Timeline for Solve can't solve my trigonometric equation—why?
Current License: CC BY-SA 4.0
14 events
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| Mar 20, 2020 at 13:58 | history | edited | m_goldberg | CC BY-SA 4.0 |
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| Mar 20, 2020 at 2:25 | review | Close votes | |||
| Mar 22, 2020 at 8:58 | |||||
| Mar 20, 2020 at 1:50 | history | became hot network question | |||
| Mar 19, 2020 at 23:09 | comment | added | Artes |
@BobHanlon As I've said Solve simply does not work, Solve[{eqs[-0, 769], -3 < eps < 3}, eps] remains unevaluated in ver.11.2 and it's ever been like this. I usually try to provide answers with the conditions as week as possible. Nonetheless I guess that automatic rationalizing numerical input wouldn't be a convenient idea.
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| Mar 19, 2020 at 22:49 | comment | added | Bob Hanlon |
@Artes - I do not have access to any versions prior to 12.0; however, I would expect Solve to rationalize the input if it could not solve with the inexact input (with the appropriate warning). The bounds on eps would be needed. You should be able to determine with your version.
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| Mar 19, 2020 at 22:08 | comment | added | Artes |
@BobHanlon I'm using version 11.2, it seems that since version 12.0 Solve automatically switches to NSolve. Even though they are internally related, Solve usually did not work with numerical input before version 12.0, as in my case here. Am I right?
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| Mar 19, 2020 at 21:51 | history | edited | Artes | CC BY-SA 4.0 |
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| Mar 19, 2020 at 19:32 | vote | accept | Eikthyrnir | ||
| Mar 19, 2020 at 18:47 | history | edited | Eikthyrnir | CC BY-SA 4.0 |
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| Mar 19, 2020 at 18:25 | answer | added | Artes | timeline score: 9 | |
| Mar 19, 2020 at 18:23 | comment | added | Eikthyrnir |
@Artes maybe I put it not quite correctly, anch is not a constant that I can define just for this equation, I obtain it from another math expression and therefore I can't predict good restriction for epsilon. And I can't believe that Mathematica can't solve it without any restrictions on epsilon
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| Mar 19, 2020 at 18:22 | comment | added | Bob Hanlon |
While using exact values is often a good idea, it is not necessary in this case. The key is putting bounds on eps as @Artes did; either Solve or NSolve will work with an inexact value for anch.
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| Mar 19, 2020 at 17:59 | comment | added | Artes |
To symbolic solvers apply exact numbers and we have to restrict eps, e.g. With[{anch = -769/1000}, Solve[{-2 anch == eps + ArcCos[Tan[Pi/4 - eps/2]], -3 < eps < 3}, eps] // Quiet] yields an exact solution.
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| Mar 19, 2020 at 17:50 | history | asked | Eikthyrnir | CC BY-SA 4.0 |