Opened 6 years ago
Last modified 4 years ago
#17428 new defect
wrong limit in derivative
Reported by: | wonder | Owned by: | |
---|---|---|---|
Priority: | major | Milestone: | sage-6.5 |
Component: | symbolics | Keywords: | derivative limit |
Cc: | kcrisman, nbruin, jakobkroeker | Merged in: | |
Authors: | Reviewers: | ||
Report Upstream: | Reported upstream. No feedback yet. | Work issues: | |
Branch: | Commit: | ||
Dependencies: | Stopgaps: | wrongAnswerMarker |
Description (last modified by )
I'm seeing this behavior in sage 6.4, just built from git:
$ ./sage ┌────────────────────────────────────────────────────────────────────┐ │ Sage Version 6.4, Release Date: 2014-11-14 │ │ Type "notebook()" for the browser-based notebook interface. │ │ Type "help()" for help. │ └────────────────────────────────────────────────────────────────────┘ sage: e = SR('a*f(x)+g(x)') sage: e a*f(x) + g(x) sage: e.limit(x=0) limit(a*f(x) + g(x), x, 0) sage: e.limit(x=0).limit(a=0) limit(g(x), x, 0) sage: de = diff(e,SR('x')) sage: de a*D[0](f)(x) + D[0](g)(x) sage: de.limit(x=0) limit(a*D[0](f)(x) + D[0](g)(x), x, 0) sage: de.limit(x=0).limit(a=0) D[0](g)(x)
The last result should be limit(D[0](g)(x), x, 0)
.
For reference, this report was also posted to sage-devel.
Change History (7)
comment:1 Changed 6 years ago by
- Description modified (diff)
comment:2 Changed 6 years ago by
- Cc kcrisman nbruin added
- Component changed from PLEASE CHANGE to symbolics
- Keywords derivative limit added
- Report Upstream changed from N/A to Not yet reported upstream; Will do shortly.
- Type changed from PLEASE CHANGE to defect
comment:3 Changed 6 years ago by
A slightly simpler example:
(%i1) dg: diff(g(x), x); d (%o1) -- (g(x)) dx (%i2) lim: limit(dg, x, 0); d (%o2) limit -- (g(x)) x -> 0 dx (%i3) limit(lim, x, 0); d (%o3) limit (limit -- (g(x))) x -> 0 x -> 0 dx (%i4) limit(lim, a, 0); d (%o4) -- (g(x)) dx
In %i3
the double limit over x
is not simplified (this might be a different problem); in %i4
taking the limit over a
(which does not occur in the expression at all) removes the limit over x
.
comment:4 follow-up: ↓ 5 Changed 6 years ago by
Well, that is definitely a problem. Did you report upstream yet?
comment:5 in reply to: ↑ 4 Changed 6 years ago by
Replying to kcrisman:
Well, that is definitely a problem. Did you report upstream yet?
I just opened https://sourceforge.net/p/maxima/bugs/2877/ for this.
comment:6 Changed 6 years ago by
- Report Upstream changed from Not yet reported upstream; Will do shortly. to Reported upstream. No feedback yet.
comment:7 Changed 4 years ago by
- Cc jakobkroeker added
- Stopgaps set to wrongAnswerMarker
The same happens in Maxima:
Possibly related: #7401 [edit: it is not]