Opened 3 years ago
Last modified 3 years ago
#22567 new defect
Unevaluated integrals to infinity have nonsense numeric value
Reported by: | pelegm | Owned by: | |
---|---|---|---|
Priority: | major | Milestone: | sage-7.6 |
Component: | calculus | Keywords: | integrate |
Cc: | kcrisman, rws | Merged in: | |
Authors: | Reviewers: | ||
Report Upstream: | N/A | Work issues: | |
Branch: | Commit: | ||
Dependencies: | Stopgaps: |
Description (last modified by )
Running
integrate(floor(x), x, 0, infinity, algorithm='sympy')
returns
integrate(floor(x), x, 0, +Infinity)
and trying
integrate(floor(x), x, 0, infinity, algorithm='sympy').n()
returns (!!!) -679.7441466712775
. This is awfully wrong. It shows with any unevaluated integral.
Change History (6)
comment:1 Changed 3 years ago by
- Description modified (diff)
comment:2 Changed 3 years ago by
- Cc kcrisman rws added
comment:3 Changed 3 years ago by
- Description modified (diff)
- Summary changed from The integral of floor(x) from 0 to inf is negative to Unevaluated integrals have nonsense numeric value
comment:4 Changed 3 years ago by
comment:5 Changed 3 years ago by
I don't think this is correct:
sage: integrate((1+x+x^2)^(1/3), x, 0, infinity) integrate((x^2 + x + 1)^(1/3), x, 0, +Infinity) sage: _.n() 8.835093500042741e+20
comment:6 Changed 3 years ago by
- Keywords floor sympy removed
- Summary changed from Unevaluated integrals have nonsense numeric value to Unevaluated integrals to infinity have nonsense numeric value
I want to point out that all these integrals involve infinity. I can't remember any more exactly where to find it (did poke about a bit) but there should be code, and not original code, for how to deal with this situation - I think it just sends it to the GSL algorithm numerical_integral
which would likely give nonsense for infinity. And indeed that is the case - compare this Sage cell:
sage: print numerical_integral(floor(x), 0, +Infinity) sage: print numerical_integral((x^2 + x + 1)^(1/3), 0, +Infinity) (-679.7441466712775, 632.307547415802) (8.835093500042741e+20, 1.6991730463958232e+21)
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Note that it doesn't happen without
algorithm='sympy'
.