Timeline for why Mathematica gives zero as eigenvalue for $y''+\lambda y=0$ for these boundary conditions?
Current License: CC BY-SA 3.0
14 events
| when toggle format | what | by | license | comment | |
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| Feb 3, 2018 at 5:11 | history | tweeted | twitter.com/StackMma/status/959655681870753792 | ||
| Feb 2, 2018 at 20:46 | history | edited | Nasser | CC BY-SA 3.0 |
corrected latex
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| Feb 2, 2018 at 19:22 | comment | added | anderstood |
@MichaelE2 The \underline{Summary} makes me believe the details were already written before :)
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| Feb 2, 2018 at 18:57 | comment | added | Michael E2 | A simple reminder that for an eigenvalue you have to have a nonzero eigenvector would have been enough. Just a brain fart. :) | |
| Feb 2, 2018 at 17:37 | history | edited | Nasser | CC BY-SA 3.0 |
typo
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| Feb 2, 2018 at 17:31 | history | edited | Nasser | CC BY-SA 3.0 |
added solution back to answer comment
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| Feb 2, 2018 at 12:13 | history | edited | Nasser | CC BY-SA 3.0 |
removed my solution as not needed
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| Feb 2, 2018 at 11:56 | comment | added | xzczd |
I agree NeumannValue is somewhat hard to use. (You may want to read this post. ) Hope DEigenvalues etc. will be more flexible and powerful in future versions.
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| Feb 2, 2018 at 11:46 | comment | added | Nasser |
@xzczd Ok, thanks. I am used to using DSolve as above to find the eigenvalues since it is easier to use than the syntax of DEigenvalues, but I did not realize that the trivial solution will be also given by DSolve. This was the confusing part for me. So I should switch to DEigenvalues from now on to check my solution.
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| Feb 2, 2018 at 11:43 | vote | accept | Nasser | ||
| Feb 2, 2018 at 11:39 | comment | added | xzczd |
"but it also claims zero is an eigenvalue" No, it doesn't. It just claims when $\lambda=0$, the BVP has a solution. If one wants to find the eigenvalue, DEigenvalues in principle can be used, but something like DEigenvalues[{-y''[x] + NeumannValue[-y[x], x == 1] + NeumannValue[y[x], x == 0]}, y[x], {x, 0, 1}, 5] doesn't work, NDEigenvalues works, though…
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| Feb 2, 2018 at 11:34 | answer | added | Sjoerd Smit | timeline score: 9 | |
| Feb 2, 2018 at 10:34 | history | edited | Nasser | CC BY-SA 3.0 |
typo
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| Feb 2, 2018 at 10:22 | history | asked | Nasser | CC BY-SA 3.0 |