Timeline for Computer algebra errors
Current License: CC BY-SA 2.5
8 events
| when toggle format | what | by | license | comment | |
|---|---|---|---|---|---|
| Oct 31, 2023 at 16:24 | comment | added | tsnao | Maybe I am wrong, but both solutions seem fine to me, because $\sqrt{z}$ is a multivalued function. The second solution corresponds to the other choice of $\sqrt{z}$. | |
| Nov 6, 2022 at 18:58 | comment | added | Jan Jitse Venselaar | @GeraldEdgar: I agree (I probably shouldn't have phrased the first line the way I did). Nevertheless, this is (or was?, at least up to and including Mathematica 12) a definite error in Mathematica's DSolve. I don't have access to Mathematica anymore, I don't know if this is still a problem, but it's interesting that this bug has existed for at least 10 years. Apparently the developers don't consider it a bug that returned functions of DSolve don't actually solve the differential equation under consideration (see the discussion in the google group above). | |
| Nov 5, 2022 at 10:34 | comment | added | Gerald Edgar | Note that $\sqrt{x^2} = |x|$ is wrong for complex $x$. Unless you tell it otherwise, Mathematica assumes $x$ is a complex variable. | |
| Mar 21, 2020 at 13:08 | comment | added | Max Horn | To my surprise, this is still present in Mathematica 12 | |
| Mar 1, 2010 at 14:00 | comment | added | Mariano Suárez-Álvarez | See groups.google.com/group/comp.soft-sys.math.mathematica/msg/… for a workaround. This is indeed a bug. | |
| Feb 27, 2010 at 9:10 | comment | added | Julián Aguirre | Mathematica also gets it right: Simplify[Sqrt[z^2], Element[z, Reals]] returns Abs[z], while Simplify[Sqrt[z^2]] returns Sqrt[z^2] unevaluated. The bug must be in the code of Dsolve, that somehow does not use this fact. | |
| Feb 26, 2010 at 16:36 | comment | added | Jacques Carette | Maple gets that one right. If the issues really is sqrt(x^2)=x, then Maple gets it right because I am the one who removed that assumption for the library in fall 1994 (Mike Monagan removed the buggy transformation from the kernel earlier that summer). | |
| Feb 26, 2010 at 15:42 | history | answered | Jan Jitse Venselaar | CC BY-SA 2.5 |