Timeline for Simplify square roots with five or more variables, assumptions not working
Current License: CC BY-SA 4.0
9 events
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| Sep 23, 2020 at 6:08 | comment | added | André | @Bob, thank you as well. It seems like simplifying Sign only works for four or less nonlinear variables by default. Seems to be the same problem and solution as in the related question/asnwer here: mathematica.stackexchange.com/questions/130290/… | |
| Sep 23, 2020 at 6:06 | comment | added | André | @Bill, thank you. PowerExpand seems the right way to deal with this. | |
| Sep 22, 2020 at 18:48 | comment | added | Bob Hanlon |
A problem seems to be with simplifying Sign. The expression Assuming[a b + x y z > 0, Sqrt[a b + x y z] Sqrt[-(1/(-a b - x y z)) // Simplify] // ComplexExpand[#, TargetFunctions -> {Re, Im}] & // FullSimplify] with v12.1.1 evaluates to 1/Sign[a b + x y z] and the Sign is obviously 1
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| Sep 22, 2020 at 17:04 | comment | added | Bill Watts |
Sqrt[a b + x y z] Sqrt[-(1/(-a b - x y z)) // Simplify] // PowerExpand
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| Sep 22, 2020 at 14:50 | comment | added | Bob Hanlon |
Since it chokes on too many variables, as a workaround reduce the number of variables. expr = Sqrt[a b + x y z] Sqrt[-(1/(-a b - x y z))]; expr /. x y z :> t // Simplify[#, a b + t > 0] &
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| Sep 22, 2020 at 14:30 | answer | added | cvgmt | timeline score: 1 | |
| Sep 22, 2020 at 14:26 | comment | added | flinty |
Try this: FullSimplify[Sqrt[a b + x y z] Sqrt[-(1/(-a b - x y z))], Element[{a, b, x, y, z}, PositiveReals]]
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| Sep 22, 2020 at 14:21 | comment | added | André | As a workaround, I can square the result and then take the square root, but I would still prefer to understand the cause of the issue. | |
| Sep 22, 2020 at 14:07 | history | asked | André | CC BY-SA 4.0 |