, the regularity of eigenfunctions should be similar to $b$. But can one rigorously rule out the possibility that the eigenfunction $f$ is smooth while $b$ is piecewisely-constant (discontinuous)?
Apr 8, 2021 at 8:53 history edited username CC BY-SA 4.0
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Apr 6, 2021 at 18:54 comment added username @JacobLu Yes, they are as smooth as is allowed by the domain and b. If the domain is very smooth, then they will have the smoothness inherited from b (the maximum smoothness b allows). For example, if $b$ is bounded but not differentiable, then $u\in W^{1-1/p,p}(\partial\Omega)$ for any $p$.
Apr 6, 2021 at 4:26 comment added Jacob Lu Many thanks for the answer! I am not very familiar with the spectrum property of the Robin problem. Do you mean that for general $b$ satisfying some integrability, there always exist eigenvalues? Is it possible for these eigenfunctions to be smooth?
Apr 3, 2021 at 9:46 history answered username CC BY-SA 4.0