Hi Aaron and all,
Maybe, P can be negative? This would require a float or maybe better, a
Rational.
After studying the related code from a pure syntactical point of view
(without knowing the mathematical concept behind), I would like to discuss
two changes which could maybe solve the problem.
In function "dup_root_upper_bound()" in file "rootisolation.py", change the
return statement from
return 2.0**(max(P)+1)
to
return Rational(2)**(max(P) + 1).
In function "dup_root_lower_bound()" in file "rootisolatin.py", change the
return statement from
return 1.0 / bound
to
return Rational(1) / bound.
Of course, Rational needs to be imported as well.
The places where dup_root_lower_bound() is called should handle the change
from float to Rational correctly.
The changes are relative to the latest version from git.
By the way, thank you for the link, I will try to avoid using strings for
this purpose in future.
Best regards,
Heiner
Am Freitag, 20. September 2013 19:32:42 UTC+2 schrieb Aaron Meurer:
>
> I guess we just need to look at why it uses floating point 2.0 instead
> of 2, which would work just fine.
>
> By the way, it's better to build up expressions using Symbols instead
> of using strings. At the very least, don't assume that arbitrary SymPy
> functions will convert strings to expressions. See
>
> https://github.com/sympy/sympy/wiki/Idioms-and-Antipatterns#strings-as-input.
>
>
> Aaron Meurer
>
> On Fri, Sep 20, 2013 at 10:28 AM, Ondřej Čertík
> <ondrej...@gmail.com<javascript:>>
> wrote:
> > Hi Heiner,
> >
> > On Fri, Sep 20, 2013 at 9:39 AM, Heiner Kirchhoffer
> > <heiner.ki...@gmail.com <javascript:>> wrote:
> >> Hello,
> >>
> >> some months ago I started using sympy for finding roots of polynomials.
> >> It works really well and it enables me to solve more and more
> complicated
> >> problems.
> >
> > I am glad SymPy is useful to you.
> >
> >>
> >> Recently, I observed a case where the function sympy.intervals(...)
> throws
> >> an "OverflowError" exception.
> >> It happens when executing the following commands:
> >>
> >> import sympy
> >>
> >> a = "(x**45 - 45*x**44 + 990*x**43 - 1)"
> >>
> >> b = "(x**46 - 15180*x**43 + 9366819*x**40 - 53524680*x**39 +
> 260932815*x**38
> >> - 1101716330*x**37 + 4076350421*x**36 - 13340783196*x**35 +
> >> 38910617655*x**34 - 101766230790*x**33 + 239877544005*x**32 -
> >> 511738760544*x**31 + 991493848554*x**30 - 1749695026860*x**29 +
> >> 2818953098830*x**28 - 4154246671960*x**27 + 5608233007146*x**26 -
> >> 6943526580276*x**25 + 7890371113950*x**24 - 8233430727600*x**23 +
> >> 7890371113950*x**22 - 6943526580276*x**21 + 5608233007146*x**20 -
> >> 4154246671960*x**19 + 2818953098830*x**18 - 1749695026860*x**17 +
> >> 991493848554*x**16 - 511738760544*x**15 + 239877544005*x**14 -
> >> 101766230790*x**13 + 38910617655*x**12 - 13340783196*x**11 +
> >> 4076350421*x**10 - 1101716330*x**9 + 260932815*x**8 - 53524680*x**7 +
> >> 9366819*x**6 - 1370754*x**5 + 163185*x**4 - 15180*x**3 + 1035*x**2 -
> 47*x +
> >> 1)"
> >>
> >> sympy.intervals( a + "*" + b )
> >>
> >>
> >>
> >> Of course, in this particular case, the exception could be avoided if
> >> sympy.intervals() is called for a and b separately.
> >> However, since I run a very large number of similar computations, I am
> not
> >> so much interested in how to solve this particular problem.
> >> Instead, I am interested in why this exception is raised at all. Is it
> due
> >> to a limitation of sympy.intervals()? Or maybe a bug? Or do I use it
> >> incorrectly?
> >
> > Here is a full log with latest sympy master:
> >
> > https://gist.github.com/certik/6640160
> >
> > looks like a bug to me.
> >
> >> What I observed so far is that the above code raises an "OverflowError"
> >> exception when function dup_root_upper_bound() tries to compute
> 2.0**1041,
> >> which obviously must fail.
> >
> > Yes, that's the error in the log:
> >
> >>>> 2.0**1041
> > Traceback (most recent call last):
> > File "<stdin>", line 1, in <module>
> > OverflowError: (34, 'Numerical result out of range')
> >
> > The question is why the intervals() function needs this, and one would
> > need to investigate how it works.
> > In any case, the exception that it throws should be more readable /
> informative.
> >
> > Ondrej
> >
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