Opened 19 months ago
Last modified 3 months ago
#14591 new defect
cosh integral incorrect because of abs_integrate
Reported by: | kcrisman | Owned by: | burcin |
---|---|---|---|
Priority: | major | Milestone: | sage-6.4 |
Component: | calculus | Keywords: | |
Cc: | tmonteil, gagern | Merged in: | |
Authors: | Reviewers: | ||
Report Upstream: | Reported upstream. No feedback yet. | Work issues: | |
Branch: | Commit: | ||
Dependencies: | Stopgaps: |
Description
See this ask.sagemath question.
sage: a = integrate(sqrt(1-1/4*cosh(x)^2),x) sage: a.full_simplify() cosh(x)
Not that I'm an expert here, but at any rate, viewed as real functions this makes no sense, though perhaps on some branch it does. This happens because
Maxima 5.29.1 http://maxima.sourceforge.net using Lisp ECL 12.12.1 Distributed under the GNU Public License. See the file COPYING. Dedicated to the memory of William Schelter. The function bug_report() provides bug reporting information. (%i1) domain:complex; (%o1) complex (%i2) display2d:false; (%o2) false (%i3) B:integrate(sqrt(1-cosh(x)^2/4),x); (%o3) 'integrate(sqrt(1-cosh(x)^2/4),x) (%i4) trigsimp(B); (%o4) 'integrate(sqrt(-(cosh(x)^2-4)/4),x) (%i5) fullratsimp(B); (%o5) 'integrate(sqrt(-(cosh(x)^2-4)/4),x) (%i6) load(abs_integrate); (%o6) "/Users/.../sage-5.9.rc1/local/share/maxima/5.29.1/share/contrib/integration/abs_integrate.mac" (%i7) trigsimp(B); (%o7) cosh(x) (%i8) fullratsimp(B); (%o8) cosh(x)
I'm not sure we want to unload abs_integrate but we need to figure something out here.
Change History (11)
comment:1 Changed 19 months ago by tmonteil
- Cc tmonteil added
comment:2 Changed 18 months ago by gagern
- Cc gagern added
comment:3 Changed 18 months ago by jdemeyer
comment:4 Changed 16 months ago by jdemeyer
- Milestone changed from sage-5.11 to sage-5.12
comment:5 Changed 10 months ago by vbraun_spam
- Milestone changed from sage-6.1 to sage-6.2
comment:6 Changed 7 months ago by vbraun_spam
- Milestone changed from sage-6.2 to sage-6.3
comment:7 Changed 6 months ago by pbruin
The answer cosh(x) is completely wrong, even in a neighbourhood of x = 0:
cosh(x) = integrate(sqrt(1 - 1/4*cosh(x)^2),x) => sinh(x) = sqrt(1 - 1/4*cosh(x)^2) => sinh(x)^2 = 1 - 1/4*cosh(x)^2 => 0 = 3/4 (substitute x = 0)
According to the ask.sagemath.org link in the ticket description, the correct answer can be expressed in terms of an elliptic integral function, which I trust much more.
comment:8 follow-up: ↓ 9 Changed 6 months ago by kcrisman
As Thierry pointed out on the ask.sagemath question. So, does #13973 fix this or not?
comment:9 in reply to: ↑ 8 Changed 6 months ago by pbruin
Replying to kcrisman:
As Thierry pointed out on the ask.sagemath question.
Yes, I just wanted to give a clear reason here why the answer couldn't possibly be right.
So, does #13973 fix this or not?
No, it doesn't. I have been doing some debugging of the Maxima command
trigsimp(integrate(sqrt(4 - cosh(x)^2),x));
which returns cosh(x) when executed after loading abs_integrate. It seems that the problem arises in ratsubst, when substituting 1 + sinh(x)^2 for cosh(x)^2. What makes it more tricky is that calling ratsubst directly with the same arguments gives a correct answer. Possibly some flag is set at some intermediate point that triggers the bug.
comment:10 Changed 6 months ago by pbruin
- Report Upstream changed from N/A to Reported upstream. No feedback yet.
Reported upstream: https://sourceforge.net/p/maxima/bugs/2737/
comment:11 Changed 3 months ago by vbraun_spam
- Milestone changed from sage-6.3 to sage-6.4
Fixed by #13973.