Opened 6 years ago

Last modified 7 weeks ago

#17709 needs_work defect

Maxima limit() regression

Reported by: rws Owned by:
Priority: major Milestone: sage-9.3
Component: calculus Keywords: limit
Cc: tmonteil Merged in:
Authors: Reviewers:
Report Upstream: Reported upstream. Developers acknowledge bug. Work issues:
Branch: Commit:
Dependencies: Stopgaps:

Description

var('n'); u = (1+sqrt(n))^(-n); limit(u(n=n+1)/u,n=infinity): this was reported in http://ask.sagemath.org/question/25647/cannot-calculate-limit/ and worked at least in Sage-4.7

Change History (13)

comment:1 Changed 6 years ago by kcrisman

  • Report Upstream changed from N/A to Reported upstream. No feedback yet.

Upstream here.

comment:2 Changed 3 months ago by mkoeppe

  • Cc tmonteil added
  • Milestone changed from sage-6.5 to sage-duplicate/invalid/wontfix
  • Status changed from new to needs_review

Seems fixed in 9.2.beta10 - 0 is returned

comment:3 Changed 3 months ago by mkoeppe

(The upstream bug in maxima is still present; it seems we are using something else for computing the limit.)

comment:4 follow-up: Changed 3 months ago by kcrisman

  • Status changed from needs_review to needs_work

My guess is that we now, as with integration, go through several "algorithms"/programs to get limits.

I guess technically this is still a Sage bug, then, if that is true and one then specifies the algorithm? Otherwise I'd at the very least add a doctest.

comment:5 Changed 7 weeks ago by chapoton

  • Keywords limit added

comment:6 in reply to: ↑ 4 Changed 7 weeks ago by chapoton

Replying to kcrisman:

My guess is that we now, as with integration, go through several "algorithms"/programs to get limits.

Not yet, as nobody did it..

I guess technically this is still a Sage bug, then, if that is true and one then specifies the algorithm? Otherwise I'd at the very least add a doctest.

comment:7 Changed 7 weeks ago by kcrisman

Hmm, that is interesting. Maxima returns a nounform 'limit((sqrt(n)+1)^n*(sqrt(n+1)+1)^((-n)-1),n,inf) inside of Sage 9.2.beta1

Maxima 5.42.2 http://maxima.sourceforge.net
using Lisp ECL 16.1.2

But I don't have the most recent Maxima. Can you test this?

sage -maxima
<messages about Maxima 5.44, hopefully>
(%i1) limit((1+sqrt(n+1))^(-n-1)/(1+sqrt(n))^(-n),n,inf);

If you get zero then they fixed it, and then a doctest suffices. Otherwise we may have something really weird going on in our own processing, though I don't see what would have changed - Frédéric is right about that, as far as I can tell.

comment:8 Changed 7 weeks ago by kcrisman

Can you also test this in maxima_calculus in the most recent Sage rc? Upstream says it is not fixed. I still get

sage: maxima_calculus("limit((1+sqrt(n+1))^(-n-1)/(1+sqrt(n))^(-n),n,inf)")
'limit((sqrt(n)+1)^n*(sqrt(n+1)+1)^((-n)-1),n,inf)

comment:9 Changed 7 weeks ago by chapoton

I get

sage: banner()                                                                  
┌────────────────────────────────────────────────────────────────────┐
│ SageMath version 9.2.rc2, Release Date: 2020-10-12                 │
│ Using Python 3.8.5. Type "help()" for help.                        │
└────────────────────────────────────────────────────────────────────┘
┏━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━┓
┃ Warning: this is a prerelease version, and it may be unstable.     ┃
┗━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━┛
sage: maxima_calculus("limit((1+sqrt(n+1))^(-n-1)/(1+sqrt(n))^(-n),n,inf)")     
'limit((sqrt(n)+1)^n*(sqrt(n+1)+1)^((-n)-1),n,inf)

EDIT: with

Maxima 5.44.0 http://maxima.sourceforge.net
using Lisp ECL 20.4.24
Last edited 7 weeks ago by chapoton (previous) (diff)

comment:10 Changed 7 weeks ago by kcrisman

That is really weird. I really can't find any branch of the code that should just avoid Maxima completely without adding an algorithm. Can you confirm Matthias' contention that

var('n'); u = (1+sqrt(n))^(-n); limit(u(n=n+1)/u,n=infinity)

now returns zero in that rc version?

comment:11 Changed 7 weeks ago by chapoton

no, this does not return 0. Maybe Matthias was looking at something else ?

comment:12 Changed 7 weeks ago by mkoeppe

I cannot confirm my claim from comment 2 above either. I don't know what I may have tested there.

comment:13 Changed 7 weeks ago by kcrisman

  • Milestone changed from sage-duplicate/invalid/wontfix to sage-9.3
  • Report Upstream changed from Reported upstream. No feedback yet. to Reported upstream. Developers acknowledge bug.

Ok, thanks - setting back settings then. At least now Maxima has acknowledged bug :-)

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