Opened 7 years ago
Last modified 5 years ago
#12152 new defect
Maxima fails to properly convert some floats to rationals
Reported by: | ddrake | Owned by: | burcin |
---|---|---|---|
Priority: | major | Milestone: | sage-6.4 |
Component: | calculus | Keywords: | maxima keepfloat integration |
Cc: | kcrisman | Merged in: | |
Authors: | Reviewers: | ||
Report Upstream: | Reported upstream. No feedback yet. | Work issues: | |
Branch: | Commit: | ||
Dependencies: | Stopgaps: |
Description
From https://groups.google.com/d/topic/sage-devel/JZ54xk51F-E/discussion :
sage: a, b, t = var('a b t') sage: f(a,b,t) = sin(t)^2/(a + b*cos(t))^2 sage: integrate(f(3/2,1,t), (t,0,2*pi)) -2/5*(sqrt(5) - 3)*pi*sqrt(5)
Works properly, but:
sage: integrate(f(1.5,1,t), (t,0,2*pi))
blows up with
RuntimeError: ECL says: Error executing code in Maxima: CRECIP: attempted inverse of zero (mod 3)
From the discussion there, this seems to be related to Maxima's attempts to convert floats to rationals, and that Sage turns off such conversion with keepfloat:true
.
Change History (7)
comment:1 Changed 7 years ago by
comment:2 Changed 6 years ago by
- Report Upstream changed from N/A to Reported upstream. No feedback yet.
Here we go - another such report.
(%i1) keepfloat:true; (%o1) true (%i2) integrate(exp(-5.3*x),x,0,1); Maxima encountered a Lisp error: Argument V is not a INTEGER: 1.0 Automatically continuing.
Based on this ask.sagemath.org post.
I've reported several similar things upstream at this Maxima bug.
comment:3 Changed 6 years ago by
Interestingly, we never considered the following from an old sage-devel conversation.
No, it means that you have not noticed the value set for ratepsilon, which governs the tolerance for conversion of floats to rationals. It is by default set to 2.0e-8, presumably for "single float" systems. It should probably be set to something more like 10e-16 for double float systems. Ah, that is very helpful. In this case the numerical approximations do indeed agree up to the output of n(). Perhaps we could potentially go back to keepfloat:false but with whatever the standard precision in Sage would equate to - Jason, would that help things with matrices?
This would probably keep a lot of problems away, especially since, as Nils says elsewhere, floats and symbolic integrals don't really mix.
Anyway, see also https://sourceforge.net/p/maxima/bugs/2510/#fd1d
comment:4 Changed 6 years ago by
- Milestone changed from sage-5.11 to sage-5.12
comment:5 Changed 5 years ago by
- Milestone changed from sage-6.1 to sage-6.2
comment:6 Changed 5 years ago by
- Milestone changed from sage-6.2 to sage-6.3
comment:7 Changed 5 years ago by
- Milestone changed from sage-6.3 to sage-6.4
See the thread above for some additional discussion, in particular about whether to not consider this a bug, and whether one should just disallow integrals with decimal points.