Opened 5 years ago

Last modified 7 months ago

#17183 new defect

Yet another abs_integrate trig integral problem

Reported by: kcrisman Owned by:
Priority: major Milestone: sage-6.4
Component: calculus Keywords: abs_integrate
Cc: Merged in:
Authors: Reviewers:
Report Upstream: Reported upstream. Developers acknowledge bug. Work issues:
Branch: Commit:
Dependencies: Stopgaps: #12731

Description (last modified by chapoton)

See this ask.sagemath question. Original report is

sage: F = sqrt((cos(x) - 1)^2 + sin(x)^2)
sage: F.integrate(x, 0, 2*pi)
0

but the answer should be 8.

EDIT: related

sage: F.integrate(x, 0, pi)
4
sage: F.integrate(x, pi, 2*pi)
-4

and the primitive is wrong:

sage: F.integrate(x)
-4/sqrt(sin(x)^2/(cos(x) + 1)^2 + 1)

Change History (13)

comment:1 Changed 5 years ago by kcrisman

  • Report Upstream changed from Not yet reported upstream; Will do shortly. to Reported upstream. No feedback yet.

comment:2 Changed 5 years ago by kcrisman

  • Description modified (diff)
  • Report Upstream changed from Reported upstream. No feedback yet. to Reported upstream. Developers acknowledge bug.

comment:3 Changed 5 years ago by kcrisman

See also #12731.

comment:4 Changed 5 years ago by jakobkroeker

  • Stopgaps set to todo

comment:5 Changed 5 years ago by jakobkroeker

I suppose, this ticket needs a stopgap?

comment:6 Changed 5 years ago by kcrisman

Maybe all the abs_integrate ones do - see #12731. But I don't think it's appropriate to just raise a warning EVERY TIME someone integrates. So there would have to be some way to limit its applicability. I think that is why I never worked on stopgaps; the stuff I was working on doesn't lend itself to easily pointing that out, other than having Sage itself start with a disclaimer "warning: computer math sometimes has errors".

comment:7 Changed 5 years ago by jakobkroeker

Sage itself start with a disclaimer "warning: computer math sometimes has errors"

+1

which in additional links to Mathematically Wrong Answers: http://trac.sagemath.org/query?status=new&status=needs_work&status=needs_review&status=needs_info&type=defect&stopgaps=!&max=0&order=id

I would support that (to warn the greenhorns), or will that have too much opposition?

but I don't think it's appropriate to just raise a warning EVERY TIME someone integrates.

Agree, so what about showing a stopgap warning only once per user+computer+sageVersion or similar? ( otherwise the user has explicitly request regular stopgap warnings)

comment:8 Changed 5 years ago by kcrisman

These are questions above my pay grade, as I did not institute the stopgap system. Again, if there is a way to invoke this when abs_integrate is used, that would be fine - we already have a way to only selectively load packages, but once loaded, I'm not sure we can "unload" it. But continue that discussion at #12731.

comment:9 Changed 5 years ago by jakobkroeker

  • Stopgaps changed from todo to #12731

comment:10 Changed 7 months ago by chapoton

  • Keywords abs_integrate added

comment:11 Changed 7 months ago by chapoton

  • Description modified (diff)

comment:12 Changed 7 months ago by chapoton

  • Description modified (diff)

comment:13 Changed 7 months ago by gh-mwageringel

Possibly related:

sage: integrate(sqrt(1/(2-cos(x))), (x, 0, pi))
0

According to Mathematica, the correct result should be 2*elliptic_kc(-2).

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