Opened 5 years ago
Last modified 2 years ago
#16422 new defect
cancellation of two indefinite limits
Reported by: | dkrenn | Owned by: | |
---|---|---|---|
Priority: | major | Milestone: | sage-6.4 |
Component: | symbolics | Keywords: | symbolic, cancellation, limit, indefinite |
Cc: | jakobkroeker | Merged in: | |
Authors: | Reviewers: | ||
Report Upstream: | N/A | Work issues: | |
Branch: | Commit: | ||
Dependencies: | Stopgaps: | wrongBehaviourMarker |
Description (last modified by )
We get
sage: limit(cos(x),x=oo) - limit(sin(x),x=oo) 0
This comes from the fact that the return value of each of these limits is a symbolic variable:
sage: limit(sin(x), x=oo) ind sage: type(limit(sin(x), x=oo)) <type 'sage.symbolic.expression.Expression'> sage: limit(sin(x), x=oo).variables() (ind,)
Change History (5)
comment:1 Changed 5 years ago by
- Description modified (diff)
comment:2 Changed 5 years ago by
comment:3 Changed 5 years ago by
- Milestone changed from sage-6.3 to sage-6.4
comment:4 Changed 4 years ago by
Still there in 6.6.
comment:5 Changed 2 years ago by
- Cc jakobkroeker added
- Stopgaps set to wrongBehaviourMarker
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This is an upstream problem (in maxima). It seems "ind" isn't a special symbol there either:
We could intercept ind whenever it comes by (from limit) and raise an exception to limit the damage, but I imagine the bad simplifications could already happen internal to maxima.
This seems to happen with infinity as well, by the way:
Sage catches those (when they happen in a way sage can see it happen), so perhaps we should recognize
ind
and a special value--leading to an exception if we can't do anything with it.